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The current study investigates for the first time the physico-chemical performances of lignins from cactus waste seeds (CWS) and spent coffee (SC) in comparison to previously isolated lignins from sugar byproducts (bagasse (SCB) and beet pulp (SBP)). In this work, lignin-phenol formaldehyde (LPF) resins were formulated using various lignin loadings (5–30 wt%), characterized and applied in the manufacturing of plywood panels. Several characterization techniques were applied to identify the chemical and morphological properties, thermal stability, and phenolic content of the extracted lignins, as well as the bonding strength and wood failure of the formulated resins. Results showed that the CWS and SC could be considered as an important source for lignin recovery with a considerable yield of 15.46 % and 27.08 % and an important hydroxyl phenolic content of 1.26 mmol/g and 1.36 mmol/g for CWS and SC, respectively. Interestingly, 20 wt% of extracted lignins in PF adhesives were the optimal formulation showing an improved modulus of elasticity (MOE) of about 3505, 3536 and 3515 N/mm2, and a higher modulus of rupture (MOR) of about 55, 55 and 56 N/mm2 for panels containing CWS, SC and SCB-lignins, respectively, over the reference panels (MOE = 3198 N/mm2 and MOR = 48 N/mm2). Additionally, formaldehyde emission from plywood remarkably decreases by up to 20 % when lignin was incorporated into the PF matrix. Herein, the treatment of the CWS and SC for the extraction of alkali lignin and its application showed a new route to produce high added-value products from underused residues. [ABSTRACT FROM AUTHOR]

The decarbonisation of industry is becoming a serious commitment in our society and it is now possible to transform CO 2 captured from industrial emissions into high added value chemical products. In this respect, chemical precursors can be obtained for use in the synthesis of highly demanded polymers on an industrial scale, such as polyurethanes, which are the basis for many formulations of adhesives, varnishes and coatings. In this work, reactive polyurethane hot-melt adhesives have been obtained from the revalorisation of CO 2 for use as bioadhesives in the footwear, wood and furniture industries. The CO 2 -based reactive polyurethane hot-melt adhesives obtained by the prepolymer method were first characterised with different experimental techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), softening temperature and melting viscosity. The adhesion properties of these adhesives were subsequently measured with T-peel tests on leather/HMPUR adhesives/SBR rubber joints in order to ensure that they met the minimum requirements for use in footwear. The performance of these new reactive polyurethane hot-melt adhesives on wood and other furniture materials was also analysed. Initially, for non-structural applications, different adhesives were tested according to standardised methods for their classification considering the use conditions and the tensile-shear strength of lap joints. The adhesives were subsequently characterised in terms of their suitability for bonding larger surfaces. In all cases, they yielded an optimal performance, and those showing the best results were validated for gluing laminated wood intended for structural purposes. Finally, the best adhesive obtained was applied to real furniture, observing no breakage nor any kind of damage. [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]

Hempseed meal, a co-product of hemp oil extraction, contains about 40 % proteins, which has recently become abundant because of the large demands of hemp oil related products. It has been an acute issue for hemp industries to utilize the hempseed meal for value-added products. On the other hand, wood industries are constantly seeking plant protein alternatives not only to secure plant protein sources but also to improve wet adhesion properties. In this study, native hempseed protein was identified to have great potential for wood adhesive applications. Hemp proteins were extracted from two types of hempseed meals: Hlesia and commercial hempseed meals. Then the extracted hemp proteins with and without modification were used to prepare wood adhesives. Glutaraldehyde, previously identified as a toxic but effective crosslinker for soybean protein adhesives, was used as the crosslinking reagent for hemp protein in this study. Results showed that the wet adhesion strength of hemp proteins without modification was similar or superior compared to published data such as modified soy protein-based adhesives. Glutaraldehyde crosslinker only improved wet adhesion of commercial hemp protein at low press temperature such as 150 °C and 150–170 °C for Hlesia hemp protein. At press temperature 170–190 °C, wet adhesion of commercial hemp protein was not affected by glutaraldehyde crosslinker, while for Hlesia hemp protein, wet adhesion was not affected by glutaraldehyde crosslinker at 190 °C. The highly hydrophobic amino acid contents of hempseed proteins were identified to attribute to the unique wet adhesion performance for low water solubility and water resistance, which is essential for plant protein-based adhesive application. This is the first time to demonstrate that native hemp proteins could be a feasible and valuable alternative source of plant protein-based adhesives. [ABSTRACT FROM AUTHOR]

[Display omitted] • Based on plant root-driven penetration achieved a sustainable and highly efficient wood bonding method. • Created a hyperactive-interface self-driven regulated wood capable of spreading adhesive into the wood. • Using only environmentally friendly polyvinyl acetate adhesives to achieve efficient gluing of wood. • Regulated wood showed high bonding strength. Wood adhesives are widely used in furniture manufacturing, the construction industry, and the fabrication of the internal components of aircraft, cars, and sports equipment. Therefore, the development of wooden adhesives with high stability, strength, and efficiency is a vital research area. Although most studies have focused on improving the bonding properties of adhesives, achieving direct interface control from wood remains a challenge. This study was designed based on the plant root-driven adhesion method to create a hyperactive-interface self-driven regulated wood capable of spreading adhesive into the wood and inducing crosslinking to improve adhesive strength. A multi-poly silicate network structure with multiple reactive sites was formed through the self-polymerization of sodium silicate and crosslinking with dimethylol dihydroxy ethylene urea (DMDHEU) to achieve densified wood and improve the reactivity of the wood surface and interior. Consequently, the environmentally friendly polyvinyl acetate (PVAc) underwent a self-driven bonding process with the wood. These findings indicate that PVAc penetrated the interior of the wood, disrupting the combination of sodium silicate and DMDHEU and grafting onto the reactive sites. This process resulted in a tightly bonded interface connection. Consequently, the shear strength increased from 4.4 to 5.5 MPa, and the wood breaking rate increased from 21.00 % to 45.80 %, representing a 25 % and 118.10 % increase, respectively. Moreover, the tensile strength of the wood in longitudinal joints, transverse joints, miter joints, and mortise–tenon joints was assessed. The results revealed that the sodium silicate/DMDHEU-regulated wood (SS/DDRW) exhibited significantly higher adhesive strength than the original wood (OW). Hence, this bionic design represents a simple and efficient strategy for developing wood adhesives. [ABSTRACT FROM AUTHOR]

The production of traditional wood adhesives relies on petrochemical resources and puts enormous pressure on the ecosystem. Therefore, it is important to use bio-based soy protein adhesives to replace traditional adhesives. However, soy protein adhesives have the problems of low solid content, high viscosity and poor water resistance. In this study, we combined enzymatic hydrolysis with cross-linking modification to reduce the molecular mass of soy protein and increase the solid content of adhesive, constructed a uniform and tight covalent bond cross-linking network in the adhesive. Through this modification strategy, we prepared a soy protein adhesive with high solid content, suitable viscosity and excellent bonding strength. The results showed that compared with 0-SPI adhesive, the viscosity of 4-SPI-18/PA/TA adhesive decreased by 61.6%, reached 21899 mPa·s. Meanwhile, the residual rate of the adhesive increased by 18% (59%), the moisture absorption rate reduced by 7.8% to reach 3.8%. The dry/wet shear strength of modified adhesive increased by 56.1% (1.28 MPa) and 44.3% (0.88 MPa), respectively, and the tensile strain at break increased by 58.1% (14.84%). This is because enzymolysis improved its coating performance, and formed mechanical interlocking with wood. In addition, the amount of SPI increased, and more protein molecules participated in the cross-linking reaction, forming a more uniform and compact cross-linking network structure in the adhesive, effectively improving the bonding strength and toughness. This study provides a novel approach for the preparation of cleaning and tenacious adhesives, aiming to explore a green development model. [Display omitted] • Preparation of soy adhesive by enzymatic hydrolysis and cross-linking modification. • The solid content of modified soy protein adhesive increased by 88.7% to reach 23.4%. • The viscosity of modified soy protein adhesive decreased by 61.6% to 21899 mPa·s. • The dry/wet shear strength of the prepared plywood increased by 56.1% and 44.3%. • The tensile strain at break of the prepared plywood increased by 58.1% to reach 14.81%. [ABSTRACT FROM AUTHOR]

Improving the performance of wood adhesive is important for the development of the veneer industry. This work investigated the effects of various durations of enzymatic hydrolysis to improve and enhance the properties of starch-based wood adhesive (SWA). The results showed that moderate enzymatic hydrolysis for 2 h of starch molecule could improve the properties of SWA. The bonding strength of SWA was increased from 2.72 MPa (0 h) to 6.87 MPa (2 h) in the dry state and from 0.87 MPa (0 h) to 2.69 MPa (2 h) in the wet state. A significant decrease in the viscosity of SWA was also observed after 2 h hydrolysis of starch molecules, which allowed smooth spreading and penetration of adhesive through the wood surface. Meanwhile, the dynamic mechanical analysis and scanning electron microscopy showed that SWA with 2 h enzymatic hydrolysis exhibited better elastic deformation and smooth surfaces compared with SWA with un-hydrolysis starch. This study provides important information regarding the possible applications of SWA in the wood industry and presents a potential alternative to less environmentally friendly formaldehyde-based wood adhesives. [Display omitted] • 2 H of enzymolysis improved the grafting and surface properties of adhesive. • Thermo-mechanical properties were enhanced by proper duration of enzymolysis. • Film and microstructure of the adhesive were improved by 2 h enzymolysis. [ABSTRACT FROM AUTHOR]

High-temperature soybean meal (HSM), a by-product of the soybean oil industry, is potentially a viable bio-adhesive for its renewability and low cost. Strong water-resistant HSM-based adhesives remain a challenge to prepare due to protein denaturation and poor dispersion in water. Based polyelectrolyte complexation enhancement strategy, the bi-anionic waterborne polyurethane (WPUS) and sulfurized polyamidoamine-epichlorohydrin (PADE) were self-prepared in this work, to synergistically reinforce and toughen HSM-based adhesives. The results indicated that the PADE/WPUS combined via the electrostatic complexation between the -COO- and -SO 3 - in WPUS and azetidinium groups in PADE, reinforcing adhesives through chemical interactions (ring-opening reactions, S-S reconstructions, etc.) and electrostatic bindings formed between PADE/WPUS and amino acids; toughening adhesives by introducing the microphase separation structure to transfer stress and forming dynamic hydrogen bond to stretch protein chains. When the amount of WPUS added was 20 % of PADE, sample HSM/PADE/WPUS20 % showed the best comprehensive performance. Specifically, the dry shear strength and the adhesion work of this sample reached to 3.37 MPa and 14.42 J, respectively exceeding those of the blank sample by 11.95 % and 601.95 %, showing an excellent toughness and strength. Besides, the wet bonding strength of PADE/WPUS20 % modified adhesive can reach to 1.55 MPa and have been comparable to many frequently-used aldehyde adhesives in practice. The strategy presented in this work provide an efficient method for developing plant protein-based adhesives. [Display omitted] • Bi-anionic polyurethane and thiol-polyamide resins were successfully prepared. • A polyelectrolyte complexation enhancement strategy used to enhance wood adhesives. • The adhesion work of the best adhesive exceeding that of the neat sample by 602 %. • Modified adhesives with splendid properties have practical application potential. [ABSTRACT FROM AUTHOR]

Plasma treatment is an eco-friendly and effective way to improve the chemical reactivity of wood surface. This study explores the improvemnet of bonding properties of heat-treated wood for outdoor construction applications through plasma treatment. In this work, the low temperature atmospheric barrier discharge (DBD) plasma was used to modify the surface of heat-treated wood, and then phenol-formaldehyde (PF) resin adhesive and modified wood were applied to prepare bonded wood. The in-situ chemical structure and mechanical properties of the bonding interphase were characterized by Raman spectrum, nanoindentation and digital image correlation technology (DIC) to indicate the effect of DBD modification on the bonding properties of heat-treated wood. Results showed that after plasma treatment, the hydrophilic functional groups in the cell wall were increased and the PF adhesive molecules had chemical interaction with the cell wall. The elastic modulus (E r) and hardness (H) of wood cell wall gradually decreased along the bonding interphase towards wood with the decrease of PF penetration depth, which resulted in the reduction of the mechanical properties difference between the cell wall and PF adhesive at the bonding interphase. As a result, the shear strain was distributed homogeneously due to the effective stress transmission more at the bonding interphase. The shear strength of the control bonded wood decreased by about 35 % after heat treatment at 215 °C for 2 h, while the shear strength of heat-treated wood was increased by up to 34 % after plasma treatment. • Mechanics of wood cell wall were enhenced by the infiltration of phenolic resin. • Mechanics of wood cell wall decreased as the distance from the bonding interphase increased. • The shear strength of wood decreased after heat treatment due to the low chemical reactivity of wood surface. • The shear strength of heat-treated wood increased after plasma treament. • The fracture location of bonded heat-treated wood is not concentrated upon the bonding interphase after plasma treatment. [ABSTRACT FROM AUTHOR]

The present study provides a comprehensive discussion on the structure and properties of a novel high-strength rapeseed protein-based adhesive, which effectively mitigates the emission of free formaldehyde in conventional wood-based panels used as adhesives. The rapeseed protein (R) extracted from rapeseed cake was integrated with glyoxalde-urea (UG) resin to prepare rapeseed protein-based adhesive (RUG). The structure of RUG was characterized by FTIR, XPS, 13C NMR, etc. The results indicate that RUG with good performance can be obtained by reacting at 80 °C for 1 h with G/U molar ratio of 2.0 and a system pH of 5–6. When preparing plywood, a small quantity of diphenylmethane diisocyanate (MDI) is introduced into the system as a crosslinking agent to further enhance the strength of the plywood. The results showed that when the amount of MDI is 3 % of the total mass of the RUG adhesive, the bonding strength of the RUG adhesive has been greatly improved, and the performance of the prepared plywoods meets the requirements of GB/T 9846-2015 for Class II plywood. The study provides a comprehensive discussion on the structure and properties of a novel high-strength rapeseed protein-based adhesive, which provided a reference for replacing formaldehyde-based adhesives. [Display omitted] • Developing an eco-friendly bio-adhesive from glyoxal, urea, rapeseed protein and MDI without any formaldehyde was used. • The reaction between glyoxal, urea, rapeseed protein and MDI endowed the adhesive with great bonding strength. • The reaction mechanism of urea-glyoxal-rapeseed protein-MDI adhesive was elucidated. • The use of rapeseed protein extracted from rapeseed meal can fully utilize the discarded rapeseed meal. • The adhesive prepared in this work has good potential to be used in wood industry production. [ABSTRACT FROM AUTHOR]

Various bio-based compounds have been attempted for adhesive development, including tannin, lignin, polylactic acid, chitosan, etc., to reduce the use of formaldehyde as well as the formaldehyde emission. Among them, tannins demonstrating as the most interesting compound, since tannin has very similar structure with synthetic phenol and has identical reactivity and chemical cross-linking with formaldehyde. As the greatest amount of tannin was found in the tree bark, therefore, this article aims to review the previous development of tannin-based adhesive generating from tropical wood barks and their performance on the manufacturing of several types of wood-based products. The properties of tannin and tannin-based adhesive from several types of tropical wood barks are presented in this review, as well as the physical and mechanical characteristics of wood-based product manufactured with tannin-based adhesive. [ABSTRACT FROM AUTHOR]

To gain a deeper understanding of the bond durability in adhesively bonded wood products, a multiscale investigation of the mechanical properties of wood joints bonded with a one-component polyurethane (PU) adhesive in successive cycles of accelerated aging treatment was conducted by combining nanoindentation (NI) and conventional tensile-shear techniques. The delamination ratio, shear strength, and wood failure ratio of the wood joints, as well as the reduced elasticity modulus (E r) and hardness (H) of the PU resin, cell walls in the interphase region (CW–I), and control cell walls (CW) were evaluated. The correlations between the macro shear strength and micromechanical properties were further established. The results showed that the average delamination ratios of the wood joints were 10%–26 % after eight cycles of hydrothermal treatment. Macromechanical and most micromechanical properties substantially decreased with an increase in the number of treatment cycles, with maximum reductions of 37 %, 24 %, 60 %, 56 %, 48 %, and 57 % for the shear strength, wood failure ratio, E r of PU, H of PU, E r of CW-I, and E r of CW, respectively. The linear regression for the mechanical properties and the number of treatment cycles indicated that the E r of PU, CW-I, and CW, as well as the H of PU, showed linear downward trends (with R 2 values of 0.765–0.921) during successive aging treatments. Significant and positive linear correlations were found between the shear strength and micromechanical properties of PU, with correlation coefficients of 0.970 (P < 0.01) and 0.941 (P < 0.05) for E r and H of PU, respectively. The wood failure ratio showed significant positive correlations with the E r values of CW-I (P < 0.01) and CW (P < 0.05), whereas the proportion of wood failure in the interphase was significantly (P < 0.05) negatively correlated with the E r value of CW. The shear strength was positively correlated with the E r of the cell walls, with correlation coefficients of 0.861 and 0.868 for CW-I and CW, respectively. In summary, both the micromechanical properties of the PU resin and the elasticity of the wood cell walls in the wood-adhesive interphase were demonstrated to be key factors affecting the bond durability of wood bond joints. [ABSTRACT FROM AUTHOR]

Starch adhesive is a commonly used bonding glue that is sustainable, formaldehyde-free and biodegradable. However, there are obviously some problems related to its high viscosity, poor water and mildew resistance. Hence, exploring a starch-based adhesive with good properties that satisfies the requirements of wood processing presents the context of the current research. Thus, corn starch was used as raw material to form oxidized starch (OCS) via oxidation using sodium periodate, it was reacted with a synthesis polyurea compound that prepared from hexanediamine-urea (HU) obtained by deamination to yield a oxidized starch-hexanediamine-urea adhesive (denoted hereafter as OCSHU). The oxidation process was optimized in terms of oxidant concentration, reaction time and temperature. Furthermore, the impact of HU addition on the mechanical properties of the adhesive was explored. Results indicate adhesive exhibited outstanding shear strength, when 13 % of NaIO 4 was used as an oxidant to treat starch at 55 °C for 24 h, and involved in a subsequent reaction with 40 % of HU. The dry shear strength, 24 h cold water strength, 3 h hot water strength and 3 h boiling water strength are 1.84, 1.50, 1.32, and 1.31 MPa. Meantime, OCSHU adhesive solution revealed good storage stability whereas cured resin exhibited mildew resistance. The developed adhesive is a simple and green biomass wood adhesive. Scheme 1. Image of OCSHU adhesive step by step preparation process. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Producing ethanol, PLA, and wood adhesive from bamboo residues. • Exhibiting the environmental benefits of biphasic pretreatment technology. • Trade-off between product yield and environmental impacts are revealed. • High-value lignin-based adhesive can bring environmental benefits. • Key drivers of environmental performance are identified. Utilizing bamboo residues to produce decarbonization energy products or materials diverts wastes from low-value treatment and supports the circular bioeconomy at the same time. This study develops a cradle-to-grave life-cycle assessment (LCA) for a biorefinery converting bamboo residues into bioproducts (ethanol, polylactic acid (PLA), and bio-based wood adhesive) in China. To combat the low enzymatic hydrolysis performance of bamboo residues and valorize the lignin, this study adopts a biphasic pretreatment by coupling phenoxyethanol and sulfuric acid solution (1%) to achieve high fermentable sugar production. The LCA study is coupled with a process simulation for an industrial-scale biorefinery based on the experimental data. Our results show that the life-cycle Global Warming Potential (GWP) is 17.0–32.1 gCO 2 e/MJ for ethanol cases and 3.2–3.7 kgCO 2 e/kg for PLA cases, when biphasic pretreatment is adopted. The lower GWP values are achieved by using 1:1 phenoxyethanol: acid solution, though it has a lower product yield than 4:1 phenoxyethanol: acid solution cases. Without biphasic pretreatment, the GWP is 135.8 gCO 2 e/MJ ethanol and 4.4 kgCO 2 e/kg PLA. For the perspective of treating 1 dry t bamboo residues, with biphasic pretreatment, the GWP is −174 to −66 kgCO 2 e for ethanol cases and −542 to −432 kgCO 2 e for PLA cases. The lower GWP is also from using 1:1 phenoxyethanol: acid solution (1%). These GWP ranges are lower than conventional landfilling (2969 kgCO 2 e) and landfilling with landfill gas recovery (−28 kgCO 2 e). [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal molding produced glueless and formaldehyde-free biocomposites. • Alkali treatment produced highly reactive alkali cellulose intermediates. • Lignin acted as an adhesive to strengthen the bonding between fibres. • The biocomposites had strong mechanical property. The efficient utilization of small-diameter shrub resources holds significant potential in averting forest resource waste and mitigating carbon emissions. Herein, glueless biocomposites were prepared using waste small-diameter Buxus megistophylla via alkali pre-treatment and thermal molding. Instead of simple hot-pressing, the biocomposites were prepared using thermal molding, which allows the release of edge stresses in a high-pressure environment. After alkali pretreatment, the flexural and tensile strength of the biocomposites increased by 66.08% and 74.12%. Alkali pre-treatment forms reactive alkali-cellulose, facilitating fiber bonding. Structural disruption leads to fiber swelling, increasing surface area and hydrogen bonding, especially on cellulose. This process disrupts and reconstitutes crystalline regions, enhancing crystallinity. Lignin liberated from the lignin-hemicellulose polymer transitions to a molten state, serving as an adhesive to fortify fiber bonds, creating a 3D lattice structure and hydrophobic surface (Water contact angle 85°). Furthermore, these biocomposites, being adhesive-free and non-emitters of harmful gases like formaldehyde, hold promise as sustainable materials for architectural decoration and furniture applications. [ABSTRACT FROM AUTHOR]

The use of biomass as a binder for the development of high-performance wood products has become a popular research topic in the context of sustainable development. In this work, wood flour obtained from agroforestry processing residues was used as an active functional filler. The wood flour was oxidized and chemically cross-linked with hyperbranched polyamines and used as a binder matrix. By applying the same oxidative treatment to the wood surface, a chemically activated bonding interface was formed. Analysis by FTIR, 13C NMR, XPS and XRD characterization showed that the key to the improved bonding property was the formation of multiple covalent cross-linked networks during hot pressing of the plywood. It is clear that the specimens with untreated wood surfaces showed no water resistance and the dry strength was only above the standard value. On the contrary, after activation of the veneer surfaces, the bond strength and water resistance were significantly improved, meeting the requirements of GB/T 17657–2013 for Class I panels. Activation of the chemically active adhesive interface by oxidation of wood materials is an effective means of improving the performance of plywood, and also provides a new idea for high-value utilization of biomass resources. [Display omitted] • A bio-based wood adhesive was prepared using renewable wood flour. • The adhesive exhibited excellent wet bonding performance. • The triplex cross-linked network structure improved the adhesive adhesion. • The water resistance of the adhesive was significantly improved. [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]

Traditional adhesives easily release toxic gases during the preparation process or apply to wood composite products, which have adverse effects on the human body and the environment. Herein, an all-water-based high-performance wood adhesive is prepared using TEMPO-oxidized cellulose nanofiber (TOCNF), acrylamide (AM), and tannic acid (TA) through free radical polymerization. Different characteristics of the prepared composites, including morphology, injectability, and adhesion properties, have been investigated. Results showed that the TA/TOCNF/PAM composite has excellent injectability. The addition of TA can enhance the lap shear strength of the TA/TOCNF/PAM composites and with the increment of TA content, the lap shear strength gradually decreases. The formation of effective hydrogen bonds and Van der Waals interaction among the rich functional groups in the composite, lead to strong lap shear strength on different substrates. The composite with 5.0 g of AM, 5.0 g of the TOCNF suspension and 0.1 g TA possesses a high lap shear strength of 10.5 MPa on wood and 1.5 MPa on aluminium. Based on strong adhesion properties and excellent injectability, the TA/TOCNF/PAM composites have great potential in the furniture construction and building industries. An all-water-based high-performance wood adhesive was fabricated through free radical polymerization. [Display omitted] • An all-water-based high-performance wood adhesive was fabricated through free radical polymerization. • TA/TOCNF/PAM composite has the strongest lap shear strength for wood substrates. • TA/TOCNF/PAM composite has excellent injectability. [ABSTRACT FROM AUTHOR]

The development of robust and bioinspired adhesives with excellent performances including fast gel time, low cost, good adhesion strength and stability, and excellent solvent and temperature resistance against harsh environment is urgent for practical applications. In this paper, kinds of natural polyphenolic adhesives have been successfully fabricated via the multiple polyphenol-diisocyanate cross-linking (PDC) reactions between natural polyphenols (extracts) and diisocyanate molecules. Under heating, as-prepared adhesives could effectively adhere onto a wide range of substrates (i.e. PTFE, PET, PMMA, Al, Cu, paper, glass, wood) through hierarchical interactions. Moreover, these adhesives exhibited great adhesion stability against complex solvents and low-temperature environments, whose adhesion strength could remain unchanged after soaking solvents after 30 days, which was conducive to their potential applications in industry and chemical fields, including petroleum, wood, metal, glass, plastics, and rubber adhesion. We believed that this work would provide new strategies towards the preparation of robust adhesives with excellent resistant against various solvents and low temperature for many fields by using naturally occurring building blocks. Natural polyphenolic adhesives were successfully fabricated via the multiple polyphenol-diisocyanate cross-linking (PDC) reactions between natural polyphenols (extracts) and diisocyanate molecules. Under heating, as-prepared adhesives could effectively adhere to a wide range of substrates (i.e. PTFE, PET, PMMA, Al, Cu, paper, glass, wood) through hierarchical interactions. Moreover, these adhesives exhibited great adhesion stability against complex solvents and low-temperature environments, and the adhesion strength could even remain unchanged after soaking solvents after 30 days. [Display omitted] • Natural polyphenolic adhesives were successfully fabricated. • As-prepared adhesives could effectively adhere to various substrates. • These adhesives exhibited great solvents and low-temperature resistance. [ABSTRACT FROM AUTHOR]

Considering the significant demands for construction products and the increasing disposals of plastic and agroforestry residues, this research evaluated the influence of recycled particles of polyethylene terephthalate (PET) inserted in the manufacture of five particleboard prototypes based on Pinus elliottii wood and castor-oil-based polyurethane resin (CPUR). The following panel traits were obtained: 100% pine wood, 0% PET and 10% CPUR (M100P-0PET-10C); 70% pine, 30% PET, and 10% CPUR (M70P-30PET-10C); 50% pine, 50% PET, and 10% CPUR (M50P-50PET-10C); 70% pine, 30% PET, and 5% CPUR (M70P-30PET-5C); and, 50% pine, 50% PET, and 5% CPUR (M50P-50PET-5C). Panels were evaluated according to physical (density, moisture content, thickness swelling, and water absorption), mechanical (modulus of rupture, modulus of elasticity, perpendicular tensile), and morphological tests (scanning electron microscope). M50P-50PET-10C particleboards revealed the best performance in the physical and mechanical tests, as well as M70P-30PET-10C and M50P-50PET-5C panels showed equivalent results. The findings suggested a notable environmental contribution and a great economic feasibility. Thus, it is possible to obtain wood-based particleboards manufactured from recycled PET, reusing this highly discarded non-biodegradable plastic and using a smaller volume of adhesive, with physical-mechanical properties that meet the expected performance for this bioresource-based product. [ABSTRACT FROM AUTHOR]

Widely used formaldehyde-based resins for modern wood-based panels are toxic to humans and the environment. Geopolymer-based adhesives (GA) are abundant environmentally inorganic materials with wide applications in engineering fields. However, the modification and design of GA with excellent properties for practical applications remain a major challenge. Here, calcium chloride (CaCl 2) solution was used to coat the wood surface, which quickly polymerized in situ with the geopolymer to form calcified geopolymer during hot-pressing, leading to the construction of a robust geopolymer/wood bonding interface. The formation mechanism of the reinforced interface between wood and geopolymer was characterized, and the wet shear strength and flammability were evaluated based on the binding application of plywood. The calcified geopolymer can achieve the dual effects of blocking the penetration of lye and promoting in situ reinforcement during hot-pressing, which effectively eliminates the impact of the weak interface layer of the alkali/wood and reorganizes the microstructure of the geopolymer/wood bonding interface. The wet shear strength of plywood with a 2.0 mol/L CaCl 2 solution loading was increased from 0.45 MPa to 0.87 MPa, an increase of 93% compared with the pristine samples. The inherent flame retardancy of geopolymers contributed to a 42.6% reduction in the first peak of the heat release rate and a decrease of 28.9% in the total heat release compared with industrial urea-formaldehyde resin. This resulting GA, which was prepared by a facile and green method with markedly increased wet shear strength and inherent flammability, may have potential applications in functional wood-based composites and be used as a replacement for formaldehyde-based adhesives. CaCl 2 -induced geopolymer calcification for the preparation of high-strength and fire-resistant plywood. [Display omitted] [ABSTRACT FROM AUTHOR]

Schematic representation of AX, DAX, and DAX-2AX adhesives synthesis, and crosslinking network of DAX-2AX. [Display omitted] • Multiple cross-linked network structures (C=N, Si-O-Si, and Si-O-C bonds) were constructed. • The adhesive bonded plywood exhibits excellent bonding strength and water resistance. • This work offers a novelty strategy for producing high-performance environmentally friendly materials. Nowadays, the development of green wood adhesives with high bonding strength and waterproofing is still challenging due to the abundance of hydrophilic groups in biomass materials resulting in suboptimal properties. Firstly, dialdehyde xylan (DAX) and aminated xylan (AX) were prepared from xylan (X) through oxidation and grafting reactions, respectively. Then, a high-performance xylan-based adhesive (DAX-2AX) was prepared by directly cross-linking DAX and AX. The chemical structure of DAX-2AX was analyzed by FTIR, 13C NMR, and XPS. The results showed that the DAX-2AX-based crosslinked network increased cohesion through covalent bonds (C=N, Si-O-Si, and Si-O-C bond), intermolecular hydrogen bonding as well as entanglement between xylan chains, which endowed the adhesive with excellent bonding properties. Compared with unmodified xylan (X), the wet bonding strength of DAX-2AX at 55 % solids broke through from 0 to 1.49 MPa (soaked in water at 63 °C for 3 h). This work provides a new strategy for the simple and efficient preparation of high-performance all-bio-based adhesives. [ABSTRACT FROM AUTHOR]

The wood-based panel industry provides industrial-scale production of engineered wood products for our daily life. In the production of wood-based panels, the most important input other than wood raw material is the adhesive. Formaldehyde-based resins are used as binders in the production of wood-based panels thanks to their cost and reactivity advantages. However, their fossil origin and formaldehyde content have increased the interest in resin synthesis studies with the use of biobased materials. Tannin is one of the most studied raw materials both in academia and industry to synthesize bio-based wood adhesives due to the suitability of its chemical structure and availability. In this review, the developed tannin-based wood resin formulations that have been developed were examined in two main sections. These are crosslinked tannin-based resins developed using crosslinkers such as hexamine, furfural, etc. And hybrid tannin-based resins prepared using other biobased resources such as starch, lignin, etc. The performance of the developed resin formulations was evaluated on the mechanical and physical properties of the final product such as particleboard and plywood. The pros and cons of each resin formulation were examined in detail regarding the final product performances. All of the obtained results showed that bio-based resin formulations synthesized with tannin and without formaldehyde have the potential to compete with formaldehyde-based resins. [Display omitted] [ABSTRACT FROM AUTHOR]

The determination of the efficiency of adhesives applied in glued joints, through the analysis of the percentage of wood failure, is one of the main validation parameters for the quality of gluing techniques and adhesive. However, the subjectivity of the interpretation, performance, and visual acuity of the evaluators makes the methodology subjective. This research aimed to establish a method for evaluating the behavior of the glue line in glued joints, using freely available software and digital camera images. Shear samples of glued joints with polyvinyl acetate - PVAc, resorcinol formaldehyde - RF, and melamine formaldehyde - MF were evaluated using digital images obtained by a 16.1-megapixel camera. The images were pre-processed to enable vectorization in Inkscape software, version 1.1.2. Each image was vectorized and subjected to the measurement of the areas of the generated vector layers (glue line and wood). The validation process was performed by evaluating the accuracy of vectorization. Thus, the photograph of each sample and the vectorized image were imported into ImageJ software, version 1.53. To ensure the reliability of the proposed methodology, statistical analyses of the Kappa coefficient, global accuracy, user, and producer were applied. To evaluate the efficiency of the proposed method in relation to the conventional method provided in ASTM D5266-13 , five evaluators analyzed the proportion of bond line and wood failure of the 10 samples submitted to the proposed methodology. Subsequently, a descriptive analysis of the data was carried out to evaluate the variability and subjectivity of the conventional analyses among the evaluators. It is noted that the proposed methodology achieved high efficiency in the analysis of the proportion of glue line and wood, and it can be assured by the accuracy tests performed. The research also showed that there was no agreement among the five evaluators using the conventional method. It is concluded that the proposed methodology meets the research objective, with high levels of accuracy, and confirms the subjectivity of the analyses performed with the conventional methodology. The results underscore the need for objective methodologies, employing computational techniques to reduce subjectivity in adhesive bond failure assessments, enhancing critical decisions in the selection of adhesives for industrial structural applications. • A new methodology for forest planning was proposed. • We consider the main forest genetic materials used in Brazil. • The methodology showed 81% assertiveness. • The proposed methodology had high precision and zero execution cost. • The proposed methodology is feasible and can be adapted to any other area. [ABSTRACT FROM AUTHOR]

EN 302-1 and EN 205 are among the most commonly used standards for the approval as well as research of wood adhesives to evaluate bond strength. The present study investigates the sensitivity of the lap-joint samples to a possible error in groove cutting as well as the influence of using steam-treated and untreated beech wood on tensile shear strength. The lap-joint specimens cut with 0.5 mm too shallow and 0.5 mm too deep grooves was compared with samples cut precisely within the tolerances mentioned in the standards. A comparison of tensile shear strength between the joints manufactured out of steam-treated and untreated beechwood has been made. The results show a significant influence of groove depth on the resulting tensile shear strength. While deep groves (+0.5 mm) underestimate, shallow grooves (−0.5 mm) overestimate it dramatically. Additionally, the joints with steam-treated beech wood delivered lower tensile shear strength than those of untreated beech wood bonds when there is a considerable wood failure percentage. When the ultimate tensile shear strength of the adhesive bond approaches the shear strength parallel to the grain of wood, the impact of steam-treated beech wood on the estimation of adhesive bond strength is higher. [ABSTRACT FROM AUTHOR]

A series of novel waterborne lignin-based epoxy resin emulsions (WLEPs) were successfully synthesized, and then the WLEPs were cured with polyamide (PA) to give formaldehyde-free wood adhesives with high-performance. The chemical structures and properties of WLEP emulsions were determined. The effects of the emulsifiers on thermal and mechanical properties of the adhesives were investigated, and the potential application of WLEPs in the formulation of plywood were also evaluated. The results demonstrated that the WLEP dispersions presented excellent storage stability (>180 days) with their viscosities range from 110 mPa·s to 470 mPa·s and particle sizes in the range of 321–696 nm, which were beneficial for the fluidity and permeability of the wood adhesives. Furthermore, the thermal and mechanical properties of adhesives could be tuned effectively by controlling the length of PEG chains. The adhesive bearing PEG 6000 exhibited the highest tensile strength of 24.0 MPa and Young's modulus of 1439 MPa. Notably, the plywood prepared with the resulting adhesives displayed good bonding performance, especially water resistance, which were much higher than the national standard requirement for exterior-grade plywood type I. These results indicated that the WLEPs could be used as sustainable alternatives for traditional formaldehyde-based wood adhesives in practical applications. [Display omitted] • A series of waterborne lignin-based epoxy resin emulsions (WLEPs) with excellent storage stability were successfully synthesized without using any solvent. • The adhesives based on WLEPs exhibited good fluidity, wettability and permeability on wood surface. • The thermal and mechanical properties of adhesives can be easily tuned by adjusting the flexible segments. • The plywood prepared with the resulting adhesives demonstrated good bonding performance, especially water resistance, exceeded the national standard requirement for exterior-grade plywood type I. [ABSTRACT FROM AUTHOR]

Adhesives are used extensively in the wood industry. As resource and environmental issues become increasingly severe, the development of green and sustainable biomass-based adhesives has attracted increasing attention. In this work, a green wood adhesive is developed from poly(vinyl alcohol) and lignin with molecular designs of lignin extending beyond those in nature. The lignin undergoes extraction from corncob residue, aldehydration, and phenolisation (phenol, resorcinol, and catechol) to significantly increase the phenolic hydroxyl groups (over 7.92 mmol/g), which has the effect of enhancing the hydrogen bonding force between the adhesive and the wood, thereby greatly improving adhesive performance. Compared with pure PVA, polyphenol lignin-containing PVA showed improved adhesion strength and hydrophobicity. PVA/resorcinol-lignin has the significantly improved wood lap shear strength (6.27 MPa, 77.6 % improvement) and hydrophobicity (almost 100 % increase in wet shear strength). This research not only provides a green and high-performance alternative raw material for wood adhesives but also broadens the path for large-scale application of biomass. • The content of phenolic hydroxyl groups of the modified lignin reaches 7.92 mmol/g. • A higher content of phenolic hydroxyl groups shows an enhanced adhesive strength. • The resorcinol structure exhibited higher adhesion strength than catechol. • PVA/resorcinol-lignin exhibits a high wood lap shear strength of 6.27 MPa. [ABSTRACT FROM AUTHOR]

The present paper investigates the bonding interface between cellulose-based adhesive and chemically activated wood to explore the contribution of cohesion and interaction force between adhesive and substrate to the bonding properties. The activated wood surface rich in –NH 2 groups is produced by brushing 3-amino-propyl triethoxysilane (APTES) on the natural wood. The amine-functionalized cellulose is made by grafting microcrystalline cellulose with APTES and the adhesive is developed by crosslinking the branched epoxide with the aminated cellulose. Subsequently, a super strong wood laminates is developed by reacting the –NH 2 groups on the activated wood surface reacted with the epoxy groups in the adhesive to construct an "amino-epoxy-amino" sandwich bonding interface. The bonding strength of laminates at dry condition and after hot and boiling water treatment is 4.04 MPa, 2.42 MPa and 1.64 MPa, respectively. The strength after boiling water treatment of the plywood laminates made of all-component adhesive enhanced from 0 MPa to 1.64 MPa contrasted with that made of pure aminated cellulose and that prepared from the activated wood surface enhanced from 0.77 MPa to 1.64 MPa contrasted with that made by the nonactivated wood surface. The cohesion of the adhesive and the interaction force between the adhesive and the wood substrate played an important role in the bonding properties. Development of strong cross-linking, chemically bonding, "sandwich" profile wood bonding interface diagram. [Display omitted] • The "amino-epoxy-amino" sandwich profile bonding interface was constructed. • The dry bonding strength of the plywood laminates exceeded 4.04 MPa. • This work provided a novel strategy for design high-quality wood composites. [ABSTRACT FROM AUTHOR]

Currently, low adhesion and poor water resistance are the main factors limiting the application of biomass adhesives. Based on these factors, in this study, branched epoxy compounds were synthesized from erythritol, xylitol and sorbitol, which were further reacted with the synthesized aminated xylan to obtain biomass adhesives. It is noteworthy that amino-rich activated wood surfaces were constructed and a "sandwich" type multiple cross-linked network was formed by chemical bonding between the adhesive and the activated wood surfaces. The dry/hot water/boiling water bond strength of the activated wood plywood were 3.13/1.54/1.18 MPa, which were 42.9%/108.1%/156.5% higher than those of the natural wood plywood, respectively. The plywood prepared from the activated wood interface showed excellent bond strength and water resistance. In this study, the wood surface was modified with orientated functional groups based on the mechanism of cross-linked network formation in the adhesive, resulting in the formation of stable chemical bonds between the adhesive and wood interfaces. This is the key to improving the interfacial adhesive interactions and ultimately the properties of the plywood. [Display omitted] • An activated wood interface equipped with -NH 2 was prepared. • Synthesis of biomass adhesives with epoxy-amine cross-linked networks. • The wet bonding strength increased by 156.5% as wood surface was activated. • This work offers an effective method for producing high-performance materials. [ABSTRACT FROM AUTHOR]

Advancements in the use and applications of engineered wood products is receiving much interest in the construction industry. This is because wood has highly credible characteristics in relation to sustainability. It acts as a carbon store and is a natural renewable material. However, achieving adequate durability requirements and ensuring satisfactory adhesive bondline integrity is fundamental for such engineered products particularly when subjected to an exposed exterior service class environment. Little information exists on the durability performance of preservative treated wood bonded using one-component polyurethanes (1C-PURs). This study therefore involved the accelerated ageing of two 1C-PUR adhesives for the bonding of untreated, copper chromate arsenic and micronised copper azole preservative treated wood of fast growing Radiata pine. The ageing involved both vacuum-pressure soak drying cycling and exposure to a constant long-term high temperature and humidity environment. Resorcinol formaldehyde bonded specimens and solid wood specimens were used as controls. The testing showed that the standard requirements for delamination were satisfied when bonding preservative treated wood with 1C-PUR adhesive. The shear strength of specimens bonded with 1C-PUR adhesive subjected to vacuum-pressure soak drying compared well to the performance of the controls. The predominant failure behaviour was wood failure. The shear strength of all bonded preservative treated wood specimens with both 1C-PUR and resorcinol formaldehyde which were exposed to a constant long-term high temperature and humidity environment demonstrated a general and comparable reduction in strength over time which was statistically significant. High wood failure percentages were recorded at the bond interface which indicated weakening of the wood adherend when subject to the ageing rather than weakening of the adhesive bond. Chemical analysis of bonded specimens after ageing demonstrated that no significant variations were experienced. [ABSTRACT FROM AUTHOR]

Using engineered wood products (EWPs) in the building technologies is very crucial in terms of sustainable approaches. They provide; low weight, high structural stiffness, carbon storage capacity and easy erection on site. EWPs are composite materials that are influenced by a variety of factors that play a critical role in their formation. The chemical ingredients of the wood, the curing process of the adhesive, the type of wood, the relationship between the adhesive and the wood species, the curing temperature, the geometric configuration of the lamellae, etc. can all be included under the heading of these factors. In contrary with massive wood, to obtain EWPs different types of adhesives can be used. Therefore adhesive type and its application method affects the quality of wooden structural element. Choosing the appropriate adhesive is one of the steps to be taken to obtain the structurally correct product. Based on this approach, it was decided to investigate the adhesion performance of different adhesive types. This paper aims to present the best bonding method among the melamine urea formaldehyde (MUF) and epoxy adhesives by considering the fiber directions of the wood and the type of adhesive according to the load. One of the aims of this study is to investigate the effect of changing the fiber direction of wood on adhesion performance, taking into account the current gap in the literature. Pull-off tests were conducted to assess the bonding performance of different types of adhesive in wood samples with varying fiber direction. The wood samples were bonded to the wood surface with varying grain directions. During the pull-off tests, ruptures in the glue line of the test samples were commonly observed. The results have shown that in cylindrical samples bonded with epoxy, the highest bonding strength values were observed in scenarios where the wood fibers were oriented parallel to the load direction and perpendicular to the ground plane. Similarly, for wood samples used as the bonding surface, the highest bonding strength values were achieved when the wood fibers were oriented parallel to the load direction and perpendicular to the surface plane. On the other hand, the highest value in pull-off test setups was found with melamine urea formaldehyde adhesive; commonly used in laminated timber, between the wood samples with grains perpendicular to the load direction and the wood adherence surfaces with a parallel grain direction. In summary, the highest strength value was obtained from the test setup in which epoxy was used as the adhesive and both the wood specimens and the wood bonding surface had fiber directions parallel to the load direction. • The fiber directions of wood in terms of bonding performance are evaluated. • Epoxy provides stronger adhesion than MUF in EWP's technology. • The parallel grain direction of wood exhibits the strongest bonding performance relative to the applied load. • The perpendicular direction of the wood fibres to the applied load is the most critical point in terms of strength. [ABSTRACT FROM AUTHOR]

Although there have been notable advances in wood-based adhesive materials, the ability to rapidly bond wood under cold curing conditions at room temperature remains a challenge in these adhesives. Here, we report a new butylphenyl-derived polymer that can achieve super strong adhesion at room temperature by fast response at the wood interface. This behavior is achieved by the external reactive groups to create strong interfacial forces and the internal construction of organic-inorganic hybrid structures to reduce energy dissipation. Our research has established an effective method to modulate the viscoelasticity of the copolymer and optimize the adhesion properties of the adhesive at room temperature. The adhesive has a lap shear strength of 4.2 ± 0.17 MPa and also has a repair function that allows the repaired wood to withstand tensile forces of up to 470 N. It is anticipated that this dry, self-supporting, low-cost functional latex will be used as a commercial product for furniture restoration, wood industry and other applications. [Display omitted] • A new cold-curing wood adhesive easily prepared by copolymerization and blending. • Lap shear strength of 4.2 MPa, repair boards can resist tensile minimum 330 N. • The wettability and adhesion strength of the boards allows the adhesive to be used in a wide range of wood restoration applications. • Huge advantages in terms of room temperature curing bonding and energy savings. [ABSTRACT FROM AUTHOR]

The fact that formaldehyde-based resins used as adhesives in the wood-based panel industry are produced from fossil sources and formaldehyde limits that are becoming more restrictive day by day have increased the focus on bio-based resin studies. Starch is one of the most preferred bioresources in biobased resin studies, thanks to its availability and suitable chemical structure. However, starch's poor water resistance, short shelf life, and high viscosity limit the use of starch-based resins. Many physical and chemical modification techniques have been studied to overcome starch's disadvantages, and the results have been reported. In this review, chemical modification techniques that will facilitate the use of starch as a resin in the wood-based panel industry are examined. Improved weaknesses of starch with applied chemical modifications have been reported. The results showed that with chemical modification techniques, starch is a potential candidate to compete with petrochemical-based adhesives and can play an important role in biobased wood resin development studies. [Display omitted] [ABSTRACT FROM AUTHOR]

Enhancing the performance of starch-based wood adhesive is vitally important for its practical applications. Accordingly, we designed the use of micronized starch (MS) to prepare micronized starch-based wood adhesive (MSWA) by incorporating 0, 2, 4 and 6% (w /w, dry basis starch) sodium dodecyl sulfate (SDS). The results showed that 2% SDS exhibited remarkable improvement in shear strength and viscosity of MSWA. The grafted reaction was demonstrated by 1H NMR and the steady shear results indicated that the adhesive possessed a pseudoplastic behavior under yield stress conditions. Besides, dynamic rheological measurements were applied to evaluate the structure of MSWA under varying frequencies, temperatures and constant stain. The transmission electron microscopy (TEM), Zeta potential and surface tension indicated that SDS could improve the surficial properties. Meanwhile, the microstructure of adhesive films and fracture surfaces of glued wood veneers by scanning electron microscopy (SEM) demonstrated that the migration of SDS led to the formation of surfactant layer. Furthermore, element analysis revealed the distribution of S/N in latex slices. The results of this study provide the detailed information about the influence of SDS on the rheological properties and microstructures of MSWA, which may facilitate the preparation of high performance bio-based adhesive for wood applications. Investigation on the effects of surfactant (SDS) on microstructure and rheological behavior of micronized starch-based wood adhesive. Unlabelled Image • Preparation of micronized starch-based wood adhesive (MSWA). • Adding sodium dodecyl sulfate (SDS) improved bonding performance and viscosity. • Rheological behavior indicated the surfactant enhanced the MSWA microstructure. • The presence of SDS improved the surface compatibility of latex. [ABSTRACT FROM AUTHOR]

Cross laminated timber (CLT) was fabricated from Acacia mangium wood by using phenol resorcinol formaldehyde (PRF) and one component polyurethane (PUR) as binders. The purpose of the study was to evaluate the bond integrity of A. mangium CLT produced using different working parameters. The assemblies were pressed at 30 °C for 30 min using three pressing pressures (0.9 N/mm2, 1.2 N/mm2, and 1.5 N/mm2). Delamination and block shear tests were conducted on the CLT according to European Standards, EN 391 and EN 392, respectively. The results revealed that PRF-bonded CLT experienced lower percent delamination compared to that bonded with one component PUR. It appears that a higher clamping pressure i.e. 1.5 N/mm2, is needed to sufficiently bond A. mangium lumbers as indicated by a marked increase in bond shear strength with an increase of pressing pressure. PRF was found to be a more superior adhesive than PUR irrespective of cramping pressure and loading direction. A. mangium wood is relatively dense thus requires quite high pressure, 1.5 N/mm2, irrespective of adhesive used. PRF appears to bond A. mangium wood better compared to PUR with shear bond strength of 21% and wood failure percentage of 220% higher. [ABSTRACT FROM AUTHOR]

• Bioadhesives were formulated from cassava starch and polycarboxylic acids. • Sustainable panels design based on bioadhesives and wood processing by-products. • BTCA bioadhesives allow to enhance panels mechanical resistance and water affinity. This work was focused on the development of ecofriendly adhesives from cassava starch modified by polycarboxylic acids evaluating their performance in the design of sustainable panels using wood by-products. Additionally, a deep insight on the adhesive-substrate interactions was carried out through ATR-FTIR studies. Bioadhesives were formulated with cassava starch suspensions (5% w/w) modified with the addition of 0–80% (polycarboxylic acid weight /100 g starch) citric acid (CA) or 1,2,3,4 butane-tetracarboxylic acid (BTCA) and loaded with native starch at 5% (w/w) as filler. Formulated adhesives presented a pseudoplastic behavior. Panels were obtained from blends of wood processing byproducts (medium-density fiberboard -MDF) and the formulated bioadhesive by thermo-compression, optimizing the processing conditions. ATR-FTIR and SEM studies revealed the substrate-adhesive interactions and the affinity between the components. The stress values increased with BTCA concentration being 19 MPa for 80%, demonstrating the better cross-linking capacity of this acid compared to CA (11 MPa). Crosslinking and plasticizing effects were occurring in panels containing CA, depending on its concentration, as was confirmed by both puncture assays and contact angle. Thus, it was possible to obtain sustainable panels based on an eco-compatible adhesive, with distinguishable characteristics by tailoring both, the formulations and the processing conditions. [ABSTRACT FROM AUTHOR]

Despite the widespread application prospect of soybean meal flour (SF) as a non-toxic and renewable wood adhesive, the practical application is limited by its poor mechanical properties and water resistance. In this work, a novel SF-based wood adhesive (CSP) was developed using citric acid (CA) as a modifier, which was further designated to produce plywood on a laboratory scale. Moreover, the effects of the mass ratio of CA/SF, hot-pressing temperature, and hot-pressing time on the bonding properties and water resistance of the resulting plywood were investigated in detail. As a result, under the optimal hot-pressing conditions (180 °C, 5 min), high-performance plywood bonded by CSP (CA/SF = 15/100) adhesive was fabricated, whose dry shear strength, cold-water wet shear strength (20 °C for 24 h), and hot-water wet shear strength (63 °C for 3 h) reached 1.65 MPa, 1.99 MPa, and 1.58 MPa, respectively. Due to the easy preparation process, sustainability, and favorable properties, the proposed fully bio-based CSP wood adhesive has great potential for the large-scale fabrication of eco-friendly wood panels in industry. A citric acid - soy protein wood adhesive was feasibly developed to fabricate formaldehyde-free plywood with high mechanical properties and water resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

Biomass resources are widely considered potential alternatives to formaldehyde-based wood adhesives because of their abundance. In this study, an environmentally friendly biomass adhesive, carboxylated chitosan-glucose (CSC-G), was prepared using chitosan, maleic anhydride, and glucose. The structure and water resistance of the adhesive were analyzed in detail. Maleic anhydride act as a bridge connecting chitosan and glucose, giving the adhesive good water solubility and resistance. The improved water resistance of the CSC-G adhesive was attributed to the formation of covalent cross-linked structures and an increased degree of system cross-linking. Additionally, the curing temperature of the CSC-G adhesive was superior to those of previously reported polyester adhesives. This study not only expands the application scope of fishery waste, but also demonstrates its great potential for the preparation of high-performance plywood. [Display omitted] • A strategy of molecular chain extension was adopted to prepare the bio-based adhesive CSC-G. • The ester cross-linking structure endowed the adhesive with high shear strength and water resistance. • A feasible solution for the wide application of chitosan in wood adhesive was justified. [ABSTRACT FROM AUTHOR]

The research on hardwood lignin is quite limited for lignin-based adhesives due to its heterogeneity and chemical complexity compared with those of softwood and non-wood lignin. Herein, a novel approach of producing entirely bio-based and nontoxic wood adhesives by self-crosslinking of industrial hardwood kraft lignin (HKL) is presented to replace formaldehyde-based resin adhesives. The key issues of converting HKL to bio-wood adhesive are their low reactivity for crosslinking capacity and high heterogeneity. For this, HKL extracted from industrial black liquor was acetone fractionated to reduce its heterogeneity, resulting in acetone-soluble HKL (AS-HKL) and acetone-insoluble HKL (AI-HKL), which were then glyoxylated to facilitate crosslinking and form a three-dimensional network structure. Lignin samples were analyzed by gel permeation chromatography (GPC), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), 31P nuclear magnetic resonance (31P NMR), solid state 13C cross-polarization/magic angle spinning (13C CP/MAS) NMR, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The adhesive strength of lignin-based adhesives was evaluated by determining the tensile shear strength of plywood. In this current research the chemical structure changes especially the crosslinked structure and adhesion performance were investigated. Results showed that the self-crosslinking was successfully formed by ether bonds formation between glyoxalated lignin. Also, the self-crosslinked acetone insoluble hardwood kraft lignin fractionation (AI-HKL) showed the best adhesion performance. FTIR, XPS and 13C CP/MAS NMR spectra revealed new peaks and ether bonds in the glyoxylated lignin. Therefore, these results indicate a successful self-crosslinking of the hardwood kraft lignin after acetone fractionation and glyoxalation for adhesives via network formation. The glyoxalated AI-HKL (AI-HKL–GLY) exhibited the highest viscosity and provided the best plywood adhesion strength (0.8 MPa) among the adhesives, and showed a good potential as wood adhesives. Thus, the results suggest that the self-crosslinking of hardwood kraft lignin after a proper fractionation and glyoxalation is a promising approach of developing lignin-based bio-adhesives for wood bonding. [Display omitted] • Totally green adhesives were developed by self-crosslinking of fractionated and glyoxalated hardwood kraft lignin. • Self-crosslinking was successfully formed by ether bonds between the glyoxalated lignin. • The self-crosslinked lignin showed better thermal stability than the control. • The self-crosslinked lignin from acetone insoluble fraction showed the best adhesion in plywood. [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]

Highlights • Comparison of wood adhesives under quasistatic and cyclic mode II fatigue fracture. • Higher elasticity modulus adhesives perform better in mode II cyclic fatigue fracture. • Short polymer fibers in the adhesive improve the mode II fatigue fracture performance. • Compliance-based, visual and Acoustic Emission location yield consistent crack length. • A new algorithm reduces scatter in determining the delamination onset point. Abstract This paper investigates the energy release rate (ERR) in Mode II in-plane shear during delamination propagation under quasi-static and cyclic fatigue fracture loading with the 4-point end notched flexure (4-ENF) fracture test specimen. Wood joints bonded with three different adhesives, one rather brittle phenol resorcinol formaldehyde (PRF) and two different one component polyurethane (1C-PUR) adhesives with relatively low modulus of elasticity were tested in order to investigate the influence of the adhesive properties on the damage propagation under quasi-static and cyclic fatigue loading. A simple reduction method based on the specimens' compliance was used to calculate the crack growth and the energy release rate during the test. Additionally, an automated analysis method was developed estimating the energy of crack initiation from quasi-static test results. This shall avoid introducing additional scatter due to operator-dependent, manual analysis. It was shown that the three tested adhesives are displaying similar ERR values under quasi-static loading. Under cyclic fatigue fracture loading, the more brittle PRF samples are showing a slower crack growth rate for similar energy release rate in comparison with the 1C-PUR adhesives. The proposed testing method, applied to adhesively bonded wood joints, has been shown to give satisfactory results. This can be used for the development of new adhesives with increased performance regarding fatigue delamination growth. The automated data analysis has potential for application on other materials under cyclic Mode II fatigue fracture loads. [ABSTRACT FROM AUTHOR]

Highlights • The exudate extracts of the African trees Vachellia nilotica and Senegalia senegal were found to be effective hardeners of tannin adhesives. • The exudates contained no aldehydes and consisted of 2,5-dihydroxymethyl furan linked to carbohydrate chains. • On reacting with flavonoid tannins 2,5-dihydroxymethyl furan detached from the carbohydrate chain to react with the tannin and harden it. • They cross-linked pine tannin resin by reaction with the 2,5-dihydroxymethyl furan either separated or still linked to the carrying carbohydrate chains. • The particleboards dry Internal Bond strength results obtained were interior grade comparable to those obtained with control panels bonded with UF adhesives. Abstract A totally "bio" hardener derived from the exudate extract of the African trees Vachellia nilotica and Senegalia senegal was investigated. It hardened a maritime pine tannin resin without any obvious presence of an aldehyde thus obtaining a completely "bio" adhesive for wood panels. MALDI-ToF and CP MAS 13C NMR analysis indicated that the hardeners cross-linking species was 2,5-dihydroxymethyl furan linked onto carbohydrate chains. The hydroxymethyl furan moieties reacted both after detachment from the carbohydrate chains but also with carbohydrate chains still attached. The carbohydrates too were then involved as part of the binder. The gel times were slower than what was obtainable with paraformaldehyde but sufficiently fast to possibly be of industrial significance. [ABSTRACT FROM AUTHOR]

Timber-mortar composite structures require rigid, strong, but also ductile connections to optimize their performances. Up to now, the preferred connection systems were based on metal fasteners and notches in wood. In this study, an alternative approach based on a fully glued connection was studied (using an epoxy-based system), and a wood pre-treatment was applied in order to enhance the compatibility and the adhesion properties at the interface between beech wood and mortar. The wood surface was functionalized with a xerogel obtained by means of a sol-gel process, consisting of two layers of silane nanofilms – namely tetra-ethoxysilane and (3-Aminopropyl) triethoxysilane. Chemical analysis of the wood surface confirmed the chemical bonding of the silanes. Microscopy images revealed that the silane pre-treatment also affects adhesive penetration into the wood. In terms of mechanical properties, 3-point bending tests on pre-treated beech wood-mortar samples showed an improved load bearing capacity in comparison to unmodified wood-mortar specimens. [ABSTRACT FROM AUTHOR]

At present, environmentally friendly high-performance wood adhesives have received widespread attention. Glucose and tris(2-aminoethyl)amine (TAEA) were used as raw materials in this study. In the absence of catalysts, glucose-based wood adhesives with the hyperbranched crosslinking structure were prepared by the one-pot based on air oxidation and crosslinking copolymerization. The structures of the polymers were characterized by FT-IR, 13C NMR, LC-MS, and XPS. The results indicated that the interaction between glucose and TAEA is achieved through the dehydration reaction of carboxylic acid and primary amine, as well as the esterification reaction of carboxylic acid and alcohol. The hyperbranched polymer resin (GT) was successfully synthesized and used as a wood adhesive. The curing and thermal stability of GT adhesive were studied by DSC and TGA, and the results showed that GT had good thermal stability. The best-performing GT adhesive was screened by changing the molar ratio of tris(2-aminoethyl)amine/glucose and reaction time using the controlled variable method. The prepared GT adhesive has reached the national standard GB/T 17657-2013 (≥0.7 MPa) through the test of adhesive strength and water resistance. The dry shear strength of the plywood reached 1.97 MPa, and the strengths were 1.64 MPa and 1.31 MPa after immersion in hot and boiling water for 3 h. The experimental process is simple and green and the prepared hyperbranched glucose-based adhesive has excellent performance. Therefore, it has potential application prospects as a formaldehyde-free wood adhesive. [Display omitted] • Glucose based boiling water resistant adhesives with good performance. • Air oxidation and crosslinking copolymerization strategy. • Green to synthesize environmentally friendly wood adhesives in one step. [ABSTRACT FROM AUTHOR]

Both increasing environmental issues and the lack of fossil resources have increased the importance of wood-based natural fiber composites. Therefore, high performance, sustainable, and environmentally-friendly bio-based wood adhesives are highly desirable. We developed a new biomass adhesive based on aminated cellulose (AC) and oxidized sucrose (OS), and reinforced it with an activated wood interface to improve its bonding performance. To this end, the natural wood interface (NWI) was customized with an epoxy group to produce the epoxy-functionalized wood interface (EFWI), one end of which is tethered to the wood surface. The epoxy group at the other end reacts with the amino group of AC, resulting in hydrophobicity and forming new covalent bonds in the adhesive layer, such as -Si-O-Si-, -Si-O-C-, -C-N-C-, and -O-C-C- bonds. Characterization of the adhesive interface is realized by FTIR, 13C NMR, XPS, XRD, and SEM. Dry and wet shear strengths are also investigated by tensile shear strength measurements in China National Standards (GB/T 9846-2015). Results show that OS-AC adhesives have better dry and wet shear strengths at EFWI in comparison with those on NWI, reaching 2.52 and 1.48 MPa, respectively. Thus, the construction of a functionalized wood adhesive interface dramatically enhances the bonding strength and water resistance of biomass adhesives. This study provides new insights for developing renewable, low cost, and green bio-based wood adhesives by chemical modification of the wood interface. Schematic diagram for the design and construction of strong wood bonding via chemical bond between epoxy-functionalized wood surface and cross-linked OS-AC bio-based adhesive. [Display omitted] • Biomass adhesive based on cellulose-sucrose cross-linked network was developed. • Bonding performance was reinforced with functionalized wood interface. • OS-AC adhesive has better shear strengths at EFWI in comparison with that on NWI. • Functionalized wood interface enhances the water resistance of the biomass adhesive. [ABSTRACT FROM AUTHOR]

Quantitative analysis of interface mechanical properties of wood laminate composites has been an urgent task of the interface mechanics, however, which is hindered by the lack of knowledge of the correlation between physiochemical structure and micromechanics of the whole wood bonding interphase. This work aimed to evaluate the influence of adhesive distribution with different variables (i.e., adhesive types, grain directions, and cells from the glue line) on the transforming interface properties. The results showed that the physiochemical structure and micromechanics performance were significantly affected by adhesive types, grain directions, or wood cells with the interphase microstructure of earlywood laminates being more sensitive to adhesive penetration than that of latewood laminates. The Phenol-formaldehyde (PF)-laminated interphase possessed a more complicated resin behavior and distribution, and microstructure compared to the one component polyurethane (1C-PUR)-laminated interphase. The distribution of resins near the glue line could recover and enhance the loss of the Er caused by the pressing and machining process. Compared with the control cells (C 1 , C 2), the improved range of Er and H are 9.2%–41.2% and 6.7%–22.2% for the PF-laminated interphase, respectively, and 1.7%–27.6% and 2.1%–8.5% for the 1C-PUR-laminated interphase, respectively. This improvement was mainly attributed to chemical fixing and physical filling into nanopores and physical supporting within cell walls, which could avoid the stress concentration to a different extent and protect the cell walls from the compressive deformation. The initial cracks probably resulting from the machining and/or shear slipping during the pressing process, could incur the global failure of wood laminates interphase. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents an overview of research and results about tailoring crystalline and amorphous form polylactic acid (PLA) polymer resin for use as an adhesive for joining a range of substrates, production of wood-based composites plywood and particle wood-based composites, and, for potential use for elevated temperature applications as for wood structures when subject to fires. The range of substrates successfully joined (with and without bio-plasticizer) ranges from metals, woods, glasses, ceramics, stones, and bricks to synthetic fluoro-polymers. Tensile bond strength for steel-to-steel bonding ranged towards 40+ MPa; superior (over 100%) bonding strength was obtained compared with EVA and other standard adhesives for wood and metal surfaces. Three successful industrial product arenas are described: 3-ply composite plywood panels meeting water soak and shear strength industry metrics; particle boards meeting-exceeding rupture strength, elasticity, and water resistance metrics similar to those expected from urea-formaldehyde based adhesive but without VOC release limitation, PVC-free luxury flooring tiles which meet strict requirements for wear cycles, distortion-free adhesion peel strength; and, production of renewable particle boards with elastic modulus and internal bond strengths comparable with boards made with urea formaldehyde. Thermal and gamma ionizing radiation research results are discussed to tailor key adhesive-relation properties: adhesion strength, viscosity, flow rate, molecular weight, hardness, flexibility, and friability. Scoping studies on radiation-based tailoring with a cross-linking agent were found to permit up to 30% improvements in bond strength as well as for enabling application as an adhesive for elevated (100 °C+) temperature applications with ∼30–50% higher operating temperatures compared with commonly used adhesives. A discussion is included about the remaining challenges and recommendations for further research. [ABSTRACT FROM AUTHOR]

Wood composites often exhibit weak interaction between urea-formaldehyde (UF) and wood, leading to edge warping and cracks at the bonding interphase. To address this issue, the high-voltage electric field (HVEF) has been effectively employed to enhance the bonding strength of wood composites. This study aims to further investigate the bonding process and the mechanism of bonding enhancement under HVEF treatment by examining the physicochemical characteristics, curing reaction of UF adhesive, and dynamic wetting behavior on the wood tangential section. The chemical reaction and bonding strength at the bonding interphase were also examined. The results revealed that the HVEF treatment increased the polarization extent of the adhesive molecules, resulting in variations in the physical properties of the adhesive. Particularly, a higher enthalpy during the adhesive curing reaction was observed, with an 85% increment observed under the N–P(−) condition. The FTIR spectra showed an increased peak intensity of UF main chemical bonds and a higher extent of chemical interaction between wood and UF functional bonds under HVEF treatment. These findings can be attributed to higher degrees of molecule activation and cross-linking between wood and UF. Furthermore, the HVEF treatment led to a decreased absorption ratio of UF and an increased wet/dry wood bonding strength of the two-layer composite. The absorption ratio of UF exhibited the highest decrement of 36%, while the wet/dry wood bonding strength showed the highest increment of 85%/100% under the N–P(−) condition. This study emphasizes the significant role of higher extents of UF polarization, activation, and cross-linking with wood in enhancing the bonding strength of HVEF-treated wood composites. [ABSTRACT FROM AUTHOR]