Properties of PAN Fibers Solution Spun into a Chilled Coagulation Bath at High Solvent Compositions
In this work, multifilament, continuous polyacrylonitrile (PAN) fiber tow was solution spun mimicking industrial processing at the small pilot scale (0.5 k tow), while carefully altering the composition of the coagulation bath, in order to determine the effect on the resulting fiber shape, density, orientation, and tensile properties at varying points in the spinning process. Novel here are the abnormally high coagulation bath solvent compositions investigated, which surpass those often reported in the literature. In addition, the coagulation bath was maintained at a slightly chilled temperature, contrary to reported methods to produce round fibers. Further, by altering the composition of the bath in a step-wise fashion during a single spinning run, variations in all other process parameters were minimized. We found that with increasing solvent composition in the coagulation bath, the fibers not only became round in cross section, but also became smaller in diameter, which persisted down the spin line. With this decrease in diameter, all else equal, came an accompanying increase in apparent fiber density via a reduction in microvoid content. In addition, molecular orientation and tensile properties also increased. Therefore, it was found that inadequate understanding of the coagulation bath effects, and spinning at low coagulation bath solvent compositions, can hinder the ability of the fiber to reach optimum properties.
High-Performance Acrylic Fibers
Abstract Acrylic fibers are among the most important man-made fibers. They rank third after polyesters and nylons [1]. The first commercially available acrylic fiber was orlon, introduced by DuPont in 1943. Soon thereafter, other companies introduced new acrylic fibers, such as Acrilan, Dralon, and so forth. During the 1950s, the acrylic fiber industry experienced a rapid growth, with 18 companies introducing acrylic fiber products into the market. In 1970 21% of the synthetic fibers produced were acrylic fiber, whereas this figure fell to about 14% in 1992. In the corresponding period, the actual production of acrylic fibers increased from 809,890 tons to 2,410,520 tons. However, the overall production of synthetic fibers increased from 4.809 million tons to 17.218 million tons (Fig. 1). Interestingly, in 1970 only 12% of the acrylic fibers were produced in Third World countries (countries other than the United States, Japan, and western Europe) whereas this figure increased to 46% in 1989 and was expect...
Effect of comonomer composition on the properties of polyacrylonitrile precursor and resulting carbon fiber
Since the itaconic acid (IA) comonomer is the potential initiator of cyclization, therefore the introduction of IA comonomer into polyacrylonitrile (PAN) precursor can depress the onset of exotherm (or cyclized temperature) and peak temperature. However, the more the IA content, the lower the conversion of acrylonitrile (AN) in the polymerization reaction. Although 2-ethylhexyl acrylate (2-EHA) comonomer in PAN precursor may prevent the cyclization propagation of nitrile groups during oxidation, PAN precursor with a few percent of 2-EHA comonomer has a more preferred orientation. As the content of 2-EHA comonomer further increases, the orientation of the resulting carbon fiber decreases correspondingly. 
 
In this study, PAN precursor, with the composition of 98 mol % AN, 1.5 mol % 2-EHA, and 0.5 mol % IA, and its resulting carbon fiber have the best mechanical properties. From the results, it is shown that there is a good relationship between the tenacity and modulus of PAN precursor and those of its resulting carbon fiber.