Volume 70, Issue 8

One of the most significant limitations for a wider utilisation of the renewable and CO 2 -storing resource wood is its low ultraviolet (UV) light stability. The protection of the wood surface without altering its aesthetic appeal requires an optically transparent but UV protective coating which should be strongly attached to the rough and inhomogeneous substrate. For this purpose, ZnO nanostructures were deposited onto the wood surface via a chemical bath deposition process. The morphology of crystalline ZnO was controlled by aluminium nitrate or ammonium citrate in the growth step resulting in nanorod arrays or platelet structures, respectively. Detailed structural, chemical and mechanical characterisations as well as accelerated weathering exposure revealed the effective performance of the platelet structure, which formed a dense and thin ZnO coating on spruce. The total colour change (Δ E in the CIE system) was calculated to be 20.5 for unmodified wood, while it was about three for the modified samples after 4 weeks accelerated weathering test. Moreover, the ZnO coating also suppressed crack initiation and propagation indicating a substantial increase in durability.

Kraft lignin (KL), a by-product in the pulping and papermaking industry, is an abundant, renewable resource. In this work, nanosphere formation of KL has been investigated via self-assembly induced by adding water to a KL/dioxane solution. The KL nanospheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (dynLS) and static light scattering (statLS). It was found that the nanoparticles have uniform nanospherical morphologies, including a small hollow cavity space in the interior. The π-π interactions between the aromatic rings of KL are demonstrated to be an important driving force in the self-assembly process. The KL nanosphere sizes can vary by hundreds of nanometers depending upon the preparation conditions. These newly obtained KL nanospheres have the advantages of biocompatibility, biodegradability, low toxicity, easy preparation, and low cost. Thus KL nanospheres are attractive for applications in life science, medicine, biology, food science, and agriculture. This approach presented here is an economically feasible and facile strategy for the sustainable utilization of kraft lignin.

The effect of thermo-hydro treatment (THT) on the properties of birch ( Betula spp.) wood veneers has been studied. THT was carried out in a multi-functional pilot scale wood modification device of wood treatment technology (WTT, Latvia) under elevated water vapor pressure conditions at four combinations of temperature and treatment time (°C/min): 150/10; 150/50; 160/10 and 160/50. After THT, the following veneer properties were examined: mass loss (ML), chemical composition, bending strength (BS), tensile strength (TS), equilibrium moisture content (EMC), resistance to decay by mould and blue stain fungi, and surface contact angle (CA). The chemical components were changed by THT. Increased THT temperature and time resulted in hydrophobization of veneers as indicated by decreasing EMC and increasing CA data. All THT were effective against wood discoloring fungi, although insufficient decay resistance was observed. The mechanical strength properties of THT veneers were also deteriorated.

Geopolymer binders are an emerging class of mineral polymer that can be manufactured from natural raw materials and industrial byproducts containing high amounts of silica (Si) and alumina (Al) in mineral compositions. Various ratios of materials used for manufacturing geopolymer binder have been tested to evaluate the bonding performance of geopolymers with wood by means of tests performed on an automated bonding evaluation system (ABES). Tests with a binder based on sodium silicate water glass (Na 50T) are partly promising, which resulted only 10% lower shear strength than that based on urea formaldehyde. The binder characteristics were significantly influenced by changing the ratio of SiO 2 :M 2 O (M=Na or K) and the ratio solid content to chemical base in the water glass. Expectedly, increasing press temperatures and pressing times showed a positive correlation with the curing performance of geopolymer binder. It was also demonstrated that the binder properties can be changed in wide ranges to obtain binders which fulfill the minimum requirements set by industrial users.

Previous research indicated that the rolling shear properties of European beech wood ( Fagus sylvatica ) are considerably higher than those of softwood. The aim of the presented investigation was to substantiate previous data on rolling shear modulus and strength of European beech wood and to further evaluate its substitution of softwoods in applications where shear properties are influential, namely as cross layers in cross-laminated timber (CLT). Further, the effect of the annual ring orientation within the boards on shear modulus and strength was of major interest. The beech specimens comprised four different sawing patterns, classified unambiguously with reference to the pith location. The shear properties were determined by 50, two-plate shear tests with specimen cross-section dimensions of 33 mm × 135 mm. A mean rolling shear modulus of 370 N mm -2 was obtained, whereby no significant detrimental effect for pith boards with cracks was observed. In agreement with continuum mechanics, the semi-quarter-sawn boards revealed the highest shear moduli whereas the quarter-sawn boards showed roughly 30% lower values. The mean rolling shear strength was 5.6 N mm -2 for all specimens, whereby pith specimens resulted in generally lower values. The 5% quantile, disregarding pith specimens, was 4.5 N mm -2 . In conclusion, the rolling shear strength and modulus exceed the respective characteristic values for softwoods by roughly factors of 5 and 7, indicating great potential for beech wood cross-layers in CLT.

Freshly harvested palm trunks and timber with their high moisture content (MC) are susceptible to fungi due to the high content of easily consumable sugars and starch as long as MC of the tissue is above fiber saturation point (FSP). To test the influence of sugars and starch on fungal development, small wood samples from oil palm ( Elaeis guineensis ) were watered and their contents of the non-structural carbohydrates were measured. Glucose was the most abundant substance in the extract, followed by starch, fructose, and sucrose. Watering for 3 and 10 days with daily water exchange reduced the content of sugars and starch considerably. Untreated and watered samples were then subjected to spore suspensions of the moulds Aspergillus niger , Penicillium commune , to a natural infection by air-born spores and to the blue-stain-fungi Alternaria alternata and Aureobasidium pullulans. The former colonized the surface of the untreated samples within a few days, while the latter caused considerable mass loss. With increasing watering both fungal activities were reduced as the nutrients for the fungi were removed. The woods of E. guineensis and Phoenix dactylifera (date palm) with MC above FSP were treated with acetic and propionic acid and subsequently infected by moulds, staining and decay fungi. Short dipping in solutions of 2% acetic acid and 2% propionic acid, respectively, protected all samples for 3 months against the mould fungi. Staining fungi and wood-decay fungi were slightly inhibited by a treatment with 5% acid concentration. Treatment with these acids offers a protection technique for the practice. Their sodium salts were ineffective due to their high pH-value.

The dimensional stability and mechanical properties of radiata pine ( Pinus radiata) has been investigated after thermo-mechanically compression (TMC) followed by oil heat-treatment (OHT). Wood specimens were first compressed in the radial direction then heat-treated in a linseed oil bath at 160–210°C. Spring-back percentage, water repellence efficiencies, and compression set recovery percentage were determined as indicators of dimensional stability. The resistance of treated wood against a brown rot fungi was assessed based on an accelerated laboratory fungal decay test. Strength, stiffness and hardness were determined as a function of different treatment parameters. After TMC, high compression set (39%) was achieved without any surface checks and cracks. Specimens undergoing TMC followed by OHT showed relatively less swelling and low compression set recovery under high moisture conditions. The fungal resistance of wood after TMC+OHT slightly increased compared to untreated wood and TMC wood. The mechanical properties of TMC+OHT wood were inferior to those of TMC wood.