Cellulose-Based Fibers from Liquid Crystalline Solutions

Abstract

Solutions of cellulose esters with different concentrations in dimethyl acetamide (DMAc) and with different types of substituents, but with nearly constant total degree of substitution and constant molecular weights, were studied in relation to their liquid crystalline solution behavior. Observations made by dynamic mechanical spectrometry and by cross-polarized optical microscopy revealed classical liquid crystalline behavior for all solutions. Critical polymer concentration levels (Vpc) were observed for all cellulose esters, and these were found to vary with substitution pattern. Vpc is highest for cellulose acetate and lowest for the cellulose acetate butyrate with maximum degree of butyration. This is opposite to expected behavior based on the classical model by Flory, which predicts an increase in Vpc with decreasing aspect ratio. Cellulose ester solutions are viscoelastic in nature.Rigid rod-like polymers are recognized for their ability to form anisotropic liquid crystalline solutions (1,2). For rod-like species, the classical Flory equation of:relates the critical volume fraction, Vp c , of the polymer in solution to the appearance of a stable anisotropic phase; where X is the aspect ratio (L/d) of the polymer; L is the contour length; and d is the average diameter of the polymer chain. Cellulose is a linear homopolymer of ^-linked 1,4-anhydroglucose units. Liquid crystalline solution behavior has been observed with many cellulose and cellulose derivatives (3). Flory is credited with first commenting on the possibility of mesophase formation in cellulosic polymers (4). The most important parameter controlling the formar tion of a liquid crystalline phase appears to be chain stiffness for cellulose 0097-6156/92/0489-0144$06.50A)