Volume 76, Issue 6

The use of resonant frequency is presently one of the most used non-destructive testing (NDT) methods to predict the mechanical properties of sawn timber. In most cases, only the first vibration mode is used to estimate the static modulus of elasticity (MOE S ). The use of other vibration modes (overtones) can improve the predictive capacity of this NDT. In this study, the dynamic modulus of elasticity (MOE dyn ) obtained from the fundamental flexural resonant frequency and overtones of 38 structural size samples (2000 × 100 × 70 mm 3 ) of Pinus sylvestris were analysed. The study was complemented with 16 small size samples (1000 × 20 × 8.7 mm 3 ) of the same species to know the shear effect in samples with a very high length-to-depth ratio. For the structural size samples, a 6% decrease in the MOE dyn was detected each time the vibration mode increased. Using the second or third vibration mode offered lower errors in the prediction of the MOE S than the fundamental resonant frequency. The lowest MOE S prediction errors were obtained combining various vibration modes through power regression. This regression turned out to be a simple alternative to avoid the shear effect in the calculation of the MOE dyn .

Full penetration-dyed solid wood has the advantage that furniture or other items fabricated from it do not require additional painting or staining. However, anatomical barriers along potential dye infiltration pathways may result in unsatisfactory dyeing in terms of depth of dye penetration or colour intensity and uniformity. Dyed wood items, even those intended for interior use, should also possess a certain degree of water fastness. In the present paper, full-thickness dyeing of radiata pine blocks was achieved with fibre-reactive and direct dyes as well as pine tannin. Leaching of the treated blocks in cold water removed excess dye but the target colours were well retained. Pectinase pre-treatment of wood blocks was shown to increase the uptake of fibre-reactive and direct dyes by tracheid cell walls and the uptake of tannin by rays, resin canals, and tracheid lumina. In the case of a direct dye and pine tannin, pectinase treatment markedly increased the intensity of the target colours. Combining tannin with laccase to achieve covalent bonding of tannin to wood lignin was associated with a small, albeit not statistically significant, shift towards the target colour.

The established methods for testing the hardness of wood are of questionable value for assessing the performance of surface-densified wood, since the density profile beneath the densified surface is an important property that needs to be considered. The purpose of this study was to evaluate the influence of the density profile of surface-densified wood and the hardness test parameters, such as indenter geometry and applied load on the measured hardness. The influence of the density profile varied considerably depending on the hardness test parameters. This can make a comparison of hardness values of surface-densified wood prone to misinterpretation. The selection of hardness test parameters should either be product-specific, or the density profile itself should be used to evaluate the hardness of surface-densified wood. A strong influence of the density profile on the indentation depth development during the hardness tests indicates the possibility of predicting the density profile based on the hardness test methods.

The density profile of surface-densified wood has a major influence on the indentation resistance of the material. A method that can predict the density profile in surface-densified wood from measurements of the indentation in a hardness test was established. The combined information of hardness and density profile is expected to better assess the performance of surface-densified wood. Density profile and hardness test data for surface-densified Scots pine have been subjected to a partial least squares analysis to determine the relationship between the indentation depth measured during a hardness test and the density profile measured by X-ray densitometry. Among seven different hardness tests, which varied in test force and indenter geometry, the Brinell method according to the EN 1534 standard showed the highest correlation between the indentation-versus-time curve and the density profile. The mean absolute error for the prediction of density profiles in an external test set was 5–10%, indicating that the method proposed in this study can be used to replace X-ray densitometry in process control and process design.

The objective of this work was to determine the effect of sodium methyl mercaptide (SMM) as an additive on the minimization of carbohydrate peeling reactions in Rock/Hard Maple ( Acer saccharum ) chips during kraft pulping. Two methods were evaluated for SMM addition to the pulping process: 1) pre-treatment before pulping and 2) co-addition with white liquor. The experimental results showed about 2.5% (on wood basis) increase in the kraft pulp yield after pre-treatment with 4.38% SMM (on wood basis) or the co-addition of the same amount of SMM with white liquor. The use of 4.38% SMM allowed a decrease in the white liquor effective alkali charge of 3% (on wood basis) to produce the target 14–15 kappa pulp. The 4.38% SMM charge was determined to be the optimum for both pre-treatment and co-addition. The increase in kraft pulp yield was mostly due to increased retention of cellulose (about 0.8% on wood) and xylan (about 1.8% on wood). The retention of glucomannan was insignificant in all cases. Based on the increase in intrinsic viscosity, it is concluded that the increased cellulose yield with SMM addition is caused by both reduced primary peeling and faster delignification rate (less alkaline hydrolysis followed by secondary peeling). The increased xylan retention is due to the lower effective alkali concentration during kraft pulping with SMM addition.

In this study, heterogeneous lignocellulosic microfines (LCMFs) with different physicochemical properties were prepared from softwood by adjusting the reaction conditions of a glycol ether-organosolv process. The dissolution properties of heterogeneous LCMFs in an NaOH–urea aqueous solution were evaluated. As the reaction time increased, the yield and residual lignin content decreased. As the amount of chemical solution used to prepare LCMFs increased, more lignin than carbohydrates were removed, but the degree of polymerization (DP) was maintained. Finally, LCMFs with different residual lignin content, DP, and crystallinity were prepared via the glycol ether-organosolv process under various conditions. It was observed that lower the lignin content of heterogeneous LCMFs, higher were their solubilities in the NaOH–urea solution. The effect of DP on solubility was not significant; however, the hemicellulose content of LCMFs had a greater effect on their solubilities in the NaOH–urea aqueous solution than the sugar composition of hemicellulose. The chemical properties of lignin present in LCMFs had no significant effect on their solubilities in the NaOH–urea aqueous solution.

Since rotational wood welding was patented in 1997, this technology has been successfully used in the field of timber structures and furniture. A growing body of literature has investigated the mechanical behaviour of wood-dowel welding joints in tension to study the effect of various factors on welding strength. However, up to now, only two predictive approaches were proposed by researchers, and due to the lack of small samples, they were applied in a limited scope. Therefore, this paper aimed to find a way to establish a multivariate model to compute their carrying capacity. A pull-out test database including 1338 trials from previous literature was used as the basis of modelling. Due to the similarity of joints with glued-in-rod, after evaluating its model validation, the modelling method was applied to the welded joints. The data analysis was carried out to determine the primary influences (such as: rotational speed, predrilled hole diameter, welded length and substrate density). Based on the non-linear regression analysis, a multivariate prediction model was proposed, and results showed positive accuracy with measured values. This study provides a new comprehensive assessment of the withdrawal strength of welded joints, and can help identify future technical guidelines within the wood industry.

Wood, a natural anisotropic material, behaves differently in the radial (R) and tangential direction (T), which also gives rise to different penetration capacity of adhesive into wood tissues. The present study investigates the penetration behavior of adhesive in the interphase of three different wood laminates, namely R-R, T-R, and T-T combinations, and its effect on microstructure and micromechanical properties of the latewood bonding interphase using confocal laser scanning microscopy (CLSM) and nanoindentation (NI). The results showed that the average penetration depth (AP) of the radial surface ( S R ) was higher than that of the tangential surface ( S T ) and a significant improvement in the mechanics of cells compared with the control cell ( C ). the maximum reduced elastic modulus ( E r ) and hardness ( H ) found at the fourth cell row were 21.7 GPa and 0.62 GPa for R-R laminate, respectively, which increased by 43% and 29% compared with C (15.1 GPa, 0.48 GPa), and the maximum E r and H found at the first cell row were 23.2 GPa and 0.65 GPa for T-T laminate, respectively, which increased by 52% and 44% compared with C (15.3 GPa, 0.45 GPa). The results provide an important platform for better understanding and predicting the properties of wood glue line and bonding interphase.

Bamboo-cultured cells (BCCs) were produced under three phytohormone conditions. BCC lignin was then isolated and characterized by heteronuclear single-quantum coherence-nuclear magnetic resonance (HSQC-NMR) analysis. HSQC-NMR analysis revealed that all three BCC lignin samples were composed of guaiacyl (G), syringyl (S), oxidized syringyl (S′), and p -hydroxyphenyl (H) units. p -Coumaric acid ( p CA) and ferulic acid (FA) were identified as well. Main lignin substructures, including β - O -4, β -5, and β - β , were also detected. However, β - O -4/ α - O -4, spirodienone, dibenzodioxocin, or tricin structures were absent in the BCC lignin. The BCC lignin contained higher proportions of H, FA, and β -5 structures, but less proportions of S, S′, and β - O -4 structures than the mature bamboo lignin. The removal of auxin 2,4-dichlorophenoxyacetic acid (2,4-D) from the subculture medium promoted G unit formations. Nevertheless, it suppressed H and p CA unit formations. Cytokinin 6-benzyladenine (BA) promoted H and β - β structure formations as well but suppressed β - O -4 formations than in the mature bamboo and BCC lignin produced under phytohormone free conditions.