Effect Of Nature Fibers And Annealing On Crystalline And Heat Resistance Properties Of Poly(Lactic Acid)

Polylactic acid(PLA)is a biodegradable polymer material,which can be polymerized by the lactic acid obtained from fermentation of starch.Since the final products of PLA degradation are environmentally friendly water and carbon dioxide,PLA is often used as a substitute for traditional petrochemical-based plastics.It is also considered to be the most promising and popular environmentally friendly material.PLA has been widely used in the fields of packaging and medicine because it has similar transparency and good biocompatibility with ethylene terephthalate.However,due to its slow crystallization rate,poor heat resistance,high cost and other shortcomings,it's application was severely limited in more areas.Aiming at these shortcomings,the modification of PLA is studied by people.Among them,the more effective ways to improve the crystallization and heat resistance of PLA are adding nucleating agent and annealing.The results show that the addition of nucleating agent can improve the crystallization rate and crystallinity of PLA,can also improve its heat resistance.However,the effect of improving the heat resistance of PLA is not very good.Therefore,this paper adopts the method of adding nucleating agent and annealing treatment at the same time,hoping to improve the crystallization and heat resistance of PLA better.In this paper,organized bamboo fiber(OBF)and organized cotton fiber(OCF)were selected as nucleating agents for PLA.Then chose the better effect of nucleating agent and optimum mass ratio.While adding the nucleating agent,the experimental temperature,time and medium were controlled to anneal the pure PLA and the mixed system.The effect of nucleating agents and annealing conditions(annealing temperature,annealing time,annealing medium)on the crystallization and heat resistance of PLA were characterized by fourier transform infrared spectroscopy(FTIR),differential scanning calorimetry(DSC),X-ray diffraction(XRD),polarized optical microscopy(POM)and vicat softening point,heat distortion temperature tester.The results of DSC showed that the addition of OBF and OCF could improve the crystallinity of PLA,but the effect of adding OBF was more obvious.When the content of OBF was 1.2%,the crystallinity was at its maximum.And the used of OBF as a nucleating agent can reduce the annealing temperature,shorten the annealingtime.Annealing treatment can effectively improve the crystallinity of PLA.POM photographs show that the crystal form of PLA is spherulite.After adding the nucleating agent OBF and OCF,the crystallization rate of PLA was accelerated,the crystal size became smaller and the nucleus density increased obviously.It indicated that OBF and OCF are effective nucleating agents for PLA.The XRD results showed that the addition of nucleating agent and annealing treatment do not change the crystal form of PLA,and it is still a stable crystal form(?-form).The FTIR results show that the addition of nucleating agent and annealing treatment will not make structure change.Through the Vicat softening point,heat distortion temperature test showed that when the addition of nucleating agent and annealing treatment are combined,the crystallization and heat resistance of PLA can be improved significantly.