Studies On The Properties Of Modified Polylactide Prepared By UV Irradiation Induced Reactive Extrusion

Polylactic acid(PLA)is derived from biomaterials and fermented by microorganisms from sugars or starches.PLA has excellent biodegradability,good biocompatibility and processing performance.Its mechanical properties are similar to those of oil-based plastics such as polyester and polystyrene.PLA plays an important role in sustainable development.PLA has low melt strength and slow crystallization rate.The product produced by PLA is difficult to form.These shortcomings restrict the PLA in foaming,injection molding,extrusion,blow molding and other forming process applications.PLA can be branched by TMPTA in melting extrusion process under ultraviolet irradiation,but the branched chain is shorter,and the melt strength is not increased excellently.In order to increase the melt strength,this paper introduced more longer branched chains on the PLA molecular chains by using the different reaction conditions between the PLA and epoxy group of Glycidyl methacrylate(GMA)and the three carbon-carbon double bonds of tri-methyl propylene acrylate(c-hydroxy),prepared the long chain branched PLA(LCB PLA)with high melt strength by two-step reaction extrusion.Change the ratio of GMA and TMPTA to produce different LCB PLAs.The structure and properties of the LCB PLAs were characterized in detail.The molecular structure,rheological properties and crystallization properties of LCB PLAs were compared by melt Flow Rate(MFR)test,gel permeation chromatograph(GPC)test,gel content test,rotational rheological test,differential scanning calorimeter(DSC)test and polarizing microscope(POM)observation.After that,the PLA was modified by the excellent crystallization properties of polypropylene(PP).The PLA-g-TMPTA-g-PP graft was produced in the two-phase interface under the action of TMPTA under the ultraviolet irradiation.The microstructure,crystallization,mechanical properties and heat resistance of the products were characterized by DSC test,Scanning Electron Microscope(SEM)test,POM observation,Rotational Rheological test,mechanical property test and VST softening point test.The specific research contents and results are as follows:1.Under ultraviolet irradiation,the changes of MFR of PLA adding only TMPTA,adding TMPTA and GMA were studied,as well as the effect of GMA on MFR and crystallization property of PLA,and the reaction mechanism of ultraviolet induced Long-Chain Branches of PLA facilitated by GMA end-capped reaction was discussed.The results of MFR of the products adding TMPTA and GMA is more lower,and the MFR of the product decreased with GMA content increased.When only add GMA,the PLA did not have the chain branching reaction,MFR rosed,and GMA played the role of plasticizer and heterogeneous nucleation,and made crystallization ability slightly higher of PLA.2.The differences in molecular structure,rheological properties and crystalline properties of the LCB PLA prepared by adding different ratio of GMA and TMPTA and only TMPTA were studied under ultraviolet irradiation.All these samples did not produce cross-linked structures.Compared with the LCB PLAs branched by adding TMPTA,the LCB PLAs branched by adding GMA and TMPTA has longer branched chains.It is shown that the melt index is lower,the molecular weight is increased but the degree of support is reduced,the entanglement of the molecular chain is serious,and the solid-phase behavior is more obvious,and the viscoelasticity is greatly enhanced.When the content of TMPTA is 3.0wt%,the latter's 0-tangent viscosity is 2.5 times than the former.The crystallization ability is weakened,and because of the existence of long chain the molecular spacing increases,and the nucleation ability is greatly weakened.It is concluded that the mechanism of GMA to promote the long chain branching reaction between PLA and TMPTA is that the GMA grafted on the end of the PLA molecular chain to produce carboxyl or hydroxyl groups,so that the PLA from the terminal access TMPTA to generate the chain PLA or long chain pla.When fixed TMPTA content,change GMA content,found that in a certain range of GMA content more can promote PLA long chain,more than a certain range,GMA plays a role in plasticizing,fluidity increases.3.Using ultraviolet irradiation to induce free radical reaction between PLA,PP and TMPTA(content fixed to 1wt%)at the two-phase interfacial,and generated PLA-g-TMPTA-gPP to increase the capacity of PLA/PP blending system.The two-phase blending system with no capacity increase has not achieved good modification effect.After increasing the compatibility,the crystallinity increased excelently,when PP content is 5wt%,the crystallinity is the best.Toughness and heat resistance of the two-phase blending system are better than those with no increase in capacity.PP content is different,the effect of increasing capacity is also different.4.When the PP content is lower than the 10wt%,the effect of increasing capacity was great.The interface is fuzzy and PP distribution size reduced by half.Crystallization ability greatly enhanced,toughness and heat resistance had more obvious improvement.When the content of PP is higher than 10%,the effect of increasing capacity is poor.TMPTA existed more in the two-phase internal,resulting in the poor increasing capacity.Phase separation and separate crystallization of two phases were observed.PLA‘s crystallization ability was enhanced by the in interface induced effect of PP spherical crystal.