Volume 69, Issue 3

Birch chips were cooked by means of the Lignofibre (LGF) organosolv process in acetic acid (AA) and phosphinic acid (H 3 PO 2 ) at 150°C. The delignification rate and structure of the dissolved lignin was followed as a function of time. The degree of delignification increased steadily up to 88% during the 120 min treatment time. The dissolved lignins were precipitated from the spent liquor (SL) by water addition, washed, and purified for the analyses. Elemental analysis, 31 P nuclear magnetic resonance (NMR), heteronuclear single-quantum coherence (HSQC) NMR, pyrolysis-gas chromatography/mass spectrometry (GC/MS), and gel permeation chromatography (GPC) were applied for the structural elucidation. It was found that the cleavage of the β-aryl ether linkages is the main reaction leading to delignification, accompanied by the formation of free phenolic hydroxyl groups and reduction in the content of aliphatic hydroxyl groups. The structure of the dissolved lignin remained the same after the drastic changes at the early stages of cooking (up to 30 min cooking time), indicating that secondary reactions (e.g., condensation) do not take place to a significant extent. H 3 PO 2 probably enhances the acidolysis reaction via an ester derivative that both boosts the cleavage reaction and prevents the formation of the carbocation intermediate that induces condensation. Homolytic cleavage reactions may take place parallel to the acidolytic reactions.

The chemical composition of black liquors obtained from the soda-AQ pulping of birch ( Betula pendula ) sawdust was studied as a function of cooking time, effective alkali content, and hot-water pretreatment of the sawdust prior to delignification. Special attention was paid on the formation of lignin-derived materials and low-molecular-mass carbohydrate-derived degradation products containing aliphatic carboxylic acids. In the case of the hot-water-pretreated feedstock, less acetic acid and formic acid and more nonvolatile hydroxy acids (especially monocarboxylic acids) were obtained. The observations can be interpreted as a result of the extensive removal of hemicelluloses during the hot-water pretreatment.

Concentrated sodium lignosulfonate (NaLS) solutions have wide industrial applications. Therefore, the viscoelastic properties of NaLS in concentrations of 55%–63% have been investigated between 5°C and 55°C by means of a dynamic rheological technique, namely, the oscillatory rheological experiments were conducted in a rheometer in the small amplitude oscillatory mode. All solutions showed “shear-thinning” behavior over frequency. The complex viscosity ( η *) increased and the loss tangent (tanδ) decreased with increasing concentrations. Both the storage modulus ( G ′) and the loss modulus ( G ″) increased with increasing frequencies and concentrations. The change in viscoelastic behavior was probably caused by stronger aggregation effects. However, the effects of temperature on the viscoelastic properties are more complex. For 60% NaLS, G ′, G ″, and η * decreased, but tanδ increased with increasing temperatures. When the temperature exceeded 20°C, G ′, G ″, and η * increased, but tanδ decreased, and the relaxation times were increased as a function of temperature. The change in viscoelasticity as a function of temperature may also be related to intermolecular aggregation and the swelling of aggregates. The conductivity experiments indicated that the formation of a greater strength of network structures at higher levels of concentrations between 55% and 63% and temperatures between 20°C and 55°C was probably responsible for elasticity enhancement.

Japanese cedar ( Cryptomeria japonica ) was treated with the ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which is a solvent for cellulose, and the changes in the chemical components and their distribution in wood cell walls have been investigated by Raman microscopy. Raman spectra, recorded from various areas of the cell walls, showed that lignin in the compound middle lamellae (CML) and cell corners (CC) was resistant to the reaction with [C2mim][Cl], but its molecular structure changed partially. The reactivity of cellulose and hemicelluloses with [C2mim][Cl] was higher than that of lignin in the cell wall, and the cell wall structure was maintained even in an advanced state of the reactions. The effects of [C2mim]-[Cl] on cellulose and hemicelluloses in the cell wall were homogeneous, whereas that of lignin was inhomogeneous.

The norlignan (NorL) is a class of secondary metabolites, which occurs in the heartwood (hW) of certain softwood species. Although the NorL is often assumed to be secondarily altered (e.g., oxidized and/or polymerized in the hW over time), the formation and the chemical structure of oxidized/polymerized products remained unclear. In this study, we focused on the question whether an NorL oligomer/polymer exists in the hW of Cryptomeria japonica . First, NorL model polymers were prepared by horseradish peroxidase-catalyzed oxidation and their chemical structures were investigated by size exclusion chromatography-high-performance liquid chromatography (SEC-HPLC), nuclear magnetic resonance (NMR), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Second, methanol (MeOH) extracted from the hW of C. japonica was fractionated, and one of the fractions contained NorL polymers as demonstrated by its chromatographic and spectrometric data in comparison with those of model polymers. Third, five kinds of agatharesinol (AGA) model dimers were synthesized and their chemical structures were determined. 13 C-NMR signals corresponding to the model dimer structures were observed in the NMR spectrum of the natural polymer fraction. In summary, an NorL polymer was found in the hW of C. japonica , and its preliminary chemical structure was proposed for the first time.

Industrially produced lignins are by-products of the pulp and paper industry and depending on the source and pulping technology they have deviating functional groups, solubility behavior and reactivity. In the present paper, kraft lignin was pretreated by mechanical milling and polyesterified with ε-caprolactone to create hydroxyl groups that are more easily available for further reactions. The products obtained were analysed by size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and functional group determination. The analytical data are presented as a function of reaction time, crosslinking reactions and the amount of ε-caprolactone input.

This work was aimed at applying vacuum-assisted resin transfer molding (VARTM) technique to reinforced polymer molding products made of vegetable fibers. Kenaf ( Hibiscus cannabinus L. Malvaceae) bast fibers were preformed into mat by means of a cold press. The unsaturated polyester resin was infused into the preforms at a vacuum pressure of 1.3–1.6 kPa. The examination of the mechanical properties and microstructure of the prepared composites indicated that the modulus of elasticity (MOE), modulus of rapture (MOR), and tensile strength (TS) of the VARTM composites were increased by 65.5%, 30.7%, and 41.7%, respectively, compared to the traditional hot-pressing composites. The dynamic mechanical analysis (DMA) revealed that the VARTM composite moduli in the temperature range of -50°C–200°C were doubled. The observations by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and mercury porosimetry confirmed that the interfacial compatibility between the kenaf fibers and the polyester resin was substantially improved.

Composites have been prepared with polypropylene (PP) as a matrix and pine flours, either thermally treated (W tr ) or not (W), as fillers resulting in wood plastic composites (WPCs). The treatment by retification at 280° mainly elevates the hydrophobicity of wood. The WPCs were fabricated with a co-rotating twin-screw extruder with the screw speeds of 500 and 1200 rpm and specimens were prepared by injection molding. Viscoelastic behavior, tensile test and Charpy impact test of W tr PC were compared with PP and WPC. W tr PC has a better dispersion and highest tensile modulus. As expected, a decrease in elongation at break and impact strength was observed for all composites. Processing at 1200 rpm improved by 60% the Young modulus of the WPC compared to 500 rpm, whereas 500 rpm was enough to obtain the highest modulus for W tr PC.

Numerical analysis of temperature profiles during thermal modification of wood was carried out. The numerical solution – based on finite element analysis, FEA – of the 3D problem of transient nonlinear heat transfer model is presented for wood as a typical anisotropic material. The numerical model was enhanced for describing chemical reactions of cellulose, hemicelluloses and lignin (pyrolysis model), which takes into account the exothermic reactions as an internal source of heat energy. Experimental as well as theoretical process schedules were applied and the influence of sample dimensions (sample geometry) and wood species was studied. The influence of wood species was negligible on heating time to reach the highest temperature, i.e., the temperature differences were about 2°C during the drying phase. A expected, the sample size played an important role in the heating duration and in terms of the exothermic reactions of wood. The experimental and numerical data are generally in good agreement. The numerical error increased in the range of higher temperatures. The results can be improved by consideration of wood species (mass of wood compounds) and boundary conditions in the pyrolysis model, thus, better insight into details of thermal modification of wood could be reached.

A fast online grading apparatus for sawn lumber based on near-infrared (NIR) spectroscopy has been developed. The method is based on a novel wavelength dispersive NIR spectrophotometer equipped with a diffraction grating linear sensor and high-intensity lighting. It was possible to acquire spectra from the entire surface of Hinoki cypress lumber sections traveling on a conveyor belt at a speed of 120 m min -1 . Additionally, predictive models for moisture content (MC) and modulus of elasticity (MOE) under various MC conditions were developed from the NIR spectra with the aid of partial least squares regression (PLSR) analysis. Both the MC and MOE predictive models demonstrated sufficient levels of prediction accuracy for use on high-speed conveyor belts, and the results of various experiments indicate that the developed device could be applied for the online quality certification of sawn lumber in commercial sawmills.

Laminated veneer lumber (LVL) is a well-known high-performance engineered wood product suitable for structural applications. However, the peeling process can induce lathe checks of the veneer with various depth and spatial frequencies. In this study, a finite element model (FEM) is proposed to describe and to analyze the influence of veneer lathe checks on the elastic properties of LVL. Firstly, the typical lathe check depths and frequencies were determined by means of different compression rates of the pressure bar when peeling. These experimental results served as input to the model to compare the influence of check depth and frequency on the elastic behavior of an LVL beam in four-point bending. The checks were modeled as free spaces in the cross-section that can be partially filled with glue. The results show that the longitudinal modulus of elasticity is marginally affected by checking, while the shear rigidity of the LVL beam is significantly reduced in edgewise bending if checks are not glued. Gluing checks, even under consideration of a low Young’s modulus of glue, highly reduces the effect of checking on the elastic mechanical properties of LVL.

Sawdust samples of ayous wood ( Triplochiton scleroxylon ) have been submitted to a warm pretreatment with NaOH and functionalized in dimethylformamide (DMF) by grafting with two amino organosilanes. The reagents were chosen for their ability to bind hydronium ions in acidic medium: 3-aminopropyltriethoxysilane (APTES) and 3-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS). The resulting materials were characterized by Fourier transform infrared (FTIR) and 13 C nuclear magnetic resonance (NMR) spectroscopies, which revealed the Si-O-C covalent bond and the polymerization of the grafted silanes through siloxane bridges (Si-O-Si) leading to the stabilization of the structure. The cyclic voltammetry analyses were performed on a glassy carbon modified with native or functionalized sawdust films in contact with electrochemical probes ([Fe(CN) 6 ] 3- and [Ru(NH 3 ) 6 ] 3+ ). By means of this method, the permselectivity and accumulation capacity of these functionalized materials could be evaluated. The presence of silanes in the functionalized sawdust leads to a progressive accumulation of anionic species, while the cationic species were repelled when the solution is gradually acidified.

Tensile tests on miniature spruce specimens have been performed by means of acoustic emission (AE) analysis. Stress was applied perpendicular (radial direction) and parallel to the grain. Nine features were selected from the AE frequency spectra. The signals were classified by means of an unsupervised pattern recognition approach, and natural classes of AE signals were identified based on the selected features. The algorithm calculates the numerically best partition based on subset combinations of the features provided for the analysis and leads to the most significant partition including the respective feature combination and the most probable number of clusters. For both specimen types investigated, the pattern recognition technique indicates two AE signal clusters. Cluster A comprises AE signals with a relatively high share of low-frequency components, and the opposite is true for cluster B. It is hypothesized that the signature of rapid and slow crack growths might be the origin for this cluster formation.

A three-step procedure has been developed for superhydrophobic coating on wood based on epoxy/silica materials in combination with hydrophobization. First, the epoxy resin is adhered to wood by immersing the samples into an epoxy resin acetone solution, then amino-functionalized silica particles are anchored by the epoxide groups, and finally, the created surface is modified by octadecyltrichlorosilane (OTS). The superhydrophobic surface not only is water repellent, as shown by the contact angle (CA) tests, but also decreases essentially the wood’s water absorption as determined by a 120-day water immersion test. The good mechanical stability of the coating was confirmed by a sand collision method.

This paper reports a new method of detecting urea-formaldehyde (UF) resin penetration into the cell walls of radiata pine ( Pinus radiata D. Don) by means of transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDXS). The quantifications of penetrated UF resin in the ultrathin cuts of cell walls were realized by detecting nitrogen (N) element by TEM-EDXS. Both line scan and area mapping revealed N in cell walls in contact with resin-filled lumens but not in those in contact with empty lumens. Thus, UF resin had penetrated the cell walls from the lumen side.