Fiber spinning from the nematic melt. I. Copolyester of poly(ethylene terephthalate) and p‐oxybenzoate

Abstract

AbstractThe Tennessee Eastman copolyester of poly(ethylene terephthalate) with 60 mol % p‐oxybenzoate units was spun with various capillaries using a constant shear rate at the wall. Variables examined were the length‐to‐diameter ratio L/D of the capillary, the spin draw ratio Vf/V0, and the spinning temperature. Fibers spun at 260°C showed improved homogeneity of orientation through the cross section, better crystallite orientation, and higher initial moduli as L/D was increased. The spin draw ratio required to optimize these fiber properties decreases as L/D is increased. For example, when L/D = 49.44, the initial modulus has nearly reached its plateau value at a spin draw ratio of 10. However, in contrast to the results of Sugiyama, Lewis, White, and Fellers, we find that some spin draw is always required to optimize fiber properties. Fibers spun with a spin draw ratio of approximately unity showed very poor crystallite orientation and initial moduli. It is suggested that loss of orientation under these conditions may be due to the different velocity profiles in the spinneret and in the solidifed fiber. Fibers were also spun at five temperatures using a capillary having L/D = 49.44. Shear in the capillary is more effective in introducing orientation when the spinning temperature is 260°C or above. At spinning temperatures of 240 and 250°C, the initial modulus increases more slowly with spin draw ratio, and appears to have a lower plateau value. Acierno, La Mantia, Polizzotti, Ciferri, and Valenti spun the same polymer under conditions in which essentially all the orientation was introduced by spin draw. They used a very low extrusion velocity at the spinneret, a small L/D, and spin draw ratios up to 3000. They reported that the initial modulus increased with decreasing spinning temperature, in contrast to our results. Thus the optimum spinning conditions may depend upon whether most of the orientation is introduced by shear in the capillary, or by a high spin draw ratio.