Volume 77, Issue 3

To improve hydrophobicity and thermal stability, polydimethysiloxane (PDMS) emulsion and silica sol were used for depositing organic/inorganic hybrid coatings in wood. PDMS emulsion could provide the hydrophobic film to improve the hydrophobicity and dimensional stability owing to its low-surface-energy. Silica sol could significantly enhance the surface hardness and thermal stability due to its penetration in cell walls, indicating the pore-filling effect in wood. Moreover, in the hybrid system, silica incorporation in PDMS emulsion helped to form integrate coatings in wood via Si-O-Si cross-linked networks. The hydrophobicity, surface hardness and thermal stability of treated wood were related to the loadings of silica sol in the PDMS. Stiff silica could compensate the negative effect on thermal stability caused by PDMS, and synergistically improve the surface hydrophobicity and hardness of wood. This work opens a facile method to produce bio-based materials with satisfied hydrophobicity and thermal stability to be used in humid environments.

The aim of the present study is to investigate the dissolving ability of a cellulosic substrate using a derivatization method, i.e. cellulose tricarbanilation and the follow-up by dynamic light scattering (DLS), for particle size measurement. The dissolving behavior of six commercial pulps, selected for their different nature and properties, were compared to the Fock test, and the analysis was completed by other methods for substrate characterization: crystallinity (XRD), DPv (in CuED), sugar analysis, molecular weight distribution (MWD) of cellulose by HPSEC-multidetectors (done on the cellulose tricarbanilates), and solubility in NaOH:urea:water. The proposed carbanilation/DLS method resulted practical and suitable for evaluating the dissolving ability of the different pulps – including hemicelluloses-containing kraft pulps – and allowed to discriminate the samples, contrary to the Fock test. Comparison and assessment of the relevance of the different methods are finally discussed.

The degradation of lignin can generate a variety of products with diverse applications. Lignin is abundant on earth; however, its high molecular weight and stable properties impede its development. Currently, acid-catalyzed degradation of lignin is a relatively common and promising catalytic method, particularly DES catalytic degradation, which is not only environmentally friendly but also features an excellent degradation effect. This report discusses the degradation mechanism and effect of the formic acid-choline chloride DES system for the degradation of alkaline lignin. According to fourier transform infrared spectroscopy (FTIR) and 1 H-NMR spectroscopy, it is evident that the phenolic hydroxyl content of lignin increases after degradation, which indicates the cleavage of β - O -4′ ether bonds in the macromolecular structure. Gel permeation chromatography (GPC) was employed to determine the molecular weight of degraded lignin, and regenerated lignin with low molecular weight and low dispersibility was obtained. The minimum average molecular weight ( M w ) was 2.3 × 10 3  g/mol. During the depolymerization process, it was also discovered that the repolymerization and degradation reactions formed a competitive relationship. The lignin oil contained primarily propanoic acid ethyl ester, acetic acid butyl ester, 2-methoxy-4-propyl phenol, 2-methoxy phenol, and apocynin, as determined by GC-MS.

Depolymerisation of kraft lignin under hydrothermal conditions was investigated at short residence times (1–12 min) with glycerol being used as a capping agent. The weight average molecular weight ( M w ) of the products decreased within the first minute of residence time, with the inter-unit ether linkages breaking accordingly. Furthermore, the M w of the product fractions decreased at increasing residence times, while the char yield increased. Short residence times thus appear to be beneficial for mitigating the formation of char. Also, addition of NaOH reduced the yield of char. Although the addition of glycerol caused a decrease in the M w of the products, it seemed to increase the yield of char and therefore might not be a suitable capping agent for kraft lignin depolymerisation.

Rubberwood was modified using a two-step process involving impregnation with maleated lignin (ML) followed by densification. The effects of ML modification and densification on the physical and mechanical properties of modified wood were studied. The successful preparation of ML was confirmed using Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. In addition, scanning electron microscopy was used to characterize the densified rubberwood structure, which featured fully compressed cell walls and cell lumina filled with ML. The rubberwood modification resulted in a more uniform structure and increased density compared to untreated wood. Further, water immersion and moisture absorption experiments revealed thickness swelling of only 27.7% and 20.9%, a reduction of nearly 76% and 55%, respectively, compared to the densified wood that was only impregnated with water. The ML modification can alleviate the embrittlement of wood caused by densification. The modulus of rupture and modulus of elasticity of ML-treated and densified wood improved by nearly 54% and 200%, respectively, compared to untreated wood. Therefore, the synergistic treatment strategy can contribute to the high-value utilization of low-quality rubberwood.

Hygrothermal treatment is an effective method for improving the dimensional stability of bamboo. In this study, changes in the physicochemical properties of Neosinocalamus affinis after hygrothermal treatment were comprehensively investigated: the hemicellulose content decreased, C=O in the acetyl group and the hydroxyl content decreased and xylan was partially degraded. The dimensional stability of N. affinis gradually increased with temperature, and optimal values were obtained at 220 °C, as indicated by a 16.5% decrease in anti-swelling efficiency and a 93.7% increase in contact angle. Alterations in the macromolecular structure of lignin were also observed: the contents of β-O-4 linkages and p -coumarate decreased by 54.3% and 23.9%, respectively; β-5 linkages disappeared at 220 °C, as determined by heteronuclear single quantum correlation spectroscopy. However, the maximum values for crystallinity, nano indentation elastic modulus, and hardness were reached at 180 °C and were higher than those of the untreated samples by 8.6%, 19.9%, and 23.5%, respectively. With the combined application of physical mechanics and dimensional stability, hygrothermal treatment at 180 °C and 100% relative humidity was proved to exert the optimal effects on N. affinis . These results provide new and comprehensive insights into the mechanism allowing the modification of N. affinis by hygrothermal treatment.

The biological deterioration of archaeological wood under oxygen-limited conditions varies due to the limited activities of microorganisms. It is essential to expand the knowledge of the degradation types and the status of archaeological monuments for selecting the proper consolidates. The physical, chemical, and anatomical properties of approximately 600–650 year old archaeological oak collected from an archaeological site in Iasi-Romania were analysed to assess the quality and to identify the degradation types. The results were compared with similar tests on recently-cut oak. X-ray photoelectron spectroscopy (XPS) revealed the presence of more lignin-related peaks in the archaeological oak, which likely reflected the degradation of the wood carbohydrates as evidenced by the decreased oxygen-to-carbon ratio C ox / C non-ox . The differences in cellulose crystallinity were not significant suggesting that any cellulose degradation occurred in the amorphous regions. This was also reflected in the dynamic water vapor sorption analysis where the differences in sorption isotherms and hysteresis of archaeological and recently-cut oaks were marginal. Microscopic analysis of the oak cells illustrated bacterial degradation patterns, while the field emission scanning electron microscopy (FESEM) showed the presence of erosion bacteria in the archaeological oak collected from the site with low oxygen conditions.

Moso bamboo is widely used in production due to its high strength-to-weight ratio, fast growth and renewability. Meanwhile, bamboo’s dimension is highly sensitive to moisture, resulting in cracking and other defects easily. This study aimed to investigate the changes in cracks, bamboo ring shapes, fiber sheath area and volume fraction, and vascular bundle group shapes from the green state to the absolute-dry state, using the target detection model and Python fitting technique. The results showed that the radius of the vascular bundle group increased while its radian and arc length decreased with a decrease in the moisture content. The decrease in the cross-sectional area was greater than that in the wall thickness and arc length. The dry shrinkage of the fibers was greater than that of the rest tissues, which was an important part of the shrinkage of bamboo rings. Obvious cracks mainly appeared in the bamboo ring with a complete radian of 2π, while almost no or very limited cracks were seen in other rings with incomplete radians. This study further elaborated on the dry shrinkage changes and differences in bamboo rings, which might be beneficial to restrain the deformation and cracking of bamboo products effectively.