Study On Structure And Properties Of Modified PVA Hollow Products Prepared By Extrusion-Blow Molding

Poly(vinyl alcohol) (PVA) is a semicrystalline polymer with many excellent properties, such as high strength, thermal and abrasion resistance, excellent oxygen and organic solvent barrier properties, thus has wide use. Furthermore, PVA can be prepared from calcium carbide or natural gas and becomes more and more important in the situation of petroleum scarcity. But the strong intra- and intermolecule hydrogen bonding in PVA make its melting point close to its decomposition temperature and its thermal processing very difficult. PVA products are usually prepared by wet process, which can only produce low-dimensional products, such as films and fibers. If PVA can be molded into hollow products by melt extrusion-blow molding, it will be a great breakthrough in PVA production and of great economic benefit.Based on the previous work of our research group, this paper tried to realize the melt extrusion-blow molding of PVA, adjusted the component of the modified PVA system and obtained the smooth and transparent PVA blown parisons and bottles. The changes of hydrogen bonding, evaporation behavior of water, effect of modifiers on thermoplastic processing of PVA, structure and properties of modified PVA blown products were studied.1. Modifiers, including water and Ac, can form hydrogen complexation with PVA and weaken its intermolecular hydrogen bonding, decrease its crystallinity and melting point. By this way, windows for thermal processing of PVA were obtained, extrusion-blow molding of PVA was realized successfully, and uniform and transparent modified PVA blown products were obtained.2. Affected by the complexation and plasticization of Ac and water, crystallinity of PVA decreased, which reduced diffusional resistance and shortened diffusional path. The addition of Ac also decreased the difference of solubility parameter between PVA and gasoline, which was beneficial to the transit of small molecule. However, the addition of Ac and water had few effects on transparence of modified PVA blown products.3. Thermal treatment can reduce the time to reach the balance water content of PVA blown products, improve its crystal structure and increase its crystallinity, resulting in the enhancement of gasoline barrier property, moisture resistance and thermal resistance of modified PVA products. However, higher treating temperature, i. e. 180℃and 200℃, will lead to the colouring of modified PVA and its tansparence droping due to the dehydration and etherification of PVA.4. Proper crosslinking can reduce the moisture absorption property of modified PVA blown products and increase its gasoline barrier property and thermal resistance. The effect of treatment with 2% borax solution in 60 min was the best.