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[Display omitted] • ST&CCL adhesive inspired by electrostatic interactions in slug mucus. • The adhesive endows strong bonding property with a 129.6% increasing for wet shear strength. • The adhesive exhibits a long-term mildew resistance for 120 days. • The bonding strength of prepared plywood is higher than E0 level after a 30-day antifungal period. Developing strong soy protein-based adhesive (SPA) to replace harmful formaldehyde-based resins in the wood-based panel industry is a hot research. However, the lack of long-term antibacterial and antifungal properties of SPA significantly impacts its durable bonding performance and limits application. The commonly used anti-mold agents often decrease the protein compatibility and strength. Inspired by the robust and resilient dissipative matrix found in slug mucus, a green and sustainable adhesive with long-term antibacterial, antifungal properties, and excellent bonding performance was prepared using classic self-assembly and building toughened crosslinked networks. Specifically, caffeic acid and L-arginine were grafted onto tubuchitosan via acylation to prepare a chitosan with strong cationic graft modification (CCL), which combined with self-made triglycidylamine as a crosslinking agent to synergically strengthen the adhesive network. The SPA demonstrated excellent antibacterial properties against Staphylococcus aureus (20 mm) and Escherichia coli (19 mm). The prepared plywood and liquid/cured adhesive showed effective antifungal periods of 30, 80, and 120 days, respectively. Moreover, the incorporation of CCL significantly enhanced the dry and wet shear strengths of the prepared plywood to 2.73 MPa and 1.86 MPa, respectively. And a dry shear strength of 2.10 MPa and a wet shear strength of 1.53 MPa maintained even after a 30-day antifungal observation period, which still meet the interior use plywood requirement (≥0.7 MPa). The corresponding plywood after placing 30 days (1.46 MPa) is obviously higher than E0 level (0.05 mg/m3, GB18580-2017, Climate chamber method) of melamine-urea–formaldehyde resin (0 MPa after ten days). This study provides a straightforward and effective strategy for developing high performance and durable bio-based composite material, including adhesive, film, hydrogel. [ABSTRACT FROM AUTHOR]

Nowadays, formaldehyde-based adhesives are still widely used in wood industry, such as urea formaldehyde resin, phenol formaldehyde resin, melamine formaldehyde resin. Emission of toxic formaldehyde is still one of the biggest problems for these formaldehyde-based adhesives in recent years for the development of wood adhesives. Lately, there has been a considerable industrial interest in the development of natural or green wood adhesives, such as lignin, tannin, protein, starch, and polysaccharides, to substitute synthetic thermosetting resins as adhesives for wood panels because of the mounting environmental pressure worldwide. As one kind of bio-based adhesives, soy protein-based adhesive has been always a hot topic since 1990s. As it is well-known that the soy-based adhesive with no modification cannot be used directly for wood panels for its poor bonding strength and water resistance especially, and the latter one is so bad. Cross-linking modification has been proved to be an effective modification method to improve the water resistance of soy-based adhesive. Some cross-linkers have to be used for this modification, such as formaldehyde-based resins, polyacrylic ester, epoxy. As a biomass material, furfuryl alcohol is more friendly than formaldehyde-based crosslinkers for protein-based adhesive. To guide the preparation of protein-based adhesive, especially the soy-based adhesive, the reaction between a simple dipeptide N-(2)-L-alanyl-L-glutamine (AG), used as a model compound of protein, and its cross-linker furfuryl alcohol was studied in this paper. The products prepared with furfuryl alcohol and AG under different pHs were analyzed by ESI-MS (electrospray ionization mass spectrometer), 13C-NMR (carbon-13 nuclear magnetic resonance) and FT-IR. It was found that the medium environment had great effects on the competition of the co-condensation reaction between furfuryl alcohol and AG and self-condensation reaction of furfuryl alcohol molecules in the mixing system with furfuryl alcohol and AG. Under alkaline conditions, both co-condensation and self-condensation were not obviously detected. Only when the value of pH was higher than 11, a few co-condensation reaction products were gotten. The reaction occurred mainly between furfuryl alcohol and the primary amido groups of AG. Under acid conditions, both co-condensation and self-condensation were observed. The more acid the preparation conditions, the easier to be observed the self-condensation of furfuryl alcohol molecules than the co-condensation between furfuryl alcohol and AG. And when the value of pH was higher than 5, both co-condensation and self-condensation were not outstanding. In this study, under pH value 3, the co-condensation and self-condensation found equilibrium. There was a great possibility for the primary amido and aliphatic amino groups of AG molecules to react with furfuryl alcohol molecules. No reaction was detected between the secondary amido groups of AG and furfuryl alcohol. Besides, the reaction mechanism between furfuryl alcohol and model compounds of soy protein had correspondence with the performance of plywood with soy protein-based adhesive, namely, soy protein-based adhesive crosslinked by furfuryl alcohol showed better bonding performance and water resistance under the pH value of 3 than that of others. In conclusion, the research has great significance to realize the scientific use and improve the market competitiveness of soy protein-based adhesives. [ABSTRACT FROM AUTHOR]

To find the effects of cross-linker phenol-formaldehyde (PF) resin on the performance of soy-based adhesives, the reaction between model compounds hydroxymethyl phenol (HPF) and glutamic acid were studied in this paper. HPF prepared in laboratory conditions showed higher content of hydroxymethyl groups than normal PF resin, which was proved by the results of Electrospray Ionization Mass Spectrometry (ESI-MS) and 13C Nuclear Magnetic Resonance (13C-NMR). The results of ESI-MS, Fourier transform infrared spectroscopy (FT-IR), and 13C-NMR based on resultant products obtained from model compounds showed better water resistance of the soy protein-based adhesive modified by PF-based resin, which indicated the reaction between PF resin and soy protein. However, it seemed that the soy-based adhesive cross-linked by HPF with the maximum content of hydroxymethyl groups did not show the best water resistance.

For improving the water resistance, bonding performance, and anti-mildew property of the soy protein-based adhesive (SPA), in this research, based on cross-linking enhancement theory, soybean meal flour as the main raw material, self-synthesizing triglycidylamine (TGA), and larch tannin (LT) were used to build efficient crosslinking water-resistant structure and develop SPA. The effect of LT addition on the physical properties, bonding strength, and anti-mildew property of the resultant adhesive was investigated. The results showed that the residual rate of SPA with 4 % LT and 3 % TGA was improved by 2.1 % and the corresponding moisture absorption rate was reduced by 20.1 % compared with the SPA only modified by 3 % TGA. In addition, the SPA with 4 % LT and 3 % TGA had a 42.3 % increase in bonding strength, reaching 1.11 MPa, which satisfied the standard requirements of interior use plywood (≥ 0.7 MPa). The improved water-resistant bonding performance is mainly because interaction forces, such as hydrogen bonds, ionic bonds, and covalent bonds, formed between tannin and protein, and under the cross-linking effect of TGA, the whole cross-linking system forms a dense network structure. LT not only had a reinforcing effect on the SPA but also could prolong the pot life of the adhesive for 60 h due to the phenolic hydroxyl groups of tannin. Compared with the commercial anti-mildew agents, the mildew resistance before and after curing is the following: 1,2-benzisothiazole in-3-one > LT > sodium tetraborate > potassium sorbate. [Display omitted] • An easy-to-produce, high-performance, and environmentally friendly bio-adhesive was developed. • The incorporation of larch tannin enhanced the cohesion and mechanical properties of adhesives. • The resultant adhesive has better water-resistant bonding performance and an anti-mildew effect. • Effectively extend durability of plywood prepared by adhesive and storage period of the SPAs. [ABSTRACT FROM AUTHOR]

To find the effects of cross-linker phenol-formaldehyde (PF) resin on the performance of soy-based adhesives, the reaction between model compounds hydroxymethyl phenol (HPF) and glutamic acid were studied in this paper. HPF prepared in laboratory conditions showed higher content of hydroxymethyl groups than normal PF resin, which was proved by the results of Electrospray Ionization Mass Spectrometry (ESI-MS) and 13C Nuclear Magnetic Resonance (13C-NMR). The results of ESI-MS, Fourier transform infrared spectroscopy (FT-IR), and 13C-NMR based on resultant products obtained from model compounds showed better water resistance of the soy protein-based adhesive modified by PF-based resin, which indicated the reaction between PF resin and soy protein. However, it seemed that the soy-based adhesive cross-linked by HPF with the maximum content of hydroxymethyl groups did not show the best water resistance. [ABSTRACT FROM AUTHOR]