CELLULOSE-BASED FIBERS FROM LIQUID-CRYSTALLINE SOLUTIONS .3. PROCESSING AND MORPHOLOGY OF CELLULOSE AND CELLULOSE HEXANOATE ESTERS

Cellulose and a cellulose hexanoate ester (DS 0.69) exhibited liquid crystalline behavior in dimethylacetamide/lithium chloride and dimethylacetamide, respectively. The experimentally observed critical volume fraction (V(p)c) of cellulose was lower than that predicted by Flory's theory, whereas the experimental and theoretical values of V(p)c were within 70% of prediction for cellulose hexanoate. The V(p)c value obtained for cellulose hexanoate was lower than that previously reported for cellulose acetate butyrate with a maximum degree of butyration (CAB-3). This indicates that bulky substituents may lower V(p)c values. Fibers were spun from isotropic and anisotropic solutions of cellulose and cellulose hexanoate by a dry jet/wet spinning method. There was an increase in mechanical properties through the isotropic to anisotropic transition with moduli reaching 152 g/d (20.8 GPa) for cellulose fibers. The formation of cellulose fibers with high modulus at large extrusion rates and large takeup speeds (draw ratio) is explained with molecular organization prior to coagulation. This unexpected enhancement is attributed to the air gap that exists in the dry jet/wet spinning process. Similar improvements were not. observed for cellulose hexanoate fibers. This is explained with incomplete development of liquid crystalline structure at the solution concentrations from which the fibers were spun.