Preparation And The Study On Properties Of Poly(Lactic Acid)Multiphase Composite

Polylactic acid(PLA)is a thermoplastic polyester,which is an environmentally friendly material.PLA has been widely used depending on its high strength and good biocompatibility.However,the characteristics of brittleness,low melt strength and slow crystallization rate of PLA limit its practical application.Therefore,the core-shell modifier(PB-g-SAG)was used to toughen PLA in this paper.The core was polybutadiene(PB)and the shell was the copolymer of styrene,acrylonitrile and glycidyl methacrylate(SAG).However,the addition of soft components will lead to the decrease in strength.In this paper,the modification ability of PB-g-SAG to PLA was improved by the epoxy-based multifunctional chain extender ADR4370s(CE),and the groups of different blends were prepared by adding multiwall carbon nanotube(MWCNT)or montmorillonite(MMT)to PLA/PB-g-SAG blends.The effects of ADR,MWCNT,and MMT on the properties of PLA/PB-g-SAG blends were investigated.The results are as follows:(1)The effects of CE and PB-g-SAG on DSC,DMA,rheological properties,mechanical properties and micromorphology of the blends were studied.The torque and temperature at the end of blending and the storage modulus and complex viscosity of the blend samples showed that compatibilization reaction and branching reaction occurred and the melt strength increased significantly.DSC and DMA results showed that the branched structure was formed by the addition of CE,which increased the glass transition temperature of the blends.When PB-g-SAG content was 20wt% and CE was 0.5wt%,the melt strength,Izod impact strength and Young's modulus of PLA/PB-g-SAG blends increased from 9.2×104Pa·s,428J/m and 1634 MPa to 1.27×105Pa·s,530J/m and1845 MPa.Compared with pure PLA,the melt strength and impact strength are increased by 1150% and 1666%,respectively.The balance of strength and toughness is achieved.The results of SEM show that the main toughening mechanism is the joint action of the shear yielding of PLA matrix,cavitation caused by PB and the debonding of interface between PB-g-SAG and PLA.(2)The effects of MWCNT and PLA/PB-g-SAG on DSC,rheological properties,electrical conductivity,mechanical properties,and micro morphology of PLA were studied.DSC test shows that the crystallization peak and melting peak of the sample move to low temperature,and the crystallization performance is greatly improved.The conductivityshows that the percolation threshold of PLA/PB-g-SAG/MWCNT blends is 1.2%.The rheological properties show that the addition of MWCNT further improves the melt strength due to the rigidity of MWCNT.When PB-g-SAG content was 20wt% and MWCNT content was 0.8wt%,the impact strength of the blends increased to 459J/m.The results of SEM show that shear yield,PB induced cavitation,and debonding of PB-g-SAG interface with PLA still are the main toughening mechanisms in the PLA matrix.The increase of impact strength is depending on the deflection and termination phenomenon during the growing process of craze and the debonding of MWCNT and matrix.(3)The effects of MMT on the properties of the PLA/PB-g-SAG system,such as DMA,rheological properties,mechanical properties and micro morphology,were studied.The tensile strength increases with the addition of MMT,and reaches the maximum value when the MMT is 0.5wt%.When the content of MMT is high,the effect of stress concentration is more obvious.The rheological properties showed that after the aggregation of MMT,the storage modulus and complex viscosity of the blends decreased.SEM showed that the dispersion of core-shell particles decreased with the addition of MMT,which was mainly due to the steric hindrance of MMT.The results of SEM also show that the toughening mechanism is shear yield of PLA matrix,cavitation caused by PB and debonding of the interface between PB-g-SAG and PLA.