Is starch a thermoplastic

Answer 1

Native starch is not a thermoplastic. It is a semi-crystalline material and, when heated on its own, degrades before reaching the glass transition temperature.

WHen starch is heated in the presence of water, glycerol or other plasticizers, the semi-crystalline arrangement present in native starch is disrupted and the result is an amorphous material composed of entangled amylopectin and amylose chains.

This material, called thermoplastic starch (TPS) is indeed a thermoplastic since its glass transition temperature is well below the degradation T. Hence starch may be processed in common industrial techniques such as melt extrusion and injection moulding like traditional thermoplastics.

Most "starch plastics" found at the market are based on TPS, and many of them consist in blends, that is mixtures, of TPS with another polymer (such as Poly(lactic acid); Poly(caprolactone); Poly (Vinyl alcohol) ; natural rubber...).

A famous example of a TPS blend is Mater-Bi by Novamont.

Hope this helps. HUGS FOR ALL!