Melamine Urea Formaldehyde Research Articles

Low temperature and moisture dependent curing behavior of selected wood adhesives

Curing kinetics of adhesives are a highly influencing factor in the manufacture of engineered wood products. Various parameters such as temperature and humidity can affect the reactivity of the adhesive and thus the curing speed and the resulting adhesive strength. This research investigates the influence of very high and low wood moisture content (MC) and low temperature on the curing kinetics of adhesives. The examined melamine-urea-formaldehyde (MUF) and one-component polyurethane (1C PUR) are used for structural timber products where mechanically stable and durable adhesive bonds are crucial. A rheometer set-up with conditioned poplar plates allowed the interaction of adhesive and substrate to simulate realistic curing conditions. Both adhesives, MUF and 1C PUR, had delayed gel times at lower temperatures and curing slowed down. For 1C PUR water absorption from the wood to the adhesive had a further important role on the curing reaction. For MUF, substrate temperature was the main influencing factor with much longer gel times at low temperatures compared to 1C PUR. Gel times increased to such an extent for a low MC of 5%, as the moisture required was not sufficiently available, that temperature influence became negligible. Resulting tensile shear strength supported the rheological results. Lower substrate temperature affected tensile shear strength of MUF negatively, while 1C PUR kept its tensile strength. Both adhesives retained their tensile properties after water immersion.

Water resistance evaluation of a MFU resins with different molar ratio catalyzed with citric acid

Urea, in either solid form or in solution, is an additive commonly used to control the viscosity or act as a scavenger in MF (melamine-formaldehyde) and MUF (melamine-urea-formaldehyde) resins for particleboard production. The aim of this work was to evaluate the influence of adding urea to MF (melamine-formaldehyde) resin in terms of the water-resistance of the final particleboards. FTIR-ATR spectroscopy, adhesive bonding evaluation system (ABES) and gravimetric techniques were used. MF and MFU (melamine-formaldehyde-urea) resins were prepared. Urea was introduced as an additive, in different percentages (0, 10, 20, and 30% (on adhesive, dry basis), and citric acid was used as catalyst. Beech veneer strips were bonded together with these formulations and then tested in dry conditions and after immersion in water for 24 h. The effect of urea load on the resin curing reaction in dry and humid joints was studied. Particleboards were produced with MF and MFU (melamine formaldehyde urea) resins with different urea loads and using industrial recycled wood particles as raw material. Particleboard evaluation indicated that the water resistance of the final particleboards decreased linearly with urea addition.

Effects of Wood Particles from Deadwood on the Properties and Formaldehyde Emission of Particleboards.

The volume of deadwood increases annually because of changes in environmental, climatic, and hydrological conditions. On the other hand, during the last decade, manufacturers of wood-based boards have been facing an acute problem of a shortage of conventional raw materials. The purpose of this study was to evaluate the possibility of using wood particles from deadwood in the production of particleboards. Three-layer particleboards with different content of deadwood particles (0%, 25%, 50%, 75%, 100%) were produced. Conventional urea-formaldehyde (UF) resin was used for gluing the particles. The physical and mechanical properties of the boards, as well as the formaldehyde content in the boards, were determined. In addition, the effect of adding melamine-urea-formaldehyde (MUF) resin to UF adhesive on the properties of the boards was investigated. Replacing conventional sound wood particles with deadwood particles leads to deterioration of the physical and mechanical properties of the boards. The boards from deadwood particles absorb more water and swell more. The bending strength (MOR), modulus of elasticity in bending (MOE), and internal bonding (IB) values for boards with 100% deadwood particles are reduced by 26.5%, 23.1%, and 72.4%, respectively, compared to reference boards from sound wood particles. Despite this, a significant advantage is that boards made from 100% deadwood particles are characterized by 34.5% less formaldehyde content than reference boards made from conventional sound wood. Moreover, adding 3% of MUF resin to UF adhesive increases MOR, MOE, and IB by 44.1%, 43.3%, and 294.4%, respectively.

Residual stresses in adhesively bonded wood determined by a bilayer flexion reporter system

The application of adhesives in modern timber engineering often introduces moisture into the wood, leading to permanent residual stresses after hardening. This paper proposes a novel approach to assess these residual stresses by using wooden bilayers as a reporter system. For thin bilayers, moisture-induced stresses lead to pronounced visible flexion that can be used to identify the stress-driving parameters of the adhesive’s gelation process. These parameters depend solely on the wood/adhesive combination and are inversely determined by fitting a finite element method model on the experimentally obtained flexion state. In a subsequent step, the determined parameters are used to calculate the residual stresses in the adhesive bondline of cross-laminated timber plates, emphasizing this approach’s scale independence and general applicability to larger scale structures. All combinations of European beech and Norway spruce with the adhesives Melamine–Urea–Formaldehyde (MUF), Phenol–Resorcinol–Formaldehyde (PRF), and Polyurethane (PUR) were investigated.

Study on the Effect of Adhesive Systems on Physical and Mechanical Behaviour of Kenaf Fiber Reinforced Beech Wood

Kenaf fiber-reinforced beech plywood was evaluated with 5variantmanufacturing adhesive methods in order to increase its acceptance in the wider industrial use. We aimed in enhancing the mechanical characteristics of beech wood kenaf fiber-reinforced using epoxy resin, Urea-formaldehyde, Melamine urea-formaldehyde, isocyanate MDI prepolymer and polyurethane and exhibited diverse effects. Tensile strength, Modulus of Elasticity, Modulus of Rupture, Shear Strength and Screw withdrawal resistance were enhanced by urea formaldehyde, while tensile strength was decreased by Urea Formaldehyde, Melamine Urea-Formaldehyde and isocyanate prepolymer. Epoxy resin, on the other hand, is well suited for kenaf fibre reinforcing. For example, polyurethane reduced the mechanical characteristics of kenaf fibre reinforced beech wood. Shear strength, Modulus of Elasticity and Modulus of Rupture were all superior than glass fibre reinforced epoxy resin bound beech wood.

STUDY OF WOOD ADHESIVES ON THE BONDING PROPERTIES IN SOLID AND HOLLOW GLULAM BEAMS OF PINUS RADIATA

The aim of this research was study of polyurethane (PUR), isocyanate polymer emulsions (EPI) and melamine-urea-formaldehyde (MUF) adhesives, on the bonding properties of solid and hollow glulam beams of Pinus radiata. The thermomechanical analysis (DMA) of theadhesives was carried out to evaluate their stiffness and reactivity. Glulam beams were evaluated by a bending test. The quality of the bonding was evaluated by resistance to shear anddelamination. The morphology of the bonding was studied by microscopy. The DMA study showed that the MUF adhesive had the highest level of stiffness and reactivity. The results of the bending test showed that the highest modulus of rupture results were obtained in solid and hollow laminated beams with MUF adhesive, achieving increases of 30% over the PUR adhesive. The lowest delamination results were obtained in solid glulam beams with MUF and EPI adhesives, while the highest results were 32% and 47% for the PUR adhesive. Finally, glulam beams manufactured with MUF adhesive presented the best performance and results.

Properties of plybamboo manufactured from two Malaysian bamboo species—

Abstract The aim of the presented investigation was to explore the physical and mechanical properties of plybamboo manufactured from two Malaysian commercial bamboo species – Gigantochloa levis (beting) and Gigantochloa scortechinii (semantan). Three-layer-plybamboo with dimensions of 12 × 350 × 350 mm was fabricated using melamine urea formaldehyde (MUF) as a binder. The moisture content, thickness swelling, water absorption, linear expansion parallel and perpendicular to the grain were done for determination of the physical properties. Whereas, mechanical properties were evaluated via bonding shear strength, modulus of rupture (MOR) and modulus of elasticity (MOE) and compression strength parallel to the grain. Results indicated that semantan plybamboo exhibited excellent mechanical properties along with better bond shear strength than beting plybamboo. MOR and MOE value for semantan and beting plybamboo were 130.86 N/mm2, 19661.30 N/mm2, 115.92 N/mm2 and 25331.5 N/mm2, respectively. Moreover, the findings proved that the properties of both plybamboo satisfy the minimum standard requirement stipulated in the Malaysian Standard.

Preparation and characterization of cellulose nanofiber/melamine–urea–formaldehyde composite aerogels for thermal insulation applications

AbstractThe inherent flammability and low strength of pure cellulose aerogels limit their use in several applications. In this study, novel cellulose nanofibers/synthetic polymeric composite aerogels with excellent flame retardancy and increased strength were prepared under aqueous conditions with an eco‐friendly freeze‐drying and post‐curing process. This composite combined a rigid melamine–urea–formaldehyde network and pentaerythritol phosphate melamine salt as an inorganic flame retardant. The latter is positively charged; hence, it could react with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐oxidized cellulose nanofibers, which are negatively charged, by the charge neutralization of pentaerythritol. The resultant composite aerogels showed excellent flame‐retardant properties, an increased compressive modulus (up to 73.1 kPa), and low densities (8.75–10.7 mg/cm3). The composite aerogels also exhibited a limiting oxygen index as high as 30.2% and a remarkable decrease in the fire indices. Therefore, we believe that the developed composite aerogel demonstrates potential as a lightweight composite thermal insulation for construction applications.

A Green Resin Wood Adhesive from Synthetic Polyamide Crosslinking with Glyoxal.

Glyoxal is considered to be the most likely substitute for formaldehyde to synthesize resin adhesives for wood bonding due to its reactivity, structural characteristics, being non-toxic, low volatility, and acceptable cost. Regrettably, the performance of the resin synthesized using glyoxal to directly replace all formaldehyde is not totally satisfactory, especially as it has almost no water resistance. This makes such a simple alternative fail to be suitable for industrial production. To prepare an environment-friendly glyoxal-based adhesive with good bonding performance, the work presented here relies first on reacting citric acid and hexamethylene diamine, producing a polyamide, with glyoxal, and then crosslinking it, thus synthesizing a thermosetting resin (namely CHG) adhesive and applying it for plywood bonding. The plywood prepared exhibits excellent dry and wet shear strength, which are better than GB/T9846-2015 standard requirements (≥0.7 MPa), and even after being soaked in hot water at 63 °C for 3 h, its strength is still as high as 1.35 MPa. The CHG resin is then potentially an adhesive for industrial application for replacing UF (urea-formaldehyde) and MUF (melamine-urea-formaldehyde) adhesives for wood composites.

Melamine Ethoxylates as Novel Formaldehyde Free Replacements of Resin Re-Tanning Agents

Melamine urea formaldehyde condensates or resin re-tanning agents are commonly used in the leather industry. They give riseto homogeneous filling, are easily and widely applicable, but generally contribute to free formaldehyde, measurable in emissionor extraction methods. Many projects to resolve this issue have been carried out. The weakness of the resin re-tanning is the reversibility of the bond formation between formaldehyde and two amino groups. The formaldehyde forms a methylene group after condensation with two amino groups and releases water. This methylene group can be hydrolyzed under acidic conditions to release formaldehyde again, reversing the synthesis.
 Melamine ethoxylates were found to be a formaldehyde free, stable, and easily applicable alternative. Besides the fact that they are made without formaldehyde, it proved to be possible to incorporate renewable components into their synthesis, giving rise to an even more sustainable product. Another sustainable aspect of this chemistry is the delivery of the potential product as a concentrated liquid versus most resin re-tanning agents being placed into the market as spray dried powders, consuming significant amounts of energy in the process.
 Melamine ethoxylates show advantages in application on leather in comparison with classical resin re-tanning agents. An insightinto the scope of application will be given, showing that melamine ethoxylates can be considered a formaldehyde free replacement for resin re-tanning agents

Application of Soy Flour Modified Resins to Hot and Cold Pressed Veneer*

Abstract Soy flour can be substituted in polymeric diphenylmethane diisocyanate (pMDI) resin for bonding plywood. Resin bleed-through is avoided by prepressing at 95°C. The boards have greater wet and dry strength than do those prepared from melamine-urea-formaldehyde (MUF) resin. Soy flour can also be substituted in emulsion polymer isocyanates for cold-press applications. The soy increases dry strength but keeps the wet strength unchanged. The optimal level of soy flour substitution is about 20 percent in all cases as determined by infrared spectroscopy.

The bond strength development of coconut wood in relation to its density variations

ABSTRACT This study examines the influence of density variations in coconut palm wood (Cocos nucifera L.) on bond strength development using three types of adhesives: urea formaldehyde (UF), melamine urea formaldehyde (MUF), and polyvinyl-acetate (PVAc). A special testing device called Automated Bonding Evaluation System (ABES) was used to investigate the bond strength development between coconut veneers as a function of adhesive type, wood density (moisture content of 10%), pressing time, and bond-temperature development. Coconut wood density was shown to greatly affect the bond line. The bond strength of medium-density material (600–700 kg/m3) was lower than that of high-density material (900–1,000 kg/m3). Interestingly, the medium-density coconut veneers achieved higher bond strength with shorter pressing times, while the high-density coconut veneers reached better results with longer pressing times. Moreover, the bond strength improved by increasing the hot-pressing time resulting in higher bond-line temperatures. A comparison was made between coconut wood and beech wood for similar bonding parameters.

Case Study: Environment Impact assessment report of Resin Manufacturing unit

This Environmental Impact Assessment (EIA) Study Report is prepared for M/s. ABC Limited which is the existing unit located at Village: Ajapar, Taluka: Anjar, Kutch, Gujarat - 370110. M/s. ABC Limited has an existing unit involved in the manufacturing of plywood with a capacity of 1250 m3 / month. The proposed expansion for manufacturing of different types of Resin such as Urea Formaldehyde, Melamine Urea Formaldehyde, and Phenol- Formaldehyde with the capacity of 100 MT/ month, 50 MT/ month, and 50 MT/ Month respectively [i.e. Plywood: 1250 m3 /month existing and Resin: 200 MT/month proposed] at their existing land. The proposal by M/s. ABC Limited need prior Environment Clearance because it falls under project activity 5(f), Category B1 as per EIA Notification 2006 and its amendment dated 25 June 2014 as the site is located outside the notified industrial estate, 1. Water consumption is less than 25 m3 /day; 2. Fuel consumption less than 25 TPD; 3. Materials and storage quantity do not cover in the category of MAH units as per the Management, Storage, and Import of Hazardous Chemical Rules. The Environmental Impact Assessment (EIA) is to provide information on the potential positive and negative environmental and social impact of the project. EIA also helps to identify externalities associated with the project related to environmental and social issues, quantify them and internalize the cost of such externalities in the project cost during the design stage itself. This would help the project proponent to make informed

Using controlled radiolysis of melamine to reinforce melamine‐urea‐formaldehyde resin impregnated wood

AbstractThe effect of electron beam (EB) irradiation (0 to 80 kGy) on the mechanical properties of melamine‐urea‐formaldehyde (MUF) impregnated wood prepared from Pinus sylvestris is investigated. The results of the compressive strength parallel to grain measurement demonstrate EB irradiation can enhance the mechanical properties of MUF impregnated wood, with optimal results achieved at 20 kGy. Additionally, the formaldehyde emission of impregnated wood has been significantly reduced. This enhancement is promoted by the dispersibility and crosslinking efficiency of melamine in the dealkylation stage under low‐dose irradiation. However, the deamination and the destruction of triazine ring becomes significant at higher irradiation dosage, resulting in deterioration of mechanical properties as demonstrated by Raman spectroscopy,13C‐NMR, and SEM.

Effects of polyethylene glycol on the flexibility of cold-setting melamine–urea–formaldehyde resin

Effects of polyethylene glycol on the flexibility of cold-setting melamine–urea–formaldehyde resin

Curing characteristics of low molecular weight melamine-urea–formaldehyde (MUF) resin-impregnated poplar wood

The curing characteristics of low molecular weight melamine-urea–formaldehyde (MUF) resin within impregnated wood during the drying process remain unclear, making the setting and optimization of the drying process highly challenging. As a result, drying efficiency and drying quality of resin-impregnated wood (RIW) are limited. This study explores the effects of resin solution concentration (moisture content) and wood on resin curing characteristics to facilitate the development and optimization of the drying schedule for RIW. Poplar wood (Populus tomentosa) impregnated with 20%, 30%, 40%, and 50% MUF resin solutions were analyzed by differential scanning calorimetry (DSC). The optimum curing temperature was obtained by extrapolation. Kinetic parameters of curing reaction of resin-impregnated wood were calculated using the Kissinger differential method, Ozawa integral method, and Crane equation. Subsequently, the function of curing time–temperature-curing degree of MUF RIW was obtained. The peak temperature shifts to a higher temperature with increased RIW moisture. The optimum curing temperatures of the four RIW samples were 103.50, 98.05, 91.34, and 84.28 °C, respectively, while their corresponding apparent curing reaction activation energies were 117.58, 91.92, 81.34, and 63.38 kJ/mol, respectively. The relationship between curing degree and curing time under 50, 60, 70, and 80 °C isothermal conditions was simulated based on the kinetic parameters of resin curing. Additionally, the complete curing time of RIW with different moisture contents was estimated under different isothermal conditions. Parametric analysis and calculation based on the kinetic model of curing reaction showed that the moisture and wood hinder the curing and cross-linking of the resin, and the curing time increases with moisture content. This study could provide data support for the drying of RIW.

Structural fire engineering considerations for cross-laminated timber walls

The current understanding of the thermo-mechanical response of cross-laminated timber (CLT) walls to fire is insufficiently developed. This paper presents results obtained using a novel experimental methodology on fire-exposed CLT walls under sustained loads. The findings demonstrate that global instability is likely to be the dominant failure mode for CLT walls in fire. Use of a polyurethane adhesive resulted in earlier structural failure than use of a melamine urea formaldehyde adhesive. Three-ply walls failed significantly earlier than those with five plies. The combination of these two factors caused a halving of failure time between different walls under identical heating conditions. In addition, CLT walls were found to collapse during artificially induced cooling phases. It is concluded that these findings are centrally relevant considerations for fire design of CLT.

Performance of particleboard made with Neolamarckia cadamba, Leucaena leucocephala, and their 50:50 Admixtures

The performance of a particleboard seems to be related to the chemical constituents of the species and the size distribution the particles. Neolamarckia cadamba (NC) and Leucaena leucocephala (LL) are fast growing species and good potential resources for particleboard production. This study examined the chemical contents of both species, as well as the mechanical and physical performance of particleboard made with 100% NC, 100% LL, and their 50:50 admixtures. High moisture resistance boards were prepared using melamine urea formaldehyde (MUF) at a content of 10, 12, and 14 %. The 30% extra buffering of LL translated to its lower performance for both mechanical and physical properties. The 50:50 admixtures provided enticing results, as it counteracts the impact of lowered performance of 100% LL. All boards passed the mechanical requirements of the BS EN 312 (2003) standard, but they did not meet the requirement for thickness swelling. The internal bond for cyclic test only failed for 100% LL with 10% resin added. With use of wax, the potential of improvement in swelling properties is possible.

Influence of Air Plasma Pretreatments on Mechanical Properties in Metal-Reinforced Laminated Wood

The use of wood-based materials in building and construction is constantly increasing as environmental aspects and sustainability gain importance. For structural applications, however, there are many examples where hybrid material systems are needed to fulfil the specific mechanical requirements of the individual application. In particular, metal reinforcements are a common solution to enhance the mechanical properties of a wooden structural element. Metal-reinforced wood components further help to reduce cross-sectional sizes of load-bearing structures, improve the attachment of masonry or other materials, enhance the seismic safety and tremor dissipation capacity, as well as the durability of the structural elements in highly humid environments and under high permanent mechanical load. A critical factor to achieve these benefits, however, is the mechanical joint between the different material classes, namely the wood and metal parts. Currently, this joint is formed using epoxy or polyurethane (PU) adhesives, the former yielding highest mechanical strengths, whereas the latter presents a compromise between mechanical and economical constraints. Regarding sustainability and economic viability, the utilization of different adhesive systems would be preferable, whereas mechanical stabilities yielded for metal-wood joints do not permit for the use of other common adhesive systems in such structural applications. This study extends previous research on the use of non-thermal air plasma pretreatments for the formation of wood-metal joints. The plasma treatments of Norway spruce [Picea abies (L.) Karst.] wood and anodized (E6/EV1) aluminum AlMgSi0.5 (6060) F22 were optimized, using water contact angle measurements to determine the effect and homogeneity of plasma treatments. The adhesive bond strengths of plasma-pretreated and untreated specimens were tested with commercial 2-component epoxy, PU, melamine-urea formaldehyde (MUF), polyvinyl acetate (PVAc), and construction adhesive glue systems. The influence of plasma treatments on the mechanical performance of the compounds was evaluated for one selected glue system via bending strength tests. The impact of the hybrid interface between metal and wood was isolated for the tests by using five-layer laminates from three wood lamellae enclosing two aluminum plates, thereby excluding the influence of congeneric wood-wood bonds. The effect of the plasma treatments is discussed based on the chemical and physical modifications of the substrates and the respective interaction mechanisms with the glue systems.

A Review of Bio-Based Adhesives from Primary and Secondary Biomass for Wood Composite Applications

Abstract Today there is a great demand in the market of wood-based panels like medium density fibreboard (MDF), plywood and oriented strand board (OSB). These boards provide functionality in various industrial fields from building to furniture production. All are produced from timber and some type of binding resin, the most often used in Europe are phenol formaldehyde (FF), isocyanate (MDI) and melamine urea formaldehyde (MUF). These resins guarantee sturdiness of the material but are toxic to humans and makes recycling of the wood-based panels very difficult. There are attempts of wood-based panels industry to transition away from fossil-based adhesives. Various resins have been developed using lignin and tannin or protein. Soy based adhesive SOYAD™ has already reached the market, other soy protein-based adhesives are integrated into ultra-low formaldehyde emission particle boards like Nu green 2® and Transform™. This paper gives an overview on bio-based adhesives that are used or have the potential to be used for wood-based panel production.