A one-pot silane-bridge strategy for synergistic wood modification: improving cinnamaldehyde fixation, mold resistance, and dimensional stability

Bamboo is naturally susceptible to mould and dimensional instability under humid conditions, which limits its durability in practical applications. This study aimed to determine whether water-based ultrasonic pretreatment could improve moso bamboo’s (Phyllostachys edulis) dimensional stability and mildew resistance by altering microstructure and physicochemical properties. Results showed that ultrasonic pretreatment increased the mass loss rate by 0.2–0.8 %. It reduced the hot-water extractive content by 6–7 %, and decreased absolute-dry density by 0.02–0.06 g/cm3. The treatment caused pit membrane rupture and parenchyma wall thinning (the distribution range narrowed to approximately 5.5–12.5 μm at 20–60 min), and removing amorphous components enhanced cellulose crystallinity by about 8.4 % and slightly reduced microfibril angle by 1.8 % (both at 10 min). These microstructural and physicochemical changes led to improved dimensional stability with about 0.2 % reduction in radial swelling, despite slightly higher moisture uptake. More importantly, mould resistance improved significantly. Mould infection decreased by about 20 % for A. niger (to around 45 % at 30 min) and about 83 % for P. citrinum (to about 10 % at 60 min). The findings demonstrate good potential for ultrasonic pretreatment as a green, non-chemical method to enhance moso bamboo’s dimensional stability and mildew resistance. Ultrasonic pretreatment could also be combined with other modification strategies to achieve superior performance in demanding service environments.

The aim of this study was to investigate the dimensional stability and mold resistance of slivers from the outer and inner layers of bamboo treated with alkali solutions at various concentrations. The microstructure of the bamboo slivers considerably changed as the parenchyma cells collapsed after alkali treatment followed by a drying process. The water absorption of the treated bamboo slivers increased, while the dimensional stability decreased, especially for the slivers from the inner layer of bamboo. The alkali treatment removed starch from the parenchyma cells in the bamboo slivers treated with a 2% to 15% alkali solution, resulting in a considerable improvement in the mold resistance. The mold resistance performance of inner bamboo slivers was greatly improved when treated at a low concentration (2%). No mold on the bamboo slivers was found even in a high humidity environment for a long period of time, i.e. 87 days. As the concentration increased up to 25%, alkali only removed starch from parenchyma cells that were near the surface of the bamboo slivers and caused partial damage to the parenchyma cells in the outer bamboo slivers. The wettability of the alkali-treated bamboo slivers was higher than that of the untreated samples due to the removal of lignin and a rougher surface. Based on the test results, alkali treatment is a simple yet highly effective method for improving mold resistance but would cause a reduction in the dimensional stability of the bamboo slivers.

Facile preparation of bamboo with improved hydrophobicity, dimensional stability and mold resistance by paraffin/tung oil modification

Wood modification by impregnation with phenol-formaldehyde (PF) resins is a promising method to improve the woods’ fungal decay resistance, weathering resistance, and dimensional stability. Recent research indicates that 30% of the non-renewable phenol may be substituted by renewable softwood kraft lignin cleavage products obtained through microwave-assisted pyrolysis. Pinus sylvestris sapwood modified with this resin has good fungal decay resistance but slightly enhanced formaldehyde emission. While these results on solid wood indicate a high potential of the method, the properties of modified plywood may differ, and the weathering resistance has not been studied. In this study, formaldehyde emission, weathering resistance and fungal decay resistance against three basidiomycetes (Trametes versicolor, Rhodonia placenta, and Gloeophyllum trabeum) of plywood modified with pure PF resin and PF resin with 30% substitution of the phenol by lignin cleavage products were analysed. The 30% lignin cleavage product substitution didn’t affect the plywood’s fungal decay resistance, with less than 1% initial mass loss in all modified specimens. While the decay resistance improved significantly for all modified samples compared to reference samples, weathering resistance slightly declined with phenol substitution compared to pure PF resin modification. The formaldehyde emissions of the plywood modified with both resins were in similar ranges to that of unmodified reference plywood. Overall, plywood with good properties for exterior applications may be produced even with the substitution of 30% of the phenol by lignin cleavage products, allowing for increased use of renewable resources.

Given the increasingly prominent contradiction between the supply of and demand for wood, the abundant resource of bamboo can be a good substitute. Bamboo scrimber can effectively improve the utilization rate of bamboo and has good mechanical properties. However, bamboo scrimber has the problem of poor mildew resistance, and does not meet the requirements for outdoor applications. In this study, in order to further improve the mildew resistance and mechanical properties of bamboo scrimber, alkali treatment was used to remove some nutrients from the bamboo bundles and change the pH of the bamboo scrimber. The results showed that nutrients such as hemicellulose, lignin, starch, and sugar were notably removed from bamboo bundles, and the pH of bamboo was slightly alkaline. The anti-mildew effect was significantly enhanced, which could allow use in outdoor environments, and the mechanical properties and dimensional stability were also improved. Among them, TB6 bamboo scrimber showed comprehensively excellent properties. The infection time in the laboratory mildew test increased from 3 days to more than 30 days, and the infection time in the outdoor mildew resistance test increased from 1 week to more than 8 weeks; the static bending intensity of TB6 increased by 62.6% to 150 MPa, and the bending modulus increased by 71.7% to 14.2 GPa; the change rate of water absorption thickness was reduced to 0.58%. This modification method effectively improved the mildew resistance of bamboo scrimber, while maintaining high mechanical strength, and provides a new method for the outdoor application of bamboo scrimber.

Bamboo is a natural and renewable building material but its application has been limited due to the low dimensional stability and poor durability against mold. In this study, monomers of hydroxyethyl methacrylate (HEMA) and N-isopropyl acrylamide (NIPAM) were impregnated in bamboo to facilitate the in situ growth of poly-HEMA and NIPAM (PHN) copolymer. Prior to that, the effects of different reaction conditions, including the molar ratio of HEMA to NIPAM and their concentrations, the amount of initiator (ammonium persulfate, APS) and crosslinking agents (N,N′-Methylenebisacrylamide (MBA), and glutaric dialdehyde (GA)) on the swelling capacity of PHN were optimized. The formation of PHN was confirmed by using Fourier transform infrared spectroscopy and thermogravimetric analysis, which shows the characteristics peaks of both HEMA and NIPAM, and increased pyrolysis and glass transition temperatures, respectively. After impregnation of PHN pre-polymerization formulation to bamboo, it was observed that PHN filled most of the pits in the bamboo cell wall and formed a tight network. Moreover, the dimensional stability of PHN treated bamboo was significantly improved with an anti-swelling efficiency of 49.4% and 41.7%, respectively, after wetting–drying and soaking–drying cycles. A mold infection rate of 13.5% was observed in PHN-treated bamboo as compared to a 100% infected control group after a 30-day mold resistance test. Combined results indicate that in situ polymerization of HEMA and NIPAM in bamboo is a promising method to develop exterior used bamboo products with enhanced dimensional stability and mold resistance.

Pinus radiata wood specimens were heat-treated at 160–210°C in linseed oil and the effects of treatment on chemical composition, color, dimensional stability, and fungal resistance were examined. The degradation of hemicelluloses was the most remarkable feature, which is the principal reason for alterations in wood properties. Removal or migration of extractives, oil uptake and the accumulation of oil on the wood surface were observed. The color of heat-treated wood became more uniform and darker, and its dimensional stability (i.e., anti-swelling efficiency) and fungal resistance were improved by up to 60% and 36%, respectively. The viscosity of the oil after treatment was elevated with the treatment temperature and was higher in comparison to heated oil without wood present.

Pinus caribaea (Pine) is an underutilized timber species in Sri Lanka due to its low density, durability, dimensional stability, and undesirable colour. This research aims to examine the enhancements in the physical and mechanical properties of Pinewood through thermal modification (TM) and compare the properties of the TM wood with kiln-dried and untreated wood and with the properties of high-graded timbers of Tectona grandis (teak) and Koompassia malaccensi (kempas). TM is a process that involves heating wood to high temperatures (2000 C) in the absence of oxygen, which removes the moisture and creates changes in the wood at the cellular level. The effectiveness of the thermal modification on density, modulus of rupture (MOR), modulus of elasticity (MOE), moisture content, dimensional stability, durability, and colour was studied. Specific gravity of thermally modified wood was 6% higher than untreated wood, but lower than teak and kempas. MOR and MOE values were 35.75% and 46.46% respectively higher than untreated wood. Equilibrium moisture content was reduced after TM and volumetric shrinkage of TM was reduced to 2.16% and swelling under liquid water contact was reduced to 2.37%. Thermally modified timber was classified as not durable (DC 5) based on field test (EN 252, 2014) results. However, TM timber was slightly durable (DC 4) according to laboratory tests and showed better fungal resistance. The wood underwent a darkening effect as a result of thermal modification, resembling the colour of teak. The cost of TM was 13.1% higher than kiln drying. Improved dimensional stability, enhanced bending strength, and attractive appearance demonstrate the potential of thermal modification as a promising alternative for transforming P. caribaea wood into high-value raw material. TM timber finds suitable applications in indoor furniture and joinery projects. However, due to its lack of termite resistance, preservative treatment is recommended for outdoor ground contact usage.
 
 Keywords: Thermally modified timber, Mechanical properties, Dimensional stability, Durability,
 Pinus caribaea

In this study, low-temperature thermally-modified (at 140°C) Scots pine (Pinus sylvestris L.) wood samples were impregnated with either one or more modifying agents, including the brown colorant, paraffin wax emulsion (PWE), and an organic preservative (4,5-dichloro-2-octyl-2H-isothiazol-3-one, DCOIT) microemulsion. All wood samples were assessed in dimensional stability, water absorption, the modulus of rupture (MOR), decay and mold resistance, and their weathering performance under both labscale and outdoor exposure. The results showed that 1) the treating groups with PWE showed obvious lower water absorption, and the lowest value appeared in the group treated with brown colorant and PWE (BCPWE); 2) thermal modification improved the dimensional stability of wood, whereas all the further treatments except the group impregnated with PWE slightly counteracted the effect of thermal modification on dimensional stability after water soaking; 3) the MOR of thermally-modified sample showed little change after further treatments; 4) and thermally-modified wood treated with BC-PWE-DCOIT showed the optimal weathering performance with the least color change and the best mold resistance.

Vapor-phase acetylation of heartwood in Japanese cedar wood (Cryptomeria japonica D. Don) was carried out as a surface acetylation method to elucidate the relationship between the depth of acetylated area and fungal decay resistance. The acetylated wood (VPAW), prepared with acetic anhydride vapor by heating at 80°C for 72 h, indicated a significant fungal decay resistance and dimensional stability in water-soaking test, similar to liquid-phase acetylated wood (LPAW). The VPAW provided more than 15% of the weight percent gain (WPG) up to a depth of 7 mm from the wood surface, while LPAW gave ∼20% WPG uniformly throughout the wood. However, 24-h vapor-phase acetylation, giving 15% WPG at a depth of 0–2 mm, showed insufficient fungal decay resistance. These results showed that at least 7 mm thickness of the acetylated region with 15% WPG was required to suppress the fungal decay of acetylated wood under laboratory conditions.

In this study, two plant derived compounds, namely tannin acid (TA) and tung oil (TO) were used to modify southern yellow pine wood (Pinus spp.) to enhance its durability. Wood samples were firstly impregnated with aqueous TA solutions at 5, 10 and 15%, respectively, and then impregnated with TO. Samples treated by TA or TO alone were also prepared. The dimensional stability, hydrophobicity, mold resistance, and thermal stability of both treated and untreated wood were evaluated. The results showed that the dimensional stability and hydrophobicity of wood treated with 10% TA and TO (T10+TO group) improved significantly. Compared with control group, the water absorption of T10+TO group decreased by 80.0% after 192 h immersion, and the antiswelling efficiency reached up to 90.7%, with the contact angle of 118° at 50 s. The mold resistance of wood after 5% TA and TO treatment presented an effectiveness of 87.5%. Meanwhile, T10+TO group presented better thermal stability. Overall, this study revealed that wood impregnated by TA and TO exhibited excellent dimensional stability and anti-mold properties, which could be applicable to indoor environment.

In this study, a novel composite was fabricated based on phenol‐formaldehyde (PF) resin and bamboo fiber bundles. Various characterization techniques including fluorescence microscope, scanning electron microscopy coupled with energy‐dispersive X‐ray, and transmission electron microscope were used to investigate the distribution of fibers and infiltration of PF resin. The water repellency, dimensional stability, and decay resistance against both white‐rot (Trametes versicolor) and brown‐rot (Gloeophyllum trabeum) of the composites were also tested. The results showed that the resin not only deposited on the fibers surface, but also entered into the cellular wall and cell lumina through the pits. A great amount of resin was found in cracks and middle lamella of cell wall in resin impregnated bamboo fiber bundles owing to the mechanical defibering process. After thermal compressing, the bamboo cells were densified. The resin was redistributed in cell lumen and glue‐joints were formed. Some chemical reactions occurred between PF and bamboo by formation of aromatic esters and ether bonds, and the ether bonds were dominant. Thus, significant improvements in water repellency, dimensional stability, and biological resistance were achieved. These results suggested the composites can be used in exterior applications where high levels of water repellency and fungi resistance were required. POLYM. COMPOS., 40:506–513, 2019. © 2017 Society of Plastics Engineers

Nano-Fe3O4/bamboo bundles/phenolic resin oriented recombination ternary composite with enhanced multiple functions

A highly effective mildew and rot-resistant finish has been developed in which methylated trimethylol melamine is padded on the fabric in the presence of a cure modifier (thiourea) and an acid-forming catalyst and then cured at 350° F for 1-3 min. Reasons and data are given to support the selection of the recommended resin and buffer combination. The principle of this continuous process and its mill application are discussed. Test results are presented which demonstrate that finished fabrics may be expected to rctain 80-100% of their initial tensile strength through long periods of weathering or soil burial even when preceded by extended water leaching. Dimensional stabilization is achieved, and the finish has little or no adverse effect on hand, abrasion resistance, or shades of mineral dyed fabric. Data are cited showing the various levels of rot resistance that can be obtained by varying the resin ccmtent. The experimental evidence obtained suggests that cellulose is chemically moditied by the resin, and it is proposed that rot resistance is achieved by this mechanism.

The inherent hydrophilicity of bamboo severely limits its dimensional stability, durability, and resistance to mold in humid environments. In this study, a waterborne rosin emulsion was employed to improve the performance of bamboo. Bamboo strips were impregnated with rosin emulsions with different solid contents using a vacuum-pressure process at ambient temperature. The effects of rosin impregnation on microstructure, pore structure, physical and mechanical properties, thermal stability, and mold resistance were systematically investigated. Results demonstrated that rosin effectively penetrated cell lumina, pits, and micropores, reducing porosity and blocking moisture transport pathways. Consequently, the treated bamboo exhibited significantly reduced water absorption, enhanced surface hydrophobicity, and improved dimensional stability with an anti-swelling efficiency of 31.54% at a relatively low weight percent gain of 4.29%. Moderate improvements in bending strength and stiffness were also observed. Thermogravimetric analysis indicated that rosin impregnation increased the thermal stability of bamboo by shifting the main degradation temperatures to higher values. Furthermore, rosin-treated bamboo demonstrated markedly improved mold resistance, particularly against Trichoderma viride and Penicillium citrinum. These results demonstrated that rosin emulsion impregnation provides a green, efficient, and scalable strategy for enhancing the performance of bamboo for applications in humid environments.