Band 79, Heft 10

The Caatinga biome in northeastern Brazil hosts diverse tree species with anatomical and chemical adaptations to semi-arid conditions. This study characterizes the wood of seven native species –  Anadenanthera colubrina var. cebil (Griseb.) Altschul, Poincianella bracteosa (Tul.) L. P. Queiroz, Cnidoscolus quercifolius Pohl, Mimosa ophthalmocentra Mart. ex Benth, Mimosa tenuiflora (Willd.) Poir., Bauhinia cheilantha (Bong.) Steud., and Aspidosperma pyrifolium Mart. – through anatomical, physical, and chemical analyses. Wood structure was assessed by light and scanning electron microscopy; basic density was determined by immersion. FTIR and Raman spectroscopy were used to identify functional groups and calculate cellulose crystallinity. Density ranged from 430 to 850 kg/m 3 ; crystallinity ranged from 34.5 % to 78.3 %. Higher density species are suitable for structural, and composite uses due to their superior mechanical properties, while lower-density woods may favor pulp production, though higher density is generally preferred for energy purposes. This integrated analysis supports species identification and highlights the corrected use and relevance of Caatinga woods.

In response to gravitropic environmental stimuli, woody angiosperms develop tension wood (TW). Typical TW fibers are characterized by an inner gelatinous cell wall (c.w.) layer (G-layer). On the other hand, in response to mechanical stimuli, woody plants develop flexure wood. Flexure wood formed under tension in angiosperms is termed tensile flexure wood (TFW). Similarly to TW, TFW represents an increased source of non-recalcitrant cellulose for biofuel production. Histochemical, SEM, and Raman microspectroscopic analyses of TFW of juvenile Populus x euramericana formed in response to severe long-term static bending were performed. The presence of lignin in the G-layer, higher syringyl/guaiacyl ratio, and differences in lignin structure in TFW compared to normal wood, revealed by histochemical analysis, was confirmed by Raman microspectroscopy. Additionally, Raman microspectroscopy indicated differences in cellulose and hemicellulose structure and pectin methylesterification. The G-layer and compound middle lamella contribute to the response to bending by opposite shifts of the orientation-sensitive cellulose band attributed to the glycosidic C–O–C bond. SEM micrographs revealed the c.w. ultrastructure of TFW fibers. The presented findings encourage further investigation of TFW in terms of both changes in c.w. structure as a mechanical acclimation to stem bending and its potential for biofuel production.

The aim was to determine the biological resistance and chemical properties of the wood of four species from an agroforestry system: Parapiptadenia rigida , Peltophorum dubium , Schizolobium parahyba and a hybrid of Eucalyptus urophylla  ×  Eucalyptus grandis . Mass loss tests were carried out with white rot fungi ( Trametes versicolor  – TV; Pycnoporus sanguineus  – PS; Ganoderma applanatum  – GA) and brown rot fungi ( Gloeophyllum trabeum  – GT), and basic density (BD), lignin, extractives, holocellulose and ash were analyzed. S. parahyba (BD: 277 kg m −3 ) in combination with the GA fungus obtained the highest mass loss (17.6 %), as well as for brown rot (7.6 %) followed by E. urophylla  ×  E. grandis (8.1 %; BD: 509 kg m −3 ). P. rigida (BD: 652 kg m −3 ) and P. dubium (BD: 488 kg m −3 ) showed lower mass loss to brown rot (3.4 %; 2.3 %) and GA (3.5 %; 3.9 %). The resistance to mass loss of P. rigida and P. dubium can be explained by the higher percentage of extractives and BD, which was validated by the principal component analysis that explained 86 % of the variance. In addition, they highlight the need for specific treatments for more vulnerable wood ( S. parahyba ), promoting greater efficiency in their use.

Understanding the natural durability of wood derived from chemical characteristics is important for forestry species, such as Larix sibirica Ledeb that is a major species in the Siberian boreal forests and is utilized for producing construction materials. Wood-color parameters, chemical properties (hot-water extracts, 1 % NaOH extracts, arabinogalactan contents, and polyphenol contents [as taxifolin equivalent contents]), and decay resistance in the heartwood were examined for L. sibirica collected from five forestry sites in Mongolia. Geographic variations of these properties were also evaluated using a mixed-effects model. Mass loss by Trametes versicolor ranged from 7.4 to 14.8 %, while Fomitopsis palustris caused mass loss from 4.8 to 6.6 %. Mass loss by F. palustris significantly correlated with arabinogalactan contents ( r  = 0.688). The L* parameter was significantly negatively correlated with arabinogalactan ( r  = −0.477), while the a * parameter showed a significant positive correlation ( r  = 0.459). A high variance component ratio of provenance was found in wood-color –  L* (13.5 %), a* (19.6 %), and b* (24.2 %) – as well as in 1 % NaOH extracts (32.1 %) and polyphenol contents (29.1 %), suggesting that geographic variations of the properties are existed. Thus, selecting trees with higher L *, lower a *, and lower arabinogalactan contents may improve decay resistance against brown-rot fungus.

In this work, the possibility of using ruthenium-based Shvo catalyst for bond cleavage of lignin model compounds and lignin has been investigated. Shvo-catalyzed degradation procedure was applied to four lignin model compounds containing β–O–4 linkages, common for native lignin fractions. The reactions, in general, resulted in C β –C γ and C γ –O γ bond cleavage, with the degradation products depending on the exact model compound studied. Distribution of the degradation products can be explained by the range of substituents and structural complexity of the model compounds. The major products of degradation were separated using preparative HPLC and characterized to enable further studies on bond cleavage in lignin. The Shvo-catalyzed degradation protocol was further applied to the lignan hydroxymatairesinol and a model diol with protected primary hydroxyl group. For both compounds, only dehydrogenation of benzylic hydroxyl group in the absence of bond cleavage was observed. With extracted lignin, only thermal degradation of the starting material was evidenced, while detailed characterization of the reaction products was not possible due to their poor solubility and structural complexity.

At times of bark beetle infestation, the sawmill industry uses mainly low-quality logs with a high proportion of salvage logging. Some countries of Central Europe, including the Czech Republic, have been greatly affected by such insect attacks as they significantly reduce the quality of sawn timber. To minimise the losses, non-destructive methods are needed to detect infestation early. Thirty Norway spruce sawlogs from loggings affected by bark beetle were processed and visually graded according to EN 1611-1 (CEN (1999) EN 1611-1:1999 – sawn timber – appearance grading of softwoods – part 1: European spruces, firs, pines and douglas firs. Brussels: European Committee for Standardization). The commonest defects were knots, but other defects such as soft rot, deep insect attack, and deep cracks had the most significant effect on quality. These defects were best detected by computed tomography using a MiCROTEC CT log scanner. The frequency-resonance method resulted in poorer coefficients of determination from R 2  = 0.004 to R 2  = 0.29 when predicting qualitative yield and therefore cannot be recommended when visually grading sawn timber. The Recommended Rules for Measuring and Grading of Roundwood in the Czech Republic 2008 should be adapted to the current situation in the industry by dividing grade III.D into two subclasses.

Surface splits occur in glued laminated timber exposed to outdoor undercover conditions, protected from precipitation, and can adversely impact a structures performance. An 18 month field exposure trial in sub-tropical Australia, investigated the occurrence and development of surface splits in unfinished glued laminated timber, manufactured from a hybrid plantation Pinus species using a polyurethane adhesive. Surface splits were assessed by measuring split length to the nearest 5 mm. Surface split development was found to reflect a sigmoid deterioration pattern with four stages; 1) no splits, 2) split initiation, 3) split extension, and 4) split stabilization. This study found minimal evidence of a size effect impacting surface splits. Surface splits were found to increase proportionally as the magnitude of solar radiation on a surface increased. Radially orientated splits on tangential surfaces were found to occur sooner and extend further than tangentially orientated splits on radial surfaces. Surface splits were found to stabilize after about 6–9 months of exposure. Latewood on gluelines was associated with more than 90 % of glueline delamination. The nature and location of latewood both on exposed surfaces in laminates, and at gluelines was found to influence surface splits in glued laminated timber.

Wood densification treatment is a process that effectively improves the soft texture of fast-growing wood, thus enhancing its mechanical properties. However, the densification process often causes cell wall damage and significant compression set recovery in densified wood, significantly limiting its applications. To address these limitations, urea-pretreated densified wood (UPDW) was developed in this study using different concentrations of urea solution. The UPDW exhibited enhanced dimensional stability and mechanical properties. The UPDW exhibited a reduced compression set recovery of 1.6–4.6 % and thickness moisture swelling of 0.9–2.3 %, which decreased by 86.8 % and 71.9 %, respectively, compared with water-pretreated densified wood, indicating superior dimensional stability. Additionally, UPDW exhibited enhanced modulus of rupture (MOR) (50.7–67.0 MPa) and modulus of elasticity (MOE) (5.5–6.4 GPa). The MOR and MOE of the optimized 50 %-UPDW increased by 41.6 % and 28.0 %, respectively, compared with the natural wood (NW). Additionally, the surface hardness of 50 %-UPDW was significantly enhanced (50.6–59.3 HD), which was 39.6 % higher than that of NW. Notably, 89.5 % of the urea in the 50 %-UPDW decomposed into gases and escaped, leaving a small amount of urea. Therefore, the UPDW demonstrates great potential application in construction and furniture materials.