Scholarly record
INFLUENCE OF WOOD PULP DRYING ON THEIR ENZYMATIC HYDROLYSIS REACTIVITY
Abstract
Kraft and sulphite wood pulps are good substrates for enzymatic sugars production. Drying is a necessary step in commercial pulp, cardboard and paper products manufacturing. During drying significant changes occur in the structure of cellulose fibers. It is associated with compression and hornification processes, which have a significant effect on fiber properties. The aim of the work was to evaluate the effect of wood pulp drying on its enzymatic hydrolysability. Softwood and hardwood kraft pulps, softwood sulphite pulp and softwood dissolving-grade sulphite pulp were used for 48-hour enzymatic hydrolysis. A new enzymatic preparation of glycosyl hydrolase from the Penicillium verruculosum was used at 10 FPU/g of pulp dosage. Unbleached and ECF-bleached pulp samples were tested in dried and never-dried conditions. Never-dried unbleached hardwood and softwood kraft pulps conversion degree was 7 ... 11 % lower in comparison with bleached samples. The enzymatic hydrolysis effect was reduced due to the lingo-carbohydrate complexes presence in kraft fibers outer layers. Drying significantly reduced all samples reactivity. The decrease of conversion degree was 17 % for kraft and 33 % for sulphite unbleached softwood pulps. The effect of drying was much more pronounced for bleached softwood pulp. The reduction in conversion degree of 31 % for kraft and 44 % for sulphite pulp was noted. Thus, the presence of amorphous fragments of lignin even at a content of 2...3 % prevents the convergence of polysaccharides and the formation of intermolecular hydrogen bonds between cellulose macromolecules. As a result, the cellulose crystallization decreased after fibers drying. Dried hardwood kraft bleached pulp samples were less susceptible for hornification compared to softwood ones due to a higher xylan contents. The lowest conversion degree was detected for softwood dissolving-grade sulphite pulp. It had the highest cellulose contents and the minimum amount of non-cellulose components. Thus, it has been shown that drying reduces the enzymatic hydrolysis reactivity of most cellulosic substrates. It is expedient to use never-dried pulp samples for the enzymatic hydrolysis and to carry out the process at pulp mills. It makes possible to organize a more efficient processing of cellulose-containing raw materials, and producing highly valuable by-products.
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