Volume 70, Issue 1

A deep understanding of alkali impregnation including the profiles of alkali concentration and hemicellulose degradation is necessary to analyze the optimization of current and innovative processes. In this paper, the impregnation of Scots pine ( Pinus sylvestris L.) wood is analyzed and modeled under consideration of deacetylation, reactions of acidic group, and galactoglucomannan (GGM) degradation. The immobile anionic groups activated by the ionization of lignin-derived OH groups are also considered for the assessment of the Donnan effect. Predicted profiles of sodium and hydroxide ions and acetyl group concentrations are compared to experimental results. The balance between impregnation and hemicellulose degradation levels is discussed based on the developed models. Expectedly, higher concentrations and temperatures speed up the impregnation process. Nevertheless, a higher OH - concentration has two benefits for the same impregnation front position – the alkali charge inside the chip is higher and the GGM degradation is lower.

The polydispersity of commercially available kraft lignins (KLs) is one of the factors limiting their applications in polymer-based materials. A prerequisite is thus to develop lignin fractionation strategies compatible with industrial requirements and restrictions. For this purpose, a solvent-based lignin fractionation technique has been addressed. The partial solubility of KL in common industrial solvents compliant with the requirements of sustainable chemistry was studied, and the results were discussed in relation to Hansen solubility parameters. Based on this screening, a solvent sequence is proposed, which is able to separate well-defined KL fractions with low polydispersity.

The process sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) has been the focus of this study. Pilot-scale (50 kg) pretreatment of wood chips of lodgepole pine ( Pinus contorta Douglas ex Loudon) killed by mountain pine beetle ( Dendroctonus ponderosae Hopkins) were conducted at 165°C with a dilute sulfite solution of pH 2 for bioconversion to ethanol and lignosulfonate (LS). The pretreatment duration was optimized in laboratory bench scale experiments with a certain severity based on a combined hydrolysis factor (CHF). The sodium bisulfite loading was 8% and the liquor to wood ratio 3. The pretreated solids were disk milled together with the spent liquid and the resultant slurry with a 25% solids content was directly (without detoxification) submitted to a simultaneous enzymatic saccharification and fermentation (SSF) with Saccharomyces cerevisiae YRH400 at cellulase loading of 35 ml kg -1 of untreated wood. At solids loading of 20%, the alcohol yield was 288 l t -1 wood (with a final concentration of 52.2 g l -1 ), which corresponds to a 72.0% theoretical yield based on total glucan, mannan, and xylan. The LS from SPORL was highly sulfonated and its molecular weight was lower than that of a purified commercial softwood LS, and therefore it has a high potential as a directly marketable co-product.

Hot water extraction (HWE) partially removes hemicelluloses from wood while leaving the majority of the lignin and cellulose; however, the lignin partially migrates to the inner surfaces of the cell wall where it can be deposited as a layer that is sometimes visible as droplets. This lignin-rich material was isolated via Soxhlet extraction with dichloromethane to investigate its rheological behavior in blends with high-density polyethylene (HDPE), a common material in wood plastic composites (WPCs). Pyrolysis gas-chromatography/mass spectrometry (Py-GC/MS) and electrospray ion mass spectrometry (ESI/MS) confirmed that the isolated material is constituted mainly of low-molecular-weight lignin oligomers. The blends of HDPE/isolated lignin, in varying ratios, were tested by means of dynamic rheology. A “shoulder” was found in plots “shear storage moduli (G′) vs. frequency sweep” and a shift of the terminal zone to lower frequencies was observed. Apparently, this shoulder is caused by the elastic contribution of the interfacial tension between the blend components. The rheology of WPCs produced from HWE wood and HDPE shows a similar shoulder in G′ plots, suggesting that the HDPE/lignin blends are in part responsible for the shape of the G′ curves.

Tree barks could be a rich source of novel bioactive compounds, which are not well explored. In this work, the chemical constituent investigation of extractives from the inner barks of Sophora japonica L. (Leguminosae) led to the isolation of a new cis - p -coumaroyl flavonol glycoside, which was elucidated as kaempferol 3- O -(4″- cis - p -coumaroyl)-α-rhamnopyranoside ( IV ). The structure of the new compound was established mainly based on extensive spectroscopic techniques. In addition, among the four known phenolics purified in this study, including three flavonol glycosides [rutin ( I ), kaempferol-3- O -(6″-galloyl)-β-glucopyranoside ( II ), and quercitrin ( V )], as well as a phenolic acid [ trans -ferulic acid ( III )], compounds II and III have never been reported in S. japonica previously.

Poplar wood ( Populus adenopoda Maxim) has been modified by glucose (GLC) in the presence of citric acid (CA) or 1,3-dimethylol-4,5-dihydroxy ethyleneurea (DM) as crosslinker agents. GLC can penetrate easily the wood cell walls, and after crosslinking, the cell wall is bulked. At 20% GLC concentration level, the leaching ratio of GLC incorporated into wood decreased from 73% to 15% in the presence of 10% CA or DM. The crosslinking efficiency of DM was higher than that of CA. The fixed chemicals in the cell walls caused ca. 6% permanent bulking, namely, a 43% reduction in volumetric swelling after water saturation. FTIR spectroscopy shows that GLC can be activated in the presence of a catalyst; however, the reaction of GLC with a wood polymer is very limited. Scanning electronic microscopy (SEM) reveals that some of the chemicals remained located in the cell lumens. The findings demonstrate that GLC alone is not efficient, but joint treatment of GLC with crosslinkers is a feasible way of wood modification.

The paper aims at the investigation of atmospheric pressure weakly ionized plasmas with argon and acetylene to deposit plasma-polymerized coatings on wood veneers (birch, maple), cellulose paper, and pine wood flour to modify their surface properties, in particular their topography and wettability. The treatment was performed in a reactor containing an array of high-voltage needles and a grounded metallic mesh as electrodes. The deposition occurred in the discharge downstream of the plasma region. The plasma-polymerized acetylene deposits form spherical nodules on the surface of the substrates and change their wettability from hydrophilic to hydrophobic. The water contact angles of the veneer were determined with a goniometer. The capillary rise was combined with the Washburn equation to assess the change in hydrophilicity of the plasma-treated wood flour.

A simple and effective method for preparing superhydrophobic conductive wood surface with super oil repellency is presented in this paper. Silver nanoparticles (Ag NPs) were prepared on wood surfaces by the treatment with AgNO 3 , followed by a reduction treatment with glucose to generate a dual-size surface roughness. Further modification of the surface coated with Ag NPs with a fluoroalkyl silane led to a superhydrophobic surface with water contact angle of 155.2°. This surface is also super repellent toward motor oil with the maximal contact angles around 151.8°. Interestingly, the dense Ag NPs coating on the surface is electrically conductive. The presented multifunctional coating could be a commercialized for various applications, especially for self-cleaning and biomedical electronic devices.

The wetting, dimensional stability and sorption properties of a range of modified wood samples obtained either by acetylation or furfurylation were compared with those of unmodified samples of the same wood species via a multicycle Wilhelmy plate method. Wettability measurements were performed with water and octane as the swelling and non-swelling liquids, respectively. It was found that acetylation reduces water uptake mainly by reducing the swelling. In comparison, furfurylation reduces both swelling and the void volume in the sample. To quantify the effect of the modification process of the wood properties, the parameters “liquid up-take reduction” and the “perimeter change reduction” were introduced, which were determined from multicycle Wilhelmy plate measurements. Compared with the acetylated wood, the furfurylated wood with a higher level of weight percent gain exhibited larger property changes on the surface and in terms of swelling and sorption properties.

The possibility for pre-grading of logs throughout the year has been evaluated based on dynamic modulus of elasticity (MOE dyn or simplified E dyn ) by means of frequency-based nondestructive testing (NDT freq ). The challenge is that E dyn is variable in the frozen, partly frozen, and unfrozen states of logs (state of matter). In the unfrozen state, NDT freq is reliable if the moisture content does not fall below fiber saturation. The state of the matter was tested via temperature measurements of air and log by means of an infrared technique and sensors, and information was evaluated from NDT freq . The temperature measurements proved to be inefficient for industrial application because of unreliable data and long measurement times, whereas the NDT freq measurements allowed the determination of meaningful damping factors. A sufficient level of predictability for more than 60% of the measurements was found. The log measurements in the partly frozen state are inconclusive because E dyn data fluctuate in the presence of both liquid and frozen water. For the completely frozen logs, a correction is introduced as a precaution that avoids an overestimation of E dyn in the unfrozen state.

Cork is a natural cellular material with a rather unique set of properties, and its best known application is as stopper for wine bottles. The cork tissue contains structural discontinuities, for example, lenticular channels (LCh), that influence the in-use performance of cork products. X-ray microtomography, in combination with image analysis, has been used for cork characterisation and provided new insights into the three-dimensional location of discontinuities, which are hidden for a visual inspection. It was demonstrated that the presence of LCh is positively correlated with cork density, and the void fraction of LCh in the lower part of a cork stopper is strongly related to the oxygen ingress in the bottle during the first month after bottling. The results contribute to better understanding the natural variation of cork properties.