Preparation Of Polyester Elastomer From Waste Pet And Its Properties

Polyethylene glycol terephthalate(PET)is one of the most commonly used plastics,which is poorly biodegradable,Thus,recycling PET waste is necessary to reduce its impact on the environment.The common physical method of recycling PET degrades its quality.Chemical recycling of PET can obtain high-quality recycled PET or other high value-added products.Chemical recycling of PET can effectively reduce the dependence on fossil resources and the burden on the environment,in line with the national requirements for the "double carbon strategy".Bio-based polyester elastomer is an original elastomer material in China,which has the same excellent properties as traditional synthetic elastomers.In this paper,polyester elastomer was regenerated from PET waste by alcoholysis polymerisation method.Poly(ethylene glycol/1,4-butanediol/1,4-butenediol/butanediol/terephthalic acid)copolyester(PEBBSP)was synthesized from bio-based ethylene glycol,1,4-butanediol,succinic acid,petroleum-based 1,4-butenediol and waste PET by two-step or one-pot route,which realised the upcycling of waste PET.The main work of this paper is as follows:(1)In the first part of this work(Chapter 2),the alcoholysis of PET with ethylene glycol was investigated.The catalyst for PET alcoholysis was screened.It was found that tetrabutyl titanate as a catalyst not only had high alcoholysis efficiency but also did not affect the synthesis of polyester elastomer.In order to synthesize amorphous polyester elastomer and control the alcohol/acid ratio,the mixed alcohol of ethylene glycol and 1,4-butanediol was used as the alcoholysis agent and the alcoholysis conditions were investigated.The final conditions for efficient alcoholysis of waste PET are as follows: 0.2 wt% tetrabutyl titanate as catalyst,n(BDO)/n(EG)/n(PET)=3/2/1,reaction temperature 196 ℃,reaction time 3 h.(2)In the second part of this paper(Chapter 3),PEBBSP-PET copolyester was obtained by adding the remaining monomers to the alcoholysis solution.In order to further simplify the process,a second process was developed in which waste PET was used as raw material to react directly with other monomers to obtain PEBBSP-PET copolyester by one-pot route.The analysis of the synthesized product(GPC,1H-NMR,DSC,WAXD and TGA,etc.)shows that: with the increase of the PTA unit content,the crystallinity of the two PET-based PEBBSP copolyesters first decreased obviously and then increased slowly,the thermal stability increased gradually and the initial decomposition temperature of all samples was higher than330 ℃.For comparison,PEBBSP-PTA copolyesters were synthesised using terephthalic acid with other monomers.It was found that the two PET-based PEBBSP copolyesters had similar properties and higher molecular weight than PEBBSP-PTA copolyesters.(3)In the third part of this work(Chapter 4),two types of wastePET-based PEBBSP copolyesters and one type of monomer-based PEBBSP copolyesters were blended with fumed silica A200 and vulcanised to prepare PEBBSP/A200 nanocomposites.The samples were characterised by RPA,DSC,HRTEM,tensile test and DMA.The results showed that the vulcanisation properties of PEBBSP/A200 nanocomposites increased significantly at first and then decreased slowly with the increase of PTA unit content.The mechanical strength also increased,but the elongation at break decreased when the content of PTA unit exceeded 20%.Due to the successful introduction of benzene ring,the loss factor of the material at 0 ℃ can reach0.44.And since some PEBBSP/A200 nanocomposites have chemical-physical double cross-linked networks,their shape memory properties were investigated.In conclusion,PEBBSP/A200 nanocomposites prepared by one-pot method with simple process have similar properties to those prepared by monomer,and have the potential to be used as engineering elastomers,thus realising the transformation of waste into wealth.