Melamine formaldehyde: Curing studies and reaction mechanism

Melamine formaldehyde (MF) resin was synthesized by the reaction between melamine and formaldehyde under alkaline condition in tetrohydrofuran medium with 1:3 melamine to formaldehyde molar ratio. The synthesized resins were characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Curing and reaction mechanism was studied by thermal and spectroscopic analysis. Two exothermic peaks were observed in the DSC analysis indicating a two-step crosslinking reaction process was correlated to TGA analysis. FTIR studies at different temperatures explained the two-stage curing mechanism which is concurring with the DSC data. At a temperature range of 140-160 °C, reversible demethylolation is dominating to the crosslinking reaction. At temperature >160 °C, the crosslinking reaction dominates. On the basis of DSC and FTIR data, a possible crosslinking reaction route was derived and explained. The first stage of curing is the conversion of methylol groups to primary amine and the second stage is the crosslinking of methylol groups to the final product, methylene bridges. The thermal stability of the methylol groups, methylene bridges and the triazine ring, as well as the evaporation of effluents at different stages of curing, are also discussed based on combined TGA and DSC results.