Formaldehyde-based Adhesives Research Articles

Epoxy as an Alternative Resin in Particleboard Production with Pine Wood Residues: Physical, Mechanical, and Microscopical Analyses of Panels at Three Resin Proportions

Given the construction challenges and the impacts of industrial waste generation and the implications of using chemical adhesives, this study aims to evaluate epoxy as an alternative resin, whose application in the production of wood particleboards is still underexplored. In this regard, its results were compared with those of widely used adhesives, such as urea-formaldehyde (UF). Pine wood particles were used, and epoxy resin was applied as a binder in 5%, 10%, and 15% proportions. Panels were manufactured under pressing parameters of 5 N/mm2 for 10 min at 110 °C. Physical and mechanical properties of panels were evaluated using Brazilian, European, and American standards. The results showed that epoxy resin is potentially convenient for the particleboard industry, as the 15% trait panels met the P4 class criteria in the Brazilian and European standards and D-2 for the American code, and the 10% trait panels achieved the M-3i class for the American document. Although 5% adhesive was insufficient to envelop wood particles, these traits with greater percentages reached high enveloping ratings in the scanning electron microscopy (SEM) test, making epoxy resin viable for the panel industry as a potential alternative to formaldehyde-based adhesives.

Carbon nanotubes (CNTs) and graphene oxide (GO) hybrid enhanced canola protein isolate (CPI) bioadhesive for interior wood applications

Growing concerns over the use of carcinogenic formaldehyde-based wood adhesives drive the need for sustainable alternatives. This study explores a novel nanocomposite adhesive made from canola protein isolate (CPI), reinforced with carbon nanotubes (CNTs) and graphene oxide (GO), to enhance bio-based adhesive performance. CNTs contribute mechanical strength, electrical conductivity, and thermal stability, while GO provides a large surface area, good dispersibility, and enhanced adhesion. The synergistic interaction between these nanomaterials significantly improves the adhesive properties of CPI. The study examined the impact of varying CNT-GO ratios on CPI’s adhesive strength under dry, wet, and soaked conditions. Results showed a positive correlation between increasing CNT-GO concentrations and adhesive performance. The adhesive strength markedly increased at a 0.5/0.5 (CNT/GO) ratio, especially in dry conditions. The optimal shear strength, however, was observed at a 0.3/0.7 ratio across all conditions. The thermogravimetric analysis confirmed that higher CNT-GO ratios enhanced the thermal stability of the nanocomposite, as indicated by increased weight loss percentages. This reflects improved resistance of the CPI matrix to thermal degradation. These findings highlight the importance of optimizing CNT-GO ratios for superior performance under diverse conditions. Overall, this study demonstrates the potential of CPI-CNT-GO nanocomposites as more sustainable alternatives to traditional formaldehyde-based adhesives, offering a promising solution to reduce the environmental and health risks associated with conventional wood adhesives.

Mussel byssus cuticle-inspired low-carbon footprint soybean meal adhesives with high-strength and anti-mildew performance

Bio-based adhesives, because of their prominent non-toxic and sustainable properties, have attracted great attention to replace conventional formaldehyde-based adhesives. However, most bio-adhesives have poor bonding properties and antimildew stability, which seriously hinder the practical application. Herein, a coordination structure-enhancement method for the preparation of bio-based adhesives was developed that avoids the use of large amounts of crosslinking agents and produces new bio-based adhesives with good properties. The wet bonding strength of this adhesive manufactured by introducing mussel byssus cuticle-inspired complexes (FeTA) and glycerol triglycidyl ether (GTE) is as high as 1.05 MPa, far exceeding that of pure soybean meal adhesive. In addition, the resulting adhesives showed superior thermal stability and mildew resistance. Life cycle assessment results indicate that the novel adhesive production process has a minimal environmental impact. Overall, this environmentally friendly bio-based adhesive demonstrated in this study could be a promising substitute for petrochemical-based formaldehyde adhesives.

Reactive hyperbranched core-shell architecture for developing high-performance bio-based adhesive

Soybean meal (SM) adhesives offer a promising alternative to formaldehyde-based adhesives; however, their broader application is hindered by suboptimal adhesive properties and inadequate water resistance. In this study, we designed a novel reactive core-shell architecture (DAS@HBPA/EP) composed of dialdehyde starch (DAS) as the core and hyperbranched epoxy (HBPA/EP) as the shell, aimed at developing an SM adhesive with excellent water resistance, high bonding strength, and superior toughness. The reactive shell of DAS@HBPA/EP formed covalent bonds with protein molecules in SM, creating a highly interconnected structure that enhanced both the adhesive properties and water resistance of SM. Additionally, the microphase separation induced by the DAS core and the flexible hyperbranched shell provided the SM adhesive with improved toughness. As a result, plywood bonded with the SM/DAS@HBPA/EP adhesive exhibited exceptional dry shear strength (up to 2.14 MPa) and wet shear strength (1.24 MPa), representing a 589 % improvement over the pure SM adhesive. This performance is comparable to commercial melamine-urea-formaldehyde (MUF) resins (E0 grade). Furthermore, the SM/DAS@HBPA/EP adhesive showed a high residue rate (82.30 %) and low water absorption rate (0.94 %), along with a uniform and dense microstructure. This simple and cost-effective strategy presents a novel approach to advancing technological innovation in the development of multifunctional composite materials.

A high-strength, environmental-friendly, and multifunctional soy protein adhesive inspired by biomineralization

Soy protein is an economical and eco-friendly adhesive material that offers significant potential for the development of bio-based adhesives. However, they have poor water resistance, low bonding strength, mold-susceptibility, and deterioration, which are serious challenges to the widespread application of soy protein adhesives in plywood. This work was inspired by the biomineralization phenomenon and the preparation of a novel soy protein adhesive (SPI-RGT-AgNPs). The SPI-RGT-AgNPs adhesive exhibited excellent viscosity, residual rate, and moisture absorption performance compared with the original soy protein isolate (SPI) adhesive, with an increase from 37° (SPI) to 81° (SPI-10RGT-10AgNPs) in water contact angle testing. The dry and wet adhesion strengths reached 2.49 MPa and 1.43 MPa, 193 % and 117 % higher than SPI adhesive, respectively. Molecular docking simulations were used to verify that the introduction of modifiers significantly improved the stability and crosslinking strength of the adhesive. The best ratio of the SPI-RGT-AgNP adhesive was confirmed using the response surface methodology (RSM). Simultaneously, SPI-RGT-AgNPs adhesive also showed excellent anti-mildew and anti-microbial efficiencies to Escherichia coli (98.18 %) and Staphylococcus aureus (99.33 %). In addition, a life-cycle assessment was used to explore the pollution emissions from the adhesives. As compared to formaldehyde-based adhesives, the SPI-RGT-AgNP adhesive had lower energy consumption and pollution emissions. Therefore, this study prepared a novel high-strength and multifunctional soy protein adhesive, guiding the production of multifunctional and green adhesives.

A Potential Replacement to Phenol–Formaldehyde-Based Adhesives: A Study of Plywood Panels Manufactured with Bio-Based Wood Protein and Nanolignin Adhesives

A Potential Replacement to Phenol–Formaldehyde-Based Adhesives: A Study of Plywood Panels Manufactured with Bio-Based Wood Protein and Nanolignin Adhesives

Cold-set, crosslinker-free wood adhesives: A comparative study of ultrasound-extracted duck feather keratin and traditional food proteins

This study investigates the potential of keratin, a waste from duck feathers, as a sustainable alternative for wood adhesive applications. Keratin was extracted by sonochemical hydrolysis, a green and innovative method. Keratin was compared in its properties with casein, soybean, and pea proteins, three of the most studied proteins, as alternative eco-friendly materials to petroleum-derived products. However, these proteins remain used in the food industry. Protein-based adhesives were activated with sodium and calcium hydroxide. A comprehensive analysis was also conducted to study the influence of solid content, alkali, pH, viscosity, polarity, and structural composition of adhesives on their mechanical properties. The thermal properties of proteins and adhesives and the effects of post-alkaline treatment on protein secondary structure, crosslinking, and water resistance were studied. The key finding is that keratin shows potential as an eco-friendly adhesive, with tensile shear strength tests on beech wood meeting European standards. In addition, it showed superior water resistance due to its effective crosslinking ability compared to other food-derived proteins. The results position keratin as a feasible replacement for food-derived and formaldehyde-based adhesives, offering a sustainable option for interior wood applications and presenting an environmentally friendly solution with appropriate performance.

Development of environmentally friendly glyoxal-based adhesives with outstanding water repellency utilizing wheat gluten protein

To reduce the release of volatile organic compounds (VOCs) from formaldehyde-based adhesives at the source, the use of low-toxicity and biodegradable glyoxal instead of formaldehyde for the preparation of novel urea-glyoxal resins is a simple and promising strategy. The limited water resistance and adhesive strength of the new urea-glyoxal resins (UG) restrict their extensive application. This study prepared a high-performance, water-resistant WP-UG wood adhesive by combining UG prepolymer with wheat gluten protein (WP). FTIR, XRD, and XPS confirmed the existence of a chemical reaction between the two components, and thermal analysis showed that WP-UG plywood had better thermal stability. Evaluation of the gluing properties revealed that the dry and wet strengths of WP-UG adhesive bonded plywood reached 1.39 and 0.87 MPa, respectively, which were significantly higher than those of UG resin by 35 % and 314 %. The bond strength increased from 0 to 0.89 MPa after immersion in water at 63 °C for 3 h. The results indicated that the introduction of WP promoted the formation of a more complex and tightly packed crosslinking network and developed a glyoxal-based adhesive with high bond strength and water resistance. This study provides a new green pathway for novel urea-formaldehyde binders to replace harmful formaldehyde-based binders, which helps to increase their potential application value in the wood industry.

Structure and properties of a green high-strength rapeseed protein-based adhesive

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.

Development of bentonite-based organo-geopolymer hybrid wood binder

The study addresses concerns associated with formaldehyde-based adhesives in wood panel board production by proposing geopolymer-based wood binders as promising, formaldehyde-free alternatives. Using bentonite, the research delves into the development and performance properties of this geopolymer wood binder. The BET method was employed for the surface characterization of precursor raw materials for binder preparation. Si and Al elements identified through XRF analysis were correlated with characteristic bands in the FTIR spectrum. Alkaline activation solutions, employing sodium silicate and sodium hydroxide with a molar ratio range of 0.5 to 2.5 (SiO2:Na2O), revealed that binders with a molar ratio of 2.5 exhibited lower pH and higher adhesion strength. Different geopolymer formulations at solution to powder ratios (s/p) of 1.33, 3, and 3.5 determined s/p 3.5 as optimal for bentonite-based organo-geopolymer binders. Viscosity, gel time, pH, and solids content were examined, showing the effectiveness of substituting 10% silica fume to enhance the geopolymerization process and improve adhesion. Modifications using citric acid, sucrose, paraffin, pMDI, triacetin, and resorcinol demonstrated wet bonding strength comparable to urea formaldehyde adhesive. Analytical techniques, including FTIR spectroscopy, XRD analysis, and SEM EDX analysis, provided insights into functional groups, crystallographic properties, and microstructural characteristics. The concentration of Si and Al compounds on the bonding line, coupled with Na element diffusion, was observed through these analyses. Light microscopy of lap shear samples revealed a thinner bonding line, affirming effective binder penetration into wood cell lumens in bentonite-based organo-geopolymer binder formulations.

Surface Roughness, Dynamic Wettability, and Interphase of Modified Melamine Formaldehyde-Based Adhesives on Jabon Wood.

The surface roughness and wettability of wood are critical aspects to consider when producing laminated wood products with adhesive applications. This study aims to investigate the surface roughness and dynamic wettability of Jabon wood in the presence of melamine formaldehyde (MF)-based adhesives. Commercial MF adhesives (MF-0) and modified MF adhesives (MF-1) were applied to Jabon wood, which includes tangential (T), radial (R), and semi-radial (T/R) surfaces. The surface roughness of Jabon wood was assessed using a portable stylus-type profilometer. The low-bond axisymmetric drop shape analysis (LB-ADSA) method was employed to identify the contact angle (θ) of the MF-based adhesives on Jabon wood. The wettability was determined by evaluating the constant contact angle change rate (K value) using the Shi and Gardner (S/G) model. Dynamic mechanical analysis (DMA) was employed to investigate the viscoelastic characteristics of the interphase analysis of the wood and MF-based adhesives. The roughness level (Ra) of the Jabon board ranged from 5.62 to 6.94 µm, with the T/R having a higher level of roughness than the R and T. MF-0 exhibited a higher K value (0.262-0.331) than MF-1 (0.136-0.212), indicating that MF-0 wets the surface of Jabon wood more easily than MF-1. The wood-MF-0 interphase reached a maximum stiffness of 957 N/m at 123.0 °C, while the wood-MF-1 had a maximum stiffness of 2734 N/m at 110.5 °C. In addition, the wood-MF-0 had a maximum storage modulus of 12,650 MPa at a temperature of 128.9 °C, while the wood-MF-1 had a maximum storage modulus of 22,950 MPa at 113.5 °C.

Desirable Strong and Tough Adhesive Inspired by Dragonfly Wings and Plant Cell Walls.

The production of wood-based panels has a significant demand for mechanically strong and flexible biomass adhesives, serving as alternatives to nonrenewable and toxic formaldehyde-based adhesives. Nonetheless, plywood usually exhibits brittle fracture due to the inherent trade-off between rigidity and toughness, and it is susceptible to damage and deformation defects in production applications. Herein, inspired by the microstructure of dragonfly wings and the cross-linking structure of plant cell walls, a soybean meal (SM) adhesive with great strength and toughness was developed. The strategy was combined with a multiple assembly system based on the tannic acid (TA) stripping/modification of molybdenum disulfide (MoS2@TA) hybrids, phenylboronic acid/quaternary ammonium doubly functionalized chitosan (QCP), and SM. Motivated by the microstructure of dragonfly wings, MoS2@TA was tightly bonded with the SM framework through Schiff base and strong hydrogen bonding to dissipate stress energy through crack deflection, bridging, and immobilization. QCP imitated borate chemistry in plant cell walls to optimize interfacial interactions within the adhesive by borate ester bonds, boron-nitrogen coordination bonds, and electrostatic interactions and dissipate energy through sacrificial bonding. The shear strength and fracture toughness of the SM/QCP/MoS2@TA adhesive were 1.58 MPa and 0.87 J, respectively, which were 409.7% and 866.7% higher than those of the pure SM adhesive. In addition, MoS2@TA and QCP gave the adhesive good mildew resistance, durability, weatherability, and fire resistance. This bioinspired design strategy offers a viable and sustainable approach for creating multifunctional strong and tough biobased materials.

Characteristics of Eco-Friendly and Sustainable Plywood Adhesive derived from Low-Quality Cat’s Eye Damar Resin

Wood panel products mainly use formaldehyde-based adhesives that release free formaldehyde and potentially cause health problems. This study aimed to develop a free-formaldehyde adhesive from cat’s eye damar (CED) resin as an alternative adhesive for plywood production. The low-quality CED resin was used to increase the added value of the resin. The adhesive formulation consists of a ratio of 30:70 (CED:benzene) dissolved for 15 minutes at 45°C. The plywood was manufactured using glue spread rates of 200, 250, and 300 g/m2 with an addition of 10% tapioca flour and hot pressed using a pressure of 2.45 MPa at 120°C for 6 minutes. The CED-based adhesive produced has a solid content of 28.76%, a pH value of 5.93, a gel time value of 70.05 minutes, and a viscosity value of 4.02 mPa.s. Fourier-transform infrared spectroscopy analysis stretching of the C-H group, indicating an alkane compound. Plywood’s physical and mechanical properties bonded with CED-based adhesive increased with higher glue spread application. Utilizing a glue spread of 300 g/m2 could produce plywood with comparable physical and mechanical properties to the urea-formaldehyde-bonded plywood. Keywords: cat’s eye damar, dynamic mechanical analysis, formaldehyde-free adhesive, plywood, Shorea javanica

Cottonseed protein bioadhesive with high adhesion performance achieved by a synergistic dual-crosslinking strategy

Plant adhesives have great potential as substitutes for formaldehyde-based adhesives due to their environmental friendliness, low cost, and nontoxicity. However, the application of this type of adhesive is challenged by its water resistance. Herein, an environmentally friendly bioadhesive was prepared from biomaterials, including waste cottonseed protein and sawdust. Isophorone diisocyanate (IPDI) and oxidized cellulose (OC) were used as double crosslinking modifiers. A protein-based bioadhesive with excellent adhesive properties and stable hydrothermal resistance was produced. The impact of IPDI and OC on the crosslinking network was evaluated by detailed Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry analysis. It was found that IPDI and OC, as crosslinking agents, synergistically improved the dry and wet bonding strength of the adhesive. At the optimal loadings of 10% OC and 20% IPDI, the wet bonding strength of the adhesive reached 1.55 MPa on average, which is more than twice that of the Chinese Type II plywood adhesive standard (0.7 MPa). The dry bonding strength also increased to 2.67 MPa with this addition. The improvements in bonding strength as well as the water-resistance of the bioadhesive were ascribed to the formation of a dual-crosslinking network between the IPDI, OC, and cottonseed protein. Both protein-oxidized cellulose and protein-isophorone diisocyanate crosslinking networks were formed in the adhesive system, tightly combining the adhesive components. Thus, the biodegradable adhesive developed in this work provides an effective and convenient approach for the development of all-biomass-derived adhesives, and the constructed high-performance adhesive presents potential application for sustainable wood products.

Preparation and Characterization of Carbon Nanotubes Enhanced Canola Protein Isolate (CNT/CPI) Bio-Adhesive for Wood Application

The current wood adhesives technologies rely mainly on formaldehyde-based adhesives produced from petrochemicals. Moreover, these adhesives are derived from non-renewable sources is known to be carcinogenic together with other serious health effects. Therefore, there is an increasing interest in the use of renewable and biodegradable sources for the evolution of an environmentally friendly adhesives for interior wood applications.The canola meal (the remnant after oil extraction from the canola seed) contains about 36 – 39% (8.5% moisture basis) can be used as a low value feed for the animals. Moreover, its protein content is currently exploring other applications such as in the adhesive technology and it can be used as an alternative to the widely used formaldehyde-based adhesives. Canola proteins (CP) as adhesives have many unique properties such as ease of handling, low cost, low pressing temperatures, and the ability to bind wood with relatively high moisture content. On the other hand, it has relatively low adhesion strength and low water resistance which are the major drawbacks. This study will address these issues by modifying CP adhesive with carbon nanotubes (CNT). CNT are one of the most encouraging strengthening nanofillers with the extraordinary tensile modulus and strength, it has been proved to significantly improve the physical and mechanical properties of the nanocomposites. Generally, this study will intend to improve the water resistance and adhesive strength of the CP adhesive by incorporating different concentrations of the CNT into the protein matrix.This study is made up of two parts: incorporation of CNT and functionalized CNT (FCNT) into the CP matrix. Incorporation of CNT at 1% (w/w) enhanced the adhesive strength from 5.98, 1.80, and 5.42 to 9.20, 5.64, and 7.44 at percentage increment of 53.85, 213.33, and 37.27% for dry, wet, and soaked strength respectively. The presence of carbonyl group in the CNT after purification as well as the polyvinylpyrrolidone (PVP) helped to attain this improvement in the water resistance and adhesion.In the second part, functionalization of the CNT greatly improved the shear strength at 1% FCNT concentration to 10.62, 8.10, and 8.13 at 77.59, 350, and 50% increase for dry, wet, and soaked strength respectively. The introduction of the carboxylic group by functionalization significantly improved the mechanical and thermal properties of the CP due to a proper dispersion giving rise for a better hydrophobic and cohesive interactions between the wood and adhesive.These results proved an enhanced water resistance and adhesion of the CP contributed by the CNT and its functionalization.

Development of eco-friendly antifungal and antibacterial adhesive derived from modified cassava starch waste/polyvinyl alcohol containing green synthesized nano-silver

Environmentally friendly biopolymer-based wood adhesives are an inevitable trend of wood product development to replace the use of harmful formaldehyde-based adhesives. In this research, a new eco-friendly modified cassava starch waste-based adhesive via carboxymethylation (CMS), and blending with polyvinyl alcohol (PVA), tannic acid (TA) and green synthesized silver nanoparticles (AgNPs) was prepared. The effects of TA content on green synthesis of AgNPs (Ag-TA) and bio-adhesive nanocomposite properties were investigated. The use of 5 wt% TA for AgNPs synthesis (Ag-TA-5) resulted in a uniform particle size distribution. The plywood prepared with Ag-TA-5 provided the highest dry and wet shear strength at 1.95 ± 0.11 MPa and 1.38 ± 0.3 MPa, respectively. The water absorption and thickness swelling of this plywood remarkably decreased up to 10.99% and 6.79%, respectively. More importantly, the presence of Ag-TA in CMS/PVA adhesive successfully inhibited the invasion of mold and bacteria. Based on the cyclic delamination test, the adhesive bond durability of bio-adhesive containing Ag-TA-5 could meet the requirement of the AITC Test T110-2007 and was comparable to commercial adhesives. The added advantage of the prepared bio-adhesive was its synthesis from agro-waste products and possible economically viable production at industrial level.

Developing multifunctional and environmental-friendly hot-pressed peanut meal protein adhesive based on peanut waste

Hot-pressed peanut meal protein (HPMP) adhesives showed great potential as an alternative to formaldehyde-based adhesives because of their renewability and environmental-friendly, but their practical applications are severely limited by the poor bonding strength, water resistance and anti-mildew properties. Inspired by the spider leg structure, the functional graded peanut shell fiber (Ag/ZnO@APSF) loaded with metal nanoparticles was constructed through the biomineralization strategy as mineralized skeleton; Luteolin Epoxide (LE) as crosslinking agent. We had developed a green strategy for fabricating a novel HPMP adhesive with strong water resistance, high bonding strength, and strong mold resistance was prepared through a steel bars-concrete network structure using peanut waste, Ag/ZnO@APSF and LE. Compared with pure HPMP adhesive, the dry shear strength and wet shear strength of adhesive increased by 114% (2.29 MPa) and 257.9% (1.36 MPa), respectively. The residual rate increased by 43.8%, the moisture absorption rate and viscosity decreased by 48% and 45.4%, respectively. The adhesive had excellent flame retardancy with a reduction of 35.2% in peak heat release rate and 28.4% in total heat release rate, respectively. The antimildew time increased from 1 d to more than 45 d. In addition, the HPMP adhesive exhibited long-term adhesion behavior (pot life of 14 d), the pre-pressing bonding strength increased by 175.7% (1.02 MPa). This strategy had enhanced the added value of peanut waste and contributed to the development of multifunctional new plant protein adhesives.

Fabrication of strong and tough multifunctional soy protein adhesives via constructing catechol-iron ion fiber-reinforced hierarchical structure inspired by mussel byssus

It is challenging to prepare strong and tough soy protein (SP) adhesives with multifunction to replace formaldehyde-based adhesives. Herein, inspired by the catechol-iron ion (Fe3+) fiber-reinforced hierarchical structure of the mussel byssus, the tannic acid-functionalized cellulose nanofiber (CNF-TA) was used to mimic the fibrous core and catechol derivative, ferric chloride mimicked the Fe3+, and the SP mimicked the protein matrix in the mussel byssus to fabricate a multifunctional SP adhesive with high strength and toughness. Due to the construction of a stable fiber-reinforced covalent crosslinked network, along with the energy dissipation of sacrificial coordination and hydrogen bonds, the dry shear strength and fracture toughness increased by 130.6% and 247.1% to 2.49 MPa and 1.18 MJ m−2, respectively. Furthermore, the water-resistant wet shear strength rose by 264.1% to 1.42 MPa benefiting from the stable crosslinked structure. The Fe3+-induced organic-inorganic hybrid structure imparted the adhesive with outstanding flame retardance. Moreover, the adhesive also exhibited excellent antibacterial properties, mildew resistance, and oxidation resistance. This research offers a viable biomimetic method for fabricating multifunctional high-performance bio-based adhesives, hydrogels, and composites.

A sustainable tannin-citric acid wood adhesive with favorable bonding properties and water resistance

Wood-based panels have been widely used in our daily life, whose performances are mainly determined by wood adhesive. However, the commonly-used formaldehyde-based adhesives nearly confront the challenge of formaldehyde release. In this paper, a novel bio-based adhesive tannin-citric acid (TCA) adhesive was prepared from tannin (TA) and citric acid (CA). The preparation parameters, such as mass ratios of CA/TA, hot-pressing temperatures, and hot-pressing time, for synthesizing the TCA adhesives and preparing the plywood were optimized. When the mass ratio of CA/TA was 0.6/1, the hot-pressing temperature was 200 °C, and the hot-pressing time was 4 min, the plywood bonded by TCA adhesive showed favorable performances with dry strength, cold water (20 °C) strength, and hot water (63 °C) strength of 1.27 MPa, 1.25 MPa, and 1.40 MPa, respectively. These properties are satisfied with the Chinese National Standard (GB/T 17657–2013). For its sustainability and feasibility, the prepared TCA adhesive shows great potential for preparing high-performance wood-based panels in industry.

Development and performance of particleboard from various types of organic waste and adhesives: A review

Environmentally friendly or green building materials are more commonly used in the construction industry and furniture making industry. The knowledge of the environmental risks including the depletion of natural resources, the impact of pesticides, as well as the amplifier and enforcement criteria of good practice have led to an increase in the practice of recycling waste materials, and in particular, the recycling of abandoned trees in particleboard production. From the adhesive aspect, in view of future constraints of formaldehyde use, suitable alternatives to formaldehyde-based adhesive systems would have to be developed and implemented in the wood processing industry. The present review represents a critical appraisal of various organic wastes and adhesives used as raw materials in particleboard development. The core of this review is an assessment of physical and mechanical properties of particleboards based on various types of organic waste and adhesive. Based on these data, we evaluated their potential to identify suitable alternative raw materials having a certain probability to meet the requirements of a large-scale industry sector. Characteristics such as density, thickness swelling, modulus of rupture (MOR) and modulus of elasticity (MOE) are significant in the studies carried out by researchers worldwide. However, they also depend on the types of raw materials, adhesives, parameters and indicators used throughout particleboard production. As an overall conclusion, some organic wastes have the potential to replace wood fibers as raw materials in particleboard production with similar performances. Natural-based adhesives have also shown the potential to substitute formaldehyde-based adhesives in terms of performance. However, toxicological investigations should be performed before a decision can been made to ensure they are safe and add value as replacements for formaldehyde-based adhesives.