Effect of Hot Water Extraction on Hardwood Kraft Pulp fibers (Acer saccharum, Sugar Maple)

Abstract

This study focuses on the properties of fibers obtained from the kraft pulping of pre-extracted sugar maple wood chips. Hot-water pre-extraction was carried out for different times characterized by P-factors in the range of 12 and 600 h. It was found that pre-extraction of the chips significantly accelerates delignification during Kraft pulping such that the H-factors necessary to obtain equivalent delignification (i.e., the same k numbers) were substantially smaller than control cooks (i.e., with unextracted chips). Unbleached pulps of k numbers of 35, 25, and 15 were prepared, and their papermaking properties were tested. The hemicellulose content of the pulps decreased with pretreatment, whereas the cellulose contents increased. Pretreatment also resulted in an increase in the pulp viscosity. The fiber lengths showed no change, but the fines content was reduced. The kink index of pre-extracted pulps showed large increases. The porosity of the cell wall also increased with extraction severity as did the mean pore size. The water retention values (WRV) also increased with extraction probably because of the increased fiber porosity. The ζ potential of the fines remained unaffected, whereas the total charge (cationic) demand of the pulps decreased with pre-extraction. There is also a significant loss of tensile and burst strengths of handsheets made with extracted pulps possibly as a consequence of the increased kink and curl index and decreased interfiber bonding ability.