Effect of Fiber-Forming Conditions on the Microstructure of Acrylic Fiber

Results on the microheterogeneity of polyacrylonitrile filaments obtained by the wet- spinning process are presented, and the effects of fiber-forming conditions, such as type of spinning bath, spinning temperature, drawing temperature, drawing ratio, and heat- treatment conditions, on the microstructure are discussed. The microvoid content of filaments that are obtained by spinning into aqueous baths is in many cases markedly larger than the microvoid content of filaments obtained by spinning into nonaqueous baths. Reduced spinning and drawing bath temperatures are favorable to improved fiber microstructure. Drawing of filaments results in great im proyement of fiber microstructure. The temperature of heat treatment in the dry state has an important meaning for the formation of the internal microstructure. The heat treatment in the wet state markedly changed the internal microstructure of both water- swollen gel-like filaments and dried filaments. A consideration of the relation between small-angle scattering power, which is a measure of the relative content of microvoids of colloidal dimensions, and the properties of the fiber, such as specific gravity, cross-sectional aspect, degree of water retention, and dyeability, leads to a better understanding of the meaning of the internal micro structure of acrylic fiber.