Polyvinyl Alcohol is the product of Poly Vinyl Acetate Solution. In the case of incomplete alcoholysis, polymer actually contains alcohol and vinyl acetate ethylene unit structure. Molecular structure of polyvinyl alcohol contains the content is very wide, for fibers, Polyvinyl Alcohol degree of polymerization, polymerization degree and alcoholysis degree, three-dimensional configuration, monomer connection mode, branched, base at the end of its most significant effect on its performance.
1. Degree of polymerization: The average degree of polymerization is closely related to the mechanical properties of fiber. Degree of polymerization of conventional fiber is 1400 to 1700. The property of water soluble fiber is low, with high strength and high modulus fibers in more than 5000.
2. Molecular weight distribution: Polymerization of vinyl acetate, chain transfer occurs frequently, so after the formation of molecular weight ranging from polyvinyl alcohol solution. The molecular weight distribution of Polyvinyl Alcohol affects the strength of the fiber and other properties. A molecular weight distribution suitable for the spinning of Polyvinyl Alcohol is 2 to 3.5. Polyvinyl Alcohol on the macromolecular position is different, can be divided into isotactic structure (I - PVA), syndiotactic structure S - (PVA) and random set structure (A - PVA) three kinds of three-dimensional structure.
3. Alcoholysis degree: Alcoholysis degrees decide the fiber properties, and effect the molecular interactions. There are large acetate molecules, not only hinder the orientation and crystallinity of fiber, but also reduce the intermolecular forces. The alcoholysis degree is low, the more the acetate containing macromolecular chain, fiber strength is low, water soluble.
4. The stereochemical structure: The different position of Polyvinyl Alcohol hydroxyl groups in the molecules, can be divided into isotactic (I-PVA), (S-PVA) a syndiotactic and atactic (A-PVA) three stereo structure.
5. Connection mode: The head - end structure of Polyvinyl Alcohol, hydroxyl ordered, with orientation and crystallization in favor of large molecules, the mechanical properties of the fiber and water resistance performance. The head - head or end - end structure, due to steric hindrance of hydroxyl, poor regularity, crystalline fibers affected.
5. Degree of branching: A small amount of branched chain is inevitable. The length of the chain is determined by the polymerization conditions. Spinning of high strength and high modulus fibers should try to use low branching degree of Polyvinyl Alcohol as raw material.
6. The carbonyl and carboxyl groups: Polyvinyl Alcohol carbonyl content is in commonly 0.01 to 0.03mol%, but carbonyl with electronegative strong, under high temperature and dehydrated to form conjugated double bonds, will make the fiber yellow. In the end of Polyvinyl Alcohol molecules in addition to containing a small amount of carbonyl, also contains a certain amount of carboxyl group, carboxyl absorption base dyes, alkali to generate sodium salt (-COONa) characteristics. The sodium salt of the Polyvinyl Alcohol oxidation at high temperature of dehydration, also make the fiber yellow.