Determination of formaldehyde evolved during the curing of melamine-formaldehyde-based coatings

Total formaldehyde in a coating is composed of both "free" and "cure" formaldehyde. It has been recognized for many years that certain coatings can contain free formaldehyde, which is present prior to the cross-linking reaction. Cure formaldehyde is generated as a byproduct during polymer cross-linking of certain coatings. Formaldehyde has been designated a Hazardous Air Pollutant (HAP) by the USEPA and will contribute to the Volatile Organic Compound (VOC) content of the coating. ASTM Task Group D01.21.51A on "Cure Formaldehyde" has been working since 1998 to develop a simple method for determining the amount of cure formaldehyde emitted from coatings. Method development involved real time monitoring of formaldehyde by FT-IR to determine the effect of time, temperature, humidity, air flow, and film thickness on the cure reaction. The proposed ASTM method involves heating a thin film of coating for thirty minutes in a constant humidity purge chamber after solvent evaporation. Formaldehyde evolved during the curing process is collected on DNPH/Silica adsorbent tubes.