Modulation Of Elasticity And Damping Of Eucommia Ulmoides Gum And Its Molecular Basis

Natural rubber(NR)is an important strategic resource,but NR in our country mainly relies on imports,and thus it is urgent to develop new renewable rubber resources.The development of bio-based Eucommia ulmoides gum(EUG)has great potential for development because EUG resource in our country has monopolistic advantages,but its crystalline hinders the emergence of flexibility.This paper aims to decrease the crystallinity of EUG,thereby giving it excellent elasticity and processing performance as well as the improved shape memory performance and wide damping performance,which has wide application including traditional rubber and new smart materials.When the triazolindione(TAD)click chemistry method was used for EUG modification,the double bonds on the main chain of EUG were isomerized to make its total number unchanged,which would not hinder the vulcanization characteristics of EUG because vulcanization and other modification methods consumed double bonds.Furthermore,modified EUG produced molecular elasticity,which was different from the network elasticity of EUG elastomer obtained by traditional overvulcanization,and had more excellent performance including low hardness,processability,and high elasticity.Besides,the concept of side chain engineering was also proposed,that is,introducing the branched and long chain alkyl pendants into the EUG side chains by the molecular basis design,effectively regulating its dynamic mechanical damping performance.Therefore,the scientific problem solved in this paper was to tune the elasticity and damping of EUG by introducing the side groups,and to verify the possibility of the transformation from plasticity to elasticity at the molecular level.The main content and results of this paper were as follows:In chapter 2,the butyl triazolindione(b TAD)was synthesized and used to prepare modified EUG,Tb_xEUG,based on the excellent properties of polymers modified by Alder-ene click chemistry reaction.The method could precisely tune the mechanical properties and effectively improve the elasticity by reducing crystallinity,introducing urazole groups,and forming hydrogen bonds between EUG molecules.By adjusting TAD feed,the modified EUG could become an excellent tough elastomer with combined high strength of27.6 MPa,elongation of 1130%,and toughness of 124.9 MJ m^-3;or a unique rubber with superhigh elongation of 1852%,low Young's modulus of 0.53 MPa,and good elastic recovery rate of 57%.Furthermore,the modified EUG displayed enhanced shape memory capability with fast shape recovery speed of 10 seconds at 60 ^oC,high cyclic shape recovery rate of80-95%after 10-cycle deformations,and large shape memory recoverable deformation of600%.Overall,Tb_xEUG with improved room temperature elasticity might become a tough elastomer or conventional rubber,which could be used in the tire industry,daily necessities,and smart materials,and it would reduce the demand of NR resources to a certain extent when it was used as raw materials in the rubber industry.In chapter 3,the resulting Tb_xEUG was cross-linked by vulcanization technology because the cross-linked rubber had higher mechanical properties and better usages.It was found that the prepared vulcanized modified EUG,V-Tb_xEUG,had the greatly improved mechanical properties from 6.57 MPa to 20.20 MPa accompanying with an unsatisfactory elongation at break ranging from 48%to 528%.Meanwhile,they had excellent damping performance under higher temperature and room temperature,different from traditional vulcanizates such as NR and EUG which only had lower temperature damping performance,indicating that b TAD changed the molecular chains and introduced polarity to EUG,so it was a potential rubber material for preparing shock-absorbing products.In addition,it was found that the room temperature damping ability of vulcanized NR was improved without sacrificing its good mechanical properties when 20%Tb_xEUG were blended,which widened rubber products application of EUG.However,the elasticity and hardness of Tb_xEUG and its vulcanizate V-Tb_xEUG were not satisfactory,and their performances needed to be further improved.Therefore,we would further design TAD modifiers with different structures that could bring better performance.In chapter 4,the branched side-chain strategy of a facile and effective ethylhexyl triazolindione(eh TAD)was used to modify EUG,Teh_xEUG,because the short-chain branched alkyl structure had more flexible molecular chains.The introduction of varied amount of polar and branched alkyl pendants by rapidly TAD modification could tune EUG to be high elastic materials with various mechanical properties and excellent wide-temperature damping performance.The effect of low glass-transition temperature(T_g),polar pendants,and hydrogen bonds produced the microphase separation and double damping peaks on tan?curve of modified EUG.When the eh TAD content was 30%,the elastic recovery of elastomer could reach to 92%that exceeds NR,and its T_g and Shore A hardness were-52 ^oC and 50^o,respectively.What is more important,the damping temperature range was broadened to 132^oC from-35 to 97 ^oC maintaining tan?over 0.3,and the damping coefficient was up to 0.53,which were much better than those of original EUG.In addition,the vulcanizates exhibited similar high elasticity and good damping properties.Therefore,the sustainable modified EUG elastomer could become a conventional and functional soft rubber with the exceptional damping performance,could absorb more energy at wide temperature range including room temperature,and have potential applications in various fields such as tires,automobile,machinery,and damping and shock absorber materials.In chapter 5,the long branched pendants strategy of hexylnonyl triazolindione(hn TAD)was synthesized and used to prepare modified EUG,Thn_xEUG,based on the outstanding development prospects of vegetable oil-based polymer with long alkane chain.It was found that the Shore A hardness,elasticity,and damping ability of modified EUG were more excellent although its mechanical strength and effective damping temperature range decreased when the alkyl side chain of the modifier was longer.Besides,the urazole pendant groups and the elevated T_g contributed the high tan?_max of 0.88 and wide effective damping temperature range of 81 ^oC from-14 ^oC to 67 ^oC to Thn_xEUG.When the hn TAD content was 30%,the elastic recovery of Thn₃₀EUG could reach to 91%,and its T_g and Shore A hardness were-43^oC and 38^o,respectively.In addition,its vulcanizate also exhibited similar high elasticity and good damping properties.Besides,the damping performance of Thn_xEUG was more excellent than Teh_xEUG modified by the TAD with short branched alkyl group,which make a preliminary study on the development of vegetable oil-based damping polymers.In chapter 6,based on the disadvantages of low modification degree and various control factors of the traditional peroxyformic acid method for preparing epoxidized EUG,a new type of epoxidized EUG,E_xEUG,was quickly and effectively prepared using m-chloroperoxybenzoic acid.It was found that the epoxidation efficiency of this new method was about 90%,and the whole reaction was carried out at medium and low temperature and the controlled reaction conditions were single,so the preparation method was simple to operate and save-energy.When the epoxy group contents were 14%,the tensile strength and elongation at break of vulcanized E_xEUG material,V_2.5-E₁₄EUG,was only 9.05 MPa and204%;when the epoxy group contents increased to 40%,the strength of V_2.5-E₄₀EUG increased to 20.15 MPa,and its elongation at break was still 203%,which was the same as the mechanical properties of vulcanized NR.Therefore,this new epoxidized EUG had excellent mechanical properties and damping properties and the preparation process was simple,and it was more possible to produce EUG elastomers on a large scale.