How Is Polyvinyl Alcohol Made?

Among its other applications, polyvinyl alcohol sometimes finds use in the food industry.

Polyvinyl alcohol is a carbon-based polymer that dissolves well in water. It consists of long chains of (CH2)(HCOH) units, where every second carbon in the chain is bonded to an OH or alcohol group. It's synthesized from polyvinyl acetate.

Features

Polyvinyl acetate is a polymer where every second carbon is linked to an (OOCHCH2) or acetate group. This group consists of a CH3, or methyl group, bonded to a COO group; one of the two oxygen atoms in the latter is double-bonded to its carbon, while the other is bonded also to the main chain or backbone of the polymer. This type of arrangement is called an ester group.

Function

The reaction that converts polyvinyl acetate to polyvinyl alcohol is called a hydrolytic reaction because it involves the splitting of water molecules. Adding methanol in the presence of sodium hydroxide, a strong base, causes a reaction that breaks the bond connecting the (CH3)(C=O) to the other oxygen atom in the acetate; now, rather than having acetate groups along the chain, the polymer has alcohol groups instead.

Considerations

Depending on the length of the chains and the degree to which the acetates attached to the chains have been replaced by alcohol groups, polyvinyl alcohol may have different characteristics and properties. Generally it's tasteless, translucent or white-cream and soluble in both water and ethanol.

References

• UN Food and Agriculture Organization: Polyvinyl Alcohol; S.K.Saxena; 2004