Methylolation of melamine with incipient condensation. II. Mathematical modeling

Abstract

A novel mathematical model is presented for the reaction between melamine (M) and formaldehyde (F) at pH ¼ 9.0 and at temperatures between 38 and 90 C. It is 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. The model predicts the distributions of molecular weights and functionalities of the evolving MF resin. Arrhenius expressions were adjusted for the seven kinetic constants on the basis of measurements reported in the first part of this series. Even though the final products contain thousands of different molecular species, 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.

Drying and curing behaviour of melamine formaldehyde resin impregnated papers

“…The basic chemical reactions involved in formation and condensation of MF resins are summarized in Scheme . In the first step, depending on the reaction conditions (mainly the melamine‐to‐formaldehyde molar ratio) up to six molecules of formaldehyde may react with melamine to form primary still water‐soluble methylolated melamine compounds, also known as methylols (methylolation) . These methylols may further condense under liberation of water to form the MF prepolymers, which consist of either methylene‐ or methylene ether‐bridged melamine rings.…”

“…In the first step, depending on the reaction conditions (mainly the melamine-toformaldehyde molar ratio) up to six molecules of formaldehyde may react with melamine to form primary still water-soluble methylolated melamine compounds, also known as methylols (methylolation). 13,14 These methylols may further condense under liberation of water to form the MF prepolymers, 15 which consist of either methylene-or methylene ether-bridged melamine rings. Typically, MF resin prepolymers intended for paper impregnation are of low-molecular weight and consist of a statistical mixture of oligomers with about three to five melamine units to keep the viscosity low and allow for good paper penetration.…”