Melamine Modified Urea Formaldehyde Research Articles

Synthesis and Properties of Melamine Modified Urea Formaldehyde Resin for Impregnation Under New Process

In this paper, the basic properties of UF and UMF resins for impregnation under conventional and new processes were compared, and their chemical structures were characterized by ¹³C NMR. The effects of synthetic process and melamine addition on the bonding strength and formaldehyde emission of UF and UMF resins were studied. The resin synthesized by the new process has higher linear and methylene ether bond content, relatively lower methylene content, longer curing time and storage life and lower free formaldehyde content than the conventional resin; When melamine was added at the initial stage of UF resin synthesis reaction, it did not significantly change the total amount of methylene ether and hydroxymethyl in the resin system, but the content of class I hydroxymethyl increased and the content of class II hydroxymethyl decreased. The reason may be that the added melamine and urea react not only with the remaining formaldehyde in the system, but also with the formaldehyde removed from hydroxymethyl due to dehydroxylation reaction, Hydroxymethylmelamine and monobasic substituted urea are produced. At this time, about 50% of melamine still exists in UMF resin in the form of free or low hydroxymethylate, and does not participate in the formation of the main structure of the resin. Melamine was added in the early stage of the reaction. The modified resin bonded plywood has high bonding strength and low formaldehyde emission.

Highly Efficient Liquid-Quantum Dot/Melamine- Modified Urea-Formaldehyde Microcapsules for White Light-Emitting Diodes

A liquid matrix is beneficial for improving the luminescence performance of quantum dots (QDs), although it is difficult to be packaged with light-emitting diode (LED) chips. In this study, liquid-QDs with chlorobenzene solution and melamine-modified urea-formaldehyde (MUF) were used as the core and shell structures, respectively, successfully yielding liquid-QD/MUF microcapsules for white LED packaging. The concentration of the liquid-QDs in the microcapsules was optimized, demonstrating an increase of 15.9% in the luminous efficiency, as compared to the traditional solid-QDs at a specific QD energy proportion. The efficiency roll-off can be attributed to the increased reabsorption and back-scattering loss at higher liquid-QDs and microcapsules concentrations. It was also confirmed that the liquid-QD/MUF microcapsules have an excellent thermal stability below 200 °C, owing to the protection of the MUF shells. Finally, white LEDs compounding the red liquid-QD/MUF microcapsules and YAG phosphor particles were fabricated, achieving a high luminous efficiency of 149.2 lm/W at 20 mA, correlated color temperature of 3301 K, and color rendering index of 88.8. This study will open new research avenues for liquid-QD packaging in white LEDs.

Preparation and thermal degradation property analysis of the tea-based melamine-modified urea–formaldehyde (TMUF) resin

In this work, tea powder was used as a filler to produce low-formaldehyde-emission tea-based melamine-modified urea–formaldehyde resin (TMUF). The thermal stabilities of TMUF and the resin without tea powder (MUF0) were characterized using thermogravimetry. The optimal amount of tea powder m(tea)/m(tea + urea) was equal to 0.15. The formaldehyde emission of the three-layer plywood produced by TMUF was reduced by 75.43%, and the wet bonding strength of the plate was increased by 26.67% as compared with the plywood prepared by MUF0. Compared with MUF0, the thermal degradation peak temperature of TMUF resin was shifted to higher temperature, while the carbon residue was increased. The thermal degradation activation energies of TMUF and MUF0 were similar, while TMUF had a lower pre-exponential A. The Flynn–Wall–Ozawa model-free method is used to estimate various activation energy values at different conversion rates and to predict possible reaction mechanisms. Judging the reaction mechanism according to the slope of the straight line fitted by different models, the best model was based on random nucleation.

Preparation and Properties of Five Biomass-based Melamine Modified Urea Formaldehyde Resins

In this paper, shell (PS), rice husk (RH), rapeseed stalk (RS), toonaciliata wood (TW) and Sinocalamus affinis (SA) were served as the modifier to modify the melamine modified urea-formaldehyde resin (MUF). The PS, RH, RS, TW, SA were ultra-fine crushed to be the powder with less than 48 um. The reactivity of PS, RH, RS, TW, SA and formaldehyde solution was measured, and PS, RH, RS, TW, SA were added in the third stage of synthesis process of the MUF resin. The basic properties of the resin and plywood were tested. The results showed that, with addition of the PS, RH, RS, TW, SA, the reactivity with formaldehyde solution became better, while the gel time became longer, the resin viscosity and the solid content increased, and the free formaldehyde content of the resin decreased. The formaldehyde emission of the plywood decreased by 60.53%, 48.25%, 41.23%, 44.74%, 56.14%, respectively, and the wet ply strength of the plywood increased by 40.00%, 56.19%, 16.19%, 24.76%, 54.29%, respectively. The use of the ultra-fined PS, RH, RS, TW, and SA showed good effects on the formaldehyde elimination of the MUF resin.

Effect of various compounding methods on acid red 18050- melamine modified urea formaldehyde resin compound as wood modifier

In order to simultaneously improve the strength and decoration properties of plantation wood, a multi-effect modifier was prepared by compounding acid red 18050(G) with melamine-modified urea formaldehyde resin (MUF). Various compounding methods for MUF synthesis such as adding dye with the first part urea (U1G) or with the second part urea (U2G), or direct blending with MUF resin (BG) were tested. Chinese fir plantation wood was impregnated with these modifiers separately, and its color, color fastness, and dyeing mechanism were studied. The results showed that G had good compatibility with MUF and could prolong its storage time, and all compound modifiers exhibited permeability and coloring effect on Chinese fir wood. Compared with G-dyed wood under the same conditions, all the compound dyed wood had better color fastness to water, and the U2G-dyed was the best, the color fastness to xenon light of U2G dyed wood was greatly improved.. Fourier transform infra-red (FTIR) analysis showed that compared with MUF-modified wood, the dye affected MUF hydroxyl-methylation reaction in U1G, lowered the polycondensation degree, and extended its storage time. The dye might have promoted the ionic reaction between resin amino and dye sulfonic groups in U2G, thus displaying better color fastness.

The flammability of expandable polystyrene foams coated with melamine modified urea formaldehyde resin

ABSTRACTUrea formaldehyde resin (UF) was modified by introducing melamine during the condensation in order to reduce the amount of free formaldehyde and increase the solid content. The melamine modified UF (MUF) was firstly mixed with intumescent flame retardant (IFR) and then coated on the surface of pre‐expanded polystyrene (PS) particles to prepare flame retardant expandable PS (EPS) foams. The flammability of EPS foam samples was characterized by limiting oxygen index (LOI), UL‐94 vertical burning and cone calorimeter tests, and the results indicated that the peak heat release rate was significantly reduced from 406 to 49 kW/m2 and LOI value could reach 36.3 with V‐0 rating in UL‐94 test after coated with IFR. The smoke density test indicated that the maximum smoke density was decreased by the addition of IFR. Thermal analysis suggested that the thermal stability and char formation were significantly improved by the presence of coated flame retardants. The residual char observation revealed that MUF and IFR were beneficial to form integrated char layers with hollow stents, which could be the main reason for the improvement of flame retardant properties. The mechanical properties of flame retardant EPS foams can still meet the standard requirements for industrial applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44423.

Dual Protection of Wood Surface Treated with Melamine-Modified Urea-Formaldehyde Resin Mixed with Ammonium Polyphosphate against Both Fire and Decay

Abstract Surface coatings of melamine-modified urea-formaldehyde resins (MUFs) containing ammonium polyphosphate (APP) have been shown to significantly improve the fire retardancy of wood by prolonging the ignition time and reducing the heat release rate, total heat released, and mass loss rate. Dual protection of wood against both decay and fire has been proposed for remedial situations and interior construction. In this study, the fire retardant MUF resin type 3 (MUF3)/APP mixture system showed strong activity against wood decay fungi via an activity inhibition test. Two species of wood were subjected to steeping with the fire retardants MUF3/APP. The treatments were evaluated for fire and decay resistance using cone calorimetry and fungal decay resistance tests. The results showed that MUF3/APP surface treatment can provide dual protection to wood against degradation by decay fungi and fire.

Effect of different catalysts on urea–formaldehyde resin synthesis

ABSTRACTFour catalysts (H2SO4, HCl, H3PO4, and NaOH/NH4OH) were studied in the preparation of melamine modified urea–formaldehyde (UFM) resins. 13C‐nuclear magnetic resonance spectroscopic analysis of the UFM resins at different synthesis stages revealed the polymer structure and detailed reaction mechanism. Three acidic catalysts (H2SO4, HCl, and H3PO4) enhanced the resin polymerization through the formation of various contents of methylene, ether linkages, and urons. H3PO4 yielded the most terminal ether linkages at the first stage and enhanced polycondensation by depleting all free urea and glycols to form the most linear methylene linkages NHCH2NH in the end. However, at the initial synthesis stage, NaOH/NH4OH catalyzed the formation of UFM prepolymer to a limited extent with a large amount of free urea left, and therefore produced the final polymer with relatively more substituted methylolureas and linear ether linkages. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40644.

Assessment of lowering formaldehyde release of particleboards using urea as a scavenger by chamber, perforator and flask method

Addition of urea to a melamine modified urea formaldehyde resin in the surface and core layer reduces significantly the formaldehyde release of the particleboards bonded therewith. Under the used boundary conditions (long press time) urea addition seems to have no noticeable negative impact on the physical–mechanical properties of the boards. The reduction of formaldehyde release due to urea addition as a scavenger can be followed by measuring the emission in the chamber according to EN 717-1, the perforator method according to EN 120 and the flask method as described in EN 717-3. The results reveal that under the used conditions a good correlation exists between the emission in the chamber and the corrected perforator values (R2 = 0·865), as well as between the chamber value and the formaldehyde emission measured by the 3h-flask method (R2 = 0·792) according to EN 717-3, a slightly better correlation was found between the measured flask values after 24 h and the emission in the chamber (R2 = 0·869). The correlations seem to hold in the emission range between 0·06 and 0·016 ppm.

The fire-retardant properties of the melamine-modified urea–formaldehyde resins mixed with ammonium polyphosphate

Fire retardancy of melamine-modified urea–formaldehyde resin (MUF) containing intumescent fire-retardant ammonium polyphosphate (APP) (MUF/APP) was conducted by cone calorimeter with surface treatment of medium density fiberboard (MDF). The results showed that the six MUF resins synthesized with different F/(M + U) and M/U molar ratios containing APP significantly improved the fire retardancy of the MDF by prolonging ignition time, reducing heat release rate and total heat release, and decreasing mass loss rate. The fire-retardant properties of the six synthesized MUF/APP acted differently even though each MUF resin containing the same mass ratio of APP. The melamine content in the MUF should not be too high, otherwise it would decrease the fire-retardant properties of MUF/APP. Based on this study, the higher the APP amounts, the better the fire-retardant performance of the resin was. The fire retardancy of MUF/APP increased with the increase in the amount of glue that spread on the material surface. However, only the amount of glue spread exceeded 250 g/m2, whereas the ability of MUF/APP in inhibiting heat release did not increase significantly any longer.

Preparation and Characterization of Melamine Modified Urea-Formaldehyde Foam

Abstract Melamine-urea-formaldehyde (MUF) foam was prepared using melamine modified urea formaldehyde resin. The effects of blowing agent, curing agent and surfactant on the properties of MUF foam such as apparent densities, compression strength, microstructure, fragility, limited oxygen index, thermal conductivity and formaldehyde emission were investigated. The best performance of MUF was obtained as the composition of blowing agent, curing agent and surfactant were 2.5%, 18% and 12% respectively. The water resistance of MUF foam, contents of foam's burning gas, curing mechanism and physical properties were also studied by Contact angle analyzer, TGA-FT-IR, FT-IR and 13C NMR.

Decay resistance and thermal stability of bamboo preservatives prepared using camphor leaf extract

Because bamboo is attacked by many fungi, bamboo products should be protected with environmentally friendly plant-based preservatives. In this study, a camphor (Cinnamomum camphor (L.) Presl) leaf extract was mixed with a melamine-modified urea formaldehyde (MUF) resin prepolymer (10% extractive + 10% MUF), and the resulting preservative compound (CEMUF) was collected. Bamboo was treated with CEMUF, camphor leaf extract (CE, 10% extractive), and distilled water, respectively. The decay resistance of treated bamboo and the heat resistance of CE, CEMUF, and MUF were investigated by thermogravimetry. The dynamic parameters of samples at each reaction stage were calculated using the pyrolysis dynamic equation to obtain the activation energy E. The results revealed that abundant microspheres were present in the parenchyma cells around the vascular bundles of bamboo after treatment with CEMUF and that this benefitted the controlled release of the active composition. Compared to the control group, the bamboo treated with CE exhibited some decay resistance, and bamboo treated with CEMUF exhibited strong decay resistance. The order of heat resistance was as follows: MUF > CEMUF >> CE. These results demonstrate the usefulness of CEMUF as a bamboo preservative.

Effect of Melamine Content in MUF Resin on the Durable Properties of Plywood

The effect of melamine content in melamine modified urea formaldehyde (MUF) resin on durable properties of plywood was investigated using ammonium chloride (NH4Cl) with different melamine/urea (M/U) ratios. The plywood specimens were exposed to laboratory accelerated aging and/or cyclic soak-dry (SD). The experiment results indicated that the melamine contents in MUF resin showed an unobservable effect on the durable properties of MUF resin bonded plywood. The mechanical properties of plywood decreased more severely after accelerated aging test in acidic condition. However, the influence of different curing catalyst contents on mechanical properties and formaldehyde emission of UF resin can be minimized by adding melamine to the resin.

Performance of melamine modified urea–formaldehyde microcapsules in a dental host material

AbstractUrea–formaldehyde (UF) microcapsules filled with dicyclopentadiene (DCPD) show potential for making self‐healing dental restorative materials. To enhance the physical properties of the capsules, the urea was partially replaced with 0–5% melamine. The microcapsules were analyzed by different microscopic techniques. DSC was used to examine the capsule shell, and the core content was confirmed by 1H NMR spectroscopy. Capsules in the range of 50–300 μm were then embedded in a dental composite matrix consisting of bisphenol‐A‐glycidyl dimethacrylate (Bis‐GMA) and triethylene‐glycol dimethacrylate (TEGDMA). Flexural strength, microhardness, and nanoindentation hardness measurements were performed on the light‐cured specimens. Optical microscopy (OM) examination showed a random distribution of the microspheres throughout the host material. The incorporation of small amounts of the microcapsules did not affect the performance of the matrix material. Scanning electron microscopy (SEM) analysis revealed excellent bonding of the microcapsules to the host material which is a characteristic of utter importance for maintaining the very good mechanical properties of a dental composite with self‐healing ability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Wheat straw as raw material for manufacture of medium density fiberboard (MDF)

Wheat straw was used to produce medium-density fiberboard (MDF). The chemical and physical characteristics of fractionated size-reduced wheat straw were investigated. The pH, pH-buffering capacity, ash, and silicon content increased as wheat straw particle size decreased. Ash of the finest straw, <0.2 mm, had high ash (15%) and silicon (18%) contents. The outer and inner parts of size-reduced straw were analyzed using scanning electron microscopy (SEM). The SEM micrographs revealed a complex ultrastructure containing a notable portion of thin-walled cells approximately 1 µm thick. Pressurized defibration of size-reduced wheat straw produced lignocellulosic fibers nearly 1.0 mm long combined with approximately 24% of small particles and dust. The high water uptake of straw-based MDF was significantly reduced using melamine-modified urea-formaldehyde (UF) resin and removing wheat straw particles and dust by screening. UF resin was added at levels of 12.5%, 13.1%, and 14%. In terms of water resistance, 12-mm-thick straw MDF displayed thickness swelling below 10%, acceptable according to the EN 622-5 MDF standards. It was concluded that manufacturing wheat straw MDF entails straw size reduction (hammer-milling), removing small particles and dust, and adding melamine-modified UF resin to attain necessary MDF quality standards.

Properties of medium-density fibreboard (MDF) based on wheat straw and melamine modified urea formaldehyde (UMF) resin

Wheat straw was investigated as a raw material for manufacturing of medium density fibreboard (MDF) in a fully equipped pilot-plant. Commercial urea melamine formaldehyde (UMF) and a mixture of UMF-resin and urea melamine phenol formaldehyde (UMPF) adhesives were used as binders in manufacturing of high performance MDF. The study evaluated the quality of MDF produced of straw (i.e., SMDF). Different qualities of wheat straw and different resin contents (14–17%) were used. Moreover, the SMDF was produced at different thicknesses of 9 and 16 mm and densities of 750–1000 kg/m 3. The properties of the resulting SMDF were evaluated by analysing mechanical and water absorption (anti-swelling) properties as a function of density. Internal bond (IB), modulus of rupture (MOR), modulus of elasticity (MOE), thickness swelling (TS), and water absorption (WABS) were the properties analysed. SMDF-panels produced with densities above 780 kg/m 3 and resin contents above 14% met the requirements for wood-based MDF standard EN 622-5:1997.

Catalytic influence of wood on the hardening behavior of formaldehyde-based resin adhesives used for wood-based panels

The aim of this work was to monitor the hardening behavior of two different ureaformaldehyde (UF) resins and to investigate the possible catalytic effect of cold water extractives of different wood species on the hardening characteristic. A pure UF resin and a melamine-modified UF resin were used for this investigation. For the experiments, ammonium chloride, ammonium sulphate, acetic acid and oxalic acid at different addition levels were used as hardeners. The gel times determined at three temperatures, the pH drop of the resins after the hardener addition, the buffering behavior and changes in the complex viscosity η * with time, as well as the development of the bond strength were chosen as parameters for characterizing the systems both with and without wood extractives. As expected, the buffering capacity of the melamine fortified resin was found to be much greater than for the pure UF resin. The gel times of the investigated resins were strongly dependent on the applied temperature, decreasing steeply at higher temperatures. Based on these data the apparent activation energies for various hardener additions have been calculated. The complex viscosity and the development of the internal bond strength indicated that cold water wood extractives had little or no effect on the curing progress of the resins.