Basic Requirements of a Plasticiser

Plasticisers must have good compatibility with the polymer, so that the mixture does not separate into two phases. The attractive forces between dissimilar (polymer and plasticiser) molecules must be comparable with, or greater than, the forces between like molecules. 

Heating PVC for a long time can increase its crystallinity, and this reduces the compatibility between the plasticiser and the polymer. 

Compatibility can often be predicted from theoretical considerations, such as tables of solubility products, provided that the polymer is mainly amorphous. The solubility parameter of the polymer and that of the plasticiser must be similar. 

Plasticisers must also have an efficient softening action, i.e., a given amoimt of additive should induce significant improvements in elongation, low temperature impact strength and heat distortion temperature. 

Many ordinary ester plasticisers reduce the flame resistance of PVC, but the aryl phosphates are helpful, being flame retardant. 

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