| abstract |
Method of preparing films of acrylonitrile polymer exhibiting very high tensile strength, stiffness, optical clarity, and outstanding gas barrier properties. Method entails extruding a hot, concentrated solution of said polymer in a solvent therefor that is water-soluble, e.g., dimethyl sulfoxide, onto a film-supporting surface, e.g., a flat surface, or a drum, which, preferably, has a low energy surface such as provided by wetting the surface with aqueous dimethyl sulfoxide, or coated with polytetrafluoroethylene, or other suitable means to thereby form a film. The resulting film is then contacted with an aqueous medium, e.g., water to remove the solvent (e.g., dimethyl sulfoxide) and partially replace it with water, this treatment being effected under conditions that will prevent the film from curling or puckering. The resulting film is composed essentially of acrylonitrile polymer and water, and is ignition resistant. This film can be then biaxially stretched in a substantially non-drying environment at 100° C or less, preferably at 50°-80° C followed by drying to remove the water, while maintaining the film under constrained conditions to prevent or limit the degree of lateral and longitudinal shrinkage. The final film thus produced has a very high tensile strength and stiffness and very low gas permeability. |