Flax fibers are often used as reinforcement for thermoset and thermoplastic to produce biocomposite products. These products exhibit numerous advantages such as good mechanical properties, low density, and biodegradability. Thermoplastics are usually reinforced with flax fiber using injection molding technology and limited research has been done on compression molded thermoplastic biocomposite. Therefore, commercial thermoplastic high density polyethylene (HDPE) and polypropylene (PP) were selected for developing compression molded flax reinforced biocomposites in this research project. The main goal of this research was to develop compression molded biocomposite board using Saskatchewan flax fiber and investigate the effect of flax fiber and processing parameters (molding temperature and molding pressure) on the properties of biocomposite. <p>The fiber was cleaned and chemically treated with alkaline and silane solution that modified the fiber surface. Chemical treatments significantly increased the mechanical properties due to better fiber-polymer interfacial adhesion and also reduced the water absorption characteristics. The silane treatment showed better results than alkaline treatment. Differential scanning calorimetry (DSC) test and scanning electron microscopy (SEM) test were performed to study the thermal and morphological properties of the untreated and chemically treated flax fiber. Flax fiber and thermoplastic resin was mixed using a single-screw extruder to ensure homogenous mixing. HDPE- and PP-based biocomposites were developed through compression molding with three different pretreated flax fiber (untreated, alkaline, silane treated fiber), three levels of fiber content, two levels of molding temperature and two levels of molding pressure. <p>Increase in fiber content increased composite color index, density, water absorption, tensile strength, Youngs modulus, bending strength, and flexural modulus. However for the HDPE composites, tensile and bending strength decreased after 20% flax fiber loading. For the PP composites the, tensile and bending strength decreased after 10% flax fiber loading. Analysis of variance (ANOVA) was performed to quantitatively show the significant effects of the process variables (molding temperature, pressure, and fiber content) and their interactions on the response variables (physical and mechanical properties of biocomposites). The duncan multiple range test (DMRT) was also performed to compare the treatment means. Superposition surface methodology was adapted for both HDPE and PP composites to determine the optimum values of process variables.

This project is aimed at developing and demonstrating highly conductive, lightweight, and low-cost thermoplastic blends to be used as flow field bipolar plates for polymer electrolyte membrane (PEM) fuel cells. <br><br> The research is focused on designing, prototyping, and testing carbon-filled thermoplastic composites with high electrical conductivity, as well as suitable mechanical and process properties. <br><br> The impact of different types of fillers on the composite blend properties was evaluated, as well as the synergetic effect of mixtures of fill types within a thermoplastic polymer matrix. A number of blends were produced by varying the filler percentages. Composites with loadings up to 65% by weight of graphite, conductive carbon black, and carbon fibers were investigated. Research results show that three-filler composites exhibit better performance than single or two-filler composites. <br><br> Injection and compression molding of the conductive carbon filled polypropylene blend was used to fabricate the bipolar plates. A Thermal Gravimetric Analysis (TGA) was used to determine the actual filler loading of composites. A Scanning Electron Microscope (SEM) technique was use as an effective way to view the microstructure of composite for properties such as edge effects, porosity, and fiber alignment. Density and mechanical properties of conductive thermoplastic composites were also investigated. During this study, it was found that 1:1:1 SG-4012/VCB/CF composites showed better performance than other blends. The highest conductivity, 1900 S/m in in-plane and 156 S/m in through plane conductivity, is obtained with the 65% composite. Mechanical properties such as tensile modulus, tensile strength, flexural modulus and flexural strength for 65% 1:1:1 SG-4012/VCB/CF composite were found to be 584. 3 MPa, 9. 50 MPa, 6. 82 GPa and 47. 7 MPa, respectively, and these mechanical properties were found to meet minimum mechanical property requirements for bipolar plates. The highest density for bipolar plate developed in this project is 1. 33 g/cm³ and is far less than that of graphite bipolar plate. <br><br> A novel technique for metal insert bipolar plate construction was also developed for this project. With a copper sheet insert, the in-plane conductivity of bipolar plate was found to be significantly improved. The performance of composite and copper sheet insert bipolar plates was investigated in a single cell fuel cell. All the composites bipolar plates showed lower performance than the graphite bipolar plate on current-voltage (I-V) polarization curve testing. Although the copper sheet insert bipolar plates were very conductive in in-plane conductivity, there was little improvement in single cell performance compared with the composite bipolar plates. <br><br> This work also investigated the factors affecting bipolar plate resistance measurement, which is important for fuel cell bipolar plate design and material selection. Bipolar plate surface area (S) and surface area over thickness (S/T) ratio was showed to have significant effects on the significance of interfacial contact resistances. At high S/T ratio, the contact resistance was found to be most significant for thermoplastic blends. Other factors such as thickness, material properties, surface geometry and clamping pressure were also found to affect the bipolar plate resistance measurements significantly.

The current research is part of a wider experimental program on creep modeling of glass mat reinforced polypropylene composites which are increasingly being used in molding automotive parts. This specific study is focused on the dimensional and thermal stability of chopped fibre mat and long fibre mat composites. The objective of the study is two-fold. First, to characterize in-situ the micro-failure mechanisms associated with damage accumulation during creep at room temperature and at service temperature (80°C) for stresses up to 67% of the ultimate tensile strength. Second, to characterize the effects of prolonged exposure at elevated temperature on the crystallinity and chemical degradation of the polypropylene matrix. In the first part of the investigation, micro-failure mechanisms including fibre-matrix interface, matrix yielding and cracking during the creep process have been captured in-situ using reflection microscopy. Specimens with 12 mm gauge length were mounted onto a Minimat tensile tester. The applied stress levels of interest were 33% and 67% of the ultimate tensile strength (UTS) at room temperature (RT) and high temperature (HT), respectively. It was found that the deformation mechanisms do not change with temperature but creep in the chopped fibre material is substantially higher than that in the long-fibre. Creep deformation is typically associated with multiple transverse crack initiation at the fibre-matrix interface, crack crazing and rapid coalescence of the small cracks leading to abrupt fracture. Debonding of the fibres is usually detected at the loading stage of the test but fibre breakage is minimal even at high temperature. The change in creep strain at room temperature is similar for both composites but creep strains are highly sensitive to the fibre-mat type at higher temperature. Long-fibre mat structures offer greater creep resistance. Micro-indentations on the matrix-rich regions showed elongation along the loading direction but shear yielding (distortion of indentations) was not noticeable. Using scanning electron microscopy (SEM), the fibre pullout was observed to be pronounced thus suggesting poor adhesion at the fibre-matrix interface. In the second part of this study, the effects of elevated temperature aging on the microstructural changes of isotactic polypropylene matrix in a composite have been studied using wide-angle X-ray scattering (WAXS) and Fourier-transform infrared spectroscopy (FTIR). The objective was to quantify small and slow changes in crystallinity due to thermal aging. To minimize sample variability, polypropylene resin was extracted from the molded composite plaque. Changes in crystallinity level and crystalline form were detected using WAXS after prolonged aging at 90 and 140 °C. FTIR was utilized to monitor in-situ crystallinity changes and to detect oxidation products due to thermal decomposition. The level of crystallinity was monitored by changes in the absorbance ratio of A997/A973 and A841/A973; the former ratio was found to be more sensitive for detecting crystallinity changes. Aging at 140°C resulted in oxidation. The kinetics of secondary crystallization for the aging conditions studied was characterized using Avrami plots.

This project is aimed at developing and demonstrating highly conductive, lightweight, and low-cost thermoplastic blends to be used as flow field bipolar plates for polymer electrolyte membrane (PEM) fuel cells. <br><br> The research is focused on designing, prototyping, and testing carbon-filled thermoplastic composites with high electrical conductivity, as well as suitable mechanical and process properties. <br><br> The impact of different types of fillers on the composite blend properties was evaluated, as well as the synergetic effect of mixtures of fill types within a thermoplastic polymer matrix. A number of blends were produced by varying the filler percentages. Composites with loadings up to 65% by weight of graphite, conductive carbon black, and carbon fibers were investigated. Research results show that three-filler composites exhibit better performance than single or two-filler composites. <br><br> Injection and compression molding of the conductive carbon filled polypropylene blend was used to fabricate the bipolar plates. A Thermal Gravimetric Analysis (TGA) was used to determine the actual filler loading of composites. A Scanning Electron Microscope (SEM) technique was use as an effective way to view the microstructure of composite for properties such as edge effects, porosity, and fiber alignment. Density and mechanical properties of conductive thermoplastic composites were also investigated. During this study, it was found that 1:1:1 SG-4012/VCB/CF composites showed better performance than other blends. The highest conductivity, 1900 S/m in in-plane and 156 S/m in through plane conductivity, is obtained with the 65% composite. Mechanical properties such as tensile modulus, tensile strength, flexural modulus and flexural strength for 65% 1:1:1 SG-4012/VCB/CF composite were found to be 584. 3 MPa, 9. 50 MPa, 6. 82 GPa and 47. 7 MPa, respectively, and these mechanical properties were found to meet minimum mechanical property requirements for bipolar plates. The highest density for bipolar plate developed in this project is 1. 33 g/cm³ and is far less than that of graphite bipolar plate. <br><br> A novel technique for metal insert bipolar plate construction was also developed for this project. With a copper sheet insert, the in-plane conductivity of bipolar plate was found to be significantly improved. The performance of composite and copper sheet insert bipolar plates was investigated in a single cell fuel cell. All the composites bipolar plates showed lower performance than the graphite bipolar plate on current-voltage (I-V) polarization curve testing. Although the copper sheet insert bipolar plates were very conductive in in-plane conductivity, there was little improvement in single cell performance compared with the composite bipolar plates. <br><br> This work also investigated the factors affecting bipolar plate resistance measurement, which is important for fuel cell bipolar plate design and material selection. Bipolar plate surface area (S) and surface area over thickness (S/T) ratio was showed to have significant effects on the significance of interfacial contact resistances. At high S/T ratio, the contact resistance was found to be most significant for thermoplastic blends. Other factors such as thickness, material properties, surface geometry and clamping pressure were also found to affect the bipolar plate resistance measurements significantly.

The current research is part of a wider experimental program on creep modeling of glass mat reinforced polypropylene composites which are increasingly being used in molding automotive parts. This specific study is focused on the dimensional and thermal stability of chopped fibre mat and long fibre mat composites. The objective of the study is two-fold. First, to characterize in-situ the micro-failure mechanisms associated with damage accumulation during creep at room temperature and at service temperature (80°C) for stresses up to 67% of the ultimate tensile strength. Second, to characterize the effects of prolonged exposure at elevated temperature on the crystallinity and chemical degradation of the polypropylene matrix. In the first part of the investigation, micro-failure mechanisms including fibre-matrix interface, matrix yielding and cracking during the creep process have been captured in-situ using reflection microscopy. Specimens with 12 mm gauge length were mounted onto a Minimat tensile tester. The applied stress levels of interest were 33% and 67% of the ultimate tensile strength (UTS) at room temperature (RT) and high temperature (HT), respectively. It was found that the deformation mechanisms do not change with temperature but creep in the chopped fibre material is substantially higher than that in the long-fibre. Creep deformation is typically associated with multiple transverse crack initiation at the fibre-matrix interface, crack crazing and rapid coalescence of the small cracks leading to abrupt fracture. Debonding of the fibres is usually detected at the loading stage of the test but fibre breakage is minimal even at high temperature. The change in creep strain at room temperature is similar for both composites but creep strains are highly sensitive to the fibre-mat type at higher temperature. Long-fibre mat structures offer greater creep resistance. Micro-indentations on the matrix-rich regions showed elongation along the loading direction but shear yielding (distortion of indentations) was not noticeable. Using scanning electron microscopy (SEM), the fibre pullout was observed to be pronounced thus suggesting poor adhesion at the fibre-matrix interface. In the second part of this study, the effects of elevated temperature aging on the microstructural changes of isotactic polypropylene matrix in a composite have been studied using wide-angle X-ray scattering (WAXS) and Fourier-transform infrared spectroscopy (FTIR). The objective was to quantify small and slow changes in crystallinity due to thermal aging. To minimize sample variability, polypropylene resin was extracted from the molded composite plaque. Changes in crystallinity level and crystalline form were detected using WAXS after prolonged aging at 90 and 140 °C. FTIR was utilized to monitor in-situ crystallinity changes and to detect oxidation products due to thermal decomposition. The level of crystallinity was monitored by changes in the absorbance ratio of A997/A973 and A841/A973; the former ratio was found to be more sensitive for detecting crystallinity changes. Aging at 140°C resulted in oxidation. The kinetics of secondary crystallization for the aging conditions studied was characterized using Avrami plots.

Flax fibers are often used as reinforcement for thermoset and thermoplastic to produce biocomposite products. These products exhibit numerous advantages such as good mechanical properties, low density, and biodegradability. Thermoplastics are usually reinforced with flax fiber using injection molding technology and limited research has been done on compression molded thermoplastic biocomposite. Therefore, commercial thermoplastic high density polyethylene (HDPE) and polypropylene (PP) were selected for developing compression molded flax reinforced biocomposites in this research project. The main goal of this research was to develop compression molded biocomposite board using Saskatchewan flax fiber and investigate the effect of flax fiber and processing parameters (molding temperature and molding pressure) on the properties of biocomposite. <p>The fiber was cleaned and chemically treated with alkaline and silane solution that modified the fiber surface. Chemical treatments significantly increased the mechanical properties due to better fiber-polymer interfacial adhesion and also reduced the water absorption characteristics. The silane treatment showed better results than alkaline treatment. Differential scanning calorimetry (DSC) test and scanning electron microscopy (SEM) test were performed to study the thermal and morphological properties of the untreated and chemically treated flax fiber. Flax fiber and thermoplastic resin was mixed using a single-screw extruder to ensure homogenous mixing. HDPE- and PP-based biocomposites were developed through compression molding with three different pretreated flax fiber (untreated, alkaline, silane treated fiber), three levels of fiber content, two levels of molding temperature and two levels of molding pressure. <p>Increase in fiber content increased composite color index, density, water absorption, tensile strength, Youngs modulus, bending strength, and flexural modulus. However for the HDPE composites, tensile and bending strength decreased after 20% flax fiber loading. For the PP composites the, tensile and bending strength decreased after 10% flax fiber loading. Analysis of variance (ANOVA) was performed to quantitatively show the significant effects of the process variables (molding temperature, pressure, and fiber content) and their interactions on the response variables (physical and mechanical properties of biocomposites). The duncan multiple range test (DMRT) was also performed to compare the treatment means. Superposition surface methodology was adapted for both HDPE and PP composites to determine the optimum values of process variables.

Three-dimensional (3D) polymer structures are very attractive because the extra structural dimension can provide denser integration and superior performance to accomplish complex tasks. Successful fabrication of 3D multilayer microstructures in thermoplastic polymers using optimized nanoimprint lithography techniques such as layer-transfer and transfer-bonding methods are developed in this dissertation work. The capability and flexibility of the techniques developed here are expected to have deep impact on the applications of soft materials such as polymers including functional polymers in micro- and nanofabricated devices and systems. Although NIL technique is developing rapidly in recent years, there are still issues that need to be addressed for broader adoption of the nanoimprint technique. One of the problems is the residual layer that remains in the polymer pattern after nanoimprint. The conventional approach, oxygen reactive-ion-etching (RIE) process, to remove the residual layers, increases the cost and lowers the overall throughput of the nanoimprint process. More severely, it can degrade or even damage the functional polymers. In order to overcome these problems, new residual layer removal techniques need to be developed. In this dissertation, two methods are newly developed, which do not negatively affect the chemistry of the polymer materials. The techniques are suitable for all thermoplastic polymers, particularly functional polymers. Another advantage of nanoimprint is its ability to directly create functional polymers structures. This is because thermal nanoimprint only needs temperature and pressure for pattern replication, which both are benign to functional polymers. This feature combined with newly developed techniques such as transfer-bonding and residue removal techniques opens up the possibilities in nondestructive functional polymers patterning at the micro- and nanoscale for novel applications in electronics, optoelectronics, photonics and bioengineering. Finally, several applications of 3D multilayer structures fabricated by the techniques developed in this dissertation are demonstrated. The first application is a multilayer metal-dielectric-metal structure with embedded microfluidic channels. This structure can be used as an on-chip tunable filter for integrated microfluidic applications. The second application is a multilayer microfluidic channels in which each layer has a different channel size. This device can be used for particle separation and filtration based on lateral fluid flow.

Thesis (M.S.)--University of Alabama at Birmingham, 2008. / Title from PDF title page (viewed Feb. 1, 2010). Additional advisors: Derrick R. Dean, Gregg M. Janowski, Selvum (Brian) Pillay (ad hoc). Includes bibliographical references (p. 76-82).

D. Tech. Chemical, Metallurgical and Materials Engineering / Aims to develop a thermoplastic matrix-based composite with a view to identifying the most suitable combinations of locally available natural fibres and matrices, which meet some basic requirements (e.g., fire and moisture resistance) for the structural and non-structural materials utilised in the building and construction industries.This general goal is divided into three distinct aims: 1. Examine the chemical surface modification of natural fibres (flax, hemp, pineapple and sisal) using water glass (WG). The study investigates the effect of WG treatment on the mechanical and thermooxidative properties of natural fibres. 2. To produce untreated and WG-treated short sisal/polypropylene (with or without maleic anhydride-grafted-polypropylene) compounds using the injection moulding process. The study also investigates the failure behaviour of the composites produced by the tensile-acoustic emission technique as well as the thermal and water absorption characteristics thereof. 3. To produce untreated and WG-treated nonwoven sisal/polypropylene (with or without maleated polypropylene) composites by using the compression moulding process. The study also investigated the fire resistance characteristics of composite materials.

The ongoing search for energy conservation in built structures and during the construction process prompted this thesis work to explore the use of sustainable technologies for floor heating systems. The thesis work explores the use of thermoplastic material as a sustainable substitute material for future floor heating systems. Concrete materials are presently used extensively for floor heating systems. Thermoplastic materials are seldom used for floor heating and the primary focus of this thesis is to explore the suitability & adaptability of thermoplastics as an innovative energy saving floor heating material. A thorough study of energy demands and the impact on environment due to greenhouse gas emissions has been done. Thermoplastic materials are environmental friendly and light weight. They exhibit high thermal conductivity which is favourable for the floor heating systems. A design technique has been developed for the use of thermoplastic materials as an energy efficient floor heating material. The present technique creates a new modular floor heating system. The design technique uses thermoplastic material of size 2.4m x1.2m with embedded electric heaters. Thermoplastic foam panels act as a single building block. A numerical simulation has been carried out to study the heat transfer characteristics of the proposed material. Limited experiments were conducted to verify the validity of the simulation results. The results from the experiments indicate good agreement with simulation results. The energy savings from the thermoplastic floor heating systems have been compared with that of electrical floor heating systems. The adaptability of the new floor heating system in terms of energy savings and cost benefit analysis is also discussed. / sustainable floor heating system