Cellulose is the most abundant renewable biopolymer in the World and cellulosic pulp fibers have excellent mechanical properties which are utilized in various products. However, the low solubility of cellulose in conventional solvents and its tight crystal structure limit the reactivity of cellulosic fiber materials for many applications. Certain ionic liquids are known to dissolve cellulose, or to swell cellulose when appropriately diluted with water, which may offer a new means for activating the fiber surface structures. Likewise, endoglucanase treatments of pulp fibers are also known to increase their reactivity in e.g. the viscose process and to reduce ballooning during dissolution. In our work, we have studied the combination of ionic liquid and endoglucanase treatments of a dissolving grade pulp and a bleached kraft pulp.<br/>In the first part of the work, different endoglucanases, representing different endoglucanase families and of different thermostability, were screened in a set of seven cellulose-swelling or –dissolving ionic liquids for ionic liquid tolerance. Several combinations of ionic liquid type and endoglucanase were found which allowed a relatively high endoglucanase activity in the screened 15 and 40 % ionic liquid solutions. The ionic liquids were also tested as fiber swelling and dissolving solvents.<br/>In the second part of the work, sequential ionic liquid and endoglucanase treatments were attempted on the studied pulps. The degree of hydrolysis, depolymerization, water retention value and fiber characteristics as analyzed by a fiber analyzer were determined for the pulp samples. As a measure of reactivity, the dissolution speed and mechanism were studied in CED solution. As a further measure of chemical reactivity, the degree of oxidation by reaction with TEMPO+ was studied. Overall, few synergistic effects were observed for sequential ionic liquid and endoglucanase treatments under the applied conditions. The endoglucanase treatments were effective in increasing the pulp dissolution speed, but the enzyme dosage needed to be carefully optimized to avoid excessive hydrolysis losses of the pulp. Ionic liquid treatments generally had slightly increasing or neutral effects on the water retention value, whereas the endoglucanase treatments clearly decreased this parameter.

Combined enzymatic-ionic liquid treatments to increase the accessibility and reactivity of pulp fibers

253rd National Meeting (2017)

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