Thermo-mechanical processing of sugar beet pulp. II. Thermal and rheological properties of thermoplastic SBP

Thermoplastic properties of extruded sugar beet pulp (SBP) are closely linked to water-polymer relationships. DSC analyses of water evaporation, water fusion and biopolymer relaxation according to SBP moisture content gave a more accurate estimation of SBP hydration steps than classical water adsorption isotherm. Three moisture contents (8%, 26%, 41% db) were then defined as limits of the different hydration behaviours. Melt viscosity measurements of SBP showed its shear thinning behaviour and the measured apparent viscosity is in the same range as thermoplastic starch viscosity. Using only water as plasticizer, to one temperature corresponded one moisture content to reach the optimal flowing properties: 110 °C/35%, 120°/25% and 130 °C/20%. This “plasticization” temperature has been estimated through DSC measurements of large amounts of moistened SBP in pressure-resistant pans. This new kind of DSC measurement revealed a new sample mass dependent second order transition between 140 and 180 °C, which temperature is linearly linked to the sample mass.