Formaldehyde Liberation and Cure Behavior of Urea-Formaldehyde Resins

Melamine-urea-formaldehyde (MUF) resin was synthesized by adding melamine with a first and second portion of urea, named M1 and M2, respectively. Different allocation proportions of M1:M2 (4:0, 3:1, 2:2, 1:3, and 0:4) were used to develop five MUF (MUF-1, 2, 3, 4, and 5) resins with an F/(U+M) molar ratio of 1.05. The chemical structures, curing behaviors, and cross-section morphology of the resins were characterized. Three-ply plywood was fabricated to evaluate wet shear strength and formaldehyde emission. Results showed that when the melamine allocation proportion was increased from 0:4 to 4:0, the total methylene ether group content increased, the curing rate was elevated, and a heterogeneous cross-section of the cured resin formed, which led to a wet shear strength increase of 42.11%. When the melamine allocation proportion decreased, the free melamine content increased, the pot life was prolonged, and a highly homogeneous morphology was formed, which resulted in a decrease of 42.86% in formaldehyde emission of the resulting plywood. These results suggested that a high melamine allocation proportion, meaning that more of the MUF resin was added initially, improved the water resistance of the resulting resin, whereas a low melamine allocation proportion decreased the formaldehyde emission reduction of the resulting plywood.

Section: Introductionmentioning

confidence: 99%

Effect of Melamine Allocation Proportion on Chemical Structures and Properties of Melamine-Urea-Formaldehyde Resins

Luo¹,

Zhang²,

Luo³

et al. 2015

“…The major resin-related factor is the formaldehyde/urea (F/U) mole ratio used in the resin syntheses (Myers 1984;Myers and Koutsky 1990;Go 1991). An average face-and core-layer mole ratio of about 1.15 has been the industry standard until recently, resulting in boards having adequate physical strength properties and largechamber formaldehyde emission values of 0.15 to 0.20 ppm, which has been within the industry standards until recently (Dunky 1998).…”

Section: Introductionmentioning

confidence: 99%

Investigation of Low Mole Ratio UF and UMF Resins Aimed at Lowering the Formaldehyde Emission Potential of Wood Composite Boards

Mao¹,

Hassan²,

Kim³

2013

Urea-melamine-formaldehyde (UMF) resins with 2.5% and 5.0% melamine levels added at the beginning of the third step of the typical urea-formaldehyde (UF) synthesis procedure were synthesized with an F/(U+M) mole ratio of 1.05 and evaluated as particleboard binders to investigate the positive effects of melamine on the formaldehyde content and physical performance of boards. Resins were tested for storage properties and analyzed by 13 C NMR. Curing catalysts were studied, curing rates were measured, and laboratory particleboards were prepared and tested for formaldehyde contents as well as strength and water-soak test values. The UMF resins resulted in slower curing rates but had adequate board strength values. The formaldehyde content values were within the newly created California emission law (5.2 to 8.0 mg/100 g board). Another objective of this work was to establish the baseline performance of these resins for use in subsequent studies that will aim to reveal the effects of methylene-ether group contents on formaldehyde emissions.

“…UF resins have the advantages of high reactivity, fast curing, water solubility, and low price. However, they have poor water resistance and emit formaldehyde, which limits their application (Myers 1982(Myers , 1984(Myers , 1990Dunky 1998). These issues have stimulated efforts to improve the performance of UF resins.…”

Section: Introductionmentioning

confidence: 99%

Effects of Melamine Addition Stage on the Performance and Curing Behavior of Melamine-Urea-Formaldehyde (MUF) Resin

Zhang¹,

Wang²,

Zhang³

et al. 2013

Three formaldehyde-based resins were prepared: urea-formaldehyde (UF) resin without melamine modifier (named UF0 resin) and melamineurea-formaldehyde (MUF) resins with melamine modifier added at two different synthesis stages (named MUF1 resin and MUF2 resin). The effects of the melamine addition stage on the performance and curing behavior of MUF resin were studied. Three-ply plywood bonded by these adhesives was manufactured, and its bond strength and formaldehyde emissions were measured. The curing behavior and functional groups of the resins were measured by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). Their activation energies were calculated using the Kissinger equation and the KissingerAkahira-Sunose (KAS) method. The results showed that melamine addition and the addition stage had significant influences on the characteristics of resins. The plywood bonded by MUF1 resin showed the highest bond strength and the lowest formaldehyde emissions. The activation energies of UF0 resin, MUF1 resin, and MUF2 resin were significantly different; the values were 99.44 kJ/mol, 105.75 kJ/mol, and 150.65 kJ/mol, respectively. According to the FT-IR spectra, the amount of methylene and methylene-ether bonds in cured MUF2 resin was the lowest, which meant that the cross-linking degree of MUF2 resin was the lowest.