Synthesis Residue
Low molecular weight ring structures formed during polyester synthesis migrate out of synthetic fibres under high temperature dyeing conditions. These small circular molecules, predominantly trimeric cyclic PET oligomers, constitute approximately one to three percent of polyalkylene terephthalate polymer mass. They possess higher melting points than the bulk polymer matrix and lack reactive functional groups for dye bonding.
The physical classification applies exclusively to closed-ring ester molecules below one thousand Daltons, excluding linear oligomeric chains or degraded polymer fragments.
Deposition Mechanism
Aqueous dye liquors heated above one hundred and twenty degrees Celsius dissolve these low molecular weight rings out of the fibre core. As dye baths cool below boiling temperature, cyclic PET oligomers precipitate into microscopic crystalline flakes on yarn surfaces and machinery walls. These white residues form dust deposits that abrade spinning guides and cause yarn tension spikes during subsequent rewinding.
Process Interference
Filtration systems in package dyeing machinery trap floating oligomer crystals, creating flow resistance across dense yarn packages. Crystalline cyclic PET oligomers cause uneven friction during high-speed knitting, leading to needle wear and thread breaks. High oligomer concentration alters yarn friction coefficients, which compromises stitch uniformity in light knit fabrics.
Mill quality teams monitor oligomer content using solvent extraction methods to avoid expensive machine downtime.
Elimination Method
Alkaline reduction clears surface deposits of cyclic PET oligomers.
