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Doctor of Philosophy / Department of Grain Science and Industry / Sajid Alavi / Extrusion processing is a technology widely used to make ready-to-eat snack and breakfast cereal products. The raw materials that result in optimal texture and consumer acceptance are mainly those with high levels of starch, which greatly limits the nutritional value of these products. One alternative to enhance the nutritional value is the incorporation of fruits and vegetables. Fruits and vegetables are consistently under-consumed by the American population and incorporation into extruded products may help increase the intake of important nutrients, such as dietary fiber. In the first part of this study a lab-scale twin screw extruder was used for processing directly expanded products based on corn flour and apple pomace (0-28%), resulting in a total dietary fiber content of 1.1-22.5%. Apple pomace increased nucleation and favored axial expansion. The change in cell size and alignment explained the higher mechanical resistance caused by apple pomace. The objective of the second part was to study the effect of preconditioning regimen on the extent of matrix transformation and impact on texture, microstructure and digestibility. The material was processed on a pilot scale extruder. The results showed that increasing the opportunity for hydration increased starch gelatinization at all pomace levels. Apple pomace promoted milder extrusion conditions, resulting in less starch gelatinization and solubilization and reduced starch digestibility. Digestibility was also affected by structure, with a strong correlation between the available starch fraction and cell wall thickness/cell size ratio (r=0.90). The third part of this study was designed to gain a better understanding of the impact of the individual cell wall components (cellulose, lignin, xyloglucan and pectin) on expansion and structure formation. The results suggest that compatibility with starch is critical for good dispersion in the matrix, therefore good expansion and structure forming properties.

Cette étude porte sur la production et la caractérisation de fils élastomères à base de polypropylène (PP) et d’élastomères thermoplastiques (TPE). L’étude du filage par voie fondue des polymères sous forme de mélanges montre une relation entre les propriétés des fibres et la morphologie du mélange. Les propriétés élastiques ne sont améliorées qu’avec le changement de morphologie, et le passage à une matrice TPE majoritaire. Les mélanges filés avec un taux de TPE élevé (80 et 90%m) montrent un changement de structure cristalline du TPE, qui augmente la récupération élastique. L’étude du filage sous forme de structure bicomposante cœur/gaine (C/G), où le TPE est introduit dans le cœur de la fibre et le PP en gaine, montre l’influence du rapport massique C/G sur les propriétés mécaniques des multifilaments. Les propriétés élastiques ne sont pas améliorées pour les différents rapports massiques C/G étudiés, en raison du comportement plastique de la gaine. Le meilleur compromis en termes de propriétés et de mise en œuvre est obtenu avec une structure hybride. Le multifilament mis en œuvre est un fil bicomposant C/G, mais avec un mélange TPE/PP en gaine et le TPE vierge en cœur. Les résultats montrent toujours une diminution des propriétés mécaniques avec l’augmentation du rapport massique C/G, mais une amélioration de la récupération élastique est observée. Pour des taux de TPE équivalents, les propriétés de la structure hybride sont supérieures à celles déterminées pour les mélanges sous forme de fibres monocomposantes. Pour finir des essais de texturation et de tissage démontrent une possible utilisation de ces multifilaments dans des procédés de transformation textile. / The aim of this work is the study of elastomeric fibers processed by melt spinning of polypropylene (PP) and thermoplastic elastomers (TPE). Multifilaments produced by a melt spinning process of polymers blend show a relationship between fiber properties and their morphology. Elastic properties are enhanced only when the majority phase is TPE. Yarns melt spun from blends with high TPE rates (80 and 90 wt.%) show a transition of the crystal structure from pseudo hexagonal to orthorhombic with the increase of drawing ratio applied which improve elastic recovery. Melt spinning of core/sheath (C/S) bicomponent fibers is performed using TPE as the core and PP as the sheath. The study reveals a decrease in mechanical properties with increasing the C/S ratio, and elastic properties are not modified for the different C/S ratios studied. This behavior can be explained by the plastic deformation of the polypropylene sheath. In order to improve processability and properties, melt spinning of core-sheath bicomponent fibers with different C/S ratios is performed using EOC and polypropylene blends as the sheath and pure EOC as the core. The results still show a decrease in mechanical properties with the increase in the C/S ratio, but elastic properties are enhanced. For the same TPE content, elastic recovery and mechanical properties are higher for hybrid fiber than for blend melt spun as monocomponent fibers. Finally texturing and weaving tests prove a possible use of the multifilaments in textile processes.

Digitized by Kansas Correctional Industries

Novel plastics that are biodegradable and made from renewable natural resources are currently being researched as alternatives to traditional petroleum-based plastics. One such plastic, thermoplastic starch (TPS) is produced from starch processed at high temperatures in the presence of plasticizers, such as water and glycerol. However, because of its hydrophilic nature, TPS exhibits poor mechanical properties when exposed to environmental conditions, such as rain or humidity. The overall objective of this thesis was to produce a thermoplastic starch based material with low water absorption that may be used to replace petroleum-based plastics. Three different methods for reducing water absorption were investigated, including the following: extrusion of starch with hydrophobic polymers, starch modifying chemicals, and citric acid/sorbitol as plasticizers. It was found that all methods reduced the water absorption of TPS.

An initial evaluation of the scalability of extrusion foaming technology is conducted in this thesis. Both lab- and pilot-scale foam extrusion systems along with annular dies and flat dies were used to investigate the effects of extrusion system scale on the foam expansion. The effects of the processing conditions including die temperature and blowing agent content on the volume expansion of extruded polystyrene foams blown with carbon dioxide are presented. A systematic comparison of the effects of extrusion system scale on the expansion behavior of polystyrene foams blown with carbon dioxide at the consistent pressure-drop rate, demonstrated that the scale of the foam extrusion system does not affect the principles of the foaming process, and the effects of extrusion system size on the scale-up of foam techniques, such as shear rate and temperature uniformity, could be suppressed by tailoring the processing conditions and experimental parameters.

In this study, crystal formation of polypropylene (PP) and poly lactic acid (PLA) in the presence of CO2 in foam extrusion process was investigated using a visualization chamber and a CCD camera. The role of pre-existing crystals on the foaming behavior of PP and PLA were studied by characterizing the foam morphology. Visualization results showed that crystals formed within the die before foaming and these crystals affect the cell nucleation behavior and expansion ratio of PP and PLA significantly. Due to the fast crystallization kinetics of PP, crystallinity should be optimum to achieve uniform cell structure with high cell density and high expansion ratio. In PLA, enhancement of crystallinity is crucial for getting foam with a high expansion ratio. It was also visualized that CO2 significantly suppresses the crystallization temperature in PP through the plasticization effect as well as its influence on flow induced crystallinity.

An initial evaluation of the scalability of extrusion foaming technology is conducted in this thesis. Both lab- and pilot-scale foam extrusion systems along with annular dies and flat dies were used to investigate the effects of extrusion system scale on the foam expansion. The effects of the processing conditions including die temperature and blowing agent content on the volume expansion of extruded polystyrene foams blown with carbon dioxide are presented. A systematic comparison of the effects of extrusion system scale on the expansion behavior of polystyrene foams blown with carbon dioxide at the consistent pressure-drop rate, demonstrated that the scale of the foam extrusion system does not affect the principles of the foaming process, and the effects of extrusion system size on the scale-up of foam techniques, such as shear rate and temperature uniformity, could be suppressed by tailoring the processing conditions and experimental parameters.

Novel plastics that are biodegradable and made from renewable natural resources are currently being researched as alternatives to traditional petroleum-based plastics. One such plastic, thermoplastic starch (TPS) is produced from starch processed at high temperatures in the presence of plasticizers, such as water and glycerol. However, because of its hydrophilic nature, TPS exhibits poor mechanical properties when exposed to environmental conditions, such as rain or humidity. The overall objective of this thesis was to produce a thermoplastic starch based material with low water absorption that may be used to replace petroleum-based plastics. Three different methods for reducing water absorption were investigated, including the following: extrusion of starch with hydrophobic polymers, starch modifying chemicals, and citric acid/sorbitol as plasticizers. It was found that all methods reduced the water absorption of TPS.