Search

Epoxide modification effectively improves the water tolerance of soy protein adhesives, showing great potential in the commercial application as alternatives to petroleum-derived formaldehyde-based adhesives. However, epoxide-modified adhesives still present problematic limitations, such as poor mildew resistance and high hot-pressing temperature. In this study, a curing system based on radical polymerization was designed and developed to prepare soy protein adhesives, instead of building a traditional epoxide cross-linking structure. First, allyl glycidyl ether (G) was grafted onto a soy protein (SP) molecule to obtain soy protein with unsaturated double bonds (G@SP). Allicin (A) was then used as a cross-linker to build a cross-linking structure (G@SP/A) via free-radical polymerization to enhance the bond performance of the adhesive. Relative to that of pure SP adhesive, the wet shear strength (WSS) and dry shear strength (DSS) of plywood bonded with the G@SP/A adhesive increased by 108% and 45%, reaching 1.08 MPa and 1.84 MPa, respectively, at 120 °C pressing temperature. Notably, the G@SP/A adhesive showed superior antibacterial (Escherichia coli and Staphylococcus aureus) activity, high mildew resistance (35 d shelf life), good cytocompatibility, and biodegradability (30 d). Moreover, the WSS of plywood bonded with the G@SP/A adhesive at 80 °C for 6 min and 20 °C for 72 h reached 1.08 MPa and 1.12 MPa, respectively, indicating the sufficient low-temperature curing ability of the resultant adhesive. Thus, building a cross-linking structure by free-radical polymerization can be extended to improve the performance of film composites, other adhesives, and engineering materials. • Free radical polymerization curing system was used to prepare soy protein adhesive. • The resultant adhesive has excellent antibacterial and mildew proof ability. • The resultant adhesive has good cytocompatibility and biodegradability. • The wet shear strength of resultant plywood increased by 108% to 1.08 MPa. • The resultant adhesive has good low temperature curing ability. [ABSTRACT FROM AUTHOR]

Developing eco-friendly soy protein-based adhesives instead of the extensively used aldehyde-based adhesives to fabricate wood-based panels can reduce environmental hazards and benefit human health. However, traditional soy protein-based adhesives lack long-term antibacterial and antimildew properties, reducing their bond strength and durability. Here, 3,4-dihydroxybenzaldehyde-grafted chitosan was prepared as a catechol structure donor and then introduced into the soy protein isolate (SPI) adhesive for the in situ reduction of silver ions to stable silver nanoparticles (Ag NPs); a biomineralization system was thus established. Notably, the catechol–quinone reversible redox reaction in the system endowed the resultant adhesive with excellent antibacterial (more than 99.99% bactericidal rate against Staphylococcus aureus and Escherichia coli , 91.67% bactericidal rate against Candida albicans) and long-term antimildew properties (40 d). The wet shear strength (1.24 MPa) and prepressing bond strength (0.80 MPa) of the plywood prepared with the adhesive were increased by 63.27% and 129.63%, respectively, relative to the SPI adhesive. The volatile organic compounds release of the adhesive was 1–2 orders of magnitude lower than that of commonly used commercial adhesives. This strategy provides inspiration for reinforcing antibacterial or antimildew bio-based adhesives, hydrogels, and composites. [Display omitted] • A system of biomineralized Ag NPs was built in the soy protein-based adhesive. • CS and SPI are used as stabilizers to avoid aggregation and agglomeration of Ag NPs. • The wet shear strength of plywood bonded by the adhesive was improved by 129.63%. • The adhesive has long-term antibacterial, mildew resistance, and low VOCs release. [ABSTRACT FROM AUTHOR]

Soy protein-based adhesives show great prospects in replacing aldehydes resin adhesives to fabricate wood-based panels, however, high doses of synthetic resins as crosslinkers must be used to obtain good bonding performance. To reduce overreliance upon crosslinkers derived from fossil resources, a 100% bio-derived crosslinker-xylitol epoxide (EX) was synthesized from epichlorohydrin and xylitol, followed by blending with soy protein isolate (SPI) to create a functional biological adhesive. After using EX, the wet and dry shear strengths of plywood prepared by the SPI/4%EX adhesive increased by 138.6% and 55.6%, respectively, compared with the pure soy protein adhesive. This was attributable to the crosslinked network formed in adhesive and the enhanced adhesive toughness. The optimized process parameters of plywood prepared with EX-modified soy protein adhesive were 110 ℃, 1.3 min/mm and 0.8 MPa. The addition of EX also improved the mildew-resist property of the adhesive to 10 days, which prolonged the adhesive storage life and the service life of the resultant plywood. Therefore, EX could be utilized to enhance the mechanical and mildew-resist properties of protein-based materials, and shows great potential applications in adhesive, film, and hydrogel. • Xylitol was epoxidized to form a bio-based crosslinker (EX). • Using soy protein and 4% EX develops a 100% bio-derived wood adhesive. • The wet and dry shear strength of plywood increased by 138.6% and 55.6%. • The mildew resistance of resultant adhesive is more than ten days. [ABSTRACT FROM AUTHOR]