Volume 74, Issue 7

Wood is one of the most widely used materials for construction projects, in the furniture industry, as well as in the field of cultural property of valuable objects. Terahertz (THz) radiation has great potential for non-contact and non-destructive analysis of wooden materials. This article reports a study of the degree of growth of Trametes versicolor in wood samples, using THz radiation. The analysis compares the THz results to microscopic examinations of the samples, common beech incubated with T. versicolor , at different growth times. The results indicate a strong correlation between the parameters extracted from THz measurements and the progress of the fungal infestation, suggesting that THz imaging may be a valuable tool for non-contact inspection of wood.

Development of physical properties of bleached eucalyptus kraft pulp is typically based on the refining process. However, many studies have reported that xylan deposition is a viable alternative. As the mechanisms of xylan and cellulose interactions are not clear, the main goal of this study was to achieve a better understanding of these interactions. Considering that a sample of pulp enriched with xylan is a very complex matrix, a model system was developed. Cellulosic thin films were prepared by spincoating and the Langmuir-Schaefer (LS) method from trimethylsilylcellulose (TMSC). Their interactions with xylan were analyzed using the quartz crystal microbalance with dissipation (QCM-D) monitoring technique. The topological changes on cellulose were studied using atomic force microscopy (AFM). For the 13 C solid-state nuclear magnetic resonance (NMR) studies, samples were prepared using commercial microcrystalline cellulose (MCC) and xylan. The xylan was extracted from bleached birch kraft pulp using a cold caustic extraction (CCE) method. The QCM-D monitoring showed deposition only with higher concentrations of xylan solution (1 mg · l −1 ) for the LS method. The AFM images showed that xylan deposits as agglomerates on the cellulose surface, and the NMR experiments showed that there are interactions for the more ordered region of the cellulose fiber and for the less-ordered region.

Softwood lignin consists mainly of guaiacyl (G) units and low amounts of hydroxyphenyl (H) units. Even in a small percentage, the ratio of H to G (H/G) and the intraspecific variation are crucial wood lignin properties. Analytical pyrolysis (Py) was already successfully used as a reference method to develop a model based on near-infrared (NIR) spectroscopy for the determination of the H/G ratio on Pinus pinaster (Pnb) wood samples. The predicted values of the Pinus sylvestris (Psyl) samples by this model were well correlated (R = 0.91) with the reference data (Py), but with a bias that increased with increasing H/G ratio. Partial least squares regression (PLS-R) models were developed for the prediction of the H/G ratio, dedicated models for Psyl wood samples and common models based on both species (Pnb and Psyl). All the calibration models showed a high coefficient of determination and low errors. The coefficient of determination of the external validation of the dedicated models ranged from 0.92 to 0.96 and for the common models ranged from 0.83 to 0.93. However, the comparison of the predictive ability of the dedicated and common models using the Psyl external validation set showed almost identical predicted values.

Lignin is the second most abundant biopolymer and will be an important source for carbon-containing compounds in the future. Based on their similar phenolic structures, lignin has great potential to become a valuable substitute for phenol in phenol-formaldehyde resin adhesives. To meet this aim, the sodium hydroxide (NaOH)-catalyzed reaction of kraft lignin with formaldehyde was studied by using paraformaldehyde (PFA) as a formaldehyde source. The advantage of using PFA, the solid polymer of formaldehyde, is the simple composition of the depolymerized solution. According to the results of differential scanning calorimetry (DSC), the lignin reaction was found to require a high NaOH concentration in order for the reaction with PFA to proceed at reasonably low temperatures compared to the curing temperature of phenol-formaldehyde resins (approximately 150°C). On the other hand, high alkalinity conditions are known to favor the disproportionation of formaldehyde to formic acid and methanol. Due to the moderate reactivity of lignin, the Cannizzaro reaction can compete with the methylolation reaction of lignin. Based on the results of 13 C, 31 P and 1 H- 13 C heteronuclear single quantum correlation nuclear magnetic resonance (HSQC NMR), methylolation was found to be the main reaction occurring in the lignin-formaldehyde reaction.

In recent years, tannin degradation has been used to obtain tannin materials with an optimal molecular weight distribution (MWD) for synthesizing tannin-formaldehyde (TF) resin with high performance, but the optimal MWD of tannins is still unknown. The excellent formaldehyde reactivity of tannins is the basis for the synthesis of high-performance TF resin. Based on the formaldehyde reactivity of tannins, bayberry tannins and larch tannins were used to explore the optimal MWD of tannins for TF resin synthesis. Progressive solvent precipitation (PSP) was used to obtain tannin fractions with different MWDs. The formaldehyde reactivity of tannins was determined using the modified Stiansy method combined with the standard curve method (GB/T 17657-2013). The bayberry tannin fraction [weight-average molecular weight (Mw) of acetylated tannin: 4115, mean degree of polymerization (mDP): 6.64] and the larch tannin fraction (Mw of acetylated tannin: 3906, mDP: 5.84) had the best formaldehyde reactivity. Furthermore, significant differences in the formaldehyde reactivity of condensed tannins (CTs) with different MWDs were observed. The obtained results can be used to purposefully degrade tannins to achieve an optimal MWD, which is beneficial for the production of TF adhesives with high performance.

The forest policies of new Congo basin countries have increased the wood timber industry output since the year 2000. Thus, a high content of underutilized wood waste from sawmill, furniture and plywood industries is generated. Among them, Khaya ivorensis A. Chev bark, sapwood and heartwood account for the less valorized wood wastes. Therefore, an attempt was made to study the chemical variability and thermal stability of tannins extracted from the sapwood and heartwood by the acetone/water method (7:3, v:v); the potential recovery of these polyphenols for industrial applications was also aimed. Quantitative analysis pointed out that the heartwood was the most abundant in phenolic units, and a significant difference (P < 0.05) was found in condensed tannin content between the bark, sapwood and heartwood. This result indicated an intra-tree variability while no significant difference was found for inter-tree tannin contents (P > 0.05). These tannins were characterized by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) and Fourier transform infrared (FTIR) spectroscopy. Their chemical structures were fisitinidin- and gallocatechin-type units. No evidence of free cathechin moiety was found in these extracts. Moreover, oligomers up to seven tannin monomers free from glycosyl structures were found in the K. ivorensis condensed tannins. Moreover, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) pointed out good thermal stability of these hardwood species’ tannin. These findings could be useful for future valorizations of African mahogany wood wastes as source of tannins for chemistry or composite materials.

For a durable improvement of the hydrophobization properties of wood Scots pine ( Pinus sylvestris L.) sapwood veneer chips were covalently modified with surfactant-like p -alkylated benzoates and a corresponding 4-cyanophenyl derivative. These esterification reactions of wood hydroxyl groups at varied temperatures and different reaction times afforded weight percent gains (WPG) ranging from 8 to 44% and quantities of covalently bonded organomaterials (QCO) of 0.3–2.6 mmol per gram, respectively. The successful covalent attachment of the functional precursors was proven by attenuated total reflection-infrared spectroscopy (ATR-IR), while the improvement of hydrophobicity was demonstrated by resulting contact angles (CAs) in a range from 113 to 150°.

This study was undertaken to elucidate the longitudinal tensile fracture behaviors of softwood at the cell wall scale by means of microscopic analyses. The fracture types of the tracheids at the different fracture surfaces were also distinguished. The results indicated that the main tracheid fracture of the earlywood (EW) sample was transverse transwall breakage. The tracheid fracture process of the transverse transwall breakage was initiated as a fracture in the S 2 layer, with the crack propagating into the S 1 /S 2 interface. For the EW/latewood (LW) sample, the strain concentration and initial crack under longitudinal tensile load generally occurred in wood rays in the EW part, which caused the tracheids to experience transverse transwall breakage. The differences in longitudinal and transverse strains between EW and LW under longitudinal tensile load led to shear stress and parallel-to-grain cracks occurring at the growth ring border. When the crack propagated along the wood grain in the EW tissue or growth ring boundary, this resulted in EW longitudinal transwall breakage. However, when the crack propagates along the wood grain in the LW tissue, it could cause the LW tracheid to undergo intrawall breakage, with the crack occurring predominantly at the compound middle lamella (CML)/S 1 interface region.