Research Of Chemical Structure Design And Fiber Forming Of Bio-based Degradable Copolyester

Polyester is one of the most widely used plastic due to its excellent mechanical and thermal properties.Poly(diethyl terephthalate)(PET),as the most industrially used polyester,has excellent performance but also has some potential defects.For example,the monomer sources of PET are based on petroleum which is non-renewable resource.From the perspective of sustainable development,the extensive use of non-renewable petroleum resources will result in the depletion of petroleum resource.Meanwhile,PET is un-degradable in the environment,and it can cause environment pollution problem due to rapid consumption.In response to the un-degradable issue,researchers have adopted some various solutions such as recycling and introducing degradable agents.The recycling process of polyester always added organic distillates,which would complicate the process.And there are some controversies about the use of degradable agents.Therefore,to solve the above problems,introducing bio-based components into the macromolecular chain of PET and synthesizing bio-based copolyester are effective ways.At present,aliphatic polyesters are the most uesd bio-based polyester,but they still have the problems such as low mechanical strength and low heat resistance which hinder their large-scale applications.So introducing bio-based rigid component and controling the addition ratio are the ways to achieve the purose of regulating the performance of polyester and obtain performance-controlled bio-based copolyester.Introducing the bio-based diol isosorbide with rigid structure into the PET macromolecular chain is an effective way to obtain high-performance bio-based copolyester.A series of poly(ethylene-co-isosorbide terephthalate)(PEIT)copolyesters with different addition amounts of isosorbide were successfully polymerized by direct esterification-polycondensation method.The sequence structure calculated by carbon spectrum showed that with the addition of isosorbide,n _ET(ethylene terephthalate)gradually decreased,and n _IT(isosorbide terephthalate)gradually increased.At the same time,the thermal performance results showed that the addition of isosorbide significantly increased the glass transition temperature of the copolyester.When the addition of isosorbide reached 80%,the T_gwas as high as 124?.However,the introduction of rigid component would destroy the regularity of the main chain,resulting in the decrease of crystallinity and melting point of the copolyester.The addition of isosorbide also improved the mechanical properties of the copolyester fiber.The breaking strength of copolyester fiber with 5%isosorbide added was 45%higher than that of PET.This is the result of high fiber orientation and high crystallinity.However,the degradation of copolyesters weren't improved.Secondly,in order to improve the degradability of PET,we introduced 2-hydroxypropinic acid segments with high flexibility and good degradability into the macromolecular chain of PET.NMR and FTIR proved the 2-hydroxypropinic acid segment was successfully polymerized into the PET molecular chain.The thermal performance test shows that the introduction of the flexible segment slightly reduce the glass transition temperature and melt point of the poly(ethylene terephthalate)-co-poly(lactic acid)(PET-LAs),but broaden the process window.Spinnability experiment shows that high-content PET-LAs copolyesters still have good spinnability.The breaking strength of 10%PET-LAs copolyester fiber is similar to that of PET,but the elongation at break is twice as high.Degradation experiments show that PET-LAs copolyester has a good degradation prospect.Finally,in order to obtain bio-based copolyesters with excellent mechanical properties and adjustable thermal properties,we macro-regulated the ratio of flexible and rigid components in the polyester segment,and synthesized poly(ethylene-co-isosorbide terephthalate))-co-poly(lactic acid)(PETIL).NMR and FTIR results proved the successfully synthesis of the PEITL copolyester.DSC test results show that the controllable thermal properties of copolyester can be achieved by adjusting the addition ratio of rigid and flexible segments.When the addition of flexible segment is fixed,the glass transition temperature of PEITL can up to 84?with only 20%rigid component,which makes it promising to be used in the field of high heat-resistant.The simultaneous introduction of flexible and rigid chains will destroy the regular structure of the macromolecular chain to a certain extent,and reduce the crystallization ability of the copolyester,which leads to the decrease in the spinnability of the copolyester.