Polyvinyl alcohol is a water-soluble synthetic polymer with excellent film-forming, emulsifying, and adhesive properties. This versatile polymer offers outstanding resistance to oil, grease, and solvents, plus high tensile strength, flexibility, and high oxygen barrier. Suitable applications for polyvinyl alcohol are largely determined by its properties. The basic properties of polyvinyl alcohol depend on its degree of polymerization, degree of hydrolysis, and distribution of hydroxyl groups. In terms of the degree of polymerization, d.p. (based on the viscosity in centipoise (cP) of a 4 percent aqueous solution of polyvinyl alcohol at 20°C), the major polyvinyl alcohol product groups are a low-viscosity group of approximately 5 cP, a medium viscosity group of 20-30 cP, and a high viscosity group of 40-50 cP, which correspond to d.p. of about 500, 1,700, and 2,000, respectively. In terms of degree of hydrolysis, the principal grades of polyvinyl alcohol produced can be classified as fully hydrolyzed (97.5-99.5 percent degree of hydrolysis) and partially hydrolyzed (87-89 percent degree of hydrolysis). In general, fully hydrolyzed grades of polyvinyl alcohol are used mainly in paper coating, in textile warp sizing of hydrophilic fibers, such as cotton and rayon staple yarns, and in laminating film in safety glass (after conversion to polyvinyl butyral). On the other hand, partially hydrolyzed grades are used mainly in protective colloids in emulsions, in remoistenable adhesives, in textile warp sizing for rayon filaments and polyester fibers, and in printing plates. The most common grades in each area of application are fully and partially hydrolyzed grades with a degree of polymerization of 1,700. Polyvinyl alcohol is used mainly in aqueous solution. Its solubility in water depends on its degree of polymerization and degree of hydrolysis, with the latter factor being especially significant. The presence of as little as 2-3 mol percent of residual acetate groups causes a significant change in the solubility at 40-60°C - fully hydrolyzed polyvinyl alcohol is only slightly soluble, but approximately 97 percent hydrolyzed polyvinyl alcohol is almost completely soluble. Crystallization induced by heat treatment prior to dissolving increases the required dissolution temperature. Heat treatment of a few minutes increases the crystallinity and greatly reduces solubility and water sensitivity. The influence of heat treatment is desirable in applications such as adhesives and paper coatings, where a greater degree of water resistance is needed, but is highly undesirable in textile warp sizing, where the polymer must be removed after a drying cycle. Polyvinyl alcohol is one of the few truly biodegradable synthetic polymers; the degradation products are water and carbon dioxide. Polyvinyl butyral, a derivative of polyvinyl alcohol, is a pliable, tough thermoplastic used as the interlayer in laminated safety glass. Polyvinyl butyral is formulated to give controlled adhesion to glass and optimum impact performance in laminated safety glass for automotive, security, and general glazing applications. Polyvinyl butyral has been used in automotive windshields since 1938, and now is available for use in laminated automotive side window applications for improved security. PVB laminated glass is also extremely versatile in residential and commercial applications for skylights, atriums, partitions, curtain walls, doors, and even roofs. Glass laminated with PVB will not shatter; even if the glass is broken, the opening is not penetrated because glass fragments adhere to the interlayer.
The polyvinyl alcohol industry has undergone several ownership changes in the past few years. Late in 2000, Celanese purchased the polyvinyl alcohol business of Air Products and Chemicals, at the time the number two producer of polyvinyl alcohol in the world and the leader in North America. The other major change in ownership recently was the purchase of Clariant's polyvinyl alcohol and polyvinyl butyral businesses by Kuraray. Supply and demand estimates are provided in this report for polyvinyl alcohol in the United States, Western Europe, and Japan. Worldwide suppliers of polyvinyl butyral are listed.
Production of polyvinyl alcohol is by the controlled hydrolysis of polyvinyl acetate, using either a belt hydrolysis or a slurry hydrolysis process. Polyvinyl acetate, in turn, is produced by free-radical polymerization of vinyl acetate monomer. Vinyl acetate is derived primarily from ethylene and acetic acid feedstocks, although processes based on acetylene are still in operation. Detailed chemistry, process descriptions, and cost estimates are provided for production of polyvinyl alcohol via the aforementioned processing sequence. The sequence is then extended to the production of polyvinyl butyral from polyvinyl alcohol. Variations in the economics of polyvinyl alcohol and polyvinyl butyral with changes in feedstock prices, investment costs, and plant capacity are included. |
