METHYLOLATION OF MELAMINE WITH INCIPIENT CONDENSATION. SYNTHESIS, CHARACTERIZATION AND MATHEMATICAL MODELING

NICOLAU, V.; ESTENOZ, D. A.; MEIRA, G. R.

Montreal, Canadá

Congreso; 8th. World Congress of Chemical Engineering; 2009

World Congress on Chemical Engineering

The reaction between melamine (M) and formaldehyde (F) is theoretically and experimentally investigated. To this purpose, several reactions were carried out between 38 and 90 ºC, considering an initial F:M ratio of 2, and a pH of 9 (Nicolau et al., J. Appl. Polym. Sci, 2008a, in press). The samples were analyzed by size exclusion chromatography (SEC), volumetric techniques, and 1H NMR. Condensation was quantified by SEC, while number-average molecular weights, average functionalities of reactive H’s, methylols, methylene bridges, and ether bridges were determined by a combined SEC/volumetric technique. In reactions at relatively low temperatures, condensation was almost negligible and the reversibility of methylolation reactions determined that equilibriums were reached in the ratios between primary, secondary, and tertiary amines. In experiments at relatively high temperatures, condensation was significant, but in all cases the mass fraction of single-ringed species was larger than that of species with 2 or more rings per molecule. Also, a novel mathematical model was developed based on a kinetic scheme that includes reversible methylolations, irreversible formation of (unsubstituted) methylene bridges, reversible formation of (unsubstituted) ether bridges, instantaneous dissolution of M, and instantaneous equilibrium for the hydration/dehydration of F (Nicolau et al., J. Appl. Polym. Sci, 2008b, in press). The model predicts the distributions of molecular weights and functionalities of the evolving MF resin. Arrhenius expressions were adjusted for 7 kinetic constants on the basis of the own measurements. Even though the final products contain thousands of different molecular species, only 21 of them constitute more than 90% of the total weights. During the initial period with negligible condensation, the undissolved M distorts the distributions of molecular weights and functionalities; but the reversibility of methylolations corrects for such distortion prior to the effective start of condensation. et al., J. Appl. Polym. Sci, 2008a, in press). The samples were analyzed by size exclusion chromatography (SEC), volumetric techniques, and 1H NMR. Condensation was quantified by SEC, while number-average molecular weights, average functionalities of reactive H’s, methylols, methylene bridges, and ether bridges were determined by a combined SEC/volumetric technique. In reactions at relatively low temperatures, condensation was almost negligible and the reversibility of methylolation reactions determined that equilibriums were reached in the ratios between primary, secondary, and tertiary amines. In experiments at relatively high temperatures, condensation was significant, but in all cases the mass fraction of single-ringed species was larger than that of species with 2 or more rings per molecule. Also, a novel mathematical model was developed based on a kinetic scheme that includes reversible methylolations, irreversible formation of (unsubstituted) methylene bridges, reversible formation of (unsubstituted) ether bridges, instantaneous dissolution of M, and instantaneous equilibrium for the hydration/dehydration of F (Nicolau et al., J. Appl. Polym. Sci, 2008b, in press). The model predicts the distributions of molecular weights and functionalities of the evolving MF resin. Arrhenius expressions were adjusted for 7 kinetic constants on the basis of the own measurements. Even though the final products contain thousands of different molecular species, only 21 of them constitute more than 90% of the total weights. During the initial period with negligible condensation, the undissolved M distorts the distributions of molecular weights and functionalities; but the reversibility of methylolations corrects for such distortion prior to the effective start of condensation.