The Crystallization Modification Study On The Biodegradable Thermoplastic Polylactic Acid

In this paper, Nucleating agent and uniaxially orientaion were studied to the crystallization of Polylactic acid(PLA). The efficiency of nucleating agent (Tm-3, Talc,etc.) were characterized. The isothermal crystallization kinetics and nonisothermal crystallization kinetics of PLA and PLA/Nucleating agent were researched by differential scanning calorimetry' (DSC). The spherulite topography and spherulite growth of PLA was investigated by polarized light microscope (POM). Multifuntional testing machine was used to study of multiples,temperature,nucleating agent on PLA's the machanical behavior,properties. DSC and wide-angle X-ray diffraction(WAXD) were used to characterize the crystallization of PLA.The isothermal crystallization kinetics and nonisothermal crystallization kinetics of PLA were studied by DSC. As the results of Avrami equation, all materials have same Avrami kinetic parameters, but their crystallization rates and activation energys are very different. Talc was the effective nucleating agent. Their crystallization behaviors under different cooling rate were analysised. It was found that Jeziorny equation, at different time, Avrami kinetic parameter n was different. Another, The efficiency of all nucleating agents were analysised, it was that Talc's efficiency of nucleating was good.Multifunctional testing machine was used to study of uniaxial multiples,temperature,nucleating agent on PLA stress-strain curve and oriented PLA product's properties. Result was that, temperature was a sensitive factor, temperature raise 20℃, strain decreased 13 MPa in the Process of uniaxially oriention; uniaxial multiples and Talc had great impacts to product's properties, when uniaxial multiples was 400%, the tensile strength of oriented product increased 24MPa, and the tensile strength of oriented product was improved 10 MPa with 1phr Wt Talc .DSC and WAXD were used to characterize uniaxially oriented PLA product's crystallization. In the experiment, it was found that a additional crystallization exothermic peak was observed prior to the major melting endothermic peak in the heating scans, and a new crystal diffraction peak was discovered near 29.9°in WAXD chart. Result is that, oriention could increase product's crystallinity and generate PLA'sαandβcrystal; when temperature above of 110℃and uniaxial multiples more 4 times, someαcrystal could change toβcrystal, Talc could accelerate this process; PLA's crystallinity increased from 18.5% to 37.48% with 1phr Wt Talc.