Synthesis And Properties Of Biodegradable Thermoplastic Elastomer Based On PBST

Designing and preparing biodegradable thermoplastic elastomer（BTPE）has important theoretical research and practical application value.Polysuccinic acid/butylene terephthalate（PBST）is an aliphatic aromatic copolyester whose ester bonds in the main chain can be degraded by microorganisms such as bacteria,fungi,and algae,giving PBST valuable biodegradability.In this paper,PBST prepolymers with different proportions of repeating structural units such as butylene succinate and butylene terephthalate and high flexibility aliphatic polyester prepolymers（SPE）with different molecular weights were designed and synthesized.Then,a series of PBST based biodegradable thermoplastic elastomers(BTPE_-PBST)with different molecular structures were synthesized using hexamethylene diisocyanate（HDI）as chain extender using hard segment PBST prepolymers and soft segment SPE blocks.The influence mechanism of the macromolecular structure and molecular weight of BTPE_-PBSTon the crystallization properties,mechanical properties,and biodegradability of BTPE_-PBSTwas emphatically studied.The main research work are as follows.1.Preparation and performance testing of hard segment and soft segment prepolymers.Using dimethyl terephthalate,succinic acid,and 1,4-butanediol as raw materials,three PBST prepolymers with different proportions of repeating structural units such as butanediol succinate and butanediol terephthalate were synthesized through esterification polycondensation and transesterification polycondensation;Two SPE with different molecular weights were synthesized by esterification polycondensation using 1,3-propanediol,1,4-butanediol,succinic acid,adipic acid,and sebacic acid as raw materials.The molecular structures of PBST hard segment prepolymers and SPE soft segment prepolymers were verified by Fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance（¹H-NMR）hydrogen spectroscopy.The results of polarization microscope（POM）,X-ray diffraction（XRD）,differential scanning calorimetry（DSC）,and other tests showed that the three types of PBST hard segment prepolymers had the same crystal form.The crystallinity and crystal size of PBST hard segment prepolymers gradually decreased with the increase in the proportion of benzene ring content in their molecular structure.The crystallinity gradually decreased from 56.8%of PBST_1/9to 24.3%of PBST_3/7,and the melting point of PBST_1/9,PBST_2/8,and PBST_3/7hard segments gradually decreased from105.5℃to 81.2℃;The crystal structure of the two SPE cannot be observed at room temperature,and the glass transition temperature is-55℃,indicating that the SPE have good low tenderness and smoothness.2.Block synthesis and performance study of BTPE_-PBST.Using PBST prepolymer as the hard segment and SPE as the soft segment,and HDI as the chain extender,three PBST prepolymers and two SPE were fused into a series of BTPE_-PBSTwith different molecular structures and molecular weights,respectively.FT-IR and ¹H-NMR spectra confirmed that PBST based BTPE was synthesized by chain extension reaction of HDI with PBST hard segment and SPE soft segment.POM,XRD,and DSC showed that the crystallization ability of BTPE_-PBSTgradually increased with the increase of the hard segment content of PBST,and gradually decreased with the increase of the benzene ring content in the hard segment of PBST.The melting point of BTPE_-PBSTprepared from PBST_1/9,PBST_2/8,and PBST_3/7gradually decreased from around 90℃to around70℃.The T_gof BTPE_-PBSTis around-50℃,indicating good low-temperature resistance.The mechanical property test results show that the tensile strength of BTPE_-PBSTis 1.0 MPa to 28.2 MPa,the elongation at break is above 491%,the 100%tensile recovery rate is 91.0%to 95.5%,the hardness is 65.1-89.6 HA,and the irreversible deformation of 300%cyclic tension is 40%to 75%.The BTPE_1-1-30prepared from hard segments with better crystallization ability and soft segments with larger molecular weight has the best mechanical properties,with tensile strength and elongation at break of 28.2 MPa and 786%,respectively.The AFM phase diagram indicates that BTPE_-PBSTforms a"sea-island"two-phase structure.3.Study on the degradation performance of BTPE_-PBST.The mass loss rate of BTPE_-PBSTin lipase degradation solution for 10 days is 31.18%-100%,and the mass loss rate in soil under natural environmental conditions for 120 days is 20.42%-53.80%.The degradation rate gradually decreases with the increase of PBST hard segment content in BTPE_-PBST.The degradation rate of BTPE_-PBSTprepared with PBST_1/9,PBST_2/8,and PBST_3/7gradually decreases,and the degradation rate of BTPE_-PBSTwith smaller molecular weight is greater in soil.Among them,a series of BTPE_-PBSTprepared from hard segment PBST_1/9exhibited the highest degradation rate in lipase degradation and soil degradation.BTPE_-PBSThas excellent mechanical properties and biodegradability.It can effectively regulate the mechanical properties and degradation properties of BTPE_-PBSTby designing the content of hard segments of PBST,the structure of PBST,and the molecular weight of BTPE_-PBST,and expand its applications in agricultural production,product packaging,construction supplies,and other fields.At the same time,it will have important significance in ecological environmental protection and sustainable development.