BIOPULPING - AN OVERVIEW OF DEVELOPMENTS IN AN ENVIRONMENTALLY SAFE PAPER-MAKING TECHNOLOGY

Treatment of wood chips with lignin-degrading fungi prior to pulping h as been shown to have great potential for mechanical as well as chemic al pulping on a laboratory scale. Ceriporiopsis subvermispora, when gr own on aspen or loblolly pine for 4 weeks, was found to be superior to other fungi. On aspen there was an energy savings of 47%, and an incr ease in burst and tear indices of 22% and 119%, respectively. With lob lolly pine, energy savings amounted to 37%, while burst and tear indic es increased by 41% and 54%, respectively. The weight loss was only 6% , but a decrease in optical properties had to be accepted. After sulfi te cooking of wood chips pretreated for 2 weeks, the Kappa number decr eased by 30% with hard- and softwood. Tensile and tear indices decreas ed by only 10%, while the brightness of unbleached pulp increased by 4 % with birch. Information obtained by immunoelectron microscopy and di fferential staining led to the conclusion that the biopulping effect o btained after 2 weeks of incubation cannot be explained by the direct action of enzymes on lignin or polysaccharides. Instead, a low molecul ar mass agent is considered to be responsible for the biopulping effec t. These results have changed the aims of biopulping from an emphasis on removing the bulk of lignin to an emphasis on a short-term process, lasting 2 weeks and yielding a low mass loss. Data on these kinetics of fungal development and the degree of asepsis will help to scale-up the process. An advanced chip pile is assumed to be the most feasible process design, rather than a controlled enclosed reactor.