| Polylactic acid?PLA?,as a kind of polymer material with the most potential development and application in biodegradable aliphatic polyester,has been produced and applied on a large scale,but the crystallization rate of PLA is slow,and the general molding products are amorphous.It greatly reduces its heat resistance and mechanical properties,and seriously restricts the application of PLA.In order to improve its crystallization performance,nucleating agents are often added,and the commonly used nucleating agents are inorganic nucleating agents and organic nucleating agents,which are contrary to environmental friendly.therefore,the study of new environmentally friendly nucleating agents is of great significance.In this paper,polyglycolide?PGA?with different molecular weight was synthesized by using lactide as monomer,1,4-butanediol?BDO?as initiator and Sn?Oct?2 as catalyst,and its isothermal crystallization behavior,isothermal crystallization kinetics,crystal structure and crystal morphology were studied.At the same time,the blends of PLA and PGA with different molecular weight and concentration were prepared,and its isothermal crystallization behavior and isothermal crystallization kinetics,non-isothermal crystallization behavior and non-isothermal crystallization kinetics,as well as crystal structure and morphology were investigated.Firstly,the effect of molecular weight on the isothermal crystallization of PGA was studied.The results show that the semi-crystallization time of PGA increases with the increase of crystallization temperature during isothermal crystallization at 160-180°C.When the intrinsic viscosity of PGA is between 0.10 and 0.66,with the increase of molecular weight,the half-crystallization time decreases and the crystallization rate constant k increases at the same crystallization temperature.The Avrami exponent of PGA is between2 and 3.POM observation showed that the crystalline morphology of PGA was not a normal spherulite,but a complex polygonal crystal,and the nucleation density of PGA increased with the increase of molecular weight.Secondly,the effect of different molecular weight PGA as nucleating agent on the isothermal crystallization of PLA was studied.The results show that when PLA was isothermal crystallized at 110-130°C,the crystallization rate of PLA increased significantly after adding different molecular weight of PGA.The semi-crystallization time of PLA increases with the increase of crystallization temperature when the molecular weight of PGA is constant.When the intrinsic viscosity of PGA is 0.10-0.66,with the increase of molecular weight of PGA,the semi-crystallization time of PLA decreases and the value of crystallization rate constant k increases.After adding PGA,the Avrami index of PLA is between 2 and 3 during isothermal crystallization at 110-130°C.POM observation showed that the nucleus density increased significantly after adding PGA,and increased with the increase of molecular weight of PGA.Finally,the effect of nucleating agent PGA concentration on the non-isothermal crystallization properties of PLA was studied.The results show that after adding PGA with intrinsic viscosity of 0.66,the Avrami index of PLA ranges from 2 to 3.When the concentration of PGA is constant,the crystallization rate constant kc of PLA increases with the increase of cooling rate.POM observation showed that with the increase of PGA concentration,PLA nucleus density increased and crystal size decreased. |
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