| At present,researches of environmentally friendly polymer materials are mainly concentrated on degradable polyester and degradable starch-based composite materials.Market shares of degradable polyesters,including polylactic acid(PLA),polyhydroxyalkanoate(PHAs),polycaprolactone(PCL),and polysuccinates,are keeping increasing.However,due to the special characteristics of the molecular structure of the degradable polymers,its mechanical properties are poor,so that limit their application.Therefore,it is challenging to broaden its application field by modifying the degradable polymer.Isosorbide can be used as a third monomer for the synthesis of aliphatic polyesters.Isosorbide has a V-bridged ring structure that can effectively increase the rigidity of the copolyester molecular chain.In this paper,a series of degradable polyester materials were prepared based on polysuccinates,and isosorbide was used as the third monomer.The effect of isosorbide on the properties of copolyesters was analyzed.The future application prospect of polyester is proposed and discussed,and the blow molding and hot-melt adhesive bonding experiments are carried out to evaluate the use value of the copolyester.First,polyethylene succinate(PES)and polybutylene succinate(PBS)were synthesized,and the synthesis conditions and the properties of the two polyesters were systematically analyzed.The results show that both PES and PBS can be synthesized by melt polymerization.The synthesized product of PBS has higher molecular weight and better product color.Thermal properties tests of polyester shows that the glass transition temperature and melting point of PES and PBS polyester are relatively close,so that the using temperature ranges of the two are the same.They have good thermal stability at 300 °C,and PBS can quickly form a relatively perfect crystal which can be processed in a short time.Mechanical properties tests showed that owing to the higer molecular weight,mechanical properties of PBS are superior to PES.The copolymerization modification of PBS polyester was carried out by using isosorbide as the third monomer,and polybutylene succinate-isosorbide(PBIS)was prepared by melt polycondensation.Due to the special molecular structure and the low reactivity of isosorbide,the higer content of isosorbide deteriorated the catalytic effect of tetrabutyl titanate.The calculation of the conformation of the copolyester oligomer by density functional theory shows that the molecular chain conformation is in a tortuous state in this case,which is not conducive to the catalytic performance catalyst with huge molecular size.So,it is necessary to carry out polymerization using a smaller molecular size of antimony trioxide as a catalyst.Analyses of the thermodynamic properties and mechanical properties of the copolyester showed that the introduction of isosorbide destroys the regularity of the molecular chain,reduces the crystallinity and melting point of the copolyester.Also,it increases the rigidity of the molecular chain so that the glass transition temperature of the copolyester is increased.The thermal stability of the copolyester is markedly increased when the content exceeds 40 mol%.The analysis of the mechanical properties of the copolyester showed increasing amount of isosorbide,increased first and then decreased the tensile strength and elongation at break of the copolyester,and the optimum mechanical properties are reached when the isosorbide content is 8 mol%.Hydrolysis tests of copolyester at different temperatures,degradation test in natural waters and degradation test in the simulated natural environment show that PBS and its copolyester can be degraded under natural conditions,and the introduction of isosorbide can accelerate the degradation process of copolyesters.In order tounderstand the mechanism of PBIS processing,non-isothermal crystallization kinetics was used to study the non-isothermal crystallization process of PBIS.The non-isothermal crystallization kinetics of PBIS copolyesters were analyzed by Ozawa method,Jeziornymethod,and Mo method,respectively.The results show that Ozawa model is not applicabily in the initial stage of PBIS crystallization,while Jeziorny and Mo models have good applicability to the nonisothermal crystallization process of copolyester.The copolyester exhibits two-dimensional growth during crystallization,and the rapid cooling causes complete crystallization of the copolyester in a short time.Therefore,the copolyester should be treated by a rapid cooling method in a short time during the processing.The non-isothermal crystallization activation energy of the copolyester was calculated by Kissinger method and Friedman method.The results show that the introduction of isosorbide increase the crystallization activation energy of the copolyester,resulting in a decrease of the crystallization ability of the copolyester molecular chain.Based on the results above,the manufacturing and possible application directions of PBIS copolyester were discussed.The PBIS copolyester can be blown into a film by a flat extrusion method,and the film prepared by blow molding has improved in tensile strength and gas barrier property compared with the film prepared by hot pressing.However,the elongation at break is lowered.The introduction of isosorbide improves the thermal coating properties of the copolyester film with the 45# steel plate.Therefore,the PBIS copolyester is used to bond the 45# steel plate as a hot melt adhesive.The test results of shear performance show that isosorbide improves the bonding strength of hot melt adhesive to 45# steel plate,so that the shear strength of PBIS80 bonding reached 7.9 MPa.The research results above show that PBIS copolyester has good processing properties,and it has a good application prospect in the field of film and hot melt adhesive. |
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