Some properties of ethyl cellulose films

Abstract An investigation of the properties of ethyl cellulose films prepared by casting on glass from a limited number of different solvents has been carried out. It appears that the solvent power of a given solvent for ethyl cellulose may be the prime factor which determines film properties in essentially amorphous polymers of this type. Briefly, it has been found that thermodynamically poorer solvents for ethyl cellulose lead to films of higher birefringence, higher densities, lower brittle-point temperatures, and in general greater toughness. Modulus of flexure and the softening point appear to be relatively independent of solvent composition. A simple theory has been proposed to correlate solvent power and cross-section birefringence. More random modifications of ethyl cellulose films have been obtained by annealing glass casts. As one would expect, the shrinkage in the plane of the films parallels the cross-section birefringence. These annealed films have lower moduli and lower brittle-point temperatures, and the long-range high birefringence of glass casts has disappeared. An exceedingly low brittle-point temperature has been obtained by annealing films cast from benzene on glass. Essentially isotropic films prepared on a nonrigid surface, i.e. mercury, also have lower moduli than glass casts, and a considerable change in the stress-elongation curve has been observed, a decrease in yield stress and tensile strength being accompanied by more than a twofold increase in elongation. The noticeable effect of solvent composition on film properties when films are prepared on rigid casting surfaces largely disappeared when films were prepared on mercury. Lower brittle-point temperatures appear to be associated with the more isotropic films obtained by annealing or by casting on mercury.