Emission of isocyanates from pur-adhesives

The time course of isocyanate emission from curing PUR-adhesives was studied in an emission test chamber. The adhesives under investigation were commercial products for fixing of textile floor coverings and based on methylene bisphenyl diisocyanate (MDI). Influence of the curing mechanism was studied by comparing the emission curves of one-component adhesive (OCA) and two-component adhesive (TCA). For TCA the decrease in isocyanate emission was found to follow a two-step process during curing. In the first step the emission is dominated by surface evaporation and the decay of emission is mainly caused by the decrease in monomer content due to reaction. In the second step the release is limited by internal diffusion. The influence of monomer reactivity on the emission profile could be demonstrated for 2,4' - and 4,4' -MDI. The less reactive 2,4' -MDI caused prolonged emission.