The solubility of cellulose in liquid ammonia/ammonium thiocyanate solutions: Thermoreversible gelation and a preliminary report on fiber formation

Abstract

AbstractThe melting temperatures of thermoreversible gels formed from solutions of cellulose in liquid ammonia/ammonium thiocyanate mixtures were measured over a volume fraction range of .01–.004. Three samples of cellulose with Mw ranging from 1 × 105 to 1.64 × 105 were used. The findings show that the structural makeup of the gels is strongly reflected in their time‐dependent behavior. The reciprocal of their melting temperature is a nearly linear function of the logarithm of the cellulose concentration. The relation between the logarithm of Mw and the reciprocal temperature of gel melting was also nearly linear. Exothermic heats of reaction ranging from 150 to 460 kcal/mol were calculated from the Ferry‐Eldridge relationship (∂ ln C/∂) = ΔHx/R for the formation of cross‐links, assuming that they result from a binary association of chains. It is inferred that the cross‐linking loci in the gel were crystallites that consisted of glucose units. In addition, an initial study is reported of the fiber‐forming potential of the liquid ammonia/ammonium thiocyanate system. Rudimentary fiber extrusion from a modified syringe was readily demonstrated. Operable coagulation systems involved proton‐donating agents as well as methanol. Tenacities of these unstretched, as spun fibers, ranged as high as 0.89 g/d.