Biomimetic water-in-oil water/pMDI emulsion as an excellent ecofriendly adhesive for bonding wood-based composites

Preparation of a high-strength, hydrophobic performance starch-based adhesive with oxidative cross-linking via Fenton's reagent

Starch is a highly attractive carbohydrate in the production for the preparation of adhesives in recent years, due to its widespread availability, renewability, and abundance of reactive hydroxyl groups. However, the mechanical properties, hydrophobicity, self-adhesion, and particularly high energy efficiency are generally unsatisfactory for current starch-based adhesives. On this premise, starch was oxidized using Fenton's reagent in a ""one-pot cooking" process. The prepared oxidized starch was chain expanded by polyvinyl alcohol (PVA) and then cross-linked with a 10 % isocyanate (PM-200) to fabricate a starch-based adhesive (SFA) with a network crosslinked structure. SF12A35%/2.5-55 adhesive shows significantly higher wet shear strength (1.18 MPa), a remarkable 94 % increase compared to SF0A35%/2.5-55. The adhesive film also demonstrates both hydrophobicity (99° contact angle) and exceptional energy efficiency, with a DSC test revealing a notable 10 % elevation in energy efficiency. In addition, the crosslinked structure increases its molecular weight, thereby increasing its self-adhesion (Fig. S1). This study opens up new possibilities for the design and manufacture of multifunctional starch-based adhesives.

Hydrothiolation of alkynes with thiol-catechol derivatives catalysed by CuNPs/TiO2: exploring the reaction mechanism by DFT calculations

Density functional theory (DFT) calculations were applied to describe the hydrothiolation reaction of activated alkynes with thiols bearing a catechol group. The thiol-yne click (TYC) process was efficiently catalysed by a CuNPs/TiO₂ nanocatalyst giving the corresponding anti-Markovnikov vinyl sulphides with high Z-stereoselectivity. Based on the experimental results and DFT studies, a plausible reaction mechanism is proposed, which implies the activation of the carbon-carbon triple bond by coordination to the copper centre, followed by a stereoselective (external) nucleophilic attack to give preferentially the Z-vinyl sulphide isomer. Additionally, experimental and theoretical studies strongly correlate with the proposed synergistic role for the TiO₂ support in the catalytic process.

Water-in-Oil Pickering Emulsions Stabilized by Hydrophobized Protein Microspheres

Water-in-oil (w/o) Pickering emulsions have gained considerable attention in colloid science and daily applications. However, for the formation of w/o emulsions, especially those with high internal water content, the particulate stabilizers are required to be sufficiently hydrophobic, and synthetic or chemically modified particles have been mostly reported until now, which are not biocompatible and sustainable. We present a zein protein-based microsphere derived from the Pickering emulsion template, in which protein microspheres are feasibly in situ hydrophobized by silica nanoparticles, enabling the stabilization of w/o Pickering emulsions. The effects of microsphere concentration, water/oil volume ratio, oil types, and pH on the stabilization of prepared w/o emulsions are systematically studied, revealing prominent characteristics of the controllable size, high water fraction, universal adaptation of oils, as well as broad pH stability. As a demonstration, the Pickering emulsion effectively encapsulates vitamin C and shows high stability for long storage duration against ultraviolet radiation/heat. Therefore, this novel proteinaceous particle-stabilized w/o Pickering emulsion has great potential in the delivery and protection of water-soluble bioactive substrates.

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.

Effects of Different Denaturants on the Properties of a Hot-Pressed Peanut Meal-Based Adhesive

Plant protein-based adhesives could fundamentally solve the problem of formaldehyde-based adhesive releasing formaldehyde, but enhancing bonding strength and water resistance is a necessary measure to realize practical applications. In this study, the effects of different denaturants on the properties of a hot-pressed peanut meal (HPM)-based adhesive before and after crosslinking were studied. Papain, sodium dodecyl sulfate (SDS), urea and crosslinker-polyamide epichlorohydrin (PAE) were used to prepare HPM-based adhesives. The functional groups, bonding strength, thermal behaviors, mass loss, moisture uptake value, viscosity and fracture surface of adhesive samples were analyzed. As a result, (1) papain was used to break HPM protein (HPMP) into polypeptide chains and to reduce the water resistance. (2) SDS and urea unfold the HPMP molecule and expose internal hydrophobic groups to improve the water resistance of the adhesive. (3) A denser network structure was formed by PAE and HPMP molecules, which significantly improved the bonding strength and water resistance of adhesives. In particular, after SDS denaturation and PAE crosslinking, compared with pure HPM adhesive, the wet shear strength increased by 96.4%, the mass loss and moisture uptake value reduced by 41.4% and 69.4%, and viscosity increased by 30.4%. This work provided an essential guide to design and prepare HPM-based adhesives.

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.

An eco-friendly wood adhesive based on waterborne polyurethane grafted with gelatin derived from chromium shavings waste

An environmentally friendly wood adhesive developed from waterborne polyurethane (WPU) grafted gelatin (G) was investigated in this research. First, the G was extracted from chromium shavings waste, and then mixed with a prepolymer emulsion of WPU to synthesis the graft copolymer (WPUG) via a solvent-free emulsion copolymerization. The synthesized copolymer was characterized using the mechanical properties test, TGA, FT-IR, and other analysis technology. The results indicated that the WPUG had a good overall performance. Specifically, the contact angle reached 111.5°, the tensile strength reached 32.91 MPa, the temperature of the maximum weight loss was greater than 350 °C. The WPUG adhesive had excellent bonding power and mechanical properties; the dry bonding strength reached 4.21 MPa when the ratio between free amino groups of the G and isocyanate-groups of the WPU (the R value) was 1.5. This preparation of the graft copolymer not only satisfies the need of environment-friendly wood adhesives, but it also effectively improves the recyclability of chromium shavings waste.

Thiol-yne click reaction: an interesting way to derive thiol-provided catechols

The hydrothiolation of activated alkynes is presented as an attractive and powerful way to functionalize thiols bearing catechols. The reaction was promoted by a heterogeneous catalyst composed of copper nanoparticles supported on TiO₂ (CuNPs/TiO₂) in 1,2-dichloroethane (1,2-DCE) under heating at 80 °C. The catalyst could be recovered and reused in three consecutive cycles, showing a slight decrease in its catalytic activity. Thiol derivatives bearing catechol moieties, obtained through a versatile Michael addition, were reacted with different activated alkynes, such as methyl propiolate, propiolic acid, propiolamide or 2-ethynylpyridine. The reaction was shown to be regio- and stereoselective towards anti-Markovnikov Z-vinyl sulfide in most cases studied. Finally, some catechol derivatives obtained were tested as ligands in the preparation of coordination polymer nanoparticles (CNPs), by taking the advantage of their different coordination sites with metals such as iron and cobalt.

An attractive approach to the synthesis of catechol derivates through thiol-yne click reaction is presented. Compounds obtained were used in the preparation of CNPs.

Eco-Friendly Bioinspired Interface Design for High-Performance Cellulose Nanofibril/Carbon Nanotube Nanocomposites

Inspired by a wood-like multicomponent structure, an interface-reinforced method was developed to fabricate high-performance cellulose nanofibril (CNF)/carbon nanotube (CNT) nanocomposites. Holocellulose nanofibrils (HCNFs) with core-shell structure were first obtained from bagasse via mild delignification and mechanical defibration process. The well-preserved native hemicellulose as the amphiphilic shell of HCNFs could act as a binding agent, sizing agent, and even dispersing agent between HCNFs and CNTs. Remarkably, both the tensile strength at high relative humidity (83% RH) and electrical conductivity of the HCNF/CNT nanocomposites were significantly improved up to 121 MPa and 321 S/m, respectively, demonstrating great superiority compared to normal CNF/CNT composite films. Furthermore, these HCNF/CNT composites with outstanding integrated performances exhibited great potential in the field of flexible liquid sensing.