PVC additives (Part 10)

Polymeric Plasticisers or Polyesters

This is the last article about plasticisers in PVC which I have been writing about this significant aspect of PVC additives. Polyester plasticisers are typically saturated polycondensates of glycols with dibasic acids, most are typically based on propan-1,2-diol or butan-1,3-diol and adipic acid. Differing molecular weights are available to suit particular needs. Polyester structures may be chain terminated by the inclusion of a monobasic acid or monohydric alcohol (2-ethylhexanol). Non-terminated polyesters contain acidic or hydroxy end groups which are beneficial in enhancing resistance to extraction by hydrocarbons. However, other performance aspects may be reduced.

An alternative form of polyester structure can be obtained by ring-opening and self-condensation of a lactone and some commercial polyesters are based on caprolactone with neopentyl glycol. These are low-melting-point paste solids that show processing advantages over more conventional polyesters.

For applications requiring good extraction resistance and heat ageing, polymeric esters are used. They are normally described as non-migratory plasticisers due to their resistance to extraction by hydrocarbon oils, vegetable oils, and solvents and their reduced migration into polymers (particularly non-polar types). A major application is for food contact approved use in PVC clingfilm.

Other applications exploiting the migration resistance of polyesters are high-temperature electrical tape, coated fabrics, solvent-resistant cable hose and tubing, and pond and tank liners.

These materials are relatively expensive. In addition, their lower compatibility and high viscosity (of some grades) makes them more difficult to handle and process.