The Influence of Cold Caustic Extraction on the Purity, Accessibility and Reactivity of Dissolving‐Grade Pulp

Prehydrolysis and cold caustic extraction (CCE) are two effective approaches to convert the traditional Kraft pulp to a dissolving‐grade pulp. Compared to prehydrolysis, CCE has several positive attributes but reduces final pulp reactivity. To gain insight into the factors that influence the reactivity of CCE treated cellulose, we compared the surface morphology, supramolecular properties and fibre properties of commercial dissolving pulp from prehydrolysis to dissolving grade cellulose upgraded using CCE. CCE treatment promoted the fibril aggregation and modified the initial cellulose I on Kraft pulps to cellulose II, thus decreasing final pulp reactivity. Various “post‐treatments” such as mechanical refining, steam explosion, induction of fibre kink and curl, sulfuric acid hydrolysis and endoglucanase hydrolysis effectively recover the reactivity lost during the production of dissolving pulp cellulose using a CCE step. Mechanical refining combined with endoglucanase treatment had the greatest effect increasing the reactivity from 32% to 75%. Cold caustic extraction (CCE) decreases the final pulp reactivity when it is used to to convert the tranditional Kraft pulp to a dissolving‐grade pulp. The reason is confirmed that CCE promoted the fibril aggregation and transferred the initial cellulose I on Kraft pulps to cellulose II. Various post‐treatments, including mechanical refining, steam explosion, induction of fibre kink and curl, acid hydrolysis and enzyme hydrolysis, effectively recovered the reactivity lost from 32% to 75%.