Study On Crystallization Behavior Of Poly(Lactic Acid)/Wood Flour Composites

From the beginning20 th,the use of biodegradable materials gradually into people's lives with the successful synthesis of poly(lactic acid)(PLA).PLA as a bio-basedmaterialswith the character of “pure green,pollution-free,recyclable”,come from the raw material of corn,suger cane,suger beet,potato and other corps,will play an important role in the manufacturing industry in our country.However,in the amorphous,PLAs are limited by its slow crystallization rate and poor crystallinity.In this paper,based on the characteristics of PLA,we selected wood flour(WF)as nucleating agent,which can conserve resources and reduce environmental pollution and extensive sources and biodegradable.We prepared PLA/WF composites by melt blending method.A seriels of PLA/WF composite samples were prepared and characterized by differential scanning calorimetry(DSC),impact properties,tensile properties,and partial optical microscopy(POM).Study on the effect of wood flour nucleating agent on mechanical properties,crystallization properties of PLA/WF composites.On the properties of PLA/WF composites,we optimized the ratio of PLA/WF composites and analysed the isothermal and non-isothermal crystallization mechanism and dynamic behavior.Wood flour can act as a nucleating agent for PLA,and adding 4wt% wood flour can increase the crystallinity of PLA by 4.2%.Compared with that of PLA,the glass transition temperature and the cold crystallization temperature are reduced by about 5.5? and 11.8?,respectively.The optimal ratio of PLA/WF composite material is added 4wt% wood flour,the impact strength is 34.6 J?m-1,but the tensile strength decreased slightly.The growth of PLA crystal is black cross,and the nucleation rate and crystal growth rate can be improved by using wood flour nucleating agent.The Avrami equation can be used to analyze the isothermal crystallization kinetics of PLA/WF composites.The addition of wood flour nucleating agent can significantly improve the crystallization and isothermal crystallization rate of PLA.But it has little effect on the growth mode and nucleation mechanism.The n of Avrami index of the isothermal melt crystallization of PLA and PLA/WF composites are all 2 to 2.8,which are not an integer,and n will not be changed by the change of the crystallization temperature or the addition of wood flour.The sampleswere crystallized at isothermal temperature of 115?,and the added of 4wt% wood powder reduced the crystallization time of PLA to 2.8min.The isothermal crystallization rate of PLA and PLA/WF composites are the highest when the crystallization temperature at 125?,the Avrami index of isothermal cold crystallization of nwere between 1.8 and 2.1,and there was a difference between the isothermal melt crystallization.The phenomenon of melting recrystallization will occur during the melting process of isothermal crystallization.The 4wt% wood flour added to the PLA increased the crystallinity to 19.3% after the above process.Modified Avrami equation,Ozawa equation and MO equation could analysisfor non-isothermal crystallization behavior of PLA/WF composites.Compared with the PLA sample,the peak area of the exothermic crystallization or the exothermic peak area of melt crystallization of the PLA/WF composites increased obviously at the same heating rate or cooling rate.The nof non-isothermal cold crystallization of PLA and PLA/WF composites were between 1.9 and 3.2,and the ? of MO index were between 1~1.5.The use of wood flour could reduce the activation energy of non-isothermal cold crystallization to a minimum of 64.9kJ/mol.The addition of 4wt% wood flour nucleating agent can increase the crystallization ability of PLA and increase the crystallization rate.The crystallization rate of PLA and PLA/WF composites have obvious effect on the non-isothermal melt crystallization,and the nwas between 1.8 and 2.4.