Research On The Relationship Between Structure And Properties Of The Preparation Of Polylactic Acid-based Thermoplastic Elastomer

A thermoplastic vulcanizates (TPV) is a rubbery material with properties and functional performance similar to those of a conventional vulcanized rubber; but it can be processed in a molten state as a thermoplastic polymer. It is a major trend to replace conventional petroleum-based plastic polymer materials with environment-friendly polymer. poly(l-lactide acid)(PLA) is a biodegradable and environment friendly polymer which has biocompatibility. In this study, Biological Elastomer (BE) consisting of PLA and PU was prepared by Dynamic Vulcanization.In this paper, there is a discussion on the influence of blend ratios, dynamical vulcanization time, cross linking agent and compatibilizer on the properties, crystal morphology and phase morphology of PU/PLA TPV.First of all, changing the content of PLA, we prepared "soft" and "hard" two kinds of PU/PLA TPV, of which the hardness varies from24Shao D to60Shao D, the tensile strength is from1O.OMPa to20.0MPa and the elongation at break is all above300%. The amount of cross linking agent has a great effect for dynamical vulcanization. When the amount of crosslinking agent is2.0phr, the modulus of rubber is moderate, and the size of rubber particles can be quite thin under shear stress and the particle disperses in the phase of PLA evenly. The tensile strength of PU/PLA TPV can be up to22.4MPa and the crystallization of PLA is very well.Secondly, Dynamical vulcanization is characterized by the torque-time curve of Haake Rheometer. From the curve, there are four stages including Plastic melting, Rubber Cross linking reaction, Crosslinked rubber crushing process and Rubber particle size smaller and dispersed process. Increasing dynamical vulcanization time, we prepared PU/PLA TPV through different stages, and we found that the modulus and mechanical properties of PU/PLA TPV increased as well as the dynamical vulcanization time. We observed the crystallization of PLA by POM and found that the crystallization speed of PLA increased as well as the dynamical vulcanization time and the size of crystals become smaller and more uniform.Finally, The blends of PLA and PU are parts compatibility. Both the molecular of PLA and PU contain hydroxyl and Chemical reaction between isocyanate and hydroxyl is excellent. So MDI was introduced as compatibilizer. The result of mechanical properties showed that the compatibilizing effect of MDI on PU/PLA TPE is significant. The grafted reaction on MDI and PLA occurred and Interactions between MDI and polyurethane is prominence. MDI improved the dispersion of PU in PLA and the interface adhesion between PU and PLA.