Migration properties of commercial polyethylene terephthalate staple fiber oligomers and influencing factors thereof
Objective With the development of fine denier and high-speed spinning technology,the phenomenon of oligomers migration and powders shedding from the surface of polyethylene terephthalate(PET)fiber became more and more serious,which would greatly impact on the production efficiency,quality and workers'health during the spinning and dyeing processes.It is necessary to solve the problem by exploring the migration mechanism and the structure-activity relationships of oligomers during staple fiber processing,and thus adjust the production conditions to prevent the migration.Method Two types of commercial PET staple fibers with obvious difference in white powder shedding properties were extracted and thermal induced to obtain extractive fibers,thermally induced fibers and oligomers,respectively.The thermal induction temperature was determined on the practical process of the post-spinning process.Scanning electron microscopy,differential scanning calorimetry(DSC),ultraviolet-visible spectrophotometry and X-ray diffractomety(XRD)techniques were carried out to analyze the structural constituent,precipitate law and precipitate mechanism of the oligomers.Results The main components of the oligomers derived from these two fibers were both cyclic trimers(C3)and a small amount of PET microcrystalline polymers(PET microlite).The fibers which shed more powders(HM)detected few oligomers with high melting point should be assigned to the C4 polymers.The C3 oligomers and PET microlites were of relatively high melting temperature at 173.5 and 146.7℃,respectively,and the melting temperature for C4 was around 274.6℃.While the C3 and PET microlites for the fibers which shed less powders(LM)have low melting temperature around 171.8℃and 139.0℃,respectively.The C3 in PET staple fiber,solvent extraction substance and pyroprocess existed as A type,B type and A/B mischcrystal type,respectively.The melting temperature of A type C3 and B type C3 from HM polymers were 173.5 and 314.5℃while the A type C3 and B type C3 from HM polymers were relatively lower,at 171.8 and 312.6℃,respectively.The HM and LM fibers showed similar oligomers mass ratio as 1.37%and 1.42%.Compared with the no shedding PET fiber,the shedding powder fibers contained significantly higher amount of oligomers and the crystallinity was 57.73%(11.25%lower).Moreover,the HM fibers maintained relatively small amount of A type trimer whose melting point was 1.7℃higher,and B type trimer was about 1.9℃higher,and relatively higher amount of cyclic polymers containing diethylene glycol residues.It is found that when the two fibers were subjected to thermal induction in hot air from 140 to 200℃for 1h,the oligomers migrated from the two of fibers possesses point-like crysta at 140,160 and 180℃,and the amount of oligomers increased with the rise of temperature,on the other hand,the low powder shedding fibers migrated less oligomers.When the induction temperature reached 200℃,the oligomers migrated from the surface of these two fibers were mainly multi-sided crystal type,the amount of precipitation increased rapidly compared with that at 140-180℃,and the crystal type and quantity tended to be the same quantity.Conclusion The powders shedding phenomenon during staple fiber processing has no corresponding relationship with the mass ratio of total oligomers,however,it holds a positive relationship with the quantity of oligomers migrated on the fiber surface,and thermal induction is an important factor affecting the migration of PET staple fiber oligomers.Fibers heat treatment process in post-processing,the crystallinity of the fibers,and the mass ratio of ethylene glycol to terephthalic acid during polymerization may be the influencing factors affecting the powder shedding properties of oligomers.The temperature during fibers post-processing,cooling craft and the mass ratio of ethylene glycol in polymerization could be effective methods to prevent fibers from shedding powders.
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