Drawing behavior and mechanical properties of highly oriented polycarbonate fibers

Abstract

AbstractFibers from bisphenol‐A polycarbonate are typical representatives of the less crystallizing synthetic fibers. Because of the high glass transition temperature, textiles produced from these fibers have outstanding laundry‐resistance and noncreasing properties. Polycarbonate fibers can be produced both by the dry or wet‐spin and by the melt‐spin process. The stretching of the fibers is carried out in accordance with the proposed textile characteristics below or above the glass transition temperature or by a special swelling–drawing process, in the course of which fibers of particularly high tenacity and elastic modulus can be obtained. The fibers produced by the latter process were investigated by a number of physical measurements of their morphological structure (density, birefringence, X‐ray wide‐ and small‐angle scattering, differential calorimetry, thermo‐mechanical analysis). These measured values of density, birefringence, and heat of fusion show that these fibers have a higher degree of crystallinity than the fibers produced by a melt or dry spinning process. Whereas with dry‐spun fibers an increase in tenacity can be obtained by raising the molecular orientation up to a limited tenacity value, it is possible with fibers produced by the swelling‐drawing process to virtually double the tenacity due to the higher crystallinity and improved crystal structure (creation of a large number of physical linkages). By means of X‐ray small‐angle scattering on annealed swollen‐drawn polycarbonate fibers, we were able to detect, for the first time, a marked two‐phase structure consisting of crystalline and noncrystalline regions with a long‐period of about 120 Å. With other crystalline polymers, a period of this kind has been known for many years.