| Rigidoporus ulmarius (Fr.) Imaz. has been reported briefly in the literature to selectively biodelignify wood both naturally in the field, and also under laboratory conditions. Selective biodelignification of lignocellulosic materials by fungi is influenced to a great extent by the environmental or cultural factors employed.; The effect of the following cultural factors: aeration; exogenous addition of hydrogen peroxide; concentration of mineral solution; addition of a surfactant (tween 80); and exogenous addition of veratryl alcohol on selective biodelignification of aspen (Populus tremuloides Michx.) refiner mechanical pulp (RMP) by R. ulmarius was studied. The objective was to optimise the depletion of lignin by R. ulmarius while maintaining the carbohydrate level, especially cellulose, at its original level. The quantitative success of this objective was defined as the selective biodelignification index (SBI), defined as the ratio of total carbohydrates to the total residual lignin. Fungal-treated pulps with the highest SBI and the greatest lignin depletion were compared with controls by physical means on handsheets.; Optimal conditions for selective biodelignification of aspen RMP included addition of mineral solution (Kirk-Schultz mineral solution, eight-fold concentration) and oxygen flushing in the absence of other chemical additives or nitrogen supplements. Pulps given this treatment were characterised by residual contents of 14.8% lignin, 51.5% glucose and 15.1% xylose. This was equivalent to a lignin reduction of 30.8%, and a xylan depletion of 23.7%, without proportional reduction in cellulose content. Consequently, the SBI was 4.5, versus 3.2 for the untreated controls.; In general, mineral solution (eight-fold concentration) enhanced selective biodelignification and lignin biodegradation under oxygen flushing. Similarly, exogenous addition of veratryl alcohol to the culture also enhanced selective biodelignification. However, exogenous addition of hydrogen peroxide to treatments containing other factors had a common effect of limiting selective biodelignification. Under high oxygen flushing, both lignin and carbohydrate biodegradation was enhanced to the same extent by exogenous addition of tween 80 (0.05%), with the result that SBI was not much affected.; Practically, the observed significant increase in brightness and tensile strength for pulps given the optimal selective biodelignification treatment makes further future studies worthwhile. (Abstract shortened with permission of author.)... |
