Volume 77, Issue 5

Although highly desirable, the nature of wood-cellulose in its native state has remained difficult to comprehend. Contrary to the traditional acceptance of wood-cellulose being crystalline, in 2016, the authors’ research found that the cellulose was not crystalline. Here, additional evidence is presented that further supports the non-crystalline model. One of the key pieces of evidence was obtained by 64% H 2 SO 4 hydrolysis of tension- and opposite-aspen woods (TW and OW, respectively). The TW (G-layer rich) yielded significant amount of CNCs (TW-CNCs, 20.7%), the OW yielded a much lower amount (OW-CNCs, 5.4%). Although a higher yield of TW-CNCs was expected due to the presence crystalline cellulose in the G-layer, the lower yield of the OW-CNCs was a surprise because, assuming absence of G-layer, based on the authors’ earlier findings no CNCs were expected to be generated. To explain this anomaly, anatomical examination of the woods using stains was carried out which showed that some OW fibers also contained the crystalline G-layer and therefore, provided an explanation as to why the OW-CNCs were produced. The results clearly showed that the acid hydrolysis did not destroy the crystalline cellulose and therefore, in the case of a normal (G-layer free) wood which, as previously reported had not generated CNCs, the cellulose must have been non-crystalline. An additional indication of the wood’s S 2 cellulose being not crystalline was the absence of the 93 cm −1 Raman band in the low frequency spectrum of the TW S 2 layer. Further evidence was obtained by comparing low frequency Raman spectra of TW-CNCs, TW-holopulp, and aspen-holopulp as well as the mixture-samples of crystalline cellulose and xylan at the concentration levels of their occurrence in these holopulps. Overall, these findings provided further support to the contention that the native wood-cellulose is non-crystalline.

Oxidation of kraft pulp using hydrogen peroxide under mild acidic conditions can be applied in order to obtain new functionality of the fibres, in the form of carbonyl groups. The hydrogen peroxide concentration must, however, be higher than consumed by the oxidation reactions meaning that the liquid must be recirculated to fully utilize the hydrogen peroxide. This paper investigates the consequences of recirculation of the oxidation liquor. It was found that recirculation results in an accumulation of ions of transition metals (copper, iron and manganese) in the oxidation liquor. The transition metal ions are known for catalytic decomposition of hydrogen peroxide, producing radicals which may react with carbohydrates, forming carbonyl groups as well as causing carbohydrate degradation. This was confirmed through the recirculation of oxidation liquor as well as through controlled addition of transition metals. At high transition metal ion concentration the reactions were fast and a severe degradation of carbohydrates was observed, accompanied by a rapid hydrogen peroxide consumption. The consequence of this, in an industrial context, is that the concentration of metal ions must be carefully controlled in order to add functionality to the cellulose without causing excessive degradation of carbohydrates or consumption of hydrogen peroxide.

Efficient and nondestructive technology for identifying wood species facilitates the transition from digital forestry to smart forestry. While near-infrared spectroscopy applied to wood identification is well documented, the detailed mechanisms for chemometrics remain unclear. In this study, twelve wood species were identified by using near-infrared spectroscopy combined with six machine learning algorithms (support vector machine, logistic regression, naïve Bayes, k -nearest neighbors, random forest, and artificial neural network). Above all, isolated forest and local outlier factor were used to detect and exclude outliers. Then feature engineering strategies were developed from three perspectives to process feature matrices: feature selection, feature extraction, and feature selection combined with feature extraction. Next, the learning curve, grid search method, and K -fold cross-validation were used to optimize the model parameters. Finally, the accuracy, operation time, and confusion matrix were used to evaluate the model performance. When the local outlier factor was used to remove outliers and principal component analysis was used to extract features, the support-vector-machine-based wood-species identification model produced the most accurate results, with 98.24% accuracy. These results offer new avenues for constructing automatic wood-identification systems.

A novel thermo-mechanical pulping (TMP) process has been developed to produce a by-product rich in high-molecular weight (MW) hemicelluloses, a potential raw material for barrier coatings and films. This process uses prehydrolysis to solubilise the hemicelluloses followed by chip compression to separate the soluble material from the wood matrix. The pressate from the chip compression stage was dark-coloured and had a high content of high-MW hemicelluloses and lignin. However, isolating the high-MW material from the pressate directly by ultrafiltration was not feasible because of membrane fouling by dissolved lignin and wood extractives, while coloured impurities are undesirable for many potential applications. To solve these problems the pressate was purified using XAD adsorbent resin to remove low-MW lignin, extractives and colour. Ultrafiltration of the purified pressate yielded lightly coloured high-MW hemicellulose with a low content of lignin and well suited for barrier films and coatings.

The effects of pressurized hot water extraction (HWE) treatment on the mould resistance of wood have not been extensively investigated yet. The activity of the mould fungi is dependent on the availability of nutrients. Therefore, the soluble degradation products produced during HWE treatment could affect the wood’s susceptibility to mould growth. Scots pine ( Pinus sylvestris L.) sapwood specimens were treated with HWE at 140 °C for 1–5 h. Afterwards, the degradation products were either removed via leaching or the wood was dried without applying the leaching procedure. The surface layer (1.5 mm) was removed from half of the leached and non-leached specimens. The resistance of the specimens against mould growth was tested in an incubation chamber. HWE treated wood showed a higher susceptibility to mould growth when it was neither leached nor subjected to surface removal. The susceptibility of wood to mould fungi depended on the availability of hemicellulose-based degradation products produced during HWE treatment. These degradation products were removable via a leaching procedure, but also by removing the outermost layer of the wood. The results show the relevance of removing HWE degradation products located on the wood surface in improving resistance against mould growth.

Wood is a biosourced material with unique aesthetic features due to its anatomy and chemical composition. White oak wood surface color can be modified with the use of iron salts, which react with wood phenolic extractives, present as free molecules in wood porous structure. The impact of modifying wood surface color with iron salts on the final appearance of wood, including its color, grain contrast and surface roughness, was evaluated in this study. Results showed that following the application of iron (III) sulphate aqueous solutions on white oak wood surface, its roughness increased, which is due to grain raising after wetting of wood surface. The color modification of wood surface with iron (III) sulphate aqueous solutions was compared with a non-reactive water based blue stain. The contrast associated to wood grain that was expressed by the standard deviation of luminance values in wood images, also increased after application of the iron (III) sulphate aqueous solution on white oak wood surface. The comparison of contrast changes showed that wood samples stained with iron (III) sulphate on their curved surface had the highest increase in grain contrast compared to iron-stained wood showing the straight grain and to wood surfaces colored by a non-reactive water-based stain for both curved and straight grains.

The structure of the bamboo node obviously differs from that of the internode and largely affects the mechanical properties of bamboo. However, the node structure of moso bamboo, an important economic and ecologic bamboo species, was still unclear. Thus, in this study, the 3D structural changes of the vascular bundle (VB) in the moso bamboo node were visualized and quantified. The compressive properties and failure mechanisms of the bamboo node were discussed based on the structural changes. The results showed that the horizontal VB in bamboo node was classified into three types: branching, cross-linking, and thickening. The cross-sectional area of the vertical VB in bamboo node increased, and the vertical VBs shifted to the outer side after passing through the node. Due to the “wire hoop” effect of the horizontal VBs, the longitudinal compressive strength of the node was greater than that of the internode. The deflection of VBs caused slippage between VBs and resulted in the decrease of the node’s transversal compressive strength. This research provided key information for a deeper understanding of the structure and mechanical properties of bamboo for potential applications.

The Japanese longhorn beetle, Anaglyptus subfasciatus , infests coniferous trees resulting in stained wood and low-value discolored lumber. In this study, the discolored Hinoki ( Chamaecyparis obtusa ) wood was analysed by GC-MS for n -hexane extract, and laboratory wood block tests against termite was carried out. Stained wood had anti-termitic resistance similar to normal heartwood, and it had about twice the n -hexane extract by weight than obtained from heartwood. One compound, nerolidol, was characteristically found in the stained wood. The results suggest that the stained wood may have produced some bioactive components due to damage by wood decay organisms.