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A method is presented herein for the design of wood bio-adhesives using sewage sludge extracts (SSE). SSE was extracted from SS using deep eutectic solvents and processed with glycerol triglycidyl ether (GTE) to disrupt the secondary structure of proteins. An additive was also used to improve mechanical performance. The resulting bio-adhesive (SSE/GTE@TA) had a wet shear strength of 0.93 MPa, meeting the Chinese national standard GB/T 9846-2015 (≥0.7 MPa). However, the high polysaccharide content in SSE would weaken the mechanical properties of wood bio-adhesives. The key to improve bio-adhesive quality was the formation of a strong chemical bond via Maillard reaction as well as higher temperatures (140 °C) to reduce polysaccharide content via dehydration. This approach has lower environmental impact and higher economic efficiency compared to incineration and anaerobic digestion of sewage sludge. This work provides a new perspective on the high-value utilization of SS and offers a novel approach to developing bio-adhesives for the wood industry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Inc.)

Eco-friendly soybean protein adhesives could be an ideal substitute for replacing traditional formaldehyde-based adhesives in wood industry. However, a large number of cross-linking agents are required in soy protein adhesive formulations to obtain sufficiently performing properties. Inspired by the high performance of nacre and branched structures, a hyper-branched amine (HBPA) was synthesized and grafted to graphene oxide (GO), generating a hyper-branched amine-functionalized GO (FGO). A novel soy protein-based adhesive was developed by mixing FGO with soy protein (SPI) and a low dose polyamidoamine-epichlorohydrin (PAE). Results showed that the addition of only 0.4 wt% FGO and 0.75 wt% PAE to the SPI adhesive formulation enhanced the wet shear strength of plywood to 1.18 MPa, which was 181% higher than that of the adhesive without enhancement. The enhanced performance is attributed to the denser cross-linking structure and improved toughness of the adhesive layer. Using FGO in the adhesive formulation also greatly reduced the concentration of the additive cross-linker by up to 78.6% when compared with values reported in the literature. Thus, using a hyper-branched functionalized nano-material to form an organic–inorganic hybrid structure is an effective and efficient strategy to reinforce the composites and polymers. It significantly reduces the chemical additive levels, and is a practical way to develop a sustainable product. [ABSTRACT FROM AUTHOR]

Soybean meal-based adhesive is a good wood adhesive mainly due to its renewable, degradable, and environmentally friendly features. To improve the enhancement efficiency for adhesives, diglycidyl resorcinol ether (DRE) containing a benzene ring and flexible chain structure was used as an efficient cross-linker to enhance the adhesive in the study. The physicochemical properties of adhesives, the dry shear strength, and wet shear strength of plywood were measured. Results suggested that DRE reacted with the functional groups of soybean meal adhesive and formed a cross-linking network during hot press process in a ring-opening reaction through a covalent bond. As expected, compared to adhesive control, the soybean meal adhesive with 4 wt% DRE incorporation showed a significant increment in wet shear strength by 227.8% and in dry shear strength by 82.7%. In short, soybean meal adhesive enhanced with DRE showed considerable potential as a wood adhesive for industrial applications. [ABSTRACT FROM AUTHOR]

Soybean meal (SM)-based adhesive exhibited a great potential to replace petroleum-derived ones to alleviate the energy crisis and eliminate carcinogenic formaldehyde. However, the bad water resistance (caused by low crosslinking density) and inherent brittleness of SM adhesive severely hindered its application. However, improving crosslinking density is generally accompanied by a toughness reduction of the adhesive. Herein, we developed a flexible long-chain starch with a hyper-branched structure (HD), and incorporated it with SM and a crosslinking agent to prepare a novel SM adhesive. Results showed that this adhesive exhibited both excellent water resistance and enhanced toughness. The wet bond strength of plywood fabricated using this adhesive was 354.5% higher than that of SM adhesive. These achievements are because introducing HD with hyper-branched groups enhanced crosslinking density, while HD's flexible long-chain structure improved toughness of the adhesive. This HD can promote the development of tough and hydrophobic bio-based composites. [ABSTRACT FROM AUTHOR]

[Display omitted] • The conversion of industrial alkali lignin into wood adhesives was achieved. • The adhesive was green without using any aldehydes, phenols, or organic solvents. • The bonding strength and debonding work increased by 175 % and 533 %, respectively. • Water resistance and mildew resistance were significantly improved. • The adhesive was low-cost compared to commercial synthetic and biomass adhesives. The conversion of industrial lignin into wood adhesives offers a solution to issues related to formaldehyde pollution and the reliance on petrochemical resources of traditional formaldehyde-based resins, while promoting environmental and energy sustainability. However, conventional methods for preparing lignin-based adhesives generally involve the use of materials like formaldehyde, organic solvents, and costly epoxy, hindering their industrial application. This study introduces a novel approach for producing eco-friendly lignin-based wood adhesives using aminated lignin-Cu nanoparticles. The lignin-Cu nanoparticles were synthesized in water as a single solvent through a sedimentation method. Amination modification was achieved by grafting amino-terminated hyperbranched polyamide onto the nanoparticles via a Schiff base reaction. The prepared adhesive demonstrated a remarkable bonding strength of 1.51 MPa and debonding work of 0.272 J, which were 2.75 and 6.33 times higher than those of the pure lignin adhesive, respectively. Moreover, the adhesive exhibited improved water resistance with a wet shear strength of 1.15 MPa and sustained mildew resistance for approximately 100 days. Notably, this adhesive was synthesized without the use of formaldehyde, phenol, acids, or organic solvents, minimizing reliance on fossil resources and lowering costs compared to many formaldehyde-based and biomass adhesives. This research opens up new avenues for the efficient utilization of industrial lignin and the production of formaldehyde-free, environmentally friendly adhesives, which holds significant promise for energy conservation, emission reduction, and sustainable development within the wood-based panel industry. [ABSTRACT FROM AUTHOR]

The development of a water-retaining and high-bond-strength soybean flour (SF) adhesive is important to improve the efficient and clean preparation of plywood, promoting the substitution of aldehyde resin adhesives in the wood-based panel industry. Soybean protein isolate (SPI) was enriched on boron nitride (BN) to form protein-functionalized BN nanosheets (BS) with dense hydrogen bonds. Drawing inspiration from the strength and toughness of muscles, bionic structures based on BS and SF were designed to enhance adhesive bonding strength and toughness. A water-retaining agent epoxy hyperbranched polyester (EHP) was also synthesized to improve water retention and further enhance the bond strength of adhesives. Results show that the prepared adhesive with BS and EHP exhibits better initial viscosity and coating performance compared with unmodified SF adhesives. The prepressing intensity and wet shear strength of the prepared plywood increased by 227% and 400% to 0.72 and 1.05 MPa. In addition, EHP significantly improved the water retention of the adhesive from 0.5 h to 2 h. After 2 h, the wet shear strength decreased by 30.5% to 0.73 MPa, still meeting the interior use plywood requirement. Notably, this study provides a simple technique of water spraying to recover the dried adhesive layer, and the wet shear strength increased from 0.73 MPa to 0.87 MPa. This preparation strategy of biomass adhesive with water retention and low environmental load bear guiding significance for the efficient and clean production of the wood-based panel. • The prepared adhesives were inspired by the strength and toughness of muscles. • Dense hydrogen bonding enhanced strength and toughness of the adhesive. • Cross-linked structure improved water resistance of the adhesive. • A water-retaining agent was synthesized and improved water retention property. [ABSTRACT FROM AUTHOR]

It is very important for industrial production to develop a strong bonding and multifunctional soy protein (SP)-based adhesive with excellent coating property and high prepressing strength especially for wet veneer. Inspired by mussels, catechol structure was grafted to soybean protein molecules (SPU) by ring opening reaction and free radical polymerization, which endowed the adhesive excellent coating performance on wet veneer. Inspired by oysters, magnesium hydroxide with unsaturated bond (MH@A172) was synthesized, and then mixed with SPU to obtain an organic-inorganic hybrid adhesive (SPU/MH@A172). During the curing process, the synergistic enhancement of the formed cross-linking structure and inorganic mineralization strategy improved the cohesion of SPU/MH@A172 adhesive and endowed strong bonding strength of prepared plywood. That is, when the SPU/MH@A172 adhesive was applied to wood veneer of 100% moisture content, it can be evenly coated and the prepressing bonding strength at 20 °C with 3 h reached 0.53 MPa, which meets the bonding strength requirement of plate forming (≥0.4 MPa). After hot-curing process, the wet and dry shear strength of the prepared plywood reached 1.07 MPa and 2.03 MPa, respectively. In addition, the adhesive had excellent stiffness (45.21 GPa) and micro adhesion (4.62 nN). Importantly, adhesives exhibited excellent mildew resistance (14 days, grade 2), flame retardancy (HRC = 114 kJ/g), low smoke suppression (Ds_max = 95.09) and volatile organic compound release (6.43*106 mg/m2⋅h). Therefore, this collaborative bionic strategy provides a possibility for the development and functional modification of underwater adhesive, film, hydrogels and composite materials. [Display omitted] • A multifunctional soy protein-based adhesive was developed by constructing organic-inorganic mineralization structure. • The prepressing strength of veneer with 100% moisture content at 20 °C and 3 h reaches 0.53 MPa. • The wet and dry shear strength of the prepared plywood reach 1.07 MPa and 2.03 MPa. • The adhesive has excellent stiffness, micro adhesion, mildew resistance, flame retardancy. • The adhesive has low volatile organic compound release and is a product with ecological value. [ABSTRACT FROM AUTHOR]

[Display omitted] • The interfacial bonding strategy of boron-nitrogen coordinated catechol-derived boronic ester was proposed. • The dynamic and stable covalent crosslinking network endowed the adhesive with excellent recyclability. • The wet shear strength and adhesion work of the adhesive were increased by 94.4% and 601.2%. • The adhesive exhibited remarkably improved mildew resistance and flame retardancy. Conventional covalent crosslinked protein adhesives are brittle and cannot be reprocessed effectively, which restricts their practical application and limits the recyclability of wood-based panels. Inspired by biological cartilage and mussels, a tough, strong, and recyclable soybean protein isolate (SPI)-based adhesive, SPI/BP@mica, was designed in this study by co-assembly of mica and SPI via dynamic boron-nitrogen (B-N) coordinated catechol-derived boronic ester (B-O) interfacial bonding. The dynamic covalent B-O, imine, and hydrogen bonds significantly improve the cohesive strength and energy dissipation capacity of SPI/BP@mica adhesive for high mechanical strength and toughness. The maximum wet shear strength and adhesion of SPI/BP@mica adhesive bonded plywood reach 1.05 MPa and 518.8 MJ, respectively, at increases of 94.4 % and 601.2 % over the original SPI adhesive. More importantly, we achieved a breakthrough in the recyclability of protein-based wood adhesives. Due to the synergistic triple dynamic mechanism and B-N coordination depolymerization of B-O bonds, second-generation particleboard prepared by recycling via hot-pressing and solvent-assisted repolymerization showed a rupture modulus of 12.1 MPa; to this effect, we fabricated a next-generation sustainable, reusable adhesive. The SPI/BP@mica adhesive showed excellent mold resistance (50-day shelf life) and flame retardancy (LOI = 29.7 %). Further, the cost of SPI/BP@mica adhesive is equivalent to the price of the phenol formaldehyde resin adhesive commonly used for wood-based panel. The proposed design strategy may promote the functional modification of composites and provide workable guidance for constructing robust, recyclable protein-based materials. [ABSTRACT FROM AUTHOR]

The preparation of a soybean protein adhesive with good prepressing intensity, mildew proof, flame retardant, and high bond strength are conducive to the wide application of a soybean protein adhesive, which is important but challenging for the wood-based panel industry. In this study, two hyperbranched functional polymers were designed. Hyperbranched polyamide (HP) was grafted by 3-hydroxyphenylphosphinyl-propanoic acid (PPA) to obtain PPA@HP and then combined with self-synthesized epoxidized tannin (ETA) to modify the soybean protein adhesive. The hyperbranched functional polymer PPA@HP and ETA reacted with soybean protein to form a hyperbranched cross-linking structure and a hydrogen bond network, which noticeably improved the toughness and bond strength of the adhesive. The wet shear strength of the resultant plywood was improved by 110.9% to 1.35 MPa. The formed hyperbranched hydrogen bond network also significantly improved the prepressing intensity (by 129.0% to 0.71 MPa). In addition, the anti-mildew time increased from 24 h to 120 h. The time to block combustibles increased from 5 s to 80 s, and the limiting oxygen index improved from 23.5% to 38.5%. The use of hyperbranched functional polymers created covalent and non-covalent hybrid networks provides an effective and convenient strategy for developing high-strength and multifunctional composites, such as bio-adhesives, hydrogels, and films. • Two hyperbranched functional polymer PPA@HP and ETA was designed and tested. • PPA@HP and ETA were combined with SPI to obtain protein-based adhesive. • The adhesive has high bond strength (1.35 MPa) and prepressing intensity (0.71 MPa). • The anti-mildew time and the limiting oxygen index were reached 120 h and 38.5%. • A new facile and universality strategy for fabricating multifunction biocomposites. [ABSTRACT FROM AUTHOR]

[Display omitted] • A muscle tissue-inspired design strategy for enhanced protein based adhesive was proposed. • The wet shear strength of the adhesive increased by 214%. • The existence of sacrificial structure increased the adhesion work by 802%. • The adhesive exhibited remarkably improved mildew resistance. Protein based adhesive is limited by poor mechanical properties and water resistance. Inspired by the structure of muscle tissue, a complex structure of layered double hydroxide (LDH) anchored chicken feather fiber (CFF) and tannic acid (TA) was constructed by self-assembly process, forming a novel organic–inorganic hybrid reinforcement structure (CFF-LDH-TA). CFF-LDH-TA was closely combined with soybean meal (SM) through covalent and hydrogen bond multiple interactions. TA simulated the function of connective tissue around fibers, significantly improving the cohesion of SM based adhesive through effective energy dissipation and load transfer. Due to the increased crosslinking density, the dry and wet shear strengths of SM/CFF-LDH-TA reached 2.12 and 1.60 MPa, respectively, which were 50 % and 214 % higher than original SM adhesive, and significantly exceeded the strength of several commercialized formaldehyde adhesives. The existence of bridging effect and sacrificial structure improved toughness of the adhesive, the work of adhesion increased by 802 %, reached 830 mJ. In addition, the SM/CFF-LDH-TA adhesive had better anti-mold and flame retardant ability. More importantly, the cost was lower than the commercial SM based adhesive. This simple and green preparation method provided a new strategy for the production of high-performance, multifunctional and economically effective SM based adhesive. [ABSTRACT FROM AUTHOR]

[Display omitted] • The nanophase-reinforced organic–inorganic hybrid structure was successful constructed. • Using PA as crosslink agent instead of traditional epoxide linked SPI and G-co-Q hybrid. • The resultant adhesive has a high performance with excellent flame-retardant, mildew resistance and antibacterial. • The wet shear strength of the resultant plywood increased by 78.7% to 1.09 MPa. • The plywood bonded by our adhesive is the absorption dominated EMI shielding material with low reflection characteristics. The development of multifunctional adhesive with high bond strength, toughness, mildew resistance, antibacterial properties, flame retardancy, and electromagnetic (EMI) shielding properties has drawn interest and simultaneously presents a challenge in the wood panel industry. Herein, inspired by the organic–inorganic hybrid structure of oysters, an antibacterial agent quaternary ammonium salted hyperbranched polyamide (QHBPA), was synthesized to modify graphene nanosheets (GNSs) via cation-π interaction, eventually forming a G-co-Q hybrid. The G-co-Q hybrid was then combined with soy protein isolate (SPI) and phytic acid (PA) to develop a plywood adhesive with an organic–inorganic hybrid structure via electrostatic interactions and hydrogen bonds. The resultant adhesive exhibited good mildew resistance and antibacterial activity (144 h shelf life). Compared with the SPI adhesive, the dry and wet shear strengths of the plywood with the SPI/PA/G-co-Q adhesive increased by 76.6% and 78.7%, respectively. Meanwhile, non-covalent cross-linking and the formation of an organic–inorganic hybrid structure endowed the adhesive with excellent toughness. Furthermore, the limiting oxygen index (LOI) of the resultant adhesive was 35.5%, reflecting an increase of 49.1% relative to that of the SPI adhesive, indicating that the adhesive possesses superior flame retardancy. Importantly, owing to its unique isolated multilayered structure, the plywood bonded by our adhesive is an absorption dominated EMI shielding material with low reflection characteristics and displays a desirable EMI shielding effectiveness of 43 dB. Therefore, this study provides a creative insight into the design of high value-added and multifunctional plywood with promising application prospects not only in conventional wood-based panels but also in advanced EMI shielding materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The SiO 2 nanohybrid (DP@SiO 2) was successful synthetized. • Using HCCP as crosslink agent instead of traditional epoxide linked SPI and DP@SiO 2. • The resultant adhesive has a high performance with excellent flame-retardant and coating ability. • The wet shear strength of the resultant plywood increased by 143% to 1.46 MPa. • The limiting oxygen index (LOI) of the resultant adhesive was as high as 39.4%. Developing an environment-friendly soy protein adhesive with high bonding strength and flame retardancy has drawn interest and simultaneously presented a challenge in the wood panel industry. Prompted by the organic–inorganic hybrid of oysters, this study proposes a nanohybrid (DP@SiO 2) consisting of the nano silica (SiO 2) and polyethyleneimine (PEI) via electrostatic interaction and grafting 3, 4-dihydroxybenzaldehyde (DBA) by Schiff base reaction. The obtained structure was then combined with a multifunctional cross-linker hexachlorocyclotriphosphazene (HCCP) and soy protein isolate (SPI) to develop a plywood adhesive. The resultant adhesive exhibited good coating ability and prepressing properties, which were attributable to the catechol groups of DP@SiO 2 and the reaction between protein and HCCP. Compared with that of the SPI adhesive, the prepressing strength of plywood with the SPI/HCCP/DP@SiO 2 adhesive was increased by 304%. The dry and wet shear strengths of the plywood adhesive were 110% and 143% higher than those of the SPI adhesive, respectively, which were attributable to the formation of the cross-linking and organic–inorganic hybrid structure, and improvement in adhesive toughness caused by the combination of covalent and multiple hydrogen bonds. The limiting oxygen index (LOI) of the resultant adhesive was 39.4%, reflecting an increase of 71% relative to that of the SPI adhesive, indicating that the adhesive has excellent flame retardancy. This efficient organic–inorganic hybrid strategy can promote the enhancement and functional modification of underwater adhesives, hydrogel, and composite materials. [ABSTRACT FROM AUTHOR]

The preparation of a soybean flour adhesive with good bonding and prepressing performance, toughness, mildew resistance, and fire retardancy to address the problem of formaldehyde pollution is crucial; however, it also presents a challenge. The core–shell structure can achieve various properties by tailoring-making the core–shell composition. In this study, a core–shell structure HBPA@TA with hyperbranched polyamide (HBPA) as the core and tannin (TA) as the shell was prepared and used to modify SF adhesives. The results showed that the pyrogallol group of the tannin shell endowed the adhesive with excellent prepressing performance (0.75 MPa of prepressing intension), toughness, and coating performance, rendering the adhesive more suitable for plywood fabrication. Owing to the dense tannins in HBPA@TA, the resultant adhesive exhibited superior mildew resistance (12 d). After closed-mouth placement for 12 d, the prepressing intension was reduced by 17.3% to 0.62 MPa, which still met the usage requirement. The wet shear strength of the plywood prepared using the resultant adhesive was 1.05 MPa—that is, 133.3% higher than that of the unmodified SF adhesive. The synthesized adhesive also showed antibacterial properties (inhibition zone = 8 mm), flame retardancy (LOI = 32.3%), and volatile organic compound release (6.86*106 mg/m2·h) lower than those of commonly used urea–formaldehyde resins and epoxy resins. [Display omitted] • A spherical hyperbranched core-shell structure HBPA@TA with pyrogallol groups was synthesized. • HBPA@TA as toughening and antifungal agent, and flame retardant modify soybean flour adhesive. • The prepared adhesive has good prepressing and coating performance, toughness, bond strength. • The prepared adhesive was mildew proof, antibacterial and flame retardant, low VOCs emission. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new design strategy of crosslinker inspired by spring structure was proposed. • A new adhesive formulation substitute for petroleum-based adhesives was proposed. • A tough keratin-based adhesive with zero formaldehyde-emission was prepared. • The adhesive exhibited high adhesion to numerous types of substrates. It is of great importance but still a great challenge to develop bio-based environmental adhesives for industrial applications. In this study, inspired by the adhesion structure of lignin and spring mechanics, a new biomimetic strategy was proposed to prepare high bonding strength, formaldehyde-free and petroleum resource-independent adhesive from biomass. Through Schiff base and Michael addition reaction between the quinone of oxidized demethylated lignin (DL) and the amino and sulfhydryl groups of soybean protein isolate (SPI) with helix chain, SPI was grafted onto DL to form reinforcement structure and crosslinker with molecular spring structure (namely SDL). Cleavage of the disulfide bonds of keratin and introduction of SDL reconstituted a strong cohesive crosslinking network (KPT-SDL), in which the α -helical peptide chain in SDL was stretched and the intramolecular hydrogen bonds were broken under tensile force, thus achieving energy dissipation and significantly improving the shear strength and toughness of the keratin-based adhesives. The maximum wet strength of the wood-based panel prepared by KPT-SDL adhesive reached to 1.22 MPa, which was comparable to the level of industrial adhesives and 197.56% higher than the original keratin-based adhesive. In addition, KPT-SDL presented high adhesion to numerous types of substrates, including steel and ceramic. This study provided a green and effective biomimetic strategy for high value-added keratin to promote the development of strong and tough composites, which had a good value of frontier research and industrial development. [ABSTRACT FROM AUTHOR]

[Display omitted] • A preparation technology of sulfhydryl chitosan was proposed. • Chitosan and soybean protein were covalently linked by disulfide bonds. • The dry strength of the adhesive increased by 61.31%. • The wet shear for 3 h soaking at 63 °C of the adhesive increased by 365.6%. • The adhesive exhibited remarkably improved mildew resistance. Soybean protein (SP)-based adhesives present low adhesive strength, poor water resistance and low mildew resistance, which generally limit their practical industrial applications. Inspired by the interesting phenomenon that the strength of hair fiber was affected by the breaking and reuniting of disulfide bonds during perming, in this study, a new biomimetic strategy was proposed to construct a soybean meal (SM)-disulfide bonds-chitosan (CS) structure to achieve enhanced adhesive strength, improved water resistance and higher mold resistance. The introduction of sulfhydryl chitosan (CSSH) with high sulfhydryl content provided sufficient reaction sites, endowing the resultant high-strength and mold resistant bio-based adhesive with increased crosslinking density and numerous hydrogen bonds. The dry shear strength and the wet shear strength for 3 h soaking at 63 °C of SM-CSSH was improved by 61.31% and 365.6% to 2.71 MPa and 1.49 MPa, respectively. The increase in residual rate and decrease in moisture absorption of adhesive illustrated the excellent water resistance of the material. More importantly, the antibacterial property of chitosan prolonged the storage time of the adhesive, which benefits to its industrial applicability. This study provided a new biomimetic strategy to prepare high-strength adhesives from agricultural and fishery wastes, exploring for green and sustainable development concept. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eco-friendly biobased adhesive with zero-formaldehyde emission was prepared. • A stable cross-linking network of covalent and hydrogen bond was formed. • The wet shear strength of adhesive was improved by 400%. • Water resistance of the adhesive were significantly improved. • The adhesive displayed flame retardant property. Development of wood adhesive combined with excellent bonding strength and water resistance is still challenging, particularly from sustainable and renewable polysaccharide–based materials instead of fossil resources. In this study, inspired by the periodate oxidation − adipic acid dihydrazide (ADH) crosslinking strategy and borate chemistry in plants, oxidized soybean polysaccharide complexed with borax (BSP) and then reacted with ADH via Schiff-base reaction to form the in-situ crosslinking skeleton, in which chitosan (CS) was introduced to improve the active sites. Through the interaction of covalent and hydrogen bond, the adhesive with multi crosslinking network (namely BSPC-ADH) was constructed. The resultant flame-resistant material showed excellent wet shear strength (0.9 MPa) and outstanding water resistance (86.9% residue rate), which met the requirements of indoor plate. This study provided a new method to develop renewable, potentially industrial-usable and environmental-friendly adhesive. [ABSTRACT FROM AUTHOR]

Environmentally friendly soybean meal-based (SM) adhesive has been developed to replace harmful formaldehyde-based adhesives in the wood-based panel industry. But, the extensive application of SM adhesives is limited by several deficiencies, including high brittleness, poor coating ability, and poor antibacterial/mildew resistance, etc. In this study, a new SM adhesive has been designed by constructing a hyperbranched cross-linked structure via the Maillard reaction instead of traditional epoxide-based crosslinking structure. Specifically, the hyperbranched poly(ethylenimine)-functionalized carboxymethyl chitosan was synthesized via a one-step procedure using carboxymethyl chitosan and polyethyleneimine, and then mixed with soybean meal and a crosslinker (2,3-butanedione) to develop a wood adhesive. The dry and wet shear strength of plywood bonded by the obtained adhesive was 55% and 357% higher than those of the original SM adhesive, respectively, which were attributed to the formation of Maillard reaction-based crosslinked structure and improvement of adhesive toughness. The corresponding wood failure percentage was increased to 70% compared to pure SM adhesive. Notably, the prepared adhesive exhibited mildew resistance for 240 h and had a uniform coating ability on the wood surface. Construction Maillard reaction based crosslinking structure has potential application in the enhancement of other bio-adhesives and protein-based hydrogels. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of efficient and sustainable formaldehyde-free adhesives has become an important strategy to solve the problems of environmental pollution, resource depletion and clean production. It is a promising and challenging task to prepare multifunctional adhesives with high adhesive strength from soybean protein (SP), an abundant and sustainable biomaterial that is largely produced from agricultural waste. Inspired by gecko toe, carboxylated paper fiber (CPF) anchored by MOFs (namely UiO66-NH 2 @CPF) was constructed as micro-nano structure reinforcing phase, and resveratrol-based epoxide (RE) was employed as crosslinking agent to formulate a series of SP-based green adhesives. In particular, plywood bonded with SP/RE13/UiO66-NH 2 @CPF1.5 presented the maximum dry/wet shear strength to 2.52 MPa and 1.43 MPa, which increased by 90.9% and 457% compared to that of adhesive made with SP alone, respectively. SP/RE13/UiO66-NH 2 @CPF1.5 displayed a 92.02% residual rate (in water at 60 °C for 6 h), showing excellent bonding strength and water resistance. More importantly, SP/RE13/UiO66-NH 2 @CPF1.5 successfully inhibited the invasion of mold, enabling to extend its shelf time to 12 h. In addition, it showed excellent fluorescent properties, exposing great potential in anti-counterfeiting of wood-based composite materials and information transmission. The development of SP-based adhesives improved the added value of industrial by-products, which not only met the demand for green and sustainable development, but also contributed to clean production by providing environmental and economic benefits along with excellent performance. [Display omitted] [ABSTRACT FROM AUTHOR]

Traditional formaldehyde-based adhesives release toxic substances such as formaldehyde and phenol, which pollutes the environment, endangers human health, and relies on petrochemical resources excessively. Developing a strong soy protein adhesive with reasonable viscosity, toughness, and mildew resistance to replace formaldehyde-based adhesive is important and also a challenge for the industry of wood adhesive. In this study, a triple network structure including covalent bonds, hydrogen bonds and ionic bonds was built in soy protein adhesive. The results showed that compared with SPI adhesive, the viscosity of resultant adhesive decreased by 94.3% to 9952 mPa s, the dry and wet shear strength of resultant plywood increased by 33.9% (2.57 MPa) and 116% (1.36 MPa), respectively. The fracture strain of plywood increased by 36.4%, and the mildew resistance of adhesive increased from 1 day to more than 15 days. This improvement resulted from the adhesive's water resistance improvement by constructing the covalent network and the toughness increasing by the synergistic effect of hydrogen bonds and ionic bonds. This work provides a new method for the preparation of eco-friendly and high-performance adhesives and promotes the development of the green adhesive. Image 1 ● An eco-friendly adhesive with triple network structure was design and developed. ● The triple network structure consists of covalent, hydrogen and ionic bonds. ● The viscosity of resultant adhesive decreased by 94.3%. ● The dry/wet shear strength of plywood increased by 33.9% and 116%. ● The mildew resistance of adhesive increased from 1 day to more than 15 days. [ABSTRACT FROM AUTHOR]