Effect of the carbohydrate composition of bleached kraft pulp on the dielectric and electrical properties of paper

Abstract

The effects of hemicellulose removal from bleached birch kraft pulp by alkaline extraction with sodium hydroxide on the dielectric, electrical and electrostatic properties of paper material have been examined. The hemicellulose content, particularly the xylan content, of birch kraft pulp has an effect on the dielectric constant and on the dielectric loss factor. The real part of the dielectric constant increases with decreasing content of hemicellulose in papers containing the extracted birch kraft pulp. Hemicellulose removal by alkaline extraction increases the direct and alternating current electrical conductivity and changes the electrostatic properties of the paper. Dielectric relaxation spectra at different temperatures analysed using the Havriliak–Negami relaxation model revealed that the dielectric properties are determined by at least two relaxation processes which are affected by the hemicellulose content. The first relaxation process originates in the polarizable groups of cellulose and hemicellulose and the second is attributed to the water–polymer structures formed during the interaction of cellulose and hemicelluloses with moisture. Both relaxation processes are compared quantitatively.