Acidic versus alkaline beating of pulp

An examination was made of the fact that beating is accomplished with less mechanical energy if carried out under alkaline conditions rather than acid ic conditions Samples of unbleached kraft pulp were ion exchanged to sodium and calcium forms (alkaline conditions) and to hydrogen form (acidic condi tion) An order of swelling (Na+ > Ca++ >H) was established by the exchange. The pulps were then beaten and all were observed to increase in swelling b ut the initial order was maintained. Trends in swelling were duplicated by the tensile properties of the pulps. It is proposed that the chemical proce ss of exchange to Na+ or Ca++ form and the mechanical process of beating mo dify fibres by a common mechanism i.e. the breakage of internal cross links . Beating proceeds faster in the alkaline state because the chemical and me chanical processes are additive. In the acidic state only the energy-consum ing mechanical process operates.