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A commercial polyethylene terephthalate fibre (PET), drawn and heat-treated, was immersed in various solvents, the solvent diluted by water or methanol at 60°C for 4 hrs at the relaxed state, and the changes of the physical properties or the internal structure were measured with regard to the swelling, density, shrinkage, birefringence, and X-ray diffractions at wide or small angles. About fifty solvents tabulated in Table 1 with their chemical formulae and solubility parameters were used for the investigation. Immersion of PET in the solvents causes swelling and shrinking, resulting in the increases of density and crystallinity, while it decreases birefringence and orientation. The relation between the solubility parameter (δ) of the solvents and the physical properties is discussed. For each relation, two maxima or minima were observed at δ=9.7 and at 12.0. The results observed are attributed to the interaction between acidic solvent and the basic groups such as carbonyl of PET or between basic solvent and the acidic group such as methylene.Effects of water or methanol dilution on the properties of PET above mentioned were investigated. The change of properties with concentration was remarkable especially in the case of aqueous phenol solution.The effects of temperature (for two hrs) and time (at 150°C) of immersion in benzyl alcohol were also investigated.

CHANGE OF INTERNAL STRUCTURE OF POLYETHYLENE TELEPHTHALATE FIBRE BY THE TREATMENT WITH SOLVENTS