synthetic products used in manufacturing plastics, carbamide glue, decorative laminated plastics, and varnishes. In terms of chemical composition, they are oligomers and are formed by polycondensation of melamine with formaldehyde.
Melamine-formaldehyde resins are synthesized in two stages with a 1:(2–12) molar ratio of melamine to formaldehyde. Various methylol derivatives of melamine are formed during the first stage at a temperature of 80°-90° C and pH 8.5; the second stage involves subsequent polycondensation of the products in an acid medium. For example, the reaction mixture must be cooled to 50°-60° C and a certain quantity of acid added to produce melamine-formaldehyde resins with the highest industrial value.
Melamine-formaldehyde resins are amorphous white products that are readily soluble in water but insoluble in organic solvents. The methylol groups in the resins undergo esterification with alcohols, primarily n-butanol and methanol, to impart to them hydrophobic properties, solubility in organic solvents (during the preparation of varnishes), and the ability to combine with plasticizers. Melamine-formaldehyde resins are cured at high temperatures, or at room temperature in the presence of slightly acidic catalysts.
REFERENCETekhnologiia plasticheskikh mass. Edited by V. V. Korshak. Moscow, 1972.
G. M. TSEITLIN