Fiber properties as an indication of yield in chemical pulping of pine and maple

Product quality and productivity of the chemical pulping depends on many process conditions, which are usually well monitored on-line. A key result of process conditions is pulp yield. Yield has proven to be difficult to monitor on line, but would be a valuable check that the conditions used were appropriate. Yield is an important element effecting profitability. Studies relating the fiber dimensions to pulping yield show limited sensitivity to modifications in the cooking process and/or provide inadequate information to be considered reliable for on-line monitoring. The present study focuses on a theory that the major yield-controlling components in the pulp (i.e. hemicelluloses and lignin) alter the behavior and/or properties (e.g. dimensions, flexibility, hygroscopicity) of at least some of the fibers. The main hypothesis studied in this investigation is that these yield related fiber properties can be isolated for closer investigation to reveal the yield information. Four cooking methods with condition to produce two different lignin contents per method were used to provide unbleached pulps both from pine and maple. Screened pulps were; analyzed regarding chemical composition based on a new NMR-technique for carbohydrates; subjected to hysteresis experiments; fractionated using a modified Bauer McNett; and the fiber dimensions determined.; Pulp yields were related to the methods in the sequence: polysulfide > kraft > biokraft > soda. Carbohydrate analysis revealed that the glucose content was related to the pulping yield (Yield/Glucose; R 2(Pine) = 0.88, R2(Maple) = 0.82). Fungal pretreatment in bio-kraft reduced the hexosan content, including cellulose, compared to kraft cooked under the same conditions. A new concept, hemi/fiber length was developed and evaluated as a yield predictor (Yield/hemi-per-length; R2(Pine) = 0.89). Results from three hysteresis cycles with uncompressed never dried fibers (80 ↔ 50 ↔ 20% RH) showed that higher yield pulps with fewer fibers, pores, and surface area held the most moisture and that the amount of retained water was dependent not only on the drying history of the pulps but especially on their hemicellulose content (Yield/Moisture at 80% RH; R2(Pine) = 0.72, R 2(Maple) = 0.85). (Abstract shortened by UMI.)...