Rozprawy doktorskie na temat „Flax”

There has been a substantial increase in the usage of natural-fibers and biodegradable polymers due to the needs of the environmental sustainability. The use of natural fibers is inclusive of wide range of applications in load bearing structures, nursing and commercial commodities. In this study, tensile behavior of flax fiber tows removed from woven fabrics were investigated at different moisture levels and compared because one of the major challenges faced in the use of natural fibers is their hydrophilicity. As the moisture content increased from 5% to 80% the tensile strength increased by 75%. The diffusion process through the flax fiber mat with different areal densities was investigated using the desorption curves obtained using an oven drying method. Diffusion coefficients were not found to significantly change with varying areal densities of 200 gsm to 400 gsm, but were significantly different when dried at 55 ?C versus 80 ?C.
Ameriflax
SunStrand
North Dakota State University. Department of Mechanical Engineering

In the field of renewable materials, natural fiber composites demonstrate the capacity to be a viable structural material. When normalized by density, flax fiber mechanical properties are competitive with E-glass fibers. However, the hydrophilic nature of flax fibers reduces the interfacial bond strength with polymer thermosets, limiting composite mechanical properties. Corn zein protein was selected as a natural bio-based coupling agent because of its combination of hydrophobic and hydrophilic properties. Zein was deposited on the surface of flax, which was then processed into unidirectional composite. The mechanical properties of zein treated samples where measured and compared against commonly utilized synthetic treatments sodium hydroxide and silane which incorporate harsh chemicals. Fourier transform infrared spectroscopy, chemical analysis, and scanning electron microscopy were also used to determine analyze zein treatments. Results demonstrate the environmentally friendly zein treatment successfully increased tensile strength 8%, flexural strength 17%, and shear strength 30% compared to untreated samples.

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.

Flax fibers, along with a number of other natural fibers, are being considered as an environmentally friendlier alternative of synthetic fibers in fiber-reinforced polymer composites. A common feature of natural fibers is a much higher variability of mechanical properties. This necessitates study of the flax fiber strength distribution and efficient experimental methods for its determination. Elementary flax fibers of different gauge lengths are tested by single fiber tension in order to obtain the stress-strain response and strength and failure strain distributions. The applicability of single fiber fragmentation test for flax fiber failure strain and strength characterization is considered. It is shown that fiber fragmentation test can be used to determine the fiber length effect on mean fiber strength and limit strain. The effect of mechanical damage in the form of kink bands and of diameter variability on the strength of elementary flax fibers is considered. Stiffness and strength under uniaxial tension of flax fiber composites with thermoset and thermoplastic polymer matrices are studied. The applicability of rule of mixtures and orientational averaging based models, developed for short fiber composites, to flax reinforced polymers are evaluated. Both the quasi-static and time dependent mechanical properties of flax fiber/thermoplastic starch based composites are analyzed. The effect of temperature and relative humidity is investigated. It is found that microdamage accumulation in this type of composites is not significant. Results show that the composite elastic modulus and failure stress are linearly related to the maximum stress reached by the matrix in tensile tests. Simple material models are suggested to account for the observed nonlinear viscoelasticity and viscoplasticity.
Godkänd; 2009; 20091029 (edgspa); DISPUTATION Ämnesområde: Polymera konstruktionsmaterial/Polymeric Composite Materials Opponent: Docent Kristofer Gamstedt, Kungliga Tekniska Högskolan, Stockholm Ordförande: Docent Roberts Joffe, Luleå tekniska universitet Tid: Onsdag den 9 december 2009, kl 10.00 Plats: E 231, Luleå tekniska universitet

Flax fibers, along with a number of other natural fibers, are being considered as an environmentally friendly alternative of synthetic fibers in fiber-reinforced polymer composites. A common feature of natural fibers is a much higher variability of mechanical properties. This necessitates study of the flax fiber strength distribution and efficient experimental methods for its determination. Elementary flax fibers of different gauge lengths are tested by single fiber tension in order to obtain the stress-strain response and strength and failure strain distributions. The applicability of single fiber fragmentation test for flax fiber failure strain and strength characterization is considered. It is shown that fiber fragmentation test can be used to determine the fiber length effect on mean fiber strength and limit strain. Stiffness and strength under uniaxial tension of flax fiber composites with thermoset and thermoplastic polymer matrices are considered. The applicability of rule of mixtures and orientational averaging based models, developed for short fiber composites, to flax reinforced polymers is evaluated.

Godkänd; 2006; 20061206 (pafi)

Research objective. Investigation of consistent patterns of the induction of flax morphogenesis process, assessment of genetic and physiological aspects of this process and optimization methodologies. Proposition: 1. MOrphogenesis capacity of flax isolated explants depends on a genotype only, but on a composition of a medium and the cultivar type (fibre flax or linseed)also. 2. Cells of different organs of the same genotype have different morphogenic capacity. 3. Combining hormonal ratio with the affect on explats by exogenic factors enables targeted control of the morphogenesis process in vitro.
Darbo tikslas - ištirti linų morfogenezės proceso indukcijos dėsningumus, įvertinti šio proceso genetinius ir fiziologinius aspektus bei optimizuoti regeneravimo metodikas. Ginamieji disertacijos teiginiai: 1. Linų izoliuotų eksplantų morfogeninė galia priklauso ne tik nuo genotipo, maitinamosios terpės sudėties, bet ir nuo veislės tipo (pluoštiniai ar sėmeniniai). 2.To paties genotipo skirtingų organų ląstelės turi skirtingą morfogeninę galią. 3.Derinant hormoninį balansą su eksplantų paveikimu egzogeniniais veiksniais galima kryptingai valdyti morfogenezės procesą in vitro.

Increasing the content of omega-3 fatty acids in the fatty acid profile of the animal products humans consume is becoming increasingly important as a way of promoting health and reducing the risk of disease. To achieve an improved fatty acid profile in milk and meat from dairy cows, it is necessary to feed the animals with high omega-3 fatty acid content feed. Flaxseed is a feed ingredient which may suffice these needs, however the nature of the omega-3 fatty acids present certain problems at the level of digestion -biohydrogenation in the rumen. Also, the extrusion method of producing a cooked flaxseed ingredient enhances the release of the oil from the flaxseed itself, but in turn increases the opportunity for oil loss during storage and transport. To limit oil loss, flaxseed was combined with three different absorbent materials (alfalfa, soy hulls, gluten) at three different ratios of absorbent to flaxseed for each absorbent (15:85, 20:80, 25:75) and the ability of the extruded samples to retain oil under compression was measured. Of the three absorbents, alfalfa performed the best (p < 0.0001) at a ratio of 25:75 (p = 0.0002). The samples were characterized in terms of the protein fractions – soluble crude protein, neutral detergent insoluble crude protein (NDICP) and acid detergent insoluble crude protein (ADICP) – and the digestibility of dry matter (DM) and crude protein (CP). The effect of extrusion, type of absorbent and the ratio of absorbent to flaxseed on the nutritional quality and some physical properties of the samples were ascertained.
Accroitre la quantité d'acide gras omega-3 dans le profil des acides gras des animaux, destinés à la consommation humaine, gagne en importance en tant que bonne façon de réduire les risques de maladie et d'améliorer la santé générale. Pour obtenir un meilleur profil d'acide gras dans le lait et dans la viande des vaches laitières, il est nécessaire de nourrir l'animale avec des rations riches en acide gras oméga-3. La graine de lin, est un ingrédient parfait pour répondre à ce besoin. Cependant la nature des acides gras oméga-3 présente un certain problème au niveau de la digestion par biodéhydrogénation dans la panse des ruminants. Également, la méthode d'extrusion pour la production de lin cuit accroit la libération d'huile de la graine de lin, cependant ce processus augmente les chances de perte d'huile lors du stockage et du transport. Pour limiter les pertes d'huile, le lin a été combiné avec trois matériaux d'absorption (luzerne, écaille de soja, gluten) selon trois différents ratios de matériaux absorbant versus graine de lin (15:85, 20:80, 25:75). La capacité de rétention d'huile des échantillons extrudés face à la compression a été mesurée. Des trois absorbants, la luzerne possède la meilleure performance (p < 0.0001) avec un ratio de 25:75 (p = 0.0002). Les échantillons ont été caractérisés en terme des fractions de protéine – protéine brute soluble, protéine brute insoluble à détergent neutre (PBIDN) et protéine brute insoluble à détergent acide (PBIDA) – ainsi que la digestibilité des matières sèches (MS) et les protéines brutes (PB). Les effets de l'extrusion, des types d'absorbant et les ratios absorbant par rapport à la graine de lin sur la qualité nutritionnelle et quelques une des propriétés physiques des échantillons ont été établis.

Due to a rising interest in natural fibres for textiles as well as environmental concerns, the demand for fibre flax has increased in recent decades. It was, therefore, with great enthusiasm that Canadian farmers welcomed, in 1997, the opening of a flaxprocessing unit in the region of Salaberry-de-Valleyfield, Quebec. The purpose of this study was to investigate the economic viability of fibre flax contracting as an alternative activity for field-crop producers in Quebec. A risk-programming model called minimization of total absolute deviation (MOTAD) was developed to better approach this issue. The MOTAD takes into account the variability in income that stems from uncertainty in commodity-market prices and yields. In addition, five different marketing strategies for pricing grain corn and soybeans were included in the model. These pricing techniques combined the use of futures and options markets.
In a global agricultural system, where international commitments force governments to cut subsidies, reducing income variability for risk-averse farmers becomes a critical challenge. This study offered to assess the contribution of both contracting and futures markets as alternative market instruments for risk management. Five portfolio farm plans were identified for 200- and 300-hectare farm sizes. The results showed that gains through fibre flax contracting, in terms of risk reduction, exist only for the farm plans with lower levels of income and risk. Moreover, simulations demonstrated that the use of futures and options markets can help maximize overall net farm return.

The use of natural fibers as reinforcement in thermoplastics presents an interesting alternative for the production of low cost and ecologically friendly composites. One of the advantages of using natural fibres is their low specific weight, resulting in higher specific strength and stiffness when compared to glass reinforced composites. Natural fibres also present safer handling and working conditions. They are non-abrasive to mixing and can contribute to significant cost reduction. This work is divided into two phases: Phase 1 deals with developing nonwoven mats composites from flax/polypropylene (PP) and evaluating their properties. Flax/polypropylene fibres (at different weight ratios) were processed by needle-punching technique in order to form nonwoven mats. The mats were compression-molded at a temperature of 180oC to form composite materials. The mechanical, thermal and viscoelastic properties of the composites were analyzed. Composites (untreated and silane-treated) were also subjected to varying conditions of temperature and humidity and the tensile properties of the conditioned and unconditioned composites were investigated. The mechanical properties (tensile, flexural and impact) of flax/PP composites were found to increase and reach maximum values at 30 per cent fibre loading and then decrease at higher fibre content. Thermal studies revealed that the composites were stable up to 320oC and samples containing 40 per cent flax fibres were found to exhibit greater thermal stability than neat PP. The dynamic mechanical analyses of the composites showed that the incorporation of flax in the composites resulted in an increase of the storage modulus with a maximum value exhibited by composite containing 40 per cent fibre loading. Composites containing chemically modified fibres exhibited low tensile modulus after conditioning. Phase 2 is based on the investigation of the effect of nano-calcium carbonate (CaCO3) on the properties of two types of polymer matrices: recycled PP and virgin PP. In this case, composites were prepared by melt-mixing and injection molding. The mechanical and thermal properties of the composites were characterized. The tensile modulus of the nano-CaCO3 filled PP (virgin and recycled) composites were found to increase and reach maximum at 30 per cent nano-CaCO3 loading, while the tensile strength decreased with increasing filler content. Thermal studies showed that the nano-CaCO3 filled PP samples exhibited a one-step degradation pattern and are thermally stable up to 450oC. The thermal stability of the samples was found to decrease following the addition of nano-CaCO3. SEM micrographs of the tensile fractured surfaces of composites of the nano-CaCO3 filled virgin and recycled PP revealed the presence of nano-CaCO3 agglomeration.

The focus of this study was to investigate flax shive and hemp hurd as alternate residue for particleboard production, investigate the lowest percentage of the pricier polymeric diphenyl methane diisocyanate (pMDI) resin that can be used to effectively bond the residues and evaluate an acrylic-based resin for particleboard manufacture. The flax shive and hemp hurd had lower bulk densities and higher aspect ratios compared with wood. Their higher aspect ratios offered greater overlap in bonding leading to consistently higher bending properties that exceeded American National Standards Institute (ANSI) requirements for low density (LD2) particleboard and in some cases, medium density (M2) particleboard. Because of their particle geometry, the flax shive and hemp hurd particleboards also showed minimal linear expansion with changes in moisture content between 50% and 90% relative humidity (at 20 ± 3°C) and were within ANSI requirements. The high absorption capacity of the residues resulted in higher thickness swell and water absorption properties in contrast to wood. Improvements in bending strength above 40% and stiffness properties above 25% was achieved for wood, hemp hurd and flax shive particleboards by incorporating 15 weight % flax and hemp fiber in continuous mat form at the points of maximum tensile and compressive stresses in particleboard. Test results confirmed the possibility of using 2.5% pMDI resin load, a percentage lower than the commercially viable 3%–6% addition levels that are commonly used with wood residues. The results further demonstrated that based on 2.5% pMDI resin load and as much as 20% mass lignin substitution boards with satisfactory mechanical properties that exceed LD2 grade requirements could be manufactured from hemp hurd and flax shive. Dynamic scanning calorimetry results and the current cost of the acrylic-based resin suggests that it is not suited for particleboard manufacture from flax shive and hemp hurd. Overall, based on mechanical performance flax shive and hemp hurd residues can be considered as alternate biomass for particleboards of greater performance to wood for use in shelving and furniture applications. But the high cost of the residues compared to wood does not currently make it economical for particleboard manufacture.
Forestry, Faculty of
Graduate

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

Ce travail de doctorat est consacré à la production, au recyclage mécanique long-terme et à la caractérisation de matériaux polymères et composites à base de polyéthylène haute densité (HDPE) et de fibre de lin. L’objectif est de déterminer l’aptitude au recyclage long-terme de ces composites et de leur matrice, tout en évaluant la perte de performance subie. Le recyclage est réalisé ici par une extrusion en boucle fermée, durant 50 cycles, sans ajout intermédiaire de matières vierges et sans prise en compte de la détérioration et de la contamination subies lors du cycle de vie des produits. Dans la première partie, une revue de littérature présente l’état de l’art concernant le recyclage mécanique des composites thermoplastiques. Les différents types de recyclage de composites sont présentés, ainsi que les différents travaux réalisés sur le recyclage de composites thermoplastiques à base de fibres naturelles ou inorganiques. Enfin, les différentes limitations rencontrées lors du recyclage de ces composites sont mises en lumière et des solutions sont présentées. Au cours de cette revue, des lacunes importantes sur le recyclage mécanique long-terme de ces composites sont observées. Dans la seconde partie de ce travail, le polyéthylène haute densité est étudié et recyclé seul afin de connaître ses propriétés et son comportement au recyclage, tout en servant de base de comparaison pour les composites produits par la suite. L’étude des propriétés physique, thermique, moléculaire et mécanique permet d’analyser les différents mécanismes de dégradation induits par le recyclage mécanique. Les résultats montrent une diminution de la contrainte au seuil d’écoulement et une forte augmentation de l’élongation à la rupture avec le recyclage, indiquant que des phénomènes de rupture de chaînes ont lieu dans le polymère. La plupart des autres propriétés demeurent constantes et confirment le maintien des performances du polymère avec le recyclage. Dans la dernière partie de cette thèse, deux séries de composites sont produites à partir du polyéthylène haute densité et de la fibre de lin (15% en masse), avec et sans polyéthylène greffé d’anhydride maléique (MAPE) comme agent couplant. Toutes deux seront caractérisées similairement au polymère afin d’évaluer l’effet de la présence de fibre dans le polymère. Une analyse de la distribution de fibres est aussi réalisée afin d’observer l’effet du recyclage mécanique sur la taille des fibres. L’analyse mécanique révèle que la fibre fournit un renfort efficace au polymère, en particulier avec l’agent couplant, mais les propriétés à la rupture diminuent. Cet effet diminue avec le recyclage, alors que les propriétés à l’élongation augmentent, du fait de la réduction de longueur des fibres. L’effet de l’agent couplant disparaît aussi au cours du recyclage. Toutefois, la majorité des performances mécaniques après recyclage restent supérieures à celles du polymère.
This thesis focuses on the production, the mechanical recycling and the characterization of polymers and composites based on high density polyethylene (HDPE) and flax fibers. It aims to determine the materials potential towards long-term recycling and to evaluate the resulting loss of performance. The recycling is realized by closed-loop extrusion, and repeated up to 50 times, without any addition of new material, and without any consideration of the possible degradation and contamination undergone during the life-cycle of the products. In the first part, a literature review presents the state of the art concerning the mechanical recycling of thermoplastic composites. The various types of composites recycling are introduced, as well as the various works conducted on the recycling of thermoplastic composites reinforced with both natural and inorganic fillers. Finally, the various limitations to the composites recycling are presented and some solutions are suggested. During this review an important lack of knowledge on the long-term mechanical recycling of these composites is observed. In the second part of this work, the high density polyethylene is studied and recycled in order to know its properties and its behavior towards recycling, as well as to be used as a comparison basis for the further parts. The study of the mechanical, thermal, molecular and physical properties leads to the better understanding of the various degradation mechanisms induced by mechanical recycling. The results show a decrease of the yield stress and an important increase of the strain at break with recycling, indicating that chain scissions take place in the polymer during recycling. Most of the other properties remained stable, and confirmed the conservation of the polymer performances with recycling. In the last part of this work, high density polyethylene is used to produce two series of composites with 15% wt. of flax fiber, with and without maleic anhydride grafted polyethylene (MAPE) as a coupling agent. Similar characterizations as for the matrix are conducted on both composites as to evaluate the effect of the fibers in the polymer matrix. A complete analysis of the fiber distribution is also performed to observe the effect of mechanical recycling on the fiber dimensions. The mechanical analysis reveals that the fibers provides an efficient reinforcement to the matrix, and especially with coupling agent, but the properties at break decrease. Nevertheless, this effect decreases with recycling, while the elongation properties increase due to the fiber size reduction. The effect of the coupling agent disappears with recycling. However, most mechanical properties remain higher for the composites after recycling than for the neat matrix.

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.

Natural fibre composites are fast emerging as a viable alternative to traditional materials and synthetic composites. Their low cost, lightweight, good mechanical performance and their environmentally friendly nature makes them an ideal choice for the automotive sector. The automotive industry has already embraced these composites in production of non-structural components. At present, however, research studies into composites made of natural fibres/bio-sourced thermoplastic resins are at infancy stage and such works are rare in the literature. This study therefore focuses on the mechanical properties of poly(lactic) acid (PLA) flax reinforced composites for structural loaded components. The aim was to investigate the performance of flax/PLA biocomposites subjected to localized low velocity impacts. To start with, a detailed literature study was conducted covering biocomposites and PLA in particular. Next, a series of composite samples were manufactured. Morphological and thermal studies were also conducted in order to develop an in-depth understanding of their thermo-mechanical properties, including crystallinity, thermal response and their related transition temperatures. This was followed by localized impact studies. The influence of temperature, water uptake and strain rates to the material tensile strength and modulus, as well as the damage characteristics and limits that lead to failure were studied. Furthermore, in the present work different methods and existing material models to predict the response of biocomposites were assessed. A case study was then performed using these models to understand, develop and improve the side crash performance of a superlight city car prototype.

With rapidly increasing interest in green composites, natural fibre reinforced plastic (NFRP) biocomposites are becoming a very real alternative composite to the synthetic/man-made composites in indoor applications. Sustainability concerns of the public and recently approved regulations made by governments, in order to reduce the landfill materials, are among the factors that have intensified interest in natural fibre composites. Natural fibres can be used as renewable, sustainable reinforcement due to their small (perceived) environmental footprint. Apart from the environmental concerns, natural fibres possess some desirable engineering related characteristics such as low cost, low density, high stiffness- and strength-to-weight ratio. Among various natural fibres, flax is one of the oldest cultivated and used fibres. It has been utilized with success in a variety of applications, and can be used as a replacement for synthetic fibres in some applications. Thermal stability and degradation, which are common drawbacks of natural fibres, are constraints for further extending the range of applications for flax fibre reinforced biocomposites. This problem can be significantly more critical for manufacturers and users when the matrix is also intended to be a sustainable material such as poly lactic acid (PLA). Since exposing flax/PLA biocomposites to high temperatures or outdoor environments leads to degradation, more research studies are necessary in order to increase our understanding about the mechanisms for degradation. In particular, a key point of interest is thermal stability when flax/PLA biocomposites are subjected to high temperatures during the manufacturing process. Degradation is a key issue and occurs in both flax fibre and PLA matrix of a biocomposite. At high temperatures, flax components such as cellulose, hemicellulose and lignin degrade. The thermo-chemical degradation of these components subsequently limits the mechanical properties of flax fibre as reinforcement. In the case of PLA, in addition to low stability at manufacture temperatures, its biodeterioration can become a significant drawback in terms of durability when exposed to moisture related environments. The degradation process during and after manufacturing of flax/PLA biocomposites can also cause separation in the bonding of flax and PLA, and further reduction in mechanical properties. Important gaps in the existing studies in this field are a lack of: (i) a methodology to construct a map or window of degradation during compression moulding for setting practical upper and lower limits to the consolidation temperature and process time, (ii) an analytical model to calculate the deterioration of PLA due to the chain-scission degradation process, (iii) a demonstrated procedure to calculate the effect of transient temperature on the degradation of flax/PLA biocomposites, (iv) study on the degradation rate of flax/PLA biocomposites at high temperatures in association with molar mass changes or degree of polymerisation, (v) a complete study on the performance of flax/PLA biocomposites in moisture related environments such as wet, freezing and humid conditions. Thus, the key objectives of this study were designed to fulfil these gaps/requirements in the existing body of knowledge. The research was divided into four stages which were carried out and the findings were published in four journal papers and one book chapter. In order to set practical upper and lower limits to the consolidation temperature and processing time (in the form of a processing window), an in-depth investigation of the degradation processes of natural fibre biocomposites during thermal processing was done. The properties and processes considered in defining the processing window were the melting temperature, thermal penetration, impregnation of matrix into fibres, pyrolysis of matrix and fibre, and thermochemical degradation of matrix and fibre. To set lower limits to the processing time, critical studies and calculations were performed on the thermal penetration as a result of heating the platens of the compression moulding machine to higher than the melting point of the PLA, and on the impregnation of matrix into flax fibres. Upper limits to the processing temperature were achieved by comparing reaction process in terms of pyrolysis and thermochemical degradation. Evaluations on the pyrolysis degradation of PLA, flax fibres and their main compositions (including cellulose, hemicellulose and lignin) were conducted based on TGA data from the literature. Moreover, assessments on the thermo-chemical (chain-scission) degradation of PLA, flax fibres and natural fibres’ main compositions were conducted; and by bringing them all together, an optimum processing window for a biocomposite was constructed. The proposed processing window was tested experimentally. Several tests measuring changes in the tensile properties of a flax/PLA biocomposite were performed to examine the validity of the concept within and outside the borders for the optimized window. Thus, the key considerations were highlighted and a quantitative guide was proposed for moulding time limits based on the available literature, along with a practical study of a representative flax/PLA biocomposite. Since calculation of the extent of the chain-scission degradation of biopolymers is the key consideration for monitoring degradation of mechanical properties during compression moulding, it is of value to develop accurate calculation procedures that can be readily implemented. Models in the current literature for biopolymer degradation require a simultaneous solution of at least three chemical rate equations making the analysis somewhat complex and cumbersome. To facilitate the calculation, a simplified and revised model was proposed which no longer requires the solution of simultaneous differential equations and, for isothermal conditions; an analytical solution is readily available. The model was examined and validated against the more complex model and experimental results for PLA degradation reported in the literature. The effect of the temperature history on the degradation progress and effects on the tensile strength was studied. A thermal degradation model which accounts for the effect of time-dependent process temperature variation during manufacture of green composites was proposed. Kinetic data was used to calculate the degradation progress parameters, defining experiment process maps for identifying the effect of the temperature history on the degradation progress and effects on the tensile strength. Thus it was demonstrated that the present model is a useful tool for predicting the degradation effect of any temperature history to which the composite is subjected during manufacture. Molar mass degradation or reduction in degree of polymerisation was taken into account as a critical indicator of the extent of thermo-chemical degradation, making it possible to determine the rate of deterioration of mechanical properties for both matrix and fibre. A link between the chemical degradation of NFRP biocomposite during thermal processing and their mechanical properties was introduced. For the first time, this study has brought the thermochemical degradation concepts together with the models which have been used for composites, to predict the tensile strength of NFRP biocomposites after thermal processing. The following processes were taken into account: (i) mechanical properties of the biocomposite can be calculated by estimating their relationship with the changes of degree of polymerization over temperature and time. This relationship has separately been proposed for both matrix and fibre, (ii) the modulus of elasticity for both the flax fibre and for PLA may be assumed to be independent of the thermal processing, (iii) a linear relationship between strength and (degree of polymerization)-1, as proposed in the literature, was used to calculate the tensile strength of matrix and fibre, and for the first time used to predict the mechanical properties of NFRP biocomposites, (iv) to predict the tensile strength of NFRP biocomposite, the linear model was found to be unreliable for extended periods of time and subsequently a new exponential model was proposed which is realistic within 10% uncertainty. The sensitivity of properties of flax/PLA biocomposites to different moisture-related environments was studied. Composites were exposed to the following conditions: water immersion, warm humid, and ‘freeze-and-thaw’ cycling environments. The mechanical performance (tensile and flexural properties), moisture content and physical changes (dimensional stability) of the composites during the exposure to the different environments were analysed. The findings were also compared with those of previous works which had been produced for various applications, and are as follows for each condition: (i) when the flax/PLA composites were immersed in water, water absorption followed Fick’s law. Tensile and flexural modulus and strength decreased significantly due to the quantity of water absorbed by the composites, which led to the development of different degradation mechanisms, such as the weakening of the flax/PLA interface and plasticisation. However, the tensile strain value found for the saturated specimens almost doubled that of “as manufactured” specimens due to the plasticising effect of water in the flax/PLA biocomposites. Physical changes were relatively large, as the thickness of the samples increased considerably during the test, (ii) after the saturation moisture content was reached in the immersion tests, some samples were completely dried to analyse the residual properties of the composites. The drying process proved to be effective in partially restoring the mechanical properties. However, the “as manufactured” properties were not reached, inferring that some permanent damage was caused after the immersion tests, which was attributed to the degradation of the fibre-matrix interface. Nevertheless, the results suggest that it is advantageous to completely dry biocomposite prior to use in structural applications if the fibres have high water content, (iii) when exposed to a warm humid environment, both water absorption and physical changes were much lower than for water immersion, leading to less significant reductions in mechanical properties. In addition, the hydrolysis process can be involved in the PLA degradation, decreasing the properties of the matrix and degrading the interfacial bonding between flax and PLA by molar mass degradation, (iv) Freeze and thaw cycling has small negative impacts on tensile and flexural properties owing to small water absorption and physical changes, causing internal stresses, (v) Freeze and thaw cycling of water-saturated specimens shows further deterioration of properties in comparison with the water saturated only specimens. Water saturated and freeze/thaw cycling damages the material because of the negative synergy caused by water trapped in the microstructure and freeze/thaw cycles, which leads to the development of internal stresses, Altogether, based on the measurements and analysis, direct contact with liquid water is the most deteriorating environment for biocomposites, and therefore underwater applications of these materials are strongly discouraged. In such cases, a drying process can restore partially the mechanical performance of these materials. On the other hand, biocomposites can endure reliably in warm humid environments and in those that could create freeze-and-thaw cycles for short-term outdoor applications. Finally, a discussion was provided for practitioners who are considering using natural fibre reinforced biomatrix products. Over all, the degradation of flax/PLA biocomposites during and after manufacturing process was studied and the findings were published in four journal papers and one book chapter. A summary of the research contributions, suggestions and recommendations for the future research in the field of NFRP biocomposites are also provided in this thesis.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Dans cette thèse, un composite unidirectionnel à renfort lin (composite UD biosourcé) a été développé et élaboré par la technique de presse à chaud. Le comportement en traction des composites à renfort végétal montre en général deux domaines, mais un troisième domaine est identifié dans ce travail. Un modèle phénoménologique développé précédemment pour décrire le comportement en traction d'un composite à renfort en fils torsadés a été testé avec le composite UD biosourcé. Nous montrons que l'ajout d'un phénomène de consolidation au modèle précédent est nécessaire pour simuler correctement le troisième domaine. Un second modèle mécanique a été par ailleurs développé pour identifier expérimentalement les propriétés mécaniques effectives du renfort en lin lorsqu'il est piégé dans la matrice. La distribution statistique de l'orientation locale du renfort a été mesurée pour pouvoir prendre en compte l'orientation des fibres. Pour cela, la technique du tenseur de structure a été appliquée sur des images optiques du pli de lin. Par ailleurs, ce modèle permet d'étudier l'influence des porosités sur les propriétés mécaniques. Les deux modèles permettent d'effectuer des prévisions efficaces du comportement mécanique du composite de fibre de lin unidirectionnel. En complément des modèles de mécanique, le comportement en sorption du composite de lin UD a également été analysé. Le modèle de Langmuir et le modèle de Fick ont été appliqués sur nos composites UD. Les résultats montrent que la configuration unidirectionnelle du renfort de lin favorise la sorption d'eau des composites associés.Résumé en anglais
In this Ph.D work, unidirectional flax fiber composite (UD biobased composite) has been designed and manufactured based on the hot platen press process. Plant fiber composites usually exhibit two regions under tensile load, but three regions have been identified in this work. A phenomenological model, previously developed to describe the tensile mechanical behavior of twisted plant yarn composites, has been tested with the UD biobased composite. We show that the addition of a strengthening phenomenon to the previous model is necessary to simulate correctly the third region. A second mechanical model has also been developed for experimental identification of the effective mechanical properties of flax reinforcement when embeded in matrix. A statistical distribution of local orientation of UD reinforcement was obtained allowing taking the fiber orientation into account. To that end, structure tensor method was applied to optical images of flax ply. Furthermore, this model allows the effect of porosity on mechanical properties to be studied. Both models provide effective forecast of the mechanical behavior of unidirectional flax fiber composite. Besides the mechanic models, sorption behavior of UD flax composite also has been analyzed. Langmuir's model and Fick's model were applied on our UD composite. The results show that the unidirectional configuration of the flax reinforcement promotes the water sorption from the associated composites

Searching for environmentally sustainable alternatives for reinforcement of composite materials, flax fibre has one of the most promising potentials due to its desired mechanical properties. The fact that flax is a bio-material, in contrast to conventional synthetic fibres, does not ensure a less environmental impact. One of the major source of environmental impact related to flax fibre as a reinforcement material is the cultivation of flax fibre. In this study the environmental impact of flax fibre cultivation was studied by performing an environmental impact analysis with a life cycle assessment inspired approach.  The result showed that the quantification of the environmental impacts varied to a large extent depending on several parameters such as allocation method and whether carbon sequestration was included in the calculations. One striking example is the results for global warming potential, ranging from 10 000 kg CO2-equivivalents to a negative value per 1 tonne of flax fibre. The study showed the production and use of fertilizers to be the major contribution to the environmental impact by as much as 70-90 %. In order to limit the environmental impact from flax fibre cultivation suggested environmental improvements are to optimise the fertiliser use according to the flax type and soil conditions, improving nitrogen fixation as well as using organic fertilizers.

2018-06-27

Natural fiber composites have been found to exhibit suitable mechanical properties for general applications. However, when high strength applications are required, natural fibers are typically not considered as a practical fiber. One method for increasing the field of application for natural fibers is by increasing their mechanical properties through hybridizing them with synthetic fibers. The effects of hybridizing flax fibers with carbon fibers were investigated in this research to determine the trends in mechanical properties resulting from varied carbon and flax fiber volumes. The research found an increase in mechanical properties when compared to 6061 aluminum at matching composite stiffness values. The following mechanical property gains were obtained: 2% tensile chord modulus, 252% tensile strength, 114% damping ratio, and a 49% weight savings. Experimental tensile values were also compared to tradition modulus prediction models such as rule of mixtures and Halpin-Tsai, and were found to be in good agreement.

Increasing concerns over depleting natural resources has led to the development of so-called biocomposites based on fibres from renewable resources such as flax. Although these fibres are seeing use in some applications, there is a lack of understanding concerning their processing requirements in relation to their unique physical and chemical properties. Furthermore, there is limited information regarding the links between their processing behaviour and mechanical performance. With the aim of addressing these missing links, this thesis presents a methodology for characterizing flax fibres for application in the resin infusion process and considers two important case studies with the overall goal of improving the state-of-the-art for this class of materials.Flax fibres were first characterized at the fibre level by advancing contact analysis, thermal gravimetric analysis, scanning electron microscopy and helium pycnometry. The advancing contact analysis revealed a reduction in the polar component of surface free energy after the application of silane and diluted epoxy treatments. A methodology was then developed for the characterization of the compaction and permeability of flax-based fabrics for the modelling of the resin infusion process. These parameters were quantified and used as input in a 1D process model that included capillary pressure. The model predictions for flow front evolution were shown to be in good agreement with experimental data. Alkaline treatments were shown to increase the required compaction pressure for a given porosity due to an increase in fibrillation. This had direct implications in the context of resin infusion processing due to the coupled nature of flow and compaction in this process. Consequently, a mechanical characterization revealed a decrease in flexural properties for alkaline-treated flax/epoxy composites manufactured by resin infusion due to a decrease in fibre volume fraction. A decrease in flexural properties was also noted with increasing void content.In an effort to improve the state-of-the-art for this class of materials, a case study was carried out on the incorporation of nano-modifiers in the resin infusion process. Nanocellulose was incorporated by two novel techniques; a 'grafting' method and a wet-layup method that incorporated an aqueous NC solution in the resin infusion pre-filling stage. Both methods were shown to lead to an increase in damage to the composites after subjection to a drop-weight impact event which suggested that the nano-modifier did not increase the interlaminar properties. However, an increase in interlaminar shear strength was observed by a short beam test due to an increase in fibre volume fraction as a result of softening and lubrication effects arising from the use of the aqueous NC solution.A second case study addressed the primary source of voids in a class of flax/epoxy prepregs which are generally used as a benchmark for composites manufactured by the resin infusion process. A series of compaction tests and thermal gravimetric analysis suggested that moisture and resin starvation were the primary source of voids in commercially available prepregs. Panels manufactured in an autoclave at varying pressures suggested that the latter of these issues was the dominant problem for the studied materials. The presence of voids was finally shown to lead to increased moisture sorption for flax/epoxy composites.This study stresses the coupled nature of the resin infusion process and the full implications of the use of chemical treated flax fibres. Additionally, it demonstrates the negative consequences of process-induced voids on the performance of flax/epoxy composites. It also provides useful data on the fibre surface chemistry, permeability, compaction and mechanical performance of flax-based composites. This assists in furthering the development of this class of materials with the goal of increasing their potential for use in load-bearing structures.
La préoccupation avec l'épuisement des ressources naturelles a conduit à l'élaboration des bio-composites à base de fibres renouvelables telles que le lin. Bien que ces fibres sont utilisées dans certaines applications, il y a un manque de compréhension au sujet de leurs besoins de traitement par rapport à leurs uniques propriétés physiques et chimiques. En outre, il y a peu d'information sur les liens entre leur comportement et la performance des traitements mécaniques. Dans le but de répondre à ces liens inconnus, cette thèse présente une méthodologie de caractérisation des fibres de lin pour une utilisation dans le procédé d'infusion de résine et tient compte de deux études de cas importantes dans le but d'améliorer l'état-de-l'art pour cette classe de matériaux.Les fibres de lin ont d'abord été caractérisé au niveau des fibres en faisant l'analyse de l'angle de contact, analyse thermique gravimétrique, microscopie électronique à balayage et la pycnométrie hélium. L'analyse de l'angle de contact a révélé une réduction de la composante polaire de l'énergie de surface après l'application des traitements silane et époxy dilué. Une méthode a été ensuite développée pour la caractérisation de la compression et de la perméabilité de lin à base de tissus, pour la modélisation du processus d'infusion de résine. Ces paramètres ont été quantifiés et utilisés comme input dans un modèle de processus 1D qui comprenait la pression capillaire. Le traitements alcalin a démontré une augmentation de la pression de compactage nécessaire pour une porosité donnée, en raison de l'augmentation de la fibrillation. Par conséquent, une caractérisation mécanique a révélé une baisse de propriétés de flexion pour le lin/époxy composites fabriqués par infusion de résine pour des tissus traités avec alcalines en raison d'une diminution de la fraction volumique de fibres. Une diminution des propriétés en flexion a également été notée quand le contenu de vide augmente.Dans un effort pour améliorer l'état-de l'art pour cette classe de matériaux, une étude de cas a été réalisée sur l'incorporation de nano-modificateurs dans le procédé d'infusion de résine. Du nano-cellulose a été constituée par deux nouvelles techniques; une méthode de 'greffage' et un procédé 'wet-layup' qui intègre une solution aqueuse NC avant l'infusion. Les deux méthodes ont démontré une augmentation de l'endommagement des composites après avoir été soumis à des impacts, qui suggère que le nano-modificateur n'a pas augmenté les propriétés interlaminaires. Toutefois, une augmentation de la résistance au cisaillement interlaminaire a été observée par un faisceau de test court en raison d'une augmentation de la fraction volumique des fibres à la suite d'effets de ramollissement et de lubrification provenant de l'utilisation de la solution aqueuse NC.Une deuxième étude de cas a abordé la principale source de vides dans une classe de lin/époxy préimprégnés. Une série d'essais de compactage et d'analyse thermique gravimétrique suggère que la manque d'humidité et de résine ont été la principale source de vides dans préimprégnés disponibles. Des panneaux fabriqués dans un autoclave à pression variant suggére que le dernier de ces questions était le problème dominant pour les matériaux étudiés. La présence de vides a finalement causé une dégradation des propriétés d'absorption d'humidité pour les composites lin/époxy.Cette étude souligne le caractère couplé du procédé d'infusion de résine et les implications de l'utilisation de traitement chimique des fibres de lin. En outre, il met en évidence les conséquences négatives de vides sur la performance des composites lin/époxy. Il fournit également des données utiles sur la chimie de surface des fibres, perméabilité, le compactage et la performance mécanique des composites à base de lin. Cette aide favorise le développement de cette classe de matériaux dans le but d'augmenter leur potentiel d'utilisation dans des structures portantes.

The aim of this thesis is to modify flax pulp fibres (Linum usitatissimum) by more friendly environmental processes. Pulp and paper research is focussing through enzyme systems investigation for developing green chemistry technologies due to existing environmental concerns and to legal restrictions. Moreover, it exists also an increasing strategic interest in using flax fibres to obtain high-quality specialty papers. That is why we study the application of biotechnology as an efficient alternative to traditional industrial processes based on the use of chemical agents. This work is framed by two of the main research topics of the Paper and Graphic Specialty Laboratory in the Textile and Paper Engineering Department of the Universitat Politècnica de Catalunya. One research line is based on pulp bleaching and is focused basically on the study of enzymatic systems as biobleaching agents; the other research topic that has been recently introduced in our investigation group is the use of enzymes as functionalisation agents by promoting the grafting of several compounds. Laccase is the main enzyme used in this thesis; it is an oxidoreductase that can assist reactions in an eco-friendly way since laccase uses air and produces water as the only by-product. Moreover, laccase can work under mill conditions and has wide application potential. The first part of this thesis involved the use of enzymes to bleach flax pulp. The aim was to explore the potential of various natural mediators (lignin-derived compounds) for delignifying flax fibres in order to identify the most efficient and ecofriendly choice among them. Afterwards, we assessed the use of various enzyme delignification stages in an industrial bleaching sequence. The ensuing totally chlorine free (TCF) sequence comprised various laccase-mediator system treatments (L stage) followed by a by a chelating stage (Q stage) and a subsequent bleaching step with hydrogen peroxide (Po stage). A xylanase pretreatment was additionally carried out. Laccases used came from the fungi Pycnoporus cinnabarinus and Myceliophthora thermophila; the performance of several natural mediators was compared with the obtained with the application of various synthetic mediators. In addition, the lack of studies on the properties of effluents from the treatment of non-wood pulp with laccase and natural mediators led A-1 A-2 us to examine effluent properties upon biotreatments and after different bleaching stages. The results obtained warrant upscaling any of the biobleaching sequences for flax pulp as they provide sustainable flax fibre with a high cellulose content and brightness above 80% ISO. The use of xylanase pretreatment was found to efficiently remove HexA and enhance delignification by laccase.

Nowadays, when environmental concerns are becoming increasingly important are there great interest in natural materials and recyclability. The possibility of reusing materials with maintained mechanical properties are essential for sustainability. Today produced approximately 90,000 tons of natural fiber reinforced composites in Europe of those are 40,000 tons compression molded of which the automotive industry uses 95%. Natural fiber reinforced composites is recyclable and therefore interesting in many applications. Also, natural fiber reinforced composites is inexpensive, light in weight and shows decent mechanical properties which makes them attractive to manufactures. However, the problem with natural fiber reinforced composites is the poor adhesion between fiber and matrix, the sensitivity of humidity and their low thermal stability. Those problems could be overcome by addition of compatibilizer and reactive filler. This study will examine the technical requirement in order to develop a sustainable and recyclable biocomposite. It investigates the composition of matrix (polypropylene), fiber (flax), compatibilizer (maleic anhydride grafted polypropylene) and reactive filler (CaO) in order to obtain various combinations of stiffness, strength and processability. The two main methods used for preparing samples were compounding and injection molding. Results shows that 20 wt% flax was the optimal fiber content and that maleic anhydride grafted polypropylene is a very good compatibilizer by enhancing the strength significant. Surprisingly was the strength impaired due to the addition of CaO. The composition of 20 wt% flax, 1 wt% maleic anhydride grafted polypropylene and 79 wt% polypropylene is the technically most favorable composition.