Hydrophobic Wood Research Articles

Cellulose nanofibers-based UV resistant and hydrophobic wood coatings

Wood and wood-based products are regarded as sustainable building materials, nonetheless, they frequently need the addition of protective coatings due to their susceptibility to abiotic and biotic degrading elements. Among the coating systems, water-borne coatings are a better choice since the majority of popular wood coatings are solvent-based and release volatile organic chemicals (VOCs). In this study, cellulose nanofibers (CNFs) were isolated from eucalyptus wood pulp using a chemo-mechanical method and used as the base substrate for wood coatings. The effect of CNF dispersion with varying concentrations (0.5 and 1 wt.%) of zinc oxide (ZnO) nanoparticles on UV-resistance of Pinus radiata and Hevea brasiliensis after 500 hrs of exposure was assessed. Wood surfaces without coating exhibited severe discolouration after 500 hrs of UV exposure. Only CNF-coating results in slight protection of wood surfaces from weathering but significantly increased water wettability of the surface. The incorporation of ZnO nanoparticles significantly reduced the colour change of the wood surfaces. As the concentration of ZnO increased, the colour stability and hydrophobicity of both the wood increased.

Assembled Wood-Polyester Fabric-Hydrogel Janus Evaporator for Sustainable Seawater Desalination.

Solar-driven interfacial evaporation technology is a novel and efficient desalination process that helps alleviate the global shortage of freshwater resources. We developed a Janus evaporator assembled from cotton hydrogel, hydrophilic polyester fabric (PF), and Hydrophobic Wood (PW). By doping graphene oxide and TiO2 as light-absorbing materials within the hydrogel, we achieved a high absorptivity of over 90% across the entire solar spectrum. The hydrophilically modified PF, combined with the PW substrate, provided robust water transport and reduced thermal losses. Subsequent optical path simulations using TracePro74 software verified that the sawtooth light-trapping design of the wood substrate increased multiple light reflections and absorption (compared to a flat structure), enhancing light absorption capabilities. The sawtooth interface also enlarged the evaporation area, further boosting evaporation performance. The cleverly designed evaporator exhibited an evaporation rate of 1.722 kg m-2 h-1 and an efficiency of 83.1% under 1 sun irradiation. Additionally, after applying polydimethylsiloxane to the single surface of the photothermal hydrogel for low surface energy treatment, the resulting Janus structure demonstrated asymmetric wettability that prevented salt ions from accumulating on the irradiated interface. After 8 h of continuous evaporation in saline water (10 wt %), only slight salt crystallization occurred at the edges. The evaporator maintained long-term stability during a 15 day cyclic test, and the produced freshwater fully met the relevant drinking water standards. The components of the evaporator are characterized by simple fabrication, low cost, and eco-friendliness, offering significant application potential in the global context of energy conservation and emission reduction initiatives.

Wood Sponge for Oil-Water Separation.

In addition to filtering some sediments, hydrophobic wood sponges can also absorb many organic solvents, particularly crude oil. The leakage of crude oil poses a serious threat to the marine ecosystem, and oil mixed with water also generates great danger for its use. From the perspective of low cost and high performance, wood sponges exhibit great potential for dealing with crude oil pollution. Wood sponge is a renewable material. With a highly oriented layered structure and a highly compressible three-dimensional porous frame, wood sponges are extremely hydrophobic, making them ideal for oil-water separation. Currently, the most common approach for creating wood sponge is to first destroy the wood cell wall to obtain a porous-oriented layered structure and then enhance the oil-water separation ability via superhydrophobic treatment. Wood sponge prepared using various experimental methods and different natural woods exhibits distinctive properties in regards to robustness, compressibility, fatigue resistance, and oil absorption ability. As an aerogel material, wood sponge offers multi-action (absorption, filtration) and reusable oil-water separation functions. This paper introduces the advantages of the use of wood sponge for oil-water separation. The physical and chemical properties of wood sponge and its mechanism of adsorbing crude oil are explained. The synthesis method and the properties are discussed. Finally, the use of wood sponge is summarized and prospected.

3D hydrophobic wood membrane with micro-nano baffle structure for multifunctional air purification filters: “Kill three eagles with one arrow”

Air pollution has presented an imminent threat to the world. Multifunctional filters with high filtration efficiency, low pressure drop, moisture resistance, antibacterial properties, and renewability are urgently needed to be developed. In this study, multifunctional wood filters are innovatively designed with a baffle structure combining macroscopic structural design and microscopic in-situ synthesis of silver nanoparticles (Ag NPs). The filter has excellent particle removal efficiency (PM0.3, 98.5 %), exceptional volatile organic compounds (VOCs) adsorption efficiency (98.4 % for formaldehyde and 91.7 % for xylene), high sterilization efficiency (99.99 %) and excellent regeneration ability (performance recovery to 98 % of the initial). Furthermore, personal protective masks were assembled by the prepared filters, whose process of replacing element is as simple as replacement of electric mosquito incense tablets. This innovative filter holds promise for applications such as daily protection, sudden accidents and prevention and control of respiratory infectious diseases. We envision that the functionally modified Ag NPs wood filters with a multilayer structure offer a comprehensive solution for more effective air purification in polluted environment.

Construction of biomass-based flame-retardant, antimicrobial and hydrophobic wood coatings with POSS organic-inorganic nanoparticles

The present study utilizes chitosan (CS) and phytic acid (PA) as natural polyelectrolytes, while incorporating Polyhedral Oligomeric Silsesquioxane (POSS), an organic–inorganic hybrid Si-O-Si cage structure, to create a flame retardant, antimicrobial, and hydrophobic coating for wood materials using the layer-by-layer self-assembly method. The POSS flame retardant bisDOPO-NH2-POSS was synthesized by combining 9,10-dihydro-9-oxa-10-phosphaphenathrene (DOPO) with octaminopropyl silsesquioxane (OA-POSS). Subsequently, AgNPs were incorporated into the cage structure of bisDOPO-NH2-POSS through in-situ reduction to fabricate Ag@bisDOPO-NH2-POSS for enhanced antimicrobial efficacy. The CS/PA coating was deposited using the LBL method, which resulted in the formation of a dense char layer during combustion due to both the presence of an inorganic Si-O-Si physical barrier and the synergistic effect of P-N-Si. As a result, self-extinguishing behavior was observed during vertical burning tests, and there was an increase in the limiting oxygen index value to 30.9%. Moreover, by incorporating chitosan, Ag@bisDOPO-NH2-POSS exhibited inhibitory effects against mold such as Aspergillus niger and Lasiodiplodia. The heat release rate (HRR) was reduced by 42.3%, while the total heat release (THR) decreased by 44.4%. The modified wood demonstrates exceptional water repellency, characterized by a static contact angle exceeding 90°. Additionally, the multifunctional coating shows remarkable resilience as it withstands 100 abrasion cycles without compromising its hydrophobic properties. This study presents a sustainable approach to developing a bio-based coating for wood materials that is flame retardant, hydrophobic, and antimicrobial, thereby expanding the potential applications of wood in construction and furniture.

Hydrophobic and thermal insulation properties of modified wood based on ATRP polymerisation

Balsa wood, despite being a cost-effective insulation material, has limited applications due to its inherent hydrophilicity. This study introduces an innovative technique for the in-situ growth of low surface energy long alkyl chain segments on balsa wood using the atom transfer radical polymerization (ARGET-ATRP) method, which not only provides durable and stable hydrophobicity but also preserves its natural texture, mechanical strength, and thermal insulation. The resulting hydrophobic wood demonstrated exceptional hydrophobicity in diverse environments, with a water contact angle up to 141.3° and a contact angle decrease of no more than 10.47 % after 150 min, confirming its hydrophobic stability. Furthermore, axial thermal conductivity of the wood was as low as 0.1012 W/m·K, the axial compressive strength decreased by only 12.8 %, further evidencing the retention of its mechanical properties. This simple yet effective strategy of in-situ alkyl chain growth on balsa wood not only preserves its structure but also opens new avenues for the multifunctional development of biomaterials.

Wood dimensional stability enhancement by multivalent metal-cation-induced lignocellulosic microfibrils crosslinking

Wood is a hygroscopic material that responds to the moisture changes of the surrounding environment through swelling and shrinkage, making it dimensionally unstable. Here, we introduce a facile metal-ion-modification (MIM) approach to enhance the dimensional stability of wood. The MIM process involved swelling the wood samples with aqueous metal ion solutions and drying. The high valent metal cations, such as Fe3+, Al3+, and Zr4+, interacted with the hydrophilic groups (e.g., OH, COOH) present in the wood fibers, limiting their access to water and moisture, thereby enhancing the wood's hydrophobicity and dimensional stability. Evaluation of three wood species, southern yellow pine, poplar, and red oak, revealed water contact angles of 120–130° after MIM, indicative of enhanced surface hydrophobicity. Fe3+ treatment decreased southern yellow pine's swelling ratio from 6 % to 4 %. Fe3+-treated wood exhibited tangential anti-swelling efficiencies ranging from 39.83 % to 57.14 % and radial anti-swelling efficiencies from 34.74 % to 48.33 %, varying across wood species. The enhancement of wood dimensional stability can be attributed to the formation of irreversible coordination bonds between metal cations and lignocellulosic microfibrils in the wood cell wall. These bonds prevent the microfibrils from slipping in response to moisture absorption and desorption.

Bioinspired Living Coating System for Wood Protection: Exploring Fungal Species on Wood Surfaces Coated with Biofinish during Its Service Life

Biofinish is an innovative wood protection system inspired by biological processes. It enhances the hydrophobicity of wood through oil treatment, resulting in improved dimensional stability. Living cells of the fungus Aureobasidium pullulans effectively protect wood from deterioration caused by other decaying fungi. The melanin pigment produced by the fungus provides an appealing dark surface and additionally protects the wood substrate against UV radiation. The significant advantage of Biofinish is its remarkable self-healing ability, which distinguishes it from conventional wood protection methods. This research aimed to explore fungal species colonising surfaces exposed to natural weathering and assess the survival of A. pullulans on wood surfaces coated with Biofinish during its in-service period. This study was performed on a facade composed of European larch wood (Larix decidua) treated with linseed oil and coated with Biofinish at the InnoRenew CoE building in Izola, Slovenia, following a 9-month exposure period. The majority of the detected species belonged to the genera Aureobasidium. The results indicated the survival and effective antagonistic action of A. pullulans, the living and active ingredient of the coating, against other wood-decaying fungi.

Self-heating, elastic, hydrophobic wood sponge for recovering spilled crude oil under sunlight and microwave dual stimuli

Water pollution caused by crude oil spills poses significant environmental concerns. In this work, multi-walled carbon nanotubes (MWCNTs) were dispersed as the carbon network on the elastic wood sponge (WS) and then encapsulated by hydrophobic polydimethylsiloxane (PDMS) coating to form a crude oil adsorbent, PDMS@CNT-WS. It demonstrated an elasticity of up to 90% compressive strain, while the height retention remained at 97% even after 100 cycles at 50% compressive strain. The shape-memory properties and 148°hydrophobic angle of the material allowed it to be repeatedly used. This is the first material to utilize sunlight and microwave as dual stimuli to absorb and recover spilled crude oil. PDMS@CNT-WS absorbed crude oil floating on water within about 80 s under 1 sun illumination. After condensation, the material was heated within only 4 s in a microwave oven at 2450 MHz, and the crude oil in the interior could be recovered by simply squeezing the material. This new approach provided a source of energy conversion for crude oil adsorbents with thermal management capabilities to clean up crude oil spills.

Novel two-step strategy for the construction of weathering-resistant hydrophobic wood to extend its service life

As a renewable biomaterial resource, the applicability of natural wood is limited by its poor weathering resistance. A properly designed multifunctional coating can enhance the weathering resistance of wood while maintaining its natural aesthetic texture. In this study, polydimethylsiloxane (PDMS), SiO2, and TiO2 were impregnated into a wood sample to fabricate coatings with UV-shielding, transparent, and hydrophobic properties. The water contact angle of the wood in three directions was investigated under different environmental conditions. Results suggested that the PDMS/SiO2/TiO2-wood (PSTW) exhibited excellent hydrophobicity under harsh environmental conditions, which includes sandpaper abrasion, ultrasonic treatment, corrosive solvent immersion, freeze–thaw cycles, and UV aging. Moreover, PSTW demonstrated outstanding repellency to the most common liquids (such as milk, juice, and tea) in daily life. The fabricated hydrophobic coatings improved the mechanical stability, anti-icing, chemical stability, antifouling, self-cleaning, and UV aging resistance of the wood. The proposed method is an effective strategy to enhance the utilization of wood in outdoor environments and extend its service life.

Click chemistry of PMHS for fabrication of robust, transparent and hydrophobic silicone resin coating on wood substrate at room temperature

Based on click chemistry of poly(methylhydrogen)siloxane (PMHS), an environment-friendly method was proposed for in-situ fabrication of robust, transparent, UV-resistant and hydrophobic silicone resin coating (SRC) at room temperature by simply brushing a mixture of PMHS, tetramethyltetravinyl cyclotetrasiloxane (V4), and Karstedt catalyst on wood surface. The mechanism for click chemistry of PMHS and the continuous curing characteristic of SRC was discussed based on the characterization of SRC by FTIR and XPS. The effects of the mass ratio of PMHS to V4 and curing time on the properties of SRC and the modified wood were investigated. Results showed that SRC with the mass ratio of PMHS to V4 of 5:1 possessed the best mechanical stability, and the mechanical stability increased with curing time and temperature. SRC improved significantly the hydrophobicity and water-repellency of wood by increasing the water contact angle from 27.2° to 123.1° and decreasing the water absorption rate from 103 % to 16 %. SRCs showed excellent transparency with an average transmittance of 92.3 % at 400–1100 nm. The UV resistance of SRC was 6 times higher than that of varnish coating. The click chemistry of PMHS will find great application in rapid fabrication of functional coatings on wood surface by using PMHS and any vinylated reagent or micro-/nano-particles.

Preparation of Superhydrophobic Wood Surfaces Modified Using MIL-88(Fe) via Solvothermal Method

A superhydrophobic wood surface was produced by employing the solvothermal method to form shuttle-like, well-crystallized MIL-88(Fe) on the surface of wood and assembling a Octadecylphosphonic acid (OPA) reagent. The nanosized MIL-88(Fe) molecule caused the wood’s surface to take on a nano mastoid shape. In addition, MIL-88(Fe) provides metal sites to capture OPA molecules, preventing the long-chain alkane hydrophobic group from contacting the surface of the wood. They both make a considerable difference in the growth of a hydrophobic wood surface. The results of the experiment indicate that the water contact angle (WCA) increases with reactant concentration. The WCA of the samples prepared with 5.0 × 10−2 M FeCl3 was 140.57°. When the reactant concentration was 10.0 × 10−2 M, the greatest WCA = 153.69° reading was obtained. The research’s findings present a novel technique for producing superhydrophobic wood surfaces.

Preparation and Superhydrophobicity of Nano-Al-Coated Wood by Magnetron Sputtering Based on Glow-Discharge Plasma

A superhydrophobic coating on wood can effectively improve the hydrophobicity and service life of wood. In this study, an Al superhydrophobic nano-coating was constructed on the transversal section of poplar wood by magnetron sputtering based on glow-discharge plasma. The structure, microscopic morphology, surface elements, and hydrophobic properties were characterized and tested. When coated for 20 s, the water contact angle on the sample surface can reach 148.9°. When coated for 30 min, the Al-coated wood had a contact angle of 157.3°, which could maintain excellent superhydrophobic properties for 300 s. The sputtered Al nanoparticles were uniformly distributed on the wood surface and formed nanoclusters. Plenty of voids between the clusters can trap air and block contact between water droplets and the coating, making the coating obtain superhydrophobic properties. When the coating time was 60 min, the characteristic peak of the Al (111) crystal plane appeared at 38.4°, while the intensities of (101), (002), and (040) peaks of cellulose were reduced. In conclusion, magnetron sputtering was used to deposit a superhydrophobic coating on wood without low surface free energy agents. Furthermore, this research provides new inspirations for the physical modification of wood and the construction of superhydrophobic coatings on wood.

Impact of thermal modification on swelling and mechanical behavior of Couratari spp.

Thermal modification mechanisms and their effects on physical and mechanical properties of native Amazon hardwoods are not yet completely understood. It is expected that such treatments can improve the properties of low-value Amazonian woods and sapwood residues. This study aimed to investigate the impact of heat treatment on the swelling and mechanical properties (strength and stiffness to Static Bending and Janka hardness) of tauari wood (Couratari spp.), a low-value Amazonian hardwood. For this, tauari wood samples were thermally modified in an electric oven under hot air irradiation at final temperatures of 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, and 210 °C for 2.5 h. The main results showed that thermal modification increased the hydrophobicity of tauari wood without any noticeable effects on the mechanical behavior of the wood up to 200 °C. It was stated that up to 200 °C thermal modification is beneficial in terms of gains in hydrophobicity. In contrast, above 200 °C, despite an increase in hydrophobicity, consistent decreases in strength (MOR) and hardness were observed.

The combined effect of essential oils on wood physico-chemical properties and their antiadhesive activity against mold fungi: application of mixture design methodology

In the heritage field, the microbial adhesion on wood, and consequently the formation of biofilm led to inestimable losses of historical and cultural monuments. Thereby, this study aimed to examine the combined effect of Thymus vulgaris, Myrtus communis, and Mentha pulegium essential oils on wood surface physico-chemical properties, and to elaborate the optimal mixture using the mixture design approach coupled to the contact angle method. It was found that both wood hydrophobicity and electron donor character increased significantly after treatment using an optimal mixture containing 57% and 43% of M. pulegium and M. communis essential oils, respectively. The theoretical and experimental fungal adhesion on untreated and treated wood were also investigated. The results showed that the adhesion was favorable on untreated wood and reduced using the optimal mixture. Moreover, the experimental data demonstrated that the same mixture exhibited an antiadhesive efficacy effect with a reduction of 36–75% in adhesion.

One-Step Process for the Fabrication of Hydrophobic and Dimensional Stable Wood Using Functionalized Silica Nanoparticles

The aim of this research was to improve the dimensional stability of wood through bulk hydrophobization, as a result of impregnation with fluorinated silica nanoparticles. The wood species European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.) were used. The characterization of the modified wood was performed using analytical methods, including scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy. The effect of fluorinated silica nanoparticles on the anti-swelling efficiency, water uptake, equilibrium moisture content, and water contact angle were investigated. The surface of the cell walls was discontinuously covered with fluorinated silica nanoparticles forming a rough surface coating. The presence of the hydrophobic silica nanoparticles improved the dimensional stability by permanently increasing the hydrophobicity of wood, besides a low weight percent gain. Furthermore, the treatment significantly decreased the equilibrium moisture content and water uptake. The modified wood surfaces showed significantly higher water contact angles, which was the main reason of the improved dimensional stability.

Wood with improved hydrophobicity and thermal stability after depositing polydimethysiloxane/silica sol hybrid

Abstract 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.

Valorization of hydrophobic wood waste in concrete mixtures: Investigating the micro and macro relations

This study investigates the effect of partially replacing fine aggregate with wood waste in concrete mixes in order to preserve natural resources (i.e., sand) and reduce the disposal of wood waste into landfill. A total of 81 specimens were prepared and divided into two groups based on their w/c ratio, namely: Group 1 with w/c = 0.46, and Group 2 with w/c = 0.42. Each group has two different percentages of replacement of fine aggregates (i.e., 5% and 7%). And each percentage was tested in two batches; namely raw wood waste and Silane-treated wood waste. The absorption, compressive strength, and tensile strength were measured for all the specimens. In addition, morphological and interfacial bonding analyses were implemented by running SEM and FTIR tests. The results show that replacing the fine aggregate with wood waste increases the absorption of the concrete mix up to 300% in certain mixes. The tensile strength was affected depending on the wood waste percentages. However, incorporating wood waste in concrete mixes reduced its compressive strength up to 65.5%. The Silane treatment of the wood waste improves the mechanical properties, as well as, the impermeability of the produced mix when compared with the raw wood waste specimens. The microstructural and interaction mechanism analyses revealed the formation of high content of ettringite and air voids in concrete with raw chippings, which negatively affect the mechanical properties of the mixture. It is recommended to avoid using raw wood waste in concrete mixes since it significantly harms its mechanical properties.

Furanic Polymerization Causes the Change, Conservation and Recovery of Thermally-Treated Wood Hydrophobicity before and after Moist Conditions Exposure.

The Whilhelmy method of contact angle, wood thermal properties (TG/DTG), infrared spectroscopy, etc. was used to define the hydrophobicity of heat-treated beech and fir wood at increasing temperatures between 120 °C and 300 °C. By exposure to wet conditions during 1 week, the hydrophobic character obtained by the heat treatment remains constant heat-treated. Heat induced wood hydrophobation, was shown by CP MAS 13C NMR and MALDI ToF mass spectrometry to be mainly caused by furanic moieties produced from heat-induced hemicelluloses degradation. This is caused by the acid environment generated by the hydrolysis of the hemicelluloses acetyl groups. Furfural polymerizes to linear and branched oligomers and finally to water repellent, insoluble furanic resins. The water repellent, black colored, cross-linked polymerized furanic network is present throughout the heat-treated wood. Wood darkening as well as its water repellency due to increasing proportions of black colored furanic resins increase as a function of the increase with treating temperature, becoming particularly evident in the 200 to 300 °C treating temperature range.

Xylan assisted construction of highly hydrophobic wood surface

Forming a nano-structured rough surface and incorporating synthetic low surface energy polymers is one of the major methods to construct a highly hydrophobic wood surface. However, most of the synthetic polymers are petroleum-based chemicals, which are toxic, non-biodegradable and lack the ability to well disperse the nanoparticles to construct an excellent nano-structured rough surface. In this study, xylans were modified by esterification reaction between dodecenyl succinic anhydride (DDSA) and the hydroxyls on xylans under alkaline condition. The DDSA modified xylans were used as a dispersant and an anchoring agent to uniformly disperse SiO2 nanoparticles and bind them on wood surface to construct a rough nano-structure. The DDSA modified xylans also demonstrated high hydrophobicity and low surface energy. The coating with SiO2 nanoparticle/DDSA modified xylan dispersions with an air-drying strategy has successfully led to a highly hydrophobic wood surface with a contact angle up to 131°. This study suggests the potential applications of xylans in the construction of highly hydrophobic wood surface for wood protection.