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Despite the recent advances in protein-based adhesives, the poor water resistance and unsatisfactory mechanical property limit the industrial application of soybean protein adhesive. It is challenging to achieve strong adhesion and high water resistance. In this work, chitosan, tannic acid and silver ion were used to modify soybean protein adhesive. Through chelation, redox reaction and hydrogen bonding, a dynamic crosslinking network structure was constructed, so as to prepare a bio-based adhesive with high water resistance and high bonding strength. It was revealed that when the tannic acid and silver nitrate were mixed at the same concentration of 10 mg/mL and the volume ratio of 1:1, silver nanoparticles with the highest content were produced. When the mass of soybean protein, chitosan, tannic-silver solution and distilled water was 15, 0.3, 30 and 55 g, respectively, the enhancement effect was the best. The dry shear strength increased by 171% to 3.03 MPa, and the wet shear strength increased by 93% to 1.29 MPa. The water resistance, thermal stability, hydrolysis stability, and the toughness and viscosity of the soybean protein adhesive were greatly improved. This study developed a new bio-based adhesive and expanded its potential application in wood products manufacturing. [ABSTRACT FROM AUTHOR]

Plant protein-based adhesives are considered to be the most potential substitutes for petroleum-based adhesives in the wood panel industry, however, the poor water resistance and unsatisfactory mechanical performance limit their large-scale application. Moreover, the development of multifunctional plant protein-based adhesives with high strength, mildew proof, and flame-retardant remains a challenge. Plant fibers have been widely used as the reinforcing phase of polymers, but the smooth surface makes them easy to pull out of the matrix, which greatly reduced the strengthening effect. Herein, the phenylboronic acid-tethered hierarchical rough kenaf fibers were constructed to strengthen soy meal (SM) adhesives while imparting multifunction. The hierarchical rough structures and reactive groups on the surface of kenaf fibers made them form stronger mechanical interlocking and chemical crosslinking with SM matrix, coupled with the entanglement and interpenetration of the fibers with a high aspect ratio, which together endowed the SM adhesive with outstanding water-resistant bonding strength. The wet shear strength of the plywood prepared by the resultant SM adhesive increased by 391.7% to 1.18 MPa, which was far higher than the standard of 0.7 MPa for type II plywood (GB/T 9846-2015) in Chinese standards. Benefiting from the phenylboronic acid component, the resultant SM adhesive exhibited excellent mildew-proof and flame-retardant properties. This biomimetic design of kenaf fibers provides a facile and efficient strategy to develop high-performance and multifunctional bio-adhesives. [ABSTRACT FROM AUTHOR]

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]

Recently, soy protein has attracted extensive attention from wood industries and consumers in the production of wood adhesives as it is non‐toxic, biodegradable, low cost, and easy to process. There are a variety of reactive groups namely OH, NH2, COOH, and SH, in protein molecules, which offer possibilities for protein denaturation, chemical modification, and increased ionic interactions. The research in protein denaturation, crosslinking modification, biomimetic modification, and organic–inorganic hybrid formulation not only focuses on enhancing the mechanical properties and tolerance to water of the adhesives but also considers its toughness, mildew resistance, and flame retardancy to further optimize the performances of the adhesives. In this paper, soy protein chemical composition, soy protein denaturation, and reinforced modification are discussed to understand these methods and further develop into a multifunctional soy protein‐based adhesive. Given the potential of bio‐based adhesives, these modification methods not only provide the theoretical basis for its development at full scale, but also the possibility for the multifunctional applications of bio‐based adhesives. [ABSTRACT FROM AUTHOR]

Soy protein (SPI) adhesives are non‐toxic and eco‐friendly that can potentially replace traditional formaldehyde‐based adhesives to ease toxic gas emissions. The development of strong and toughness SPI adhesive benefits its bonding stability but is challenging. In this study, inspired by nacre structure, a soft–hard double network structure was constructed in SPI adhesive. The triglycidylamine (TGA) cross‐linked protein served as the hard phase to provide cohesion. In addition, the self‐synthesizing epoxidized rubber (ER) as soft phase cross‐linked protein and enhanced the interfacial force between hard and soft phase to dissipate energy during fracture, which improved the toughness of adhesive. The results showed that: compared with original SPI adhesive, the residue rate of SPI/4%TGA/3%ER adhesive increased by 7.9%, and the moisture absorption rate decreased by 16.7%. The dry and wet shear strength of the plywood prepared by SPI/4%TGA/3%ER adhesive increased by 58.9% and 160.4% to 1.86 and 1.38 MPa, which was higher than commercial polyamide‐epichlorohydrin modified SPI adhesive. The elongation at break increased by 55.2%–45%, the fracture energy increased by 233% to 2.96 MJ/m2, and the cracks on the adhesive surface disappeared, indicating that the strength, toughness, and water resistance of the adhesive were significantly improved. In this research, a soft–hard double network structure is constructed in a bio‐based adhesive to obtain excellent performance, this eco‐friendly adhesive opens up a new way to replace harmful formaldehyde‐based adhesives. [ABSTRACT FROM AUTHOR]

Nanoparticle enhancement has been used as an effective means to improve the performance of biomass adhesives. However, there is an inevitable problem of stress concentration caused by particle agglomeration and thus the adhesive layer is susceptible to damage. Therefore, in this paper, a sol–gel method was used to generate uniformly distributed manganese dioxide (MnO2) nanoparticles on the surface of diatomite (Dia) and used for the modification of soybean meal based wood adhesives. The results showed that MnO2 nanoparticles have been successfully anchored on the surface of Dia during the sol–gel process without agglomeration. MnO2/Dia particles could fill in the adhesive gaps and form hydrogen bonds with soy protein molecules, which ensured that the adhesive wet shear strength was increased by 33% to 0.89 MPa. This study provided an idea for the preparation of highly dispersed nanoparticle reinforced adhesives. [ABSTRACT FROM AUTHOR]

Soybean protein adhesives are environmentally friendly biomass‐based aldehyde‐free adhesives that have good economic value for the wood industry; however, it remains challenging to produce soybean protein adhesives with excellent water resistance, toughness, and mildew resistance through a simple modification method. In this work, inspired by plant polyphenols, a novel crosslinked soybean meal adhesive (SMPT) is obtained using a facile economic method. Polyamidoamine‐epichlorohydrin (PAE) and tannic acid (TA) are combined with a soybean meal matrix to form a tough co‐crosslinked network through strong intermolecular forces (covalent bonds, ionic bonds, and hydrogen bonds) in adhesive system. The results show that the wet bonding strength of SMPT adhesives for plywood is 134.1% higher than the unmodified soybean meal adhesive. The adhesion properties met the standard requirements for interior‐use plywood. And the compact cross‐linking network structure is accelerated the greater energy dissipation, which improves the toughness of adhesive. Moreover, cationic azetidinium groups in PAE and phenol hydroxyl groups in TA synergistically not only exhibit the good antibacterial activities but also improve mildew resistance for SMPT adhesives. This facile strategy provides an economic sustainable method to prepare high‐performance environmentally friendly wood adhesives. [ABSTRACT FROM AUTHOR]

Crosslinking modification can effectively improve the water resistance of soy protein isolate (SPI) adhesive, but it often depends on petroleum‐based reagents, violating the concept of green environmental protection. Here, inspired by the breaking and recombination of the disulfide bond in the perm process, a high‐performance wood adhesive is prepared by incorporation of SPI (modified by sodium sulfite to cleave the disulfide bonds of protein chains) and feather keratin (FK, extracted from waste chicken feathers by breaking the disulfide bond) without using any other crosslinkers. The crosslinking reaction occurs by disulfide bonds derived from the sulfhydryl group of FK and SPI. Thus the wet shear strength of the SPI/FK‐20 adhesive is improved from 0.57 to 1.18 MPa, an increment of 107%. This study provides a green strategy to prepare high‐performance protein‐based adhesive from the waste products‐chicken feathers, which will contribute to the development of the environmentally friendly wood adhesive industry. [ABSTRACT FROM AUTHOR]

Soy meal-based wood adhesive has received much interest for its environmentally friendly properties, as it is thought to provide an effective alternative to conventional formaldehyde-based wood adhesives. However, the abundant hydrophilic groups and weak internal structure result in poor water resistance and low bonding strength of soy meal-based wood adhesives. In this study, bio-based carboxymethylated wood fibers (CMWFs) were used to develop a high-performance soy meal-based adhesive. Wood fibers (WFs) were pre-treated via carboxymethylation to endow WFs with abundant carboxyl groups and facilitate their dispersion in soy protein matrix. CMWFs containing abundant carboxyl groups served as a multiple "crosslinking core" and effectively cross-linked with soy protein side-chain, resulting in the construction of a stable adhesive system. The modified soy meal-based adhesive exhibited excellent bonding strength and water resistance. In particular, tension tests indicated that the water-resistant bonding strength of the adhesive modified with CMWFs reached 1.69 MPa, which was 160% higher compared with the unmodified adhesive; the wood failure percentage of the plywood bonded by CMWF-modified soy meal-based adhesive was as high as 100%. Moisture uptake and residual rate tests indicated that high water resistance of the adhesive was achieved. This design provides a facile and sustainable strategy for developing high-performance soy meal-based adhesives. [ABSTRACT FROM AUTHOR]

Mussel‐inspired dopamine chemistry is popular among engineers for surface modification on various substrates due to its high efficiency, handy operation process, and strong reactivity. However, the high cost of dopamine does not allow for mass production. In the present study, low‐cost dopamine analogues (alkali lignin and tannic acid) were used to fabricate high‐reactivity silkworm silk fiber (SF) via a simple dip‐coating approach, and were then applied to a soy‐based adhesive to enhance its performance. The SF tightly combines with soy protein mainly via a Schiff base reaction between polydopamine or dopamine analogue and the amine or thiol groups of soy protein; this forms a multiple crosslinked system and "reinforced concrete"‐like structure, as confirmed by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetry, and scanning electron microscopy analyses. As expected, the toughness of the soy‐based adhesive obviously improved and the highest wet shear strength of the adhesive samples attained 1.50 MPa, which is far greater than relevant interior use requirements. Though dopamine‐coated SF could significantly enhance the wet shear strength of the soy‐based adhesive by 387.1% compared to the pristine SM adhesive, lignin‐coated and tannic acid‐coated SFs are more suitable for practical application due to the lower cost of raw materials. The results of this study may represent an effective and low‐cost approach to mussel‐inspired surface modification chemistry for the mass production of high‐performance soy‐based adhesives. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48785. [ABSTRACT FROM AUTHOR]

Fiber agglomeration and poor interfacial combination with the matrix restrict the performance of composites. Herein, soybean meal-based adhesives were fabricated via the addition of dialdehyde cellulose (DAC) obtained from waste paper dissolved in an alkali–urea system and oxidized with sodium periodate. Due to the dissolution by the alkali–urea system, DAC dispersed well in the solution and did not aggregate in the adhesive matrix. Because of the oxidation treatment, DAC was crosslinked with the adhesive matrix via a Schiff base reaction. Meanwhile, hydrogen bonds were formed at the interface between the DAC and the adhesive matrix. Plywood with the SM/DAC/PTGE adhesive reached its highest wet bonding strength of 1.27 MPa (4 wt% DAC addition), a 95% increase compared to that with the unmodified SM/PTGE adhesive. Fine DAC-to-SM interfacial bonding and a dense crosslinking network were constructed in the SM/DAC/PTGE adhesive systems. The cycle of reuse for the alkali–urea system in the experiments demonstrated that the preparation method of the cellulose solution was scalable and sustainable. [ABSTRACT FROM AUTHOR]

Wood adhesives fabricated from biomass can substitute formaldehyde‐based ones, reducing the consumption of fossil resources and eliminating formaldehyde pollution. In this study, a novel and sustainable water‐soluble soybean polysaccharide (WSSPS)‐based adhesive is designed. Specifically, a hyperbranched aminated polysaccharide (HBPA–g–WSSPS), as an adhesive matrix, is synthesized via grafting reaction between oxidized WSSPS and hyperbranched polyamide (HBPA). Triglycidylamine, a bio‐based epoxide cross‐linker, reacted with the HBPA–g–WSSPS to afford a cross‐linked hyperbranched network, providing strong cohesion for the adhesive. Additionally, polyacrylamide imparted an adjustable viscosity to the adhesive. The resultant WSSPS‐based adhesive enhanced the wet shear strength of plywood (1.24 MPa) by 49% compared to the E0‐level industrial‐use melamine‐urea‐formaldehyde (MUF) resin and by 26% compared to the industrial‐use soybean meal/polyamidoamine‐epichlorohydrin (PAE) adhesive. In addition, the adhesive has characteristics similar to those of the MUF resin, including viscosity, coating performance, hot‐pressing conditions, and dry bond strength, which are superior to those of the soybean meal/PAE adhesive. This developed polysaccharide‐based adhesive can potentially enhance various composites and can be used in industrial sectors. [ABSTRACT FROM AUTHOR]

Urea formaldehyde, phenolic, and melamine formaldehyde resins are currently the most common wood adhesives. However, these modern wood adhesives have toxicity problems and most of the raw materials come from non-renewable resources. Ideally, future alternative adhesives will be prepared from non-toxic, inexpensive, and renewable natural materials. We found that borate chemistry can crosslink soy protein (SP) and soy polysaccharides (SPSs) to produce a strong adhesive, which is the core of the stable structure in higher plants. Hyperbranched polyester (HBPE) was added to the adhesive as a toughening agent. The resulting crosslinked protein adhesive bound wood with high strength and in some cases its force exceeded the force that the wood itself could withstand. In addition, the borate crosslinked protein adhesive displayed antimicrobial and flame-retardant properties. Simple borate chemistry can provide a way to produce low-cost, renewable, and high-performance materials. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, a low-cost diatomite was used to partly substitute wheat flour as one type of melamine-urea-formaldehyde (MUF) resin filler. Five-ply plywood was fabricated, and its performance was measured. The crystallinity, fracture surface, and functional groups were tested to determine the effects of diatomite on the performance of the MUF resin. The results show that diatomite was well distributed in the MUF resin system and formed an embedding structure; this improved the wet shear strength of the resulting plywood by 33% to 1.36 MPa. Diatomite captured the free formaldehyde in the resin and the microporous structure formed in the resin accelerate formaldehyde release of the plywood. Consequently, the formaldehyde emission of the plywood was reduced. The diatomite partly replaced wheat flour as an MUF resin filler and could be applied in the plywood industry. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44095. [ABSTRACT FROM AUTHOR]

ABSTRACT A novel soybean protein-based wood adhesive with good bond strength, excellent water resistance, and the desired technological applicability was formulated by combining thermal alkali degradation, thermal acid treatment, and crosslinking. The characterization results indicated that thermal alkali degradation could effectively improve the technological applicability, thermal acid treatment could positively improve the water resistance, and appropriate crosslinking modification could significantly enhance the bond strength and water resistance of the soybean protein adhesive. The crosslinker species, crosslinker level, and ratio of thermal alkali-degraded soybean protein (DSP) to thermal acid-treated soybean protein (TSP) had important effects on the primary properties of the soybean protein adhesives. The modified polyamide aqueous solution was the most preferable crosslinker because of its low viscosity, good crosslinking efficiency, and excellent miscibility with soybean protein solution. The optimal soybean protein adhesive that was formulated from 20 wt % modified polyamide as the crosslinker and a DSP/TSP ratio of 1:3 had a solid content of more than 35 wt %, suitable viscosity (∼2180 mPa s), a long work life (>16 h), good dry bond strength (2.94 MPa), and 28 h of boiling-dry-boiling cycled wet strength (1.29 MPa) that met the required values for structural use according to JIS K6806-2003 commercial standards. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43586. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, polyisocyanate (pMDI) was introduced into epoxy resin modified soybean meal-based bioadhesive to address the issue of low dry bond strength. Specifically, we investigated the effects of adding pMDI in terms of amount and storage time on dry bond strength, water resistance, and pot life of adhesive. Factors examined included shear strength, apparent viscosity, chemical reaction, crystallinity, and morphology of modified adhesives. Results indicated that the dry bond strength and water resistance of the resultant plywood was respectively improved 29.5% and 39.7% by adding 2% pMDI. In addition, the pot life of modified adhesive reached in 4 h. Results also shown that the cross-linking reactions between epoxy group and carbonyl as well as isocyano and amino increased the cross-linking density and formed a denser cross-linking network structure of cured adhesive. The composite cross-linked soybean meal-based adhesive is environmental-friendly and high-performance, which will promote the industrial application of the soy protein-based adhesives. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43362. [ABSTRACT FROM AUTHOR]

Soybean meal flour, polyethylene glycol (PEG), sodium hydroxide (NaOH), and a melamine-urea-formaldehyde (MUF) resin were used to formulate soybean meal/MUF resin adhesive. Effects of the adhesive components on the water resistance and formaldehyde emission were measured on three-ply plywood. The viscosity and solid content of the different adhesive formulations were measured. The functional groups of the cured adhesives were evaluated. The results showed that the wet shear strength of plywood bonded by soybean meal/NaOH adhesive increased by 33% to 0.61 MPa after adding NaOH into the adhesive formulation. Addition of PEG reduced the viscosity of the soybean meal/NaOH/PEG adhesive by 91% to 34,489 cP. By using the MUF resin, the solid content of the soybean meal/MUF resin adhesive was improved to 39.2%, the viscosity of the adhesive was further reduced by 37% to 21,727 cP, and the wet shear strength of plywood bonded by the adhesive was increased to 0.95 MPa, which met the interior plywood requirements (≥0.7 MPa). The formaldehyde emission of plywood bonded by the soybean meal/MUF resin adhesive was obtained at 0.28 mg/L, which met the strictest requirement of the China National Standard (≤0.5 mg/L). FTIR showed using the MUF resin formed more CH2 group in the cured adhesive. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

The article discusses two new types of synthesis methods in preparing phenol-urea-formaldehyde (PUF) co-condensed resins where effects on the structure, composition and shifts in chemical assignments of the resins were analyzed by liquid C nuclear magnetic resonance (C-NMR). The synthesis was done by reacting mixtures of methylolureas (MMU), phenol and formaldehyde. It describes how the synthesis resulted in solving the slow curing rate and high cost of using PF resins as wood adhesives.

Polysaccharide-Based Adhesives: A High-Performance Bio-Adhesive Using Hyperbranched Aminated Soybean Polysaccharide and Bio-Based Epoxide (Adv. Keywords: hot-pressing conditions; hyperbranched cross-linking structure; industrial applications; polysaccharide-based adhesive; soybean polysaccharide EN hot-pressing conditions hyperbranched cross-linking structure industrial applications polysaccharide-based adhesive soybean polysaccharide 1 1 1 05/09/20 20200507 NES 200507 A novel water-soluble soybean polysaccharide (WSSPS)-based adhesive is developed by hyperbranched polyamide grafting in conjunction with eco-friendly cross-linking. Hot-pressing conditions, hyperbranched cross-linking structure, industrial applications, polysaccharide-based adhesive, soybean polysaccharide. [Extracted from the article]

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]

Bio-based adhesives have low water resistance and they are less durable than synthetic adhesives, which limits their exterior applications. In this study, a bio adhesive was developed from soybean meal and larch tannin that was designed for exterior use. Phenol hydroxymethylated tannin oligomer (PHTO) was synthesized and then mixed with soybean meal flour in order to obtain a soybean meal-based adhesive (SPA). The results showed that the moisture absorption rate, residual rate, and solid content of SPA with 10 wt % PHTO (mass ratio with respect to the entire adhesive) were improved by 22.8%, 11.6%, and 6.8%, respectively, as compared with that of pure SPA. The wet shear strength of plywood with SPA with 10 wt % PHTO (boiling in 100 °C water for 3 h) was 1.04 MPa when compared with 0 MPa of pure SPA. This met the bond strength requirement of exterior-use plywood (GB/T 9846.3-2004). This improved adhesive performance was mainly due to the formation of a crosslinked structure between the PHTO and the protein and also PHTO self-crosslinking. The formaldehyde emission of the resulting plywood was the same as that of solid wood. The PHTO-modified SPA can potentially extend the applications of SPAs from interior to exterior plywood. [ABSTRACT FROM AUTHOR]

Despite the recent advances in protein-based adhesives, achieving strong adhesion and mold resistance in wet environment is challenging. Herein, a facile fabrication technology of preparing tough bio-adhesive by incorporating soybean meal and blood meal is presented. Inspired by the marine mussel byssi and brown algae, metal coordination was introduced into a loosely bound protein system to construct multiple chemical cross-linking networks. Mixed alkali-modified blood meal (mBM) was mixed with soybean meal, then 1,6-hexane dioldiglycidyl ether (HDE) and zinc ion were introduced to fabricate soybean meal and blood meal-based adhesives. The attained adhesives exhibited good thermal stability, water resistance (the wet shear strength is 1.1 MPa), and mold resistance, with appropriate solid content (34.3%) and relatively low moisture uptake (11.9%). These outstanding performances would be attributed to the reaction of 1,6-hexane dioldiglycidyl ether with protein to form a preliminary cross-linking network; subsequently, the coordination of zinc ions with amino or carboxyl strengthened and toughened the adhesive. Finally, the calcium ions gelled the adhesives, providing cohesion force and making the network structure more compact. This study realized the value-added utilization of protein co-products and developed a new eco-friendly bio-based adhesive. [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]

Chemical modification of soy protein, via crosslinking, is the preferred method for creating non-toxic, renewable, environmentally friendly wood adhesives. The denaturing process of protein is important for the adhesive performance improvement. In order to investigate the effect of different denaturing agents on the performance of soy protein-based adhesives before and after crosslinking modification. In this study, three different denaturing agents—urea (U), sodium dodecyl sulfate (SDS), and sodium hydrogen sulfite (SHS) and an epoxide crosslinking agent—Triglycidylamine (CA) were used to prepare soy protein-based adhesives. The results showed: (1) The denaturing agent unfolded protein molecules and exposed more hydrophobic groups to prevent water intrusion, which was mainly a contribution for the water resistance and performance improvement of soy protein-based adhesives. The wet shear strength was improved up to 91.3% (denaturing by urea). (2) After modifying by the crosslinking agent, the properties and performance improvement was due to the fact that the active groups on soybean protein molecules reacted with the crosslinking agent to form a crosslinking structure, and there is no obvious correlation with the hydrophobic groups of the protein. (3) The unfolded soybean protein molecules also expose hydrophilic groups, which facilitates the reaction between the crosslinking agent and protein to form a denser crosslinking structure to improve the performance of the adhesive. Particularly, after denaturing with SHS, the wet shear strength of the plywood bonded by the SPI-SHS-CA adhesive increased by 217.24%. [ABSTRACT FROM AUTHOR]

Soybean meal-based adhesives are attractive potential environmentally friendly replacements for formaldehyde-based adhesives. However, the low strength and poor water resistance of soybean meal-based adhesives limit their practical application. This study was conducted to develop a natural fiber-reinforced soybean meal-based adhesive with enhanced water resistance and bonding strength. Pulp fiber (PF), poplar wood fiber (WF), and bagasse fiber (BF) were added as fillers into the soybean meal-based adhesive to enhance its performance via hydrogen bonding between the PF and the soybean meal system. The enhanced adhesive exhibited a strong crosslinking structure characterized by multi-interfacial interactions wherein PF served as a bridging ligament and released residual stress into the crosslinking network. The crosslinked structure and improved interfacial interactions were confirmed by Fourier transform infrared (FTIR) spectrophotometry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) measurements. Plywood bonded with 4 wt % PF-containing soybean meal-based adhesive exhibited a wet shear strength (1.14 MPa) exceeding that of plywood bonded with the control group by 75.4% due to the stable crosslinking network having efficiently transformed stress and prevented the permeation of water molecules. [ABSTRACT FROM AUTHOR]

The objective of this study is to use wheat flour (WF) and hydroxymethyl melamine prepolymer (HMP) to develop a low cost, highly water-resistant, starch-based bio-adhesive for plywood fabrication. Three-layer plywood was fabricated using the resultant adhesive, and the wet shear strength of the plywood samples was measured under various conditions. After determining that water resistance was significantly improved with the addition of HMP, we evaluated the physical characteristics of the starch-based adhesive and functional groups and analyzed the thermal stability and fracture surface of the cured adhesive samples. Results showed that by adding 20 wt.% HMP into WF adhesive, the sedimentation volume in the resultant adhesive decreased by 11.3%, indicating that the increase of crosslinking in the structure of the adhesives increased the bond strength, and the wet shear strength of the resultant plywood in 63 °C water improved by 375% when compared with the WF adhesive. After increasing the addition of HMP to 40 wt.%, the wet shear strength of the resultant plywood in 100 °C water changed from 0 MPa to 0.71 MPa, which meets the exterior use plywood requirement. This water resistance and bond strength improvement resulted from (1) HMP reacting with functions in WF and forming a crosslinking structure to prevent moisture intrusion; and (2) HMP self-crosslinking and combining with crosslinked WF to form a microphase separation crosslinking structure, which improved both the crosslinking density and the toughness of the adhesive, and subsequently, the adhesive's bond performance. In addition, the microphase separation crosslinking structure had better thermostability and created a compact ductile fracture surface, which further improved the bond performance of the adhesive. Thus, using a prepolymer to form a microphase separation crosslinking structure within the adhesive improves the rigidity, toughness, and water resistance of the material in a practical and cost-effective manner. [ABSTRACT FROM AUTHOR]

In this study, sodium carbonate (Na2CO3) was used as a catalyst to prepare high‐ortho phenol‐formaldehyde (HOPF) resin, and ester and carbonate curing accelerators were used to increase its curing rate. The physicochemical properties of the prepared resins and the mechanism of curing acceleration were investigated. The results showed that, with the addition of Na2CO3, the ortho/para ratio of methylol groups increased from 7.257 to 27.800. The gel time of the cure‐accelerated HOPF resins decreased from 620 to 240 s as compared with PF resin. The bonding strength of plywood bonded with the cure‐accelerated HOPF resins were all above 0.70 MPa. The curing acceleration was caused by the carbonate ions rather than the metal ions, and a temporary incorporation mechanism apparently occurred for the ester accelerators. The prepared phenolic resin had fast curing rate, low curing temperature, high thermal stability, and favorable mechanical performance, which has potential for industry applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47229. [ABSTRACT FROM AUTHOR]

The purpose of this study was to improve the performance of soy protein isolate (SPI) adhesives using a polyurethane elastomer. Triglycidylamine (TGA), SPI, thermoplastic polyurethane elastomer (TPU), and γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH-560) were used to develop a novel SPI-based adhesive. The residual rate, functional groups, thermal stability, and fracture surface micrographs of the cured adhesives were characterized. Three-ply plywood was fabricated, and the dry/wet shear strength was determined. The experimental results suggested that introducing 2% TGA improved the residual rate of the SPI/TGA adhesive by 4.1% because of the chemical cross-linking reaction between epoxy groups and protein molecules. Incorporating 7% TPU into the SPI/TGA adhesive, the residual rate of the adhesive increased by 5.2% and the dry/wet shear strength of plywood bonded by SPI/TGA/TPU adhesive increased by 10.7%/67.7%, respectively, compared with that of SPI/TGA adhesive. When using KH-560 and TPU together, the residual rate of the adhesive improved by 0.9% compared with that of SPI/TGA/TPU adhesive. The dry and wet shear strength of the plywood bonded by the SPI/TGA/TPU/KG-560 adhesive further increased by 23.2% and 23.6% respectively when compared with that of SPI/TGA/TPU adhesive. TPU physically combined with the SPI/TGA adhesive to form a interpenetration network and KH-560 acted as a bridge to connect TPU and SPI/TGA to form a joined crosslinking network, which improved the thermo stability/toughness of the adhesive and created a uniform ductile fracture section of the adhesive. [ABSTRACT FROM AUTHOR]

To improve the performance of a soy flour (SF)-based adhesive, a low-cost hydroxymethyl melamine prepolymer (HMP) was synthesized and then used to modify the SF-based adhesive. The HMP was characterized, and the performance of the adhesive was evaluated, including its residual rate, functions, thermal stability, and fracture section. Plywood was fabricated to measure wet shear strength. The results indicated that the HMP preferentially reacted with polysaccharose in SF and formed a cross-linking network to improve the water resistance of the adhesive. This polysaccharose-based network also combined with the HMP self-polycondensation network and soy protein to form an interpenetrating network, which further improved the water resistance of the adhesive. With the addition of 9% HMP, the wet shear strength (63 °C) of the plywood was 1.21 MPa, which was 9.3 times that of the SF adhesive. With the HMP additive increased to 15%, the shear strength (100 °C) of the plywood was 0.79 MPa, which met the plywood requirement for exterior use (≥0.7 MPa) in accordance with Chinese National Standard (GB/T 9846.3-2004). With the addition of 9% and 15% HMP, the residual rates of the adhesive improved by 5.1% and 8.5%, respectively. The dense interpenetrating network structure improved the thermal stability of the resultant adhesive and created a compact fracture to prevent moisture intrusion, which further increased the water resistance of the adhesive. [ABSTRACT FROM AUTHOR]

Conventional tannin-based adhesives have limitations such as formaldehyde emission, inadequate strength and toughness, which restrict their practical applications. Herein, motivated by the natural mechanisms of 'phenol-amine' cross-linking and biomineralization, a strong, tough and formaldehyde-free tannic acid-based adhesive was prepared by using all-biomass feedstock. The adhesive was prepared by integrating tannic acid-Zn nanoparticles (TA-Zn NPs), hyperbranched polyamide-grafted dialdehyde chitosan (HPCS), and triglycidylamine (TGA), which formed the fundamental cross-linking network of the prepared adhesive through a Schiff base reaction. The dry and wet bonding strength of the adhesive achieved 1.91 MPa and 1.54 MPa, respectively. The presence of sacrificial bonds such as N...Zn complexation and hydrogen bonding in the adhesive significantly enhance its toughness with a debonding work of 0.595 J. Benefiting from the exceptional antimicrobial properties of TA, chitosan, and Zn2+, the prepared adhesive demonstrated excellent mechanical properties even after being stored in a humid environment for 2 days, with wet and dry bond strength of 1.42 MPa and 1.10 MPa, respectively. Moreover, this adhesive exhibited remarkable resistance to mildew for a duration of 30 days and emitted lower volatile organic compounds compared to other synthetic and biomass adhesives. This innovative bionic strategy holds great potential in enhancing the toughness and functionality of adhesives and composites. [Display omitted] • Preparation of a tannic acid-based adhesive based on bio-inspired 'phenol-amine' cross-linking and mineral reinforcement. • Dense cross-linking network constructed between TA-Zn NPs and HPCS by Schiff base reaction. • The adhesive is characterized by excellent water resistance, mildew resistance, high toughness and strength. • The formaldehyde-free tannic acid-based adhesive has low VOC emissions. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) is a promising substitute for formaldehyde-based adhesives for wood bonding due to its low carbon footprint, formaldehyde-free and flame-retarding natures. However, the poor water resistance and weak interfacial compatibility with wood limits their practical applications. Herein, inspired by mussels, we reported an eco-friendly and versatile strategy to develop MOC-based wood adhesive with desirable water resistance, high adhesive strength and strong bonding interface. Amino-functionalized sepiolite (KSep) was selected as the nano fillers and inorganic fibers to enhance the structural compactness and resist cracks propagation of MOC. Gallic acid (GA) was employed as the crosslinking agent to induce multiple reinforcement network based on phenol-amine crosslinking and ion chelation in MOC system. The synergy of inorganic fiber enhancement and multiple reinforcement network not only strengthens the cohesive properties, but also enhances the physical anchorage and chemical reactions at the bonding interface, thus endowing MOC with outstanding adhesion ability to wood. The MOC/KSep/GA composite exhibits dry and wet shear strength of 2.63 MPa and 1.75 MPa, being respectively 14.85 % and 42.28 % higher than those values of the pristine MOC. This strategy provides a new route for the development of high-performance cementitious materials and adhesives. [Display omitted] • An eco-friendly, flame-retardant and non-formaldehyde wood adhesive was proposed. • A mussels-inspired magnesium oxychloride cement was prepared as wood adhesive. • The amino-functionalized sepiolite was used as inorganic fiber reinforcer. • A multiple reinforcement network based on phenol-amine crosslinking was formed. • Adhesive showed good adhesion strength and strong bonding interface. [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]

Soybean meal (SM)-based adhesive can solve the issues of formaldehyde emission and over-reliance of aldehyde-based resins but suffers from poor water resistance, weak adhesion strength, and high brittleness. Herein, a high-performance adhesive inspired by lobster cuticular sclerotization was developed using catechol-rich condensed tannin-functionalized boron nitride nanosheets (CT@BNNSs), amino-containing chitosan (CS), and SM (CT@BNNSs/CS/SM). The oxidative crosslinking between the catechol and amino, initiated by oxygen at high temperatures, formed a strengthened and water-resistant interior network. These strong intermolecular interactions induced by phenol–amine synergy accompanied by the reinforcement of uniformly dispersed BNNSs improved the load transfer and energy dissipation capacity, endowing the adhesive with great cohesion strength. Given these synergistic effects, the biomimetic CT@BNNSs/CS/SM adhesive caused noticeable improvements in water tolerance, mechanical strength, and toughness over the neat SM adhesive, e.g., enhanced wet shear strength (1.46 vs. 0.66 MPa, respectively), boiling water shear strength (0.92 vs. 0.43 MPa, respectively), and debonding work (0.368 vs. 0.113 J, respectively). Thus, this study provided a green and low-cost bionic strategy for the preparation of high-performance biomass adhesives. • An advanced adhesive inspired by lobster cuticular sclerotization is reported. • Oxygen at high temperatures initiated the crosslinking between CT@BNNSs and CS/SM. • Such phenol–amine synergy endowed the adhesive with great cohesion strength. • Strong intermolecular interactions and BNNSs reinforcement improved the adhesive's toughness. [ABSTRACT FROM AUTHOR]

Exploring the reusability of wood-based panels is imperative in the wood industry for sustainable development and carbon balance. Non-reusable adhesives make wood-based panel recycling difficult. In this study, inspired by the adhesion and de-adhesion behavior of snail slime, we built dynamic covalent/hydrogen hybrid networks into adhesive system for achieving both high bonding performance and reusability. Specifically, the softwood lignin was purified and pretreated by ultrasonication to form a catechol structure (UAL) and then combined with soybean protein to develop a 100 % bio-based wood adhesive. The catechol structure of UAL formed dynamic covalent bonds (C N) with the amino groups of the protein to improve the water resistance and formed multiple hydrogen bonds as a sacrificial network to improve the toughness of the adhesive. Thus, the wet shear strength of plywood bonded by the resultant adhesive improved by 101.4 % to 1.37 MPa. The adhesive also exhibited flame retardancy (LOI = 37.7 %), mildew resistance (60 h), and antibacterial performance (inhibition zone = 8 mm). Notably, owing to the rearrangement of dynamic covalent/hydrogen hybrid networks and the thermoplastic property of UAL, the resultant adhesive was reusable (3 cycles) and degradable (2 months), which provides a potential method for the reuse of wood-based panels. • Ultrasonic treats lignin to form catechol structure (UAL) and combine with SPI to obtain adhesive. • Dynamic covalent/hydrogen hybrid networks were constructed in adhesive system. • The SPI/UAL adhesive has good coating, prepressing intension, and bonding performance. • The SPI/UAL adhesive exhibited good antibacterial, flame-retardant, and mildew resistance. • The resultant wood-based panel was reusable and biodegradable. [ABSTRACT FROM AUTHOR]

Human health and environmental protection demand wood-based panel industry for innovative soy-based adhesives with high production efficiency, straightforward synthesis processes, non-toxicity, and high bonding performance. A simple and efficient microwave pretreatment process and low addition of bio-derived crosslinking agent was used in this study to prepare a non-toxic and high-bonding performance soybean protein-based adhesive. After 4 min of microwave pretreatment time, the complex quaternary structure of soybean protein molecule unfolds, the soybean protein disperses evenly and stably, and active groups of soybean protein molecules are exposed. After adding 3.85% crosslinking agent, the moisture absorption rate of the soybean protein-based adhesive decreases by 41.77%, the residual rate increases by 3.68%, and the wet shear strength of the resultant plywood increases to 1.12 MPa, which satisfies requirement of interior use plywood. Compared with previously reported soy-based adhesives, this adhesive is dependent on fewer chemical reagents, but has good bonding performance. The 204.41% of relative cell viability indicates the resultant adhesive was non-toxic. The proposed high-efficiency, high-performance, non-toxic biomass adhesive has great prospects for the industrial application. • A non-toxic and high-performance soybean protein-based adhesive was developed. • Microwave treatment (MT) breaks soybean protein molecule and exposes active groups. • After 4 mins MT, the wet shear strength of resultant plywood increased by 160.47%. • MT reduces the dosage of chemical reagent for soybean protein-based adhesive. • Relative cell viability of modified soybean protein-based adhesive reaches 204.41%. [ABSTRACT FROM AUTHOR]

Simultaneously improving the strength and toughness of soybean protein adhesives is a huge challenge. The multi-scale enhancement strategy proposed in this study introduced MXene nanosheets and oxidized sodium alginate (OSA) to improve mechanical properties. The polymer network framework with high crosslink density dissipates energy by restricting the slip of the SPI molecular chains, and MXene act as stress dispersers in the polymer network in order to solve the challenge of the strength-toughness balance. The prepared biomass-based adhesives with high adhesion (dry/wet shear strength 1.93 MPa/1.33 MPa), high toughness (adhesion work 810.9 mJ), high thermal stability, high residual rate (92.53 %), low moisture absorption rate (11.18 %), and long storage time (12 d). Additionally, the application of SOM-5 adhesive reduces the burden of petrochemical resource extraction for adhesive production and contributes to the sustainable development of the wood industry. Most importantly, it presents an adoptable strategy for resolving the tension between strength and toughness of composite materials. [Display omitted] • The adhesive shows excellent wet bond performance for wood, 1.33 MPa. • The toughness of prepared adhesive increased by 377 % compared to unmodified one. • Multiple interactions greatly improve the properties of the adhesive. • Liquid adhesive storage time is effectively extended. [ABSTRACT FROM AUTHOR]

The development of clean adhesives with agricultural renewable resources for wood-based panels that maintain high bond performance, easy-coating, and remarkable prepressing performance while not releasing hazardous substances presents a significant challenge. In this study, inspired by the special stolon structure of ascidian larvae's adhesion, a bottlebrush polymer of epichlorohydrin grafted aminated dialdehyde starch named AE, which was incorporating an epoxy terminal group was constructed. The prepared AE was introduced into a soy flour (SF) adhesive system to obtain a high-performance SF/AE adhesive. The rich branched chain structure and crosslinking effect of the terminal epoxy group in the AE polymer induced dual-crosslinking structure network, reinforcing the adhesive cohesion and enhancing the interface bonding between wood and adhesive. Compared to SF adhesive, the modified SF/AE adhesive exhibited an integrated improvement in coating ability, prepressing performance, and bonding performance, presenting a uniform distribution of the roller coating. The prepressing intension and dry/wet bonding strengths the of the resultant SF/EA-8 % adhesive increased from 0.57 MPa/1.05 MPa/0.06 MPa to 1.16 MPa/1.82 MPa/1.02 MPa, respectively. Furthermore, the antimildew properties of the SF/AE adhesive were improved from 24 h to 48 h under natural conditions. Notably, this modified SF/AE adhesive has lower emission on harmful gases compared with other aldehyde adhesives. This stolon-bionic bottlebrush polymer has the potential of molecular design for application in green bio-adhesive and other composite materials, and hydrogels to enable strong comprehensive performance. [Display omitted] • An ascidian larvae-inspired bottlebrush polymer with epoxy terminal groups was constructed. • The dry/wet shear strength of bonded plywood increased by 73.3 %/1600 %, respectively. • After modified by AE, the prepressing intension of the bonded plywood increased by 103.5 %. • The AE polymer endowed the resultant adhesive with excellent coating performance. • The adhesive has low harmful gas emission and extended period for the mildew resistance. [ABSTRACT FROM AUTHOR]

Soybean protein adhesive, as an aldehyde-free biomass adhesive, has gained significant attention as an environmentally friendly material in recent years. It not only aligns with the objectives of the double carbon strategy but also contributes to the environmental protection strategy of reducing carbon emissions. And the functional modification of soybean protein adhesive and its wood composite hold great importance in expanding its application domains and meeting specialized requirements. This research focused on developing a robust, antistatic adhesive derived from soy protein as an alternative to formaldehyde-based resins, which represents a critical path in the advancement of wood-based composites that are free from formaldehyde and possess functional properties. However, ensuring the bonding strength of soy protein adhesive while developing antistatic adhesives and their wood-based composite materials is of great research value and challenge. Inspired by the organic-inorganic hybrid structure, this study aimed to prepare a strong and durable soy protein adhesive with excellent mechanical strength and multifunctionality by using a self-synthesized crosslinking agent called AP and the loaded two-dimensional MXene, which was stabilized in a dispersion of nanocellulose (CNC). The dry and wet shear strength of the resulting adhesive increased by 103.8 % and 113.8 % to 2.21 MPa and 1.24 MPa, indicating the stable crosslinking structure formed in adhesive system by the covalent bond between self-synthesized crosslinking agent AP and the carboxyl groups on proteins, as well as the hydrogen bond interactions between C-M and the proteins. Furthermore, the adhesive exhibited significant antistatic and self-extinguishing properties, with the particleboard modified by adhesive SPI/C-M/AP having a resistivity of 9.212 × 1011 Ω cm. The resistivity decreased with increasing MXene content, providing potential applications for places such as school computer rooms and factory electronic equipment rooms. This breakthrough in multifunctional biomass-based adhesives and composite materials enriches the preparation of new types of biomaterials with antistatic and flame retardant properties. • A new crosslinking agent AP was synthesized by click chemistry. • The mixing of biomass nano-cellulose (CNC) and MXene solves the problem of poor dispersibility. • The resultant plywood has good bonding performance with a 113.8 % increase in wet shear strength. • The resulted adhesive has an elevated antistatic property and retardancy. [ABSTRACT FROM AUTHOR]

Given the severe protein denaturation and self-aggregation during the high-temperature desolubilization, denatured soy meal (DSM) is limited by its low reactivity, high viscosity, and poor water solubility. Preparing low-cost and high-performance adhesives with DSM as the key feedstock is still challenging. Herein, this study reveals a double-enzyme co-activation method targeting DSM with the glycosidic bonds in protein-carbohydrate complexes and partial amide bonds in protein, increasing the protein dispersion index from 10.2 % to 75.1 % improves the reactivity of DSM. The green crosslinker transglutaminase (TGase) constructs a robust adhesive isopeptide bond network with high water-resistant bonding strength comparable to chemical crosslinkers. The adhesive has demonstrated high dry/wet shear strength (2.56 and 0.93 MPa) for plywood. After molecular recombination by enzyme strategy, the adhesive had the proper viscosity, high reactivity, and strong water resistance. This research showcases a novel perspective on developing a DSM-based adhesive and blazes new avenues for changes in protein structural function and adhesive performance. [Display omitted] • An all-biomass adhesive was developed by enzyme activation and enzyme crosslinking. • A double-enzyme co-activation method targeted protein-carbohydrate complexes in DSM. • TGase crosslinker replaced the traditional chemical crosslinkers. • The adhesives achieved excellent bonding strength for wood and metal. • Low-cost raw materials and simple steps achieved cost effectiveness of adhesives. [ABSTRACT FROM AUTHOR]

Developing low-cost renewable bio-based adhesives with excellent properties remains a challenge. Soybean meal (SM) adhesives have gained widespread attention for being green. However, it still has the problems of poor water resistance, low toughness, and easy to mildew. Herein, a waterborne polyurethane (TWPU) with carboxyl side chains was synthesized from tartaric acid (TA). It was used as chelating ligands to form the metal chelating to synergistically modify (SM) adhesives. This overall improved the adhesives bonding strength, toughness and water resistance. The coordination interactions between the polyurethane molecules and the protein molecules of SM were formed by multi-crosslinking via metal chelating, covalent bonding, and hydrogen bonding to enhance the adhesive's toughness, bonding strength and water resistance. As a result, the wet bond strength and toughness of the modified SM adhesives were 166.7 % and 275.3 % higher than blank sample, respectively, reaching 1.29 MPa and 0.61 J. Considering of the used raw materials and synthesis method in our process are simple and widely available, this study provides an eco-friendly and effective method for green, low-cost, and high-performance wood-based composite adhesives. [Display omitted] [ABSTRACT FROM AUTHOR]

Faced with many challenges such as energy crisis and environmental protection issues, biomass soy protein-based adhesives for replacing aldehyde-based adhesives have gradually become one of the research hotspots for wood industry upgrading. However, soy protein-based adhesives still have many shortcomings. Low bonding strength, poor water resistance and high viscosity restrict their widespread industrial application. In this work, a modified soy protein isolate (SPI) based adhesive with strong water-resistant bonding strength and low viscosity was prepared. Oxidized sodium alginate (OSA) and calcium ions were employed in SPI adhesive system. Results showed that cross-linking between OSA, calcium ions and SPI occurred successfully. The mechanical properties of SPI were significantly improved. The dry and wet bond strengths were 2.05 MPa and 0.97 MPa, respectively, in 65.3 % and 49.2 % increments for comparison. The adhesive samples also showed a reduction in viscosity and an increase in thermal stability. It can be developed as a facile method for preparing bio-adhesives. [Display omitted] • Oxidized sodium alginate and Ca2+ were employed to modify SPI adhesive. • The adhesive shows high bond strength, good water resistance and viscosity. • The wet shear strength reaches 0.97 MPa. • Schiff bases reaction improves the cross-linking density of adhesive. • Hydrogen bonding network provides additional cohesion. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement (MOC) has the advantages of no formaldehyde emission, fire resistant and curing at ambient temperature, which make it to be a promising wood adhesive for wood industry. However, the poor permeability of MOC on wood surface and the inherent brittleness of MOC limit its practical application. To solve these problems, citric acid (CA) and polyvinyl alcohol (PVA) fibers were demonstrated to synergistically promote the bulk penetration of MOC in wood surface and enhance the toughness of MOC, which resulted from the pH regulating effect of CA and the toughening effect of PVA fibers and CA. Based on this synergistic method, the compressive strength and toughness of the obtained MOC/CA/PVA adhesive were higher than that of pure MOC adhesive. Moreover, the wet adhesive strength of the MOC/CA/PVA adhesive reached 1.81 MPa, which increased by 33% than pure MOC adhesive. In addition, the wood products bonded by the modified adhesives possessed excellent flexural performance and fire resistance. This modification strategy makes the modified MOC-based wood adhesive have great application potential in wood and building industry. • Magnesium oxychloride cement was modified by citric acid and PVA fibers. • Citric acid and PVA fibers improved the water resistance and strength. • The enhanced mechanism was the chelation of CA and the filling effect. • The modified magnesium oxychloride cement has good adhesive strength. • The wood product bonded by modified adhesives has better flexural strength. [ABSTRACT FROM AUTHOR]

The exploitation of the environment-friendly and renewable biomass adhesive is a promising alternative compared to petroleum-based ones in the wood industry. In this study, soybean flour (SF) was chosen as a renewable starting material for the preparation of the biomass adhesive. The soy protein structure was unfolded by the calcium hydroxide and multiple reactive groups (-COOH, –NH 2 , –OH, –SH) of the protein chain were exposed. Inspired by the marine mussel protein, tannic acid (TA) with many poly-catechol/pyrogallol groups was capable of interacting with protein molecules under the alkaline conditions and the strong metal coordination between Ca2+ and TA enable to reinforce the network structure of adhesive. Furthermore, the incorporation of 1,6-Hexanediol diglycidyl ether (HDE) into the pristine protein adhesive had reacted with protein molecules via chemical covalent bonds to form the stable and toughness cross-linking network. The as-obtained adhesive showed improved bonding strength and comparable water resistance. Notably, the enhanced adhesive showed an outstanding wet shear strength of 1.12 MPa, meeting China's interior furnishing requirements (≥0.7 MPa). Additionally, in contrast to unmodified adhesive, the mildew resistance of the cooperation modified adhesive was improved and the storage life extended. This research provides a novel and green way to develop a formaldehyde-free adhesive for the wood industry. [Display omitted] • A renewable resource of soybean flour was used to prepare an eco-friendly adhesive. • The multiple interactions promoted to form a denser cross-linked network. • The bonding strength and water-resistance of adhesive were significantly improved. • The mildew resistance of protein adhesive was improved by the introduction of HDE. [ABSTRACT FROM AUTHOR]

As a renewable biomass resource, soy protein adhesives are a potential alternative to petroleum-based ones. However, synthesizing soy protein adhesives with excellent performance via a low-cost and facile strategy for practical application in the wood industry remains challenging. Herein, an innovative approach for fabricating a strong, tough, low-cost soy protein adhesive via dual cross-linked tailoring-making technology was proposed to impart multiple excellent performances. Specifically, the new strategy involved using calcium lignosulfonate (CLS), a residue from the pulping industry, as an anionic surfactant to untwist the spherical structure of soy protein, stretch the protein chains, and knit a reversible dynamic network structure with the protein chains and soybean polysaccharide molecules by multiple non-covalent interactions, and synergize with the robust cross-linked network of 1,6-hexanediol diglycidyl ether (HDE) to tailor the adhesive structure system. Notably, this design reflects the vital role of remolding the protein structural and soybean polysaccharide molecules network in optimizing the adhesive properties, including excellent bonding strength, anti-mildew, and flame retardancy performances. Therefore, this facile strategy can be explored to develop green and renewable protein adhesives for industrial wood applications. [Display omitted] • Eco-friendly adhesive was prepared by a dual cross-linked tailoring-making strategy. • Non-covalent and covalent linkages render adhesive robust network structure. • Multiple functions of adhesive were achieved successfully in a low-cost method. • This strategy could prepare adhesive using heat-temperature soybean meals. [ABSTRACT FROM AUTHOR]

Formaldehyde adhesive is the primary source of indoor formaldehyde pollution, posing a serious threat to human health. Soybean meal (SM), as an abundant biomacromolecule and co-product of soybean oil industry, emerges as a promising alternative to formaldehyde adhesive. However, the SM adhesive exhibits inferior water resistance and unsatisfactory bonding strength. In this study, a novel core–sheath structure with an inexpensive pulp cellulose core and a hyperbranched polymer sheath is synthesized and introduced into SM to develop a robust bio-based adhesive. Specifically, aldehyde-functionalized pulp cellulose is grafted with hyperbranched polyamide, which is terminated via epoxy groups, to synthesize a core–sheath hybrid (APC@HBPA-EP). The core–sheath APC@HBPA-EP serves as both a crosslinker and an enhancer. The results show that the wet shear strength of the modified SM adhesive exhibits a remarkable 520 % increase to 0.93 MPa, and its dry shear strength reaches 2.10 MPa, meeting the established indoor use standards. The Young's modulus of the modified SM adhesive shows a significant 282 % increase to 19.27 GPa. Additionally, the modified SM adhesive exhibited superior impact toughness (7.48 KJ/m2), which increased by 24 times compared with pure SM adhesive. This study provides a versatile strategy for developing robust protein adhesives, hydrogel patch, and composite coatings. [Display omitted] [ABSTRACT FROM AUTHOR]

Poor water resistance and curing layer brittleness are significant challenges of greener soybean meal (SM) adhesive promotion and application. In this study an elastic network was built to crosslink the SM adhesive and improve the cured layer toughness of the resultant adhesive. Long-chain organo-sepiolite (OSEP) was first prepared by compound modification using KH-560 and KH-602 silane coupling agents. Triglycidylamine (TGA), a greener crosslinking agent with a large number of effective epoxy functional groups, was then synthesized. SM-based adhesives were fabricated using SM, OSEP and TGA. Results indicated that an elastic network was fabricated by the cross-linked reaction of SM, OSEP, and TGA. The elastic network effectively improved the toughness of the resultant adhesive. The wet shear strength of the plywood (PlyW) bonded by SM with 1% OSEP (SM/TGA/OSEP-1 adhesive) increased by 60% to 1.25 MPa relative to that of the SM/TGA adhesive. This study provided a greener, simple and cheap method improving the toughness and wet shear strength of SM-based adhesive, which contributes to the industrialized application of the product. Image 1 • A greener soybean-meal based bioadhesive was prepared. • Long-chain OSEP was first prepared by compound modification using KH-560 and KH-602 silane coupling agents. • A greener crosslinking agent TGA with a large number of effective epoxy functional was prepared. • A flexible network was fabricated by the reaction of soy protein molecules, OSEP, and TGA. • The wet shear strength and toughness of the soybean-meal based bioadhesive was improved. [ABSTRACT FROM AUTHOR]

Petroleum-derived formaldehyde resin adhesives are serious hazards to human health and depend on limited resources. Abundant, cheap and renewable biomass materials are expected to replace them. However, the contradictory mechanisms of high mechanical strength and fracture toughness affect the use of bioadhesives. Herein, a biomimetic soybean meal (SM) adhesive inspired by the structure of insect cuticles and shell pearl layer was proposed. Specifically, chitosan (CS@DA) modified 3,4-dihydroxybenzoic acid (DA, rich in catechol moiety) was anchored on molybdenum disulfide nanosheets (MoS 2) to construct a biomimetic structure with copper hydroxide and SM substrate (SM-MoS 2 /CS@DA-Cu). Schiff base, ionic, and hydrogen bonding strengthened the cohesion of the adhesive. The ordered alternating stacking "brick-mortar" structure stimulated the lamellar sliding and crack deflection of MoS 2 , synergistically reinforcing the toughness. Compared to SM adhesive (0.57 MPa and 0.148 J), the wet shear strength and adhesion work of the SM-MoS 2 /CS@DA-Cu were 1.68 MPa and 0.867 J, with 194.7 % and 485.8 % increases, respectively. The multiple antimicrobial effects of CS@DA, Schiff base, and Cu2+ increased the applicability period of the adhesive to 40 days. The adhesive also displayed favorable water resistance and flame retardancy. Therefore, this peculiar and efficient biomimetic structural design inspired the development of multi-functional composites. [ABSTRACT FROM AUTHOR]

Preparation of soybean meal adhesives offering good water resistance, prepressing adhesion as well as antimildew properties through a green and simple strategy remains challenging. In the present study, a self-assembled nanostructure-based filling enhancement strategy was proposed. Tannic acid (TA) is grafted onto the chitosan framework through free radical grafting, followed by ultrasound induced self-assembly into nanospheres. Chitosan based nanospheres (CS@TA) and ferric chloride (FeCl 3) complexing with nanospheres are combined to modify soybean meal (SM) based wood adhesives synergistically. CS@TA enables interaction with protein chains through hydrogen bonding and Schiff base reactions, which in combination with its nanostructure allows for a more homogeneous dispersion in the SM system. At the same time the Fe (III) ions chelate with the catechol, forming ionic bonds and obtaining a denser structure. The results showed that the dry and wet shear strength (DWSS) of SM/1,2,3-propanetriol triglycidyl ether (GTE) /5%CS@TA/Fe increased by 79% and 693% to 2.28 MPa and 1.27 MPa. At the same time, the residual rate (RD) increased by 9.3–72.5% and prepressing adhesion now reaches 0.71 MPa compared with SM adhesives. And CS@TA nanospheres as well as Fe (III) ions act on the cell membrane of bacteria to provide stronger antibacterial effect, the anti- mildew time has been extended from the initial 2 d to more than 15 d. The construction of multi-network reinforcement strategies through self-assembled nanostructures improves the application potential of SM adhesives and provides ideas for the reinforcement of other engineering materials. [Display omitted] • Self-assembled nanospheres chitosan-based prepared using free radical grafting combined with ultrasonic induction. • Preparation of environmentally friendly adhesives from processing residues soybean meal and biomass materials. • The adhesive has high bond strength, good water resistance and prepressing adhesion. • The anti-mildew of soy protein adhesive was enhanced and extends the storage life. [ABSTRACT FROM AUTHOR]

• A stable EDTA-TA synergistic system was constructed to enhance MOC composites. • EDTA can effectively aggregate 5-phase crystals. • The effect of the synergistic system on the crystallisation of hydration products was investigated. • The modified MOC composites have good water resistance and compressive strength. • MOC composites have excellent flame retardant properties and can be used in the wood industry. The high CO 2 emissions and instability of silicate cement binders during production and use have encouraged the development of low-carbon materials. In this study, an environmentally friendly and flame-retardant building material was produced from magnesium oxychloride cement (MOC) and wood. In practice, the considerable microcracking that forms during the hardening process makes MOC materials very sensitive to water, which limits their further use. Inspired by the predation of crabs, a simple and effective method was proposed to obtain better water resistance and mechanical strength of MOC composite by co-modifying with ethylenediaminetetraacetic acid (EDTA) or disodium ethylenediaminetetraacetic acid (EDTA-Na) in conjunction with tartaric acid. The four –COOH of EDTA and EDTA-Na coordinated well with the 5-phase structure and tightly aggregated the 5-phase crystals, effectively reducing the formation of microcracks. The synergistic effect between EDTA/EDTA-Na and tartaric acid prevented the disruption of 5-phase crystal structures by water molecules, thus improving the water resistance of the MOC composite. The softening coefficients of the MOC composite modified by EDTA and EDTA-Na in cooperation with tartaric acid after soaking for seven days were 0.97 and 0.98, respectively, which is significantly higher than that of the MOC composite modified by tartaric acid alone (0.54). At the same time, the co-modified MOC composite can be utilised as an inorganic adhesive for plywood, and the wet strength of plywood modified with EDTA in cooperation with tartaric acid being 25% higher than that of the unmodified MOC composite. In addition, the resulting composites showed great potential for application in low-carbon building materials, which can help alleviate the environmental impact of construction industries. [ABSTRACT FROM AUTHOR]