Design,Synthesis And Process Research Of Bio-Based Thermoplastic Polyester Elastomer

Thermoplastic polyester elastomer(TPEE)has both the repeatable machinability of plastic and the high elasticity of rubber.TPEE consists of two parts,namely the hard segment with strong crystallinity and rigidity and the soft segment with flexibility,but the soft segment of traditional TPEE is mostly polyether diol which depends on petrochemical resources,which has a large environmental load.It is of great significance to develop green bio-based TPEE in line with the country’s requirements for the two-carbon strategy.This paper mainly focuses on the design and synthesis of bio-based thermoplastic polyester elastomers.Using polybutylene terephthalate(PBT)as the hard segment,the bio-based polyester designed and synthesised as the soft segment was prepared to obtain bio-based TPEE,the main work of this paper is as follows:(1)The first part of this paper adopts the two-step feeding method,the prepolymer PBT was synthesised from petroleum terephthalic acid and 1,4-butanediol,and prepolymer poly(succinic acid/1,4-butanediol/2,3-butanediol)(PBBS)was synthesised from biobased 1,4-butanediol,succinic acid and 2,3-butanediol.Then the two prepolymers were melt polycondensed,with PBT as the hard segment and random copolyester PBBS as the soft segment,by controlling the polycondensation time and the ratio of soft and hard segments,a series of bio-based copolyesters with different molecular weights or different ratios were synthesised.The degree of transesterification will affect the microphase separation structure of TPEE,which in turn affects its mechanical properties.During the polymerization process of TPEE,the terminal hydroxyl group of the soft segment PBBS can undergo transesterification with the ester group of PBT,thereby reducing the hard segment of PBT,forming a random structure.Therefore,the degree of molecular segment arrangement and transesterification of TPEE can be regulated by the polymerization time of TPEE.The molecular structure of the products were characterized by ~1H-NMR in this part,through the calculation of randomness and the characterization of the microscopic morphology of the products by XRD,the optimal polycondensation time and the arrangement of molecular segments to form the microscopic phase-separated structure of the thermoplastic polyester elastomer were discussed.(2)The second part of this thesis builds on the first part,aiming at the disadvantages of high glass transition temperature(T_g)and narrow operating temperature range of PBT-PBBS system,a new type of soft segment was designed and synthesised.Using biobased glutaric acid,1,4-butanediol and 1,2-propanediol as raw materials,a random copolyester poly(glutaric acid/1,4-butanediol/1,2-propanediol)(PPBG)with lower T_g and good flexibility was synthesised.Similarly,a series of biobased TPEE were synthesised by using a two-step feeding method.The T_g of the elastomer is between-32.2℃and-12.9°C,which is significantly lower than that of the PBT-PBBS system.By changing the content of PBT,the tensile strength of PBT-PPBG can be increased from 6.2 MPa to 36.4 MPa.When the content of PBT is 60%,the stress-strain curves of PBT-PPBG shows a slight yield.(3)In order to save resources and reduce the pollution of waste PBT,the third part of this paper carries out chemical upgrading and recycling of waste PBT,using 1,4-butanediol as the alcoholysis agent,and through the one-pot method to alcoholysis PBT and polycondensate it with polytetramethylene glycol(PTMG).By adjusting the amount of alcoholysis agent and the ratio of soft and hard segments,a series of chemically recycled thermoplastic polyester elastomers were synthesised.The breaking strength of PBT-PTMG can reach up to 16.52 MPa,and the elongation at break can reach 1345%.Its performance is good,and it has important application value and social significance.