Properties and phase morphology of cellulose/aromatic polysulfonamide alloy fibers regulated by the viscosity ratio of solution

Cellulose/aromatic polysulfonamide (PSA) alloy fibers with good flame retardant properties were successfully prepared by changing the viscosity ratio of cellulose and PSA solutions. To reduce the content of PSA in the alloy fibers, cellulose and PSA with different molecular weight were adopted to prepare the alloy fibers. From the results of the limiting oxygen index(LOI) and the self-extinguishing time away from the flame, it was shown that the flame retardant properties of the alloy fibers were improved as the viscosity of PSA/[BMIM]Cl solution was lowered. The contact angle and the water retention values of the alloy fibers showed that the moisture absorption was strengthened with the addition of cellulose. To verify the properties of the alloy fiber, phase morphologies were characterized by laser scanning confocal microscope (LSCM). An analogous “sheath-core” structure in the cross section of the alloy fibers was shown when the viscosity of PSA/[BMIM]Cl solution was lower enough than that of cellulose/[BMIM]Cl solution. The lower viscosity PSA component was observed to migrate to the outer layer of the fiber, while the higher viscosity cellulose remained within the inner core of the fiber during the spinning process. This behavior improved the flame retardant properties of the alloy fibers at certain weight ratios. This work provides an effective way to prepare cellulose/PSA alloy fibers with improved flame retardancy, hygroscopic behavior, and mechanical strength by the regulating the phase morphology.