Despite the structural, load‐bearing role of cellulose in the plant kingdom, countless efforts have been devoted to degrading this recalcitrant polysaccharide, particularly in the context of biofuels ...and renewable nanomaterials. Herein, we show how the exposure of plant‐based fibers to HCl vapor results in rapid degradation with simultaneous crystallization. Because of the unchanged sample texture and the lack of mass transfer out of the substrate in the gas/solid system, the changes in the crystallinity could be reliably monitored. Furthermore, we describe the preparation of cellulose nanocrystals in high yields and with minimal water consumption. The study serves as a starting point for the solid‐state tuning of the supramolecular properties of morphologically heterogeneous biological materials.
Vapor over the cracks: The adsorption of hydrogen chloride vapor on water‐covered cellulose microfibrils results in rapid degradation and increased crystallinity without a change in fiber morphology. This process constitutes an example of supramolecular tuning of native biological materials directly in the solid state.
X-ray scattering methods allow efficient characterization of cellulosic materials, but interpreting their results is challenging. By creating molecular dynamics models of cellulose microfibrils and ...calculating the scattering from them, we investigated how different properties of the structures affect their scattering intensities. We studied the effects of hemicelluloses and crystal size on small-angle and wide-angle X-ray scattering (SAXS, WAXS). Microfibril models with and without surface-bound hemicelluloses were built based on the chemical composition of spruce secondary cell walls. The effect of fibril size was investigated by comparing the scattering from fibrils with 14 to 40 cellulose chains. The hemicelluloses appeared in the SAXS region as an increase in the fibril radius and as a clear contribution of a shell around the fibril. The hemicelluloses also increased the crystal size as determined from the broadening of the 200 diffraction peak of cellulose
I
β
. The SAXS and WAXS analysis provided consistent estimates for the size of the microfibrils, and their special features and challenges were discussed. In particular, the results of 18-chain microfibrils were consistent with prior experimental results. Carrying out the simulations in wet and dry environments had the most pronounced effect on fibrils with a hemicellulose coating. Twisting of the fibril had very little impact on most properties, except for a minor effect on the WAXS peaks. The results allow for more correct interpretation of experimental scattering results, leading to more accurate descriptions of microfibril structures in natural and processed cellulosic materials.
Small‐angle scattering methods allow an efficient characterization of the hierarchical structure of wood and other cellulosic materials. However, their full utilization would require an analytical ...model to fit the experimental data. This contribution presents a small‐angle scattering model tailored to the analysis of wood samples. The model is based on infinitely long cylinders packed in a hexagonal array with paracrystalline distortion, adapted to the particular purpose of modelling the packing of cellulose microfibrils in the secondary cell wall of wood. The new model has been validated with small‐angle neutron and X‐ray scattering data from real wood samples at various moisture contents. The model yields reasonable numerical values for the microfibril diameter (2.1–2.5 nm) and packing distance (4 and 3 nm in wet and dry states, respectively) and comparable results between the two methods. It is particularly applicable to wet wood samples and allows changes in the packing of cellulose microfibrils to be followed as a function of moisture content.
A small‐angle scattering model for wood is presented and its capabilities for studying the nanoscale structure and moisture behaviour of wood are demonstrated.
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► Fibrillated cellulose with varying xylan content was hydrolysed with enzymes. ► Xylanase pre-hydrolysis removed the easily accessible and less bound xylan fraction. ► Crystalline ...cellulose was poorly hydrolysed in substrates with original xylan content. ► Enzymes acted efficiently and simultaneously in substrates with reduced xylan content.
The role of xylan as a limiting factor in the enzymatic hydrolysis of cellulose was studied by hydrolysing nanocellulose samples prepared by mechanical fibrillation of birch pulp with varying xylan content. Analyzing the nanocelluloses and their hydrolysis residues with dynamic FT-IR spectroscopy revealed that a certain fraction of xylan remained tightly attached to cellulose fibrils despite partial hydrolysis of xylan with xylanase prior to pulp fibrillation and that this fraction remained in the structure during the hydrolysis of nanocellulose with cellulase mixture as well. Thus, a loosely bound fraction of xylan was predicted to have been more likely removed by purified xylanase. The presence of loosely bound xylan seemed to limit the hydrolysis of crystalline cellulose, indicated by an increase in cellulose crystallinity and by preserved crystal width measured with wide-angle X-ray scattering. Removing loosely bound xylan led to a proportional hydrolysis of xylan and cellulose with the cellulase mixture.
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•Composites of bacterial cellulose and wood hemicelluloses were hydrolysed by enzymes.•Presence of hemicelluloses, especially xylan, increased the hydrolysis of cellulose.•Small-angle ...X-ray scattering was used to follow the hydrolysis in situ.•The results demonstrated the important role of cellulose nanostructure.
The production of biofuels and other chemicals from lignocellulosic biomass is limited by the inefficiency of enzymatic hydrolysis. Here a biomimetic composite material consisting of bacterial cellulose and wood-based hemicelluloses was used to study the effects of hemicelluloses on the enzymatic hydrolysis with a commercial cellulase mixture. Bacterial cellulose synthesized in the presence of hemicelluloses, especially xylan, was found to be more susceptible to enzymatic hydrolysis than hemicellulose-free bacterial cellulose. The reason for the easier hydrolysis could be related to the nanoscale structure of the substrate, particularly the packing of cellulose microfibrils into ribbons or bundles. In addition, small-angle X-ray scattering was used to show that the average nanoscale morphology of bacterial cellulose remained unchanged during the enzymatic hydrolysis. The reported easier enzymatic hydrolysis of bacterial cellulose produced in the presence of wood-based xylan offers new insights to overcome biomass recalcitrance through genetic engineering.
Wood and other cellulosic materials are highly sensitive to changes in moisture content, which affects their use in most applications. We investigated the effects of moisture changes on the nanoscale ...structure of wood using X-ray and neutron scattering, complemented by dynamic vapor sorption. The studied set of samples included tension wood and normal hardwood as well as representatives of two softwood species. Their nanostructure was characterized in wet state before and after the first drying as well as at relative humidities between 15 and 90%. Small-angle neutron scattering revealed changes on the microfibril level during the first drying of wood samples, and the structure was not fully recovered by immersing the samples back in liquid water. Small and wide-angle X-ray scattering measurements from wood samples at various humidity conditions showed moisture-dependent changes in the packing distance and the inner structure of the microfibrils, which were correlated with the actual moisture content of the samples at each condition. In particular, the results implied that the degree of crystalline order in the cellulose microfibrils was higher in the presence of water than in the absence of it. The moisture-related changes observed in the wood nanostructure depended on the type of wood and were discussed in relation to the current knowledge on the plant cell wall structure.
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In this paper, the significance of xylan on the behaviour of kraft birch pulp based nanofibrillated cellulose (CNF) is discussed. The influence of CNF xylan content on fibril morphology, charge and ...stability as well as on the film formation ability was investigated, and the features detected on nanoscale and on macroscale are compared. In addition to this, the ability of fibrils to uptake water molecules were investigated by bulk and surface sensitive methods which are dynamic water sorption analysis (DVS) and quartz crystal microbalance with dissipation monitoring (QCM-D) equipped with the humidity module, respectively. Surface xylan plays a significant role as an electrosteric stabilizer in dilute CNF dispersions when the surface forces are dominant whereas the removal of xylan drastically changes the CNF dispersion properties. The settling of the unstable CNF dispersions displays behaviour which is typical for hindered sedimentation. When considering thin nanoscale layers of CNF, nanofibrillated cellulosic materials with high content of surface xylan has somewhat higher ability to bind water molecules. However, it seems that in more concentrated CNF dispersions where the fibrillar network itself plays also a decisive role, especially with respect to film formation ability, the impact of xylan diminishes. Solvent cast macroscale CNF films are still enough dense to maintain good oxygen barrier performance at higher humid conditions although agglomeration tendency of fibrils is higher due to the excessive xylan removal. These findings are of high relevance when considering nanocellulosic materials, especially in the form of gels and films, as templates for high added value material solutions.
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