SYNOPSISUni-and biaxial stretching of various polymer films has been studied under well-defined conditions of temperature and elongational strain rate in order to determine the relationship between stress and recoverable strain for both modes of deformation. The extent of molecular orientation has been investigated with the aid of stress optical methods: In amorphous polymers birefringence was found to be directly proportional to the frozen-in internal entropic stress irrespective of the latter's relationship with recoverable strain. In a first approximation, molecular orientation can be understood in terms of deformation of a rubberlike network with temporary junction points. The total internal stress in an oriented glassy polymer may be significantly larger than the entropic stress. Experimental methods based on retractive force measurements, able to distinguish between internal stresses of different nature, are described.In uni-and biaxially drawn films of polyethylene terephtalate preferred planar orientation of ( 1 00) planes has been studied by means of X-ray diffraction and measurement of the three principal refractive indices. The intrinsic birefringence of completely oriented PET films has been estimated from these measurements with the aid of the Lorentz-Lorenz theory. The effect of draw ratio and temperature on the rate of crystallization and its consequences (increase of stretching stress and density, decrease of shrinkage) has also been studied.Finally, the effect of molecular orientation on various mechanical properties: modulus, tensile strength, impact resistance, creep compliance, is discussed for both amorphous and semicrystalline polymers, with special emphasis on the predominant influence of amorphous phase orientation.

SynopsisThe structure development of a PET f i l m is studied during drawings under constant load. The evolution of crystallinity, amorphous orientation, and axial and planar birefringence is described along a deformation path. The influence of the stretching force and stretching temperature is also analysed.

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SynopsisThe deformation of amorphous and isotropic polyester film is studied using a device which simulates on a laboratory scale the continuous stretching between rolls by a drawing under constant load. The kinetics of deformation is compared to the kinetics involved in a conventional drawing at constant speed of elongation. The results of drawing under constant load are applied to the industrial case of stretching between rolls.

Polypropylene ionomers have been prepared by sulfonation of copolymers of propene and 7 methyl, 1‐6 octadiene, followed by neutralization to cesium salts. Both WAXS and SAXS were used to study the morphology of the samples, while their thermal properties were studied by DSC and their mechanical properties by DMTA. The sulfonation process is shown to cause a further drop in crystallinity in addition to the effect of comonomer incorporation. Ion clustering is observed when the extent of sulfonation is high enough, the limit being dependent on the copolymer composition. The ion pairs which are not incorporated into the cluster cause a small‐angle upturn in the WAXS pattern. The mechanical properties are strongly affected by the drop in crystallinity, but may be partly recovered due to ion clustering. No disruption of the ion clusters is observed before thermal decomposition of the polymer.