| Polyethylene terephthalate(PET)is the most produced and widely used polyester product at present.Due to its stable structure and difficulty in natural degradation,a large amount of PET waste has caused a huge pressure on petroleum resources and ecological environment,and how to enhance the recycling of waste PET has become a hot spot of concern in the world.The chemical regeneration of polyester is the focus of research and application,its principle is based on the equilibrium reaction characteristics of polyester synthesis,the waste PET and depolymerization agent reaction to generate monomers or oligomers,and then the depolymerization products will be recycled to re-prepare the regeneration of polyester method,in which ethylene glycol as an alcoholic solvent for PET alcoholysis reaction has mild conditions,simple process,good safety,suitable for industrial promotion,etc.Advantages,but the glycolysis method also has a slow rate of alcoholysis,regenerated polyester products and the quality of virgin products vary greatly and other problems.In addition,there are basically no new products of regenerated polyester.Therefore,based on the advantages and shortcomings of glycolysis and the lack of new product development of regenerated polyester,this paper proposes the R&D idea of combined glycolysis of waste PET(EG)/diethylene glycol(DEG)and direct repolymerization to produce regenerated low melting point co-polyester,explore the combined alcoholysis conditions,optimize the synthesis process of regenerated co-polyester,study the performance of regenerated low melting point polyester,and provide reference for the recycling of waste PET.The study will provide a reference for the high value recycling of waste PET.Firstly,based on the EG alcoholysis technology of PET,a combined EG/DEG alcoholysis process was proposed,focusing on the effects of parameters such as EG/DEG ratio,catalyst zinc acetate content,reaction time,reaction temperature and total diol to PET mass ratio on the alcoholysis efficiency of waste PET,and the alcoholysis rate and the main product bis(2-hydroxyethyl)terephthalate(BHET)were taken as the indexes for investigation.The results showed that the alcoholysis conditions were efficient at the ratio of DEG to PET of 10 mol%,the feeding mass ratio of total diol to PET of 1:2,the mass fraction of zinc acetate of 0.1%,the reaction temperature of 200°C and the reaction time of 1?1.5 h,and the alcoholysis rate of PET reached 100%and the yield of BHET could reach 75%under this condition.The reaction time of combined alcoholysis with the addition of DEG was shorter than that of EG only,and the amount of zinc acetate added as catalyst was reduced.Secondly,the modulation of the activity of the stabilizer TPP on the zinc acetate activity of the alcoholysis catalyst was investigated.Firstly,the inhibitory effect of TPP on the catalytic activity of Zn(Ac)2 was investigated by simulating the BHET polycondensation reaction using DSC and TG test methods,which showed that TPP could better regulate the catalytic activity of Zn(Ac)2;then the addition of TPP was optimized in the reactor based on the direct repolymerization process of the EG alcoholysis product of waste PET.The results showed that the TPP/Zn(Ac)2 ratio of0.5:1 resulted in a suitable polycondensation reaction time and the end carboxyl content,b-value and color of the product were close to that of virgin PET.Finally,two low melting point regenerated polyesters,PEDT(co-polyester with DEG)and PEDTI(co-polyester with DEG and IPA(isophthalic acid)),were synthesized based on the above combined EG/DEG alcoholysis process and direct repolymerization of regenerated PET alcoholysis products with the addition of TPP,and the effects of the addition of DEG and IPA on the synthesis process and product properties were investigated.The effects of DEG and IPA addition on the synthesis process and product performance were investigated.The results showed that:(i)the PEDT produced by adding DEG has similar characteristic viscosity,end-carboxyl content and b-value as the recycled PET,while the DEG content is slightly larger than the actual addition;the thermal stability,glass transition temperature(Tg)and melting point(Tm)of PEDT decreased with the increase of DEG addition;(ii)the PEDTI co-polyester produced by adding both DEG and IPA has similar b-value and end-carboxyl content.value,end carboxyl content and other indicators are similar to those of recycled PEDT,and the characteristic viscosity gradually decreases with the increase of IPA addition;the Tm of PEDTI decreases substantially with the increase of IPA content,and the Tg and thermal stability slightly decrease;the diffraction peak position of PEDTI in XRD test is similar to that of PET,but its crystallinity gradually decreases with the increase of IPA addition.In this paper,by studying the combined EG/DEG alcoholysis process and the direct repolymerization process of regenerated PET alcoholysis products with the addition of stabilizer TPP,PEDT copolyester containing 10%DEG was synthesized,with a melting point of about 240?,which can be used as a masterbatch carrier or an atmospheric pressure dyeable polyester;PEDTI copolyester containing 6%DEG and5?20%IPA was synthesized,with a melting point of 180??220?.In the future,the melting point of co-polyester can be further reduced by increasing the addition of IPA to achieve a wider melting point range of regenerated low melting point co-polyester preparation,enriching the products and applications of regenerated polyester. |
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