as those described the polyol plasticisers used have a range of molecular sizes and hydroxy groups that allow different degrees of association with starch after gelatinisation the type and level of plasticiser used has a dramatic effect on the physical properties of the final thermoplastic starch polymer higher molecular weight plasticisers such as maltitol increase the modulus and decrease the elongation at break some plasticisers such as erythritol result in a desirable improvement in flexibility and increase the elongation at break glycerol is very volatile and may be lost during drying or processing some plasticisers such as sorbitol erythritol and mannitol readily re crystallise and may migrate within the polymer and move to the surface causing bloom a combination of plasticisers is needed to achieve the balance of properties required in the final material with these detrimental side effects it has been found that higher levels of plasticiser generally tend to decrease the modulus and increase the elongation at break unplasticised tps polymers have a very high modulus gt 2500 mpa but are unable to be processed by conventional means it appears that a minimum level of plasticiser water or polyol is required in order to process the material as sheet film or moulded part the highest modulus obtained with injection mouldable materials plasticised with polyols is u02dc 1000 mpa with a minimum plasticiser level of about 20 the preferred plasticiser is a mixture of polyols in particular one or more other polyols particularly maltitol glycerol sorbitol erythritol and xylitol the plasticizer plays a triple role it provides suitable rheology for.