Volume 76, Issue 5

The market share of European beech ( Fagus sylvatica L.) wood in the construction sector is low despite an increase in beech stock in Central European Forests in recent years. More efficient sawing techniques, higher lamella grading yields and solving of adhesion challenges may increase the competitiveness of beech glulam and promote its use. The aim of this paper is to revise the lamella grading system in the current German technical approval for beech glulam Z-9.1-679:2019 (DIBt (2019). BS-Holz aus Buche und BS-Holz Buche Hybridträger und zugehörige Bauarten . Allgemeine bauaufsichtliche Zulassung Z-9.1-679:2019. Deutsches Institut für Bautechnik) and to suggest modifications in the lamella grading rules for glulam production allowing higher yields and reliable tensile strength values at the same time. The unique dataset in this study combined different origins of lamellas and covered a wide range of visual, physical and mechanical wood characteristics including a high amount of low quality material. Indicating properties (IPs) for tensile strength, such as knot parameters and dynamic modulus of elasticity, were contrasted with tensile strength and static modulus of elasticity. Beech lamellas, graded by means of Z-9.1-679:2019 (DIBt (2019). BS-Holz aus Buche und BS-Holz Buche Hybridträger und zugehörige Bauarten . Allgemeine bauaufsichtliche Zulassung Z-9.1-679:2019. Deutsches Institut für Bautechnik), did not achieve the tensile strengths required for glulam production in many grading classes and the yield was low. A machine grading approach with dynamic modulus of elasticity as a single grading criterion gave higher yields than the current grading procedure and high reliability for tensile strength prediction with a prediction accuracy of R 2  = 0.67.

Bio-based building materials are susceptible to degradation by decay fungi when exposed to favourable conditions for fungal growth. The risk of decay depends on both the environmental conditions and material resistance. Although durability data is available for solid wood, standard tests mainly focus on mass loss assessment after a fixed degradation period. In-depth knowledge on time-dependent decay patterns is lacking, yet could prove relevant for optimisations of the structural design of engineered wood products to increase their service life. Here, a novel X-ray CT scanning set-up and analysis pipeline for non-destructive assessment of the influence of material structure on temporal decay patterns under laboratory conditions is presented. Wood specimens that were severely degraded showed a pattern in which the density decreased substantially after 2 weeks, due to wood mass being metabolised into mycelium, carbon dioxide and water. The influence of various anatomical features, such as the vessel orientation and the number of growth rings, on wood degradation patterns was demonstrated. This approach is a starting point for further in-depth research on the influence of material structure on decay. The method is especially interesting to assess the efficacy of structural modification strategies that are expected to inhibit decay or enhance service life.

The purpose of this work was to ascertain the influence of the nondestructive testing (NDT) method, as well as the location and number of measuring points, on the correlation between NDT indices and the flexural modulus (MOE) of small clear specimens of aged wood. The MOE of the Tibetan Populus cathayana specimens sawed from an ancient floor beam were measured, and multiposition NDT was carried out with a stress wave and resistography detector. Unary and multivariate linear methods and the stepwise regression method were used to discuss the correlation between the NDT indices and MOE. The results indicated that the NDT index of M f , which combined stress wave velocity and microdrilling resistance, had the highest correlation coefficient ( R ) with MOE. When the number of measuring points was increased from 2 to 8, R could be increased by up to 180.2%. The stepwise regression method is efficient in determining the optimal combination of variables while avoiding colinearity. Thus, using appropriate NDT indices while considering the texture characteristics of the specimen can effectively improve the MOE prediction accuracy.

Poplar is an important tree species in the phytoremediation of Cadmium (Cd) in the soil. However, the research on its transport and accumulation mechanism in wood cells has not been conducted. In this paper, Poplar 69 [ Populus deltoides Bartr. cv. ‘Lux’ (I-69/55)] was selected to study the distribution of Cd accumulated in the wood, both macroscopically, by Cd analysis along the trunk heights, and microscopically, by scanning electron microscope with energy dispersion spectrum (SEM-EDS) observation, through a pot experiment, where four treatments with different Cd application in the soil and one control without Cd addition were set. The results demonstrated that the Cd concentration in the wood of all heights increased significantly with the increase of Cd addition in the soil and it also increased, though not significantly, from the basal to the top along the trunk heights at all treatments. Through SEM-EDS Cd was found to be accumulated in the inner wall and pits of the vessels, the wood fibers, and the wood rays, indicating that Cd could enter all three types of wood cells. The distribution of Cd in the three types of wood cells followed the order as wood fiber > vessel > wood ray, based on the calculation of the proportion of Cd enrichment spots in different types of cells. About half of the Cd in the wood was stored permanently in the wood fibers with the rest being in the vessels and wood rays probably temporally.

The wood-water interactions of modified beech wood ( Fagus sylvatica L.) were studied. Specimens were thermally modified at 180 (TM 1 ), 200 (TM 2 ) and 220 °C (TM 3 ), acetylated (Acet), and melamine formaldehyde (MF) resin (Mel) modified. Afterwards, the water vapour characteristics, i.e. water vapour sorption isotherms, equilibrium moisture content (EMC), dimensional stability of specimens conditioned at 30, 65 and 90% RH and liquid water characteristics, i.e. water absorption, maximum moisture content (MC), leachability and swelling kinetics, were determined and the results compared with reference (Ref) specimens. From the results, it is evident that the scale of wood-water interactions was highly dependent on the thermal modification temperature and type of chemical modification. The water vapour isotherms of thermally modified wood decreased, whereas more severe treatment exhibited more distinct reduction. The EMC values of the Mel and TM 1 specimens decreased only at high RH, whereas the most significant decrease, within the whole range of observation, was found in the Acet group. The maximum MC reduction was achieved by acetylation. As a consequence of swelling reduction, dimensional stability expressed as anti-swelling efficiency (ASE) was considerably improved. A relatively high initial linear-phase swelling rate was found for the Ref specimens, whereas modified wood exhibited comparatively slow and gradual swelling.

The low density and light color of faber fir [ Abies. fabri (Mast.) Craib] wood have limited its applications in interior decoration and wall panels. In order to increase the density of faber fir and thus expand its scope of application, this study chemically pretreated the wood firstly, and then pressed it at high temperatures to make densified wood. The microscopic morphology and mechanical property tests showed that the performances of densified wood were greatly enhanced compared with the natural wood. When the pretreatment time was 10 h, the cell lumen size of densified wood became extremely small, resulting in a density of 1160 kg m −3 and a relative crystallinity of 76.9%. Moreover, the mean flexural strength and elastic modulus of the densified wood with a pretreatment process of 10 h were 191 MPa and 23.4 GPa, which were 170% and 230% higher than the natural wood. In addition, the obtained high-strength wood was infused with paraffin to improve dimensional stability without compromising the high strength of the densified wood. The performance test showed that the thickness swelling of the treated densified wood was only 0.6% (after 72 h water absorption), showing excellent dimensional stability.

Hot-pressing high-yield pulp-based paper, at a temperature well above the softening temperature of lignin, increases paper density and strength. Here, it is investigated whether improved paper strength can be achieved and whether lower pressing temperatures can be used in combination with the increased sulphonation of high-temperature chemi-thermomechanical pulp (HTCTMP). Moist paper sheets from low-energy Norway spruce HTCTMP were hot pressed at temperatures up to 270 °C. Sulphite charges of 25–120 kg/bdt were used during impregnation, preheating, and refining at 180 °C with an electric energy demand of 370–500 kW h/bdt to a shive content of 1%. The pulps were mixed with 20% bleached unrefined kraft pulp to ensure that the sheet formation would not be hampered by the pulp coarseness. A tensile index of 70 kN m/kg was reached with the highest sulphite dosage at a pressing temperature of only 150 °C, versus 60 kN m/kg for the corresponding market CTMP. To obtain high wet strength, the highest temperature was required, while the sulphite charge was found to be of minor importance. This study has shown that it is possible to obtain strong and wet-stable paper products from HTCTMP, with a yield of 94–96% and a low energy demand at reduced pressing temperature.

Paper-grade pulp, rich in hemicellulose content, is a cheap source for producing dissolving pulps. The main challenge in the conversion of a cheap paper-grade pulp to a higher-valued dissolving pulp is the selective removal of hemicelluloses, while maintaining the pulp reactivity. This paper presents a comparison of different hemicellulose extraction methods such as cold caustic extraction, IONCELL-P(ulp) and xylanase treatment on converting fully bleached soda bagasse paper-grade pulp to dissolving pulp. IONCELL-P(ulp) treatment, using an optimized1-ethyl-3-methylimidazolium acetate/water as the extraction medium, yielded 85% xylan removal, which is comparable to the cold caustic extraction or a combination of xylanase treatment and cold caustic extraction. A complete separation of the two polymers by IONCELL-P(ulp) is not possible due to the overlap of the molecular masses of the cellulose and xylan molecules, an inherent characteristic of sugarcane bagasse pulp. All the investigated methods effectively removed xylan, with differences in the selectivity and the reactivity of the remaining pulp.