Urea-formaldehyde Adhesives Research Articles

Utilization of hydrophilic/hydrophobic hyperbranched poly(amidoamine)s as additives for melamine urea formaldehyde adhesives

Hyperbranched poly(amidoamine)s (PAMAMs), exhibiting various levels of hydrophilicity, were used as modifiers for melamine urea formaldehyde (MUF) adhesives. The modification was achieved either with or at expense of sodium hydroxide during the last pH adjustment. Their apparent co‐condensability was expected from the measured gel times and further proved using Fourier transform infrared (FTIR) spectroscopy as well as 13C nuclear magnetic resonance (13C NMR). Utilization of these structures as modifiers for MUF, which are frequently used in particleboards production, resulted in manifold advantages. Considering the economic point of view, their use is more practical and cheaper with respect to dendritic structures. Additionally, their application in finite quantities as final additives, either immediately before the final use or at the last stage of preparation, yielded considerable upgrading of the dry internal bond (IB) strength of the produced particleboards. The improvement was extended to the resistivity to hydrolytic degradation as revealed by the wet IB strength and thickness swelling. The results were explained on the light of an extensive investigation on the resins using thermomechanical analysis (TMA) while taking into account the relevant hydrophilicity and degree of branching of each hyperbranched structure. POLYM. COMPOS., 36:2255–2264, 2015. © 2014 Society of Plastics Engineers

Avaliação de adesivos à base de taninos de <i>Pinus caribaea</i> var. bahamensis e de <i>Acacia mearnsii</i> na fabricação de painéis aglomerados

http://dx.doi.org/10.5902/1980509814588Este trabalho teve por objetivo avaliar os métodos para a extração dos taninos da casca do Pinus caribaea var. bahamensis, assim como verificar a viabilidade técnica de utilização dos taninos da casca de Pinus caribaea var. bahamensis, de Acacia mearnsii, de misturas de taninos de acácia negra e pinus e de misturas do adesivo ureia-formaldeído (UF) com taninos de acácia e pinus na produção de adesivos para aglomerados. As cascas de Pinus caribaea var. bahamensis foram fragmentadas em moinho de martelo, peneiradas, extraídas sob refluxo, por 2 horas, utilizada uma relação casca:licor de 1:15 p:v, em nove tratamentos. A melhor forma de extração foi utilizada para obtenção de grandes quantidades de extratos, que foram utilizados na confecção de adesivos tânicos e nas misturas com adesivo UF e com taninos comerciais de acácia negra na fabricação de painéis aglomerados. A adição de sulfito de sódio proporcionou maior extração de taninos, sendo recomendável a extração com adição de 5% de sulfito de sódio. Os resultados mostraram que tanto os taninos de acácia, quanto os de Pinus caribaea var. bahamensis, apresentam boas propriedades de colagem. É possível a adição de solução tânica de pinus à solução tânica de acácia e também substituir parte do adesivo UF pelos taninos de acácia em até 25% sem comprometer a qualidade da colagem. A substituição de 10% de UF por extrato tânico, tanto de pinus quanto de acácia, não alterou os valores de inchamento em espessura (IE) dos painéis. É possível obter boas propriedades mecânicas com adesivos UF modificados com extratos tânicos na proporção de 10%. Os altos valores encontrados para ligação interna (LI) dos painéis fabricados com extratos tânicos evidenciaram o potencial desses taninos para colagem de painéis de madeira.

Use of tannin adhesive from Stryphnodendron adstringens (Mart.) Coville in the production of OSB panels

Stryphnodendron adstringens (Mart.) Coville is a species from the Cerrado (Brazilian tropical savanna) popularly known as barbatimao. Its main use of economic value lies in the extraction of the tannins found in its bark and leaves. The purpose of this study was to assess the technical viability of using a tannin-based adhesive coming from the bark of Stryphnodendron adstringens (Mart.) Coville for the production of Oriented Strand Board (OSB) panels. Tannin-based adhesives were produced from tannins extracted from the bark of barbatimao, and these adhesives were used in proportions of 0, 25, 50, 75 and 100 % with commercial urea–formaldehyde adhesive. The properties of the pure adhesives and the mixtures were determined. Subsequently, OSB panels were produced with urea–formaldehyde adhesives, tannin–formaldehyde adhesives and their mixtures. The panels were produced with wood from Pinus oocarpa, with 8 % adhesive, a press cycle of 40 kgf cm−2, and temperature of 160 °C for a period of 8 min. Only the OSB panels produced with 100 % urea–formaldehyde adhesive, 100 % barbatimao tannin adhesive and 25 % barbatimao adhesive combined with 75 % urea–formaldehyde fulfilled all the pre-requisites stipulated in the standard EN 300 (2006) for type 1 panels, thus proving to be technically viable for application in OSB panels.

First/second generation of dendritic ester-co-aldehyde-terminated poly(amidoamine) as modifying components of melamine urea formaldehyde (MUF) adhesives: subsequent use in particleboards production

Particleboards production, which depends mainly on thermoset resins, e.g., such as melamine urea formaldehyde (MUF) and urea formaldehyde (UF), can result in subsequent liberation of the carcinogenic formaldehyde of the panel in service. This situation needs the substitution of formaldehyde with less active aldehydes. However, to date, the resins prepared from less active aldehydes suffer from markedly lower reactivity, difficult processing, short shelf-life and inferior performance after application to particleboards manufacture. The current work addresses such an issue, which is of both health and environmental concern while keeping in mind the economic aspect. It depends upon two routes of modification of MUF resins: first by using different generations of a hyperbranched ester-terminated-co-aldehyde-terminated poly(amidoamine)s, HB(PAMAM-(COOCH3)n(CHO)m), after their preparation and characterization using fourier transform infrared (FTIR), 13C nuclear magnetic resonance (NMR), and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS), as reactive additives and property enhancers in the first reaction step without altering the usual ratios of the reactants as in the basic recipe. Second, the use of the additives in the first step involved a parallel systematic substitution of formaldehyde, without seriously influencing resin properties or their relevant particleboards. The upgrading of either some resins or particleboards properties was confirmed by contact angle measurements, mechanical properties as well as thermomechanical analysis (TMA). It could be suggested that HB(PAMAM-(COOCH3)n(CHO)m) worked in the second case as a co-condensing agent rather than a bridging agent as in the first case.

Synthetic Adhesives for Wood Panels

Synthetic polycondensation adhesives have dominated for the last 80 years, and still dominate, the field of wood panel bonding. They constitute about 50%–60% by volume of all adhesives produced in the world today. This review presents through their chemistry and technology the main categories of adhesives, namely urea-formaldehyde adhesives, melamine- and melamine-urea-formaldehyde adhesives, phenolic adhesives and isocyanate adhesives and their most recent industrial modifications.

Poly(amidoamine)s dendrimers of different generations as components of melamine urea formaldehyde (MUF) adhesives used for particleboards production: what are the positive implications?

Poly(amidoamine)s dendrimers (PAMAM)s of different generations (Gn, where n = 1–3) were prepared via Michael addition/amidation reactions following a well-established procedure and their molecular weights were determined using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF). The existence of amine functional groups on the molecules periphery was proved with proton nuclear magnetic resonance (1H NMR) whereas the main features of such polymers were additionally evidenced with 13C NMR. The polymers were included as modifiers during the synthesis steps of melamine-urea-formaldehyde (MUF) resins for the purpose of probable enhancement of some properties. The contact angle measurements of the modified resins indicated better wetting over wood substrates while their active participation in the condensation and crosslinking reactions with wood substrates was ensured with thermomechanical analysis (TMA). The positive impact on the modulus of elasticity (MOE) of the corresponding particleboards can be attributed to their ability to impart sufficient flexibility to the resulting network structure after effective incorporation via chemical bonds. This effect, led to improvement of the particleboards strength and resistance to swelling after immersion in boiling water for 2 h. This improvement occurred for a wide range of MUF resins prepared: (i) with different formaldehyde:(M + U) ratios; (ii) in some cases with more urea charged as a substitute of the expensive melamine at a fixed formaldehyde ratio. This is considered to be an advantage due to (i) lower toxicity for the lower proportion of formaldehyde used. (ii) Economically, as less of the expensive melamine is added without affecting the performance of particleboards manufactured with these resins even upon exposure to hydrolytic conditions.

Effect of adhesive type and glue-line thickness on the fatigue strength of mortise and tenon furniture joints

The fatigue strength of rectangular mortise and tenon rubberwood furniture joints made from polyvinyl-acetate (PVAc) and urea-formaldehyde (UF) adhesives were compared. The results showed that the allowable design stress for PVAc adhesive joints could be set at 30 % of its ultimate bending moment as compared to 25 % for the UF adhesive joint. Further, PVAc adhesive joints have large working tolerances for glue-line thicknesses which make it suitable for mass production furniture manufacturing.

Influence of Press Pressure on the Properties of Parallel Strand Lumber Glued with Urea Formaldehyde Adhesive

The effects of press pressure on laboratory-made parallel strand lumbers (PSLs) that were manufactured from fast-growing rotary-peeled I-77/51 (Populus deltoides) hybrid poplar clones' veneer strands with a urea formaldehyde (UF) adhesive using press pressures ranging from 7.5 to 15 kg cm−2 in increments of 2.5 kg cm−2 were investigated. The physical and mechanical properties of PSL were affected by the press pressures. However, press pressures did not affect the combustion properties. Results indicated that higher press pressures lead to higher densification or compaction rates and specific gravities (SGs). For improved physical and mechanical properties, higher press pressures were found to be necessary. A press pressure of 12.5 kg cm−2 was found to be the optimum press pressure in relation to PSL properties. There are positive correlations among SG and mechanical properties as well as press pressures. The results may provide valuable information to assess the behavior of structural composite lumbers, including PSLs, that are manufactured using low and high press pressures. Utilization of fast-growing tree species is possible because their strength properties are improved through pressing.

Decreasing the formaldehyde concentration in indoor air by improving the adhesives used in engineered wood materials in Korean apartment buildings

Engineered wood materials, such as the urea-formaldehyde resin adhesives used to make plywood, are known to be one of the primary sources of formaldehyde emissions in the building industry. This study presents the results of measuring indoor formaldehyde concentrations in newly built apartment buildings at the pre-occupancy stage for more than three years. Formaldehyde emissions from engineered wood materials used in floorings and furniture were measured using the small chamber method. Indoor formaldehyde concentrations were measured by following, for the most part, the procedure proposed by the Korean Ministry of Environment. These measurements verified that improving the engineered wood materials used in the apartment buildings had an effect on lowering the formaldehyde concentrations. The results showed apparent decrease in formaldehyde concentrations when low-emission engineered wood materials were used. Regardless of the absolute decrease, seasonal fluctuations in formaldehyde concentrations were also observed. It was assumed that these fluctuations were caused by changes in the indoor air temperature and relative humidity. Nevertheless, it will be necessary to conduct further studies to identify the factors causing the weak correlation of formaldehyde concentrations with the indoor air temperature and relative humidity in each housing unit.

Utilization of extract of fresh tree leaves as extender in synthetic adhesives for laminated veneer lumber (LVL)

This study investigated potential utilization of the extraction yield of ash and cedrus tree leaves as extender in urea–formaldehyde (UF) and polyvinylacetate (PVAc) adhesives. The extraction solutions of ash and cedrus leaves (10% by weight) were added into the liquid UF and PVAc adhesives. 9-layer laminated veneer lumber (LVL) boards were produced using the UF and PVAc adhesives modified with the extraction solution. For comparison of the extraction solution, water (10wt%) was added in the adhesives. The LVLs bonded with extraction solution/UF adhesive were hot pressed for 10min at 105°C while the ones bonded with the extraction solution/PVAc adhesive were hot pressed for 2h at 20°C. As compared to the addition of water, the bending strength and splitting strength in transverse direction of the LVLs increased by 8.2% and 13.9%, respectively, as the extraction solution of ash leaves were incorporated into the UF adhesive. The extract of ash leaves had better adhesion performance in the UF and PVAc adhesives than that of cedrus leaves. The extract of the leaves was more compatible with the UF adhesive than the PVAc adhesive. Based on the findings of the study, it was concluded that the extracts of ash and cedrus leaves could be efficiently used as extender in the UF adhesive.

Study of glycidyl ether as a new kind of modifier for urea‐formaldehyde wood adhesives

AbstractIn this work, the multiepoxy functional glycidyl ether (GE) modified urea‐formaldehyde (UF) resins were synthesized via a traditional alkaline‐acid process under low formaldehyde/urea (F/U) molar ratio. The synthesized resins were characterized by 13C magnetic resonance spectroscopy (13C‐NMR), indicating that GE can effectively react with UF resins via the ring‐opening reaction of epoxy groups. Moreover, the residual epoxy groups of GE could also participate in the curing reaction of UF resins, which was verified by Fourier transform infrared spectroscopy. The storage stability of GE‐modified UF resins and the thermal degradation behavior of the synthesized resins were evaluated by using optical microrheology and thermogravimetric analysis, respectively. Meanwhile, the synthesized resins were further employed to prepare the plywood with the veneers glued. For the modification on bonding strength and formaldehyde emission of the plywood, the influences of addition method, type, and amount of GE were systematically investigated. The performance of UF adhesives were remarkably improved by the modification of GE around 20–30% (weight percentage of total urea) in the acidic condensation stage during the resin synthesis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Effect of Jatropha Seed Oil Meal and Rubber Seed Oil Meal as Melamine Urea Formaldehyde Adhesive Extender on the Bonding Strength of Plywood

Effect of Jatropha Seed Oil Meal and Rubber Seed Oil Meal as Melamine Urea Formaldehyde Adhesive Extender on the Bonding Strength of Plywood

Influence of the degree of condensation of urea-formaldehyde adhesives on the tangential penetration into beech and fir and on the shear strength of the adhesive joints

The objective of this work was to evaluate the influence of the degree of condensation of urea formaldehyde (UF) resins on the tangential penetration into fir and beech and on the tensile shear bond strength of wood joints.

Particle Board and Oriented Strand Board Prepared with Nanocellulose‐Reinforced Adhesive

Adhesives on the basis of urea‐formaldehyde (UF) and melamine‐urea‐formaldehyde (MUF) are extensively used in the production of wood‐based panels. In the present study, the attempt was made to improve the mechanical board properties by reinforcing these adhesives with cellulose nanofibers (CNFs). The latter were produced from dissolving grade beech pulp by a mechanical homogenization process. Adhesive mixtures with a CNF content of 0, 1, and 3 wt% based on solid resin were prepared by mixing an aqueous CNF suspension with UF and MUF adhesives. Laboratory‐scale particle boards and oriented strand boards (OSBs) were produced, and the mechanical and fracture mechanical properties were investigated. Particle boards prepared with UF containing 1 wt% CNF showed a reduced thickness swelling and better internal bond and bending strength than boards produced with pure UF. The reinforcing effect of CNF was even more obvious for OSB where a significant improvement of strength properties of 16% was found. For both, particle board and OSB, mode I fracture energy and fracture toughness were the parameters with the greatest improvement indicating that the adhesive bonds were markedly toughened by the CNF addition.

Improved Plywood Strength and Lowered Emissions from Soybean Meal/Melamine Urea-Formaldehyde Adhesives

The objective of this study was to improve the wet shear strength and reduce the formaldehyde emissions for the soybean meal/melamine urea-formaldehyde (MUF) adhesive–bonded plywood by optimizing the hot pressing parameters in plywood manufacturing. An L(44) experimental design was used. A dynamic mechanical analyzer (DMA) was used to study the curing process of the adhesive during hot pressing. The DMA results showed that the storage modulus (E′) first decreased to a minimum at 72.9°C and then increased as the temperature increased to a maximum at 157.2°C. At temperatures higher than 157.2°C, the storage modulus decreased as the temperature increased. The hot press temperature had a significant effect on both the wet shear strength and the formaldehyde emissions from 120°C to 150°C, while no significant effect was found by varying the hot press time from 50 to 80 s/mm and changing the pressure from 0.8 to 1.2 MPa. The adhesive spread rate had a significant effect on the formaldehyde emissions. No significant effect was found on the wet shear strength of plywood by varying the adhesive spread rate from 145 to 205 g/m2. The optimum hot pressing parameters were found: 150°C hot press temperature, 70 s/mm in hot press time, 1.2 MPa in hot press pressure, and 165 g/m2 in adhesive spread rate. Under such optimum processing conditions, the wet shear strength of the plywood was improved by 24.2 percent from 0.95 to 1.18 MPa, while the formaldehyde emissions was reduced by 21.4 percent from 0.28 to 0.22 mg/liter, which met the type II plywood requirement for wet shear strength and the level E0 requirement for formaldehyde emissions described in the China National Standard GB/T 9846.3-2004.

Suitability of Melia dubia (malabar neem wood) for plywood manufacture

The plywood industries had been utilizing plantation timbers and other lesser known timbers for making plywood because of non-availability of conventional timbers. Melia dubia (malabar neem wood) has been identified as one of the fast growing species that would be suitable for plywood making and a study was carried out for determining its suitability for plywood manufacture. Investigations have shown that type-B surface veneers could be produced by peeling and the veneers could be dried without major degrades. Gluing and bonding properties have been studied and found that the panels made using urea formaldehyde and phenol formaldehyde adhesives meets the requirement of MR and BWR grade plywood as per relevant specification.

Impact of Resin Content on Swelling Pressure of Three Layer Perticleboard Bonded with Urea-Formaldehyde Adhesive

When particleboards are exposed to water or moist environment, they tend to swell and expand in all directions. The degree of swelling or expansion depends on the type of adhesive used, its share, and the time of exposure and pressure used at hot pressing. The expansion of particleboard, exposed to water or high moisture content, is accompanied by swelling and/or expansion pressure. The purpose of this paper is to present the impact of adhesive share on thickness swelling and swelling pressure of three layer particleboard bonded with urea-formaldehyde adhesive. The resin content was altered in both layers ; in core layer it was between 6 and 9 %, and in surface layer between 11 and 13 %. Thickness swelling and swelling pressure were determined with 24-hour immersion lest. For the swelling pressure measurement, special force gauge device was used. The biggest changes in swelling and pressure were observed when the resin content was changed in core layer The fastest change in swelling and swelling pressure was observed in the, first few hours after immersion in water.

The Influence of FRW-1 Fire Retardant Treatment on the Bonding of Plywood

In this work the influence of FRW-1 fire retardant treatment on the bonding strength of plywood was studied. The results showed that the bonding strength of FRW-1 fire-retardant-treated Poplar plywood decreased by 25.3% as compared to untreated plywood; furthermore, free formaldehyde in the fire-retardant-treated Poplar plywood decreased by 64.9% when compared to untreated plywood. In our studies we also analyzed: the pH value and the buffering capacity of fire-retardant-treated and untreated wood powder; and the influence of FRW-1 fire retardant treatment on the gelation time of urea-formaldehyde (UF) adhesives. The results show that FRW-1 fire retardants reduced the pH value and increased the buffering capacity of FRW-1 fire-retardant-treated wood powder. The gelation time of the UF adhesive mixed with FRW-1 fire-retardanttreated wood powder was shortened by 15% as compared with the untreated wood powder. The results of the scanning electron microscope analysis showed that the FRW-1 fire retardant was mainly confined to: the trachea lumen of the Poplar wood; the wall of trachea; as well as around the pits when using an impregnation method at ambient temperature and pressure. It is possible that this has led to the decrease in mechanical action between the veneer and the adhesive.

EVALUACIÓN DE TRES ADHESIVOS EN LA FABRICACIÓN DE TABLEROS ENLISTONADOS DE Aspidosperma quebracho blanco ESTABILIZADO CON POLIETILENGLICOL

This study analyzed what type of adhesive is most suitable for use in the manufacture of Aspidosperma quebracho-blanco wood blockboards impregnated with polyethylene glycol (PEG). Three types of adhesives that could potentially be used to form the boards were analyzed: polyvinyl acetate (PVAc), urea-formaldehyde (UF) and phenol-formaldehyde (PF). Bond quality was determined by the glue-line strength in boards made with impregnated and non-impregnated wood. The use of PEG as a stabilizer of Aspidosperma quebracho-blanco wood did not interfere in the adhesion process when UF and PF adhesives were tested. The PVAc adhesive decreased (

Curing kinetics of two commercial urea-formaldehyde adhesives studied by isoconversional method

Differential scanning calorimetry (DSC) was used to evaluate the curing kinetics of two commercial urea-formaldehyde (UF) adhesives having different formaldehyde to urea (F/U) ratio of 1.112 (UF1) and 1.086 (UF2). DSC measurements were done in dynamic scanning regime with heating rates of 5, 10, 15 and 20?C?min-1 in order to determine the activation energy for each adhesive. Obtained data were analyzed using isoconversional methods with application of Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose kinetic models. In addition, different catalyst levels were tested at the heating rate of 10?C/min. Results showed that the adhesive with higher F/U ratio achieved higher activation energy, while having lower peak temperature of curing reaction. It was also noticed that the increase of catalyst level influenced the increase of reaction enthalpy of the adhesive with lower F/U ratio.