Study Of The Preparation And Property Of Nano-mica/poly(Lactic Acid) Composites

Poly(lactic acid)(PLA) is a kind of biodegradable polymer synthesized from renewableresources. Its production can be finally completely decomposed into water and carbon dioxidethus PLA can reasonably be substituted for conventional petrol based polymer materials.However, some drawbacks such as brittle nature and a lack in crystallinity, poor thermal stabilitystill limit its practical applications. As PLA/layered silicate composites provide a way that mayhelp to solve those problems mentioned before, in this paper, self-prepared nano-mica particleswere used to modify PLA and the PLA/mica composite was prepared through melt blendingmethod. By using twin-bore capillary rheometer and its Haul-off equipment, polarizingmicroscope with heating and freezing stage, differential scanning calorimetry, thermogravimetricanalysis, the rheological behavior, the spinnability, the crystallization properties and the thermalproperties were studied, respectively.As mica particles can improve the thermal conductivity ofPLA, a heat transfer model of mica particles reinforced polymer composite was also establishedand an finite element method was also used to investigate its thermal conductive behavior. Theresults showed that:1.Mica particles hindered the flow of PLAmelt, but didn’t change its flow type, PLAand itsmica blends are all pseudoplastic, non-Newtonian fluid and exhibit shear-thinning behavior atgiven shear rate range. Values of non-Newtonian index of blends melt increased obviously withthe addition of mica particles at the shear rate ranged from100-3000s-1but somehow evendecreased when shear rate exceeded3000s-1.The viscous flow activation energy of PLA/Micablends were larger than pure PLA melt which means PLA/Mica blends were more sensitive totemperature. The spinnability of PLA/Mica blends also decreased with increasing amount ofmica particles.2. The crystalline property of pure PLA was rather weak, nano-mica particles could play as nucleating agents during the crystallization of PLA thus increased the degree of crystallinity ofPLA.The growth of crystals of PLA was greatly influenced by the crystallization time,crystallization temperature and the content of nano-mica. The non-isothermal crystallizationstudy showed that, with faster cooling rate, both of the half time of non-isothermal crystallizationand the crystalline peak temperature decreased. With Ozawa’s method and Mo’s method, wesuccessfully describe the non-isothermal crystallization process of PLS/Mica composite.Thermogravimetric analysis showed an decreased thermal stability after the incorporation ofmica particles.3. Based on the law of ratio effective thermal conductivity, a simple heat transfer model ofmica particles reinforced PLA composite was established and its effective thermal conductivitywas derived. Result from finite element method simulation and our model revealed that, thesubstaintial factor that makes the flake fillers with high aspect ratio like mica disk perform betterin enhancing thermal property of composite is the longer conductive path of the flake fillers.