Study On Characterization And Content Control Of Oligomers In Poly (ethylene Terephthalate)

Poly(ethylene terephthalate) owns excellent properties and is widely used in textile as well as bottle, package material, film, engineer plastics and so on. Recent years, together with the development of super high speed spinning and bi-oriented film producing, the requests for the PET properties become more and more strictly. Oligomers, which are byproducts during PET polymerization and decomposition, contain polymerization degree from 2 to 10. Their negative influence on PET spinning, film producing and dying properties attracts the attention of PET manufactures and research centers.In this thesis, supersonic extraction was used as the qualitative analysis method for quick estimate the oligomer content of polyester, soxhlet extraction was adopted as the quantitative analysis method for oligomer content. Based on the selecting of extraction technology and confirming of extraction time, the oligomers were completely separated and the content were calculated, TLC and chromatographic column were used to separate the oligomes, NMR and TG were used to analysis the structure and thermal properties of the oligomers. Results show that the extracted oligomers were composed by liner oligomer and circle oligomer.PTA route was adopted in PET polymerization, methods for reducing oligomer content were tested through adjustment of technical reference of polymerization. Orthogonal test was carried out to analyze the influence of time, temperature, catalyst and stabilizer to oligomer content. The results show that based on a reasonable polymerization degree a moderate polymerization environment would benefit for low oligomer content in polyester.Crystallization property was analyzed thermodynamically and kinetically. the results show that oligomers have influence on both the formation of nuclei and the growth of crystallites of PET matrix. Film and spinning were tested on PET with different oligomer contents, the results show that oligomer would cause high film rupture rate and low film property in film drawing and bad spinning ability in spinning.The influence of melt transportation to oligomers was studied. The oligomer contents in different melt temperature and melt keeping time were compared. It shows that the increasing of oligomers in melt transportation was cause by thermal degradation, thermal oxidative degradation and mechanical degradation.According to the needs of fast removing oligomers from roller of BOPET, different solvents were test. Tetrahydrofuran (THF), with its excellent volatility, was proved to be a proper solvent for fast dissolve oligomers on roller surface in production.