Volume 70, Issue 10

Birch samples were subjected to non-isothermal autohydrolysis to obtain a solution of hemicellulosic saccharides and a solid phase mainly made up of cellulose and lignin. Based on kinetic modeling, operational conditions were identified which give rise to soluble saccharides and furfural derived from xylan in a yield of 80.5%. The soluble mixture was supplemented with 1% sulfuric acid and heated (directly or in the presence of methyl isobutyl ketone, MIBK) for furfural production. MIBK is used as an extraction agent to limit furfural consumption by side reactions. Operating in single phase at 170°C, up to 44.8% of the potential substrates were converted into furfural. In experiments performed in biphasic media, the effects of MIBK were assessed by empirical modeling and about 75% of the potential substrates were converted under selected conditions.

The potential of halogen-free and imidazolium-free phosphonium-based amino acid ionic liquids (AAILs) has been investigated as new solvents for cellulose pretreatment for the subsequent enzymatic hydrolysis of cellulose. AAILs alone did not dissolve cellulose (Avicel), even at 120°C. However, when polar solvents such as dimethylsulfoxide (DMSO) were added as cosolvents, AAILs became an acceptable solvent for cellulose at 30°C. The solubility of cellulose in tetrabutylphosphonium glycine ([TBP][Gly])/cosolvent reached 15%. The enzymatic hydrolysis of cellulose was dramatically enhanced by pretreatment with AAIL/cosolvent, and the glucose yield reached 100% when the novel AAIL tetrabutylphosphonium N , N- dimethylglycine ([TBP][DMGly]) was used in combination with DMSO as cosolvent. The enzymatic conversion of cellulose to glucose in 6% and 13% [TBP][DMGly]/DMSO buffer solutions reached 98% and 79%, respectively. The decrease in cellulase activity owing to residual [TBP][DMGly]/DMSO was not significant. Hence, it is possible to conduct the dissolution and enzymatic hydrolysis of cellulose in a one-batch process in a phosphonium-based AAIL/cosolvent system.

Polyethylene glycol (PEG) treatment is an effective approach to endow wood with higher dimensional stability (DS), which is still a concern under humid conditions. In this study, poplar wood was first treated with methacryloyl chloride to introduce methacryl groups in the cell wall. Then functional PEG served as modifier, and copolymerization was conducted in the second step to prepare PEG-diacrylate (PEGDA) modified samples. The resultant wood polymer composites (WPCs) were characterized by solid state NMR, field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD). The physical and mechanical properties of the WPCs were also evaluated, such as anti-swelling efficiency (ASE), water uptake, dynamic hydrophilicity (contact angles), and thermal stability. The results show that the copolymerized WPC achieved 51.4% ASE with leaching <3.0%. Moreover, the surface hardness and water resistance of the wood are also greatly improved.

A formaldehyde-free adhesive has been developed from defatted lupine flour (defLF), glycerol, and a novel curing agent (CA). The CA was prepared from reactions of epichlorohydrin (ECH) and 3-(dimethylamino)-1-propylamine (DMAPA) and characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance ( 1 H NMR) spectroscopies. The adhesive has a low viscosity of 472 cP at a total solids content (SC) of 60% and could be easily applied onto wood particles for the production of particleboards (PBs). The internal bond (IB) strength, modulus of rupture (MOR), and modulus of elasticity (MOE) of the resulting PBs exceeded the industrial requirements. The adhesive with defLF/glycerol/CA mass ratio of 2:4:3 led to the best overall properties of the resulting PBs. The curing mechanisms of the adhesive were mainly attributed to the reactions between lupine protein and the CA.

Phosphorylated kraft lignin (PKL), a novel lignin polymer, has potential application in the preparation and modification of inorganic materials. In this article, the adsorption characteristics of PKL at the solid/liquid interface were investigated under different pH conditions. Quartz crystal microbalance combined with dissipation monitoring (QCM-D), UV spectroscopy, and atomic force microscopy (AFM) were applied for monitoring the adsorption. The adsorbed amount of PKL gradually decreased as a function of pH increment on the gold covered QCM-D crystals, which were pretreated with an adsorbed layer of poly(diallyldimethylammonium chloride) (PDAC). This was also the case for quartz slide substrates pretreated with PKL/PDAC multilayers by the method relying on the layer-by-layer (LBL) electrostatic self-assembly. The hydrophobicity of adsorbed PKL films increased with increasing pH from 3 to 12. In the course of this process, the adsorption morphology changed from a compact rigid state to a less compact soft state. Under acidic conditions, the adsorption is governed mainly by cation-π interaction between PKL and PDAC, and the adsorption configuration is mushroom-like. Under neutral and alkaline conditions, the cation-π interaction is less relevant owing to the longer distances between the anionic groups in PKL and the cation in PDAC. This causes stretching of the molecular chains in PKL, while the adsorption configuration changes to a planar pancake structure so that the electrostatic interaction dominates. The knowledge on adsorption characteristics of PKL at different pH values is helpful to prepare some lignin-based composite materials.

Modified wood can provide protection against a range of wood deteriorating organisms. Several hypotheses have been put forward regarding the protection mechanisms against wood decaying fungi including fungal enzyme inefficiency due to non-recognition, lower micropore size, and insufficient wood moisture content. The aim of this study was to obtain new insight into the protection manner of furfuryl alcohol (FA) modified Scots pine sapwood (W FA ), and to examine biochemical mechanisms and adaptive changes in gene expression utilised by Postia placenta during early colonisation of W FA . Samples were harvested after 2, 4, and 8 weeks of incubation. After 8 weeks, the mass loss (0.1%) and wood moisture content (21.0%) was lower inW FA , than in non-modified Scots pine sapwood samples (W), 26.1% and 46.1%, respectively. Microscopy revealed needle-shaped calcium oxalate crystals, at all harvesting points, most prominently present after 4 and 8 weeks, and only in the W FA samples. Among the findings based on gene profiles were indications of a possible shift toward increased expression, or at least no down regulation, of genes related to oxidative metabolism and concomitant reduction of several genes related to the breakdown of polysaccharides in W FA compared to W.

The equilibrium moisture content (EMC) of a wood specimen is known to be a function of the (absolute) temperature T and humidity h of the environment. In the present paper, it is directly derived from equilibrium thermodynamics that EMC is more specifically a function of the water chemical potential μ = RT ln h (Polanyi’s postulate). It is shown that wood moisture thermodynamics then becomes considerably simplified, allowing the calculation of the energy of wood-water interactions from the data of a single-temperature moisture adsorption. A critical comparative analysis on the theoretically calculated adsorption enthalpy and published data, obtained from isosteric and calorimetric measurements, is given. It is deduced from the theory that all bound moisture is non-freezing and that the heat capacities of bound and free wood moisture are equal.

European beech ( Fagus sylvatica L.) was thermally modified in a closed reactor system under various process conditions. Sorption cycles, dynamic vapor sorption (DVS) measurements, and a three-point bending test were performed on thermally modified wood (TMW) to assess hygroscopicity and mechanical properties. As a function of mass loss (ML), the initial equilibrium moisture content (EMC) measured at 20°C/65% relative humidity (RH) directly after the process was strongly influenced by the RH during the process. This effect is explained by realignments of amorphous polymers in the cell wall ultra-structure in the course of thermal modification (TM). However, the EMC of TMW gradually increased after sorption cycles consisting of conditioning over liquid water and water-soaking. This increase was most distinct for TMW modified at low RH, which is an indication for reversible ultra-structural realignments. Results of the bending test suggest that structural realignments also hindered the plastic flow of amorphous cell wall polymers, thereby reducing inelastic toughness and inelastic deflection, while other bending properties were solely affected by ML alone. Process conditions in a closed reactor systems have a profound impact on resulting wood properties, and thus, the partial reversibility of these property changes need to be considered during the application.

An integral calculation method (ICM) is presented for fully estimating the fiber orientation and fundamental physical and mechanical properties of softwood (SW) logs and lumber. The proposed ICM reproduces with great detail the most important anatomical features of SW, including annual rings, seasonal variations, main growth patterns (straight, spiral, and interlocked grain), and especially fiber distortions due to knot clusters for each annual ring. The failure load of the lumber has been predicted with an absolute error of 10.2%. In addition, the ICM has shown very strong robustness and high calculation speed as most of the calculations are performed analytically, and only one final simplistic computation is conducted by finite element analysis (FEA). This article describes the proposed ICM in detail and shows the initial verification with experiments. The ICM should contribute not only to lumber research and grading but also to research and optimization of logging and sawing industrial processes.

The tension wood (TW) of Tilia cordata (lime tree) does not contain gelatinous fibers. Based on anatomical studies of secondary phloem (secPhl) and xylem by means of microscopy, digital imaging, and biomechanical tests, it was hypothesized that there is an interaction between the phloem and xylem as a response of gravitropic forces on lateral branches. The goal of the present study was to check this hypothesis. The results demonstrated that dilated phloem rays are longer and wider on the upper side (US) of a branch compared to the lower side (LS) and that the ratio of fiber/ray parenchyma in the phloem is lower on the US of the branches. Bark strips consisting of secPhl with periderm have higher elastic modulus (MOE) on the US of branches. The results support the hypothesis that the compression stress of ray parenchyma may cause phloem fibers to stretch, which may result in the development of axial tensile stresses that are higher on the US of branches. However, the wider rings of xylem formed on the US of branches and the results of biomechanical tests can be interpreted that a higher MOE of wood in the US of lateral branch are the main factors responsible for gravitropic reaction of Tilia branches. TW can be considered as a kind of biotensegrity.