**8. Future directions**

Improved processing techniques due to equipment design (screw element design, feed stages, steam release and plasticiser addition) to accommodate retention of water content. Plasticiser structures that are specific to starch and can be used with starch–filler composites, while limiting moisture susceptibility are required. Where plasticisers are not able to enhance properties, polymer blends may be more suited due to the large size of polymer molecules compared with plasticisers. The primary limitations to TPS are moisture variation and retrogradation causing embrittlement during storage that is not desired for packaging materials. A challenge is for starch with more specific initial properties to be available. The structure of synthetic properties can be controlled better than that of biopolymers causing a major set-back for materials from natural resources where properties may change with source, season or plant variant. This makes preparation of commercial products with precise tolerances difficult.
