Preparation And Properties Research Of Biodegradable Poly (lactide) Composites

Poly(lactide) (PLA) is a biodegradable aliphatic polyester, which derived from renewable resources, and it has good mechanical properties and biocompatibility, thus being a promising polymer either for biomedical applications or to replace petrol based polymers in medical, packaging and other fields. Unfortunately, with the inherent brittleness, low heat resistant, slow crystallization rate, and poor impact properties, PLA is restricted to apply in more fileds. In this thesis, the major goal is to improve the heat resistant and toughness of PLA by physical blending. Moreover, the novel PLA composite remain its excellent biodegradable with adding biodegraded fillers.PLA/ Bamboo Fiber (BF)/ Talc composites have been gained by mixing in Haake mixture and their properties have been investigated by heat-resistant testing (HDT), differential scanning calorimetry (DSC), polarized optical microscope (POM), dynamics mechanical analysis (DMA) and wide X-ray (WAXD). The effect of bamboo fiber and talc on heat resistant and crystallization of PLA have been studied carefully. Great high HDT value of PLA hybrid bio-composites was obtained which was loading BF and talc simultaneously after heat treatment. However, there was little improvement in HDT of PLA bio-composites which has only BF or talc loaded. With 20 wt% BF and 20 wt% talc loading; the HDT of PLA composites increased about 40?. This is due to the hybrid and synergism of BF and talc in PLA composites. Transcrystallization was observed in PLA composite which has BF and talc simultaneously loaded and no similar phenomenon in other kinds of PLA composite. Improvement in HDT of PLA composite was not due to the effect of crystallinity. Furthermore, the formation of transcrystallization was the main effect in HDT of PLA composites and mechanism of forming transcrystallization was proposed. Transcrystallization improves the mechanical properties of PLA/ BF/ Talc in certain content of fillers and heat treatment.By DSC, polarized light method and XRD, the isothermal and non-isothermal crystallized kinetics of PLA/ BF/ Talc composites have been researched, and the influences of cooling rate or heating rate on thermal properties of PLA composites are also studied. Isothermal kenetic of PLA/ BF/ Talc composites could fit the Avrami equation in only low temperature. The non-isothermal kinetic of PLA/ BF/ Talc composites has been also investigated by Jeziorny, Ozawa and Synthesis methods. The non-isothermal kinetic of Pure PLA fits the Ozawa equation and non-isothermal of all composites fit the Synthesis equation. With different cooling rates and heating rates, the double-melting peak has been gained and the mechanism of forming double-melting peak has been proposed. The defects of BF structure promoted the recrystallization in the melting process and the talc promoted forming small crystals. With this reason, the main melting peak temperature was at a low temperature.PLA/TPS/GPOE composites have been gained by mixing of PLA, thermal starch (TPS, prepared by starch and glycerol) and glycidyl methacrylate grafted POE (GPOE). The mechanical, dynamic mechanical, phase structures, degradation properties and toughness mechanism of PLA/TPS/GPOE have been investigated in details. Important improvements in the elongation at break and impact properties of PLA with the addition of TPS and GPOE are reported here. For 10 wt% GPOE, the ternary blends (with 20 wt% TPS content) have improved mechanical properties. The blends have nearly 200% elongation at break and more than 10 kJ/m2 in impact strength. GPOE reduces the size of the TPS phase and improves the compatibility of the PLA blends as shown in the SEM images. The binary and ternary blends have excellent biodegradation by using composting method. In thermal decomposition, ternary blends have higher decomposition temperatures than pure PLA due to glycerol plasticization. A possible reaction mechanism and schematic diagram has also been proposed. The mechanism of reactions has been proved by many characterized methods.At the end, the natural nano-fiber (NC) was prepared by simply method and the PLA/NC non-woven mats have been prepared by electrospun method. We have researched the mechanical, thermal properties and appearance structures of PLA non-woven mats with different testing ways. Natural nano-fiber and maleic anhydride (MAH) grafted PLA (MPLA) have been prepared before mixing PLA and natural fiber in the solvent. Also, the PLA/NC or MPLA/NC non-woven mats have been gained by electrospun and the diameter of MPLA non-woven mats were smaller than that of PLA non-woven mats. The diameter of MPLA/5 wt% NC is only about 132 nm. The tensile mechanism and processing of non-woven mats and normal films have been studied carefully. From the results of mechanical and thermal properties, the PLA/5 wt% NC and MPLA/5 wt% NC non-woven mat has the best mechanical property and the MPLA/NC non-woven mat with lower NC content has the better thermal property in MPLA/NC mats. The degradation properties of PLA and MPLA nanocomposites were studied carefully through in vitro degradation method and SEM.