Influence of plasticiser on the barrier, mechanical and grease resistance properties of alginate cast films.

Alginate cast films were plasticised by two plasticisers--glycerol and sorbitol--in different concentrations. As a function of the plasticiser type and concentration, the following parameters were investigated: equilibrium moisture content (EMC), colour measurement, microscopic analysis by SEM, grease resistance, oxygen permeability (OP), water vapour transmission rate (WVTR) and the mechanical properties. Both plasticisers have a positive influence on the mechanical properties but differ in their effect on the barrier properties. Whilst an increasing concentration of glycerol increases the permeability of alginate films to oxygen and water vapour, sorbitol did not influence the barrier properties to oxygen or water vapour. The behaviour of glycerol is in accordance with the free volume theory. The effect of sorbitol is assumed to be due to the good steric fit of sorbitol into the alginate network. The good embedding of sorbitol between the alginate polymer chains means it can lower the intermolecular bonding while still offering bonding possibilities. Therefore the flexibility of the cast films is increased while maintaining the barrier properties.