Preparation of high‐strength poly(vinyl alcohol) fibers by crosslinking wet spinning

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Abstract
High‐strength poly(vinyl alcohol) (PVA) fiber was obtained by the crosslinking wet‐spinning technique, which is an improved technique of the conventional non‐crosslinked type wet‐spinning of PVA. High tensile strength as well as high Young's modulus was achieved by introduction of the borate ion‐aided crosslinks during the coagulation process. The drawability of the as‐spun fiber greatly depends on the fiber thickness. The thinner the fiber, the higher the drawability. Since thinner fiber is subject to a very high shear rate on extrusion, the crosslinks introduced are believed to maintain topological memory of the oriented chains, which have a low density of entanglements. This allows drawing the fiber to a higher draw ratio. The strength and Young's modulus of the resultant highly drawn PVA fiber were achieved to be 22 g/d (2.3 GPa) and 430 g/d (50 GPa), respectively. The mechanism of the spinning was discussed and the spinning condition was carefully examined in order to optimize the final mechanical properties of the PVA fibers.