Engineering and modeling of compatibilized bio-based polymer blends using reactive extrusion

Two bio-based polymers, cellulose acetate (CA) and starch, were selected in this study to prepare compatibilized polymer blends. These blends were prepared by adding a reactive copolymer-poly (styrene- co-maleic anhydride (SMA)), generating graft copolymer of a CA-SMA or a Starch-SMA copolymer in situ by reactive extrusion to act as compatibilizer. In order to improve the compatibility of the blends, different grades of SMA having various molecular weights and various maleic anhydride contents were studied.; The grafting reaction (e.g. reactant concentration, temperature and catalyst concentrations), morphology and the mechanical properties of CA/SMA blends were investigated under both solution and melt conditions. We observed that a third order kinetic model of the grafting reaction parameters gave adequate fit and could be used to describe the compatibility of the blends under different reaction conditions. The morphology and the mechanical properties of CA/SMA blends having different compositions were also studied. Our results indicate that it is possible to prepare compatible CA/SMA blends having high tensile properties and good moisture resistance, which should make such blends suitable for a wide range of commercial applications. Furthermore, the preparation process itself was studied and optimized. Our results indicate that if the blends contain more than 15 wt% high molecular SMA, the extrusion proceeds smoothly without the need to add any plasticizer. Generally, the tensile strength was inversely proportional to the SMA content and the highest tensile strength was obtained when a minimum amount of SMA was used.; The relationship between the morphology of the blends and the extent of grafting reactivity was also studied. In the melt, the phase dispersion affects the grafting reaction via increasing the interface area while the grafting reaction affects the phase dispersion by reducing the interfacial tension. Additionally, shear rate, interfacial tension, temperature and composition as well as the injection molding conditions further impact the compatibility of the blends and were used to optimize the injection process.; In starch/SMA blend, the addition of glycerol as a plasticizer greatly improves the processability due to grafting of glycerol onto SMA as well as additional cross-linking between starch, SMA and glycerol. This modified starch/SMA blend was blended with poly (butylene adipate-co-terephthalate) (Ecoflex) and the resulting compatible blend was blown into films. Such blends of Ecoflex and modified starch exhibit good mechanical properties, excellent processability, low cost (compared with Ecoflex and starch blend), and are biodegradable.; In the last part of this thesis, vinyltrimethoxysilane was used as a grafting agent to prepare organic-inorganic hybrids based on Ecoflex and Magnesium Silicate Hydroxide (Talc). The grafting reactions of this silane were studied in relation to the mechanic properties of the blends.