Improved Reactivity of Cellulose via Its Crystallinity Reduction by Nondissolving Pretreatment with an Ionic Liquid

The improvement of the reactivity of cellulose by means of an efficient pretreatment method is critical for the optimal valorization of this biorenewable polymer within a biorefinery context. In this work, a nondissolving procedure for the pretreatment of cellulose, based on the direct solid-liquid contact of cellulose with an ionic liquid, namely tetrabutylphosphonium acetate, or with its mixtures with water or dimethyl sulfoxide, was found to lead to an effective reduction of the cellulose crystallinity. Due to the nondissolving nature of the method, the cellulose thus pretreated can be simply recovered by filtration from the pretreatment fluid. The use of the molecular cosolvents, as compared to the use of the neat ionic liquid, results in a less viscous pretreatment fluid and also in a larger reduction of the cellulose crystallinity. An improvement in the reactivity of the pretreated cellulose was evidenced via the determination of the kinetics of an enzymatic hydrolysis. A relationship between this reaction kinetics and the degree of crystallinity of the cellulose was inferred: the lower the crystallinity, the faster the hydrolysis. The thermal stability and degree of polymerization of the pretreated cellulose samples were comparable or essentially unaltered with respect to the untreated cellulose.