The effect of glycerol/sugar/water and sugar/water mixtures on the plasticization of thermoplastic cassava starch

The use of 2 wt% sugars as co-plasticizer in combination with glycerol was investigated for thermoplastic starch (TPS) from cassava. The results were compared to those for whole cassava root TPS, which naturally contains sugars in the same proportion. The main objective was to investigate the influence of natural sugars present in the cassava root on the properties of thermoplastic starch produced with cassava root. TPS produced with sugar and water without the addition of glycerol was also investigated. The materials were prepared by melt-processing cassava starch or ground and dried cassava root in a high-power batch mixer, Haake Rheomix 600, at 120 °C. The samples were tested by X-ray diffraction (XRD), dynamic mechanical thermal analysis (DMTA), scanning electron microscopy (SEM) and water absorption experiments. The results showed that the addition of 2 wt% sugars (glucose, fructose and sucrose) to the starch-glycerol systems causes a reduction in the glass transition temperature (Tg) of the TPS accompanied by a reduction in the storage modulus determined by DMTA and inhibits the formation of VH-type crystal structures in the resulting TPS. The use of only sugar and water as plasticizers in the TPS causes a considerable reduction (∼60%) in the subsequent water uptake.