Pitch Problems in Making Japanese Papers (IV) Occurrence of Deposits in Pulping and Bleaching of Pokasa Bast Fibers

Deposition of organic and inorganic substances in pokasa (Broussonetia papurifera) bark pulping and bleaching sequences was studied from the view point of material balance between the/organic and the inorganics fractions. Little differences among the fractions were found, but better recovery yields of Fr.Ⅱ chip neutrals indicated lower solubilities of these substances in aqueous phase or higher depositabilities on pulp. Fr.Ⅱ contained triterpene acetates which were shown to interact easily with either acids or calcium as descibed in a previous paper. The higher depositability again confirmed its contribution to speck formation. Moreover, mass balance of the inorganics suggested that calium carbonate was formed during pulping and readsorbed onto the fibers. Calcium cation (Ca^<++>), calcium carbonate (CaCO_3) or calcium oxalate (CaC_2O_4) have almost the same degree of contribution to the speck formation. A hypothetical mechanism for the interactions among fibers, calcium, any organic acids was presented as follows: 1. Acidic components react with Ca^<++> or CaCO_3 to form salts or complexes with positive charges, which were adsorbed onto pulp with negative charges on its surface. 2. In pulping, Ca^<++> ions are generates and adsorbed on the vicinities of the resinous materials to form colloids with positive charges and adsorb onto pulp which have negative charges. 3. Calcium carbonate in aqueous medium may be coordinated by six molecules of H_2O to form Ca(H_2O)_6^<++> due to the coordinating properties of the ligand OH anion being substituted by H_2O molecule. Resinous materials may be directly bonded to the ions and may also bond with hydroxyl groups in cellulosic fibers