Fabrication of an Ultrastrong Formaldehyde-Free Wood Adhesive with an Organic-Inorganic Cross-Linking Network.

The wood industry faces challenges in producing eco-friendly, high-performance, and formaldehyde-free adhesives. In this study, carboxylated styrene-butadiene rubber (XSBR) was blended with polyamidoamine-epichlorohydrin (PAE) resin, and a controlled amount of CaCO3 powder was incorporated to create an adhesive with exceptional strength. The resulting three-layer plywood demonstrated remarkable dry and wet shear strengths of 3.09 and 2.36 MPa, respectively, and of 2.27 MPa after boiling water tests, comparable to that of phenolic resins. Additionally, the adhesive exhibited strong adhesion across various materials including glass, metal, etc. This exceptional performance was due to two primary factors: (1) the high-density chemical cross-linking reaction and the physical entanglement between XSBR and PAE; (2) the organic-inorganic hybrid involving metal ion complexation developed by CaCO3, which fostered molecular chain connections and enhanced the adhesive-material interface. These findings offer valuable references for further research in the field of wood adhesives.

Wood-inspired nanocellulose aerogel adsorbents with excellent selective pollutants capture, superfast adsorption, and easy regeneration.

Heavy metal ions can cause a series of hazards to environment and humans. Herein, we developed a wood-inspired nanocellulose aerogel adsorbent with excellent selective capability, superfast adsorption, and easy regeneration. The premise for the design is that the biomimetic honeycomb architecture and specific covalent bonding networks can provide the adsorbent with structural and mechanical integrity yet superfast removal of target contaminants. The as-obtained adsorbent showed the maximum adsorption capacity for Pb(II), Cu(II), Zn(II), Cd(II), and Mn(II) of 571 mg g-1, 462 mg g-1, 361 mg g-1, 263 mg g-1, and 208 mg g-1, respectively. The adsorbent could remove Pb(II) species with super-rapid speed (87% and 100% of its equilibrium uptake in 2 min and 10 min, respectively). Furthermore, the adsorption isotherm and kinetics models were in accord with the Langmuir and pseudo-second-order models, indicating that the adsorption behavior was dominated by monolayer chemisorption. The aerogel adsorbent had better affinity for Pb(II) than other coexisting ions in wastewater and could be regenerated for at least five cycles. Such a wood-inspired aerogel adsorbent holds great potential in the application of contaminant cleaning.

Polyphenol-induced cellulose nanofibrils anchored graphene oxide as nanohybrids for strong yet tough soy protein nanocomposites.

Network-nanostructured cellulose nanofibrils (CNFs) is a promising template onto which to anchor and expand 2D sheets. It is still a huge challenge to regulate the dispersion/interface toward strong yet tough hybrid materials. This paper reports a novel design for interface anchoring GO nanosheets with TEMPO-oxidized CNFs (TA@rGO-CNFs) that is induced by the self-polymerization of catecholamine-based tannic acid (TA). The high-functionality TA@rGO-CNFs nanohybrids were investigated as both physical and chemical cross-linkers to the natural plant-derived soy protein isolate (SPI) based films, which facilitate multiple interfacial adhesion and a covalent network between the SPI matrix and TA@rGO-CNFs nanosheets bearing poly (tannic acid) (PTA) adhesion layers. As expected, remarkable improvement in tensile strength (up to 280.7%) and toughness (up to 258.3%) was achieved simultaneously in the resulting nanocomposites due to the efficient energy dissipation mechanisms derived from the synergistic interfacial interactions between TA@rGO-CNFs-"load distributers" and the SPI matrix. The nanocomposites also showed favorable gas barrier behavior (55% reduction) and water-resistance properties. The proposed method may represent a facile and environmentally-friendly approach to integrate multi-nanoscale building blocks into biopolymers with strong yet tough mechanical properties.

Simultaneously Toughening and Strengthening Soy Protein Isolate-Based Composites via Carboxymethylated Chitosan and Halloysite Nanotube Hybridization.

Chemical cross-linking modification can significantly enhance the tensile strength (TS) of soy protein isolate (SPI)-based composites, but usually at the cost of a reduction in the elongation at break (EB). In this study, eco-friendly and high-potential hybrid SPI-based nanocomposites with improved TS were fabricated without compromising the reduction of EB. The hybrid of carboxymethylated chitosan (CMCS) and halloysite nanotubes (HNTs) as the enhancement center was added to the SPI and 1,2,3-propanetriol-diglycidyl-ether (PTGE) solution. The chemical structure, crystallinity, micromorphology, and opacity properties of the obtained SPI/PTGE/HNTs/CMCS film was analyzed by the attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis spectroscopy. The results indicated that HNTs were uniformly dispersed in the SPI matrix without crystal structure damages. Compared to the SPI/PTGE film, the TS and EB of the SPI/PTGE/HNTs/CMCS film were increased by 57.14% and 27.34%, reaching 8.47 MPa and 132.12%, respectively. The synergy of HNTs and CMCS via electrostatic interactions also improved the water resistance of the SPI/PTGE/HNTs/CMCS film. These films may have considerable potential in the field of sustainable and environmentally friendly packaging.

Improvement of Interfacial Adhesion by Bio-Inspired Catechol-Functionalized Soy Protein with Versatile Reactivity: Preparation of Fully Utilizable Soy-Based Film.

The development of materials based on renewable resources with enhanced mechanical and physicochemical properties is hampered by the abundance of hydrophilic groups because of their structural instability. Bio-inspired from the strong adhesion ability of mussel proteins, renewable and robust soy-based composite films were fabricated from two soybean-derived industrial materials: soluble soybean polysaccharide (SSPS) and catechol-functionalized soy protein isolate (SPI-CH). The conjugation of SPI with multiple catechol moieties as a versatile adhesive component for SSPS matrix efficiently improved the interfacial adhesion between each segment of biopolymer. The biomimetic adherent catechol moieties were successfully bonded in the polymeric network based on catechol crosslinking chemistry through simple oxidative coupling and/or coordinative interaction. A combination of H-bonding, strong adhesion between the SPI-CH conjugation and SSPS matrix resulted in remarkable enhancements for mechanical properties. It was found that the tensile strength and Young's modulus was improved from 2.80 and 17.24 MPa of unmodified SP film to 4.04 and 97.22 MPa of modified one, respectively. More importantly, the resultant films exhibited favorable water resistance and gas (water vapor) barrier performances. The results suggested that the promising way improved the phase adhesion of graft copolymers using catechol-functionalized polymers as versatile adhesive components.