Influence of blend ratio and water content on the rheology and fragility of maltopolymer/maltose blends

The rheological behavior of blends of a fractionated maltopolymer (M _w = 1.4⋅10 ⁴ Da) and the disaccharide maltose is investigated as a function of water content and temperature, with emphasis on the viscosity and molecular relaxations in the approach to the glass transition. Shear rheology is combined with dynamic mechanical thermal analysis to probe viscosities between 1 mPa s and 10 ¹² Pa s. Differential scanning calorimetry is used to determine glass transition and enthalpy relaxation of the carbohydrate blends. The rheology data are fitted with a modified version of Williams–Landel–Ferry equation (Williams et al., 1955). The fragility of the blends is quantified using Angell's fragility parameters m and F _1/2 (Angell, 1991) and Roos’ strength parameter S (Roos, 1995b). The increase in fragility of the maltopolymer systems with increasing water and maltose contents is interpreted as a reduction of the entanglement density and an interference of water molecules with the hydrogen bonding between the carbohydrate chains.