Polyacrylonitrile (PAN) fibers of high porosity and hygroscopicity.
Part II. PAN fibers formed from thiocyanate solutions
Polimery 1997, No 9, 560
Technical conditions were established to spin high-porosity high-hygroscopicity PAN fibers in coagulating baths of industrial thiocyanate solutions containing a (93:5.3:1.7 w/w) acrylonitrile/methylacrylate/itaconic acid terpolymer. The porous structure of the fibers and the irsorptive and mechanical properties were studied in relation to the as-spun draw ratio, temperature, and coagulating bath composition. As compared with DMF as solvent, the thiocyanate solution allowed to prepare fibers with differentiated sheath-core structures and much narrower parameter variability. As the draw ratio was increased, the mechanical properties of the fibers improved and the total pore volume rose to provide good sorptive properties and high water retention (Figs. 1—3). The porous fiber structure was affected by the coagulating bath temperature and composition: total pore volume, water retention and moisture absorption were all higher at elevated bath temperatures (Figs. 4—6); strong (i.e., low-thiocyanate) or mild baths, the latter atelevated temperatures only, favored the formation of the sheath-core structure. As the thiocyanate was raised to 12-13% in the bath, water retention and moisture absorption rose and so did tenacity though slightly (Figs. 7, 8). Optimum as-spun draw ratio, temperature and coagulating bath temperature allowed to produce fibers with the sheath-corestructure, internal surface area 56—85 m2/g and total pore volume 0.53—0.65cm3/g. Under the 100% R.H. conditions, these fibers sorbed 25 times as much moisture and retained about 8 times as much water as did conventional PAN textile fibers; fiber tenacity was slightly lower (Table 1). The assumption made in Part I, concerning the formation of PAN fibers in DMF as solvent endowed with differentiated sheath-corestructures, high porosity and high hygroscopicity, was also found to hold true for the thiocyanate solutions.