Research Articles

Wood fiber sludge is a by-product of the pulp and paper industry, and 750,000 tons are generated per year in Finland. When aqueous fiber sludge (solid matter content 10 to 20%) is modified with water and enzymes, it is called biotechnologically modified fiber sludge (BMFS). So far, native fiber sludge has been only a waste material in Finland, but according to a new waste law, its waste tax is 70 € per ton. According to the present EU and Finnish strategies on waste materials, circular economy, and material-efficiency, all waste must be utilized primarily as material (reuse, recycling) and secondarily as energy. For these reasons, it is very important to develop new eco-, cost- and material-efficient utilization methods for this aqueous “pure waste” instead of landfilling and combustion. Continuing earlier experiments, which proved that BMFS is a good and efficient binding agent for combustion pellets, BMFS was studied in new utilization applications such as bedding pellets for horses as well as a road and horse riding hall dust binding agent. In laboratory measurements and field experiments, BMFS is a very efficient dust-binding agent and effective binding agent for bedding pellets.

Smart hydrophobic-hydrophilic self-switching cellulosic materials were synthesized by regioselective functionalization of cellulose in green Ionic Liquids (ILs). The thermal analysis indicated that the introduction of a macromolecular structure including a trityl or heptafluorobutyric group onto the cellulose chain increased the thermal stability of the cellulose derivatives. Wetting contact angle of the surface decreased from 103° to 73° as the holding time increased at ambient conditions (19.8 °C, 65%). After wetting, the surface free energy increased from 11.03 to 34.09 J·m, of which the polarity component increased from 60.92% to 94.19%. The XPS analysis indicated that the content of oleophobic-hydrophobic CF3-CF2-CF2-CO- groups at the exposed surface decreased after wetting, while the hydrophilic HOOC- groups increased, which verified the self-switching process between the hydrophobic and hydrophilic properties within the cellulosic materials. The self-switching characteristic means that the biodegradable cellulosic materials have suitable selectivities for high-impact applications in various fields.

The use of raw boron minerals (i.e. tincalconite, colemanite, and ulexite) was evaluated to increase the fire performance of wood plastic composites (WPCs) in comparison with commercially available fire retardants (FRs). Cone calorimetry and limited oxygen index tests were performed to evaluate the fire properties of WPC specimens. Artificial weathering and 3-point bending tests were also performed on the test specimens loaded with the highest loading level of FRs. The most important decrease in the heat release rate values was 42% and 40% in the magnesium hydroxide- and colemanite-added WPCs at a loading level of 15% (w/w), respectively. Incorporation of colemanite and ulexite into the WPCs increased the limited oxygen index levels by nearly 13% at the same loading level. An increase was observed in the peak heat release rate values in all of the WPC specimens after accelerated weathering. All of the FRs had statistically improved MOE values compared with the control WPC specimens. In particular, the incorporation of zinc borate and borax increased the MOE values by approximately 48% and 42%, respectively. Similar to the effect on the MOE values, zinc borate and borax improved the modulus of rupture the most (approximately 18%).

Green liquor (GL) combined with ethanol (GL-ethanol) was selected to pretreat sugarcane bagasse (SCB). The results showed that the maximum lignin removal of 85.2% was achieved at 160 °C and a GL loading of 1.5 mL/g-dry substrate. The glucose yield of pretreated SCB increased with increased pretreatment temperature, and the maximum glucose yield of 97.7% was reached from SCB pretreated at 160 °C. Simons’ stain (SS) showed that the glucose yield was affected by cellulose accessibility instead of lignin content when lignin removal was > 70%. The cellulase adsorption isotherm fitted by the Langmuir model showed that the strength of interaction between the cellulase and substrate of GL-ethanol-100/1.5 (100 °C, 1.5 mL GL/g-dry substrate) was declining with increased pH. The adsorption was pH-dependent, and negatively controlled by the pH value. Electrostatic interactions can account for the pH-dependency of cellulase adsorption.

This paper presents the shades of color of Quercus robur L. wood obtained in the processes of thermal treatment and color modification by saturated water vapor, with temperatures: t_I = 112.5 ± 2.5 °C for t = 5.5 h (mode I), t_II = 127.5 ± 2.5 °C for t = 6.5 h (mode II), and t_III = 137.5 ± 2.5 °C for t = 7.5 h (mode III).  The color of oak wood by thermal treatment in mode I changes minimally with mild browning in the CIE-L*a*b* color space: L* = 65.5 ± 1.7; a* = 8.8 ± 0.4; b* = 20.7 ± 0.5. A brown shade with coordinates: L* = 56.8 ± 1.3; a* = 9.3 ± 0.5; b* = 19.4 ± 0.5 is achieved in mode II. Oak wood thermally modified by mode III acquires an original brown-gray color with the color coordinates: L* = 47.5 ± 2.1; a* = 9.4 ± 0.5; b* = 17.1 ± 1.1. The irreversible changes in the color of the oak wood, achieved by some of the color modifications of wood using saturated water steam, extend the possibilities of its use in the field of building-joinery, the artistic field, and the field of design.

This research aimed to determine the isothermal drying kinetic parameters of grain sorghum using a thermogravimetric analyzer (TGA). The kernels were placed in the TGA under isothermal drying conditions, i.e., 40, 50, 60, 70, 80, 90, and 100 °C. Changes in the sample weight were determined from the TGA and the data were used to determine the moisture ratio and the derivative of the weight loss curves. The moisture ratio data obtained experimentally were fitted to four well-known models, namely Page, Newton, Logarithmic, and Henderson, to determine the best-fit model for the experimental data. The goodness of fit criteria was used to determine the best-fit model. An increased drying temperature from 40 °C to 100 °C accelerated the drying process and decreased the moisture ratio from 0.6091 to 0.2909, after 1 h. The Page model was the best fit for 71.4% of the drying curves, whereas the Logarithmic and Henderson models were the best fit for 28.6% of the studied cases. Increasing the drying temperature from 40 °C to 100 °C increased the effective moisture diffusivity from 0.96 × 10−8 m2/s to 1.73 × 10−8 m2/s. The drying activation energy value reached 9.4 kJ/mol under isothermal drying conditions.

An efficient method for the internal structural imaging of cultural wooden relics was explored through experimental techniques of three-dimensional (3-D) tomography and reconstruction. The techniques of filtering and segmentation were applied to the 3-D scanned data of wooden cultural relics.To obtain high resolution 3D data model, it was necessary to preprocess the raw data after CT scanning. Preprocessing included denoising, filtering, and segmentation. After completing these three steps, three-dimensional reconstruction experiments were carried out (including surface rendering and volume rendering). After the 3-D reconstruction, the wood internal properties were visually analyzed and used to create internal structural imaging of wooden artifacts. On the basis of volume rendering, wooden artifacts could be graphically divided at any angle and any position. The textures of local wooden relics were clearly revealed in the segmentation of the reconstruction pictures, and these were compared with the presented internal structural image testing of the wooden artifacts. This study showed that the proposed technology can successfully create internal structural images of wooden artifacts, as well as provide important data and models to support the renovation and recovery of the cultural wooden relics.

The effects of glycerol pretreatment and thermal modification on poplar wood was examined using thermogravimetric analysis (TGA). The total mass losses of thermally-treated samples before and after glycerol impregnation were studied. The thermal degradation process was divided into three stages based on natural breaks in the slope of the TGA curves. The set-on and set-off temperatures, mass loss, and activation energy (Ea) of each stage were compared. Pretreatment with 60% glycerol followed by thermal modification at 160 °C produced pronounced differences in the three decomposition stages. Fewer wood components were decomposed in the first stage in glycerol-pretreated wood, which suggested that the pretreatment had modified the wood components into more thermally stable substances. However, the mass losses were higher in the next stage, suggesting that the effect on thermal stability was limited. The Ea values of wood decomposition during the first stage were decreased, while those during the second and third stages were increased. These results illustrate the potential for using a glycerol pretreatment to alter the thermal stability of wood.

Densification parameters were investigated for the fast-growing pine and eucalyptus. Both woods showed optimal results in terms of apparent density and mechanical properties when milder treatments of 150 °C were applied. Pine showed mass loss and improved mechanical properties with a longer heating time of 60 min, while eucalypt performed better with shorter treatments of 30 min. Eucalypt has more highly acetylated hemicelluloses, mainly composed of xylose units, which degrade more quickly with consequent decrease in mass and mechanical properties. However, apparent densities close to 1.0 g·cm-3 were obtained, and greatly enhanced bending properties, hardness, and impact resistance were observed, especially when the optimal parameters were used. Treatments at 170 °C or greater, while resulting in well-densified specimens, yielded inferior mechanical properties. The densified woods also presented initial apparent contact angles greater than 85°, highlighting a considerable increase of hydrophobicity. The densification process therefore allows these less valuable timber species to be used in applications such as flooring and decking.

This article focuses on the evaluation of the process of planar milling of natural and thermally modified oak wood. The standard Thermowood process was used for the thermal modification. The quality of the machined surface was evaluated after planar milling. Various machining process parameters were set for individual samples. The effects of individual technical and technological factors on the quality of the newly created surface were subsequently evaluated. The mean arithmetic deviation of the waviness profile (Wa) was chosen as the evaluation parameter for milling. The effects of the following factors were monitored: cutting speed, feed rate, rake angle, and their mutual combinations. Natural and thermally modified oak wood were milled and subsequently evaluated. The quality of the machined surface was determined using a contact measuring device. Reducing the cutting speed increased the waviness, and decreasing the feed rate decreased the waviness. However, the cutting speed was not a statistically significant factor. The rake angle proved to be a factor that significantly affected the surface waviness. Thermal modification had a statistically significant effect on the surface waviness.