Description
Polyvinyl alcohol is a synthetic resin that is prepared by polymerization of vinyl acetate, followed by partial hydrolysis of the resulting ester in the presence of an alkaline catalyst. The number of acetate groups in
polyvinyl alcohol is determined by the degree of hydrolysis (86.5–89.0% hydrolysis for this food additive specification).
Polyvinyl alcohol is used as a coating, binder, sealing and surface finishing agent in food products such as dairy-based desserts, confectionery and cereal products and dietary supplement tablets, in the range of 0.2–1.8% by weight.
Polyvinyl alcohol (synonyms, vinyl alcohol polymer, PVA, ethenol homopolymer) is a water-soluble synthetic resin, prepared by the polymerization of vinyl acetate, followed by partial or complete catalysed hydrolysis. The primary raw material used in the manufacture of
polyvinyl alcohol is vinyl acetate monomer dissolved in methanol. The polymerization involves the presence of two proprietary cataytic agents. After polymerization, the material undergoes controlled hydrolysis with aqueous sodium hydroxide, during which the ester groups in the vinyl acetate are replaced with hydroxyl groups. Polyvinyl alcohol is precipitated, washed and dried to form an odourless, tasteless, white or cream-coloured granular powder.
Properties
Polyvinyl alcohol has excellent film forming, emulsifying, and adhesive properties. It is also resistant to oil, grease and solvent. It is odorless and nontoxic. It has high tensile strength, flexibility, as well as high oxygen and aroma barrier. However these properties are dependent on humidity, in other words, with higher humidity more water is absorbed. The water, which acts as a plasticiser, will then reduce its tensile strength, but increase its elongation and tear strength.
PVA has a melting point of 230°C and 180–190°C for the fully hydrolysed and partially hydrolysed grades. It decomposes rapidly above 200°C as it can undergo pyrolysis at high temperatures. PVA is an atactic material but exhibits crystallinity as the hydroxyl groups are small enough to fit into the lattice without disrupting it.
