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Yes / Extrusion-a unit operation in polymer processing has been in extensive use since the great age of plastic technology. It is a simple operation that enables within one equipment the sequential conveying of solid polymer chips or powder, their melting, mixing, pumping and shaping via a die into a variety of high tonnage and/or value products. Pipes, bottles, films are the most common examples but the list of applications is endless from tiny micromoulded parts to large structural profiles. Extrusion is not limited to plastics but is used hot or cold to process soft solids like food, industrial and pharmaceutical pastes, as well as metals and ceramics. Most of the advances in extrusion processing have concentrated in improving the essential functions of extrusion: solid conveying, melting, pumping and mixing. The literature abounds with descriptions of such advances pushing the limits of the extrusion in an incremental way. In this paper, we describe step-changes in enhancing extrusion, which opens up new applications to better old technology-make them safer, cheaper and cleaner. The new designs presented in this paper have also the potential to develop new reactor technology for viscous fluids.

Wheat gluten, wheat gliadin, and corn zein agricultural proteins were evaluated as multifunctional additives that: (1) provided reinforcement, (2) improved thermal stability, and (3) lowered the cost of polymer composites. Wheat proteins were utilized in two polymer matrices: poly(vinyl alcohol) (PVA) and synthetic cis-1,4-polyisoprene rubber (IR). The proteins were hydrolyzed and dispersed in the polymer matrix, where they cooperatively self-assembled into nanostructures called amyloids. Amyloids have the potential for high rigidity and stability due to high β-sheet content. In Chapter II, trypsin hydrolyzed wheat gluten (THWG) proteins were incubated in aqueous PVA solutions, then the composite solutions were air dried and compression molded into films. Anisotropic protein aggregates formed through a typical mechanism of β-sheet self-assembly, where a greater molding time and pressure and/or a lower PVA molecular weight allowed for more protein aggregation. The larger protein structures provided less reinforcement. In Chapters III and IV, THWG and trypsin hydrolyzed gliadin (THGd), a component protein in wheat gluten, were compounded in synthetic polyisoprene rubber to form nanocomposites. The reinforcement correlated to the protein β-sheet content and varied with protein concentration, protein batch preparation, processing temperature, and compounding time. The isotropic β-sheet containing structures were very thermally stable, even under harsh rubber compounding conditions. By optimizing the processing parameters uniform protein dispersion and optimal IR reinforcement were achieved, although the protein and IR phases had poor compatibility. In Chapter V, the THGd-IR composites were cured using a typical cure package and molding process. Protein aggregation into nanostructured β-sheets was observed during the curing process. Rubber reinforcement increased as a function of protein concentration and curing time. In Chapter VI, a hydrophobic protein (zein) was substituted for the hydrophilic protein (gliadin) used previously to improve protein-IR compatibility. The zein protein was better at reinforcing IR, while gliadin improved mechanical stability. Both zein and gliadin improved the thermal stability of IR. The results from Chapters II-VI showed an interesting concept: in situ filler formation in polymer matrices where the choice of protein, polymer, and processing conditions influenced the final morphology and composite properties. / Doctor of Philosophy / We use plastics every day for a wide range of applications, from food packaging to automobile tires. Many of these plastics are composite materials, called “polymer composites,” meaning they are made of two or more chemically distinct materials where one material is a polymer. For reference, a polymer is a long chain molecule made of many (“poly-”) units (“- mer”). Polymer composites often contain additives which modify the properties of the polymer. For example, many soft polymers, such as tire rubber, need to be made stiffer and so a “reinforcing additive” is used to improve the stiffness of the rubber. Many composite materials are made stiffer so less material can be used. This process is called “lightweighting.” The automotive industry and food packaging industry use this process to reduce weight and fuel costs. In this research, plant proteins are tested as reinforcing additives in polymer composites. Plant proteins, such as wheat gluten, are abundant, non-toxic, sustainable, and can self-assemble into extremely small, stiff structures. For these reasons, plant proteins offer an environmentally friendly alternative to typical reinforcing additives. This dissertation shows that plant proteins can reinforce two polymers with very different properties. The first polymer is poly(vinyl alcohol) (PVA), which is biodegradable, hydrophilic (i.e., “water loving”), and is commonly used in flexible food packaging. The second polymer is synthetic cis-1,4-polyisoprene rubber (IR), which is non-biodegradable, hydrophobic (i.e., “water fearing”), and is commonly used in automotive tires. In Chapters II-V, the wheat gluten protein is hydrolyzed, i.e., chemically “chopped” into short chain peptides, to encourage the self-assembly of the plant protein into small, stiff structures. The self-assembled protein structures survive typical industrial processing techniques, such harsh rubber compounding conditions which involve high heat, pressure, and shear forces (i.e., the material is pushed in opposing directions). In Chapter VI, full corn and wheat proteins are incorporated into IR using standard industrial mixing and curing processes. The corn and wheat proteins reinforce the synthetic rubber and inhibit the degradation of the chemical structure of cured rubber under high heat. At certain protein concentrations, the proteins improve the elasticity and lessen the permanent deformation in the polymer composite. Together, Chapters II-VI show that proteins from diverse plant sources can be used to improve the performance of polymers with dissimilar properties.

<div>For over 20 years, biaxially oriented polypropylene (BOPP) has been used in capacitors as the dielectric material. BOPP has very high breakdown strength, low electric loss, and is relatively inexpensive however, it suffers from low dielectric constant and low usage temperature. The ever growing technology market requires more robust capacitors which can be used in high temperature and pulsed power applications, and the aim of this research is to meet or exceed dielectric properties of BOPP by combining specific polymer materials in layered structures, biaxially orienting the films, and heat setting the films to further improve thermal stability. Post-processing is done on custom built machines which track real-time true stress, true strain and birefringence values, allowing for a more complete picture of mechano-optical properties generated during the stretching process. These data, along with offline characterization techniques such as X-ray scattering and DSC, were coupled with dielectric property testing to help form relationships between polymer processing, morphology, and dielectric properties.</div><div><br></div><div>In Chapter 3, microlayer PET and PVDF (50:50 ratio) films with 32 total layers and thickness around 125 micron were provided by PolymerPlus. Films were first stretched uniaxially at varying temperatures in order to optimize processing conditions. Characterization confirmed PVDF crystal form transformation from alpha to beta form when films were stretched at 95^oC, and presence of - PVDF when stretched in molten state at 185^oC, sandwiched between solid PET layers. Dielectric properties were tested for films stretched at 150^oC, which exhibited low dielectric constant when PVDF spherulites or smaller, broken up fibrils were present, but improved dielectric constant when PVDF morphology consisted of long, highly ordered fibrils. Uniaxial drawing helped lower dielectric loss, and it further signicantly decreased at very high strains. In this case, morphology of uniaxially drawn PET did not have a strong correlation with dielectric constant, but higher PET crystallinity and orientation likely helps to lower dielectric losses.</div><div><br></div><div>Polymer microlayer fims consisting of 32 layers, 50:50 ratio PET to PVDF films were also studied extensively using thermal heat setting technique. Samples with good thickness uniformity after stretching were selected for these experiments, and offline characterization techniques were applied to study morphology. Films were annealed at temperatures around PVDF melting peak, which caused transformation of PVDF polymorphs from primarily alpha to combined gamma and/or gamma' forms. When oriented at 150^oC to 1.5X1, and ' -PVDF were detected in small amounts (via DSC) after annealing at 172^oC, and only ' after higher temperature annealing. Stretching at 150^oC to higher strains produced high amounts of '-PVDF only when annealed at 155^oC for films stretched to 3.5X1, and annealed at 150^oC for films stretched to 2.5X1. Offline characterization led to development of a structural model for PVDF layers alone, by de-laminating film layers. Then, morphology was correlated with dielectric properties by testing lms at room temperature, and at constant frequency, in temperature ramping experiments. Temperature ramping dielectric experiments showed that high percent crystallinity of PET may also help improve loss behavior at high temperatures. Furthermore, samples containing gamma and/or gamma'-PVDF had increasing dielectric constant with increasing temperature, however dielectric loss also greatly increased with increasing temperature. A significant conclusion was that the annealed sample without gamma or gamma'-PVDF present had only a slightly lower dielectric constant at high temperature testing, but also had much lower loss, making it a potential candidate for high temperature capacitor applications.</div><div><br></div><div>Other materials for potential dielectric film applications were studied as well. Two fluoropolymer films consisting of monolayers of ETFE and THV were uniaxially oriented and their morphology was characterized offline to elucidate structure-process-property relationships. Film samples produced were not large enough to be tested for dielectric properties, however morphology development during uniaxial orientation was evaluated. Both films showed nearly affine stretching behavior, and mechano-optical properties were studied during stretching at several temperatures. Combinations of X-ray scattering experiments and AFM led to proposed morphological structure models for each material at varying levels of deformation.</div><div><br></div><div>Finally, in collaboration with A. Schulman, Inc., PET and EVOH compounded blend and three layer PET-EVOH-PET films were oriented uniaxially and the morphology of the two was compared to each other. Potential applications include high barrier food packaging applications, due to the very high oxygen barrier but poor water vapor barrier of EVOH, which can be complimented by PET's high water vapor barrier. Uniaxial orientation of these two film systems showed that mechano-optical behavior was significantly different for blend versus layered films. Crystalline orientation factors were calculated from 1D WAXS data, which showed PET orientation was largely unaffected by increasing EVOH content in blend films, but blending decreased orientation of EVOH. PET's orientation in layered films was also largely unaffected by amount of EVOH in inner layer. EVOH's orientation factor was higher in all layered film compositions compared to neat EVOH film after stretching, suggesting that the coextrusion process is beneficial to increasing orientation of EVOH.</div><div><br></div>

While hollow glass microspheres are commonly used in syntactic foam, their abrasive and brittle properties usually result in poor processability and have adverse effects on the foam performance. Therefore, a number of attempts have been made in the industry to replace hollow glass microspheres with polymeric foamed microspheres. Among many choices, expandable thermoplastic (ETP) microspheres filled syntactic foam has shown its high potential to become a novel class of engineering materials, especially for lightweight structural applications. However, conventional processing techniques for syntactic foam usually experience difficulties such as high processing viscosity, low loading of foam fillers, and ineffective microsphere expansion. To address these emerging issues, a microwave expansion process to produce thermoset-matrix syntactic foam containing thermoplastic foam beads was developed in this thesis work. In this process, unexpanded ETP microspheres were directly foamed in uncured thermoset matrix via microwave heating. Expandable polystyrene (EPS) microspheres and epoxy resin were chosen as a model material system. The resin viscosity and specific microwave energy are found to be the two primary control parameters determining the process window. Mechanical characterization showed that the syntactic foam can outweigh neat polymer in lightweight structural applications and was effectively toughened by foamed EPS. Furthermore, the microwave expansion process was found to be capable of molding syntactic foam parts of relatively sophisticated geometry with smooth surfaces. In order to broaden its impact, the microwave expansion process was extended to produce composite EPS foam. This process converts an expandable suspension into a composite foam with a honeycomb-like barrier structure. The suspension viscosity was found to highly influence the foam morphology. Results from mechanical tests showed that the existence of the barrier structure can considerably improve the mechanical performance of the composite foam. Fire-retardation tests demonstrated that the barrier structure can effectively stop the fire path into the foam, suppress toxic smoke generation, and maintain foam structure integrity. A general formulation was developed to model the EPS expansion to optimize the microwave expansion process. A semi-analytical solution was first obtained based on the case of a single bubble expansion in an infinite matrix. The dimensionless bubble radius and pressure are defined and found to be as exponential functions of dimensionless expansion time. The semi-analytical solution can qualitatively predict the radial expansion of EPS microsphere observed in a real-time experiment. To have an accurate prediction, a numerical solution was obtained to the model that couples the nucleation and expansion of multiple bubbles in a finite matrix. The results show that the numerical solution can quantitatively predict the radial expansion of EPS. A parameter sensitivity study was performed to examine the effect of each parameter over the expansion process.

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