Thesis (M.Eng.)--Chulalongkorn University, 2001

This work is aimed to study the tensile properties, morphology and chemical resistance of thermoplastic polyurethane (TPU) and polydimethylsiloxane (PDMS) blends. The blends at low content (0%-1.0%) of PDMS were prepared by melt mixing using a twin screw extruder. The properties of the blends including the ultimate tensile strength, the elongation at break, Youngʼs modulus, energy to break and the physical property were studied systematically. The resultant blends show an increase in the elongation at break up to 30% and in Youngʼs modulus up to 40% at the optimum PDMS concentration at around 0.6%-0.8%, when compared to virgin TPU, beyond which the properties diminish. While the ultimate tensile strength and the energy to break are decreased about 20% and 10%, respectively. The results are in agreement with the morphology of the fractured surface of TPU/PDMS blends observed by Scanning Electron Microscope (SEM) that there are less fibrous characteristics when increasing PDMS content in the blends. The SEM micrographs of the blends show dispersed phase of PDMS in matrix TPU and the domain size of PDMS phase is smaller when increasing PDMS content from 0.2% to 0.8%. For the study of the effects of chemical resistance to the tensile properties and morphology of TPU/PDMS blends, three types of chemical reagents, i.e. water, sulfuric acid (H2SO4, 3% v/v) and sodium hydroxide (NaOH, 10% w/v) are selected. The results on the chemical resistance to tensile properties and morphology of the blends show that NaOH solution has strongest effect to the tensile properties and morphology of virgin TPU and the blends comparing to water and H2SO4 solution. It was found that the ultimate tensile strength and the energy to break of virgin TPU after base immersion is strongly decreased by 42% and 55%, respectively. The effect of PDMS contents in the blends on the base resistance to tensile properties is similar to results before immersion, i.e. the effective PDMS contents in the blends that can generally improve tensile properties of the blends after immersion in NaOH does not excess 0.8%. The results are in agreement with the weight loss of TPU/PDMS blends after base immersion and the morphology of the fractured surface of TPU/PDMS blends after base immersion that exhibits very small amount of fibrous characteristic and there are some small particles detached at the surface. This could be the result of an occurrence of a corrosive reaction between the sample surface and NaOH solution.