Core-Shell Nanohybrid Elastomer Based on Co-Deposition Strategy to Improve Performance of Soy Protein Adhesive

DNA Organogels Gaining Multifunctions from the Contribution of Molecular Design on Cross-Linker

DNA gels have been receiving considerable attention for their good therapeutic and biomedical potential. However, it remains a great challenge for DNA gels to achieve a good combination of high mechanical performance and stimuli responsiveness. In this work, a molecular designing strategy is developed for fabricating a high-performance DNA gel using long sequenced DNA and a tetraphenylethene-containing surfactant. Comprising different structural motifs, the designed surfactant could serve as a contact point for creating a strong and flexible cross-linking network between DNA molecules through noncovalent interactions. The resulting DNA gel gains an impressive adhesion of 7.58 ± 0.49 MPa, which addresses the top level of high-performance DNA gels. Such a DNA gel shows generous adhesion with various materials and good temperature tolerance. The good biosafety and wound-healing promoting effect would also open its potential use in biological and biomedical areas. Additionally, this DNA gel possesses fluorescence for easy detection, achieving a combination of high mechanical performance and stimuli responsiveness. This work presents a design strategy for gaining robust DNA materials with a combination of different physicochemical properties together.

Mantis shrimp-inspired functionalized plant fibers to fabricate a soy protein adhesive with high strength and mildew resistance

Soy protein-based adhesives present a promising alternative to petroleum-based adhesives in the wood industry. Nevertheless, their limitations, including insufficient water resistance, low bonding strength, and inadequate mold resistance, constrain their industrial applications. Plant fiber-reinforced composites find extensive applications across various sectors, including furniture, automotive, and aerospace. However, the smooth surfaces of the fibers adversely impact the reinforcement effect. Inspired by the multilayered microscale structure of peacock mantis shrimp chelipeds, this work presents an eco-friendly method to develop hierarchical functionalized kenaf fibers (KF) for reinforcing soybean meal (SM) adhesive. Specifically, ZnO was deposited onto the KF surface to impart micro-nano roughness, thereby enhancing their mechanical interlocking effect with the SM matrix. Bio-based lipoic acid (LA) and limonene (LIM) were employed to create a highly reactive layer on the fiber surface, facilitating the formation of multiple chemical crosslinking structures with the SM matrix. The synergistic mechanical and chemical effects between KF and SM endowed adhesive with improved performance. The wet shear strength of the three-layer plywood prepared with the synthetic adhesive was remarkably increased by 450 % to 1.21 MPa. Additionally, the combined anti-mold effects of ZnO, LA, LIM, and triglyceride amine (TGA) extend the adhesive's storage time to 7 days. This sustainable and eco-friendly design of multilayered bionically functionalized KF offers an efficient approach for the high-value utilization of agroforestry residues, presenting broad application prospects in SM-based adhesives.

Develop a novel and multifunctional soy protein adhesive constructed by rosin acid emulsion and TiO2 organic-inorganic hybrid structure

Soy protein adhesives (SPI) exhibit broad prospects in substituting aldehyde-based resin due to the economic and environmental-friendly characteristics, but still face a challenge because of the dissatisfied bonding strength and terrible water resistance. Herein, prompted by organic-inorganic hierarchy, a multifunctional and novel soy protein adhesive (SPI-RAE-TiO2) consisting of rosin acid emulsion (RAE) and TiO2 nanoparticles (TiO2) were proposed. In comparison with original SPI, the dry and wet shear strengths of modified adhesive reached 2.01 and 1.21 MPa, respectively, which were increased by 130 % and 200 %. Furthermore, SPI-6RAE-0.5TiO2 was selected as the best proportion via the method of response surface methodology (RSM). What's more, SPI-6RAE-0.5TiO2 adhesive demonstrated prominent coating performance in both dry and wet surface conditions. Meanwhile, SPI-6RAE-0.5TiO2 adhesive possessed excellent mildew resistance and antibacterial ability with Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), reflecting the antibacterial rates 97.71 % and 98.16 %, respectively. In addition, SPI-6RAE-0.5TiO2 adhesive also exhibited the outstanding green features such as the reduction of formaldehyde pollution and greenhouse effect through Life Cycle Assessment (LCA). Thus, this work provided a novel and functional approach to design multifunctional, superior-property and low-carbon footprint soy protein adhesive.

Aqueous Cellulose Solution Adhesive

In the context of sustainable development, research on a biomass-based adhesive without chemical modification as a substitute for petroleum-based adhesive is now crucial. It turns out to be challenging to guarantee a simple and sustainable method to produce high-quality adhesives and subsequently manufacture multifunctional composites. Herein, the inherent properties of cellulose were exploited to generate an adhesive based on a cellulose aqueous solution. The adhesion is simple to prepare structurally and functionally complex materials in a single process. Cellulose-based daily necessities including straws, bags, and cups were prepared by adhering cellulose films, and smart devices like actuators and supercapacitors assembled by adhering hydrogels were also demonstrated. In addition, the composite boards bonded with natural biomass wastes, such as wood chips, displayed significantly stronger mechanical properties than the natural wood or commercial composite boards. Cellulose aqueous adhesives provide a straightforward, feasible, renewable, and inventive bonding technique for material shaping and the creation of multipurpose devices.

Pulp cellulose-based core-sheath structure based on hyperbranched grafting strategy for development of reinforced soybean adhesive

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.

A multiple cross-linking strategy to develop an environment-friendly and water resistance wheat gluten protein wood adhesive

Wheat gluten (WG) shows great promise to synthesize environment-friendly wood adhesives. However, their weak bonding strength and poor water resistance have limited its application in the commercial wood-based panel industry. In this study, a novel WG-based adhesive was developed by constructing a multiple cross-linking network generated by covalent and non-covalent bonds. The potential mechanism was revealed by FT-IR analysis. Furthermore, their surface morphology, thermal stability, viscosity, and residual rate of adhesives with different compositions were systematically characterized and compared. The results showed that the hydrogen bonding, reactions between amine groups and tannin, and ring opening reaction of epoxy, synergistically contributed to generate a highly crosslinked network. The wet/boil water strength of the plywood prepared from WG/tannin/ethylene imine polymer (PEI)-glycerol triglycidyl ether (GTE) adhesive with the addition of 15 % GTE could reach 1.21 MPa and 1.20 MPa, respectively, and a mildew resistance ability was observed. This study provides a facile strategy to fabricate high-performance plant protein-based adhesives with desirable water resistance for practical application.

Sucrose-tannin-nanosilica hybrid bio-adhesive based on dual dynamic Schiff base and disulfide bonds with enhanced toughness and cohesion

Herein, a high-performance sucrose-tannin bio-based adhesive is developed based on consisting of oxidized sucrose (OS), tannin acid (TA), SiO2 nanoparticles and 2,2'-disulfanediylbis (ethan-1-amine) (DBA) by a facile chemical cross-linking strategy. The OS-TA and OS-TA@SiO2 bio-based adhesives are characterized by XPS, FTIR, and 13C NMR, while the bonding performance is also investigated using shear strength test. Results show that the optimal formulation of OS-TA bio-based adhesive is a 2:1:1 mass ratio for OS: TA: DBA. When the mass fraction of SiO2 is 15 % and the solid content of main components is 50 %, the OS-TA@SiO2 bio-based adhesive has excellent bonding strength. Relative to OS-TA, the wet bonding strength of the OS-TA@SiO2 enhanced from 1.16 MPa to 1.85 MPa, while the dry bonding strength improved from 1.90 MPa to 2.50 MPa. The wood failure rate of the plywood fabricated by using the OS-TA@SiO2 bio-based adhesive reaches 80 %. Therefore, relying on the high flexibility of dynamic disulfide bonds, adding SiO2 nanoparticles into the adhesive system can facilitate greatly the mechanical interlocking effect and make the chemical cross-linking network more compact through the synergistic chemical interactions. This work provides new insights into producing green and renewable bio-based wood adhesives using sucrose and tannin.

Valorization of sewage sludge for facile and green wood bio-adhesives production

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.

Effective and eco-friendly safe self-antimildew strategy to simultaneously improve the water resistance and bonding strength of starch-based adhesive

Starch adhesive, as a sustainable biomass-based adhesive, could be used to solve environmental problems from petroleum-derived adhesive. But its application is hindered by poor water resistance, mildew resistance, and storage stability. Here, a fully bio-based citric acid-starch adhesive (CASt) with high properties was successfully introduced by a simple method. Liquid chromatography/mass spectrometry (LC-MS), and Fourier Transform Infrared spectroscopy (FT-IR) determined that esterification of citric acid (CA) and starch (St) occurred to form a stable three-dimensional crosslinking structure, which strengthened water resistance and bonding strength of the starch adhesive. Compared with native starch (100 %), the soluble content of cured CASt was 1-16 %. CASt adhesive has well storage stability and high mildew resistance. Even after being stored for 5 months, the CASt-1 adhesive (mass ratio of CA/St = 1:1, and reaction time = 1 h) still have good liquidity. And its hot water strength (1.05 ± 0.22 MPa) also satisfied the standard requirements (≥0.7 MPa). The exhibited CASt adhesive is eco-friendly with components from plant resources, which performed as a bright alternative that can substitute petroleum-based adhesives in the artificial board industry.

Molecularly Engineered Protein Glues with Superior Adhesion Performance

Naturally inspired proteins are investigated for the development of bioglues that combine adhesion performance and biocompatibility for biomedical applications. However, engineering such adhesives by rational design of the proteins at the molecular level is rarely reported. Herein, it is shown that a new generation of protein-based glues is generated by supramolecular assembly through de novo designed structural proteins in which arginine triggers robust liquid-liquid phase separation. The encoded arginine moieties significantly strengthen multiple molecular interactions in the complex, leading to ultrastrong adhesion on various surfaces, outperforming many chemically reacted and biomimetic glues. Such adhesive materials enable quick visceral hemostasis in 10 s and outstanding tissue regeneration due to their robust adhesion, good biocompatibility, and superior antibacterial capacity. Remarkably, their minimum inhibitory concentrations are orders of magnitude lower than clinical antibiotics. These advances offer insights into molecular engineering of de novo designed protein glues and outline a general strategy to fabricate mechanically strong protein-based materials for surgical applications.

Preparation and Characterization of Plant Protein Adhesives with Strong Bonding Strength and Water Resistance

Plant protein adhesive has received considerable attention because of their renewable raw material and no harmful substances such as formaldehyde. However, for the plant protein adhesive used in the field of plywood, low cost, strong water resistance, and high bonding strength were the necessary conditions for practical application. In this work, a double-network structure including hydrogen bonds and covalent bonds was built in hot-pressed peanut meal (HPM) protein (HPMP) adhesive, soybean meal (SBM) protein (SBMP) adhesive and cottonseed meal (CSM) protein (CSMP) adhesives. The ether bonds and ester bonds were the most in CSMP adhesive, followed by SBMP adhesive, while the hydrogen bond was the most in HPMP adhesive. The solubility of the HPMP, SBMP, and CSMP adhesives decreased by 14.3%, 24.2%, and 19.4%, the swelling rate decreased by 56.9%, 48.4%, and 78.5%, respectively. The boiling water strength (BWS) of HPMP (0.82 MPa), SBMP (0.92 MPa), and CSMP adhesives reached the bonding strength requirement of China National Standards class I plywood (type I, 0.7 MPa). The wet shear strength (WSS) of HPMP, SBMP, and CSMP adhesives increased by 334.5% (1.26 MPa), 246.3% (1.42 MPa), and 174.1% (1.59 MPa), respectively. This study provided a new theory and method for the development of eco-friendly plant meal protein adhesive and promotes the development of green adhesive.

A biomimetic adhesive with high adhesion strength and toughness comprising soybean meal, chitosan, and condensed tannin-functionalized boron nitride nanosheets

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.

Preparation of a High-Temperature Soybean Meal-Based Adhesive with Desired Properties via Recombination of Protein Molecules

A soybean protein-based adhesive with desired adhesion properties and low processing cost is prepared by a simple and practical method, which is of great significance to the sustainable utilization of resources and human health. Nevertheless, the protein of high-temperature soybean meal (HSM) has a high degree of denaturation and low solubility, endowing the resultant soybean-based adhesive with a high viscosity and unstable bonding performance. Herein, we propose the strategy of protein molecular recombination to improve the bonding properties of the adhesive. First, chemical denaturation was carried out under the combined action of sodium sulfite, sodium dodecyl sulfate, sodium hydroxide, urea, or sodium dodecyl sulfate/sodium hydroxide to reshape the structure of the protein to release active groups. Then, thermal treatment was employed to facilitate the protein repolymerization and protein-carbohydrate Maillard reaction. Meanwhile, the epichlorohydrin-modified polyamide (PAE) as a crosslinking agent was introduced to recombine unfolded protein and the products from Maillard reaction to develop an eco-friendly soy protein-based adhesive with an excellent and stable bonding performance. As expected, the highest cycle wet bond strength of the adhesive sample of 1.20 MPa was attained by adding a combination of 2% SDS and 0.5% sodium hydroxide, exceeding the value required for structural use (0.98 MPa) of 22.44% according to the JIS K6806-2003 commercial standard. Moreover, the adhesive possessed the preferable viscosity and viscosity stability accompanied by good wettability. Noteworthily, the adhesive had a short time of dry glue, which could be solved by combining it with soybean meal (SM) at the ratio of 30:10.

An Eco-Friendly Wood Adhesive Consisting of Soybean Protein and Cardanol-Based Epoxy for Wood Based Composites

Formaldehyde-derived wood adhesives have dominated in woody composites production up to now, while facing a significant challenge in non-renewable raw materials and the formaldehyde emission. To solve these problems, an eco-friendly soybean protein-based wood adhesive was explored via the addition of renewable cardanol based epoxy (CBE) as cross-linking agent. The curing mechanism and viscosity of the adhesives were investigated and the bonding performance was evaluated with three-ply plywood. Fourier transformed infrared spectroscopy (FTIR) analysis confirmed the formation of new ether linkages and the consumption of epoxy groups in the cured adhesives, thereby improving the thermal stabilities and cohesion. Plywood bonded with the CBE-modified soybean protein-based adhesive reached the maximum wet shear strength of 1.11 MPa (4 wt.% CBE addition), a 48% increase compared to the control, whereas the viscosity of adhesive decreased by 68.2%. The wet shear strength of the plywood met the requirements of the Chinese National Standard GB/T 9846-2015 for interior plywood application. The formaldehyde-free adhesive with excellent water resistance adhesiveness performance shows great potential in woody composites as an alternative to formaldehyde derived wood adhesives.

Biomimetic lignin-protein adhesive with dynamic covalent/hydrogen hybrid networks enables high bonding performance and wood-based panel recycling

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 (CN) 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.

Fabrication of edible and biodegradable cutlery from morning glory (Ipomoea aquatic) stem fiber-reinforced onto soy protein isolate

This study aimed to investigate the preparation of soy protein isolated (SPI) cutlery incorporated with 5–20% (w/w) crude morning glory stem fiber (MGSF). SPI cutlery samples without and with MGSF were subjected to hydraulic hot press molding at 160 °C for 5 min pressing time. SPI with 5% MGSF showed decreased lightness values compared to the control SPI (without MGSF) (p < 0.05). Flexural modulus attained in SPI with 5% MGSF was higher and subsequently showed decreases in impact strength and compression load compared to the control SPI (p < 0.05). SPI with 5% MGSF sample showed slightly lower water absorption followed by decreases in degree of swelling and solubility with that of the control SPI (p < 0.05). Micrographs revealed a 5% MGSF formed uniform matrix with SPI in comparison to the control and other treatments that showed cracks with the increased fiber addition. Additionally, stiffness decreased with the addition of 5% MGSF to SPI thereby increasing deflection in comparison to the control SPI and other treatments. Thus, SPI cutlery added with 5% MGSF potentially retained the physical and mechanical properties of edible and biodegradable cutlery for food applications.

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MGSF at 5% level improved water resistance properties than the control SPI.

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Mechanical properties were enhanced in SPI sample treated with MGSF.

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Impact strength decreased with the increments of MGSF fiber in SPI cutlery.

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SEM micrographs confirmed the uniform fiber distribution in SPI treated with 5% MGSF.

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SPI at 5% MGSF can be exploited to produce edible and eco-friendly cutlery.

Dynamic reversible adhesives based on crosslinking network via Schiff base and Michael addition

It is of practical interest to obtain polymers with complex material properties in a simplified synthetic manner for a broader range of practical applications. In this work, we constructed a dynamic reversible adhesive based on branched polyamine (PA) and p-formylphenyl acrylate (FPA) by simultaneously performing Michael addition reaction and Schiff base reaction. Branched polyamines provide a large number of amino groups as reaction sites that can react with both carbon-carbon double bonds and aldehyde groups. This enables the branched polymeric adhesive system to have a large number of Schiff base bonds within it, an important property of Schiff base bonds is that they are dynamically reversible. This allows us to prepare adhesives with hyperbranched crosslinking networks and recycling properties, and we have verified that FPA-PA adhesives do not exhibit significant fatigue after multiple recycling through the gluing-destruction-gluing process. The resulting FPA-PA adhesives produce tough bonding on multi-substrates such as steel, aluminum, glass, PVC, PTFE, birch and moso bamboo, which exhibited by lap shear strength of 2.4 MPa, 1.7 MPa, 1.4 MPa, 1.3 MPa, 0.4 MPa, 1.6 MPa, and 1.8 MPa, respectively. The feasibility of the synthesis idea of simultaneous Michael addition reaction and Schiff base reaction was demonstrated, as well as the excellent performance and great application potential of FPA-PA adhesives to be recyclable on multi-substrates.

Conversion of soybean oil extraction wastes into high-performance wood adhesives based on mussel-inspired cation-π interactions

As a soybean oil extractive byproduct, high temperature defatted soy meal (HSM) presents great potential as a raw material for vegetable protein adhesives to replace aldehyde-based adhesives in the wood-based panel production. However, the application has been hindered by its poor cold-pressing adhesive performance. Herein, a novel HSM-based adhesive with excellent cold-pressing adhesion performance was developed based on mussel-inspired cation-π interactions. Highly reactive polyamidoamine-epichlorohydrin (PAE) and folic acid (FA) were added into an HSM-based adhesive to construct a dual-network system stabilized by strong cation-π interactions. The coacervate formed by PAE and FA served as an "internal adhesive" to bond HSM particles together, yielding high initial viscosity but easy sizing. As expected, the prepared adhesive exhibited an excellent cold-pressing bonding strength of 423 kPa, showing a 295% improvement compared to the soy protein (SP) adhesive. To improve the hot-pressing bonding strength of the adhesives, inorganic calcium carbonate (CaCO₃) particles were introduced into the adhesive system to build an organic-inorganic hybrid adhesive system. The wet shear strength of the SPAE-FA-CaCO₃ adhesive significantly improved from 0.63 MPa to 0.96 MPa, meeting the requirements for the practical application. This method provides a novel strategy to exploit high-performance vegetable protein-based wood adhesives.

A New Wood Adhesive Based on Recycling Camellia oleifera Cake-Protein: Preparation and Properties

In order to improve the initial viscosity and stability of Camellia oleifera cake-protein adhesive, Camellia oleifera cake-protein was blended with defatted soybean protein (DSP), soybean protein isolate (SPI), and casein, followed by adhesive preparation through degradation and crosslinking methods. The performance of Camellia oleifera cake-protein adhesive was investigated by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopic (SEM), and thermogravimetric (TG) and X-ray diffraction (XRD). The results showed that DSP, SPI, and casein likely promoted the effective degradation of Camellia oleifera cake-protein, and, thus, more active groups were formed in the system, accompanied by more reactivity sites. The prepared adhesive had a lower curing temperature, and higher initial viscosity and stability, but the storage time was shortened. Moreover, DSP, SPI, and casein, themselves, were degraded into peptide chains with lower molecular weights; thus, improving the overall flexibility of the adhesive, facilitating a better elastic contact and regular array between crosslinking products, and further strengthening the crosslinked structure and density of the products. After curing, a compact and coherent reticular structure was formed in the adhesive layer, with both bonding strength and water resistance being significantly improved. According to the results obtained, the next step will be to study the DSP-modified Camellia oleifera cake-protein adhesive in depth.

Graphene Oxide Functionalized Cottonseed-Lignin Resin with Enhanced Wet Adhesion for Woody Composites Application

With rising interior air pollution, health, and food shortage concerns, wood adhesives derived from non-food sustainable materials have therefore attracted considerable attention. Here we developed an eco-friendly cottonseed-lignin adhesive consisting of non-food defatted cottonseed flour (DCF), alkali lignin (AL), and graphene oxide (GO). The cation-π interaction, and hydrogen and covalent bonds between AL@GO and DCF collectively enhanced the cross-linking structure of the cured cottonseed-lignin adhesive, based on the Fourier-transform infrared spectroscopy, thermogravimetric analyses, scanning electron microscopy, and sol-gel tests. The high performance of the developed cottonseed-lignin adhesive was evidenced by its increased wet/dry shear strength and decreased rheological properties before curing and improved thermal stability and decreased soluble substances after curing. Particularly, the highest wet shear strength of poplar plywood bonded with cottonseed-lignin adhesive was 1.08 MPa, which increased by 74.2 and 54.3% as compared to the control and requirement of the Chinese standard GB/T 9846-2015 for interior plywood (≥0.7 MPa), respectively. The technology and resultant adhesives showed great potential in the preparation of green woody composites for many applications.

Polyphenol-Metal Ion Redox-Induced Gelation System for Constructing Plant Protein Adhesives with Excellent Fluidity and Cold-Pressing Adhesion

Soy protein (SP) adhesives can resolve several problems with aldehyde-based adhesives, including formaldehyde release and excessive dependence on petroleum-based materials. Nevertheless, their development is hindered by the lack of balance between fluidity and high cold-pressing adhesive strength. A dynamically cross-linked SP adhesive with excellent fluidity and cold-pressing adhesion was developed in this study based on the polyphenol-metal ion redox-induced gelation system. SP was blended with acrylamide (AM), ammonium persulfate (APS), and the tannic acid (TA)-Fe³⁺ complex to prepare an adhesive gel precursor with good fluidity. In situ gelation of SP adhesive was then achieved via AM polymerization, as initiated by redox between TA and Fe³⁺. As expected, the prepared adhesive gel exhibited outstanding cold-pressing bonding strength (650 kPa) to the veneers compared to the neat SP adhesive, which has almost no cold-pressing bonding strength to the veneers. The TA-Fe³⁺ complex induced an in situ gelation system, which endowed the SP adhesive with strong cohesion; the topological entanglement of the adhesive gel in the veneers contributed to tight interfacial combinations. The TA-Fe³⁺ complex served not only as an accelerator of SP adhesive gelation but also as a "cross-linking core" for the cross-link SP adhesive system. The prepared SP-based adhesive also exhibited outstanding hot-pressing bonding strength and mildew resistance. The proposed polyphenol-metal ion-induced in situ gelation strategy may provide a new approach for developing advanced vegetable protein adhesives to replace aldehyde adhesives.

Novel Bionic Soy Protein-Based Adhesive with Excellent Prepressing Adhesion, Flame Retardancy, and Mildew Resistance

Soy protein (SP)-based adhesives can replace traditional aldehyde-based adhesives for the manufacturing of wood-based panels. However, developing a SP-based adhesive with excellent prepressing bonding strength, flame retardancy, and mildew resistance remains a challenge. Herein, an inorganic crystal cross-linked hybrid SP adhesive was developed inspired by the "secreting-hardening" process of the mussel adhesive protein and the organic-inorganic hybrid adhesive system of the oyster. Calcium sulfoaluminate (CSA) was introduced into the adhesive mixture of SP and acrylic acid to induce the in situ polymerization of acrylic acid to achieve adhesive gelation. The generation of the inorganic crystals by hydration of CSA not only contributed to the formation of a stable cross-linked hybrid adhesive system for strong cohesion but also provided strong interfacial adhesion between the adhesive layers and the plywood veneers. As anticipated, the prepared plywood sample bonded with the hybrid adhesive gel had an excellent prepressing bonding strength of 544 kPa, representing a significant increase compared to that of the pure SP adhesive (19 kPa). Moreover, the generated inorganic crystals endowed the adhesive with excellent mildew resistance and flame retardancy. This study provides a novel and effective strategy for the preparation of high-performance SP-based adhesives.

Improved performance of soy protein adhesive with melamine-urea-formaldehyde prepolymer

In recent years, soy protein adhesive, as an environmentally friendly bio-based adhesive, has attracted extensive attention. In this study, in order to ameliorate the bonding quality of soy protein isolate (SPI) adhesive, the melamine–urea–formaldehyde prepolymer (MUFP) was synthesized, and different amounts of it were introduced into the SPI adhesive as a cross-linking agent. Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric analyze (TGA), and scanning electron microscopy (SEM) were used to analysis the mechanism of modification. The results of plywood test indicated that the wet bonding strength of the adhesives was first increased and then decreased with an increase in the amount of MUFP additive. FT-IR, TGA, and SEM tests suggested that the introduction of MUFP could promote the establishment of a cross-linking structure in the cured adhesive layer to improve the bonding quality of adhesives, but presence of excessive MUFP could introduce hydrophilic groups and adversely affect water resistance.

In recent years, soy protein adhesive, as an environmentally friendly bio-based adhesive, has attracted extensive attention.