Accessibility and enzymatic degradation of native and model cellulose substrates

This thesis investigated two issues relevant to the bioconversion of lignocellulosic biomass. The first part relates to the accessibility of cellulose in wood, more specifically, the impact of initial drying on wood ultrastructure. The second part of this thesis pertains to the enzymatic hydrolysis of cellulose, including a characterization of a model film of amorphous cellulose and its subsequent utilization in a fundamental evaluation of the mechanism of cellulase action. In addition, the impact of cellulase treatment on the properties and the morphology of wood pulp fibers was evaluated. The impact of drying on the ultrastructure of fresh wood was studied by deuterium exchange coupled with FT-IR analysis. Initially, the experimental concept and its reliability were evaluated using fresh wood samples. The same experimental concept was then applied to study the impact of initial drying on wood pulps of different characteristics and composition. The objective was to correlate the trends in drying-induced alterations observed for wood and for pulps, bleached chemical pulp in particular. Drying-induced alterations of a native wood sample exhibited a remarkable similarity to those observed for wood pulp samples. The results suggest that the supramolecular rearrangements in the native wood matrix upon dehydration are qualitatively identical to the well-known changes occurring in pulp fibers after drying, although the changes are considerably different in quantity. Quantitative studies of cellulose degradation by cellulase enzymes were carried out using an amorphous cellulose model film with well-defined characteristics. First, the films were extensively characterized, particularly their crystalline nature and swelling behavior. The film swelled excessively in water, doubling its thickness, but returned to the original thickness upon water removal, while retaining its amorphous nature. This film was then used as a substrate in studying the action of monocomponent endoglucanase (EG) that acts on amorphous cellulose. The study was carried out using a quartz crystal microbalance with dissipation monitoring (QCMD). The main objectives were to study the impact of film thickness on the rate of hydrolysis and to directly quantify the extent of hydrolysis (decrease in thickness of films after hydrolysis). It was demonstrated that the amount of substrate available for hydrolysis did not have an impact on the rate of hydrolysis. The investigation also demonstrated impacts of various factors on the kinetic evaluation of the cellulase action. The investigation of the action of a commercial celobiohydrolase on wood pulp fibers showed that the treatment had no significant impact on the strength properties of the pulp. Changes of fiber morphology and of fracture type in the treated fibers during zero span evaluation,