Study On Low Temperature Impact Resistance And Stiffness Balance Of PPR By Natural Rubber/Ethylene-Propylene Rubber Composite System

Natural rubber（NR）is an important forestry chemical with excellent overall performance,which can be used to prepare rubber products such as tires and gloves,and has important uses in the field of polymer toughening.Random copolymer polypropylene（PPR）has the advantages of non-toxicity,heat insulation,heat resistance and high transparency,and is widely used in packaging,hot and cold water pipes and other fields.However,poor low-temperature toughness and easy cracking have severely limited the application of PPR materials under certain working conditions.Therefore,the preparation of PPR materials with low-temperature impact resistance and balanced stiffness and toughness has been a hot spot in the field of polymer toughening,and the related research is of great scientific significance and application value.Previous studies have shown that compounded rubber can combine the advantages of multiple rubbers and weaken the disadvantages of a single rubber used alone.Therefore,in this study,a compound rubber composed of ethylene propylene rubber（EPR）and NR,which is more compatible with PPR,was used to systematically study the effects of different NR/EPR composition compound rubbers on the toughening of PPR and the toughening mechanism behind,and on this basis,the synergistic toughening effects of nano Si O₂ and the compound rubber on PPR and the synergistic toughening effects of nano Si O₂ and micro vulcanization were investigated.The main research results are as follows:（1）Toughening modification of PPR by compound rubber.The effect of compound rubber composition and rubber to polymer ratio on the mechanical properties of the blends in the PPR/（NR:EPR）toughening system was systematically investigated,and the results showed that when NR:EPR was 3:7,only 25 parts of compound rubber were required to reduce the brittle transition temperature(T_bd)of PPR from 30℃to-30℃,which was better than-20℃for PPR/EPR and 0℃for PPR/NR with the same number of rubber parts.NR,and the modulus of the blends showed only a slight decrease after using the compound rubber.The microscopic morphology,microstructure and dynamic mechanical properties show that the excellent low temperature toughness of PPR/（NR:EPR）blends is obtained by the synergy of the appropriate particle spacing and wider particle size distribution,the"core-shell"structure formed by EPR wrapped around NR and the excellent low temperature damping of NR.（2）Synergistic toughening modification study of nano Si O₂ and compound rubber on PPR.Based on the first part of the study,nano Si O₂ was introduced into the PPR/（NR:EPR）system using a two-step method to investigate the synergistic toughening effect between nano Si O₂ and the compound rubber,and the results showed that there was a synergistic toughening effect between nano Si O₂ and the compound rubber,and only 10 parts of nano Si O₂ and 25 parts of the compound rubber were required,and the PPR/（NR:EPR）/Si O₂ T_bd can be reduced to-40°C,and the modulus and tensile properties of the composites were improved.The microscopic morphology results show that the presence of nano Si O₂ can effectively reduce the particle spacing,and part of the nano Si O₂ is distributed at the PPR/EPR interface,which can increase the interfacial adhesion,thus maintaining the original rigidity of the material by reducing the amount of rubber.（3）Synergistic toughening study of nano Si O₂ and slight vulcanization on PPR.The effects of the degree of cross-linking and nano Si O₂ addition on the mechanical properties of PPR composites were investigated by dynamically vulcanizing PPR/EPR/Si O₂ composites.The results showed that slight vulcanized rubber and nano Si O₂ could synergistically toughen the PPR composites,inducing a decrease in T_bd of the composites（80/20/9/0.1）from-20°C to-40°C with no significant loss of rigidity.The improvement of low-temperature toughness originates from the moderate vulcanization of the rubber phase promoting the interfacial loading of Si O₂ nanoparticles,improving the damping energy dissipation process of the rubber phase,and reducing the particle spacing.This study provides theoretical and technical guidance for the preparation of low-temperature impact-resistant and stiffness-balanced PPR composites,and presents directions for expanding the application of important forest products NR.