Thermoplastics are polymers that can flow when heated above a melting or vitrification
temperature. They undergo plastic deformation, meaning viscous flow with often-complex
rheology due to their large molar mass, entanglements, interactions and chain branches.
Starch is a natural polymer with complex levels of structure that impinge upon
thermoplastic deformation. Natural polymers are no different to synthetic polymers once
some added levels of structural complexity are understood (Wunderlich, 2011). Starch is a
semi-crystalline polymer that does not melt in the traditional sense to form a liquid. Starch
melting does mean loss of crystallinity due to disruption of hydrogen bonds, however
melting occurs in the presence of a moderate (10-30 %·w/w) water content. Starch crystals
contain about 9-10 %·w/w of bound water, where bound water means water that does not
freeze when cooled below 0 °C. Additional water is required for melting of starch at
convenient temperatures below the boiling temperature of water and the degradation
temperature of the starch.