Effects of alkaline or liquid-ammonia treatment on crystalline cellulose: changes in crystalline structure and effects on enzymatic digestibility (original) (raw)
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Structural Changes and Reactivity of Cellulose after Alkaline Treatment
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Cellobiose and glucose are valuable products that can be obtained from enzymatic hydrolysis of cellulose. This study discusses changes in the crystalline form of celluloses to enhance the production of sugars and examines the effect on structural properties during enzymatic hydrolysis. Various crystalline celluloses consisting of group I (cell I, cell IIII, cell IVI) and group II (cell II, cell IIIII, cell IVII) of similar DPs were prepared as starting materials. The similar DP values allowed a more direct comparison of the hydrolysis yields. The outcomes were analyzed and evaluated based on the residues and supernatants obtained from the treatment. As a result: 1) action of the cellulase of Trichoderma viride decreased both DP and crystallinity, with greater changes in group II celluloses, 2) the polymorphic interconversion process that occurred for cell IIII, cell IVI, cell IIIII and cell IVII during the treatment was independent of the enzymatic hydrolysis, thus, the hydrolysis behaviors depended on the starting material of the celluloses, and 3) higher sugar production was obtained from cell IIII and group II. Therefore, the hydrolysis behavior of the various crystalline celluloses depended on the particular polymorph of the starting material.
Effect of Cellulose Structure on Enzymatic Hydrolysis
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Enzymatic hydrolysis of non-dried and dried cellulose samples having various particles size, degree of polymerization, porosity, crystalline polymorph, and content of non-crystalline domains has been studied. Regression analysis was carried out to determine contribution of various structural features of cellulose samples to their hydrolysability. It was found that particle size, degree of polymerization, and crystalline polymorph had a negligible influence on the conversion degree of cellulose into glucose under the effect of the cellulolytic enzyme. Such characteristics as the pores volume had a fair impact on the conversion degree of cellulose. Drying of the wet samples caused decreasing of the hydrolysability of cellulose due to irreversible collapse of the pores volume. The content of non-crystalline domains (A x) in cellulose had the highest effect on the rate of enzymatic hydrolysis and average conversion degree (α a) of cellulose into glucose. A linear dependence α a = f(A x) was established both for dried and non-dried cellulose samples.
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