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

Abstract

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.

Effect of different acids during the synthesis of urea‐formaldehyde adhesives and the mechanical properties of medium‐density fiberboards bonded with them

“…The MDF bonded with the UF adhesives with H 3 PO 4 and H 2 SO 4 produced relatively the most methylene linkages and linear methylol content (NHCH 2 OH), which indicate a higher catalytic reactivity in adhesive crosslinking. In this traditional method of producing UF adhesive, H 2 SO 4 has relatively good performance, which is in contrast with previous studies in UMF resin, but it was shown that HCOOH had a better performance than H 2 SO 4 and other catalysts.…”

“…Many studies have focused on modifying UF resin properties by investigating resin manufacturing parameters, like reaction pH and temperature, different F/U molar ratios, and the use of additives . 13 C‐NMR analysis is a valuable tool for determining the changes in the structures that are synthesized at different temperatures and F/U molar ratios (Figures ).…”

Characterization of the crystalline regions of cured urea formaldehyde resin

“…The other observed peaks of 1130 cm À1 and 1035 cm À1 were assigned to C-O aliphatic ether and methylene bridge (-NCH 2 N-), respectively. 17 The occurrences of the bands conrmed the polymerization of UF resins during a curing process. The obtained results were similar to the other FTIR spectra of cured UF resins with the addition of hardeners.…”

Physical and mechanical properties of particleboards manufactured using charcoal as additives

“…Other studies showed that formaldehyde emission can be reduced by over 42% by decreasing the melamine allocation proportion (in the alkaline hydroxymethylation step -M1 and/or alkaline post amino addition step -M2) in three-layer plywood bonded by MUF resin (Luo et al 2015). According to these authors, cheap sepiolite can replace wheat flour as glue mass filler (80%) with MUF resin in plywood production, with an observed reduction of emissions by 7.8%.…”

“…Alternatively, the addition of melamine to UF resin allow to obtain the MUF resin, which captures the formaldehyde and decrease its emission (Luo et al 2015). However, melamine addition significantly increases the production cost of panels, thus its use is often limited.…”