Youming Dong

Soy protein isolate-based films cross-linked by epoxidized soybean oil

Epoxidized soybean oil (ESO) is an environmentally friendly cross-linking agent derived from soybean, having multiple epoxy groups in its molecules. It can effectively improve tensile strength and water resistance of soy protein isolate (SPI)-based films. The properties of the SPI-based films were characterized by X-ray diffraction and attenuated total reflectance Fourier transform infrared spectroscopy. The best performance of the SPI-based films was achieved when the ESO addition was 2.5%, for which tensile modulus, tensile strength and 10% offset yield strength were increased to 265.0 MPa, 9.8 MPa and 6.8 MPa, respectively. Compared to untreated SPI-based films, these were increases of 695.6%, 139.8%, and 246.6%, respectively. However, the elongation at break was decreased by 67.6% due to the cross-linking between SPI and ESO. The SPI-based film modified by 5% ESO had the best water-resistance property and reduced the 24 hour water absorption from 209.1% to 45.9%, which was a significant decrease of 78.1%.

Optimization of reaction parameters and characterization of glyoxal-treated poplar sapwood

Abstract Glyoxal as a non-formaldehyde cross-linking agent was employed with ammonium persulfate as a novel catalyst to improve the dimensional stability and water resistance of poplar sapwood. The effects of various cross-linking parameters (e.g., glyoxal concentration, curing temperature, glycol-to-glyoxal molar ratio and catalyst concentration) on the properties of wood were investigated, and the parameters were optimized. In comparison with the unmodified wood, the glyoxal-modified wood exhibited improved dimensional stability and reduced water uptake. Moreover, the addition of glycol further strengthened the dimensional stability and anti-leaching ability. Modified wood was characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM) and contact angle instrument. IR indicated that the network structure was formed between the agent itself or cross-linking between wood components and glyoxal. SEM revealed the precipitation and filling effect of the cured glyoxal in the cell wall. Contact angle measurement further confirmed the improved hydrophobicity of wood after modification. All the results suggested that the improved dimensional stability and water resistance of the treated wood could attribute to both bulking effect and cross-linking reaction or network structure formed. However, it is not clear whether network structure by glyoxal itself or the cross-linking between the glyoxal and wood components is formed in wood.

Enhancement of mechanical and thermal properties of Poplar through the treatment of glyoxal-urea/nano-SiO2

Glyoxal is a cross-linking agent that could effectively improve dimensional stability and water resistance with compromising the mechanical properties of wood materials. This study explores relevant disadvantages of glyoxal-treated wood, and in an effort to overcome the drawbacks, an environmental-friendly glyoxal-urea (GU) resin is synthesized from urea and glyoxal, and combined with nano-SiO2 to treat Poplar wood. Results showed that the mechanical properties of the GU resin-treated wood were significantly increased compared to those of wood treated with glyoxal alone, and that incorporation of nano-SiO2 in the GU resin further improved performance. The fracture morphology of GU/nano-SiO2-treated wood was also characterized, indicating increased elasticity. Scanning electron microscopy and energy dispersive X-ray (SEM-EDX) results showed that GU and nano-SiO2 existed not only in the wood cell lumens, but also in the cell walls. Fourier transform infrared spectroscopy (FT-IR) test results showed the formation of GU resin and the incorporation of GU resin into the wood samples. Thermal analysis results demonstrated that thermal properties were improved after the incorporation of GU and nano-SiO2 compared to samples solely glyoxal-treated. Improvement can most likely be attributed to increased cross-linkage length among the celluloses, and/or the filling effect of GU/SiO2 in the voids in wood cell walls.

Mussel-inspired chemistry for preparation of superhydrophobic surfaces on porous substrates

A facile and versatile mussel-inspired surface modification approach was used to modify porous materials (wood, sponge and stainless steel mesh) to fabricate a superhydrophobic surface. The as-formed polydopamine (PDA) coating can tightly adhere on the porous structure surface, which also provides a versatile platform for secondary reactions to anchor hydrophobic long-chain groups for hierarchical superhydrophobic surfaces preparation. The as-prepared surfaces showed excellent superhydrophobicity with a water contact angle (CA) of about 153°, even after being subjected to harsh conditions, including strong acid–base and organic solvent immersion, high-temperature boiling, ultrasonic washing, and ultraviolet aging. The produced superhydrophobic sponge exhibited an oil absorption capacity of 73–156 times its own weight for a series of oils and organic solvents and showed good recyclability. The obtained stainless steel mesh also presented good oil–water separation ability. Importantly, this modification method provides an efficient, versatile, easy, and mild route to prepare superhydrophobic surfaces for various porous substrates, resulting in a wide range of potential applications.

Preparation of Stable Superhydrophobic Coatings on Wood Substrate Surfaces via Mussel-Inspired Polydopamine and Electroless Deposition Methods

Mussel-inspired polydopamine (PDA) chemistry and electroless deposition approaches were used to prepare stable superhydrophobic coatings on wood surfaces. The as-formed PDA coating on a wood surface exhibited a hierarchical micro/nano roughness structure, and functioned as an “adhesive layer” between the substrate and a metallic film by the metal chelating ability of the catechol moieties on PDA, allowing for the formation of a well-developed micro/nanostructure hierarchical roughness. Additionally, the coating acted as a stable bridge between the substrate and hydrophobic groups. The morphology and chemical components of the prepared superhydrophobic wood surfaces were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The PDA and octadecylamine (OA) modified surface showed excellent superhydrophobicity with a water contact angle (CA) of about 153° and a rolling angle (RA) of about 9°. The CA further increased to about 157° and RA reduced to about 5° with the Cu metallization. The superhydrophobic material exhibited outstanding stability in harsh conditions including ultraviolet aging, ultrasonic washing, strong acid-base and organic solvent immersion, and high-temperature water boiling. The results suggested that the PDA/OA layers were good enough to confer robust, degradation-resistant superhydrophobicity on wood substrates. The Cu metallization was likely unnecessary to provide significant improvements in superhydrophobic property. However, due to the amazing adhesive capacity of PDA, the electroless deposition technique may allow for a wide range of potential applications in biomimetic materials.

Grafting polyethylene glycol dicrylate (PEGDA) to cell walls of poplar wood in two steps for improving dimensional stability and durability of the wood polymer composite

Abstract Polyethylene glycol (PEG) treatment is an effective approach to endow wood with higher dimensional stability (DS), which is still a concern under humid conditions. In this study, poplar wood was first treated with methacryloyl chloride to introduce methacryl groups in the cell wall. Then functional PEG served as modifier, and copolymerization was conducted in the second step to prepare PEG-diacrylate (PEGDA) modified samples. The resultant wood polymer composites (WPCs) were characterized by solid state NMR, field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD). The physical and mechanical properties of the WPCs were also evaluated, such as anti-swelling efficiency (ASE), water uptake, dynamic hydrophilicity (contact angles), and thermal stability. The results show that the copolymerized WPC achieved 51.4% ASE with leaching <3.0%. Moreover, the surface hardness and water resistance of the wood are also greatly improved.

Highly hydrophobic and self-cleaning bulk wood prepared by grafting long-chain alkyl onto wood cell walls

Highly hydrophobic bulk wood was successfully prepared by grafting long-chain octadecyl isocyanate (OTI) onto wood cell walls via a urethane linkage. The resulting wood was highly hydrophobic and showed significantly reduced surface free energy. The microstructure and chemical composition of the untreated and treated wood were characterized using the scanning electron microscopy, energy-dispersive X-ray spectrometry, and Fourier transform infrared spectroscopy. The hydrophobic property of the wood was characterized using contact angle measurements. The mechanical and physical properties as well as the chemical durability of the highly hydrophobic wood were evaluated. The results suggested that the resultant OTI-treated wood presented fairly low surface free energy, high hydrophobicity even in the wood core, and excellent stability and durability against chemical corrosion and mechanical abrasion. Furthermore, the physical properties, including self-cleaning, dimensional stability, and water uptake, were significantly improved in the treated wood.

Coordination-Driven Controlled Assembly of Polyphenol-Metal Green Coating on Wood Micro-Grooved Surfaces: A Novel Approach to Stable Superhydrophobicity

A versatile, fast, and nature-inspired polyphenol chemistry surface modification was applied to prepare superhydrophobic surfaces with micro-grooved structures in this study. Tannic acid and iron ion (TA–FeIII) complexes were employed as a molecular building block for anchoring biomimetic coating onto the wood substrate with catalytically reducing formative Ag ions as the rough surface to ensure well-developed micro/nanostructure hierarchical roughness. TA–FeIII complexes also acted as stable bridges between the substrate and hydrophobic groups. The thickness and architecture of TA–FeIII complex coatings can be tailored by coordination-driven multistep assembly. The results indicated that the micro/nano hierarchical roughness structure was well-developed with increased coating times and increased deposition of reduced Ag nanoparticles, resulting in excellent superhydrophobic properties (e.g., water CA (contact angle) of about 156° and a rolling angle of about 4°). The superhydrophobic material exhibited outstanding stability and durability in harsh conditions, including strong acid/base or organic solvent, high-temperature water boiling, ultrasonic cleaning, and ultraviolet aging. A series of superhydrophobic models are proposed to clarify the effect of the micro/nano hierarchical structure on these superhydrophobic properties.