Cross-linked peach gum polysaccharide adhesive by citric acid to produce a fully bio-based wood fiber composite with high strength.

As a natural polysaccharide, efficiently converting peach gum (PG) into practical materials remains a significant challenge due to its complex structure and high molecular weight. This study developed a polysaccharide adhesive using PG as the primary raw material and citric acid (CA) as a cross-linking agent to produce a fully bio-based wood fiber composite. The chemical compositions of PG and the synthesis process of PG-CA/55-45 adhesive were mainly discussed. The properties of the composites were explained through a microscopic perspective. The gel permeation chromatography (GPC) analysis revealed that the mean molecular weights of PG and PG-CA/55-45 adhesive were 9.07 × 106 Da and 9.98 × 104 Da, respectively. CA was introduced to depolymerize PG and cross-linked the degraded PG to form macromolecules with higher strength by the esterification reaction. PG-CA/55-45 adhesive demonstrated good mildew resistance and thermal stability. In addition, the composites exhibited excellent mechanical properties and water resistance. This study provided a simple and feasible approach to developing a polysaccharide adhesive for producing higher strength wood fiber composites, which can propose a new strategy for realizing the high-value utilization of PG.

A high-performance bio-based adhesive comprising soybean meal, silk fibroin, and tannic acid inspired by marine organisms.

The sustainable development of high-performance bio-based adhesives is both important and challenging for the wood industry. Herein, inspired by the hydrophobic property of barnacle cement protein and the adhesive property of mussel adhesion protein, a water-resistant bio-based adhesive was developed from silk fibroin (SF) rich in hydrophobic ß-sheet structures and tannic acid (TA) rich in catechol groups as reinforcing components and soybean meal molecules rich in reactive groups as substrates. SF and soybean meal molecules formed a water-resistant tough structure through a multiple cross-linking network including covalent bonds, hydrogen bonds, and dynamic borate ester bonds constructed by TA and borax. The wet bond strength for the developed adhesive achieved 1.20 MPa, exhibiting its excellent application capabilities in humid environments. The storage period of the developed adhesive (72 h) was 3 times that of pure soybean meal adhesive owing to the enhanced mold resistance of the adhesive by TA. Furthermore, the developed adhesive demonstrated excellent biodegradability (45.45 % weight loss in 30 days) and flame retardancy (limiting oxygen index of 30.1 %). Overall, this environmental and efficient biomimetic strategy provides a promising and feasible route to develop high-performance bio-based adhesives.

Renewable bio-based adhesive fabricated from a novel biopolymer and soy protein.

In this study, a bio-based soy protein adhesive derived from environmentally friendly and renewable enzymatic hydrolysis lignin (EHL), epoxidized soybean oil (ESO), and soy protein isolate (SPI), was successfully prepared. A novel biopolymer (EHL-ESO), as a multifunctional crosslinker, was firstly synthesized from modified EHL and ESO, and then crosslinked with soy protein isolate to obtain a bio-based soy protein adhesive. The structure, thermal properties, and adhesion performance of the obtained soy protein adhesives were determined by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and wet shear strength. The maximum degradation temperature of SPI/EHL-ESO adhesives (332-343 °C) was higher than that of the pristine SPI adhesive (302 °C). Moreover, plywood bonded by the modified adhesive reached a maximum wet shear strength value of 1.07 MPa, a significant increase of 101.8% from the plywood bonded by pristine SPI adhesive. The enhancements in the thermal stability and wet shear strength were attributed to the formation of a dense crosslinking network structure. This work not only highlights the potential to replace petroleum-based polymers, but also presents a green approach to fabricate fully bio-based soy protein adhesive for preparing all-biomass wood composite materials.

Preparation and characterization of a soy protein based bio-adhesive crosslinked by waterborne epoxy resin and polyacrylamide.

A simple and useful approach by using non-toxic and water-soluble raw material to improve the bonding properties of soy protein adhesive has attracted much attention recently. The objective of this research was to provide a simple and environmentally friendly approach for preparing a high adhesion performance soy protein adhesive in aqueous solution by using waterborne-epoxy resin, soy protein and water-soluble polyacrylamide (PAM). The chemical structure and curing characteristics, as well as the initial viscosity and adhesion performance of the resulted soy protein adhesive were characterized by 1H nuclear magnetic resonance (1H-NMR), differential scanning calorimetry (DSC), a rotary viscosity meter and a plywood panel test. The 1H-NMR analysis results confirmed that epoxy resin was successfully crosslinked with the -NH2 groups of the soy protein molecule to form a water-resistance network structure, and the resulting adhesive contains active epoxy groups. It was found that the addition of PAM can decrease the apparent viscosity, lower curing temperature, and enhancing the wet shear strength of soy protein adhesives effectively, which were capable of facilitating their application as wood adhesives. The resulting soy protein adhesive containing 4% epoxy resin and 0.05% PAM dosage had a reasonable viscosity and lower cure temperature, and showed good water resistance and wet shear strength, which met the requirement for interior use plywood of the Chinese Industrial Standard. These results suggested that waterborne-epoxy resin can be used to prepare high-performance environmentally friendly soy protein adhesives, which might provide a feasible methodology to prepare bio-adhesive adhesives for plywood industrial applications.