The sorption of glucomannan and xylan on α‐cellulose wood fibers

Abstract The rates of sorption of spruce glucomannan and of a modified birch xylan (containing less than 3% uronic anhydride) upon never‐dried α‐cellulose wood fibers in 0.02N alkali have been measured at 4 temperatures ranging from 5–40°C. By labeling the glucomannan with carbon‐14 and the xylan with tritium it was possible to measure the rates of sorption of each hemicellulose alone or in solution together at the same concentration. In both cases the rates of sorption of the glucomannan were about twice those for the xylan. Average activation energies (kcal./mole) derived from the rates were as follows: glucomannan alone, 3.8; glucomannan in admixture with xylan, 3.1; xylan alone or in admixture with glucomaunan, 6.3. The initial rates of sorption, estimated graphically by a methods which is shown to have severe theoretical limitations, gave higher values for the activation energies, viz.: glucomannan alone, 6.6; glucomannan in admixture with xylan, 5.8; xylan alone, 10.0; xylan in admixture with glucomannan, 10.1 kcal./mole. All these values suggest that the sorption of both hemicelluloses is physical. Although the initial rate of sorption of the xylan was not significantly affected by the presence of the glucomannan, its total sorption after 10 min was reduced by an average of 18% when glucomannan was present. The lower rate of sorption of the xylan is ascribed to the presence of its uronic acid carboxylic groups. A small percentage of these groups can apparently override the conformational similarity of xylan and cellulose.