Chemical, Structural and Thermal Changes in PET Caused by Solvent Induced Polymer Crystallisation

The structural and thermal properties of solvent-induced poly(ethylene terephthalate) (PET) polyester have been investigated. Flat, high twist and spun yarns were treated with trichloroacetic acid-methylene chloride (TCAMC) mixed solvent for 5 min at about 25 °C. The treatment influenced the solvent- induced crystallisation in PET, and the high interacting power of TCAMC with PET was substantiated. An increase in X-ray crystallinity was observed in the treated flat yarn but the orientation was reduced. The variation in crystallinity was measured by X-ray and DSC techniques and is discussed. The melting and recrystallisation behaviour of the crystallites were indicated by DSC measurements. The treatment improved the crystallite stability and perfection. Flat yarn exhibited a distribution of the more stable crystals with higher heat of fusion than the respective spun and high twist yarns. The study shows that the crystalline structure reorganises to a more stable and uniform form as a result of the treatment. Double melting peaks were seen in the DSC of the high twist treated samples.