| Abstract: | Liquid crystalline solutions of cellulose in an ammonia/ammonium thiocyanate solvent will form thermoreversible gels at temperatures below 30°C. These gels are of interest both for processing the cellulose/ammonia/ammonium thiocyanate system and because they have an unusual structure, containing neither crystalline nor covalently bonded crosslinks. Although these gels contain neither crystalline nor covalently 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 crystalline crosslinks with a loss tangent, tan δ, independent of frequency. The kinetics of the gelation process was monitored via dynamic elastic modulus, G′. All samples revealed an exponential increase in G′ with time during gelation, very different from that observed in covalently bonded or crystalline crosslinked systems. Measurements of the loss tangent enabled precise determination of the gelation time for these systems as a function of cellulose concentration and temperature. We found the gel time to be inversely related to cellulose concentration and directly related to temperature. The strong dependence of gel time on these parameters offers a windows of spinnability that can be tailored for processing high modulus cellulose fibers. © 1996 John Wiley & Sons, Inc. |
