Compatibilizing Poly(Lactic Acid)/Elastomer Immiscible Blends Using ADR Or OMMT

Poly(lactic acid)(PLA)is thermal-plastic polyester obtained from renewable resources with good biological compatibility,high mechanical strength and excellent processability.However,its inherent brittleness and slow crystallization rate limit its practical application.Multiepoxy compound(ADR)is used to in-situ compatibilize PLA and elastomer,such as thermolplastic polyester elastomer(TPEE)and poly(butylene adipate-co-terephthalate)(PBAT).Nano-organic montmorillonite(OMMT)is used to physically compatibilize PLA and ethylene propylene diene rubber(EPDM).Three types of PLA blends with high toughness are prepared.Heat resistance and high crystallinity of PLA blends are obtained by thermal treatment,and relationship of crystallinity and mechanical properties is established.Film properties of PLA/TPEE/ADR and PLA/EPDM/OMMT are preliminary explored.The main research contents are as follows:(1)Effects of ADR on rheological properties,microstructure and tensile properties of PLA/TPEE(80/20)are studied.Results of torque and melt flow index tests prove that the in-situ chain extension reaction took place between PLA,TPEE and ADR,leading to a significant increase in viscosity of these PLA/TPEE blends.SEM pictures show that the compatibilization decrease the dispersed phase size as well as strengthen the interfacial adhesion.The incorpration of ADR can increase tensile toughness of PLA/TPEE(80/20)blend significantly.With 0.3 phr ADR added,elongation at break of blends up to 193%from 53%.DSC and TGA results indicate that ADR has little influence on samples’thermal performance.PLA/TPEE/ADR films are prepared by extruded blowing.Because of the in-situ compatibilization of ADR,PLA/TPEE film blown stability and tensile properties are improved due to the increased melt strength and compatibility.Isothermal cold crystallization kinetics of PLA/TPEE/ADR blends are investigated by DSC,the complete crystallization time of PLA/TPEE(80/20),PLA/TPEE/ADR(80/20/0.5)and PLA/TPEE/ADR(80/20/1.0)are 23,31,34 min,respectively,under 80℃.The crystal type of samples is confirmed to be a’ crystal,independent of crystallinity and crystal size;VST of samples increases to a maximum of 140℃,and tensile yield strength increases slightly,and the elongation at break decreases.When the crystallinity of PLA/TPEE(80/20)increases from 4.3%to 40.2%,the elongation at break falls largely to 28%.However,for PLA/TPEE/ADR(80/20/0.5),when its crystallinity(Xc)increases from 5.3%to 36.3%,the elongation at break is still larger than 100%.It is obvious that PLA/TPEE/ADR samples can keep higher tensile extensibility with increasing the crystallinity.(2)Effects of ADR on rheological properties,microstructure and tensile properties of PLA/PBAT(80/20)are studied.The increasing torque and diminishing MFR prove that ADR can react with PLA and PBAT.SEM pictures show that the incorpration of ADR can improve the compatibilization of PLA/PBAT blends,resulting in a decrease in PBAT domain size.The tensile test shows that the compatibilization effect of ADR can enhance the tensile extensibility of PLA/PBAT blends.Melt isothermal crystallization kinetics of PLA and PLA/PBAT blends were studied.t1/2 increases as Tc rises from 110 to 120℃.When thermally treated under certain Tc,t1/2 of PLA/PBAT is longer than that of PLA.However,with 0.5 phr ADR added,t1/2 of PLA/PBAT/ADR becomes shorter.Xc of PLA and its blends rises to maximum with the heat treatment time prolonging and then maintains at maximum value.It takes 15,20 and 15min,respectively,for PLA,PLA/PBAT(80/20)and PLA/PBAT/ADR(80/20/0.5)to reach the maximum crystallinity when isothermal treated under 110℃.Samples’ VST increases with the increase of Xc.The PLA samples show brittle fracture regardless of the Xc.Elongation at break of PLA/PBAT(80/20)decreases dramatically from 256%to 11%with increasing Xc.However,when ADR of 0.5phr was incorporated,the downward trend on elongation of PLA/PBAT/ADR blends can be inhibited effectively,the elongation at break of samples remains 131%with highest crystallinity.As a result,PLA/PBAT blends with excellent comprehensive properties are obtained(3)PLA/EPDM/OMMT blends are prepared by twin screw extruder.The effects of OMMT content on the microstructure,mechanical properties and thermal stability of the blends are investigated.According to SEM,TEM and XRD results,the incorporation of OMMT can reduce the dispersed phase size effectively,and improve the compatibility of PLA and EPDM.OMMT selectively distributes on the interface and in EPDM phase with an intercalation form.The toughening mechanism of blends is the craze-shear mechanism.The elongation at break and the notched impact strength of PLA/EPDM/OMMT blends reach maximum with OMMT optimal loading of 1 phr.TGA test shows that OMMT is helpful to improve the heat resistance of EPDM components.Study of the isothermal crystallization kinetics shows that samples’ isothermal cold crystallization ability elevated as Tc increases from 80 to 90℃.Half crystallization time is shortest with 1 phr OMMT due to the nucleation of OMMT.As OMMT loading increases further,crystallization ability slows down because of the inhibition effect of nanoparticle on PLA chains.Blown stability and tensile toughness of films are improved with the introduction of OMMT due to the reduced interfacial tension and better compatibility.