HIGH-STRENGTH AND HIGH-MODULUS POLY(VINYL ALCOHOL) BY THE GEL AGING METHOD

The get ageing method was proposed for producing high strength and high modulus poly(vinyl alcohol) (PVA) materials. The PVA gel prepared from a solution in a mixed solvent of dimethylsulfoxide water (v/v) = 80:20 at -34 degrees C was moulded into a gel sheet and then aged in water at 10 degrees C for several months. The gel sheet was dried and then drawn at 200 degrees C. The tensile strength and the modulus of the drawn film were 2.8 and 72 GPa, respectively. These excellent properties are discussed in relation to the structures of the aged gel, the dried gel (namely the film) and the drawn film using the results from X-ray diffraction, differential scanning calorimetry and birefringence measurements. As a result, the most important process was shown to be the ageing process. If the crystallites with relatively low melting temperatures, which were called the B and C crystallites, were grown in the aged gel, the mechanical properties of the drawn film from it were as high as those described above. The orientation of the crystallites mildly caused during drying of the gel sheet was also shown to be a key structure which facilitated the high extension of the chain in the subsequent drawing process.