Polyvinyl alcohol (PVOH) is a synthetic water soluble polymer, a white powder, that melts, with decomposition and pyrolysis, at 230°C. PVOH is stable in dry form, odorless, nontoxic, considered to be safe to handle and environmentally friendly, notably its ability to undergo
biodegradation. For most end-use applications, few substitutes for PVOH are available. PVOH accounts for a small to moderate percentage (20% maximum) of the final cost of the wide variety of final products in which it is an input. Pricing pressure on PVOH appears to have little effect on the cost of final products, but natural gas feedstock prices can be significant in the cost of
PVOH. PVOH is manufactured by hydrolysis of polyvinyl acetate and commercial grades have 80-100% hydrolysis and 13 000-200 000 molecular weight. The degree of hydrolysis of PVOH affects a variety of physical properties, such as solution interfacial tensions, compatibility, reaction kinetics, rheology, and water solubility Partially hydrolyzed PVOH has a lower melting temperature; higher hydrolysis results in lower solubility; viscosity increases with increasing molecular weight. PVOH can be fabricated into films and coatings that have high tensile
strength and flexibility and that are resistant to penetration by oxygen, carbon dioxide, and other aroma vapors. PVOH is soluble in hot and cold water. PVOH is insoluble in petroleum-based solvents and is quite useful in coatings and films. PVOH finds use in plastic/molding
compounds (e.g., epoxy will not stick to PVOH coatings), surface coatings and films resistant to gasoline and fuels, textile sizes and finishes, adhesives, printing inks, laminated glass, cosmetics, pharmaceuticals (viscosity increasing agent), ophthalmic lubricant, and fibers as a reinforcement in concrete. In Western Europe and the United States, the largest market sector for PVOH is for the manufacture of polyvinyl butyral (PVB) for laminate glass; coating textiles and paper products are the next largest market sector. Increasing use of recycled fibers in printing stock favors PVOH, which has a higher strength than other binders, e.g., casein, soy protein, and
starch. PVOH production is centered in Asia, with an estimated 75% of world-wide capacity, but much of the production is used internally and not exported. PVOH is relatively immune from competition. No "drop-in" substitutes for PVOH exist for most applications, but, in some applications starch, carboxy methyl cellulose, polyvinyl acetate, styrene butadiene latex could
substitute for PVOH. Starch can be used as a sizing agent in textile production and styrene butadiene latex can be used as a binder and optical brightener in paper production, although PVOH is more effective in both applications.
posted by Colin Cook, R&D - Applied/ Formulation/ Product development at Neschen Coating UK Ltd
Boric acid and borate salts will insolubilise polyvinyl alcohol. This can be achieved in coatings such as inkjet paper by formulating the solutions with acetic acid. The mix is stable for long enough to coat the paper. On drying, the acetic acid is evaporated off and crosslinking and insolubilisation occurs. The resulting coating is not entirely water-repellent, otherwise it could not work as an ink receiver, but it does swell in water and becomes quite rubbery in bulk.
More insight into aqueous solubility - Mar 20, 2012
posted by Titus Sobisch, R&D - Applied/ Formulation/ Product development at L.U.M. GmbH
I was surprised about aqueous solubility decreases with the degree of hydrolysis. What is the reason - internal H bonds?
There should be an optimum degree of hydrolysis for best aqueous solubility.