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Wood is an increasingly important material in the sustainable transition of societies worldwide. The performance of wood in structures is intimately tied to the presence of moisture in the material, which directly affects important characteristics such as dimensions and mechanical properties, and indirectly its susceptibility to fungal decomposition. By chemical modification, the durability of wood in outdoor environments can be improved by reducing the amount of moisture present. In this study, we refined a well-known chemical modification with acetic anhydride and showed how the spatial distribution of the modification of Norway spruce (Picea abies (L.) Karst.) could be controlled with the aim of altering the wood-water interactions differently in different parts of the wood structure. By controlling the reaction conditions of the acetylation it was possible to acetylate only the cell wall-lumen interface, or uniformly modify the whole cell wall to different degrees. The spatial distribution of the acetylation was visualised by confocal Raman microspectroscopy. The results showed that by this targeted acetylation procedure it was possible to independently alter the wood-water interactions in and outside of cell walls. The cell wall-lumen interface modification altered the interaction between the wood and the water in cell lumina without affecting the interaction with water in cell walls while the uniform modification affected both. This opens up a novel path for studying wood-water interactions in very moist environments and how moisture distribution within the wood affects its susceptibility towards fungal decomposition.

Lignocellulose breakdown in biorefineries is facilitated by enzymes and physical forces. Enzymes degrade and solubilize accessible lignocellulosic polymers, primarily on fiber surfaces, and make fibers physically weaker. Meanwhile physical forces acting during mechanical agitation induce tearing and cause rupture and attrition of the fibers, leading to liquefaction, that is, a less viscous hydrolysate that can be further processed in industrial settings. This study aims at understanding how mechanical agitation during enzymatic saccharification can be used to promote fiber attrition. The effects of reaction conditions, such as substrate and enzyme concentration on fiber attrition rate and hydrolysis yield were investigated. To gain insight into the fiber attrition mechanism, enzymatic hydrolysis was compared to hydrolysis by use of hydrochloric acid. Results show that fiber attrition depends on several factors concerning reactor design and operation including drum diameter, rotational speed, mixing schedule, and concentrations of fibers and enzymes. Surprisingly, different fiber attrition patterns during enzymatic and acid hydrolysis were found for similar mixing schedules. Specifically, for tumbling mixing, slow continuous mixing appears to function better than faster, intermittent mixing even for the same total number of drum revolutions. The findings indicate that reactor design and operation as well as hydrolysis conditions are key to process optimization and that detailed insights are needed to obtain fast liquefaction without sacrificing saccharification yields.

Enzymes and mechanics play major roles in lignocellulosic biomass deconstruction in biorefineries by catalyzing chemical cleavage or inducing physical breakdown of biomass, respectively. At industrially relevant substrate concentrations mechanical agitation is also a driving force for mass transfer as well as agglomeration of elongated biomass particles. Contrary to the physically induced particle attrition, which typically facilitates feedstock handling, particle agglomeration tends to hinder mass transfer and in the worst case induces processing difficulties like pipe blockage. Understanding the complex interplay between mechanical agitation and enzymatic degradation during hydrolysis is therefore critical and was the aim of this study. Particle size analyses revealed that neither mechanical agitation alone nor enzymatic treatment without mechanical agitation had any noteworthy effect on flax fiber attrition. Similarly, successive treatment, where mechanical agitation was either preceded or proceeded by enzymatic hydrolysis, did not induce any substantial segmentation of flax fibers. Simultaneous enzymatic and mechanical treatment on the other hand was found to promote fast fiber shortening. Higher hydrolysis yields, however, were obtained from nonagitated samples after prolonged enzymatic treatment, indicating that mechanical agitation in the long run reduces activity of the cellulolytic enzymes.

Accelerated lignocellulosic biomass degradation, depending on its application, can be both beneficial as well as undesirable. Enhanced degradation of bio-based materials, e.g. wood structures, may substantially reduce their service life and therefore is unwanted. Fast lignocellulose fractionation to soluble sugars, on the other hand, is particularly advantageous in biorefineries, where the efficient lignocellulose depolymerisation is central. Lignocellulose degradation, occurring in nature or driven in biorefineries, is a highly complex process where a number of biotic and abiotic factors may contribute to the degradation in a confounded way. Simultaneous exposure to several degrading factors, for instance, could potentially synergistically accelerate degradation of plant biomass. This study investigated the interrelationship between mechanics and enzymes in degradation of two substantially different lignocellulosic biomass materials, namely flax (Linum usitatissimum L.) fibres and Scots pine (Pinus sylvestris L.) veneers. Mechanical and enzymatic treatments were applied either individually, simultaneously or in a sequential manner, where enzymatic hydrolysis was preceded or proceeded by mechanical treatment. During the enzymatic hydrolysis of flax fibres, mechanical treatment was also applied interruptedly. In addition, factors which potentially enhance physical fibre breakdown (i.e. agitation intensity, type of agitation) as well as impact enzymatic catalysis rate (i.e. enzyme concentration, solid loading) were investigated. To learn more about the enzymatic breakdown of lignocellulose (e.g. enzyme specificity), hydrochloric acid, instead of enzymes was used to mitigate flax fibre attrition during mechanical treatment. This study showed for the first time that there is a synergistic effect between enzymatic and mechanical degradation on solid wood. For individual fibres, mechanical forces as well as enzyme concentration and solid loading were found to cons