Mechanical loss processes in polysaccharides

Dynamic mechanical properties of cellophane, amylose, and dextran have been obtained over the temperature range 100–520°K and frequency range 10^?2 to 10⁺² Hz on specimens containing various amounts of water. Four mechanical transitions have been characterized. At about 180°K, there is a γ transition that has been assigned to rotation of methylol groups; no comparable transition was found to exist in dextran. At about 240°K, there is a β transition that has been assigned to rotation of methylol–water complexes, but the β transition in dextran appears to be due to some other kind of motion. In cellophane at about 450°K there is an α₂ transition which appears to have contributions from motion of chain segments in disordered regions. The α₁ transition for cellophane occurs at temperatures too high to measure and may be due to segmental motions in chains within crystalline regions. Dextran and amylose were found to have at these same temperatures α loss processes that probably correspond to glass–rubber transitions in amorphous material. The changes in these mechanical loss mechanisms due to moisture uptake suggest that sorbed water associates with glucose repeat units in ways ranging from those which stiffen molecular structure to those which allow greater freedom for other types of motion to occur.