Thermal and mechanical properties of polyurethanes derived from mono- and disaccharides

Thermal and mechanical properties of polyurethane (PU) sheets prepared from the glucose/fructose/sucrose-polyethylene glycol (PEG)-diphenylmethane diisocyanate (MDI) system were examined by differential scanning calorimetry, thermogravimetry, dynamic mechanical analysis and tensile tests. The saccharide content was varied at a constant NCO:OH ratio of 1.0. The glass transition temperature (T-g) increased with increasing saccharide content. The incorporation of saccharides into the PU structure results in a higher crosslinking density and a higher content of hard segments. The thermal decomposition was dependent on the saccharide content, an increase leading to a lower thermal decomposition temperature (T-d). The dissociation of saccharide OH groups and NCO groups is a major part of the thermal decomposition of these PUs. Dynamic mechanical analysis revealed two kinds of relaxation: the high temperature relaxation corresponds to main chain motion and the other is a local mode relaxation due to non-reacted isocyanate groups. The tensile stress and Young's modulus increased with the saccharide content.