Rozprawy doktorskie na temat „Carbon-based fillers”

In the recent past it has been found that a considerable pressure drop occurred during the extrusion of linear polyethylene in the course of capillary flow. The pressure drop resides within a narrow temperature window of one to two degrees Celsius. In this research the hydrodynamic condition and molecular origin of the extrusion window of linear polymer were investigated further. The advantage of the extrusion window, viz. smooth extrudate with less die swell ratio attained at low extrusion pressure and temperature, has potential in industrial applications. However, the extrusion window, corresponding to linear polyethylene (PE) with relatively low polydispersity (<7), has a narrow window temperature interval, circa 1~2°C, thus it could not be applied to industrial scale processing at the industrial scale. To have a fundamental insight and make the process industrially viable, research in this thesis was devoted to broaden the extrusion window to tolerate the thermal fluctuations in conventional processing. To achieve this goal molecular weight dependence of window temperature and flow criticalities is revealed. The hydrodynamic conditions of the extrusion window observed in a rate-controlled rheometer and stick-slip flow studied in a stress-controlled rheometer could be traced back to the same origin, viz. slip flow arises due to the disentanglement of adsorbed chains on capillary wall from free chains in the bulk. Secondly, a dual window effect was uncovered in the course of capillary flow of a bimodal PE, which is consistent with the window temperature dependence on molecular weight. Moreover, it was found that flow induced orientation within the window effect is even less than that observed in steady state flow at a relatively low shear rate. This implies that in the window region only relaxed free chains are extruded through the capillary die and most of the adsorbed chains, which could be disengaged from the entangled melt, remain sticking to the inner capillary wall. This observation is consistent with the hydrodynamic origin of high-surface-energy-die slip flow. Finally, a unimodal linear PE with extremely broad molecular weight distribution, i.e. polydispersity (PDI) is 27, showed a broad window effect, circa 8°C, at an appropriate apparent shear rate. The molecular origin of such a broad window effect is due to its broad molecular weight distribution. These results have further implications for energy efficient processing.

La società moderna è in gran parte fondata sulle infrastrutture che garantiscono la fornitura di beni, trasporti e mezzi di comunicazione. La loro salvaguardia e il risparmio delle risorse necessarie per il loro funzionamento è di crescente importanza per l’Ingegneria civile. Per questo motivo, la ricerca sui materiali da costruzione si sta concentrando sul riutilizzo di sottoprodotti industriali riciclati, per un’industria edilizia più sostenibile. L’Ingegneria dei materiali, grazie al recente sviluppo di nanomateriali ad alte prestazioni, propone molteplici spunti per la realizzazione di materiali strutturali multifunzionali. La presente ricerca mira a sviluppare compositi multifunzionali a base di leganti idraulici, con l'aggiunta di filler e fibre a base di carbonio di origine riciclata, ottenuti da sottoprodotti industriali. Sono stati studiati i miglioramenti in termini di resistenze meccaniche e di durabilità, nonché le loro proprietà disinquinanti e fotocatalitiche. Le proprietà elettriche delle miscele sono state studiate, per la valutazione delle capacità di schermatura delle interferenze elettromagnetiche delle aggiunte, e come base di studio per lo sviluppo di materiali auto-sensibili per il monitoraggio strutturale. Sono state realizzate paste e malte contenenti grafene o altri filler a base di carbonio di origine riciclata (da 0.25 a 4% sul peso del legante) e fibre di carbonio (da 0.05 a 1.6% sul volume della miscela). Sui composti sono stati eseguiti test di resistenza meccanica e durabilità, nonché test di adsorbimento degli inquinanti, di fotocatalitisi e di resistività elettrica. La sensibilità elettrica alla deformazione è stata valutata misurando la variazione percentuale della resistività su provini soggetti a carichi di compressione semi-statici. I risultati mostrano che l’aggiunta di filler a base di carbonio riciclati porta a un raffinamento della microstruttura della matrice e a un incremento delle resistenze meccaniche, nonché a un decremento della permeabilità all’acqua. L’aggiunta di micro-fibre di carbonio riciclate porta a un incremento delle resistenze meccaniche a flessione, e a un notevole aumento della conducibilità elettrica (di svariati ordini di grandezza, rispetto ai tradizionali materiali cementizi).
Today's society is largely based on infrastructures that guarantee goods, transport and communication networks. Their safeguarding and saving of resources for their operation is becoming increasingly important in the field of building engineering. For this reason, research on building materials is increasingly focused on the re-use of recycled industrial by-products, for a more sustainable construction industry. Materials engineering, thanks to the development of high performance nanomaterials, offers several ideas for the construction of multifunctional building materials. The present research aims to develop multifunctional hydraulic binder-based composite with the addition of recycled carbon-based fillers and fibers obtained from industrial by-products. The enhancement of mechanical strength and durability of the composites have been studied, together with their de-polluting and photocatalytic properties. The electrical properties of the mixtures have been studied to analyze the Electromagnetic interference shielding capability of carbon-based admixtures, and to provide a basis for the development of strain-sensing materials for structural health monitoring. Pastes and mortars containing graphene or other commercial and recycled carbon-based fillers (from 0.25 to 4.0% on binder weight) and fibers (from 0.05 to 1.6% by mixture volume) were realized. Tests of mechanical resistance and durability were performed on the mixtures, together with test of pollutants adsorption, photocatalysis and electrical resistivity. Strain-sensitivity has been evaluated by measuring the fractional change in resistivity of the specimens subjected to quasi-static compressive loads. Results show that the addition of recycled carbon-based fillers leads to a refinement of the matrix microstructure, increasing the mechanical strength and decreasing the water permeability. The addition of recycled carbon micro-fibers leads to an increase in flexural strengths and to a noticeable increase in electrical conductivity (up to several orders of magnitude compared to the traditional cementitious materials).

Polymeric membranes exhibit a trade-off between permeability and selectivity in gas separations which limits their viability as an economically feasible post-combustion carbon capture technology. One approach to improve the separation properties of polymeric membranes is the inclusion of particulate materials into the polymer matrix to create what are known as mixed matrix membranes (MMMs). By combining the polymer and particulate phases, beneficial properties of both can be seen in the resulting composite material. One of the most notable challenges in producing mixed matrix membranes is in the formation of performance-hindering defects at the polymer-filler interface. Non-selective voids or polymer chain rigidification are but two non-desirable effects which can be observed. The material selection and synthesis route are key to minimising these defects. Thin membranes are also highly desirable to achieve greater gas fluxes and improved economical separation processes. Hence smaller nano-sized particles are of particular interest to minimise the disruption to the polymer matrix. This is a challenge due to the tendency of some small particles to form agglomerations. This work involved introducing novel nanoscale filler particles into PEBAX MH1657, a commercially available block-copolymer consisting of poly(ethylene oxide) and nylon 6 chains. Poly(ether-b-amide) materials possess an inherently high selectivity for the CO2/N2 separation due to polar groups in the PEO chain but suffer from low permeabilities. Mixed matrix membranes were fabricated with PEBAX MH1657 primarily using two filler particles, nanoscale ZIF-8 and novel nanoscale MCM-41 hollow spheres. This work primarily investigated the effects of the filler loading on both the morphology and gas transport properties of the composite materials. The internal structure of the membranes was examined using scanning electron microscopy (SEM), and the gas transport properties determined using a bespoke time-lag gas permeation apparatus. ZIF-8 is a zeolitic imidazolate framework which possesses small pore windows that may favour CO2 transport over that of N2. ZIF-8-PEBAX membranes were successfully synthesised up to 7wt.%. It was found that for filler loadings below 5wt.%, the ZIF-8 was well dispersed within the polymer phase. At these loadings modest increases in the CO2 permeability coeffcient of 0-20% compared to neat PEBAX were observed. Above this 5wt.% loading large increases in both CO2, N2 and He permeability coeffcients coincided with the presence of large micron size clusters formed of hundreds of filler ZIF-8 particles. The increases in permeability were attributed to voids observed within the clusters. MCM-41 is a metal organic framework that has seen notable interest in the field of carbon capture, due to its tunable pore size and ease of functionalisation. Two types of novel MCM-41 hollow sphere (MCM-41-HS) of varying pore size were incorporated into PEBAX and successfully used to fabricate MMMs up to 10wt.%. SEM showed the MCM-41 generally interacted well with the polymer with no signs of voids and was generally well dispersed. However, some samples of intermediate loading in both cases showed highly asymmetric distribution of nanoparticles and high particle density regions near one external face of the membrane which also showed the highest CO2 permeability coeffcients. It is suspected that these high permeabilities are due to the close proximity of nanoparticles permitting these regions to act in a similar way to percolating networks. It was determined that there was no observable effect of the varying pore size which was expected given the transport in the pores should be governed by Knudsen diffusion.

碩士
逢甲大學
紡織工程所
94
Due to the conventional resistance wire has the disadvantages of high energy consumption and high voltage demand. In this study, the electrothermal film based on fabric is made of different carbon conduct fillers and epoxy resin. The supply voltage is 30 volt (V) that is considered to be a safety voltage. This is contribute to a low energy consumption. In this study, the different carbon fillers was added to the epoxy resin to form a paste. Then, the paste was either printed with half-tone screen or dipped and padded with press roller onto a nonwoven fabric. The relationship between the surface resistance and the impact factor, such as filler quantity, diameter, shape and structure of filler, were studies. In addition, the effect of supply voltage on the temperature of electrothermal film was also referred. The results show that the surface resistance is decreased with the increment of filler quantity, then it descents smoothly beyond the threshold value of percolation. In the processing of dipping and padding, the filming of paste is independent of fabric substrate. The temperature test reveals that the surface temperature is increased with the increment of supply voltage. On the contrary, it is increased with the descent of surface resistance. The optimal condition for a lowest energy consumption at 40℃ is also discussed in this study.

碩士
國立中山大學
材料與光電科學學系研究所
107
Development of electric sensors from polymers/carbon conductors have drawn increasing research attention and with this prospect, we prepared stretchable and healable random copolymers M1 and M2, from radical polymerization of methyl methacrylate (MMA), methacrylic acid (MAA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) monomers, for homogeneously blending large amounts (up to equivalent weight) of MWCNTs for the preparation of healable and stretchable conductive nanocomposite sensors with keen responses toward minute, medium and large strain deformations. With the reversible hydrogen bond (H bond) interactions between the inherent pendant groups, random copolymers are healable and highly-stretchable (with fracture strain ef up to 2446%) and after being mixing with different amounts of MWCNTx, the resulting composite films are highly conductive (with conductivity up to 2.06 x 103 S m-1) and are healable and stretchable (ef up to 1890 %). The suitability of the composite films as electric sensor for stain deformations was evaluated and discussed in this study.

Composites are the advanced engineering materials invented by men with exceptional properties over traditional materials. These attractive and delightful materials are the result of developments in the area of engineering and materials science. Composites are heterogeneous materials, obtained by combining two or more components known as matrix and fillers. The matrix may be metallic, ceramic or polymeric in nature. It decides the shape, surface quality, environmental tolerance and durability of the composite while the filler, change or improve the mechanical and physical properties of matrix. Hence, the composites are wonderful materials with a combination of most desirable properties of matrix and filler, suppressing their unwanted properties. Since the last few decades, developments in the field of nanotechnology has been inspired by the discovery of various carbon structures in nanoscale. The era of carbon nanostructures started and gathered massive attention from researchers, with the finding of fullerene in 1985 and has continued till today. Outstanding work by Andre Geim and Konstantin Novoselov on carbon flake of just 1-atom thickness or graphene fetching them the Nobel prize in the year 2010, opened another new chapter in the history of carbon nanostructures. Even a small variation in the orbital or macroscopic structures of carbon, can give rise to variety of new and fascinating properties. Thus, carbon nanomaterials such as carbon nanotubes, graphene, bucky balls, carbon nanofibers and many more are the supreme filler materials in the growth of nanotechnology. The area of research based on carbon nanomaterials is extraordinary, motivated by exceptional and ground-breaking findings evolving both science and technology. This has encouraged the birth of research journals dedicated to research findings exclusively in the field of carbon nanotechnology. The study of composites with these superior filler materials over the last decade, have given birth to polymer nanocomposites with enhanced electrical, thermal and mechanical properties in addition to lower density and ease of processability. Here we are reporting about polymer composites with polydimethylsiloxane (PDMS) as matrix which has distinctive properties such as optical transparency, flexibility, biocompatibility and ease of moulding. PDMS composites with carbon nanostructures make them ideal candidates for various applications. In this thesis, dielectric, electrical, mechanical and electromagnetic shielding properties of various PDMS-carbon nanostructure composites are compared and discussed to understand the effect of macroscopic structural forms of carbon on PDMS. The thesis is divided into eight chapters to put forward the understanding of PDMS composites with variety of carbon-based fillers from different aspects.

碩士
逢甲大學
紡織工程所
94
Due to the conventional resistance wire has the disadvantages of high energy consumption and high voltage demount, a new generation material--electrothermal film was developed in this study to improve the above-mentioned demerits. In this study, the electrothermal film is made of carbon black, graphic anode and the carbon fiber which were used as filler to mix with epoxy resin. The impact of parameters, such as added ratio of filler, process, diameter and shape of carbon black, length of carbon fiber, on the electrothermal film are also discussed in this study. Finally, after connecting with electrodes on both sides, the temperature profile on the film’s surface under various voltage and time are observed. The results show that the above-mentioned factors play an important roll on the surface resistance before the critical value of Percolation. The material has a significant influence on the surface resistance when it above the critical value of Percolation. In addition, the least energy consumption is only 1.75 W at the temperature of 100 ℃; furthermore, considering the safety in usage, the supply voltage can be low down to 16.5 V, which is quite below the Safety Voltage. It is proved that the electrothermal film has a significant improvements in energy consumption and safety.

abstract: Traditionally, for applications that require heat transfer (e.g. heat exchangers),metals have been the go-to material for manufacturers because of their high thermal as well as structural properties. However, metals have some notable drawbacks. They are not corrosion-resistant, offer no freedom of design, have a high cost of production, and sourcing the material itself. Even though polymers on their own don’t show great prospects in the field of thermal applications, their composites perform better than their counterparts. Nanofillers, when added to a polymer matrix not only increase their structural strength but also their thermal performance. This work aims to tackle two of those problems by using the additive manufacturing method, stereolithography to solve the problem of design freedom, and the use of polymer nanocomposite material for corrosion-resistance and increase their overall thermal performance. In this work, three different concentrations of polymer composite materials were studied: 0.25 wt%, 0.5 wt%, and 1wt% for their thermal conductivity. The samples were prepared by magnetically stirring them for a period of 10 to 24 hours depending on their concentrations and then sonicating in an ice bath further for a period of 2 to 3 hours. These samples were then tested for their thermal conductivities using a Hot Disk TPS 2500S. Scanning Electron Microscope (SEM) to study the dispersion of the nanoparticles in the matrix. Different theoretical models were studied and used to compare experimental data to the predicted values of effective thermal conductivity. An increase of 7.9 % in thermal conductivity of the composite material was recorded for just 1 wt% addition of multiwalled carbon nanotubes (MWCNTs).
Dissertation/Thesis
Masters Thesis Mechanical Engineering 2020

Yes
In this paper, two types of nano carbon materials including 0D nano carbon black and 2D graphene are assembled through electrostatic adsorption to develop smart cement-based composites. Owing to their excellent mechanical, electrical properties and synergistic effect, self-assembled 0D/2D nano carbon materials can form toughening and conductive networks in cement-based materials at low content level and without changing the preparation process of conventional cement-based materials, thus endowing cement-based materials with smart and multifunctional properties including high toughness, self-sensing property to stress/strain and damage, shielding/absorbing property to electromagnetic wave. The developed smart cement-based composites with self-assembled 0D/2D nano carbon materials have promising application in the fields of oil well cementing, structural health monitoring, and electromagnetic protection and anti-electromagnetic pollution. It can therefore conclude that electrostatic self-assembled 0D/2D nano carbon materials provide a simple preparation method and excellent composite effect for developing nano cement-based materials, which can be applied in large-scale infrastructures.
The National Science Foundation of China (51908103) and the China Postdoctoral Science Foundation (2019M651116).
The full-text of this article will be released for public view at the end of the publisher embargo on 22 Nov 2021.

Over the last few years, ecological concern and global warming has initiated a considerable interest in using natural materials to produce green products and reduce anthropogenic carbon dioxide emissions by all possible means. Kyoto protocol has further highlighted this issue by which many countries including India has committed to reduce combined CO2, CH4 and N2O emissions. India and China are becoming important players in the Global GHG arena. The CO2 emission in these countries increased by 9% and 6% respectively in 2011, relative to the previous years of their share in global CO2 emission now equals that of Organization for Economic Co-operation and Development (OECD). In the present scenario, natural fibers have excellent potential to reduce not only CO2 emissions but also save non-renewable resources by substituting glass fiber reinforcements in plastic composites. Traditionally, glass fibers/wool has been extensively used as building insulation material and reinforcement in auto sector thermoplastics. However, environmental performance of glass fiber mat thermoplastics (GMTs) has several drawbacks due to extensive energy consumption and potential health risks during production and handling. Glass fibers cause severe abrasion to process equipment and their composites may transform into sharp splints during collision causing extra injuries to passengers. Moreover GMTs are non-recyclable and their incineration generates clinker like mass that is hard to dispose off except land filling. There are many potential natural resources, which India has in abundance. Most of it comes from the forest and agriculture. Wood apple (Aegle marmelos) belongs of family rutaceae is highly reputed medicinal tree. Its fruit is commonly known as the “Stone apple” or “Bael”. It is an indigenous fruit of India and found abundantly in sub-Himalayan forest, Bengal central, south India, Sri Lanka, Pakistan, Bangladesh, Burma, and Thailand. The peel of the fruit is very hard. Wood apple shell contains 39.54% cellulose, 26.06% hemicellulose, and 30.86% lignin. Coconut (Cocos nucifera) is a member of the palm family. The coconut palm is used for decoration as well as for culinary and non-culinary uses; virtually every part of the coconut palm has some human use. Coconut shell is non-food part of coconut, which is hard lignocellulosic agro-waste. Coconut shell consists of 30.04% cellulose, 20.16% hemicellulose, and 25.76% lignin.If the density (low) of these materials is taken in to consideration, then its specific stiffness and strength are comparable to the respective quantities of glass fibers. The wood apple shell and coconut shell composites can be very cost-effective material especially for pipe lines carrying coal dust, slurries, desert structure, low cost housing, boats/sporting equipment, partition boards, doors and window panels. As far as composite industries are concerned in recent period, carbon has been one of the outstanding elements that have revolutionized science of materials. Carbon provides the materials with excellent properties for a wide range of industrial applications. From carbon we receive the strongest fibers (carbon fibers), to one of the best solid lubricants (graphite), one of the best electrically leading materials (graphite electrodes), the best structural material for high temperature tribological application (carbon–carbon composites), one of the best porous absorbers (activated carbon), an essentially non-crystalline impermeable material (vitreous carbon), the hardest material (diamond), and now the most fascinating material, the fullerenes. All these forms are made by meticulously choosing the raw materials and processing conditions Over the last century the production of carbon black (CB) is found to be relatively very expensive, which is produced by incomplete combustion of oil feed stocks. As a result the focus is now shifting towards agricultural waste products which are found to be good source of raw materials for the production of CB. This CB is produced by the pyrolysis of coal, wood, coconut shell, oil palm shell, jute, banana, bamboo, and other lignocellulosic biomass based materials which are carbonaceous in nature and rich in organic materials. Such agricultural by-products are usually inexpensive, for which the effective utilization has not been tried so far. It is unlikely that the use of products made from renewable resources will provide a complete solution to the pressing problems of industrial society. The activated carbon was introduced for the first time industrially in the first part of the 20th century, Activated carbon is a trade name for a carbonaceous adsorbent, which can be prepared from a large number of carbonaceous raw materials including agricultural and forestry residues by either a physical method or a chemical method. The most commercial products are made from agricultural waste such as coconut shell, bamboo, wood, sawdust, hard shell, nut shells and fruit pits. Therefore the present research work has been under taken with an objective to produce carbon and activated carbon from the natural waste (wood apple shell and coconut shell) in the laboratory by utilizing the method of pyrolysis process. It is also planned to use these raw, carbon and activated carbon as reinforcing material in polymer composite of different weight fraction 5, 10, 15 and 20wt%. Direct usage of natural filler alone in polymer composite is inadequate in satisfactorily tackling all the technical needs of a fibre reinforced composite. It is reported that if natural fibre are carbonized to remove the waste material (volatiles and moisture) and increase the carbon percentage the strength of the composites are increased. In this work an attempt has also been made to prepare carbon and activated carbon from wood apple shell and coconut shell. Efforts are made to study the effect of carbonization temperature on the tensile strength, flexural strength, tensile modulus and flexural modulus of the composite. Experiment is also carried out to study the erosive wear behavior of the composite developed. Effect of different parameters like impingement angle and velocity on the erosive wear behavior of carbon and activated carbon composite has also been studied and reported in the thesis. The test results indicate that there is an increase in both tensile and flexural and as well as the modulus for raw, carbonous and activated carbon of wood apple and coconut particulate filled composites. The trend observed for both wood apple and coconut particulate are almost same and the trend is raw