Preparation And Solid State Polycondensation Of Regenerated Polyethylene Terephthalate-1,4-cyclohexanedimethanol Copolyester

Due to the increasing accumulation of waste polyester textiles in China,which has brought great pressure to the environment and resources,how to strengthen the recycling of waste polyester textiles has become a hot topic in the polyester industry.The ethylene glycol alcoholysis methanol transesterification technology uses ethylene glycol to alcoholize waste textiles to obtain ethylene terephthalate（BHET）,which is then transesterified with methanol to prepare dimethyl terephthalate（DMT）.DMT is easier to purify compared to BHET,and can be used to prepare high-purity regenerated DMT for the synthesis and development of regenerated high-value products.Although there have been many reports on regenerated PET at home and abroad,the development of high-quality regenerated polyester based on waste textiles is still an extremely complex and significant technical challenge.Currently,there is little development of high value-added regenerated polyester fibers and new regenerated polyester materials for engineering purposes,and there is an urgent need to develop a series of high-value regenerated polyester products based on high-purity regenerated monomers.Polyethylene terephthalate 1,4-cyclohexanedimethanol copolyester（PETG）is prepared by introducing the third monomer 1,4-cyclohexanedimethanol（CHDM）into conventional PET polyester.It can improve related properties by regulating the content of CHDM in the copolyester.Its products have high transparency and good impact resistance,and can be widely used in fields such as food packaging,daily necessities,cosmetic containers,photochemistry,and medical devices.Therefore,based on the current situation of the lack of new product development in regenerated polyester,this article proposes a research idea of synthesizing regenerated PETG copolyesters using high-purity regenerated DMT,optimizes the synthesis process of the copolyesters,and conducts a solid phase viscosity increase study on the synthesized regenerated PETG copolyesters,exploring the process conditions for their solid phase polycondensation,providing some reference for the recovery and high value reuse of waste polyester textiles.Firstly,primary PETG copolyesters were synthesized using primary PTA and DMT as raw materials through PTA and DMT routes,respectively.Intrinsic viscosity,differential scanning calorimetry（DSC）,thermogravimetric analysis（TG）,and nuclear magnetic resonance analysis were used to test them.The results showed that with the increase of the feed ratio of CHDM,the intrinsic viscosity of PETG copolyesters with the same apparent viscosity first decreased and then increased.The glass transition temperature of PETG copolyesters increased,the melting temperature decreased,and the methylene content in the polymer increased.When the actual copolymerization ratio of CHDM exceeded 15%,the melting point of PETG disappeared,and PETG was in an amorphous state;The melting point and initial decomposition temperature of PETG copolyesters synthesized by DMT route were higher than those synthesized by PTA route at the same feed ratio of CHDM;The actual copolymerization ratio in PETG copolyesters is higher than that in CHDM feed ratio;The characteristic peak positions of PETG copolyester are the same as the three main crystal planes of crystalline PET,and it is a triclinic system.With the increase of CHDM content,the crystallinity of PETG copolyester decreases.Secondly,the recycled DMT raw material prepared from the foam material was analyzed by gas chromatography and tested by nuclear magnetic resonance hydrogen spectrum,and the recycled PETG copolyester was prepared from the recycled DMT by melt polycondensation,and its intrinsic viscosity,DSC,TG,XRD,FT-IR,¹H-NMR and other tests were carried out.The results showed that the purity of the regenerated DMT raw material was 99.8%;The actual copolymerization ratio of CHDM in the prepared regenerated PETG copolyester is higher than the feed ratio;The glass transition temperature and melting temperature of regenerated PETG copolyesters have the same trend as that of primary copolyesters,but are lower than that of primary PETG copolyesters The infrared spectrum peak patterns and characteristic absorption peaks of regenerated and native PETG copolyesters are basically the same,and there is no significant difference in their chemical structures,and they have similar basic structural characteristics.Finally,on the basis of the above-mentioned synthesis process of PETG copolyesters,a solid state polycondensation process was carried out to synthesize PETG copolyesters,and a high viscosity copolyester was prepared.The effects of reaction time and temperature on the intrinsic viscosity,sample color,carboxyl end group content,crystallization,and other properties were discussed.The results showed that at the same reaction temperature and time,the intrinsic viscosity and carboxyl end group content of the samples prepared by PTA route were higher than those prepared by DMT route;The intrinsic viscosity of regenerated PETG₁₀ increases with the increase of reaction time and temperature,and the growth rate becomes slower.The intrinsic viscosity is linearly proportional to the square root of time;The melting point of regenerated PETG₁₀ increases with increasing reaction temperature and time;The crystallinity of regenerated PETG₁₀ increases after viscosity increasing;With the increase of reaction temperature or reaction time,the carboxyl end group content of regenerated PETG₁₀ samples decreased;As the reaction temperature increases,the b value of regenerated PETG₁₀ increases,and the surface of the chip begins to appear a yellowing phenomenon.In this paper,recycled PETG copolyesters with different CHDM copolymerization ratios were synthesized by melt polycondensation using high-purity recycled DMT as the main raw material.The melting point of PETG copolyesters with 10%CHDM feed ratio was about 215℃,and the melting point of PETG copolyesters with more than 15%copolymerization ratio was zero.The intrinsic viscosity of recycled PETG copolyesters was improved by solid state polycondensation,which enriched the products and application fields of recycled polyester.