Method of preparing high strength and modulus polyvinyl alcohol fibers

Claim 1

A process comprising the steps: (a) forming a solution of a linear polyvinyl alcohol having a weight average molecular weight at least 500,000 in a first solvent at a first concentration between about 2 and about 15 weight percent polyvinyl alcohol, (b) extruding said solution through an aperture, said solution being at a temperature no less than a first temperature upstream of the aperature and being substantially at the first concentration both upstream and downstream of said aperture, (c) cooling the solution adjacent to and downstream of the aperture to a second temperature below the temperature at which a rubbery gel is formed, forming a gel containing first solvent of substantially indefinite length, (d) extracting the gel containing first solvent with a second, volatile solvent for a sufficient contact time to form a fibrous structure containing second solvent, which gel is substantially free of first solvent and is of substantially indefinite length; (e) drying the fibrous structure containing second solvent to form a xerogel of substantially indefinite length free of first and second solvent; and (f) stretching at least one of: (i) the gel containing the first solvent, (ii) the fibrous structure containing the second solvent and, (iii) the xerogel, at a total stretch ratio sufficient to achieve a tenacity of at least about 10 g/denier and a modulus of at least about 200 g/denier.