Melamine Urea Formaldehyde Resin Research Articles

Effect of pH Value on the Structure and Properties of n-Eicosane@Melamine Urea-Formaldehyde Phase Change Microcapsules

In this article, n-eicosane@MUF phase change microcapsules were prepared by in-situ polymerization with n-eicosane as the core material and melamine urea-formaldehyde (MUF) resin as the shell material. The effects of pH values from 3.5 to 6.0 on the surface morphology, particle size distribution, latent heat of phase transformation, encapsulation degree, thermal stability, and permeability resistance of the microcapsules were investigated. The results showed that the surfaces of the microcapsules gradually became smooth with the increase of pH value, and their encapsulation degree and impermeability also increased roughly. When the pH = 5.5, the particle size of the microcapsule samples ranged from 1.5 to 9.7 μm, the melting enthalpy was 178.8 J/g, and the encapsulation degree was 86.6%, which had the best thermal stability and impermeability. However, when the pH = 6.0, the phenomenon of microcapsule shell rupture occurred and the above performance no longer occurred.

Material properties of particleboards produced from Ciol®-treated wood shavings

ABSTRACT This study investigated the potential of wood particles from Ciol®-treated wood in particleboard production. Ciol® is a renewable formulation from water, citric acid, and sorbitol, which has been commercially developed as a promising alternative for wood modification. Radiata pine wood was impregnated with 60% and 85% concentrations of the Ciol® solution for 150 mins. The impregnated boards were cured and subsequently planned. Particleboards were thereafter produced from the wood shavings using urea formaldehyde (UF) and melamine urea formaldehyde resin (MUF). The boards were produced with or without the use of ammonium nitrate as a hardener. The wood particles and produced boards were characterized via analytical techniques and standard test methods. The effect of Ciol® treatment and its concentration on the properties of the shavings and the particleboards was investigated as well as the effect of the resin type on the panel properties. The use of MUF without the hardener gave the best bending strength of 13 N/mm² and modulus of elasticity of 3187 N/mm². However, there was no significant difference in the results obtained when the hardener was added to MUF resins. Recycling Ciol®-treated wood shavings in particleboard production proved to be a promising approach with MUF resins.

Surface property enhancement of impregnated paper decorative panel by MUF-polyelectrolyte complex@Nano-Al2O3 blending

The surface properties of melamine-urea-formaldehyde (MUF) impregnated paper decorative panels are unsatisfactory, characterized by brittle surfaces, poor abrasion resistance, and limited flame retardancy. A modification was introduced to the MUF resin by incorporating a blend of polyelectrolyte complex polyethyleneimine (PEI)-phytic acid (PA) and Nano-Al2O3 with the aim of enhancing the surface properties of the decorative panel. The modified resin underwent characterization, and subsequent analyses were conducted to investigate the properties of both the modified impregnated paper and the decorative panel. The results showed that the thermal stability of the modified resin was improved with a curing temperature of 124 °C. In comparison to the control, the modified impregnated paper showed an increase of 146.0 % in tensile strength and 154.5 % in elongation at break. The improved toughness of the modified MUF-impregnated paper resulted in a notable upsurge in both surface bond strength and cracking resistance of the decorative panel. The combustion test results indicated that the modified impregnated had a LOI value of 40.0 % and self-extinguishing behavior. In addition, due to the inclusion of Nano-Al2O3, the decorative panel exhibited a low abrasion value of only 14.1 mg/100r. Overall, the technology proposed in this study can improve the surface properties of decorative panels, increase their added value, and provide a new strategy for modifying MUF resin in the impregnated paper-decorated wood-based panels industry and for researchers.

Industrial-scale manufacturing of particleboards using agricultural waste camellia oleifera shells

The search for materials made from renewable resources and free of toxic substances is a global trend towards cleaner production, which can be extended to the development of wood-based panels. However, the industrial sector of wood-based panels has been facing several gaps and challenges related to the shortage of wood raw materials for panel manufacturing with the toxic emissions of traditional adhesives. Camellia oleifera shell (COS), as a common waste, is a potential alternative raw material for wood-based panels and also has an important role in alleviating environmental stress. Faced with these problems, the aim of this study was to assess the technical feasibility and environmental aspects of manufacturing particleboard from COS waste at scale. For this purpose, particles made from conventional eucalyptus species were used as particleboard reinforcing phase. Particleboard was manufactured and tested by varying some production parameters, namely: of 10, 20 and 30% content of COS addition; and adhesive types of melamine-urea-formaldehyde (MUF) and polymeric 4–4 diphenylmethane diisocyanate (pMDI) adhesives. The results showed that the physical-mechanical properties of COS-based particleboards were satisfactory for a 10% MUF resin loading or a 3.5% pMDI resin loading. COS-based particleboards with 20–30% COS content similarly met the standards and requirements for non-structural applications. This study presents an informative discussion for decision makers in the wood-based panel industry, providing a trade-off between lower adhesive application and higher COS substitution that is more suitable for direct production at total plant scale.

Preparation of waterborne intumescent flame-retardant coatings using adenosine-based phosphonates for wood surfaces

Here, organic solvent-free adenosine-based waterborne flame retardant curing agents were synthesized and introduction into a melamine urea-formaldehyde resin (MUF) to construct flame-retardant coatings for wood surfaces. Adenosine-based phosphonate (APU), composed of adenosine, urea, formaldehyde, and phosphorous acid, was synthesized by the Mannich reaction. The chemical structure of APU was investigated by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and 31P nuclear magnetic resonance (NMR) spectroscopy. In contrast to MAW0, the coatings containing APU exhibited similar physical characteristics. MAW4 achieved a vertical combustion (UL-94) V-0 rating and an impressive limiting oxygen index (LOI) of 54.5 %. Cone calorimetry indicated that the time to ignition (TTI) of MAW4 was 89 s, an increase of 790 % compared with MAW0, which may significantly prolong the escape time from a fire. Scanning electron microscopy (SEM), thermal infrared imaging, and Raman spectroscopy all confirmed that continuous and dense char layers reduced the transport of heat, ignitable gases, and smoke. This limited the further pyrolysis and combustion of wood, showing that the waterborne intumescent flame-retardant coatings proposed in this research endowed wood with excellent flame retardancy.

Physical and mechanical properties of particleboard mixed with waste ACQ-treated wood

In this study, we recycle alkaline copper quaternary (ACQ) -treated wood used as a material for pyrolysis and gasification. The physical and mechanical properties of particleboards manufactured according to the mixing ratio and resin type (phenol–formaldehyde resin; PF, urea–melamine formaldehyde resin; UMF) were compared as materials for particleboard, which are used for wood recycling. According to the increase of ACQ particle input ratio, the PF particleboard did not differ in density; however, the thickness welling rate (TSR) and water absorption rate (WAR) decreased. The density of the UMF particleboard increased and the TSR and WAR also decreased. Although the bending strength (BS) of the PF particleboard increased, the internal bond strength (IB) did not show a difference. The UMF showed no difference in BS, but the IB improved. Through physical and mechanical properties, the mixing ratio of ACQ particle and untreated particles was 70:30 as the optimal mixing ratio. The surface was activated by the copper ions of the ACQ treated, which affected the improvement of adhesion and physical and mechanical properties. When ACQ-treated wood, which is classified as waste, was reused as a particleboard, its properties were superior to that of a board manufactured with untreated particles.

Evaluation of the microcapsules on the rheological and self-healing performance of asphalt

The objective of this study was to prepare microcapsules and investigate their impact on the self-healing properties of asphalt. Microcapsules with various core–shell ratios were prepared by enveloping soybean oil with Melamine-Urea-Formaldehyde (MUF) resin through an in-situ polymerization method. The laser particle size analyzer, thermogravimetric analyzer, and scanning electron microscope were utilized to character the microcapsules and determined the optimal core–shell ratio. The rheological and self-healing performance of the microcapsule-modified asphalt were examined through frequency sweep, multi stress creep and recovery (MSCR), and Fatigue-Healing-Fatigue (F-H-F) tests conducted using a dynamic shear rheometer (DSR). The results indicate that microcapsules with various core–shell ratios exhibit uniform particle distribution and excellent thermal stability. Specifically, microcapsules with a core–shell ratio of 1:2 display a smooth appearance. The incorporation of microcapsules into asphalt impedes the flow of asphalt molecules and increases the initial flow temperature. When the microcapsules rupture, the released soybean oil modifies the rheological behavior of the asphalt, leading to a decrease in stress sensitivity and rutting resistance. Simultaneously, the remaining MUF resin imparts additional elastic recovery properties to the asphalt. The self-healing performance of microcapsule-modified asphalt was significantly enhanced, with a notable improvement observed as the microcapsule dosage increased. Moreover, elevating the healing temperature and extending the healing time were found to be effective strategies for enhancing the self-healing properties of microcapsule-modified asphalt. When the healing temperature matches the initial flow temperature, the healing index HI of 5% microcapsules modified asphalt approached nearly 100% within 5 min of healing time.

Melamine–Urea–Formaldehyde Resin Adhesive Modified with Recycling Lignin: Preparation, Structures and Properties

The wettability, bonding strength and flexibility of modified melamine–urea–formaldehyde resin adhesive with hydroxymethyl lignin (LMUF) were investigated. Moreover, the curing performance, thermal properties and chemical structure of LMUF were analyzed by differential scanning calorimetry (DSC), thermogravimetry (TG), scanning electronmicroscopy (SEM), X–ray diffraction (XRD), Fourier–transform infrared spectroscopy (FTIR) and 13C nuclear magnetic resonance (13C–NMR). The synthesis mechanism of LMUF was also discussed. The results demonstrated that: (1) LMUF resin is characterized by low free formaldehyde and a short pot life. (2) With the increase in hydroxymethyl lignin, the bonding strength and flexibility of the LMUF increased first and then decreased. They reached their maximum when the hydroxymethyl lignin content was 6%–8%, which represented increases of 36% and 102%, respectively. (3) The DSC and TG analyses showed that the LMUF resin had a high hot-pressing temperature, but its thermostability was increased. (4) The XRD and SEM analyses proved that the LMUF resin was characterized by flexibility failure, especially at 6% of hydroxymethyl lignin. (5) Hydroxymethyl lignin is a type of flexible long-chain molecule, which was introduced into spaces between the rigid triazine rings through adhesion and penetration, thus improving the regular single structural form of MUF resin and increasing the compactness of the system. As a result, the resin had stronger deformability and cohesion in the molecules. The bonding strength and flexibility were improved to different degrees.

Synergizing mechanical properties and vibrant aesthetics: Nanosilver-treated flax woven fabric reinforcement for polymeric composites

Innovation and research in the field of natural fiber-reinforced composites have garnered significant attention in recent times due to the pursuit of sustainable materials for diverse applications in the automotive, building and construction, marine, defense, and aviation industries. Woven fabric lamination has emerged as a crucial reinforcement technique for fabricating structural composites using thermosetting polymers. Advanced characteristics of nanoparticles renders them instrumental in enhancing the thermomechanical and physical properties of composites. Researches are actively going on to explore alternative approaches to develop AgNPs that are safe, environmentally friendly, and conducive to their integration into composites. In this study, hornbeam leaves (Carpinus betulus), abundant in central European countries like Hungary, were employed as a stabilizing and reducing agent to in situ synthesize AgNPs onto flax woven fabrics at varying concentrations. The resulting nanosilver-coated and uncoated fabrics were then laminated with MUF (melamine urea formaldehyde) resin using five layers of flax, thereby producing nanocomposites. Extensive analyses were conducted on the compositted products, encompassing inductively coupled plasma optical emission spectroscopy (iCP-OES), morphological examinations of both fractured and intact samples, assessment of mechanical properties, evaluation of physical characteristics (including water absorption, moisture content, and thickness swelling), thermal stability using TGA (Thermogravimetric analysis)/DTG (Derivative thermogravimetry) study, FTIR (Fourier transform infrared spectroscopy), and colorimetric data. The nanocomposites treated with AgNPs exhibited vibrant colors and uniform dispersion of nanoparticles across the surface compared to the control samples. These results suggest that AgNPs were successfully incorporated into flax-woven fabrics, facilitating the production of sustainable composite production.

Interactions of hydrophilic birch wood (Betula pendulaRoth) extractives with adhesives for load-bearing timber structures

This study investigated how water-soluble extractives of silver birch (Betula pendulaRoth) wood interact with the most common adhesives used for producing engineered wood products (EWPs), i.e., melamine-urea-formaldehyde (MUF) and one-component polyurethanes (PUR). Therefore, the extractives were characterized via various chromatographic techniques and mass spectrometry. The effects of extractives on the curing kinetics were investigated using rheometry. The impact of extractives on the chemical and mechanical properties of the cured adhesives was investigated with FTIR spectrophotometry and tensile stress-strain measurements, respectively. Moreover, a comparative study on the shear strength of birch wood with and without extractives was performed.The organic fraction of the water extractives of birch mainly consisted of phenolic glycosides, carboxylic (fatty) acids, and saccharides. The extractives decelerated the curing process of MUF, as observed in a rheological small-angle oscillatory shear experiment using wood substrates as the lower plate. This was indicated by a reduced gel time from 5 to 3.8 h on pristine vs. extracted wood. When measuring MUF on extracted wood, this deceleration was also reached by adding ∼1% (W/W) of the isolated extractives into the MUF resin. Similar experiments with PUR showed a slight acceleration when dispersing extract into the adhesive, indicated by a reduction of vitrification time of −0.9 ± 0.3 h per percent of extractives added. However, measurements with pure PUR on pristine and extracted wood showed no significant difference in curing kinetics due to the extractives’ limited mobility and solubility in PUR. Both PUR and MUF cured adhesive films showed a reduced stiffness, elastic stress limit and tensile strength in uniaxial tensile stress-strain measurements of adhesive films upon increasing the amount of hydrophilic birch extractives concentration. Comparative standard tensile shear strength measurements on pristine and extracted wood indicate a 7–19% strength increase due to extraction when bonding with MUF, while the bond strength of PUR bond lines was less affected by the extraction procedure.

Characterization of plywood made from heat-treated rubberwood veneers bonded with melamine urea formaldehyde resin

The objective of the study is to evaluate the properties of the plywood made from rubberwood veneers thermally treated at various temperatures. Rotary-peeled rubberwood veneers were thermally treated at 160, 170, 180, and 190 °C under 1 bar pressure. 5-ply plywood panels were produced using melamine urea formaldehyde (MUF) resin as binder. Dimensional stability, i.e., water absorption (WA) and thickness swelling (TS) as well as mechanical properties of the plywood were assessed. The results demonstrated that the dimensional stability of the plywood made from thermally treated rubberwood veneers improved as indicated by lower WA and TS values. The reduction in WA and TS values increased along with treatment temperatures. Darkening in the plywood as a result of heat treatment was observed. Meanwhile, heat treatment at 170 °C and 180 °C resulted in plywood with the highest modulus of rupture (MOR), modulus of elasticity (MOE) and shear strength. However, beyond that temperature, the mechanical strength of the plywood started to decline. Based on the findings in this work it appears that heat treatment of rubberwood veneers at temperatures ranging from 160 to 180 °C could have a potential to improve overall properties of plywood panels.

Application of the Artificial Neural Network to Predict the Bending Strength of the Engineered Laminated Wood Produced Using the Hydrolyzed Soy Protein-Melamine Urea Formaldehyde Copolymer Adhesive

The artificial neural network (ANN) was used to predict the modulus of rupture (MOR) of the laminated wood products adhered by melamine/urea formaldehyde (MUF) resin with different formaldehyde to melamine/urea molar ratios combined with different weight ratios of the protein adhesive resulting from the alkaline treatment (NaOH) of the soybean oil meal to MUF resin pressed at different temperatures according to the central composite design (CCD). After making the boards and performing the mechanical test to measure the MOR, based on experimental data, different statistics such as determination coefficient (R2), root mean square error (RMSE), mean absolute error (MAE) and sum of squares error (SSE) were determined, and then the suitable algorithm was selected to determine the estimated values. After comparing estimated values with the experimental values, the direct and interactive effects of the independent variables on MOR were determined. The results indicated that using suitable algorithms to train the ANN well, a very good estimate of the bending strength of the laminated wood products can be offered with the least error. In addition, based on the estimated and measured strengths and FTIR and TGA diagnostic analyses, it was found that the replacement of the MUF resin by the protein bio-based adhesive when using low F to M/U molar ratios, the MOR is maximized if a high range of temperature is used during the press.

Thermal cure kinetics of cold-setting melamine–urea–formaldehyde resins with high melamine content

Thermal cure kinetics of cold-setting melamine–urea–formaldehyde resins with high melamine content

Ternary mixture thermochromic microcapsules for visible light absorption and photothermal conversion energy storage

Thermochromic microcapsules with photothermal conversion properties were prepared by melamine urea formaldehyde resin (MUF) coated ternary mixtures (color coupler, color developer and solvent). The particle characteristics, chemical structure, heat storage properties, discoloration effect, thermal cycling durability and photothermal conversion properties of microcapsules were analyzed and characterized by ESEM and LPSA, FTIR and XRD, DSC and TGA, SC-10 and UV–Vis, thermal cycling test and solar simulator. The thermochromic and photothermal conversion mechanisms of microcapsules were analyzed. The results showed that the thermochromic microcapsules with a core material ratio of (1:3:60) have the best comprehensive performance. The chromatic aberration value of RTPCMs-C3 and RTPCMs-O3 is 23.35 and 12.14, respectively, which has a certain visible light absorption capacity and excellent thermal cycle durability. The photothermal conversion efficiencies of RTPCMs-C3 and RTPCMs-O3 under simulated solar irradiation were 55.4% and 72.9%, respectively. The conjugated organic polymer core material selectively absorbs the electromagnetic radiation frequency which are matching its internal electronic transition, causing the atomic lattice vibration to generate heat. The heat changes the state of the core material and dissociates the internal conjugated double bonds, eventually causing the microcapsules to change color.

Flexural Properties in Edgewise Bending of LVL Reinforced with Woven Carbon Fibers.

This paper presents the results of experimental testing of the bending strength and modulus of elasticity in edgewise bending of unreinforced and reinforced seven-layer LVL (laminated veneer lumber) poplar veneer panels. The aim of the research is to determine the influence of woven carbon fibers on the improvement of the bending properties and modulus of elasticity of LVL bending in the plane of the plate, as well as the influence of adhesives on the bending properties of the composite product, in order to test the potential of using this newly obtained material as a structural element. Bending was performed on small-scale samples. The main research task is the examination of three types of reinforcement, which differ from each other in position, orientation, and number of layers of reinforcement, using two different types of adhesives: epoxy adhesive and Melamine Urea Formaldehyde Resins (MUF). The composite material was produced in four different combinations in relation to the orientation and position of the reinforcement in the layup. The applied reinforcement is defined through three different configurations (EK1, EK2, and EK3) and a fourth control sample (EK4). Each configuration was produced by applying the two previously mentioned types of adhesives. The research findings showed that in the case of samples produced by applying CFRP (carbon fiber reinforced polymer) using epoxy adhesive, it significantly affected the increase in bending strength and flexural modulus of elasticity. The average improvement in bending strength is 32.9%, 33.2%, and 38.7%, i.e., the flexural modulus of elasticity is 54.1%, 50.7%, and 54.7%, respectively, for configurations EK1, EK2, and EK3, compared to control sample EK4. During the testing, the test samples from reinforced panels EK1 and EK2 showed partly plastic behavior up to the fracture point, while the diagram for the test samples from reinforced panels EK3 shows elastic behavior to a considerable extent, with a significantly smaller plastic behavior zone. This research proved the impossibility of using melamine-urea formaldehyde adhesive to form a composite product based on veneer and carbon fabric. The greatest contribution of this work is the experimentally verified and confirmed result of the possibility of applying poplar veneer to design structural elements in LVL using epoxy adhesive.

Performance Evaluation of an Improved ANFIS Approach Using Different Algorithms to Predict the Bonding Strength of Glulam Adhered by Modified Soy Protein–MUF Resin Adhesive

Despite studies on the potential replacement of synthetic resins by bio-based adhesives such as proteins in recent years, there is still no reliable method for estimating the strength of wood products made using the combined parameters in the literature. This limitation is due to the nonlinear relationship between strength and the combined components. In the present research, the application of artificial intelligence techniques was studied to predict the bonding strength of glulam adhered by protein containing different ratios of MUF (melamine–urea–formaldehyde) resin with different F-to-U/M molar ratios at different press temperatures. For this purpose, the ANFIS artificial intelligence model was used as basic mode or combined with ant colony optimization (ACOR), particle swarm optimization (PSO), differential evaluation (DE) and genetic algorithms (GA) to develop an optimal trained model to predict the bonding strength of glulam based on experimental results. Comparison of the obtained results with the experimental results showed the ability of the above methods to estimate the bonding strength of glulam in a reliable manner. Although the basic ANFIS alone and in combination with other algorithms was not able to achieve an ideal performance prediction to estimate bonding strength, the combination of GA and ANFIS offered an excellent ability compared to the combination of other algorithms combined with ANFIS. Hence, the developed ANFIS-GA model is introduced as the best prediction technique to solve bonding strength problems of laminated products. In addition, using the developed optimal model, a precise attempt was made to show the nature of the parameters used to produce glulam and determine the optimum limit.

MUF Resins Improved by Citric Acid as Adhesives for Wood Veneer Panels

This article presents the first applied results of using citric acid in combinations with a melamine-urea-formaldehyde (MUF) resin for bonding wood veneers. The chemical reactions involved are shown based on a MALDI ToF analysis of the reaction of the MUF resin with citric acid. The preliminary results of the physical and mechanical properties of the LVL prepared are also presented. Veneers from Populus sp were used to manufacture 5-layer laminated veneer lumber (LVL) of small dimensions. Five combinations of the amount of citric acid, MUF spread rate and pressing parameters were tested. LVL bonded with 20% of citric acid + 100 g/m2 of MUF, hot-pressed using a 3-step process with maximum 1.5 MPa of pressure yielded the board with better dimensional stability and mechanical properties. It could be concluded that citric acid in combination with MUF can be used for bonding wood veneer and the research should be continued to study further the parameters involved and to enhance the results.

Urea–Melamine Formaldehyde Resin for the Manufacture of Water-Resistant Plywood

Urea–Melamine Formaldehyde Resin for the Manufacture of Water-Resistant Plywood

Utilization of carbon black from Mao bamboo as reinforcing agent for melamine urea formaldehyde resin wood adhesive

The effect of carbon black from Mao bamboo (MBCB) as a reinforcing agent in melamine urea formaldehyde (MUF) resin wood adhesive is evaluated in this work. The incorporation of MBCB improved the adhesion strength and decreased the heat resistance of adhesive and the formaldehyde emission from plywood. Compared with MUF resin filled with flour, the wet bonding strength of that filled with MBCB was increased by 22.02% (from 1.68 to 2.05 MPa), and the formaldehyde emission was decreased by 21.24% (from 1.158 to 0.912 mg·L−1). Unfortunately, with the increase in the substitution ratio of MBCB to flour, the pre-pressing performance of wood adhesives was reduced. The enthalpy was increased from 24.25 to 25.27 J·g−1. It is suggested that MBCB participated in the curing process of MUF resin, which makes the curing reaction of MUF resin easier. Overall, these findings offer new insights into exploiting the utilization of carbon black in wood adhesives.

Effect of low molecular weight melamine-urea-formaldehyde resin impregnation on poplar wood pore size distribution and water sorption

This study aimed to investigate the relationship between the properties of pore size distribution and water sorption in melamine-urea-formaldehyde (MUF) resin-impregnated wood by scanning electron microscopy (SEM), nitrogen adsorption (NAD) measurement, mercury intrusion porosimetry (MIP), water-soaking, and moisture adsorption over saturated salt solutions. The results showed that MUF resin not only filled the macropores and mesopores of the wood, such as those of vessels and wood fibers, but also penetrated the cell walls and replaced some hygroscopic groups of cell wall polymers, thus significantly reducing the water sorption. The porosity and cumulative pore volume of the RI140 and RII140 samples (impregnated with 10% and 20% MUF resin solution, respectively, with each dried at 140 ℃) were 19.25% and 1.20 mL·g−1, and 9.85% and 0.89 mL·g−1, respectively, which were lower than those obtained for the control group (CK). The specific surface area of RII140 was lower than that of CK. The pore size range of the CK and RII140 samples was 3.1–22.9 nm and 2.5–5.1 nm, respectively. The water absorption rate and equilibrium moisture content values for MUF resin-impregnated wood were inversely proportional to the drying temperatures and weight percent gain (WPG). The MUF resin leaching efficiency was inversely proportional to the drying temperature but proportional to the WPG.