High strength and modulus polyvinyl alcohol fibers and method of their preparation

DETAILED DESCRIPTION OF THE INVENTION The process and fibers of the present invention employ a linear ultrahigh molecular weight polyvinyl alcohol (PV-OH) described more fully below that enables the preparation of PV-OH fibers (and films) of heretofore unobtained properties by extrusion of dilute solutions of concentration lower than used in Wet Spinning, Dry Spinning, Gel Spinning or Phase Separation Spinning, all as described by Zwick, Zwick et al.
and UK Patent Specification No.
1,100,497.
Furthermore, the preferred solvents of the present invention do not phase-separate from PV-OH on cooling to form a non-PV-OH coating or occluded phase, but rather form a dispersed fairly homogeneous gel unlike that achieved in Phase Separation Processes.
The ability to process such gels formed by extruding and cooling dilute solutions is different from conventional gel spinning of PV-OH, which, according to Zwick et al, requires an even higher solid content of the spinning dope (45-55%) to allow the polymer to be extruded and fibers to be collected in the form of a concentrated, tough gel without prior removal of solvent.
The PV-OH polymer used is linear and of weight average molecular weight at least about 500,000, preferably at least about 750,000, more preferably between about 1,000,000 and about 4,000,000 and most preferably between about 1,500,000 and about 2,500,000.
The term linear is intended to mean no more than minimal branches of either the alpha or beta type.
Since the most common branching in polyvinyl acetate (PV-Ac) manufacture is on the acetate side-groups, such branching will result in side-groups being split off during hydrolysis or methanolysis to PV-OH and will result in the PV-OH size being lowered rather than its branching increased.
The amount of total branching can be determined most rigorously by nuclear magnetic resonance.
While totally hydrolyzed material (pure PV-OH) is preferred, copolymers with some vinyl acetate remaining may be used.
Such linear ultrahigh molecular weight PV-OH can be prepared by low temperature photoinitiated vinyl acetate polymerization, followed by methanolysis, using process details described in the copending, commonly assigned application of J