Phenol Urea Formaldehyde Research Articles

Surface characteristics of phenolic resin coatings

Phenolic resins are commonly used as polymer binders for metal, paper and mineral wool substrates. For such applications, mechanical, adhesive and thermal properties are considered most important, and the effect of synthesis and structural parameters on such end-use characteristics are well-documented. However, surface characteristics of cured phenolic resins can be equally relevant and are often overlooked. Widely used resins are phenol-urea-formaldehyde (PUF) and phenol-formaldehyde (PF). It is believed that the inherent chemistry and curing procedure of these resins result in coatings with distinct surface properties and wettability. To gain more insight into surface characteristics such as morphology, chemical composition and wettability of cured PUF and PF resins, different binder formulations were applied on glass substrates and subsequently characterised by Scanning Electron Microscopy (SEM), Contact Angle Goniometry (CAG) and X-Ray Photoelectron Spectroscopy (XPS). The effect of catalyst, chemical composition and curing conditions on surface characteristics of various PUF and PF coatings were investigated. The curing temperature was found to have a strong influence on surface properties; curing at 200 °C yields a surface with varying degrees of oxidation, differences in linkages between phenolic and urea species, and a lower overall nitrogen content in case of urea-containing coatings, resulting in stronger fluctuations in water-wettability compared to surfaces hardened at lower temperatures.

Effects of different pressures and veneer moisture content in adjacent layers on properties of PUF bonded plywood

In practice, for the manufacture of plywood, the veneer is usually dried to a moisture level suitable for bonding. However, anatomical differences within and between veneer sheets are a significant factor and some of them may contribute to significant differences in moisture content (MC). The novelty of this work was to study the possibility of using wood veneers of different MC in adjacent layers in one structure of plywood panels and how this affects the physical and mechanical properties of the panels. The Norway spruce (Picea abies L. Karst) wood veneers with mean MC approximately of 2%, 5% and 7% and phenol-urea-formaldehyde (PUF) resin were used in the experiments. The five-layers plywood panels were manufactured at the two pressing pressures of 0.8 MPa and 1.2 MPa. There was no significant difference in the bending and bonding properties, but only wood failure as measured on bonding specimens which showed higher average values on specimens manufactured with high pressure during hot pressing. Higher differences in MC of each veneer with constant MC of the veneer stack didn’t worse bending and bonding properties of plywood.

Wood modification with phenol urea formaldehyde (PUF) resin: the influence of wood species selection on the dimensional stability

Wood modification is an excellent way to improve material properties, prolong service life, and pave the way for new applications for timber in the built environment. The aim of this study is to establish the influence of wood species in the modification process with phenol urea formaldehyde resin. Seven hardwoods and four softwoods were compared in an identical treatment. Since the wood species is the main variable, the study provides a clear insight as to its influence on modification—something not previously investigated. Small wood blocks of all eleven species were impregnated with low-molecular weight phenol urea formaldehyde resin and were subsequently heat-cured at 150 °C. Mass and dimensions of specimens were carefully monitored throughout three cycles of oven-drying and water-soaking to determine anti-swelling efficiency, bulking coefficient, and swelling coefficient. The results showed a clear relationship between density, bulking-, and swelling coefficients. Beyond this well-known relationship it was observed that species with similar density (e.g., lime and sycamore) had significantly different bulking coefficients and anti-swelling efficiencies. Reasons for these differences, which are independent of density, are discussed. The soaking solution was analysed to determine the nature of leached substances showing a correlation between the amount of leachate and the UV-absorbance (272 nm) of the solution.

Encapsulation of bioinsecticide oil in phenol-urea-formaldehyde terpolymer

Novel microcapsules were developed by in situ polymerization of phenol-urea-formaldehyde (PUF) terpolymer and employed for the first time for the encapsulation of neem oil bioinsecticide. Neem oil’s rapid degradation in open environment does not permit its use in crops fields. Therefore, microencapsulation seems to be better method to protect it, make it effective and user-friendly. The prepared PUF microcapsules were analyzed by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, optical microscopy and particle size analyzer. The controlled release properties of prepared microcapsules were studied by using loss on drying method and by ultraviolet spectrometry. The release kinetics and stability of prepared microcapsules were studied under different pH and temperature conditions. In conclusion, spherical microcapsules with mean particle size 29.8 μm and good thermal stability have been developed. They could release core more at alkaline pH (26%) than acidic (9%) and neutral (18%). Microcapsules follow first order release kinetics and are operational at or below 45 °C. We propose here further that an environment friendly microcapsule suspension formulation of neem oil is possible for application in agriculture which is not explored yet by using terpolymer.

Which fraction of stone wool fibre surface remains uncoated by binder? A detailed analysis by time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy.

Biodurability of man-made vitreous fibres (MMVF) is often measured on naked fibres, i.e. fibres devoid of the phenol-urea-formaldehyde (PUF) binder that is sprayed and baked on the commercial product to reduce dustiness and to provide mechanical strength to fibre mats. This simplification of the hazard assessment relies on the assumption that the binder would not actually coat the entire fibre surface, but would occur only at the touching points where two fibres are glued together. We challenged this assumption by using surface analysis by X-ray photoelectron spectroscopy (XPS) and Time-of-Flight Secondary Ion mass spectrometry (ToF-SIMS). We analysed commercial stone wool MMVF sourced from Denmark, United Kingdom and Germany. XPS as well as ToF-SIMS-mapping combined with gas-cluster-ion-sputtering revealed that all mineral fibres investigated show a complete layer of organics over the surface of the fibres with only a few defects: before sputtering, organic components (PUF binder and oils) uniformly cover the spatial structures; only after sputtering, the inorganic components of the stone wool emerge on the visible surfaces. A preferential localisation of PUF binder on fibre-to-fibre touching points or as droplets was not observable. We finally explored the correlation to dissolution rates, but found that total PUF binder content and the experimentally determined thickness of the PUF binder layer are not sufficient to predict dissolution rates, which instead must consider chemical composition and other properties. In summary, none of the investigated stone wool fibre surfaces were uncoated by the PUF binder.

Wettability and hydrolytic stability of 3-aminopropylsilane coupling agent and phenol-urea-formaldehyde binder on silicate surfaces and fibers

The stability of phenol-urea-formaldehyde (PUF) binder and 3-aminopropylsilane (APS) on composite silicate materials (fibers and wafers) was studied with surface sensitive techniques (X-ray photoelectron spectroscopy (XPS) and streaming potential) through a wide range of humidity and temperature and ab initio modelling complemented the results. Behavior was compared for wettability properties, determined by vapor adsorption and contact angle analysis. APS and PUF, deposited on the silicate surfaces, decrease surface energy and wettability but water adsorption remains high, facilitating hydrolytic decomposition of the composite material. Deposited APS is unstable at T>50°C and 75% RH, while PUF is less sensitive to high humidity and temperature. Molecular dynamics confirmed APS sensitivity to humidity. Water adsorption and surface energy decrease, and material stability increases when a hydrophobization agent is applied to APS/PUF treated surfaces. The direct correlation between wettability and stability of PUF/APS/fiber composites can contribute in designing new materials with controlled hydrophobic properties.

Nitrogen-containing high surface area carbon cryogel from co-condensed phenol–urea–formaldehyde resin for CO2 capture

A cost-effective nitrogen-doped super high surface area carbon cryogel has been successfully synthesized from phenol–urea–formaldehyde (PUF) resin. Pore structure and chemical characteristics were investigated using scanning electron microscopy, Fourier transform infrared spectroscopy, element analysis, X-ray photoelectron spectrometry, mercury porosimetry and N2 adsorption–desorption. It was found that the organic cryogel with mesopores and macropores from PUF resin having a N content of 9.03 wt%, which is an ideal precursor for preparing N-doped carbon cryogels. The carbon cryogel obtained having a high apparent surface area of up to 1710 m2/g, large micropore volumes up to 0.64 cm3/g, a small average micropore width of 1.04 nm and a moderate nitrogen content of 2.08 wt%. The lab-made carbon cryogel showed good CO2/N2 sorption selectivity, 15.8:1 at 273 K and 16.4:1 at 298 K. The CO2 capture capacities as high as 5.5 mmol/g at 273 K and 4.5 mmol/g at 298 K up to 1 bar were obtained, which were among the highest compared to other commercial carbon materials.

Eco-Friendly Phenol-Urea-Formaldehyde Co-condensed Resin Adhesives Accelerated by Resorcinol for Plywood Manufacturing.

Eco-friendly and good-performance resin adhesives are needed for wood manufacturing. In this study, phenol–urea–formaldehyde (PUF) resin adhesives were modified by adding various ratios of resorcinol. The properties of PUF, phenol–resorcinol–urea–formaldehyde (PRUF) resin adhesives, and the performances of the prepared plywood were tested. The curing behaviors and the structural features of the PUF and PRUF resin adhesives were investigated via dynamic scanning calorimetry, thermal gravimetric analysis, 13C NMR, and cross polarization magic angle spinning 13C NMR. The results indicated that 1.3% resorcinol (based on resin, w/w) could decrease the curing temperature and accelerate the curing process after PUF resin modification. The PRUF resin adhesives demonstrated a lower activation energy during the curing process, with up to 28.8% less energy than that of PUF resin adhesive without any curing agent. The plywood demonstrated low formaldehyde emissions (<0.1 mg L–1) and acceptably high bonding strengths (>1.00 MPa). This work provided a method for preparing an easy-cured and high-performance phenolic resin for wood manufacturing.

Impact of curing time on ageing and degradation of phenol-urea-formaldehyde binder

Phenol-urea-formaldehyde (PUF) resin is one of the most important thermosetting polymers. It is widely used in many industrial and construction applications as an organic coating and adhesive. For example, in production of mineral wool for insulation, PUF is used together with the coupling agent (3-aminopropylsilane, APS) and serves as a binder for attaching mineral fibers to each other and to create the necessary mechanical integrity and shape of the final product. However, during ageing under high humidity (95%) and temperature (70 °C), hydrolysis can degrade PUF, decreasing product quality. A better understanding of the chemical processes caused by hydrolysis would promote development of more stable PUF binders. We investigated the composition and stability changes during ageing of cured PUF powder binder and mineral wool fibers where PUF binds the fibers together. We aged the samples in hot water (80 °C) or in a controlled climate chamber (70 °C; 91% RH) and analyzed them using X-ray photoelectron spectroscopy (XPS), element analysis and thermogravimetric (TG) analysis. We investigated the composition of species released from PUF during hydrolysis by electrospray ionization (ESI) of the aqueous solutions. The results show that the extent of PUF curing and the presence of APS as the coupling agent have an important impact on its stability. XPS revealed that poorly cured PUF contains a high fraction of NHCH2OCH2NH bonds which are easily hydrolyzed, while longer curing results mostly in more stable methylene bridges, NHCH2NH. We also observed evidence for urea NHCO bond decomposition by ESI analysis. Mineral wool fiber ageing studies showed that PUF rearranges on the fiber surface and detaches from it, together with the APS coupling agent. This improved understanding of the effects of ageing provides clues for designing a more robust binder, leading to increased quality and stability of mineral wool insulation.

Preparation and Characterization of Nitrogen-Containing Cellular Activated Carbon for CO2 and H2 Adsorption

New monolithic nitrogen-containing microporous cellular activated carbon was successfully prepared from phenol-urea-formaldehyde (PUF) organic foam for CO2 and H2 adsorption and was characterized by thermogravimetric analysis (TG), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), a mechanical testing machine, N2-sorption and H2/CO2 sorption. The carbon yield was approximately 50% for carbonization and the burn off for activation ranged from 40% to 56%, which linearly increased with activation time. The macroporosity corresponded to the connected network of cells with diameters ranging from 100[Formula: see text][Formula: see text]m to 600[Formula: see text][Formula: see text]m, and the pinholes in the cell walls had diameters ranging from 1[Formula: see text][Formula: see text]m to 2[Formula: see text][Formula: see text]m. The micro/mesoporosity is located at the inner surface of the cells. Thus, higher adsorption kinetics than usual from activated carbon are expected. The developed carbon with the highest [Formula: see text] (1674 m2/g) and highest [Formula: see text] (0.86[Formula: see text]cm3/g) contained 1.5% nitrogen, had a CO2 adsorption capacity of 3.53[Formula: see text]mmol/g at 298[Formula: see text]K, and had an H2 adsorption capacity of 1.9[Formula: see text]wt.% at 77[Formula: see text]K, both at atmospheric pressure (1 bar), which were among the best in activated carbons from physical activation.

Urea-phenol-formaldehyde Microcapsules Containing Linseed Oil For Self-healing Anticorrosive Coating Applications

Novel self-repairing Urea-Phenol-Formaldehyde (UPF) microcapsules containing linseed oil were prepared via in-situ polymerization in an oil-in-water emulsion. The main purpose of encapsulation is to control the release of linseed oil, when external conditions such as mechanical stress or energy cause microcapsules to break. These controlled release mechanisms of linseed oil make them suitable for application in self-healing coatings. Chemical structure analyses of microcapsules were studied by Fourier transform infrared spectroscopy (FTIR), optical microscopy and scanning electron microscopy for their structural & morphological illustrations. Controllable particle sizes were determined under optical microscope and as well using particle size analyzer. To determine the healing efficiency, the microcapsules, were incorporated in the epoxy coatings in varying proportions. The effects of the same on anti-corrosion performance was carried out in 5% NaCl aqueous solution (ASTM B117) and Decreasing trend of pencil hardness, scratch hardness, Impact resistance with the increase in concentration of microcapsules was observed. Chemical resistance could also be attributed to the presence of aromatic structures in epoxy which impart chemical stability. Secondary hydroxyl moiety in epoxy chain forms hydrogen bonding with the metal substrate that would contribute to good adhesive forces. Epoxy coatings incorporated with microcapsules showed better corrosion resistance than neat epoxy coating, where neat epoxy coating showed rust and spreading of rust observed on tested panel. Mechanical properties decreased on incorporating microcapsules into epoxy matrix, hence development of mechanical properties without effecting the corrosion properties shall be studied further. Copyright © 2016 VBRI Press.

Phenol–urea–formaldehyde resin co-polymer synthesis and its influence on Elaeis palm trunk plywood mechanical performance evaluated by 13C NMR and MALDI-TOF mass spectrometry

This study evaluated a new method of producing phenol–urea–formaldehyde (PUF) adhesives formulated differently under actual “in-situ” resin synthesis conditions. This was carried out by co-polymerizing urea formaldehyde (UF) resin with phenol–formaldehyde resin in the core layer of low molecular weight (LMW) phenol–formaldehyde (PF) resin treated Elaeis palm trunk veneers during the gluing process of Elaeis palm plywood. Matrix assisted laser desorption Ionization time of flight (MALDI-TOF) mass spectrometry (MS) illustrated and confirmed a series number of the phenol–urea co-condensates repeating unit in the prepared PUF resins which corroborated well with its mechanical properties (modulus of elasticity and modulus of rupture), bonding quality (dry test and weather boil proof or WBP test) and physical properties. A series of PF, UF and PUF resins oligomers forming repeating units up to 1833Da were identified. Besides that, the solid state 13Carbon nuclear magnetic resonance (NMR) interpretation identified that the signal at 44–45ppm and 54–55ppm corresponding to methylene bridges were co-condensated in between phenol and urea in the PUF resin system. The 13C NMR investigation showed that the synthesis process of PUF resin contained no free formaldehyde elements. Furthermore, the proportion of urea and methylolureas in the mixture to synthesis PUF resin were sufficient and incorporated well into the formulation by reacting with LMWPF units to form co-condensed methylene bridges. This study showed a new and useful method to synthesize PUF resin during the gluing process of manufactured Elaeis palm plywood which can also enhance the performance of Elaeis palm plywood panels for structural instead of utility grade applications.

Effects of surfactants on the mechanical properties, microstructure, and flame resistance of phenol–urea–formaldehyde foam

To study the effect of surfactants on the foaming behavior of phenol–urea–formaldehyde foam, silicone oil (Dow Corning DC-193) and Tween-80 surfactants were selected to study their effects on the mechanical properties, microstructure, and combustion characteristics of the foams. The results show that the surface tension of the phenol–urea–formaldehyde resins decreased with increasing surfactant concentration. Both the foaming temperature and foaming capacity of the phenol–urea–formaldehyde foam first increased and then decreased with increasing surfactant concentration. The compressive strength and oxygen index of the phenol–urea–formaldehyde foam first decreased and then increased with increasing surfactant concentration, which is probably related to the foaming capacity of the foam. The microstructure of the foams showed that the average pore diameters first increased and then decreased with increasing surfactant concentration. The combination of DC-193 and Tween-80 surfactants significantly improved the compressive strength, uniformity of the cells, and the number of closed cells in the final foam product.

Formaldehyde emissions from particle board made with phenol–urea–formaldehyde resin prepared by different synthesis methods

This paper suggests the optimum NAF resin preparation to reduce the quantity of pollutant emissions from the particle boards by using PUF resin. The pollutant emissions performance of the prepared NAF resin was evaluated by comparison with eMDI resin. Each PF and PUF resin was made by variation of the molar ratio and synthesis methods according to order of addition of the basic products. In addition, after verifying the properties of the resins, the quantity of pollutant emitted from boards made with the PUF resins were evaluated. Of the cases of boards made with each resin, the formaldehyde emission was the lowest for PB #7. The eMDI resin used in this board showed good quality as an eco-friendly resin, because it had less than half the formaldehyde emission of the other formaldehyde-based resins. In addition, the mechanical properties of the particle board met the KS criteria; therefore, there should be no restriction on use in manufactured goods.

Synthesis and Comparison of Phenol-Urea-Formaldehyde (PUF) Thermosetting Resin with Commercial Synthetic Resins

Phenol-urea-formaldehyde (PUF) thermosetting resin was synthesized by reacting methylol phenol with urea under acidic condition and its bonding strength was compared with commercial synthetic resins (PF resin, UF resin and PUF resin made by mechanical blending of PF and UF resins). The results indicated that PUF resin made by this process performed better bonding strength than commercial UF resin and mechanical blending of PF and UF resins in both dry and wet conditions. Its bonding strength was found to be intermediate to UF and PF resins.

Synthesis of novel monolithic activated carbons from phenol–urea–formaldehyde resin

Phenol–urea–formaldehyde (PUF) organic foams have been firstly synthesized from phenol–urea–formaldehyde resin under alkaline conditions, which can be used as precursor to produce cellular activated carbon foams.

13C NMR study on the structure of ZnO-catalyzed phenol–urea–formaldehyde resin during its synthesis process

The structure of ZnO-catalyzed phenol–urea–formaldehyde (PUF) resin at different synthesis stages was analyzed by liquid 13C nuclear magnetic resonance spectroscopy. The results showed that the general structure of ZnO-catalyzed PUF resin was almost the same as the control PUF resin. Addition reaction between phenol and formaldehyde mainly occurred at the first stage. Total methylol groups amount between phenols of the control resin was a little lower than that of the ZnO-catalyzed PUF resin. Co-condensation and self-condensation reaction occurred at the second stage. The preparation method of ZnO-catalyzed PUF resin favored the co-condensation reaction between phenol methylol groups and urea units, while self-condensation reaction dominated the control resin at the second stage. Formaldehyde completely reacted for both the control and ZnO-catalyzed PUF final resin. The total amount of methylol and methylene groups between urea units and phenols, respectively, was almost the same for the two final resins. The total quantity of methylol groups between phenols represented a continuing downward trend from the first stage to the final stage, and the amount of methylol group (p-Ph–CH2OH) of ZnO-catalyzed PUF resin was 30% more than that of the control resin. Total co-condensed methylene groups amount of ZnO-catalyzed PUF resin was greater than that of the control resin, which indicated that ZnO could make the urea units well incorporated into the co-condensed PUF resin.

Synthesis and Structure Characterization of Phenol-Urea-Formaldehyde Resins in the Presence of Magnesium Oxide as Catalyst

The objective of this research was to provide a useful approach of polymer synthesis for accelerating the fast cure of phenol-urea-formaldehyde (PUF) resin as wood adhesive by optimizing its structure and composition. The PUF resins containing high contents of very reactive groups such as para-methylol groups were synthesized by reacting methylolurea, phenol, and formaldehyde in the presence of magnesium oxide (MgO) as catalyst. The effects of synthesis parameters including F/(P + U), OH/P, and MgO/P mole ratios on the structure, composition, curing characteristics, and their relationships of PUF resins were investigated. The results indicated that MgO seemed to be an efficacious catalyst for PUF resin synthesis and promote its faster cure. The increase in the F/(P + U) mole ratio or/and OH/P mole ratio appeared to be beneficial for the formation of para-methylol groups and cocondensed methylene linkages between phenolic methylol groups and urea units, and for the removal of unreacted urea. In case of Catalyst/P mole ratio, an appropriate dosage of added metal-ion was very important for synthesizing the high-content reactive groups of PUF resins, otherwise leading to the reverse effects.

Ordered nitrogen doped mesoporous carbon assembled under aqueous acidic conditions and its electrochemical capacitive properties

With urea as nitrogen source, soluble phenol–urea–formaldehyde (PUF) resin is synthesized under basic conditions, and then an N-containing mesophase is obtained by co-assembly of the obtained PUF resin and block copolymer of F127 in acidic aqueous solution. The pyrolysis of the resultant mesophase in inert atmosphere produces a nitrogen-doped mesoporous carbon, which possesses a well-defined ordered mesoporous structure, large surface area (up to 537m2/g), uniform pore size (∼3.6nm) and large pore volume (∼0.49cm3/g). Multi-techniques, such as elemental analysis, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) are performed to characterize the samples; these analytic results indicate that the doped nitrogen mainly exists as pyridinic and pyrrolic nitrogen is successfully and homogeneously introduced into the skeleton of the mesoporous carbon. And more, the nitrogen content in the final ordered mesoporous carbon can be easily adjusted up to 3.85 wt.% by increasing the original ratio of urea to phenol. Electrochemical measurements show the nitrogen doped mesoporous carbon presents a higher specific capacitance (up to 225F/g) than nitrogen-free ones (169F/g) and exhibits a good electrochemical stability even after 1000 cycles at current density of 5.0A/g.

Synthesis and characterization of phenol‐urea‐formaldehyde foaming resin used to block air leakage in mining

In this study, phenol, urea, and paraformaldehyde were used as the monomers for the one‐step synthesis of phenol‐urea‐formaldehyde (PUF) foaming resin that was used to block air leakage in mining. An orthogonal test was used to study the effects of urea amount, catalyst amount, reaction temperature, and reaction time on the foaming property of the resin. The results showed that the optimum parameters for synthesizing PUF resin are as follows: 1 mol phenol, 0.5 mol urea, 3 mol formaldehyde equivalents of paraformaldehyde, and 0.05 mol catalyst at 75°C for 3 h. The infrared and 13C nuclear magnetic resonance spectra of the PUF resin showed that the chemical structure of the PUF resin was significantly different from that of phenol‐formaldehyde resin, indicating that a copolymerization reaction has occurred among the three components, that is, phenol, urea, and paraformaldehyde. In this study, PUF foam was prepared from catalysts and PUF resin. The results showed that the foaming capacity and oxygen index of the PUF foam were significantly improved by using urea, whereas the shrinking percentage decreased with no change in compression strength. POLYM. COMPOS., 35:2056–2066, 2014. © 2014 Society of Plastics Engineers