High modulus poly (vinyl alcohol) fibers by zone drawing

Abstract

Dried gel films of poly (vinyl alcohol) were drawn at high temperature using zone heating devices. Hot air zones 5 and 10 mm wide were used to draw the gels to draw ratios up to λ = 23 × at 200 °C. A 3.2 mm wide heated bar in direct contact with the specimen enabled use of drawing temperatures up to 235°C and resulted in draw ratios of 25-38 ×. Drawn films had a highly fibrous nature, were well oriented, and contained crystals about 10 nm long. Gel permeation chromatography studies of the material before and after drawing showed that drawing at high temperatures caused some changes in molecular weight and dispersity. Storage moduli of the fibers increased with draw ratio, reaching a high of 59 GPa at 31× but, in general, leveled off at high A. Low draw ratio (10-15 ×) fibers drawn in the 5 mm air zone had moduli comparable to high draw ratio (25-38 ×) fibers drawn with the high-temperature contact heater (20-60 GPa). Retraction studies showed that low modulus fibers, even those highly drawn, had low effective molecular extension. Drying the fibers increased both their room temperature modulus and glass transition temperature.