Study On Toughening And Shape Memory Effect Of Poly(Lactic Acid)

Poly(lactic acid)is completely biodegradable.It has good mechanical properties,biocompatibility and has excellent shape memory effects.In recent years,it has become a hotspot in the field of degradable plastics and shape memory polymer.Under the premise of maintaining the strength of PLA,the effective toughening of PLA has been a hot research topic.Therefore,N-ethyl-p-toluene sulfonamide(N-PTSA)was used as the toughening agent in PLA matrix.The PLA/N-PTSA composites were prepared by melt compounding method.N-PTSA with a mass fraction of 9% could significantly toughen PLA,while the tensile fracture strength of the composite did not decrease significantly.At the same time,the PLA/N-PTSA composite material can be stretched at normal temperature and recover its shape above the transition temperature.The PLA/N-PTSA composites were analyzed systematically from aspects of mechanical properties,thermal properties,crystal structures and shape memory effect.The results showed that the hydrogen bond formed between N-PTSA and molecular chain of PLA,which weakened the interaction between PLA molecular chain,improved the activity of molecular chain,and improved the brittleness of PLA.The molecular structure model of N-PTSA toughened PLA was established.It was found that the PLA/N-PTSA composite could be stretched at room temperature and partially recovered at the transition temperature.Therefore,the shape memory effect of pure PLA was systematically studied.The factors affecting the shape memory effect of PLA were investigated by tensile strain of 100%-400% at 50?,60?,70? and 80? of three crystallinity samples.It was found that the recovery stress of PLA tended to decrease with the increase of tensile temperature.When the tensile temperature exceeds the glass transition temperature(Tg),the recovery ratio and stress decrease obviously.As the crystallinity of PLA increases,its recovery ratio decreases,the recovery stress increases.During the tensile process,oriented crystals and mesomorphic phase are formed,accompanied by the destruction and formation of some crystal regions.The brittle pure PLA could not be stretched at room temperature,so the sample of pure PLA with good toughness was prepared by special processing and heat treatment.The tensile strain of this PLA can reach about 220% at normal temperature,and its strength does not change.Unlike traditional thermally induced shape memory polymers,it does not require the steps of deformation at high temperature,cooling and shaping to preserve internal stress.The shape memory effect of PLA was further studied from the aspects of tensile and recovery temperature,recovery force and recovery process of shape deformation.Based on the previous data,the change of crystal phase structure of PLA in shape memory effect was analyzed and discussed.It is speculated that PLA is a heat-induced shape memory polymer with amorphous region as reversible phase,entanglement and crystal region as fixed phase.The structural change model of PLA in the process of deformation recovery is established.