Contribution of interferometry and mechanical parameters in evaluating molecular orientation for drawn polyester

Mechanical and structural parameters related to the optical properties of p olyester (PET) (woollen type) fibres drawn at room temperature have been in vestigated. The changes in the strain were evaluated to obtain the molecula r orientation factors < P-2(cos theta)> and < P-4(cos theta)>. From the opt ical orientation, the values of f(2)(theta), f(4)(theta) and f(6)(theta) or ientation parameters were calculated. The structure and properties of orien ted PET have been studied in the light of the rubber elasticity theory. The dielectric constant, magnetic susceptibility, number N' of chains between crosslinks per unit volume, optical configuration parameter and the segment anisotropy, were among the calculated parameters. The results of the exten sion were used to calculate the shrinkage factor. Relationships between the calculated parameters and the draw ratios, together with micro-interferogr ams, are given for illustration. The present study throws light on how the applied stress changes the molecular orientation factors and the structural parameters. (C) 1999 Society of Chemical Industry.