Volume 72, Issue 5

Poplar sapwood chips were autohydrolyzed at three severity levels and subsequently treated with alkali for the production of chemi-mechanical pulp (CMP). The aim was to study the variation of the principal pathways for sodium hydroxide solution and the alkali concentration and distribution inside the autohydrolyzed chips as a function of autohydrolysis (AH) severity. The tyloses in the vessels and some pit membranes were partly dissolved after AH, while the skeletal structure of the fiber and vessel cell walls remained intact. AH had a positive influence on the diffusion and the uniform distribution of NaOH solution both in the axial and radial direction of the chips, but the axial direction was more favored than the radial one.

Substitution of phenol in phenol-formaldehyde (PF) resin preparations by technical lignins is hindered by the inherently lower reactivity of lignin compared to phenol. Demethylation of an industrial softwood kraft lignin (SKL) to improve its reactivity is the focus of this paper. To this purpose, kraft lignin (KL) was treated with two commercial laccases, NS51002 (L1) and NS51003 (L2), for 24 h in combination with three mediators, 2,2′-azinobis-(3-ethyl-benzothiazoline-6-sulfonic acid) diammonium salt (ABTS), 1-hydroxybenzotriazole (HBT) and 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). The characterizations of the reaction solution and the resultant KL showed that methanol was released as a result of the methoxy group splitting from the aromatic rings, while such demethylation was dependent on the laccase-mediator system (LMS). The catechol structures formed, which were further oxidized to a quinone structures prone to polymerization, led to molecular mass increment. Also this reaction was LMS dependent. The same is true to the cleavage of β-O-4′ linkages, which resulted in depolymerization. The L1-ABTS, L1-TEMPO and L2-HBT combinations are the most efficient and the resulting modified lignin would be suitable to phenol substitution. Challenging is the lignin polymerization following the demethylation, especially in case of L1-ABTS, which might inhibit the reactivity of the treated lignin.

A novel way to prepare mesoporous activated carbon fibers (ACFs-P) has been developed, while the ACFs-P with high surface area were obtained from liquefied wood by combining polyvinyl butyral (PVB) blending and steam activation. The porosity properties of the new material was investigated by N 2 adsorption and the Brunauer–Emmett–Teller (BET) surface area was found to be 2710 m 2 g −1 and a pore volume of 1.540 cm 3 g −1 , of which 58.2% was mesoporous with diameters between 3 and 6 nm. ACFs-P had a higher methylene blue (MB) adsorption capacity (962 mg/g) than the PVB-added carbon fibers (CFs-P) and ACFs-P without PVB (ACFs-C). Flexible all-carbon yarn supercapacitors can be produced from ACFs-P as powder or fiber. The fiber approach led to yarn supercapacitors with a less favorable electrochemical performance than the powder based production owing to the poor strength of the fibers. A 10 cm long yarn supercapacitor from the powdered ACFs exhibited a high specific length capacitance of 43 mF cm −1 at 2 mV s −1 . Yarn supercapacitors showed an excellent mechanical flexibility and its capacitor properties were not diminished after bending or crumpling.

Graphene oxide/wood (GOW) composite was fabricated by a vacuum-pulse dipping technique, and the resulting composites were characterized by scanning electron microscope (SEM), Raman spectroscopy and thermogravimetric analysis (TGA). As demonstrated, the wood matrix became filled by the dense multilayer graphene oxide (GO) membrane structure, which was formed by the layer-by-layer self-assembly of GO nano-sheets. X-ray diffraction (XRD) revealed that the amorphous GO decreased the composite’s relative degree of crystallinity. Additionally, the filled GO generated improvement in the thermal stability of GOW composites in comparison with that of the natural wood (NW).

The physical properties and thermal decomposition kinetics of wood-inorganic composites (WICs) were in focus, which were prepared from methyltriethoxysilane (MTEOS), tetraethoxysilane (TEOS) and titanium (IV) isopropoxide (TTIP) by the sol-gel process. The hydrophobicity and dimensional stability of the composites were better than those of unmodified wood (W contr ), but the performance of SiO 2 -based WICs (WIC SiO 2 ) was the best. The SEM-EDX micrographs show that silica is only distributed within the cell wall of the WIC SiO 2 . By contrast, titania was deposited principally in the cell lumens of the WIC TiO 2 . The thermal decomposition kinetic experiments show that the average apparent activation energies with conversion rates between 10% and 70% were 156–168 (W contr ), 178–180 (WIC MTEOS ), 198–214 (WIC TEOS ) and 199–204 (WIC TTIP ) kJ mol −1 at the impregnation level of 20% weight gain. The reaction order values calculated based on the Avrami theory were 0.51–0.57, 0.39–0.51, 0.36–0.47 and 0.28–0.51 in the same order of species indicated above. Accordingly, the dimensional and thermal stability of the wood could be enhanced effectively by the sol-gel process with silicon- and titanium-based alkoxides.

Wood of radiata pine ( Pinus radiata Don) was treated with an aqueous styrene/acrylic acid (St/AA) copolymer dispersion leading to weight percent gains (WPGs) of 10–42%. The reactivity of St/AA in wood and the modifying effects on wood properties were investigated. The St/AA precipitated in the cell lumens and condensed under catalysis at elevated temperatures was shown via scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Treatment did not cause positive bulking efficiency and anti-swelling efficiency, because St/AA cannot diffuse into the cell walls due to its high molecular mass. The modulus of elasticity and rupture (MOE and MOR, respectively), and the surface hardness of the wood were improved by 24.4, 22.2, and 40.6%, respectively. Compression strength increased by 81.6 and 48.2% in radial and longitudinal directions, but the impact strength was hardly influenced by the treatment. In addition, the treated wood was slightly more hydrophobic than untreated controls as shown by reduced moisture content and water uptake. Accordingly, treatment with St/AA leads to mechanical reinforcement of wood and enhances its water resistance, and as a consequence, it has an application potential to improve the wood quality.

X-ray tomography and densitometry (XRT and XRD) were applied to characterise wood fibre based insulation materials, which were produced by the foam forming technology. XRT is a high resolution approach with long measurement times of around 29 h, while XRD measurement needs only a few minutes. The determination of density distribution of boards in the thickness direction was the focus of this study. Both approaches visualised well the impact of raw materials and manufacturing processes on the structure of the panels. The density profiles were dependent on the pulp applied for panel production, and the processing conditions were also influential. Air flow resistance correlated with the maximum density measured inside the board. Both XRT and XRD revealed similar trends, which are useful for the characterisation of insulation materials.

Non-destructive techniques (NDTs) are well suited for rapid estimation of timber properties, but NDT results are affected by several factors, the most important of which is the moisture content (MC) of wood. Much of the research in this context was limited to ultrasound measurement of a few wood species, mainly to Norway spruce. The present paper investigates the MC influence on the NDT results obtained by instruments based on ultrasound (two devices), impact stress waves (one device) and longitudinal vibrations (two devices). A hundred large cross-section specimens of four timber species were tested, namely: radiata pine, Scots pine, Salzmann pine and maritime pine. The influence of MC on velocity was found to be stronger below the fiber saturation point (FSP) than above FSP. MC adjustment factors below FSP are proposed for these wood species.

The dimensional changes of the cell wall and cell lumens are revisited based on literature data and on the mathematical cylindrical model. The external swelling ratio in the cross-section of the wood cell is considered as a function of the moisture content (MC) m from the point of view of the swelling ratio of the cell wall, the swelling parameter k , which is defined as the ratio of the outer variation to the cell wall thickness variation, and the cell wall density d s . The swelling behavior of the cell lumen is evaluated based on the parameter k calculated from experimental observations, which accounts for both the swelling direction and variation degree of the lumen: the lumen radius (i) decreases at k <1, (ii) remains fixed at k =1, and (iii) increases at k >1. The derived equation was applied to 176 wood species from the literature, and it was found that 0.4< k <1.4, while in most cases 0.8< k <1.0. In other words, the lumen radius in most wood species is decreasing with water sorption. As expected, the S2 layer swelling is differently restricted in the circumferencial direction by the S1 and S3 layers with their different cell wall architecture.

The viscoelastic properties of waterlogged wood (WLW) were investigated via dynamic mechanical analysis (DMA) at room temperature and under water saturated conditions, aiming at the investigation of the relationships between viscoelasticity and chemical composition. Different softwoods (SWs) and hardwoods (HWs) from several archaeological sites were sampled, which had different levels of decay (from highly-decayed to little changed). The analytical methods included lignin and holocellulose determination by Fourier transform infrared (FTIR) spectroscopy, moisture content (MC), basic density (BD), micromorphological observations, and the DMA was performed in three-point bending and submersion mode. Both HWs and SWs showed an exponential decrease of both storage modulus (E′) and loss modulus (E″), which are related to the amount of crystalline and paracrystalline cellulose left in the cell wall, respectively. The ratio E″/E′ (tanδ) varied with the frequency in different ways depending on the preservation state of the samples. Less decayed material had a higher tanδ than the fresh reference wood and lower (or similar) tanδ in the case of highly decayed samples. Accordingly, the long-term behaviour under a certain sustained load of WLW is decay dependent.