Effect Of Interfacial Compatibility On Crytallization And Mechanical Behavior Of PLA

Polymer materials are widely used in all aspects of the national economy and daily life.At the same time,it is a large number of polymer materials that bring convenience to people,but has a negative impact to the living environment which can not be ignored.Polylactic acid(PLA)is one of the most biodegradable materials with the most potential for research.However,PLA is a semicrystalline polymer material.And the problem of PLA which is slow crystallization rate,poor heat resistance and low toughness has limited its wider application.There is still a long way in replacing traditional petroleum-based plastics with PLA.Therefore,improving the crystallinity and toughness of PLA has an important theoretical significance for the development of new PLA products.As a kind of lamellar inorganic nanoparticle,montmorillonite(MMT)can be used as a nucleating agent to improve the crystallinity of PLA,and its lamellar structure can also give the material better heat resistance,barrier and other properties.MMT is widely used as norganic nano-filler.However,natural MMT is hydrophilic,and thus the interfacial interaction with PLA is poor.Its nucleation does not play well,and the mechanical properties of the material decrease due to the introduction of poor interface.Therefore,to improve the interaction between PLA and MMT,and then to optimize the well dispersion of MMT in PLA matrix and to maximize the nucleation of MMT are still needed to be solved.With respect to the toughness of PLA,the elastomer glycidyl methacrylate(EGMA)has good toughness,and its molecular chain contains epoxy groups,which can react with the carboxyl and terminal hydroxyl groups of the PLA.However,when the content of EGMA is low,the toughness of PLA is not good.When the content of EGMA is high,the toughness of PLA is greatly improved,but the strength and modulus of PLA are greatly reduced.Therefore,to obtain super-tough PLA,while maintaining its excellent strength and modulus is still an urgent problem to be solved.In view of the above two problems,this paper designed two systems.First,OMMT was prepared by the modification of MMT with dopamine,then PLA/OMMT composites were prepared by melt-blending,and the interfacial compatibility,crystalline properties and mechanical properties of the composites were investigated.Secondly,The PLA/EGMA/DCP composites were prepared by melt blending.The effect of initiator DCP on the interfacial compatibilization of PLA matrix and elastomer EGMA was studied.The mechanical properties and toughening mechanism of blends were studied systematically.The results are as follows:When MMT is modified treated by dopamine,OMMT lamellar structure is opened.With the increase of dopamine concentration and the time of polymerization,the interlayer distance of OMMT layer increases,and the content of PDOPA on the OMMT lamellae increases.The first diffraction peak,which reflects the MMT lamellar structure,is clearly visible in XRD,and it is known that the OMMT is still a lamellar structure.Compared with pure PLA,the nucleation density of PLA/MMT composites enhanced.MMT is an effective nucleating agent.However,in the PLA/OMMT composites,the nucleation density of PLA increases,the spherulites grow faster,the spherulites are smaller.OMMT has better heterogeneous nucleation than unmodified MMT.So it has promoted the crystallization of PLA.In addition,the interfacial debonding of the PLA/OMMT composites is not obvious,and some particles can be completely immersed in the PLA matrix,indicating that OMMT and PLA compatibility is better.The tensile strength of PLA/OMMT composites is similar to that of PLA/MMT composites,but the elongation at break is increased by 2.9 times compared with pure PLA.PLA is a brittle material with high strength,high modulus and low elongation at break.The addition of 5 wt% EGMA increases the elongation at break from 5% to 10%.After adding 0.05 ~ 0.2phr DCP,the elongation at break of PLA/EGMA is significantly increased,and the notched impact strength also increases accordingly.More importantly,the tensile strength and modulus of the material are not reduced compared to pure PLA.The addition of DCP promotes the PLA compatibilization at the interface of EGMA and the interfacial adhesion between PLA and EGMA.The particle size of dispersed phase EGMA is significantly smaller and uniformly dispersed in the PLA matrix.During the stretching process,strong interfacial adhesion prevents the interfacial debonding,which promotes the internal cavitation of the EGMA elastomer particles,effectively triggering the shear deformation of the substrate and absorbing a large amount of energy.Promoting the material from brittle fracture into ductile fracture,and the high strength and toughness of the PLA-based composite material is prepared.