Effect Of Compound Nucleating Agent On Crystallization Property Of Poly (Lactic Acid)

Polylactic acid(PLA)is a new type of fully biodegradable material with high mechanical properties.It can be widely used in biomedical,daily-use products,engineering applications and other fields,and in recent years,it has been developed rapidly in the field of disposable products,especially.However,PLA has a low glass transition temperature,slow crystallization rate,low heat resistance temperature of the product,and high brittleness.These defects greatly limit its application in disposable products.In order to improve the heat resistance of PLA,the main way is adding a nucleating agent,and adding a composite nucleating agent is an effective way to improve the efficiency of nucleation.In this paper,the organic hybrid calcium salt is compounded with ultrafine talcum powder and modified cotton fiber respectively to form composite nucleating agents,which are denoted as MTN and MCN.We discussed the influence of this two kinds of composite nucleating agents on the crystallization properties of PLA.The research results shows that the two composite nucleating agents are both effective nucleating agents of PLA,and both can improve the crystallization performance of PLA.Among them,MCN is more efficient.The crystallinity of PLA with 0.8%MCN was 56.0%when the cooling rate was 45?/min,and the crystallization ability was still discernible when the cooling rate was 60?/min.Next,the effects of copolymer of butanediol adipate and butanediol terephthalate(PBAT)and ethylene propylene diene rubber grafted glycidyl methacrylate(EPDM-g-GMA)on the toughness of PLA were investigated.The results demonstrate that EPDM-g-GMA has better toughening effect than PBAT.The notched impact strength of the composite system with EPDM-g-GMA content of 20%is 7.2 KJ/m~2,which is about 3.3 times that of PLA and and 35.8%higher than that of the composite system with PBAT content of 20%.To discussing the influence of MCN on the crystallization properties of PLA/EPDM-g-GMA system,and the influence of EPDM-g-GMA on the mechanical properties and heat resistance of PLA/0.8MCN system,We combined the selected MCN with EPDM-g-GMA and then added it to PLA for melt blending.Studies have shown that MCN is also an effective nucleating agent for the PLA/EPDM-g-GMA system,which can significantly improve the crystallization performance of the toughening system.The crystallinity of the system is more than 50%when the cooling rate is 45?/min.EPDM-g-GMA joined the PLA/MCN,as EPDM-g-GMA content increased,the elongation at break and impact strength of toughening system increases,EPDM-g-GMA that not only can improve the PLA toughness,also can improve the toughness of PLA/MCN system,and from the heat analysis shows that the MCN and the addition of EPDM-g-GMA,improves the crystallization properties and toughness of complex system,but can't improve the composite system under 25?mould products of heat resisting temperature.The preferred ratio of PLA/MCN/EPDM-g-GMA is 89.2/0.8/10(wt%,referred to as P-M0.8-E10).Finally,we studied the effect of annealing time and mold temperature on the heat resistance of the material by annealing or adjusting the mold temperature.We found that extending the annealing time and increasing the mold temperature can both increase the heat deflection temperature of P-M0.8-E10.The HDT of P-M0.8-E10increases to about 93?under a shorter annealing time(45 s).Or at a lower mold temperature(80?),the HDT is increased to about 86?;this two treatment methods make the heat-resistant temperature of the P-M0.8-E10 sample higher than that of pure PLA.