Processing and properties of melt-spun and drawn 2-methyl-l,3-propanediol substituted poly(ethylene terephthalate)

The preparation of fibers from copolymers of PET in which up to 25 mol% 2-methyI-l,3-propanediol (referred to as MPDiol) was substituted for ethylene glycol were studied. The purpose of this study was to determine if the copolymers provided any specific advantages over PET homopolymer in either processing or properties. Filaments Were melt spun from resins containing 0, 4, 7, 1.0 and 25 mol% MPDiol over a range of spinning conditions, including spinning at speeds up to about 5500 m/min and mass throughput between about 1.15 and 8.25 g/min/hole. Some filaments that were melt spun at low speeds were subjected to hot drawing. Characterization of the filaments was carried out by measurement of filament diameter, birefringence, DSC crystallinity, wide angle X-ray diffraction patterns, boiling water shrinkage, tenacity and elongation to break. The results showed that the 25% MPDiol substituted resin did not crystallize in thespinline at any spinning speed investigated. The other resins did crystallize in the spin line at high spinning speeds, but, compared to the PET homopolymer, increasing substitution of MPDiol reduced the rate at which crystallinity of the melt spun filaments increased with spinning speed. Increasing MPDiol also reduced the ultimate crystallinity that could be achieved by high speed spinning (about 33% for PET homopolymer and 22% for the10 mol% MPDiol substituted resin). The rate of development of molecular orientation, as measured by birefringence, also decreased somewhat with increasing MPDiol content.Shrinkage in boiling water decreased at high spinning speeds as the amount of crystallinity developed increased; however, the shrinkage decreased more slowly with increase in spinning speed as MPDiol content increased due to the slower development of crystallinity. Tenacity also decreased slightly at any given spinning speed as MPDiolcontent increased, but there was no significant effect on the elongation-to-break. A major advantage of adding MPDiol is that increasing substitution of MPDioI up to 7 mol%increased the maximum take-up velocity that could be achieved at a given mass throughput. This could potentially increase the productivity of melt spun yams via the use of higher spinning speeds. Drawn samples containing 10 mol% MPDiol were readily processed into highly oriented fibers having slightly less birefringence, crystallinity and density than similarly processed PET homopolymer.