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Graphical abstract Highlights • Soy protein-derived fibers self-reinforced soybean meal system is introduced. • Soy protein fiber skeleton-induced crosslinking network was established. • Tri-epoxy crosslinker (PTGE) served as bridge for dense interfacial combination. • Favorable bi-phase compatibility and enhanced mechanical properties were achieved. Abstract Self-reinforced composites (SRCs) exhibit excellent interface compatibilities and have similar constituents for easy recycling, thereby making them competitive with traditional polymeric composites in various industrial areas. However, there is still a lack of research regarding the biodegradable plant protein-based SRCs plywood adhesives with rigid strength. In this study, the "self-gluing" concept of the binding of the soy protein isolate fibers (SPFs) network skeleton with the soybean meal (SM) matrix was explored. To avoid the SPFs' aggregation and to improve their dispersity, a batchwise feeding of SM was applied before and after the SPFs were added. The 1,2,3-propanetriol-diglycidyl-ether (PTGE) was the cross-linker, which readily formed dense physicochemical interactions with the multiple side groups (COOH/ NH 2 / OH) in both the SPFs reinforcement phase and the SM matrix. A set of SPFs addition amounts (0.5%–2.0%) were employed in order to manufacture the self-reinforced SPFs/SM/PTGE plywood adhesives, and their bonded three-layer plywood was produced for testing. The wet shear strength of the plywood bonded with the SPFs/SM/PTGE adhesives fulfilled China's interior furnishing requirements (≥0.7 MPa, GB/T 9846-2015). The SPFs/SM/PTGE adhesive bonded plywood reached its highest wet shear strength of 1.12 MPa (1.5 wt.% SPFs addition), which was a 70% increase compared to the unmodified SM/PTGE-bonded plywood sample. The morphology, the infrared spectra, the crystallinity observations, and the thermal behaviors of the SPFs/SM/PTGE adhesives showed fine SPFs-to-SM interfacial bonding and a dense crosslink network in the SPFs/SM/PTGE adhesive systems. In this study, the "self-reinforced" concept of biodegradable plant protein-based composites was evaluated and showed a great potential to apply into the plywood adhesive systems. [ABSTRACT FROM AUTHOR]

The development of eco-friendly, non-formaldehyde, and high-performance bio-based adhesives is a great strategy for relieving environmental pressure and health concern, especially for the wood adhesive industry. In this work, a green soybean meal (SM)-based adhesive with excellent performance was developed by embedding modified kenaf fibers (KF). The synergistic bionic design with gecko structure and mussel chemistry endowed KF with improved rough surface and increased reactive sites, resulting in robust mechanical interlocking and multiple chemical crosslinking ability for SM-based adhesive. The resultant adhesive exhibited excellent bonding properties, compared to the SM adhesive, the wet shear strength was improved from 0.41 MPa to 1.52 MPa, and the moisture absorption was decreased from 10.1% to 8.6%. These results met the standard of type II plywood (≥0.7 MPa) according to the national standard of China (GB/T 9846.3-2004). This eco-friendly SM-based adhesive opens a new way to replace harmful formaldehyde-based adhesives and contributes to the development and use of agricultural and forestry byproducts for practical application. Image 1 • Biomimetic bio-based soybean adhesive was prepared via a facile method. • Kenaf fiber was functionalized with a modified Stöber technique (SSKF). • SSKF serves as multi-functional network skeleton. • Tannic acid (TA) acts as a "bridge" between the SM matrix and SSKF. • Adhesive strength and thermal stability of the resulting adhesive are improved. [ABSTRACT FROM AUTHOR]