Volume 74, Issue 10

Schizolobium parahyba var. amazonicum (paricá) is a promising forest species that has been planted in some states of the Amazon region in Brazil, to meet the demand of the plywood panel industry. The present work involves a study of the variations of the cambium and their impact on derivative tissues at different heights in the stem of S. parahyba var. amazonicum . Except for the tangential diameter of the fusiform initials (DFI) and the width of the xylem cell layer in differentiation (WXD), there was significant statistical variation between the evaluated axial positions for all anatomical parameters of the cambium. A strong positive correlation was noticed between the length of the fusiform initials (LFI) with ray height (RH) [r = 0.79, degree of freedom (DF) = 7, P < 0.05], vessel element length (VL) (r = 0.78, DF = 7, P < 0.05) and fiber length (FL) (r = 0.74, DF = 7, P < 0.05). The results of this study give quantitative support that the LFI is an important prognosis, not only for the VL and FL, but also for the rays, in hardwood species.

Trees with high levels of growth stress begin to show log end splits (LES) immediately after harvesting, usually reaching its maximum end split in a week, and these tensions also create splits during lumber manufacturing. Interlocked grain is another characteristic that impacts the properties of eucalyptus wood. The aim of this study was to evaluate the effect of growth stress and interlocked grain patterns on log end splitting of seven different hybrid clones of Eucalyptus grandis  ×  Eucalyptus urophylla planted in Brazil. The growth stress indicator (GSI) was measured in standing trees before harvesting. Splits were measured on logs in three different stages, and interlocked grain from wood blocks was obtained across the center of the cross-section. The results showed that LES occurred as soon as the trees were harvested; however, for better selection of clones, LES should be evaluated after a week of harvesting. There were statistically significant correlations for GSI with LES. Clones that presented higher values of interlocked grain tended to develop lower values of GSI and LES. Using GSI and interlocked grain measurements, it was possible to select the most indicated eucalyptus clones for lumber production.

Softwood is commonly used in timber structures, whose dynamic compressive properties along the grain direction under seismic rate actions are of major concern. In the present study, 108 samples were examined from three species of softwoods (spruce, Dahurian larch and pine) and subjected to four levels of strain rates (10 −4 s −1 , 10 −3 s −1 , 10 −2 s −1 and 0.1 s −1 ) under parallel-to-grain monotonic and repeated compression. The seismic strain rate effects on softwood were investigated by observing the failure mechanisms, engineering stress-strain curves, initial crushing strength, elastic modulus and peak strain. Results demonstrated the high sensitivity of softwood to seismic strain rates. Finally, a rate-dependent constitutive model was developed to predict the stress-strain relationship (both monotonic and repeated loading cases) of softwood under different seismic strain rates.

In Central Europe, European beech ( Fagus sylvatica L.) is the most frequently occurring hardwood species. An efficient grading method has the potential to promote its utilisation as construction material. Wood density, eigenfrequency and length were measured in 99 European beech logs for calculating the dynamic modulus of elasticity ( MOE dyn ) obtained by longitudinal vibration (resonance). In addition, the log taper was measured. Of those logs, 867 boards were cut using a bandsaw. The MOE dyn in green condition was determined on 505 of the boards and the MOE dyn in dry conditions was determined on all of them. The r 2 value between the MOE dyn of a log and the mean of MOE dyn of its boards was 0.72 in the wet condition. The MOE dyn,12% of boards significantly increased by 88 N mm −2 for each centimetre away from the pith. The negative effect of log taper on MOE dyn of boards was barely significant (P-value = 0.050). The MOE dyn,12% was highly dependent on the MOE dyn,wet (r 2  = 0.83) and was 17% higher than the MOE dyn,wet . The mechanical properties of European beech timber exceed those of European softwood species. However, the relationships regarding MOE dyn between different grading levels in the processing chain appear to be similar to those of softwoods.

The cell wall of plant fibers may contain irregular regions called dislocations. This study evaluated the effect of chemical pretreatment as a mechanochemical dislocation initiator in unbleached and bleached Eucalyptus sp. fibers. Accordingly, bleached and unbleached pulps of eucalyptus were subjected to chemical pretreatments with sodium hydroxide at concentrations of 5% for 2 h, 10% for 1 h and 10% for 2 h or with hydrogen peroxide. The extent of dislocations was evaluated by polarized light microscopy. Based on the observation, an index of dislocations (ID) expressing their ratio of cell wall as per two-dimensional (2D) imaging and their angle relative to the longitudinal direction of the fiber were estimated. Chemical pretreatments increased the ID for bleached and unbleached fibers as well as increased the changes in the curl of bleached and unbleached fibers for chemical pretreatments. Chemical pretreatment extracted the hemicellulose of the fiber cell wall causing some fiber to curl, which in turn generated new dislocations and modifications in the dislocation angles which may be useful for improving the deconstruction process of the cellulose fibers.

The flame retardancy and dimensional stability of wood were improved by pretreating wood with succinic anhydride (SA), and then impregnating the SA-treated wood with melamine-urea-formaldehyde (MUF) resin. The SA-treated wood obtained graft anchors on the cell wall, which reduced the water-absorbing groups of wood and enhanced the retention of the MUF resin, leading to an efficiently fire-proof protection layer and water repellency. Field-emission scanning electron microscopy and Fourier-transform infrared spectroscopy demonstrated that the grafting experiment was successful. The water repellency experiments revealed that the pretreated wood impregnated with MUF resin had enhanced hydrophobicity and great improvement in dimensional stability. In addition, the limiting oxygen index value of the modified wood increased by 74%, the flame-retardant performance was improved, and precious rescue time was provided for when a fire occurs. The facile two-step wood modification process substantially enhanced the thermal stability, water repellency, and fire-retardant performance of wood, and therefore represents a novel direction toward hydrophobic and fire-retardant structural materials.

Improving the interaction between the wood cell wall and a modifying agent is fundamental to enhancing the efficacy of wood modification. The extent of interaction is, nevertheless, difficult to evaluate due to the highly heterogeneous nature of the modified wood. In this study, methacryl groups were grafted onto the wood cell wall polymers, via the reaction between 2-isocyanatoethyl methacrylate (IEMA) and hydroxyl groups, to improve their compatibility and reactivity. Subsequently, methyl methacrylate (MMA) was introduced into methacrylated wood and copolymerized with the bonded methacryl groups. The distribution of IEMA and poly MMA (PMMA) in the wood cell walls was investigated by scanning electron microscopy (SEM) and confocal Raman microscopy. The results showed that MMA penetrated the wood cell walls and formed strong interfacial interaction, which was confirmed by confocal Raman microscopy combined with principal component analysis (PCA). With copolymerization, the highest anti-swelling efficiency (ASE) (57%) was achieved, because of the effect of methacrylation. Compared to the reference, the water resistance and hardness were significantly improved. In addition, the dynamic wettability was also altered largely due to copolymerization.

Roughness is an important property of wood surface and has a significant influence on the interface bonding strength and surface coating quality. However, there are no theoretical models for basswood-veneered medium-density fiberboard (MDF) by fine sanding from existing research work. In this paper, the basswood-veneered MDF was fine sanded with an air drum. Orthogonal experiment was implemented to study the effects of abrasive granularity, feed rate, belt speed, air drum deformation and air drum pressure on the surface roughness of basswood-veneered MDF. The simulation models of the parallel-grain roughness and the vertical-grain roughness of the sanded surface were conducted based on the BP (error back propagation) neural network, which was optimized by a genetic algorithm (GA) (GA-BP neural network), and these models were verified by extensive experimental data. The results showed that the influence of sanding parameters on parallel-grain roughness was similar to that on vertical-grain roughness. The order of influence was that: abrasive granularity > belt speed > feed speed > air drum deformation and air drum pressure. Based on the work, the parallel-grain roughness and vertical-grain roughness of basswood-veneered MDF could be well predicted by the GA-BP neural network. The average relative errors on parallel-grain roughness and vertical-grain roughness were 3.4% and 1.9%, respectively.

The bark of the tree species Myrcia eximia DC., which occurs in secondary forests in the Brazilian Amazon, is described for the first time. The aim was to provide a broad knowledge of its composition, to add value, and to direct uses to the bark of this species based on its polyphenolic content and antioxidant capacity. The bark is formed by conducting phloem, nonconducting phloem, and rhytidome. In addition, dead phloem occurs between the periderms. The average chemical composition of the bark was 45.6% total extractives, 1.4% suberin, 1.7% ash, and 21.1% lignin. The ethanol-water extract had a high content of flavonoids and condensed tannins [300.8 and 877.3 mg catechin equivalents (CE) g −1 of the extract, respectively]. High-performance liquid chromatography (HPLC) was used to quantify the presence of rutin, quercetin, and gallic, ferulic, and o-coumaric acids. The bark extract showed strong 2,2 - diphenyl - 1 - picrylhydrazyl hydrate (DPPH) free radical scavenging activity, which was superior to that of the commercial antioxidant butylated hydroxytoluene (BHT), with an IC 50 of 85.2 μg mL −1 . Based on these results, it is evident that the bark of M. eximia from the Brazilian Amazon rainforest is a new and potential natural source of phenolic compounds and antioxidants, and its extracts can be used in the food and pharmaceutical industry and in various condensed tannin-based products.