Small-angle and wide-angle X-ray analyses of syndiotactic poly(vinyl alcohol) microfibrils

The crystal and microstructures of the novel microfibrillar poly(vinyl alco hol) fibers (PVA fibrils) having different syndiotactic diad (S-diad) conte nts of 56-65% have been investigated by small- and wide-angle X-ray methods . The PVA fibrils were directly prepared from the saponification and insitu fibrillation without spinning procedure. Small-angle X-ray scattering data show that these PVA fibrils had various microvoid structures due to differ ent stereoregularities, which was similar to those found in various natural cellulose fibers. Also, the higher the syndiotacticity was, the more regul ar and elongated the microvoids in PVA fibril were. This might be explained by a better alignment of PVA chains with higher syndiotacticity. To effect ively orient the molecular chains of high molecular weight syndiotactic PVA fibril, a high-temperature zone drawing technique was applied. Degree of c rystal orientation up to 0.991 was achieved by stretching the PVA fibril wi th S-diad content of 63.1% and with original degree of crystal orientation of 0.887 at around 250 degreesC close to its melting temperature. The maxim um draw ratio of the PVA fibril increased with a decrease in the S-diad con tent, indicating that the crystal was more stable in higher syndiotactic PV A. When the same draw ratio was applied to the fibrils, higher crystal orie ntation was achieved for the fibrils having higher syndiotacticity. The cry stallinity, the apparent lateral and longitudinal crystal sizes, and the cr ystal to amorphous length in long period of drawn PVA fibrils were larger i n higher syndiotacticity. It turns out that PVA fibril drawn at 230 degrees C had a well-oriented lamellar structure. Moreover, dimensions of these lam ellae were enlarged with increasing syndiotacticity.