Method for the rapid crystallization of polyesters and copolyesters in - line by stretching and flow induced crystallization

摘要

The present invention relates to a process for introducing strain-induced crystallization to polyesters. Specifically, amorphous polymer from the melt phase reactor is first extruded through a traditional strand die. However, instead of going directly into a pelletizer/cutter, it is stretched uniaxially at a temperature only slightly higher than Tg. The chain alignment resulting from stretching makes crystallization occur at a considerably higher rate than with traditional thermal crystallization. After this stretching process, the strand is annealed and fed to the pelletizer and chopped. The process of the present invention is advantageous for crystallizing polymers having slow rate of thermal crystallization half time from the glass. Optically clear polymers having at least about 15% crystallinity and a single melting point endotherm are produced.