Thermal analysis study of viscoelastic properties and activation energy of melamine-modified urea-formaldehyde resins

The objective of this research was to investigate the activation energy and viscoelastic properties of urea-formaldehyde (UF) resin, melamine-formaldehyde (MF) resin and UF-MF resin mixtures by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The purpose of adding MF resin to the UF resin was to reduce the formaldehyde emission. As the MF resin content was increased in the UF-MF resin mixture, the formaldehyde emission decreased. The storage modulus (E), loss modulus (E '') and loss factor (tan delta) of each resin were measured by DMTA. With increasing temperature, as the resin cured, the storage modulus (E') increased in all resin systems. The storage modulus (E') increased both as a function of increasing temperature and with increasing MF content. The activation energies (E-a) of the curing reactions of the UF and MF resins alone, as well as the mixed resins, on different substrates, were calculated on the basis of the variation of the temperature of the maximum of each DSC scan exotherm using the Kissinger equation. The E-a value of the UF resin decreased as the MF resin content ratio increased, and because of this lower activation energy the UF-MF resins cured faster than the UF resin. Formaldehyde is incorporated more easily and completely into melamine than into urea. The results showed that MF resin reacts with formaldehyde faster than UF resin because of its high -NH content.