Synthesis Of PLA/PIp Block Copolymer And Research On The Toughness Of Polylactic Acid

Polylactic acid(PLA)is a polymer material with very good biocompatibility.It can be completely degraded into CO2 and water after composting,and there is no plastic residue in the soil or water.Polylactic acid has many advantages,such as high strength and strong plasticity.It has been widely used in many fields such as textile and medicine.However,polylactic acid has high brittleness and poor toughness,which limits its use.In order to meet the needs of different industries,polylactic acid must be modified to make up for its defects.Natural rubber(NR)is one of the most widely used polymer compounds in the world,and it comes from nature entirely.It has a series of advantages,including good elasticity,high insulation,and strong plasticity.It has become one of the most popular universal rubbers in various countries.Natural rubber is a renewable resource,its biocompatibility and degradation property are very superior.Adding natural rubber to plastics to improve the toughness of plastics has always been a key research direction in the field of materials.Toughening mechanism of rubber:there are many rubber particles dispersed in the matrix of the main material.When the composite material is subjected to external impact,these rubber particles quickly generate a large number of microcrack,and the external impact energy is quickly absorbed by microcrack.These microcrack are interrupted by the stress field between each other,and many of them are terminated by other rubber particles.Two adjacent rubber particles can hinder the development of micro-cracks,so the toughness of the material is improved.P olylactic acid/natural rubber composite material has the advantages of polylactic acid about strength,plasticity and elasticity,toughness of natural rubber,which has attracted more and more attention from scientists.However,the polarities of natural rubber and polylactic acid are different,they cannot be well fused with each other,resulting in obvious macro-phase separation,which makes the improvement of the mechanical properties of the material undesirable,so regulating the compatibility of them are very important.On this basis,several block copolymers were synthesized in this paper and their effects on the polylactic acid/natural rubber hybrid system were researched.The research contents are as follows:The first,PLA-b-PIp diblock copolymer was synthesized using RAFT polymerization with controllable activity.The diblock copolymer was composed of two different segments,one was a polylactic acid segment,and the other was a polyisoprene segment.Lactide was used as the raw material to start be ring-opened and polymerized into polylactic acid,then polylactic acid was esterified with a small molecule chain transfer agent.The esterified polylactic acid was used as the macromolecular chain transfer reagent and isoprene were RAFT polymerized to synthesize several PLA-b-PIp block copolymers with different molecular weights.The molecular weight of the copolymer was determined by gel permeation chromatography,the structure was determined by Fourier infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy,verifying that the product was PLA-b-PIp block copolymer.The second,PIp-b-PLA-b-PIp triblock copolymer was synthesized using RAFT polymerization with controllable activity.One chain of the triblock copolymer is composed of three segments,the middle segment is a polylactic acid segment,and the left and right are polyisoprene segments,which is an ABA-type three-stage copolymer.The product was also determined by gel permeation chromatography,molecular structure was determined by Fourier infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy,verifying that the product was PIp-b-PLA-b-PIp block copolymer.Thirdly,PLA-b-PIp and PIp-b-PLA-b-PIp block copolymers was added as a compatibilizer to the polylactic acid/natural rubber mixed system.We explore the compatibilizing effect,thermal stability and toughness on the mixed system.The results show that the compatibilizer has a significant effect on compatibilizing and toughening.Fourthly,on the basis of the feasibility of the above modification research,we synthesize of PIp-co-MAH block copolymer.Maleic anhydride and isoprene are copolymerized by RAFT,then the PIp-co-MAH and PLA were crosslinked under the affect of mechanical force.We explore the compatibilizing effect,thermal stability and toughness on the mixed system.The results show that the copolymer can also be used to compatibilize and toughen.