The functional characteristics of plant cell walls depend on the composition of the cell wall polymers, as well as on their highly ordered architecture at scales from a few nanometres to several microns. Raman spectra of wood acquired with linear polarized laser light include information about polymer composition as well as the alignment of cellulose microfibrils with respect to the fibre axis (microfibril angle). By changing the laser polarization direction in 3° steps, the dependency between cellulose and laser orientation direction was investigated. Orientation-dependent changes of band height ratios and spectra were described by quadratic linear regression and partial least square regressions, respectively. Using the models and regressions with high coefficients of determination (R2 > 0.99) microfibril orientation was predicted in the S1 and S2 layers distinguished by the Raman imaging approach in cross-sections of spruce normal, opposite, and compression wood. The determined microfibril angle (MFA) in the different S2 layers ranged from 0° to 49.9° and was in coincidence with X-ray diffraction determination. With the prerequisite of geometric sample and laser alignment, exact MFA prediction can complete the picture of the chemical cell wall design gained by the Raman imaging approach at the micron level in all plant tissues.

No abstract

No abstract

Lignin-phenol-formaldehyde (LPF) resoles were prepared using different types of lignin at various levels of phenol replacement by lignin (0 to 40 wt.%). Adhesive properties including thermal behavior as determined by differential scanning calorimetry (DSC), time-dependent development of bond strength during hot pressing as determined by automated bonding evaluation system (ABES), tensile shear strength of solid beech wood lapjoints, and free formaldehyde content of the adhesives were investigated. Preparation of phenol-formaldehyde (PF) resole was accomplished using molar ratios of formaldehyde/phenol and NaOH/phenol of 2.5 and 0.3, respectively. Four different types of technical lignins were studied: Sarkanda grass soda lignin, wheat straw soda lignin, pine kraft lignin, and beech organosolv lignin. The synthesis of the resoles was optimized for 20 and 40 wt.% phenol replacement by lignin. Increasing substitution of phenol resulted in faster gain of LPF viscosity for all studied lignins. The best curing performances of the LPF resoles were observed for pine kraft lignin at both 20 and 40% phenol replacement. The amount of formaldehyde not consumed during cooking increased with increasing level of phenol replacement. However, no differences in free formaldehyde content were observed between the different lignin samples at comparable levels of phenol replacement.

Hardness and elastic modulus of spruce wood cell walls parallel to their axial direction were investigated by means of nanoindentation. In the secondary cell wall layer S2 of individual earlywood and compression wood tracheids, a systematic pattern variability was found. Several factors potentially affecting nanoindentation results were investigated, i.e. specimen orientation related to the indenter tip, cutting direction during specimen preparation, tip geometry, specimen and fibre inclination, respectively, and finally micro fibril orientation. Mechanical property measurements were correlated with structural features measured by confocal Raman spectroscopy. It was demonstrated that very high variability in the measurement of micromechanical cell wall properties can be caused by unintentional small fibre misalignment by few degrees with regard to the indentation direction caused by sub-optimal specimen preparation.

Three-dimensional scaffolds (3D) with controlled shape, dual porosity and long-term mechanical and dimensional stability in biofluids are of interest as biotemplates in tissue engineering. Herein, self-standing and lightweight cellulose-based biogenic scaffolds with a spatially structured morphology, macropores and interconnected micropores were fabricated using a combination of direct ink writing 3D printing and freeze-drying techniques. This was achieved by developing a water-based and low-cost bicomponent ink based on commercially available nanofibrillated cellulose (NFC) and carboxymethyl cellulose (CMC). Physical cross-linking through dehydrothermal treatment significantly increased the surface hardness, indentation modulus, compression strength, as well as the dimensional stability of the scaffolds in biofluids, in comparison to untreated materials. However, no differences in the spectra of solid state nuclear magnetic resonance or infrared were observed for dehydrothermal treated samples, suggesting that the increase of mechanical properties and dimensional stability is based on the physical cross-linking of functional groups both at the interface between NFC and CMC. The supramolecular structure of the polymers was well-preserved as disclosed by X-ray diffraction measurements. The cross-linked scaffolds showed high proliferation, viability, and attachment of human bone tissue derived osteoblast cells (hFOB). The simple and straightforward avenue proposed here for the design of cellulose-based fibrous inks and dual porous scaffolds from the commercially available materials and without the need of any additional cross-linkers should pave the way for the development of implantable, degradable scaffolds and cell-laden biomaterials for bone tissue regeneration and 3D bioprinting applications.

Hydroxymethylfurfural (HMF) is a high‐value platform chemical derived from renewable resources. In recent years, considerable efforts have been made to produce HMF also at industrial scale, which still faces some challenges regarding yield as well as sustainable and economic process designs. This critical Review evaluates the industrial process development of sustainable biomass conversion to HMF. Qualitative and quantitative guidelines are defined for the technological assessment of the processes described in patent literature. The formation of side products, difficulties in the separation and purification of HMF as well as catalyst regeneration were identified as major challenges in the HMF production. A first small‐scale, commercial HMF production plant with a capacity of 300 t HMF per year has been operating in Switzerland since 2014.

The aim of this study was to observe the radial shrinkage of Norway spruce [Picea abies (L. Karst.)] trunkwood specimens with different hydraulic vulnerability to cavitation from the fully saturated state until the overall shrinkage reaches a stable value, and to relate wood shrinkage and recovery from shrinkage to cavitations of the water column inside the tracheids. Radial shrinkage processes in standard-size sapwood specimens (6 mm x 6 mm x 100 mm; radial, tangential and longitudinal) obtained at different positions within the trunk, representing different ages of the cambium, were compared. Cavitation events were assessed by acoustic emission (AE) testing, hydraulic vulnerability by the AE feature analysis and shrinkage was calculated from the changes in contact pressure between the 150 kHz AE transducer and the wood specimen. Two shrinkage processes were observed in both juvenile (annual rings 1 and 2) and mature wood (annual rings 17-19), the first one termed tension shrinkage and the second one cell wall shrinkage process, which started when most of the tracheids reached relative water contents below fiber saturation. Maximum tension shrinkage coincided with high-energy AEs, and the periods of shrinkage recovery could be traced to tension release due to cavitation. Juvenile wood, which was less sensitive to cavitation, had lower earlywood tracheid diameters and was less prone to deformation due to tensile strain than mature wood, showed a lower cell wall shrinkage, and thus total shrinkage. Earlywood lumen diameters and maximum tension shrinkage were strongly positively related to each other, meaning that bigger tracheids are more prone to deformation at the same water tension than the smaller tracheids.