Investigations on Crystalline Modification of Nylon 6 (γ-form)

III. Optical Study on Deformation Mechanism of Nylon 6 Spherulites

Abstract

It has been ascertained by X-ray measurement that the positive spherulite which is obserbed in undrawn gut of Nylon 6 spun from the melt through a wide nozzle has a crystalline modification (γ-form) different from the structure (α or β-form) well established by Bunn.
When subjected to drawing, its form changes from a sphere to an ellipsoid and, in the extreme, to a cylinder.
It is revealed that the birefringence measured at the circular section of an elongated spherulite has a larger positive value with respect to the direction of radius than that found for the unelongated one.
The morphological change accompanies the transformation of crystalline form from γ to α(or β), resulting in parallel alignment of the molecular chains along direction of cylindrical axis of the elongated spherulite.
Based on the general concept about polymer spherulites in which molecular chains are oriented tangentially, the above phenomenon was analysed with the measured values of refractive indices along three directions of the oriented films having the two different kinds of crystalline structures (γ and α(or β) form). From the determination of the molecular chain (unit cell) arrangement in the spherulites before and after deformation, it has been concluded that the deformation mechanism of the spherulites by stretching is essentially consistent with that assumed before by us for the film made from the formic acid solution and also for the single crystal obtained from the glycerine solution, both having the same crystalline structure as that in the spherulites.