Tailoring The Morphology And Properties Of Biodegradable Poly(Lactic Acid )/Poly(?-caprolactone) Blends By Nucleating Agents

Poly(lactic acid)(PLA)is an important bio-based biodegradable plastic,with great potential in replacing traditional non-degradable plastics.In spite of this,the wide application of PLA is limited by its brittleness and low crystallization rate.Blending PLA with biodegradable flexible poly(?-caprolactone)(PCL)is expected to increase its toughness without sacrificing the biodegradability.However,PLA and PCL are incompatible,leading to uncontrolled morphology,weak interfacial bonding,and poor mechanical properties.Up to now,the morphological structure and properties of PLA/PCL blend were tailored mainly by the addition of nano fillers in literature.In this work,the effect of a nucleating agent,zinc phenylphosphonate(PPZn),and a self-assembly nucleating agent,multiamide(TMC),on the morphology and properties of PLA/PCL blends was investigated.The main results are as follows:(1)The effect of PPZn on the crystallization behavior and properties of PLA/PCL blends.The PLA/PCL blends with various compositions(100/0,90/10,80/20 and 70/30)were prepared by melt blending.The content of PPZn was fixed as1 wt% of PLA/PCL blends.The crystallization behavior and properties of the blends were investigated by differential scanning calorimetry(DSC),polarized optical microscopy(POM),atomic force microscopy(AFM),universal material tester,and dynamic mechanical analyzer(DMA).The results show that PLA and PCL are incompatible and present an island-like distribution.The addition of PPZn promotes PLA crystallization in the blends significantly but inhibits the crystallization of PCL.It can be ascribed to the crystallization of PLA at higher temperature upon cooling from the melt,which hinders the subsequent crystallization of PCL at lower temperature.With the addition of PPZn,the particle size of PCL in the blends is reduced and the distribution is much narrowed.For example,the average particle size of PLA/PCL(80/20)and PLA/PCL/PPZn(80/20/1)were 0.55 and 0.16 ?m,respectively.The tensile testing results show that PCL has a significant toughening effect on PLA,and the addition of PPZn further improves the toughness of PLA/PCL blends.The DMA results show that the addition of PPZn enhances the heat-resistanceof PLA/PCL blends.(2)The effect of a self-assembly nucleating agent,TMC,on the morphological structure and crystallization behavior of PLA/PCL blends.The PLA/PCL/TMC blends(PLA/PCL content was fixed at 70/30,and nucleating agent TMC contents were 0.3 and 1 wt%,respectively)was prepared by melt blending.The crystallization behavior and morphological structure of the blends were investigated by DSC and POM.The DSC results show that TMC promotes the crystallization of PLA in PLA/PCL blends effectively but inhibits PCL crystallization.The POM results show that TMC mainly disperses in the interface of PLA/PCL and PCL phase,and moves with the coarsening of PCL particles.For the blends with 0.3 wt% of TMC,the TMC self-assembles into fibrous in the interface of PLA/PCL blends,and induces the shish-kebab structure of PLA.For the blend with 1 wt% of TMC,short rod-like crystals of PLA are formed.