Flow-induced Crystallization Of PLA Structured Melt

Polylactic acid(PLA)is a semi crystalline polymer with good biodegradability and biocompatibility.The mechanical properties,heat resistance and degradation performance of PLA products depend on the crystal morphology.Because of the difficulty of nucleation and slow crystallization rate of PLA,the amorphous products are usually obtained under the condition of forming,which thus makes its application limited.Improving the nucleation density can promote the crystallization of PLA and improve its performance,so the research related to the nucleation and regulation of PLA has attracted wide attention.In order to improve the crystallinity of PLA,the nucleating agent was added to improve the nucleation density.The nucleation and crystallization behavior of polymer are the key factors that affect the crystal morphology and the structure of the polymer,and the flow and self-seeding can obviously accelerate the nucleation and enhance the nucleationdensity.In this paper,we mainly study the influence of the flow field on the crystallization behavior of PLA and the contents and results of the research are as follows:The melting and crystallization behavior of PLA was studied by in situ X-ray scattering and diffraction.By changing the partial melting temperature and partial melting time,we prepared with different thermal history of the melting of PLA and found in the static isothermal crystallization of subsequent experiments:(1)With the increase of partial melting temperature,crystallinity decreases;(2)With the extension of the melting time,the crystallinity decreased slightly;(3)Cooling from the melting crystallization process orderly,among the fastest crystallization temperature in 110 ? to 120 ?,110 ? 5 min in isothermal crystallization,the crystallization degree reached 5 %.In 120 ? isothermal crystallization 5 min crystallinity reached about 3 %.Shearing on the structured melt,we found in the subsequent isothermal crystallization process:(1)Compared with the blank melting,melting shearing ordered crystalline degrees are obviously improved;(2)Compared with the static melting crystallization process orderly,the crystallization after applied shearing is significantly improved;(3)With the increase of partial melting temperature,crystallinity decreases;(4)With the increase of shearing stress,the sample orientation degree increases and the crystallization process was accelerated;(5)The rate of crystallization of polylactic acid after applying shearing melting orderly significantly accelerated and in 110 ? and 120 ? isothermal crystallization 5 min,it can even reach more than 40 % the degree of crystallization.