Dissertations / Theses on the topic 'Natural fibre reinforced composites'

This thesis explains the manufacturing of recyclable, eco-friendly composites and their fabrication into hollow cores. The composites have been manufactured using compression moulding and extrusion techniques; each representing batch manufacturing and continuous manufacturing respectively. A statistical design of experiments based on Taguchi method has been used to study the multivariable system involved in the process of continuous extrusion. Factorial design of experiments (DoE) has been used to determine the best material formulation to obtain maximum mechanical properties. The composite sheets produced after the DoE were pelletised in a hammer mill and reprocessed by passing them through another cycle of extrusion. The effect of recycling on the mechanical properties, which were determined by performing static tests as per ASTM standards, has been investigated. The extruded composite sheets have been thermoformed into half-hexagonal and sinusoidal profiles using matched-die and roll forming processes. As the process involves bending and stretching the sheet to conform to the geometry of the mould, it is usually accompanied by large strains. These strains have been analysed using grid strain analysis, and the strain path taken during the forming operation has been determined using strain space diagrams. Due to the stretching and bending of the composite sheet during thermoforming process, a stress field is induced in the material, which upon extraction in that state, would result in either spring-forward or spring-back of the material causing dimensional instability, but by holding the part in that deformed state for a period of time will allow the stresses in the materials to relax. This time-stress information (stress relaxation behaviour) has been experimentally investigated and modelled using springs and dashpots arranged in series and parallel. The spring-back and spring-forward phenomena, occurring in the formed part upon de-moulding, have been investigated using single curvature vee-bending experiments. The profiled sheets obtained after forming have been assembled and bonded into honeycomb cores using adhesives and ultrasonic methods. These cores have been sandwiched between two wood veneer facings to form eco-friendly sandwich panels. The compressive and shear properties of these sandwich panels have been modelled and experimentally investigated. The compressive behaviour of the sisal-PP honeycomb cores has been modelled considering the honeycomb cell wall as a linear elastic specially orthotropic plate/lamina under plane stress and as a quasi-isotropic material. A finite element model of the sandwich panel has been developed in ANSYS classic finite element environment, to study the behaviour of the panel and the core, under flexural loading. Some non-structural properties such as, sound absorption, structural damping and energy absorption have been experimentally determined. The sound absorption ability of the honeycomb has been experimentally evaluated using a standing plane wave impedance tube. Three configurations; one with hollow cores, and the other two filled with polyurethane foam and wood fibres, respectively have been tried. The natural frequencies and structural damping have been experimentally determined by subjecting the sandwich beam to harmonic vibrations. The energy absorption characteristic has been experimentally determined by subjecting the honeycomb cores to quasi-static compressive loading.

Le soudage par transmission laser des thermoplastiques nécessite l’optimisation de l’adhérence interfaciale au niveau du joint de soudure. A cet égard, la modélisation du procédé et le développement d'outils de simulation numériques sont indispensables pour optimiser la résistance mécanique du joint de soudure. La tâche est plus difficile dans le cas de matériaux composites très hétérogènes et anisotropes. De plus, la transmission laser est encore difficile dans le cas de milieux opaques ou semi-transparents tels que les composites thermoplastiques renforcés de fibres naturelles. Les propriétés thermiques et optiques des composites dépendent des propriétés et de la morphologie des constituants tels que les fibres et le polymère, qui peuvent affecter le spectre de transmission dans le domaine infrarouge. L’absorption et la réfraction de la propagation du rayon laser dans les matériaux composites conduisent à une réduction de l’énergie transmise arrivant à l’interface da soudure, ce qui influence directement la qualité de la soudure et ses performances mécaniques.Dans cette thèse, l'effet des phénomènes d'absorption et de diffusion sur le développement du champ de température à l'interface de la soudure est analysé numériquement et expérimentalement. Compte tenu de l’orientation, de la forme, de la longueur et de la fraction volumique des fibres, des géométries numériques 3D représentant les matériaux composites sont générées pour simuler la propagation des rayons laser avec l'algorithme "Ray tracing". Des modèles numériques pour estimer la résistance de la soudure sont présentés tout en tenant compte de l'influence des paramètres de soudage (tels que la puissance du laser, la vitesse d’alimentation et la position du foyer), les propriétés du matériau et l'interdiffusion moléculaire à l'interface de la soudure. La résistance de la soudure est mesurée par des essais mécaniques et leurs résultats sont comparés aux résultats de la modélisation numérique
Laser transmission welding of thermoplastics requires the optimisation of interfacial adhesion at the weld joint. In this regard, the process modelling, and the development of numerical simulation tools are indispensable to optimize the mechanical strength of the weld joint. The task is more difficult in the case of highly heterogeneous and anisotropic composite materials. Moreover, the laser transmission is still difficult in the case of opaque or semi-transparent media such as natural fibre reinforced thermoplastic composites. The thermal and optical properties of composites depend on the properties and morphology of the constituents such as fibres and polymer, which can affect the transmission spectrum in the infrared range. The absorption and refraction of laser ray propagation in the composite materials lead to a reduction of the transmitted energy arriving at the weld interface, which directly influences the quality of the weld and its mechanical performance. In this dissertation, the effect of absorption and diffusion phenomena on the development of temperature field at the weld interface is analysed numerically and experimentally. Considering the fibre orientation, shape, length and volume fraction, numerical 3D geometries representing composite materials are generated to simulate the propagation of laser rays with “Ray tracing” algorithm. Numerical models to estimate the strength of weld are presented while considering the influence of welding parameters (such as laser power, feeding speed and focus position), material properties and molecular interdiffusion at the weld interface. The weld bonding strength is measured by mechanical tests and their results are compared with numerical modelling results

Thesis (MEng)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The building industry is responsible for a substantial contribution to pollution. The production of building materials, as well as the operation and maintenance of structures leads to large amounts of carbon-dioxide (CO2) being release in the atmosphere. The use of renewable resources and construction materials is just one of the ways in which the carbon footprint of the building industry can be reduced. Sisal fibre is one such renewable material. Sisal fibre is a natural fibre from the Agave Sisalana plant. The possibility of incorporating sisal fibre in a cement-based matrix to replace conventional steel and synthetic fibres has been brought to the attention of researchers. Sisal fibre has a high tensile strength in excess of polypropylene fibre and comparable to PVA fibre. Sisal fibre consists mainly of cellulose, hemi-cellulose and lignin. The disadvantage of incorporating sisal fibre in a cement-based matrix is the degradation of the composite. Sisal fibres tend to degrade in an alkaline environment due to changes in the morphology of the fibre. The pore water in a cement base matrix is highly alkaline which leads to the degradation of the fibres and reduced strength of the composite over time. Sisal fibre reinforced cement-based composites (SFRCC) were investigated to evaluate the durability of the composites. Two chemical treatments, alkaline treatment and acetylation, were performed on the fibre at different concentrations to improve the resistance of the fibre to alkaline attack. Alkaline treatment was performed by using sodium hydroxide (NaOH), while acetylation was performed by using acetic acid or acetic anhydride. Single fibre pull-out (SFP) tests were performed to evaluate the influence of chemical treatment on fibre strength, to study the fibre-matrix interaction and to determine a critical fibre length. A matrix consisting of ordinary Portland cement (OPC), sand and water were used for the SFP tests. This matrix, as well as alternative matrices containing fly ash (FA) and condensed silica fume (CSF) as supplementary cementitious material, were reinforced with 1% sisal fibre (by volume) cut to a length of 20 mm. The OPC matrix was reinforced with untreated- and treated fibre while the alternative matrices were reinforced with untreated fibre. Alternative matrices containing varying fibre volumes and lengths were also produced. Three-point bending- (indirect), direct tensile- and compression tests were performed on specimens at an age of 28 days to determine the strength of the matrix. The remainder of the specimens were subjected to ageing by extended curing in water at 24˚C and 70˚C respectively and by alternate cycles of wetting and drying, after which it was tested at an age of 90 days from production to evaluate the durability of the fibre. An increase in fibre volume led to a decrease in compressive strength and peak tensile strength. The optimum fibre length at a volume of 1% was 20 mm for which the highest compression strength was recorded. The combination of alkali treatment and acetylation was the most effective treatment condition, followed by alkali treatment at low concentrations of sodium hydroxide. At higher concentrations of sodium hydroxide, a significant reduction in strength was recorded. The addition of supplementary cementitious materials also proved to be effective in mitigating degradation, especially in the cases where CSF was used. FA proved to be less effective in reducing the alkalinity of the matrix. However, the use of FA as fine filler resulted in higher strengths. Specimens manufactured by extrusion did not have superior mechanical properties to cast specimens. The conclusion was made that the use of sisal fibre in a cement-based matrix is effective in providing ductile failure. Chemical treatment and the addition of supplementary cementitious materials did improve the durability of the specimens, although degradation still took place.
AFRIKAANSE OPSOMMING: Die boubedryf is verantwoordelik vir 'n aansienlike bydrae tot besoedeling. Die produksie van boumateriale, sowel as die bedryf en instandhouding van strukture lei tot groot hoeveelhede koolstof dioksied (CO2) wat in die atmosfeer vrygestel word. Die gebruik van hernubare hulpbronne en boumateriale is maar net een van die maniere waarop die koolstof voetspoor van die boubedryf verminder kan word. Sisal vesels is 'n voorbeeld van 'n hernubare materiaal. Sisal vesel is 'n natuurlike vesel afkomstig vanaf die Agave Sisalana plant. Die moontlikheid om sisal vesels in 'n sement gebasseerde matriks te gebruik om konvensionele staal en sintetiese vesels te vervang, is tot die aandag van navorsers gebring. Sisal vesel het 'n hoër treksterkte as polipropileen vesels en die treksterkte vergelyk goed met die van PVA vesels. Sisal vesel bestaan hoofsaaklik uit sellulose, hemi-sellulose en lignien. Die nadeel verbonde aan die gebruik van sisal vesels in 'n sement gebasseerde matriks is die degradasie van die komposiet. Sisal vesels is geneig om af te breek in 'n alkaliese omgewing as gevolg van veranderinge wat in die morfologie van die vesel plaasvind. Die water in die porieë van 'n sement gebasseerde matriks is hoogs alkalies wat lei daartoe dat die vesel afgebreek word en die sterkte van die komposiet afneem oor tyd. Sisal vesel versterkte sement gebasseerde komposiete is ondersoek om die duursaamheid van die komposiete te evalueer. Twee chemiese behandelings, alkaliese behandeling en asetilering, is uitgevoer op die vesels teen verskillende konsentrasies om die weerstand van die vesels teen alkaliese aanslag te verbeter. Alkaliese behandeling was uitgevoer met natrium-hidroksied (NaOH) terwyl asetilering met asynsuur en asynsuurhidried uitgevoer is. Enkel vesel uittrek toetse is uitgevoer om die invloed van chemiese behandeling op veselsterkte te evalueer, om die vesel/matriks interaksie te bestudeer en om die kritiese vesellengte te bepaal. 'n Matriks wat uit gewone Portland sement (OPC), sand en water bestaan, is gebruik vir die enkel vesel uittrek toetse. Dieselfde matriks, sowel as alternatiewe matrikse wat vliegas (FA) en gekondenseerde silika dampe (CSF) as aanvullende sementagtige materiaal bevat, is versterk met 1% vesel (by volume) wat 20 mm lank gesny is. Die OPC matriks was versterk met onbehandelde- en behandelde vesels, terwyl die alternatiewe matrikse met onbehandelde vesels versterk is. Matrikse wat wisselende vesel volumes en lengtes bevat het is ook vervaardig. Drie-punt buigtoetse (indirek), direkte trek toetse en druktoetse is uitgevoer op proefstukke teen 'n ouderdom van 28 dae om die sterkte van die matriks te bepaal. Die oorblywende proefstukke is onderwerp aan veroudering deur verlengde nabehandeling in water teen 24˚C en 70˚C onderskeidelik en deur afwissilende siklusse van nat- en droogmaak waarna dit op 'n ouderdom van 90 dae vanaf vervaardiging getoets is om die duursaamheid van die matriks te evalueer. 'n Toename in vesel volume het tot 'n afname in druksterkte en piek treksterkte gelei. Die optimum vesel lengte teen 'n volume van 1% was 20 mm, waarvoor die hoogste druksterkte opgeteken is. Die kombinasie van alkaliese behandeling en asetilering was die mees effektiewe behandeling, gevolg deur alkaliese behandeling by lae konsentrasies natrium-hidroksied. Vir hoë konsentrasies natrium-hidroksied is 'n aansienlike afname in sterkte opgeteken. Die toevoeging van aanvullende sementagtige materiale was ook effektief om die degradadering van die vesels te verminder, veral in die gevalle waar CSF gebruik is. FA was minder effektief om die alkaliniteit van die matriks te verminder. Die gebruik van FA as fyn vuller het nietemin hoër sterkte tot gevolg gehad. Proefstukke wat deur ekstrusie vervaardig is, het nie beter meganiese eienskappe gehad as proefstukke wat gegiet is nie. Daar is tot die gevolgtrekking gekom dat sisal vesel in 'n sement gebasseerde matriks wel effektief is om 'n duktiele falingsmode te voorsien. Chemiese behandeling en die toevoeging van aanvullende sementagtige materiale het die duursaamheid van die proefstukke verbeter, alhoewel degradering steeds plaasgevind het.

The effect of different fibre volume fractions of hemp and nanoclay reinforcement on the mechanical, thermal and environmental properties of unsaturated polyester composites has been investigated experimentally. Due to the incorporation of different fibre volume fractions of hemp into polyester resin an improvement in tensile strength and tangent modulus was realised. Likewise, the flexural strength and modulus of unsaturated polyester (UPE) matrix increased with the introduction of hemp fibre. The mechanical tests results suggest that the tensile and flexural properties of composites are related to the fibre volume fractions and interfacial bond strengths between the fibre and matrix. Flexural properties of the composites were found to be comparable to those of chopped strand mat (CSM) glass fibre reinforced UPE composites. Low velocity instrumented falling weight impact tests were conducted to evaluate impact and damage characteristics of hemp and nanoclay reinforced composites. A significant improvement in load bearing capability and impact energy absorption was found by introducing hemp fibre and nanoclay as reinforcement. The impact test results in this study show that the total energy absorbed by the 0.21 fibre volume fraction of hemp reinforced specimen is comparable to the energy absorbed by the composites specimen equivalent in fibre weight percentage of CSM E-glass fibre. All nanoclay reinforced nanocomposite specimens have shown a significant improvement in their impact strength and energy absorption properties compared to unreinforced UPE matrix. The effects of various loading levels of nanoclay reinforcement on the nanomechanical properties of UPE/layered silicate nanocomposites were investigated by a nanoindentation test method. It has shown that the nanoindentation behaviour is strongly influenced by nanoclay reinforcement and the extent of clay dispersion in the polymer matrix. The creep behaviour of hemp fibre reinforced unsaturated polyester (LIFRUPE) composites was investigated using a three-point bending clamp system. Creep strain decreased as the hemp fibre reinforcement increased. The creep deflection value was significantly higher for unreinforced samples compared to hemp fibre reinforced samples. Thermal properties were evaluated using Thermogravimetric Analysis (TGA), Thermo Mechanical Analyser (TMA), Differential Scanning Calorimetry (DSC) and thermal conductivity analysis. TGA results suggest that various concentrations of nanoclay and hemp reinforcement increases the thermal stability of UPE/layered silicate nanocomposites and IIFRUPE composites. Glass transition temperatures (Tg) were also increased with the introduction of clay and hemp fibre reinforcement. Hemp reinforced specimens also showed increased thermal stability indicated by an increased Tg value and decreased decomposition rate. Thermal conductivity values were found to be higher for both clay and hemp reinforced specimens compared to unreinforced polyester. Different fibre volume fraction of HFRUPE composites were subjected to water immersion tests in order to study the effects of water absorption on a range of properties. Water absorption tests were conducted by immersing specimens in a de-ionised water bath at room temperature and 100 °C for different time durations. The tensile, flexural and nanohardness properties of water immersed specimens subjected to both aging conditions were evaluated and compared alongside dry composite specimens. The percentage of moisture uptake increased as the fibre volume fraction increased. The tensile, flexural and nanohardness properties of HFRUPE specimens were found to decrease with increase in percentage moisture uptake. However, the impact properties of HFRUPE composites were found increased after water immersion. Moisture induced degradation of composite samples was significant at elevated temperature. The water absorption pattern of these composites at room temperature was found to follow Fickian behaviour, whereas at elevated temperatures it exhibited non- Fickian. Keywords: Polymer matrix composites (PMCs); Layered silicate nanocomposites; Natural fibre reinforced composites (NFRC); Mechanical properties; Mechanical testing; Moisture absorption; Thermal stability

Includes abstract.
Includes bibliographical references (leaves 83-85).
A multi-scale methodology for small strain linear elasticity is presented in this thesis. The homogenisation process is discussed in general, with particular attention to the required boundary constraints on the micro-domain and the extraction of an effective elastic modulus. For the case of a non-linear problem the enforcement of the required boundary constraints becomes non-trivial and thus implementation via the penalty method and lagrange multipliers is investigated.

Les effets du caoutchouc nitrile (NBR), du traitement de la surface des fibres et du noir de carbone sur les propriétés des composites à base de caoutchouc naturel renforcé par des fibres d'ananas (NR / PALF) ont été étudiés. L'incorporation de NBR et le traitement de surface de la fibre ont été utilisés pour améliorer les propriétés mécaniques des composites à faible déformation, alors que le noir de carbone a été utilisé pour améliorer ces propriétés à forte déformation. La teneur en fibres a été fixée à 10 phr. Les matériaux composites ont été préparés à l'aide d'un mélangeur à cylindres et ont été réticulés sous presse permettant ainsi le maintien de l'orientation des fibres. Ces composites ont été caractérisés à l’aide du rhéomètre à matrice mobile (MDR), par analyse thermique mécanique dynamique (DMTA) et par tests de traction. La morphologie après fracture cryogénique a été observée à l'aide de la microscopie électronique à balayage (MEB). L'effet du NBR dont la teneur varie de 0 à 20 phr par rapport à la teneur totale en caoutchouc, a été également étudié. Le NBR est utilisé afin d’encapsuler totalement les fibres d’ananas (PALF) ; ceci conduisant à un meilleur transfert de contraintes entre la matrice et les fibres. La méthode de mélange a également été étudiée. Plusieurs types de silanes tels que le propylsilane, l'allylsilane et le silane-69 ont été utilisés pour traiter les fibres pré-nettoyées à l’aide d’un traitement alcalin. Les fibres silanisées ont été caractérisées par spectroscopie infrarouge à transformée de Fourier (FTIR), par spectroscopie de photoélectrons aux rayons X (XPS) et par MEB. Le traitement de la fibre par le silane-69 a permis d’augmenter fortement le module du matériau composite à faible déformation. Ce traitement a été plus efficace que l'incorporation de NBR dans les composites NR / PALF. Ceci peut s’expliquer par une possible réticulation chimique entre le caoutchouc et la fibre traitée au silane-69 plutôt qu’une simple interaction physique du NR, du NBR et de la fibre. Cependant, le renforcement par fibre réduit la déformation à la rupture. Par conséquent, du noir de carbone a également été incorporé dans les composites NR/NBR/PALF et NR/ PALF traitée, afin d’améliorer leurs propriétés ultimes. En incorporant du noir de carbone à un taux de 30 phr dans les deux composites, les propriétés mécaniques des composites ont été améliorées et peuvent être contrôlées à la fois à des déformations faibles et hautes
The effects of nitrile rubber (NBR), fiber surface treatment and carbon black on properties of pineapple leaf fiber-reinforced natural rubber composites (NR/PALF) were studied. The incorporation of NBR and surface treatment of fiber were used to improve the mechanical properties of composites at low deformation, whereas carbon black was used to improve these properties at high deformation. The fiber content was fixed at 10 phr. The composites were prepared using two-roll mill and were cured using compression moulding with keeping the fiber orientation. These composites were characterized using moving die rheometer (MDR), dynamic mechanical thermal analysis (DMTA) and tensile testing. The morphology after cryogenic fracture was observed using scanning electron microscopy (SEM). The effect of NBR from 0 to 20 phr of total rubber content was investigated. NBR is proposed to encase PALF leading to higher stress transfer between matrix and PALF. The method of mixing was also studied. For the fiber surface treatment, propylsilane, allylsilane and silane-69 were treated on the alkali-treated fiber. Treated fibers were characterized using Fourier-Transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS) and SEM. Silane-69 treatment of fiber increased the modulus at low deformation more than the incorporation of NBR of NR/PALF composites due to the chemical crosslinking between rubber and fiber from silane-69 treatment rather than the physical interaction of NR, NBR and fiber. However, reinforcement by fiber reduced the deformation at break. Hence, carbon black was also incorporated into NR/NBR/PALF and NR/surface-treated PALF composites to improve the ultimate properties. By incorporation of carbon black 30 phr in both composites, the mechanical properties of composites were improved and can be controlled at both low and high deformations

Commonly encountered accidental impact, e.g. due to roadway stone hitting, is detrimental not only because it can produce apparent surface defects, but also because barely visible impact damage (BVID) can be induced inside the material, which is not easy to detect by routine inspection. Reliable prediction of the amount of damage of this type induced under known service conditions is particularly important. Therefore, this type of impact was chosen as the focus of the present investigation. A combination of experimental techniques and finite element modelling was used to explore the behaviour of a fibre reinforced natural gas powered vehicle (NGV) pressure cylinder subjected to a low energy impact. In order to identify the modes of failure and understand the structural response, quasi-static indentation tests were carried out on sections of composite pipes and of a composite pressure cylinder. Delamination and matrix cracking were established to be the two major failure modes induced by indentation. Experimental findings were used as a basis for assessing the validity of the modelling approach. Thick shell and three dimensional finite element models were developed using PAFEC, a general purpose finite element code for dynamic and static analysis. It established that the composite pressure cylinder under this type of impact behaves quasi-statically, i.e. the impact phenomenon predominately excites low frequency response. Repeated impact was considered in order to extend the study to include the impact behaviour of a cylinder with pre-existing damage. It was found that a bulging effect was produced in the pressure cylinder at the impact site, where a weak spot was created due to fibre breakage. A fully three dimensional finite element model with static analysis was developed to investigate the damage and material degradation during the BVID phenomenon. The contact pressure distribution based on the Hertzian contact' relationship was applied. Failure mode identification criteria proposed by Hashin (1980) and Chang and Springer (1986) were used to establish the mode and extent of damage in the composite cylinder under quasi-static loading. The predicted failure modes agreed well with the experimental results. Finally, the present study sets out the methodology allowing systematic design of structures having optimal impact tolerance. Based on the findings of this project, suggestions for the improvement of impact resistance of NGV cylinders were given in Chapters ix.

Cette thèse présente un aperçu des composites thermodurcissables à base de fibres de lin de deux points de vue : fabrication par moulage par injection de résine et caractérisation mécanique. En particulier, deux matrices thermodurcissables ont été étudiées, à savoir l’époxy classique et la benzoxazine biosourcée. L’influence des propriétés intrinsèques des fibres de lin tels que la variabilité, le gonflement de la fibre et l’absorption de liquide sur la fabrication de pièces composites est étudiée. En considérant le gonflement des fibres et l’absorption des liquides, un modèle mathématique pour l’ascension capillaire des liquides dans les fibres de lin est proposé. Les modèles classiques de perméabilité ne pouvant être adoptés pour les fibres de lin en raison de leurs irrégularités de section et des diamètres de fibres, cette étude a recours à des simulations numériques pour estimer statistiquement la perméabilité. L’influence de la pression d’injection lors du moulage par transfert de résine sur la teneur en vides dans les plaques de lin/époxy est caractérisée et modélisée afin de comprendre les différences entre la formation de vides dans les composites renforcés par fibres de verre et fibres de lin. L’effet du cycle de polymérisation sur les propriétés mécaniques des composites est étudié par des tests de traction de composites de lin unidirectionnels afin de souligner l’évolution d’accroche mécanique à l’interface fibre / matrice provoquée par la pénétration de la résine dans les fibres élémentaires avec l’augmentation de la température de traitement. Enfin, le comportement à long terme des composites est examiné pour les composites lin/époxy et les composites lin/benzoxazine, par test de vieillissement hygrothermique
This dissertation presents insights into flax fiber based thermoset composites from two standpoints; manufacturing the composites by resin transfer molding and their mechanical characterization. In particular, two thermoset matrices have been investigated, i.e. conventional epoxy and bio-based benzoxazine. The influence of the intrinsic properties of flax fibers such as variability, fiber swelling and liquid absorption on the manufacturing of composite parts is investigated. By considering fiber swell and liquid absorption, a mathematical model for the capillary rise of liquid in flax fibers is proposed. As classical tow permeability models cannot be adopted for flax fibers due to their irregularities in cross-section and fiber diameter, this study resorts to numerical simulations to statistically estimate the permeability. The influence of injection pressure during resin transfer molding on void content in flax/epoxy plates is characterized and modeled to understand the differences in void formation from glass fiber composites. The effect of cure cycle on the mechanical properties of composites is investigated by tensile tests of unidirectional flax composites to emphasize the evolution of the mechanical locking at fiber/matrix interface caused by resin penetration into elementary fibers with increase in processing temperature. Finally, the long-term behavior of composites is examined for flax/epoxy composites and flax/benzoxazine composites, by hygrothermal aging test

Currently, the production of most non-asbestos organic (NAO) friction materials depends on a long and energy intensive manufacturing process and an unsustainable supply of synthetic resins and fibres; it is both expensive and bad for the environment. In this research, a new, more energy efficient, manufacturing process was developed which makes use of a naturally derived resin and natural plant fibres. The new process is known as 'cold moulding' and is fundamentally different from the conventional method. It was used to develop a new brake pad for use in low temperature (<400 °C) applications, such as rapid urban rail transit (RURT) trains. A commercially available resin based upon cashew nut shell liquid (CNSL) was analysed and found to have properties suitable for cold moulding. In addition, hemp fibre was identified as a suitable composite reinforcement. This was processed to improve its morphology and blended with aramid to improve its thermal stability. Each stage of cold mould manufacture was thoroughly investigated and the critical process parameters were identified. The entire procedure was successfully scaled up to produce an industrially sized 250 kg batch of material and the resultant composites were found to have appropriate thermal and mechanical properties for use in a rail brake pad. The tribological performance of these composites was iteratively developed through a rigorous testing and evaluation procedure. This was performed on both sub- and full-scale dynamometers. By adding various abrasives, lubricants, and fillers to the formulation it was possible to produce a brake pad with similar friction characteristics to the current market material, but with a 60% lower wear rate. In addition, this brake pad caused 15% less wear to the brake disc. A detailed examination of both halves of the friction couple found that cold moulded composites exhibit a different wear mechanism from the current market material, which was suggested to be the reason for their superior properties. Cold moulding is 3.5x faster and uses 400% less energy than the conventional method.

Bio-based flax fiber polymer composites (FFPC) have the potential to replace metals and synthetic fibers in certain applications due to their unique mechanical properties. However, the long term reliability of FFPC needs to be better understood. In this study, the fatigue limit was evaluated using mathematical, thermographic, and energy-based approaches. Each approach determined fatigue limits around 45% load of ultimate tensile strength at a loading frequency of 5 Hz. Thermographic and energy-based approaches were also implemented at different loading frequencies (5, 7, 10, and 15 Hz) to define the effect of loading frequency on the fatigue life. Fatigue limit was found to decrease slowly with increasing loading frequency. Moreover, two forms of damage energy (thermal and micro-mechanical) during cyclic loading was separated using an experimental approach to pinpoint the main responsible damage energy for decreasing fatigue limit with increasing loading frequency.

Interest in natural fiber reinforced composites (NFRCs) is increasing rapidly thanks to their numerous advantages such as low cost, biodegradability, eco-friendly nature, relatively good mechanical properties, and a growing emphasis on the environmental and sustainability aspects of engineering materials. However, large scale use of NFRCs is still considered as challenging due to the difficulties in manufacturing, limited knowledge of its machinability and appropriate parameter settings, and being prone to machining-induced defects. These materials are known as hard-to-machine materials due to their heterogeneous structure, mechanical anisotropy and tendency to damage while exposed to mechanical stresses. High rejection rate of composite parts at the assembly stage because of poor quality hole due to several vital drilling induced damages such as matrix cracking, fiber pull-out, delamination, fiber and matrix separation and thermal degradation is a serious concern for manufacturing industries. Among all these defects, delamination was found to be the most vital life-limiting factor which affects the mechanical strength and structural integrity of the component significantly in terms of dimensional tolerances and load carrying capability. Therefore, the main objective of this research is investigating the influence of drilling process parameters on the machinability of flax/poly(lactic acid) bio-composites along with characterization, modelling, and condition monitoring of drilling operation through extensive experimental and analytical investigations. The effect of key drilling parameters and tool geometry such as cutting speed, feed rate, drill diameter, drill material and point angle at different levels were studied experimentally to analyse the relations between resultant quality of the produced holes, cutting forces and size of delamination. Damages and defects associated with the drilling process such as delamination, fiber breakage, fiber pull-out, and matrix cracking were studied through qualitative measurements, optical microscopy and scanning electron microscopy examination. Experimental results revealed that the choice of drill bit in terms of diameter, material and point angle has a considerable effect on the machinability and hole performance. Drilling with HSS drills resulted in nearly 60% lower thrust force and better hole quality compared to that with carbide drills. In addition, the analysis of variance (ANOVA) was applied to identify the significance of each individual cutting parameter. Analytical model was developed to predict the critical thrust force related to the onset of delamination propagation during drilling FF/PLA laminates. The delamination zone was modelled as an elliptical plate, with clamped edge and the analytical model developed based on theory of virtual work, LEFM methodology and theory of plate bending. An experimental investigation was carried out, in addition to the analytical model, through a punching test on different configurations of blind hole to characterize the critical thrust force at the onset of delamination. The developed model has been verified by experimental data and compared with the results of existing models and the presented model considering the effect chisel edge and cutting edges. Based on the results, the predicted values by the proposed model present better correlation with the experimental values than those predicted by other models. A relationship exists between cutting variables (thrust and cutting forces), tool wear and the final quality of the drilled hole. Accordingly, the quality of drilled holes can be improved by in-process monitoring in order to record the whole process status through measuring the thrust force and other indicators. An experimental investigation on online monitoring and non-destructive evaluation of drilling operation using vibration, acoustic emission and thrust force signals was conducted and the correlation between the cutting parameters, delamination, cutting thrust force and the pattern of the signals was detected. The response of material through acceleration, force and AE signals were analysed using different signal analysis tools and statistical parameters to derive the features of signals that can express the key characteristics of machining condition. It is observed that the AE rms values are affected by variation in the cutting parameters and it follows a similar trend as observed in the case of drilling thrust force by varying cutting conditions. The variation of vibration and acoustic emission signals were in correlation with delamination factor and damage severity. Four major damage mechanisms have been identified generally as the main sources of AE energy wave in drilling of FF/PLA composites namely fiber breakage, delamination, matrix cracking and friction. A process for detection and discrimination of various damage mechanisms can be correlated to the frequency of damages. Furthermore, among several statistical parameters applied on the effective segment of the time signals, Kurtosis was found the most competent statistical parameter for condition monitoring of the drilling process to to differentiate between poor and good quality of the drilled holes and enhance the quality of composite component. The findings from this research concluded that damage severity can be assessed through AE parameter analysis and it has a considerable potential for the application of in-process monitoring.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text

Thesis (M.S.)--Michigan State University. Dept. of Civil and Environmental Engineering, 2008.
Title from PDF t.p. (viewed on Aug. 3, 2009) Includes bibliographical references (p.129-132). Also issued in print.

In this thesis the Hybrid Composites reinforced with nano-material, natural fibres and bio-material are prepared as an alternate to the synthetic fibres, to provide sustainable and environmental friendly material which is better alternate to the existing composites. The Mechanical and Thermal properties are studied and results are consistent with the existing trends of the field. This study would help researchers to find new application of this environmental friendly material in various fields. The contents of the thesis are as follows: Chapter 1: This chapter illustrates the advantages of natural fibres filled composites over the synthetic fibres from various features. Types of fibres, their extraction and various treatment processes to enhance the reinforcement. The advantages of hybrid composites with nano-materials. Chapter 2: This chapter is on literature review of composites with various polymers as matrix and various filler as reinforcements. It reviewed various chemical treatment methods and grafting methods for better mixing and homogeneous material. The various methods and parameters for preparing hybrid composites are discussed. Advantages, limitations are compared for various processing methods. It also includes analysis of research gap, objective of research work. Chapter 3: This chapter discussed the various characterization techniques, including standards, details of equipments and conditions for studying the prepared Hybrid Composites for various Mechanical and Thermal properties. Chapter 4: This chapter deals with synthesis of the Hybrid Composites with details of the various constituents and details about the composition with varying percentage to prepare the samples of the specimens. It also includes the details of extrusion and injection moulding process and their parameters. Chapter 5: This chapter deals with the finding of results and discussions of the reinforced constituents to get the maximum values of Mechanical, Physical and Thermal properties of the prepared hybrid composites. Chapter 6: It summarizes present research investigation for the successfully prepared hybrid composites having comparable properties to synthetic composites, while having advantages such as the reduction of plastic waste and energy savings advantages of natural xiii fibres and bio-material. It also includes the future scope for further research in this field for new application of these composites.

The aim of the research is to develop new high performance composite materials that would potentially compete with existing man made materials and to investigate the physical, mechanical and thermal properties of crushed (powdered) olive stones (pits) reinforced epoxy composites. This research focuses on development of a new range of sustainable reinforced polymer composite materials using powdered olive pits as a novel filler material to be used with synthetic resins. A full review has been made of the previous work on different types of natural fibres and fillers used as reinforcement for synthetic polymers. This project attempts to clarify the advantages and limitations resulted from using these fibres/ fillers and endeavours to provide explanation on the mechanical behaviour of these materials. Prior to investigating the mechanical properties of the powdered olive pits-epoxy composites the density and the mechanical properties of the olive pits were fully characterised. The influence of the untreated and treated powder loading (weight fraction) on the void content and the mechanical properties of the composites was examined using different tests, including flexural, tensile, microhardness and impact testing. The composites showed significant improvements in mechanical properties including flexural strength (139%) and flexural modulus (149%), tensile strength (121%) and tensile modulus (46%), microhardness (170%), and impact strength (167%) following treatment of the olive pits powder with 2% Al 100 coupling agent. Composites consisting of epoxy resin reinforced with untreated powder exhibited weaker powder to matrix interfacial bonding compared to those with treated powder composites. The improvements in properties have been attributed to the treatment of the powder with coupling agent, which has resulted in enhanced powdermatrix interaction. Hence it was possible to develop an experimental model of the behaviour of these materials subjected to the above mentioned testing conditions. Furthermore different thermal analysis techniques including dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) have been used to investigate the influence of the coupling agent on the olive pits powder composites properties by carefully analysing the changes in the thermal properties of the composites; glass transition temperature increased by 38%, tan delta peak decreased by 50%, and room temperature storage modulus improved by 17% and loss modulus peak decreased by 60%. The corroborated mechanical and thermal analysis results support the formation of a strong and efficient interfacial bond between the filler and epoxy matrix. The influence of powder content and interfacial bond strength on the damage and failure mechanisms operating in the different samples subjected to the destructive testing regime have been examined using optical and scanning electron microscopy (SEM).

Biocomposites exhibit properties like many petrochemical-based polymers composites. They have the potentials be used in the automotive and decking industries and as biodegradable packaging. However, the high cost as well as, poor mechanical and thermal properties have restricted their widespread use. There are a number of technical issues that need to be addressed before bio-composites can be widely used. In this research Polylactic acid (PLA) composites, reinforced with natural fibres (wood, flax) and mineral fillers (talc) were investigated. The thermal and mechanical properties of the composites were studied by means of Differential Scanning Calorimetry (DSC), Tensile Testing and Dynamic Mechanical Analysis (DMA), while morphology and crystallization processes of the composites were studied by hot stage optical microscopy. The experimental results are also compared with different theoretical models of the response of the composites. PLA / wood composites were developed by mixing PLA with wood in different ratios using a melt compounding process. PLA/wood (90/10. 80/20, 60/40), PLA/wood/copolymers (85/10/05, 80/10/10, 75/20/05, 70/20/10, 55/40/05, 50/40/10) and PLA/wood/coupling agent (80/20/silane coating) were the three different composite systems that were developed. Adding increasing amount of wood into the PLA, the thermal properties remain unchanged but the mechanical properties increased significantly, bringing a stiffening effect to the composites. Tensile modulus increased from 4.1± 0.6 to 9.8 ± 1.2 (GPa) as the wood content increased from 0 to 40 (wt %), but the tensile strength at break reduced from 43.8 ± 3.1 to 31.8 ± 2.8 MPa. The experimental results of the PLA-wood composites were modelled according to the Halpin-Tsai equation. The addition of copolymer affected the thermal properties considerably by decreasing the glass transition temperature of the composite. The glass transition temperature dropped from 54 ± 0.7 (0C) to 48 ± 0.36 (0C) when the content of copolymer was increased from 0 to 10 (wt %). The cold crystallization temperature also decreased from 127 ± 1.41 (0C) to 103 ± 2.58 (0C) when the copolymer was incorporated into the PLA/wood composites. The significant aspect was the occurrence of a double peak in the melting endotherm. The degree of crystallinity also increased from 2 ± 0.83 (%) to 11 ± 1.23 (%) when the amount of copolymer was increased to 10 (wt %). PLA, flax and expoidizied natural rubber (ENR) composites were also developed using a melt compounding process. The mechanical properties were affected significantly when the flax fibres were mixed with PLA in the ratios of 10, 20 and 30 (wt %). Addition of flax fibres increased the elastic modulus significantly but reduced the tensile strength and strain at break. To improve the toughness of the PLA- Flax composites, ENR was incorporated into the PLA- Flax composites. In order to balance the modulus of the reinforcement and the matrix, the PLA- Flax and ENR composites were annealed above the glass transition temperature and the degree of crystallinity increased from 2 to 35 (%). The integral blending of PLA, Flax and ENR did not affect the brittle fracture but introducing a masterbatch of flax fibres and ENR into the PLA matrix during melt processing had a considerable effect on the fracture behaviour of the composites. The elastic modulus of the composites decreased due to the elastomeric content in the composites and there was an increase in elongation-to-break. The effect of talc on the crystallinity and mechanical properties of a series of polylactic acid (PLA) / talc composites was investigated. PLA talc composites were developed by incorporating different types of the talc into the PLA in the ratios of 10, 20 and 30 (wt %). The composites were prepared by melt blending followed by compression moulding. It was found that talc acted as a nucleating agent and increased the crystallinity of the PLA from 2% to 25%. There was significant improvement in Young s modulus of the composites with increasing talc addition and these results were found to fit the Halpin Tsai model. Thermo-mechanical tests confirmed that the combination of increased crystallinity and storage modulus leads to improvement in the heat distortion properties.

Les composites renforcés à fibres de carbone (CRFC) sont des matériaux de haute technicité appliqués à de nombreux domaines, du sport à l’aéronautique. Cette dernière décennie a vu leur demande croitre continuellement, générant en conséquence une augmentation du volume de déchets. Incités par les directives Européennes sur la gestion des déchets, des traitements thermiques de recyclage industriel ont été développés afin de récupérer les fibres de carbone issues des CFRC, principalement à matrice thermodurcissable. Actuellement, les CRFC en développement et/ou de dernières générations, utilisent des matrices thermostables telles que le Poly Ether Ether Cétone (PEEK). Une partie des travaux de thèse consiste à étudier la faisabilité de recyclage de ce composite thermostable, seul et en mélange avec d’autres types de composites à matrice thermodurcissable et thermoplastique. Un pilote semi-industriel a été employé sous atmosphères inerte (pyrolyse) et réactives (vapo-thermolyse et air). Les premiers résultats sur des mélanges ont montré que sous atmosphère inerte la récupération des fibres de carbone issues des matrices thermostables est quasi impossible. A l’inverse, les essais sur les composites PEEK en atmosphères oxydantes permettent l’extraction de la fibre mais induisent des modifications morphologiques et chimiques de la surface ainsi qu’une réduction de la résistance en traction. Les travaux de thèse se focalisent également sur des solutions alternatives de valorisation des fibres de carbone recyclées. Ces fibres ont été recouvertes de nanocellulose en tant qu’agent d’ensimage, en vue de leur réutilisation dans de nouvelles formulations. La perte de propriétés mécaniques induite par le recyclage a été partiellement compensée par ce traitement de surface. Des fibres recyclées ont également été incorporées dans un composite à renfort naturel de jute et matrice PA6 dans le but de créer un composite hybride offrant des propriétés équilibrées en termes de résistance, prix et impact écologique
Carbon Fiber Reinforced Composites (CFRC) are high technical materials applied in various fields from sports to aeronautics. During the last decade, the demand of CFRC has extended significantly resulting in increasing the volume of composite waste generated each year. Incited by European directives, thermal recycling treatments have been developed at industrial scale to recover carbon fibers, mostly from thermosetting composites. Nowadays CFRP in development used thermoresistant resins such as Poly Ether Ether Ketone (PEEK). Part of this work is to study the recycling feasibility of this type of CFRP alone and mixed with thermosetting and thermoplastics matrix based composites. Semi-industrial pilot was used in inert (pyrolysis) and reactive (steam-thermolysis, oxydation) atmosphere conditions. First results of mixture perform in nitrogen have revealed that inert atmosphere cannot allow the recovery of carbon fibers from thermoresistant resins. On the contrary trials on PEEK in oxydative atmospheres enable the extraction of fiber, but induce morphological and chemical modifications and tensile strength reduction. New approach on the recycled carbon fiber valorization have also been studied. These fibers have been coated by nanocellulose as sizing agent for their reuse in new composite formulations. Mechanical properties loss induce by recycling have been offset thank to this surface treatment. Recycled fibers was also incorporate in jute/PA6 composite to create a hybrid composite with balance properties in terms of strength, price and environmental impact

Biobased thermoset resins were synthesized by functionalizing the tall oil fatty acid with hydrogen peroxide and then methacrylic anhydride. The obtained resins were characterized by FTIR to confirm the conversions. The cross-linking ability of the resins were checked by curing experiments and followed by DSC analysis regarding the extent of cross linking. TGA analysis was conducted to identify the thermal degradation patterns of cured resins. The obtained resins (blended with or without 33wt% styrene) were used as matrix and knitted viscose fibers were used as reinforcements to make bio-based composites. Ten layers of knitted viscose fibers were stacked crosswise (0/90⁰С) and hand lay-up impregnation was performed. The fiber ratio of all composites was around 63-66%. The composites were characterized by flexural testing, dynamic mechanical thermal analysis and charpy testing. This work demonstrates that manufacture of composites with both matrix and reinforcement fiber coming from renewable resources is feasible, and the resulted composites have satisfied mechanical performance.
Program: MSc in Resource Recovery - Sustainable Engineering

Nowadays, exceptional advantages of silk fibroin over synthetic and natural polymers have impelled the scientists to application of this biomaterial for tissue engineering purposes. Recently, we showed that embedding natural degummed silk fibers in regenerated Bombyx mori silk-based scaffold significantly increases the mechanical stiffness, while the porosity of the scaffolds remains the same. In the present study, we evaluated degradation rate, biocompatibility and regenerative properties of the regenerated 2% and 4% wt silk-based composite scaffolds with or without embedded natural degummed silk fibers within 90 days in both athymic nude and wild-type C57BL/6 mice through subcutaneous implantation. In all scaffolds, a suitable interconnected porous structure for cell penetration was seen under scanning electron microscopy. Compressive tests revealed a functional relationship between fiber reinforcement and compressive modulus. In addition, the fiber/fibroin composite scaffolds support cell attachment and proliferation. On days 30 to 90 after subcutaneous implantation, the retrieved tissues were examined via gross morphology, histopathology, immunofluorescence staining and reverse transcription-polymerase chain reaction as shown in Figure 1. Results showed that embedding the silk fibers within the matrix enhances the biodegradability of the matrix resulting in replacement of the composite scaffolds with the fresh connective tissue. Fortification of the composites with degummed fibers not only regulates the degradation profile but also increases the mechanical performance of the scaffolds. This report also confirmed that pore size and structure play an important role in the degradation rate. In conclusion, the findings of the present study narrate key role of additional surface area in improving in vitro and in vivo biological properties of the scaffolds and suggest the potential ability of these fabricated composite scaffolds for connective tissue regeneration.

Ce travail de thèse vise à développer un traitement de surface de fibres de lin pour l’amélioration des propriétés mécaniques de biocomposites à matrice polymère et renforts en lin. Cette modification de surface s’inspire des structures hiérarchiques présentes dans les systèmes biologiques (os, nacre ou bois), constitués de nano-objets permettant un meilleur transfert de charges dans ces matériaux. Cette présence d’objets de dimensions nanométriques permet notamment d’atteindre des valeurs de contrainte et ténacité élevées et de limiter la propagation de fissures. Dans ces travaux de recherche, des produits dérivés de la biomasse ligno-cellulosique, à savoir les nanocristaux de cellulose (CNC) et le xyloglucane (XG), ont été choisis pour leurs propriétés et leur affinité mutuelle afin de créer des fibres de lin hiérarchiques. Dans un premier temps, l’adsorption de XG et CNC sur les fibres de lin a pu être localisée et quantifiée grâce à des marqueurs fluorescents. De plus, des mesures de force d’adhésion en microscopie à force atomique ont révélé la création d’un réseau extensible XG/CNC sur la surface de la fibre. Par la suite, deux voies ont été proposées avec l’élaboration de biocomposites thermoplastiques (polypropylène/fibres de lin) et thermodurcissables (résine époxy/tissu de lin) utilisant ces fibres nanostructurées. Dans les deux cas, une augmentation du travail à la rupture a été mesurée en micro-tractions et/ou tractions uniaxiales, permettant une plus grande dissipation de l’énergie lors de la rupture. L’ensemble de ces travaux a permis d’évaluer le potentiel de différents renforts en lin hiérarchiques(tissu unidirectionnel ou fibres courtes)pour le développement de biocomposites structuraux avec un focus fait sur la zone d’interphase fibre / matrice
This thesis project aims at developing flax fibres surface treatment for the improvement of the mechanical properties of biocomposites with polymeric matrix and flax reinforcements. This surface modification is inspired by the hierarchical structures present in biological systems (bone, nacre or wood), composed of nano-objects which allow a better transfer of loads in these materials. This presence of nano-sized objects makes it possible to reach impressive strength and toughness values and to limit cracks propagation. In this project, products derived from lingo-cellulosic biomass, namely cellulose nanocrystals (CNC) and xyloglucan (XG), were chosen for their interesting properties and mutual affinity to create hierarchical flax fibres. In a first step, the adsorption of XG and CNC onflax fibres w as localized and quantified using fluorescent markers. In addition, atomic force microscopy measurements of adhesive force revealed the creation of an extensible XG/CNC netw ork on the fibre surface. Subsequently, two paths were proposed with the elaboration of thermoplastic (polypropylene/flax fibres) and thermoset (epoxy resin/flax fabric) biocomposites using these nanostructured fibres. In both cases, an increase of the work of rupture has been measured by micro-and/or uniaxial tensile tests, allowing dissipating more energy upon breakage. All this work has allowed evaluating the potential of different hierarchical natural reinforcements (unidirectional fabric or short flax fibers) for the development of structural biocomposites with a focus on the fiber/matrix interphase zone

De nouveaux materiaux composites, resultant de l'association originale d'un latex polymere filmogene et d'une suspension aqueuse de monocristaux (whiskers) de cellulose, ont ete elabores sous forme de films, par evaporation directe du melange aqueux. Pour des temperatures superieures a la temperature de transition vitreuse des composites, un effet de renfort remarquable et inhabituel pour les faibles fractions volumiques de whiskers mises en jeu (inferieures a 0. 1) a ete observe. Il se traduit par une forte augmentation du module elastique ainsi que du seuil de contrainte et une nette amelioration de la tenue en temperature. L'etude morphologique, l'analyse des essais mecaniques aux faibles et fortes deformations couplees a l'utilisation de differents modeles, ont permis de comprendre l'origine de ce renforcement. Ce dernier est attribue a un effet de percolation mecanique. Au-dela d'une fraction volumique critique (seuil de percolation estime dans le cas present a 0. 01), les whiskers forment un reseau connexe au sein de la matrice polymere. Les monocristaux de cellulose sont alors lies par des liaisons hydrogene qui controlent la cohesion et la rigidite du reseau. Des simulations par elements finis de structures aleatoires percolantes ont permis de prendre en compte le role de ces liaisons. Lorsque des procedes de mise en uvre empechant la formation du reseau - tels que l'extrusion - sont employes, on observe une chute des proprietes mecaniques. Celles-ci peuvent etre alors predites par des modeles plus classiques de type champ moyen

In this study, several types of modified methods were tried for improving natural fiber reinforced composites and also three kind of natural fibers were used for reinforced composite. Plasma polymerization increased fiber tensile and composites mechanical properties. It is higher effect than alkali treatment. Resin impregnation was expected cheaper method than plasma polymerization. Polyvinyl Alcohol resin impregnation method can increase fiber tensile strength, interfacial shear strength between fiber and composites mechanical properties. And with Bamboo/polypropylene/maleic anhydride polypropylene water absorption ratio also can decrease.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University

A utilização de fibras vegetais como reforço constitui um grande interesse na obtenção de novos materiais para a construção civil produto de seu baixo custo, alta disponibilidade e reduzido consumo de energia para sua produção. Este trabalho avalia a incorporação de fibras de sisal, de comprimento 20 e 40 mm, e fração volumétrica de 0,5 e 1%, em concretos para a alvenaria de blocos estruturais e determina o uso destas unidades na execução de prismas e mini-paredes. Foram realizados os testes de caracterização da fibra, blocos e argamassa de assentamento e os ensaios de resistência à compressão axial das unidades, prismas e mini-paredes. O sisal apresentou baixa massa específica aparente e elevada absorção de água, constituindo uma característica comum desse tipo de material pela grande incidência de poros permeáveis. As propriedades físicas dos blocos com e sem adição cumpriram com os requisitos das normas estabelecidas validando sua utilização. Os resultados do ensaio à compressão mostraram que as mini-paredes reforçadas com fibras obtiveram valores muito próximos ou mesmo superiores aos obtidos para as mini-paredes sem fibras, apresentando melhor desempenho que os blocos e prismas. Todos os elementos com adição mostraram um ganho da capacidade de deformação e ductilidade conferida pelas fibras, observado nas curvas tensão x deformação. O modo de ruptura dos blocos, prismas e mini-paredes de referência foi caracterizado por uma fratura brusca e catastrófica e os reforçados mantiveram suas partes unidas pelas fibras, não perdendo sua continuidade e tornando a ruptura um processo progressivo.
The use of natural fibers as reinforcement is a great interest in obtaining new materials for construction, owing of its low cost, high availability and reduced energy consumption for its production. This paper evaluates the incorporation of sisal fibers of 20 mm and 40 mm length and volume fraction of 0.5 and 1%, for concrete for masonry structural blocks, and determines the use of these units in making of prisms and mini-walls. The laboratory tests were carried to characterize physical properties the fiber, blocks and mortar, and besides axial compression tests of the units, prisms, and mini-walls. The sisal had low apparent density and high water absorption, constituting a common feature of such material by the high incidence of permeable pores. The physical properties of the blocks with and without addition complied with the requirements of standards established by validating their use. The axial compression test results showed that mini-walls reinforced with fibers obtained values very close to or even superior to those obtained for the mini-walls without fibers, showing better performance than the blocks and prisms. All elements with the addition had increased the deformation capacity and ductility afforded by the fibers, observed in the curves stress/strain. The rupture mode of blocks, prisms and mini-walls reference was characterized by an abrupt and catastrophic fracture, and elements reinforced maintained their shares together by the fibers, without losing its continuity and becoming a progressive rupture.

Biocomposites made from biodegradable polymer as matrix and natural fiber as reinforcement are certainly environmentally friendly materials. Both constituent materials are fully biodegradable and do not leave any noxious components on Earth. The natural fibers have been used as reinforcement due to their advantages compared to glass fibers such as low cost, high specific strength and modulus, low density, renewability and biodegradability. Major aims of this work were to produce natural fibers and/or nanoparticles with polyethylene (PE), polypropylene (PP) and polylactide (PLA), poly(hydroxybutyrate-co-hydroxyvalerate)(PHBV) matrices and determine their structure-property relationships. Following abstracts of the present research work are manifold: BINARY COMPOSITES Polylactide (PLA)/flax mat composites The polylactide (PLA)/flax mat and modified PLA/flax mat composites were produced by hot press technique. Two additives of non-regulated wax/ethylene acrylate copolymer/butyl acrylate and acrylic were used as modifier for PLA. The dispersion of the flax mat in the composites was studied by scanning electron microscopy (SEM). The PLA composites were subjected to instrumented falling weight impact test. The mechanical and thermal properties of the composites were determined in tensile test, thermogravimetric analysis (TGA) and dynamic-mechanical thermal analysis (DMTA), respectively. It was found that the PLA based composites increased the impact resistance. The tensile strength value of modified PLA/flax mat composite decreased slightly compared to the PLA. The elongation at break data indicated that an improvement in ductility of modified PLA and its composites. Moreover, addition of thermal modifier enhanced thermal resistance below processing temperature of PLA and had a marginal effect on the glass transition temperature of PLA. The storage modulus master curves were constructed by applying the time-temperature superposition (TTS) principle. The principle of linear viscoelastic material was fairly applicable to convert from the modulus to the creep compliance for all systems studied. Polylactide (PLA)/woven flax textiles composites The polylactide (PLA)/woven flax textiles 2x2 twill and 4x4 hopsack composites were produced by interval hot press technique. Two weave styles of flax used to reinforce in PLA. The dispersion of the flax composite structures in the composites was inspected in scanning electron microscopy (SEM). The PLA composites were subjected to instrumented falling weight impact test. The mechanical properties (tensile, stiffness and strength) of the composites were determined in tensile and dynamic-mechanical thermal analysis (DMTA) tests, respectively. SEM observed that the interfacial gaps around pulled-out fibers were improved when produced by the interval hot press. It was also found that the both styles of flax composites increased the impact resistance compared to the neat PLA. The tensile strength and stiffness value of PLA/flax composites were markedly higher than that of the neat PLA and reflect the effects of composite structures. The calculated storage creep compliance was constructed by applying the time-temperature superposition (TTS) principle. The calculated creep response of these flax composites was much lower than that of the neat PLA. Polyethylene and polypropylene/nano-silicon dioxide/flax composites Composites composed of polylactide (PLA), modified PLA and woven flax fiber textiles (Flax weave style of 2x2 twill and 4x4 hopsack) were produced by hot press technique. Two structurally different additives used to modify PLA. The dispersion of the flax composite structures in the composites was studied by scanning electron microscopy (SEM) and computed microtomography system (µCT). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The thermomechanical and creep properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA)and short-time creep tests, respectively. It was found that the modified PLA and its composite increased the impact resistance compared to the unmodified PLA. Incorporation of flax decreased resistance to thermal degradation and increased water uptake. The impact energy and stiffness value of PLA/flax composites was markedly higher than that of PLA but reflect the effects of composite structures and flax content. The storage modulus master curves were constructed by applying the time-temperature superposition (TTS) principle. From the master curve data, the effect of modified PLA on the storage modulus was more pronounced in the low frequencies range. Polylactide (PLA)/woven flax fiber textiles/boehmite alumina (BA) composites The textile biocomposites made from woven and non-woven flax fibre reinforced poly(butylene adipate-co-terephthalate) (PBAT) were prepared by compression moulding using film stacking method. The mechanical properties (such as tensile strength and stiffness, flexural strength and modulus, and impact strength) of textile biocomposites were determined in tensile, flexural and impact tests, respectively. The PBAT-based composites were subjected to water absorption. The comparison of the mechanical properties was made between pure PBAT and textile composites. The influence of flax weave styles on the mechanical properties was also evaluated. The results showed that the strength of the textile biocomposites was increased according to weave types of fibers, especially in the stiffness was significantly increased with the higher densification of the fibers. The 4x4-plain woven fibers (4-yard-wrap and 4-yard-weft weave direction) reinforced biocomposite indicated the highest strength and stiffness compared to the other textile biocomposites and pure PBAT. This was considered to be as the result of the character of weave style of 4x4-plain woven fibers. The aminopropyltriethoxysilane affected the mechanical properties and water absorption of the resulting composites laminates due to the surface compatibility between flax fiber and PBAT. HYBRID COMPOSITES Polyethylene/nanoparticle, natural and animal composites Binary and ternary composites composed of high-density polyethylene (HDPE), boehmite alumina (BA) and different kinds of natural-, animal fibers, like flax, sponge gourd (SG), palm and pig hair (PH) were produced by hot press technique. Aqueous BA suspensions were sprayed on the HDPE/flax mat to prepare nanoparticle/natural fiber reinforced ternary polymer composites followed by drying. The dispersion of the natural-, animal fibers and BA particles in the composites was studied by scanning electron microscopy (SEM) and discussed. The thermomechanical and stress relaxation properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA) and short-time stress relaxation tests (performed at various temperatures), respectively. The HDPE based composites were subjected to water absorption and instrumented falling weight impact tests. It was found that the all composites systems increased the stiffness, stress relaxation and reduced the impact toughness. The stress relaxation modulus of natural-, animal fiber composites were higher compared to that of the neat HDPE. This modulus increased greatly with in corporation of BA. The relaxation master curves were constructed by applying the time-temperature superposition (TTS) principle. The inverse of Findley power law could fairly applicable to describe the relaxation modulus vs. time traces for all systems studied. Incorporation of BA particles enhanced the thermal resistance which started to degrade at higher temperature compared to the HDPE/flax mat composite. The HDPE/flax mat/BA composite could reduce the water uptake. Polyethylene/Flax/SiO2 Composites Composites composed of high-density polyethylene (HDPE), woven flax fiber textiles (Flax weave style of 2x2 twill and 4x4 hopsack) and silicon dioxide (SiO2) were produced by hot press with nano spraying technique. The SiO2 slurries were sprayed by a hand onto the both surface of the woven flax fiber. The HDPE /woven flax fibers composites with and without used nano-spraying technique were produced by hot pressing in a laboratory press. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy (SEM). The related HDPE based composites were subjected to instrumented falling weight impact test. The thermal resistance, stiffness and tensile strength properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA) and tensile tests, respectively. It was found that the impact energy and stiffness value of HDPE/flax composites was markedly higher than that of HDPE but reflect the effects of composite structures and flax content. Incorporation of SiO2 particles enhanced resistance to thermal degradation. It was established that the linear viscoelastic material principle are fairly applicable to convert from the modulus to the creep compliance results. Un- and Modified Polylactide (PLA) /woven Flax Fiber composites Hybrid composites composed of polypropylene (PP) or high-density polyethylene (HDPE), different flax fibers (unidirectional-, biaxial and twill2x2) and silicon dioxide (SiO2) were produced by hot press technique. The ternary polymer composite was effectively fabricated by spraying SiO2 solvents onto the surface of flax fiber. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy (SEM). The related PP and HDPE based composites were subjected to instrumented falling weight impact test. The thermal and mechanical properties of the composites were determined by thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA), creep and stress relaxation tests, respectively. It was found that thermal decomposition temperature of the PP or HDPE/flax composites increased by the addition of SiO2 particles. The impact energy, stiffness, creep resistance and relaxation modulus value of all flax composites increased markedly compared to the PP and HDPE matrix. Time–temperature superposition (TTS) was applied to estimate the creep and relaxation modulus of the composites as a function of time in the form of a master curve. The activation energies for the all PP and HDPE composites systems studied were also calculated by using the Arrhenius equation. The generalized Maxwell model was fairly applicable to the stress relaxation results. Polylactide (PLA)/woven flax fiber textiles/boehmite alumina (BA) composites Composites composed of polylactide (PLA), woven flax fiber textiles (weave style of 2x2 twill and 4x4 hopsack) and boehmite alumina (BA) were produced by hot press. The spraying technique served for the pre-dispersion of the alumina nanoparticles. The aqueous alumina slurry was produced by mixing the water with water dispersible alumina. The dispersion of the flax structures and alumina particles in the composites was studied by scanning electron microscopy (SEM). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The creep and thermomechanical properties of the composites were determined in short-time creep tests (performed at various temperatures), thermogravimetric analysis (TGA) and dynamic-mechanical thermal analysis (DMTA), respectively. It was found that the incorporation of alumina particles reduced the water uptake compared to the PLA/flax blends. The impact energy and stiffness value of PLA/flax blends was markedly higher than that of PLA but reflected the effects of composite structures. Incorporation of alumina particles enhanced storage modulus and the creep resistance compared to the PLA/flax blends but slightly incremented thermal resistance at high temperature. No clear trend in the flax weave style- effect was found in the thermal behaviour. The creep master curves were constructed by applying the time-temperature superposition (TTS) principle. The Findley power law could satisfactorily describe the creep compliance vs. time traces for all systems studied. Poly(hydroxybutyrate-co-hydroxyvalerate)/sisal natural fiber/clay composites Poly(hydroxybutyrate-co-hydroxyvalerate)(PHBV) biocomposites different sisal containing with the fiber length of 0.25 and 5 mm, and addition of clay particles were prepared by hot compression technique. Silane (Bis(triethoxysilylpropyl)tetrasulfide) treatment has been used to modify in order to enhance the properties of related hybrid composites. The all composites were subject to water absorption test. The mechanical properties of hybrid composites such as tensile stiffness and strength, toughness and hardness determined in tensile, impact and hardness tests, respectively. It was found that tensile strength, stiffness and impact strength of long sisal fiber improved with increasing fiber content. Hardness of short sisal fiber improved with increasing fiber content. Treated Silane of long fibers at 20 wt.% loading was found to enhance the tensile strength fiber by 10% and impact strength by 750% as compared to the neat PHBV. Note that this feature was also confirmed by the appearance of a scanning electron microscopy. Moreover, the hardness and water resistance of the PHBV/sisal composites increased by the addition of clay particles. The diffusion coefficient for the PHBV and hybrid composites systems studied were also calculated
Bioverbundwerkstoffe aus biologisch abbaubarem Polymer als Matrix und Naturfasern als Verstärkung sind ohne weiteres umweltfreundliche Materialien. Beide Bestandsmaterialien sind vollständig biologisch abbaubar und hinterlassen keine schädlichen Bestandteile auf der Erde zurück. Die als Verstärkung verwendeten Naturfasern wurden aufgrund ihrer Vorteile gegenüber Glasfasern, wie z.B. geringe Kosten, hohe spezifische Festigkeit und Steifigkeit, geringe Dichte, Erneuerbarkeit und Kompostierbarkeit ausgesucht. Der Hauptfokus dieser Arbeit lag darin Naturfasern und/oder Nanopartikel mit Polyethylen (PE), Polypropylen (PP) und Polylactid (PLA) herzustellen, sowie Poly-Hydroxybutyrat-Co-Hydroxyvalerat (PHBV) Matrizen und deren Struktur-Eigenschaft-Verhältnis zu bestimmen. Die folgenden Kurzfassungen der vorliegenden Forschungsarbeit sind vielfältig: BINÄRE VERBUNDWERKSTOFFE Polylactid (PLA)/ Flachsmatten-Verbundwerkstoffe Die Polylactid (PLA)/Flachsmatte und modifizierte PLA/Flachsmatten-Verbundwerkstoffe wurden im Pressverfahren hergestellt. Als Modifikator für das PLA wurden zwei nicht regulierte Wachs/Ethylen-Acrylat-Copolymer/Butyl-Acrylat und Acryl Additive verwendet. Die Verteilung der Flachsmatte in den Verbundwerkstoffen wurde mit dem Rasterelektronenmikroskop (SEM) untersucht. Die PLA-Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die mechanischen und thermischen Eigenschaften der Verbundwerkstoffe wurden im Zugversuch, der thermogravimetrische Analyse (TGA) und der dynamisch mechanischen Thermoanalyse (DMTA) jeweils bestimmt. Es zeigte sich, dass die PLA/Flachsmatten-basierten Verbundwerkstoffe eine erhöhte Schlagzähigkeit aufwiesen. Die Zähigkeitswerte der modifizierten PLA/Flachsmatten-Verbundwerkstoffe waren leicht verringert im Vergleich zum PLA. Die Bruchdehnungswerte zeigten eine Verbesserung der Verformbarkeit des modifizierten PLAs und dessen Verbundwerkstoffe. Nach Zugabe eines Wärme-Modifikators verbesserte sich der Wärmewiderstand auf unter Verarbeitungstemperatur des PLA und hatte nur einen unwesentlichen Einfluss auf die Glasübergangstemperatur des PLA. Die Hauptkurve des Speichermoduls wurde mit der Zeit-Temperatur-Überlagerung (TTS) aufgestellt. Auf alle untersuchten Systeme konnte das dafür gut geeignete Prinzip der linear viskoelastischen Werkstoffe angewendet werden um die Steifigkeit in die Kriechneigung umzuwandeln. Polylactid (PLA)/Flachstextilgewebe-Verbundwerkstoffe Die Polylactid (PLA)/Flachstextilgewebe 2x2 Körper und 4x4 Gewebe mit Leinwandbindung-Verbundwerkstoffe wurden im Intervall-Pressverfahren hergestellt. Das PLA wurde mit zwei Flachsgewebeformen verstärkt. Die Verteilung der Flachs-Verbundwerkstoffstrukturen in den Verbundwerkstoffen wurde mit dem Rasterelektronenmikroskop (SEM) untersucht. Die PLA Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die mechanischen Eigenschaften (Zugfestigkeit, Steifigkeit und Festigkeit) der jeweiligen Verbundwerkstoffe wurden in Zugversuchen und dynamisch mechanischen Thermoanalysen (DMTA) bestimmt. Das Rasterelektronenmikroskop zeigte auf, das der Grenzflächenzwischenraum von rausgezogenen Fasern sich durch das Herstellen im Intervall-Pressverfahren verbessert hat. Auch zeigte sich, dass beide Arten der Flachs-Verbundwerkstoffe die Schlagzähigkeit der Verbundwerkstoffe erhöht im Vergleich zum puren PLA. Die Zugfestigkeit- und Steifigkeitswerte der PLA/Flachs-Verbundwerkstoffe waren deutlich höher als die der puren PLA und spiegeln die Effekte von Verbundwerkstoffstrukturen wieder. Die berechnete Kriechneigung im Speichermodul wurde durch die Anwendung des Zeit-Temperatur-Überlagerung (TTS) Prinzips aufgestellt. Die errechnete Kriechgeschwindigkeit der Flachs-Verbundwerkstoffe war wesentlich geringer als im puren PLA. Polyethylen und Polypropylen/Nanosilikon Dioxid/Flachs-Verbundwerkstoffe Verbundwerkstoffe hergestellt aus Polylactid (PLA), modifiziertem PLA und Flachsfasertextilgewebe (Flachsgewebeform von 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) wurden im Pressverfahren hergestellt. Zwei strukturell unterschiedliche Additive wurden verwendet um das PLA zu modifizieren. Die Verteilung der Flachs-Verbundwerkstoffstruktur wurde unter dem Rasterelektronenmikroskop (SEM) und dem computergestütztes Computer-Tomography-System (µCT) untersucht. Die PLA Verbundwerkstoffe wurden dem Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die Kriech- und thermomechanischen Eigenschaften der respektiven Verbundwerkstoffe wurden in der thermogravimetrischen Analyse (TGA), der dynamisch mechanischen Thermoanalyse (DMTA) und dem Kurzzeit-Kriechversuch bestimmt. Das modifizierte PLA und dessen Verbundwerkstoffe zeigten eine Erhöhung der Schlagzähigkeit im Vergleich zum unmodifizierten PLA. Die Einbindung von Flachs verringerte den Widerstand gegenüber thermischer Degradierung und erhöhte die Wasseraufnahme. Die Schlagenergie- und Steifigkeitswerte der PLA/Flachs-Verbundwerkstoffe war deutlich höher als die der PLA aber spiegelt die Effekte von Verbundwerkstoffstrukturen mit Flachsinhalt wieder. Die Hauptkurve des Speichermoduls wurde mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Das Datenmaterial der Hauptkurve zeigte den Effekt des modifizierten PLAs auf dem Speichermodul deutlich ausgeprägter im Bereich der Niederfrequenz. Polylactide (PLA)/Flachfasertextilgewebe/Böhmit Aluminumoxid (BA)-Verbundwerkstoffe Die textilen Bioverbundwerkstoffe wurden aus flachsfaserverstärkten Poly(Butylen Adipat-Co-Terephtalat) (PBAT) Gewebe und Vlies im Formpressverfahren mit der Folien-Stapelmethode hergestellt. Die mechanischen Eigenschaften (wie Zugfestigkeit und Steifigkeit, Biegefestigkeit, Steifigkeit und Schlagzähigkeit) der jeweiligen textilen Bioverbundwerkstoffe wurde in Zug-, Biege-, und Schlagtests ermittelt. Die PBAT basierten Verbundwerkstoffe wurden dem Wasseraufnahmetest unterzogen. Der Vergleich der mechanischen Eigenschaften wurde zwischen reinem PBAT und textilen Verbundwerkstoffen durchgeführt. Der Einfluss der Flachsgewebeformen auf die mechanischen Eigenschaften wurde ebenfalls untersucht. Die Ergebnisse zeigten das die Festigkeit der textilen Bioverbundwerkstoffe mit der Webart der Fasern anstieg, signifikant in Bezug auf die Steifigkeit bei einer erhöhten Verdichtung der Fasern. Die 4x4 flachfasergewebten (4-Schussfaden-Windung und 4-Kettfaden-Windung) verstärkten Bioverbundwerkstoffe zeigten die höchste Festigkeit und Steifigkeit im Vergleich zu den anderen textilen Bioverbundwerkstoffen und dem puren PBAT. Dieses Resultat wurde der Beschaffenheit der 4x4-flachfasergewebten Webart zugewiesen. Das Aminopropyltriethoxysilan beeinträchtigte die mechanischen Eigenschaften und Wasseraufnahme der entstandenen Verbundlaminate durch Oberflächenkompatibilität zwischen der Flachsfaser und dem PBAT. HYBRIDE VERBUNDWERKSTOFFE Polyethylen/Nanopartikel, natürliche und tierische Verbundwerkstoffe Binäre und ternäre Verbundwerkstoffe, bestehend aus hoch dichtem Polyethylen (HDPE), Böhmit Aluminumoxid (BA) und verschiedenen natürlichen und tierischen Fasern wie Flachs, Schwammgurke (SG), Palmfaser und Schweinehaar (PH), wurden im Pressverfahren hergestellt. Vorbereitend wurden wasserhaltige BA-Suspensionen auf die HDPE/Flachsmatte gesprüht um nanopartikel/naturfaserverstärkte ternäre Polymer-Verbundwerkstoffe nach dem Trocknen zu erhalten. Die Verteilung der Natur-,Tierfasern und der BA-Partikel in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop untersucht und diskutiert. Die thermomechanischen und Spannungsrelaxation-Eigenschaften der jeweiligen Verbundwerkstoffe wurden in der thermogravimetrischen Analyse (TGA), der dynamisch mechanischen Thermoanalyse (DMTA) und dem Kurzzeit-Stressrelaxationstest (bei unterschiedlichen Temperaturen durchgeführt) bestimmt. Die HDPE-basierten Verbundwerkstoffe wurden Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstests unterzogen. Es wurde festgestellt, dass alle Verbundwerkstoffsysteme eine Erhöhung der Steifigkeit und Spannungsrelaxation und eine Verminderung der Kerbschlagzähigkeit aufzeigten. Die Spannungsrelaxations-Steifigkeit von Naturfaser-, Tierfaserverbundwerkstoffen war größer im Vergleich zu reinem HDPE. Diese Steifigkeit steig deutlich an mit der Einbindung von BA. Die Hauptkurven der Relaxation wurden mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Die Umkehrung des Findley Potenzgesetzes konnte gut für die Beschreibung der Relaxations-Steifigkeit vs. Zeitüberwachung in allen untersuchten Systemen angewendet werden. Die Einbindung der BA-Partikel erhöhte den Wärmewiderstand, welcher bei höherer Temperatur zu sinken begann im Vergleich zu HDPE/Flachsmatten-Verbundwerkstoff. Der HDPE/Flachsmatte/BA-Verbundwerkstoff konnte die Wasseraufnahme verringern. Polyethylen/Flachs/SiO Verbundwerkstoffe Verbundwerkstoffe bestehend aus hoch dichtem Polyethylen (HDPE), Flachsfasertextilgewebe (Flachsgewebeform 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) und Siliziumdioxid (SiO2) wurden im Pressverfahren mit Nanospritztechnik hergestellt. Die SiO2 Schlämme wurden auf beide Oberflächen des Flachsfasergewebes per Hand gesprüht. Die HDPE/ Flachsfasergewebe-Verbundwerkstoffe wurden in einer Laborpresse im Pressverfahren mit und ohne Nanospritztechnik hergestellt. Die Verteilung der SiO2-Partikel und des Flachs in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop (SEM) untersucht. Die ähnlichen HDPE-basierten Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Der Wärmewiderstand, Steifigkeit- und Zugfestigkeit-Eigenschaften der jeweiligen Verbundwerkstoffe wurden in thermogravimetrischen Analysen (TGA), dynamisch mechanischen Thermoanalysen (DMTA) und Zugversuchen bestimmt. Es zeigte sich, dass die Aufprallenergie und Steifigkeitswerte der HDPE/Flachs-Verbundwerkstoffe deutlich höher als die des HDPE waren aber die Effekte von Verbundwerkstoffen mit Flachsinhalt widerspiegeln. Die Einbindung von SiO2-Partikeln erhöhte den Widerstand von thermischer Degradierung. Es wurde bestimmt, das das Prinzip der linear viskoelastischen Werkstoffe gut anwendbar auf die Umwandlung der Steifigkeit zu Kriechneigungsergebnissen ist. Modifizierte und nicht modifizierte Polylactid (PLA)/Flachsfasergewebe-Verbundwerkstoffe Hybride Verbundwerkstoffe aus Polypropylen (PP) oder hoch-dichtem Polyethylen (HDPE), verschiedenen Flachsfasern (unidirektional, biaxial und 2x2 Körper) und Siliziumdioxid (SiO2) wurden im Pressverfahren hergestellt. Der ternäre Polymer-Verbundwerkstoff wurde wirkungsvoll durch das Aufbringen von SiO2 Lösemitteln auf die Oberfläche der Flachsfaser hergestellt. Die Verteilung der SiO2-Partikel und des Flachs in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop (SEM) untersucht. Die ähnlichen PP- und HDPE-basierten Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die thermischen und mechanischen Eigenschaften der respektiven Verbundwerkstoffe wurde in thermogravimetrischen Analysen (TGA), dynamisch mechanischen Thermoanalysen (DMTA), Kriech- und Spannungsrelaxations-Tests bestimmt. Es zeigte sich, dass die thermische Zersetzungstemperatur der PP oder HDPE/Flachs-Verbundwerkstoffe durch das Auftragen der SiO2-Partikel ansteigt. Die Aufprallenergie-, Steifigkeit-, Kriechbeständigkeit- und Relaxation-Steifigkeitn-Werte aller Flachs-Verbundwerkstoffe stiegen deutlich an im Vergleich zur PP und HDPE Matrix. Die Zeit-Temperatur-Überlagerung (TTS) wurde angewandt um die Kriech- und Relaxation-Steifigkeit für die Verbundwerkstoffe als Funktion der Zeit in Form einer Hauptkurve zu schätzen. Die Aktivierungsenergien aller untersuchten PP und HDPE-Verbundwerkstoffsysteme wurden mit der Arrhenius Gleichung errechnet. Das generalisierte Maxwell Model war gut auf die Spannungsrelaxationsergebnisse anwendbar. Polylactide (PLA)/Flachsfasertextilgewebe/Böhmit Aluminiumoxid (BA)-Verbundwerkstoffe Verbundwerkstoffe bestehend aus Polylactid (PLA), Flachfasertextilgewebe (Gewebeform 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) und Böhmit Aluminium (BA) wurden im Pressverfahren hergestellt. Für die Vordispergierung der Aluminiumoxid-Nanopartikel wurde die Spritztechnik angewendet. Die wasserhaltigen Aluminiumoxid-Schlämme wurden durch das Vermischen von Wasser mit wasserdispergierbarem Aluminiumoxid hergestellt. Die Verteilung der Flachsstrukturen und Aluminiumoxid-Partikeln in den Verbundwerkstoffen wurde mit einem Rasterelektronenmikroskop (SEM) untersucht. Die PLA-Verbundwerkstoffe wurden Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstests unterzogen. Die Kriech- und thermomechanischen Eigenschaften der jeweiligen Verbundwerkstoffe wurden in Kurzzeit-Kriechversuchen (bei unterschiedlichen Temperaturen durchgeführt), thermogravimetrischen Analysen (TGA) und dynamisch mechanischen Thermoanalysen (DMTA) bestimmt. Es zeigte sich, dass das Einbringen der Aluminiumoxid-Partikel die Wasseraufnahme im Vergleich zu PLA/Flachs-Gemischen reduziert. Die Aufprallenergie- und Steifigkeitswerte der PLA/Flachs-Gemische waren signifikant höher als die des PLA aber spiegelten die Effekte von Verbundwerkstoffstrukturen wieder. Das Einbringen von Aluminiumoxid-Partikeln verbesserte die Lagerungs-Steifigkeit und die Kriechbeständigkeit im Vergleich zu PLA/Flachs-Gemischen, erhöhte allerdings leicht den Wärmewiderstand bei hohen Temperaturen. Kein klarer Trend in der Flachswebart konnte dem Temperaturverhalten zugeordnet werden. Die Kriech-Hauptkurven wurden mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Das Findley Potenzgesetz konnte zufriedenstellend die Kriechneigung vs. Zeitüberwachung für alle untersuchten Systeme beschreiben. Poly(Hydroxybutyrat-Co-Hydroxyvalerat)/Natursisalfaser/Ton-Verbundwerkstoffe Poly(Hydroxybutyrat-Co-Hydroxyvalerat) (PHBV) Bioverbundwerkstoffe die Sisalfasern in Längen von 0,25 und 5 mm und Ton-Partikeln enthalten wurden im Heißpressverfahren hergestellt. Die Silan (Bis(Trithoxysilylpropyl)Tetrasulfide) Behandlung wurde für die Modifizierung verwendet um die Eigenschaften von ähnlichen hybriden Verbundwerkstoffen zu verbessern. Alle Verbundwerkstoffe wurden dem Wasseraufnahmetest unterzogen. Die mechanischen Eigenschaften der jeweiligen hybriden Verbundwerkstoffe wie Zugsteifigkeit und Festigkeit, Zähigkeit und Härte wurden in Zugversuchen, Schlagtests und Härteprüfungen bestimmt. Es zeigte sich, dass die Zugfestigkeit, Steifigkeit und Schlagzähigkeit von langen Sisalfasern sich mit der Erhöhung des Fasergehalts verbessert. Behandeltes Silan von langen Fasern mit 20 wt.% Belastung zeigte eine Verbesserung der Faser-Zugfestigkeit um 10% und Schlagzähigkeit von 750% im Vergleich zu reinem PHBV. Diese Besonderheit wurde auch von einem Rasterelektronenmikroskop bestätigt. Weiterhin ist die Härte und Wasserbeständigkeit in PHBV/Sisal-Verbundwerkstoffen durch das Einbringen von Ton-Partikeln angestiegen. Die Diffusionskoeffizienten für die untersuchten PHBV- und hybriden Verbundwerkstoffsysteme wurden auch errechnet

Biocomposites made from biodegradable polymer as matrix and natural fiber as reinforcement are certainly environmentally friendly materials. Both constituent materials are fully biodegradable and do not leave any noxious components on Earth. The natural fibers have been used as reinforcement due to their advantages compared to glass fibers such as low cost, high specific strength and modulus, low density, renewability and biodegradability. Major aims of this work were to produce natural fibers and/or nanoparticles with polyethylene (PE), polypropylene (PP) and polylactide (PLA), poly(hydroxybutyrate-co-hydroxyvalerate)(PHBV) matrices and determine their structure-property relationships. Following abstracts of the present research work are manifold: BINARY COMPOSITES Polylactide (PLA)/flax mat composites The polylactide (PLA)/flax mat and modified PLA/flax mat composites were produced by hot press technique. Two additives of non-regulated wax/ethylene acrylate copolymer/butyl acrylate and acrylic were used as modifier for PLA. The dispersion of the flax mat in the composites was studied by scanning electron microscopy (SEM). The PLA composites were subjected to instrumented falling weight impact test. The mechanical and thermal properties of the composites were determined in tensile test, thermogravimetric analysis (TGA) and dynamic-mechanical thermal analysis (DMTA), respectively. It was found that the PLA based composites increased the impact resistance. The tensile strength value of modified PLA/flax mat composite decreased slightly compared to the PLA. The elongation at break data indicated that an improvement in ductility of modified PLA and its composites. Moreover, addition of thermal modifier enhanced thermal resistance below processing temperature of PLA and had a marginal effect on the glass transition temperature of PLA. The storage modulus master curves were constructed by applying the time-temperature superposition (TTS) principle. The principle of linear viscoelastic material was fairly applicable to convert from the modulus to the creep compliance for all systems studied. Polylactide (PLA)/woven flax textiles composites The polylactide (PLA)/woven flax textiles 2x2 twill and 4x4 hopsack composites were produced by interval hot press technique. Two weave styles of flax used to reinforce in PLA. The dispersion of the flax composite structures in the composites was inspected in scanning electron microscopy (SEM). The PLA composites were subjected to instrumented falling weight impact test. The mechanical properties (tensile, stiffness and strength) of the composites were determined in tensile and dynamic-mechanical thermal analysis (DMTA) tests, respectively. SEM observed that the interfacial gaps around pulled-out fibers were improved when produced by the interval hot press. It was also found that the both styles of flax composites increased the impact resistance compared to the neat PLA. The tensile strength and stiffness value of PLA/flax composites were markedly higher than that of the neat PLA and reflect the effects of composite structures. The calculated storage creep compliance was constructed by applying the time-temperature superposition (TTS) principle. The calculated creep response of these flax composites was much lower than that of the neat PLA. Polyethylene and polypropylene/nano-silicon dioxide/flax composites Composites composed of polylactide (PLA), modified PLA and woven flax fiber textiles (Flax weave style of 2x2 twill and 4x4 hopsack) were produced by hot press technique. Two structurally different additives used to modify PLA. The dispersion of the flax composite structures in the composites was studied by scanning electron microscopy (SEM) and computed microtomography system (µCT). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The thermomechanical and creep properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA)and short-time creep tests, respectively. It was found that the modified PLA and its composite increased the impact resistance compared to the unmodified PLA. Incorporation of flax decreased resistance to thermal degradation and increased water uptake. The impact energy and stiffness value of PLA/flax composites was markedly higher than that of PLA but reflect the effects of composite structures and flax content. The storage modulus master curves were constructed by applying the time-temperature superposition (TTS) principle. From the master curve data, the effect of modified PLA on the storage modulus was more pronounced in the low frequencies range. Polylactide (PLA)/woven flax fiber textiles/boehmite alumina (BA) composites The textile biocomposites made from woven and non-woven flax fibre reinforced poly(butylene adipate-co-terephthalate) (PBAT) were prepared by compression moulding using film stacking method. The mechanical properties (such as tensile strength and stiffness, flexural strength and modulus, and impact strength) of textile biocomposites were determined in tensile, flexural and impact tests, respectively. The PBAT-based composites were subjected to water absorption. The comparison of the mechanical properties was made between pure PBAT and textile composites. The influence of flax weave styles on the mechanical properties was also evaluated. The results showed that the strength of the textile biocomposites was increased according to weave types of fibers, especially in the stiffness was significantly increased with the higher densification of the fibers. The 4x4-plain woven fibers (4-yard-wrap and 4-yard-weft weave direction) reinforced biocomposite indicated the highest strength and stiffness compared to the other textile biocomposites and pure PBAT. This was considered to be as the result of the character of weave style of 4x4-plain woven fibers. The aminopropyltriethoxysilane affected the mechanical properties and water absorption of the resulting composites laminates due to the surface compatibility between flax fiber and PBAT. HYBRID COMPOSITES Polyethylene/nanoparticle, natural and animal composites Binary and ternary composites composed of high-density polyethylene (HDPE), boehmite alumina (BA) and different kinds of natural-, animal fibers, like flax, sponge gourd (SG), palm and pig hair (PH) were produced by hot press technique. Aqueous BA suspensions were sprayed on the HDPE/flax mat to prepare nanoparticle/natural fiber reinforced ternary polymer composites followed by drying. The dispersion of the natural-, animal fibers and BA particles in the composites was studied by scanning electron microscopy (SEM) and discussed. The thermomechanical and stress relaxation properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA) and short-time stress relaxation tests (performed at various temperatures), respectively. The HDPE based composites were subjected to water absorption and instrumented falling weight impact tests. It was found that the all composites systems increased the stiffness, stress relaxation and reduced the impact toughness. The stress relaxation modulus of natural-, animal fiber composites were higher compared to that of the neat HDPE. This modulus increased greatly with in corporation of BA. The relaxation master curves were constructed by applying the time-temperature superposition (TTS) principle. The inverse of Findley power law could fairly applicable to describe the relaxation modulus vs. time traces for all systems studied. Incorporation of BA particles enhanced the thermal resistance which started to degrade at higher temperature compared to the HDPE/flax mat composite. The HDPE/flax mat/BA composite could reduce the water uptake. Polyethylene/Flax/SiO2 Composites Composites composed of high-density polyethylene (HDPE), woven flax fiber textiles (Flax weave style of 2x2 twill and 4x4 hopsack) and silicon dioxide (SiO2) were produced by hot press with nano spraying technique. The SiO2 slurries were sprayed by a hand onto the both surface of the woven flax fiber. The HDPE /woven flax fibers composites with and without used nano-spraying technique were produced by hot pressing in a laboratory press. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy (SEM). The related HDPE based composites were subjected to instrumented falling weight impact test. The thermal resistance, stiffness and tensile strength properties of the composites were determined in thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA) and tensile tests, respectively. It was found that the impact energy and stiffness value of HDPE/flax composites was markedly higher than that of HDPE but reflect the effects of composite structures and flax content. Incorporation of SiO2 particles enhanced resistance to thermal degradation. It was established that the linear viscoelastic material principle are fairly applicable to convert from the modulus to the creep compliance results. Un- and Modified Polylactide (PLA) /woven Flax Fiber composites Hybrid composites composed of polypropylene (PP) or high-density polyethylene (HDPE), different flax fibers (unidirectional-, biaxial and twill2x2) and silicon dioxide (SiO2) were produced by hot press technique. The ternary polymer composite was effectively fabricated by spraying SiO2 solvents onto the surface of flax fiber. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy (SEM). The related PP and HDPE based composites were subjected to instrumented falling weight impact test. The thermal and mechanical properties of the composites were determined by thermogravimetric analysis (TGA), dynamic-mechanical thermal analysis (DMTA), creep and stress relaxation tests, respectively. It was found that thermal decomposition temperature of the PP or HDPE/flax composites increased by the addition of SiO2 particles. The impact energy, stiffness, creep resistance and relaxation modulus value of all flax composites increased markedly compared to the PP and HDPE matrix. Time–temperature superposition (TTS) was applied to estimate the creep and relaxation modulus of the composites as a function of time in the form of a master curve. The activation energies for the all PP and HDPE composites systems studied were also calculated by using the Arrhenius equation. The generalized Maxwell model was fairly applicable to the stress relaxation results. Polylactide (PLA)/woven flax fiber textiles/boehmite alumina (BA) composites Composites composed of polylactide (PLA), woven flax fiber textiles (weave style of 2x2 twill and 4x4 hopsack) and boehmite alumina (BA) were produced by hot press. The spraying technique served for the pre-dispersion of the alumina nanoparticles. The aqueous alumina slurry was produced by mixing the water with water dispersible alumina. The dispersion of the flax structures and alumina particles in the composites was studied by scanning electron microscopy (SEM). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The creep and thermomechanical properties of the composites were determined in short-time creep tests (performed at various temperatures), thermogravimetric analysis (TGA) and dynamic-mechanical thermal analysis (DMTA), respectively. It was found that the incorporation of alumina particles reduced the water uptake compared to the PLA/flax blends. The impact energy and stiffness value of PLA/flax blends was markedly higher than that of PLA but reflected the effects of composite structures. Incorporation of alumina particles enhanced storage modulus and the creep resistance compared to the PLA/flax blends but slightly incremented thermal resistance at high temperature. No clear trend in the flax weave style- effect was found in the thermal behaviour. The creep master curves were constructed by applying the time-temperature superposition (TTS) principle. The Findley power law could satisfactorily describe the creep compliance vs. time traces for all systems studied. Poly(hydroxybutyrate-co-hydroxyvalerate)/sisal natural fiber/clay composites Poly(hydroxybutyrate-co-hydroxyvalerate)(PHBV) biocomposites different sisal containing with the fiber length of 0.25 and 5 mm, and addition of clay particles were prepared by hot compression technique. Silane (Bis(triethoxysilylpropyl)tetrasulfide) treatment has been used to modify in order to enhance the properties of related hybrid composites. The all composites were subject to water absorption test. The mechanical properties of hybrid composites such as tensile stiffness and strength, toughness and hardness determined in tensile, impact and hardness tests, respectively. It was found that tensile strength, stiffness and impact strength of long sisal fiber improved with increasing fiber content. Hardness of short sisal fiber improved with increasing fiber content. Treated Silane of long fibers at 20 wt.% loading was found to enhance the tensile strength fiber by 10% and impact strength by 750% as compared to the neat PHBV. Note that this feature was also confirmed by the appearance of a scanning electron microscopy. Moreover, the hardness and water resistance of the PHBV/sisal composites increased by the addition of clay particles. The diffusion coefficient for the PHBV and hybrid composites systems studied were also calculated.
Bioverbundwerkstoffe aus biologisch abbaubarem Polymer als Matrix und Naturfasern als Verstärkung sind ohne weiteres umweltfreundliche Materialien. Beide Bestandsmaterialien sind vollständig biologisch abbaubar und hinterlassen keine schädlichen Bestandteile auf der Erde zurück. Die als Verstärkung verwendeten Naturfasern wurden aufgrund ihrer Vorteile gegenüber Glasfasern, wie z.B. geringe Kosten, hohe spezifische Festigkeit und Steifigkeit, geringe Dichte, Erneuerbarkeit und Kompostierbarkeit ausgesucht. Der Hauptfokus dieser Arbeit lag darin Naturfasern und/oder Nanopartikel mit Polyethylen (PE), Polypropylen (PP) und Polylactid (PLA) herzustellen, sowie Poly-Hydroxybutyrat-Co-Hydroxyvalerat (PHBV) Matrizen und deren Struktur-Eigenschaft-Verhältnis zu bestimmen. Die folgenden Kurzfassungen der vorliegenden Forschungsarbeit sind vielfältig: BINÄRE VERBUNDWERKSTOFFE Polylactid (PLA)/ Flachsmatten-Verbundwerkstoffe Die Polylactid (PLA)/Flachsmatte und modifizierte PLA/Flachsmatten-Verbundwerkstoffe wurden im Pressverfahren hergestellt. Als Modifikator für das PLA wurden zwei nicht regulierte Wachs/Ethylen-Acrylat-Copolymer/Butyl-Acrylat und Acryl Additive verwendet. Die Verteilung der Flachsmatte in den Verbundwerkstoffen wurde mit dem Rasterelektronenmikroskop (SEM) untersucht. Die PLA-Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die mechanischen und thermischen Eigenschaften der Verbundwerkstoffe wurden im Zugversuch, der thermogravimetrische Analyse (TGA) und der dynamisch mechanischen Thermoanalyse (DMTA) jeweils bestimmt. Es zeigte sich, dass die PLA/Flachsmatten-basierten Verbundwerkstoffe eine erhöhte Schlagzähigkeit aufwiesen. Die Zähigkeitswerte der modifizierten PLA/Flachsmatten-Verbundwerkstoffe waren leicht verringert im Vergleich zum PLA. Die Bruchdehnungswerte zeigten eine Verbesserung der Verformbarkeit des modifizierten PLAs und dessen Verbundwerkstoffe. Nach Zugabe eines Wärme-Modifikators verbesserte sich der Wärmewiderstand auf unter Verarbeitungstemperatur des PLA und hatte nur einen unwesentlichen Einfluss auf die Glasübergangstemperatur des PLA. Die Hauptkurve des Speichermoduls wurde mit der Zeit-Temperatur-Überlagerung (TTS) aufgestellt. Auf alle untersuchten Systeme konnte das dafür gut geeignete Prinzip der linear viskoelastischen Werkstoffe angewendet werden um die Steifigkeit in die Kriechneigung umzuwandeln. Polylactid (PLA)/Flachstextilgewebe-Verbundwerkstoffe Die Polylactid (PLA)/Flachstextilgewebe 2x2 Körper und 4x4 Gewebe mit Leinwandbindung-Verbundwerkstoffe wurden im Intervall-Pressverfahren hergestellt. Das PLA wurde mit zwei Flachsgewebeformen verstärkt. Die Verteilung der Flachs-Verbundwerkstoffstrukturen in den Verbundwerkstoffen wurde mit dem Rasterelektronenmikroskop (SEM) untersucht. Die PLA Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die mechanischen Eigenschaften (Zugfestigkeit, Steifigkeit und Festigkeit) der jeweiligen Verbundwerkstoffe wurden in Zugversuchen und dynamisch mechanischen Thermoanalysen (DMTA) bestimmt. Das Rasterelektronenmikroskop zeigte auf, das der Grenzflächenzwischenraum von rausgezogenen Fasern sich durch das Herstellen im Intervall-Pressverfahren verbessert hat. Auch zeigte sich, dass beide Arten der Flachs-Verbundwerkstoffe die Schlagzähigkeit der Verbundwerkstoffe erhöht im Vergleich zum puren PLA. Die Zugfestigkeit- und Steifigkeitswerte der PLA/Flachs-Verbundwerkstoffe waren deutlich höher als die der puren PLA und spiegeln die Effekte von Verbundwerkstoffstrukturen wieder. Die berechnete Kriechneigung im Speichermodul wurde durch die Anwendung des Zeit-Temperatur-Überlagerung (TTS) Prinzips aufgestellt. Die errechnete Kriechgeschwindigkeit der Flachs-Verbundwerkstoffe war wesentlich geringer als im puren PLA. Polyethylen und Polypropylen/Nanosilikon Dioxid/Flachs-Verbundwerkstoffe Verbundwerkstoffe hergestellt aus Polylactid (PLA), modifiziertem PLA und Flachsfasertextilgewebe (Flachsgewebeform von 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) wurden im Pressverfahren hergestellt. Zwei strukturell unterschiedliche Additive wurden verwendet um das PLA zu modifizieren. Die Verteilung der Flachs-Verbundwerkstoffstruktur wurde unter dem Rasterelektronenmikroskop (SEM) und dem computergestütztes Computer-Tomography-System (µCT) untersucht. Die PLA Verbundwerkstoffe wurden dem Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die Kriech- und thermomechanischen Eigenschaften der respektiven Verbundwerkstoffe wurden in der thermogravimetrischen Analyse (TGA), der dynamisch mechanischen Thermoanalyse (DMTA) und dem Kurzzeit-Kriechversuch bestimmt. Das modifizierte PLA und dessen Verbundwerkstoffe zeigten eine Erhöhung der Schlagzähigkeit im Vergleich zum unmodifizierten PLA. Die Einbindung von Flachs verringerte den Widerstand gegenüber thermischer Degradierung und erhöhte die Wasseraufnahme. Die Schlagenergie- und Steifigkeitswerte der PLA/Flachs-Verbundwerkstoffe war deutlich höher als die der PLA aber spiegelt die Effekte von Verbundwerkstoffstrukturen mit Flachsinhalt wieder. Die Hauptkurve des Speichermoduls wurde mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Das Datenmaterial der Hauptkurve zeigte den Effekt des modifizierten PLAs auf dem Speichermodul deutlich ausgeprägter im Bereich der Niederfrequenz. Polylactide (PLA)/Flachfasertextilgewebe/Böhmit Aluminumoxid (BA)-Verbundwerkstoffe Die textilen Bioverbundwerkstoffe wurden aus flachsfaserverstärkten Poly(Butylen Adipat-Co-Terephtalat) (PBAT) Gewebe und Vlies im Formpressverfahren mit der Folien-Stapelmethode hergestellt. Die mechanischen Eigenschaften (wie Zugfestigkeit und Steifigkeit, Biegefestigkeit, Steifigkeit und Schlagzähigkeit) der jeweiligen textilen Bioverbundwerkstoffe wurde in Zug-, Biege-, und Schlagtests ermittelt. Die PBAT basierten Verbundwerkstoffe wurden dem Wasseraufnahmetest unterzogen. Der Vergleich der mechanischen Eigenschaften wurde zwischen reinem PBAT und textilen Verbundwerkstoffen durchgeführt. Der Einfluss der Flachsgewebeformen auf die mechanischen Eigenschaften wurde ebenfalls untersucht. Die Ergebnisse zeigten das die Festigkeit der textilen Bioverbundwerkstoffe mit der Webart der Fasern anstieg, signifikant in Bezug auf die Steifigkeit bei einer erhöhten Verdichtung der Fasern. Die 4x4 flachfasergewebten (4-Schussfaden-Windung und 4-Kettfaden-Windung) verstärkten Bioverbundwerkstoffe zeigten die höchste Festigkeit und Steifigkeit im Vergleich zu den anderen textilen Bioverbundwerkstoffen und dem puren PBAT. Dieses Resultat wurde der Beschaffenheit der 4x4-flachfasergewebten Webart zugewiesen. Das Aminopropyltriethoxysilan beeinträchtigte die mechanischen Eigenschaften und Wasseraufnahme der entstandenen Verbundlaminate durch Oberflächenkompatibilität zwischen der Flachsfaser und dem PBAT. HYBRIDE VERBUNDWERKSTOFFE Polyethylen/Nanopartikel, natürliche und tierische Verbundwerkstoffe Binäre und ternäre Verbundwerkstoffe, bestehend aus hoch dichtem Polyethylen (HDPE), Böhmit Aluminumoxid (BA) und verschiedenen natürlichen und tierischen Fasern wie Flachs, Schwammgurke (SG), Palmfaser und Schweinehaar (PH), wurden im Pressverfahren hergestellt. Vorbereitend wurden wasserhaltige BA-Suspensionen auf die HDPE/Flachsmatte gesprüht um nanopartikel/naturfaserverstärkte ternäre Polymer-Verbundwerkstoffe nach dem Trocknen zu erhalten. Die Verteilung der Natur-,Tierfasern und der BA-Partikel in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop untersucht und diskutiert. Die thermomechanischen und Spannungsrelaxation-Eigenschaften der jeweiligen Verbundwerkstoffe wurden in der thermogravimetrischen Analyse (TGA), der dynamisch mechanischen Thermoanalyse (DMTA) und dem Kurzzeit-Stressrelaxationstest (bei unterschiedlichen Temperaturen durchgeführt) bestimmt. Die HDPE-basierten Verbundwerkstoffe wurden Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstests unterzogen. Es wurde festgestellt, dass alle Verbundwerkstoffsysteme eine Erhöhung der Steifigkeit und Spannungsrelaxation und eine Verminderung der Kerbschlagzähigkeit aufzeigten. Die Spannungsrelaxations-Steifigkeit von Naturfaser-, Tierfaserverbundwerkstoffen war größer im Vergleich zu reinem HDPE. Diese Steifigkeit steig deutlich an mit der Einbindung von BA. Die Hauptkurven der Relaxation wurden mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Die Umkehrung des Findley Potenzgesetzes konnte gut für die Beschreibung der Relaxations-Steifigkeit vs. Zeitüberwachung in allen untersuchten Systemen angewendet werden. Die Einbindung der BA-Partikel erhöhte den Wärmewiderstand, welcher bei höherer Temperatur zu sinken begann im Vergleich zu HDPE/Flachsmatten-Verbundwerkstoff. Der HDPE/Flachsmatte/BA-Verbundwerkstoff konnte die Wasseraufnahme verringern. Polyethylen/Flachs/SiO Verbundwerkstoffe Verbundwerkstoffe bestehend aus hoch dichtem Polyethylen (HDPE), Flachsfasertextilgewebe (Flachsgewebeform 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) und Siliziumdioxid (SiO2) wurden im Pressverfahren mit Nanospritztechnik hergestellt. Die SiO2 Schlämme wurden auf beide Oberflächen des Flachsfasergewebes per Hand gesprüht. Die HDPE/ Flachsfasergewebe-Verbundwerkstoffe wurden in einer Laborpresse im Pressverfahren mit und ohne Nanospritztechnik hergestellt. Die Verteilung der SiO2-Partikel und des Flachs in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop (SEM) untersucht. Die ähnlichen HDPE-basierten Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Der Wärmewiderstand, Steifigkeit- und Zugfestigkeit-Eigenschaften der jeweiligen Verbundwerkstoffe wurden in thermogravimetrischen Analysen (TGA), dynamisch mechanischen Thermoanalysen (DMTA) und Zugversuchen bestimmt. Es zeigte sich, dass die Aufprallenergie und Steifigkeitswerte der HDPE/Flachs-Verbundwerkstoffe deutlich höher als die des HDPE waren aber die Effekte von Verbundwerkstoffen mit Flachsinhalt widerspiegeln. Die Einbindung von SiO2-Partikeln erhöhte den Widerstand von thermischer Degradierung. Es wurde bestimmt, das das Prinzip der linear viskoelastischen Werkstoffe gut anwendbar auf die Umwandlung der Steifigkeit zu Kriechneigungsergebnissen ist. Modifizierte und nicht modifizierte Polylactid (PLA)/Flachsfasergewebe-Verbundwerkstoffe Hybride Verbundwerkstoffe aus Polypropylen (PP) oder hoch-dichtem Polyethylen (HDPE), verschiedenen Flachsfasern (unidirektional, biaxial und 2x2 Körper) und Siliziumdioxid (SiO2) wurden im Pressverfahren hergestellt. Der ternäre Polymer-Verbundwerkstoff wurde wirkungsvoll durch das Aufbringen von SiO2 Lösemitteln auf die Oberfläche der Flachsfaser hergestellt. Die Verteilung der SiO2-Partikel und des Flachs in den Verbundwerkstoffen wurde unter dem Rasterelektronenmikroskop (SEM) untersucht. Die ähnlichen PP- und HDPE-basierten Verbundwerkstoffe wurden dem instrumentalisierten Fallgewichtsschlagzähigkeitstest unterzogen. Die thermischen und mechanischen Eigenschaften der respektiven Verbundwerkstoffe wurde in thermogravimetrischen Analysen (TGA), dynamisch mechanischen Thermoanalysen (DMTA), Kriech- und Spannungsrelaxations-Tests bestimmt. Es zeigte sich, dass die thermische Zersetzungstemperatur der PP oder HDPE/Flachs-Verbundwerkstoffe durch das Auftragen der SiO2-Partikel ansteigt. Die Aufprallenergie-, Steifigkeit-, Kriechbeständigkeit- und Relaxation-Steifigkeitn-Werte aller Flachs-Verbundwerkstoffe stiegen deutlich an im Vergleich zur PP und HDPE Matrix. Die Zeit-Temperatur-Überlagerung (TTS) wurde angewandt um die Kriech- und Relaxation-Steifigkeit für die Verbundwerkstoffe als Funktion der Zeit in Form einer Hauptkurve zu schätzen. Die Aktivierungsenergien aller untersuchten PP und HDPE-Verbundwerkstoffsysteme wurden mit der Arrhenius Gleichung errechnet. Das generalisierte Maxwell Model war gut auf die Spannungsrelaxationsergebnisse anwendbar. Polylactide (PLA)/Flachsfasertextilgewebe/Böhmit Aluminiumoxid (BA)-Verbundwerkstoffe Verbundwerkstoffe bestehend aus Polylactid (PLA), Flachfasertextilgewebe (Gewebeform 2x2 Körper und 4x4 Gewebe mit Leinwandbindung) und Böhmit Aluminium (BA) wurden im Pressverfahren hergestellt. Für die Vordispergierung der Aluminiumoxid-Nanopartikel wurde die Spritztechnik angewendet. Die wasserhaltigen Aluminiumoxid-Schlämme wurden durch das Vermischen von Wasser mit wasserdispergierbarem Aluminiumoxid hergestellt. Die Verteilung der Flachsstrukturen und Aluminiumoxid-Partikeln in den Verbundwerkstoffen wurde mit einem Rasterelektronenmikroskop (SEM) untersucht. Die PLA-Verbundwerkstoffe wurden Wasseraufnahme- und instrumentalisierten Fallgewichtsschlagzähigkeitstests unterzogen. Die Kriech- und thermomechanischen Eigenschaften der jeweiligen Verbundwerkstoffe wurden in Kurzzeit-Kriechversuchen (bei unterschiedlichen Temperaturen durchgeführt), thermogravimetrischen Analysen (TGA) und dynamisch mechanischen Thermoanalysen (DMTA) bestimmt. Es zeigte sich, dass das Einbringen der Aluminiumoxid-Partikel die Wasseraufnahme im Vergleich zu PLA/Flachs-Gemischen reduziert. Die Aufprallenergie- und Steifigkeitswerte der PLA/Flachs-Gemische waren signifikant höher als die des PLA aber spiegelten die Effekte von Verbundwerkstoffstrukturen wieder. Das Einbringen von Aluminiumoxid-Partikeln verbesserte die Lagerungs-Steifigkeit und die Kriechbeständigkeit im Vergleich zu PLA/Flachs-Gemischen, erhöhte allerdings leicht den Wärmewiderstand bei hohen Temperaturen. Kein klarer Trend in der Flachswebart konnte dem Temperaturverhalten zugeordnet werden. Die Kriech-Hauptkurven wurden mit dem Zeit-Temperatur-Überlagerung (TTS) Prinzip aufgestellt. Das Findley Potenzgesetz konnte zufriedenstellend die Kriechneigung vs. Zeitüberwachung für alle untersuchten Systeme beschreiben. Poly(Hydroxybutyrat-Co-Hydroxyvalerat)/Natursisalfaser/Ton-Verbundwerkstoffe Poly(Hydroxybutyrat-Co-Hydroxyvalerat) (PHBV) Bioverbundwerkstoffe die Sisalfasern in Längen von 0,25 und 5 mm und Ton-Partikeln enthalten wurden im Heißpressverfahren hergestellt. Die Silan (Bis(Trithoxysilylpropyl)Tetrasulfide) Behandlung wurde für die Modifizierung verwendet um die Eigenschaften von ähnlichen hybriden Verbundwerkstoffen zu verbessern. Alle Verbundwerkstoffe wurden dem Wasseraufnahmetest unterzogen. Die mechanischen Eigenschaften der jeweiligen hybriden Verbundwerkstoffe wie Zugsteifigkeit und Festigkeit, Zähigkeit und Härte wurden in Zugversuchen, Schlagtests und Härteprüfungen bestimmt. Es zeigte sich, dass die Zugfestigkeit, Steifigkeit und Schlagzähigkeit von langen Sisalfasern sich mit der Erhöhung des Fasergehalts verbessert. Behandeltes Silan von langen Fasern mit 20 wt.% Belastung zeigte eine Verbesserung der Faser-Zugfestigkeit um 10% und Schlagzähigkeit von 750% im Vergleich zu reinem PHBV. Diese Besonderheit wurde auch von einem Rasterelektronenmikroskop bestätigt. Weiterhin ist die Härte und Wasserbeständigkeit in PHBV/Sisal-Verbundwerkstoffen durch das Einbringen von Ton-Partikeln angestiegen. Die Diffusionskoeffizienten für die untersuchten PHBV- und hybriden Verbundwerkstoffsysteme wurden auch errechnet.

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
BRITISH COUNCIL
UNIVERSIDADE FEDERAL DA PARAÍBA
A presente tese estuda as propriedades de curta e londa duração de argamassas de cimento reforçadas com fibras de coco e sisal. O trabalho experimental visou a determinação das propriedades físicas e mecânicas do reforço e o estudo da influência do tipo, fração volumétrica e tamanho de fibra, orientação e composição da matriz nas propriedades mecânicas do compósito. Estudos foram executados com o objetivo de se determinar a influência do reforço na retração plástica, com e sem restrições, das matrizes de argamassa. Fissurações resultantes da imposição das restrições e o fenômeno de cicatrização das fissuras foram também investigados. O modo de ruptura e as propriedades de aderência interfacial fibra-matriz foram determinados através de ensaios de arrancamento. As propriedades de longa duração dos compósitos foram determinadas através dos ensaios de fluência, retração e durabilidade. A influência da adição de várias frações volumétricas e tamanhos de fibras na fluência das matrizes de argamassa foi determinada usando-se corpos de prova, selados e não selados, submetidos a uma pressão de 14,4 MPa durante um período de 210-350 dias. Recuperações das deformações elásticas foram monitoradas por um período de 56-180 dias. A influência dos tipos de fibra, fração volumétrica, tamanho de fibra, tipo de cura, traço da argamassa e substituição parcial do cimento Portland por micro-sílica e escória de alto forno na estabilidade dimensional das matrizes de argamassa foi determinada com o uso de ensaios de retração por um período de 320 dias. A durabilidade das fibras de coco e sisal, imersas em soluções alcalinas de hidróxido de cálcio e de sódio e em água de torneira, foi determinada através da realização de ensaios de resistência à tração em idades variando de 30-420 dias. A durabilidade das argamassas reforçadas com fibras naturais após 320-360 dias imersas em água, expostas a ciclos de molhagem e secagem bem como ao ambiente natural foi determinada através de resultados de ensaios de flexão e de observações de imagens obtidas com o uso de microscopia eletrônica. Um mapeamento de elementos químicos foi realizado com o objetivo de se verificar possíveis migrações de produtos da matriz de cimento Portland para o lúmen e paredes das fibras. Tratamentos para garantir a durabilidade dos compósitos foram estudados, a saber: (a) modificações na matriz através da substituição parcial do cimento Portland por micro-sílica e escória de alto orno; (b) carbonatação da matriz de cimento Portland; (c) imersão das fibras em micro-sílica líquida antes de serem incorporadas à matriz de cimento Portand.
This thesis studies both the short-term and long- term behaviour of sisal and coconut fibre reinforced mortar composites.The experimental work involved extensive laboratory testing to determine the physical and mechanical properties of the fibre reinforcement and to study the influence of fibre type, volume fraction, fibre length, fibre arrangement and matrix composition on the mechanical properties of the composite.Studies were also made to determine the influence of fibre reinforcement in controlling free and restrained shrinkage during the early age of mortar mixes. Cracking due to restraint and the phenomenon of crack self-healing were also investigated. The mode of failure and the properties of the resistance to fibre-matrix interfacial bonding were determined using the single fibre pull-out test.The long-term properties of the sisal and coconut fibre reinforced-mortar composites were assessed throughout creep, shrinkage and durability tests. The influence of the addition of sisal and coconut fibres, of various volume fraction and lengths, on the creep of a mortar matrix was determined using sealed and unsealed specimens subjected to a pressure of 14.4 MPa over a period of 210-350 days. Recovery strains were recorded for a period of 56-180 days.The influence of fibre types, volume fraction, fibre lengths, cure types, mix proportions and replacement of OPC by slag and silica fume on the dimensional stability of mortar matrices was determined using drying shrinkage tests for a period of 320 days. The durability of sisal and coconut fibres exposed to alkaline solutions of calcium and sodium hydroxide and stored in tap water was measured as strength loss over a period of 420 days. The durability of fibre-reinforced mortars after 320 to 360 days, stored under water, exposed to cycles of wetting and drying as well as to the natural weather,was assessed from results of flexural tests and from observations of the photomicrographs obtained using backscattered imaging and secondary electron imaging. Dotting maps of chemical elements were obtained in order to verify possible migration of cement products from the matrix to the lumen and voids within of the fibres. Treatments to enhance the durability performance of the composites were studied,including: (a) modifications to the matrix through the replacement of Portland cement by undensified silica fume and by blast-furnace slag; (b) carbonation of the cementitious matrix and (c) immersion of the fibres in slurry silica fume prior to being incorporated into the Portland cement matrix.

Natural fibre composites (NFCs) possess relatively good specific strength and stiffness properties. However, natural fibres (NFs) often show relatively poor interfacial adhesion with respect to polymeric matrices, may contain relatively high levels of moisture and have variable mechanical properties due to the route by which they have been harvested and manufactured. These aspects may result in inconsistent mechanical properties of such composites, especially evident in a poor interlaminar fracture toughness. Thus, the present work investigates the mode I interlaminar fracture toughness, of NFCs based upon an anhydride-cured diglycidyl ether of bisphenol-A (DGEBA) epoxy matrix. Further, this matrix was used as a ‘control’ or modified with silica nanoparticles and/or rubbery microparticles. Two types of natural fibres were employed: unidirectional flax fibre (FF) and plain-woven regenerated cellulose fibre (CeF). Two very different routes were explored for the production of the NFCs based upon these materials. One route was via a resin infusion under flexible tooling (RIFT) process and a second route employed a resin transfer moulding (RTM) process. A very low value of the interlaminar fracture energy of about 20 J/m2 was measured for the flax fibre-reinforced plastics (FFRPs), using the ‘control epoxy matrix, produced by the RIFT manufacturing process which was initially employed. However, such composite manufactured via the RTM process possessed fracture energy of about 963 J/m2. Further, this value was found to increase to 1264 J/m2 when the epoxy matrix was modified using a combination of silica nanoparticles and rubbery microparticles. Hence, optimization studies using the RIFT manufacturing process were undertaken which led to a simple modification of this manufacturing route whereby the natural fibres were first oven-dried. This resulted in the final RIFT process giving values of the fracture toughness of the same order as those obtained from the RTM process. Also of note was the observation that the FFRPs manufactured via the RTM or the final RIFT process had similar values of toughness as those measured for glass fibre-reinforced plastics (GFRPs) made using the equivalent type of epoxy matrix. Similar observations were recorded in the case of the cellulose fibre-reinforced plastics (CeFFRPs). The present study has also considered the underlying mechanisms for the above observations and used analytical models to predict the toughening mechanisms and a good agreement between the predictions and the experimental data for the NFCs was obtained.

This study shows that an all-thermoplastic (nano- or micro-fibre) polymer can be created using coaxial electrospinning to create fibre mats akin to pre-impregnated fabric, which can be formed into a composite without the addition of other materials. This has not yet been accomplished by using the coaxial electrospinning production process. Experimentation to investigate the maximum fibre volume ratio found that these composites were successfully formed at 0.73 fibre volume fraction, which is higher than the maximum found in traditionally formed composites (0.60 – 0.70). The formation of the composite from the fibre mats was investigated, and found that the composites formed at the lowest temperature and pressure (70 °C and 1 bar) exhibited the higher tensile strength, up to 84 % higher than at other temperatures and pressures. Higher pressure and temperature caused deformation in the reinforcing fibres, resulting in lower tensile strength. The composites were shown to have more consistent Young’s modulus and higher tensile strength compared to a composite made from the same materials, but with the fibres and matrix materials produced separately, and combined during the composite forming procedure. The finalised composite produced in this research exhibited an average Young’s Modulus of 2.5 GPa, ultimate tensile strength of 33.2 MPa, and elongation at break of 3.8 %.

Polylactic acid (PLA) is a well-known biodegradable and sustainable polymer, derived from renewable agricultural sources. Its high price in the past limited its applications to mainly biomedical materials such as bone fixation devices. As the growth of awareness in global environment protection and sustainable development, PLA has attracted increased attention and development. Nowadays, the applications of PLA have been broadened into plastics, textiles and composites etc. Composites have been widely used in industrial applications for several decades, due to their high strength-to-weight ratio and good structural properties. However, most traditional composite materials are composed of two distinct fossil fuel based components. They are not eco-friendly and are difficult to recycle. This study aims at the development of PLA biodegradable composites and the optimisation of the processing parameters to achieve the best mechanical properties of PLA self-reinforced composites (PLA-SRC) for various end-uses. A variety of polymer analytical techniques were used to evaluate crystallinity, thermal properties, and chemical structures of the PLA reinforcement and matrix. Further study was carried out to assess the effects on mechanical properties of PLA-SRC caused by the processing temperature, pressure and holding time. The composites produced at high temperature and/or high pressure have significantly better matrix penetration (fibre wetting), which enhances mechanical properties. However, holding time was found to have no significant effect on the properties of PLA-SRC.

Following an extensive literature survey focusing on the machinability of carbon fibre reinforced plastics (CFRP), three main phases of experimental work were undertaken to evaluate the drilling of CFRP and associated stack materials. Phase 1 and 2 involved small diameter holes (1.5 mm) in thin CFRP laminates (3 mm thick) while Phase 3 addressed the feasibility of one-shot drilling (6.35 mm diameter holes) in multilayer workpiece stacks comprising titanium, CFRP and aluminium. Machinability was assessed in terms of tool life/wear, force/torque, hole size and geometrical accuracy, workpiece surface integrity and chip morphology.

The awareness of environmental sustainability drives the composite industry to utilize natural fibres. Natural fibres are a readily available resource with a relatively low price. In this study natural fibre flax reinforced polylactic acid (PLA) biocomposites were made using a new technique incorporating an air-laying nonwoven process. Flax and PLA fibres were blended and converted to fibre webs in the air-laying process. Composite prepregs were then made from the fibre webs. The prepregs were finally converted to composites by compression moulding. The relationship between the main process variables and the properties of the biocomposite was investigated. It was found that with increasing flax content, the mechanical properties increased. As the moulding temperature and moulding time increased, the mechanical properties decreased. The physical, thermal and morphological properties of the biocomposites were also studied. The appropriate processing parameters for the biocomposites were established for different fibre contents. The biodegradability and water absorption properties of the composites were evaluated. The composites were incubated in compost under controlled conditions. The percentage weight loss and the reduction in mechanical properties of PLA and biocomposites were determined at different time intervals. It was found that with increasing flax content, the mechanical properties of the biocomposites decreased more rapidly during the burial trial. The increasing of flax content led to the acceleration of weight loss due to preferential degradation of flax. This was further confirmed by the surface morphology of the biodegraded composites from Scanning Electron Microscope (SEM) image analysis. This study also investigated the manufacturing of 3D PLA/Flax nonwoven prepregs by using a new system of 3D nonwoven web formation, and 3D biocomposite was made using these prepregs. A new mould unit for web and a new aluminium mould for biocomposite were developed. The physical properties of 3D biocomposites were investigated and it was found that there is no significant difference between 2D and 3D biocomposites in density and void content. The effects of fibre content and processing variables on the crushing behaviour, energy absorption and failure mode of 3D shell biocomposites were experimentally studied.

The present study considers the dependence of mechanical properties in composite laminates on the fibre architecture. The objective is to characterise the mechanical properties of composite plates while varying the fibre distribution but keeping the constituent materials unchanged. Image analysis and fractal dimension have been used to quantify fibre distribution and resin-rich volumes (RRV) and to correlate these with the mechanical properties of the fibre-reinforced composites. The formation, shape and size of RRV in composites with different fabric architectures is discussed. The majority of studies in literatures show a negative effect of the RRV on the mechanical behaviour of composite materials. RRV arise primarily as a result of (a) the clustering of fibres as bundles in textiles, (b) the stacking sequence, and/ or stacking process, (c) the resin properties and flow characteristics, (d) the heating rate as this directly affects viscosity and (e) the consolidation pressure. Woven glass and carbon/epoxy fabric composites were manufactured either by the infusion or the resin transfer moulding (RTM) process. The fractal dimension (D) has been employed to explore the correlation between fabric architecture and mechanical properties (in glass or/ carbon fibre reinforced composites with different weave styles and fibre volume fraction). The fractal dimension was determined using optical microscopy images and ImageJ with FracLac software, and the D has been correlated with the flexural modulus, ultimate flexural strength (UFS), interlaminar shear strength (ILSS) and the fatigue properties of the woven carbon/epoxy fabric composites. The present study also considers the dependence of fatigue properties in composite laminates on static properties and fibre architecture. Four-point flexural fatigue test was conducted under load control, at sinusoidal frequency of 10 Hz with amplitude control. Using a stress ratio (R=σmin/σmax) of 0.1 for the tension side and 10 for the compression side, specimens were subjected to maximum fatigue stresses of 95% to 82.5% step 2.5% of the ultimate flexural strength (UFS). The fatigue data were correlated with the static properties and the fibre distribution, in order to obtain a useful general description of the laminate behaviour under flexural fatigue load. The analysis of variance (ANOVA) technique was applied to the results obtained to identify statistically the significance of the correlations. Composite strength and ILSS show a clear dependence on the fibre distribution quantified using D. For the carbon fabric architectures considered in this study, the fatigue properties of composite laminates have significant correlations with the fibre distribution and the static properties of the laminates. The loss of 5-6 % in the flexural modulus of composite laminates indicates an increasing risk of failure of the composite laminates under fatigue loads. The endurance limits, based on either the static properties or the fibre distribution, were inversely proportional to the strength for all laminates.

This thesis describes a method of development of a novel fibre based on fibre reinforced polymers (FRP), for use fibre reinforcement in concrete. Thermosetting epoxy resin matrix were reinforced with E-glass, S-glass, and Carbon fibre to produce different types of composite fibres. The FRP panels were produced using the Vacuum Infusion technique, and then cut to different fibre sizes. The volume fractions of reinforcements within the FRP fibre were controlled by using woven and unidirectional fabrics. The number of layers of reinforcing fibres were also changed, to obtain the optimal thickness of the fibres. The FRP material was characterized by means of tensile tests and microscope image analysis. Four different compositions of FRP were produced with tensile strengths ranging from 195 MPa to 950 MPa. The different combinations in geometry broadened the total number of fibres investigated to 12. Single fibre pullout tests were performed to obtain the fundamental fibre-matrix interfacial bond parameters for the different FRP fibres. The FRP fibres, being hydrophilic, along with having a unique rough surface texture, showed a good bond with cement matrix. A bond strength superior to industrially available straight steel fibres and crimped polypropylene fibres has been observed. The 3 best fibres were then chosen to examine the flexural behaviour FRP fibre reinforced concrete beams. The optimized FRP fibres, one each of Glass FRP and Carbon FRP were then further investigated to study the effect of matrix maturity, temperature, fibre inclination, and loading rate on the fibre-matrix interfacial behaviour using single fibre pullout tests. Scanning Electron Microscope (SEM) analysis was carried out to identify the effect of above-mentioned factors on the surface characteristics of the fibre. An attempt was also made to optimize the fibre-matrix interface to achieve an optimized failure mechanism by coating the fibre with oil. The ability of the fibre to transfer stresses across a cracked section over extended periods has been investigated by means of fibre-relaxation tests. Finally, to assess durability, the fibres were conditioned at high pH and high temperature after which single fibre pullout, direct tension tests, & SEM analysis were conducted.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

The automotive and construction industries are actively involved in substituting natural fibre composites (NFCs) for other engineering materials in motor vehicles and buildings. In this work, emphasis has been placed on evaluating agave fibre composites containing well aligned, closely packed straight fibre bundles and focussing on the development of different types of practical joints for NFCs in composite structures. Two novel co-cured joints were proposed and evaluated, based on laminated and intermingled configurations.

It is generally accepted that the mechanical properties of short fibre reinforced thermoplastics do not correspond with the high mechanical properties of fibres used to reinforce them. A study is made into the methods of compounding reinforcing fibres into thermoplastics to produce short fibre reinforced thermoplastics of enhanced properties. The initial method chosen for investigation is the twin screw extrusion compounding process. Variables such as fibre feeding arrangement and extrusion screw design are found to be factors influencing the properties of carbon and glass reinforced nylon 6,6. Use is made of computer programs to predict properties, assess compound quality and estimate fibre-matrix bond strength. Investigations indicate that the presence of reinforcing fibres with enhanced lengths does not result in the predicted property increases. The reasons for this shortfall are believed to lie in unfavourable fibre orientation in injection mouldings and the reduced strain to break of these materials. Short Kevlar reinforced thermoplastics are compounded and their mechanical properties assessed. The reasons for the poor mechanical properties for these materials are identified as a poor bond strength between fibre and matrix, the formation of points of weakness within the fibres by the compounding and moulding processes and the coiled arrangement of fibres present in injection mouldings. A method suitable for the routine assessment of fibre-matrix bond strength is used to examine combinations of fibre and thermoplastic matrix. A comparison is made of the values derived from this method with values calculated from stress-strain curves of injection mouldings. This allows an understanding of the nature of the fibre-matrix bond yielded by compounding and injection moulding steps. A description is given of a novel method designed to overcome the limitations of conventional compounding routes to produce long fibre reinforced injection moulding feedstock. Further work is necessary before this method is a feasible production technique.