RHEOLOGY AND GELATION OF CELLULOSE AMMONIA/AMMONIUM THIOCYANATE SOLUTIONS/

Liquid crystalline solutions of cellulose in an ammonia/ammonium thioc yanate solvent will form thermoreversible gels at temperatures below 3 0 degrees C. These gels are of interest both for processing the cellul ose/ammonia/ammonium thiocyanate system and because they have an unusu al structure, containing neither crystalline nor covalently bonded cro sslinks. Although these gels contain neither crystalline nor covalentl y bonded crosslinks, the dynamic rheological behavior of the system at the gel point was found to be the same as for gels with covalent or c rystalline crosslinks with a loss tangent, tan delta, independent of f requency. The kinetics of the gelation process was monitored via dynam ic elastic modulus, G'. All samples revealed an exponential increase i n G' with time during gelation, very different from that observed in c ovalently bonded or crystalline crosslinked systems. Measurements of t he loss tangent enabled precise determination of the gelation time for these systems as a function of cellulose concentration and temperatur e. We found the gel time to be inversely related to cellulose concentr ation and directly related to temperature. The strong dependence of ge l time on these parameters offers a windows of spinnability that can b e tailored for processing high modulus cellulose fibers. (C) 1996 John Wiley & Sons, Inc.