| Urea-formaldehyde particleboard (PB) binder resins modified with low levels of melamine were synthesized and evaluated. The initial and final formaldehyde/(urea +1.5 × melamine)(F/(U+1.5M)) mole ratios in these resins were 2.1 and 1.15, respectively, as commonly used in the industry, so that board performances can be compared with those bonded with industrial OF resins. The melamine-urea-formaldehyde (MUF) resins were tested for storage stability and analyzed by 13C nuclear magnetic resonance (NMR) spectroscopy. MUF resins were stable and revealed the methylene and methylene-ether and methylol groups. The co-condensed methylene linkages between urea and melamine were identified.; Dynamic mechanical analysis (DMA) was also used to study the curing parameters of MUF resins. The catalyst level, the resin temperature and the time interval between catalyst addition and DMA tests were examined. The gel time and the cure time of resins measured by DMA were well correlated with the catalyst level and the resin temperature, and the cure rate was strongly affected by the time interval between catalyst addition and DMA tests. The rigidity and thermal stability of cured MUF resins were higher than those of UF resins, especially at higher curing temperatures. The rigidity and cure rate of MUF resins were highly affected by melamine levels (6 and 12%) and F/(U+1.5M) mole ratios (1.05, 1.15, and 1.25).; Particleboards bonded with MUF resins (MUF-PB) were manufactured using two different press times and temperatures, and their mechanical properties, water resistance, and formaldehyde emission values were measured. OF resins were used as a control. The F/(U+1.5M) mole ratios in MUF and OF resins were 1.05, 1.15, and 1.25. MUF-PB exhibited better physical properties and water resistance than boards bonded with OF resins for all F/(U+1.5M) mole ratios. Lower F/(U+1.5M) mole ratios and higher melamine levels reduced the formaldehyde emission of boards without lowering the strength values of boards. |
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