| This work presents an approach to preparing polyethylene/thermoplastic starch blends with exceptional properties. Thermoplastic starch (TPS), as opposed to dry starch, is capable of flow and hence when mixed with other synthetic polymers can behave in a manner similar to conventional polymer-polymer blends. In this study, a one-step combined twin-screw/single screw extrusion setup was used to carry out the melt-melt mixing of the components. Glycerol was used as the starch plasticizer and its content in the TPS was varied from 29 to 40%.; The shear viscosity of raw PE and TPS was determined on-line from the twin-screw extruder using a series of capillary dies attached to the extruder head. PE/TPS blends prepared in a one-step process were evaluated from its composition, morphology, tensile properties and percent continuity.; Under the particular one-step processing conditions used it is possible to develop continuous TPS (highly interconnected) and co-continuous polymer/TPS blend extruded sheet which possess a high elongation at break, modulus and strength in the machine direction.; The second part of this work is devoted to the study of the thermal and rheological properties of TPS (glycerol content 29 to 40%) prepared in a TSE. Those properties are compared to those of LDPE. DSC analysis revealed the presence of a glass transition temperature (Tg) below ambient temperature, which indicated the complete gelatinization of starch granules. The Tg decreased from −45.6°C to −56.2°C as glycerol content increased from 29% to 40%.; In the third part of this study, the morphology of LDPE/TPS blends prepared by a one-step extrusion/shaping process is compared to that obtained by reprocessing of the original blends. The influence of composition and melt drawing is examined. Blends prepared in the one-step extrusion process show increased levels of anisotropy as a consequence of a combination of coalescence and particle deformation during melt drawing.; In the fourth part of this work, the tensile properties of LDPE/thermoplastic starch (TPS) blends prepared in a one-step process are studied more in detail as a function of TPS composition, glycerol content, morphology and relative humidity. Blends with TPS containing 36% and 40% glycerol, show an unusually high ductility. Blends prepared with TPS containing 29% glycerol and a high viscosity PE are also ductile and possess an improved modulus. Blends of a low viscosity PE and the same TPS result in a material with significantly reduced elongation at break. (Abstract shortened by UMI.)... |
