Raman micro-spectroscopy of two types of acetylated Norway spruce wood at controlled relative humidity.

Water is a key element for wood performance, as water molecules interact with the wood structure and affect important material characteristics such as mechanical properties and durability. Understanding wood-water interactions is consequently essential for all applications of wood, including the design of wood materials with improved durability by chemical modification. In this work, we used Raman micro-spectroscopy in combination with a specially designed moisture chamber to map molecular groups in wood cell walls under controlled moisture conditions in the hygroscopic range. We analyzed both untreated and chemically modified (acetylated to achieve two different spatial distributions of acetyl groups within the cell wall) Norway spruce wood. By moisture conditioning the specimens successively to 5, 50, and 95% relative humidity using deuterium oxide (D2O), we localized the moisture in the cell walls as well as distinguished between hydroxyl groups accessible and inaccessible to water. The combination of Raman micro-spectroscopy with a moisturizing system with deuterium oxide allowed unprecedented mapping of wood-water interactions. The results confirm lower moisture uptake in acetylated samples, and furthermore showed that the location of moisture within the cell wall of acetylated wood is linked to the regions where acetylation is less pronounced. The study demonstrates the local effect that targeted acetylation has on moisture uptake in wood cell walls, and introduces a novel experimental set-up for simultaneously exploring sub-micron level wood chemistry and moisture in wood under hygroscopic conditions.

Hydration and dehydration induced changes in porosity of starch microspheres.

Characterization and tuning of the porosity of amorphous starch materials are important for many applications, including controlled release of encapsulated proteins. The porosities of these materials in dry and hydrated states can have different physicochemical origins and properties. Here, porosities of dry cross-linked starch microspheres and their hydration-induced transformations were characterized by small angle X-ray scattering, scanning electron and optical microscopies, thermogravimetric analysis, sorption calorimetry, nitrogen sorption, and helium-pycnometry. The analyses revealed that dry microspheres consist of porous cores with pore diameters below 100 nm and shells which appeared to be denser but contained wider pores (100-300 nm). The outer crust of the microspheres shell is non-porous, which restricts diffusion of nitrogen, water, and ethanol. Partial hydration triggered an irreversible collapse of dry porosity at 12 wt% water. Further hydration resulted in interfacial changes and promoted wet porosity, related to characteristic distances between polymer chains.

Investigating the role of mechanics in lignocellulosic biomass degradation during hydrolysis: Part II.

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.

How much water can wood cell walls hold? A triangulation approach to determine the maximum cell wall moisture content.

Wood is a porous, hygroscopic material with engineering properties that depend significantly on the amount of water (moisture) in the material. Water in wood can be present in both cell walls and the porous void-structure of the material, but it is only water in cell walls that affects the engineering properties. An important characteristic of wood is therefore the capacity for water of its solid cell walls, i.e. the maximum cell wall moisture content. However, this quantity is not straight-forward to determine experimentally, and the measured value may depend on the experimental technique used. In this study, we used a triangulation approach to determine the maximum cell wall moisture content by using three experimental techniques based on different measurement principles: low-field nuclear magnetic resonance (LFNMR) relaxometry, differential scanning calorimetry (DSC), and the solute exclusion technique (SET). The LFNMR data were furthermore analysed by two varieties of exponential decay analysis. These techniques were used to determine the maximum cell wall moisture contents of nine different wood species, covering a wide range of densities. The results from statistical analysis showed that LFNMR yielded lower cell wall moisture contents than DSC and SET, which were fairly similar. Both of the latter methods include factors that could either under-estimate or over-estimate the measured cell wall moisture content. Because of this and the fact that the DSC and SET methods are based on different measurement principles, it is likely that they provide realistic values of the cell wall moisture content in the water-saturated state.

Investigating the role of mechanics in lignocellulosic biomass degradation during hydrolysis.

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. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2754, 2019.