X-ray and optical study of the morphology and the orientation processes in polyethylentereftalat (PET)

Polyethyleneterephtalat (PET) is a raw material for production of synthetic fibres of ''yambolene'' type. Owing to its low crystallization rate, a wide spectrum of morphological structures with various properties can be obtained in it by appropriate mechanical and heat treatment. In order to study the variations in the crystal grain orientation, average grain size and the degree of crystallinity (Xc) depending on the temperature of annealing (Ta) X-ray analysis is applied. Morphological microscope analysis of thin cuts in polarized light is also carried out. Optical scattering of laser beams gives information about the type and radius of the spherolite structures. It is found that for the stretched samples Xc depends linearly on Ta. For the nonstretched samples Xc is practically constant in the interval 140 to 2200C, and after that rapidly increases. This fact is explained by a transition in the amorphous chains. The employed methods are easily applicable in a industrial laboratory equipped with X-ray facilities. They allow for an express and precise quality control of the production by measuring the three parameters - Xc, degree of orientation and average size of the crystal grains. Express information about the type and size of the above molecular structures is obtained by the use of the gas laser. (N.K.)