We reported that syndiotactic poly(vinyl alcohol) (s-PVA) fiber of well-oriented microfibrillar structure, similar to a natural cellulose fiber, was directly formed during saponifying poly(vinyl pivalate) (PVPi) or copolymers of vinyl pivalate (VPi) and vinyl acetate (VAc) without the spinning process. Recently, we found critical molecular parameters such as syndiotacticity, molecular weight, and degree of saponification (DS) for the microfibrillation of PVA. Firstly, syndiotactic diad (S-diad) content is an important factor for the microfibrillation of PVA. The structures of PVAs with a similar number-average degree of polymerization (Pn) of 7800 prepared by saponification of copolymers of VPi and VAc show a consistent sharp transition between 55 and 56% S-diad content. PVAs with lower S-diad contents have sharpless morphologies, but at 56% S-diad content the polymers were fibrous, with a higher degree of crystallinity and orientation of the crystallites. The order improves steadily with the S-diad content above the transition and correlates with the observed changes in the thermal and mechanical properties. Secondly, molecular weight is a significant factor, also. The PVA with Pn of 800 and S-diad content of 62.5% revealed a well-defined fibrous morphology. Each fiber was composed of a number of microfibrils. As the Pn of PVA decreased, some morphological change was observed. The specimen with Pn of 660 and S-diad content of 62.4% formed a longitudinally developed precipitate during saponification. Distinct difference of this specimen is that it did not exhibit a fibrous morphology nor include a fiber-like inner structure. A final critical factor is the DS. The fibrous morphology developed as DS increased with trends that the fibrils having Pn of 14000 and S-diad content of 64.5% become longer and narrower. Also, a strong elliptical scattering was observed due to the presence of regular and elongated microvoids. Although PVAs had similar fibrillar morphologies, th
By: Won Seok Lyooa, Jeong Hyun Yeumb, Joon Ho Kima, Sam Soo Kima, Byung Chul Jib, and Chul Joo Leec a
Submit Date: 12/31/1999 20:00