Development of a Highly Oriented Poly-biphenylenebisoxazole Fiber Obtained via a Precursor Polymer Spun From a Liquid Crystalline Aqueous Solution

A novel route for the production of the rigid rod fiber poly-2,2'-(p-phenylene)-6,6'-bibenzoxazole (biPBO) was investigated. This fiber was prepared via its precursor polymer poly(3,3'-dihydroxybenzidine terephthalamide), abbreviated as DHBTA. The dissolution behavior of the precursor polymer was tested in various solvents and it was found that basic aqueous solutions are suitable for spinning purposes. A highly concentrated solution (15 wt %) of the precursor polymer in aqueous tetramethylanimonium hydroxide (TMAH) shows liquid crystalline behavior. Oriented DHBTA fibers were produced by wet spinning of the precursor polymer from liquid crystalline TMAH solutions. The resulting yam showed much higher orientation and considerably better mechanical properties than a yam spun from an isotropic solution of the precursor polymer in N-methyl-2-pyrrolidone. Highly oriented biPBO fibers were obtained after heating the precursor yam to temperatures up to 450 degrees C in order to achieve ring closure. In conclusion, biPBO yarn with promising tensile properties was obtained by spinning from aqueous solutions instead of corrosive sulfuric acid, phosphoric acid or organic solvents.