New laboratory cell to evaluate emissions from PUR hotmelts

Reactive polyurethane hotmelts have a wide variety of uses because of their favourable processing and application properties. However, the elevated temperatures required for processing these adhesives mean that monomer emissions have to be taken into consideration. These monomer emissions can be described by their material-specific emission rates (SER=mass of emitted substance [μg]/emitting area [m2]×emission time [h]) and this is an important criterion for assessing the risks associated with these adhesives. In this work, the experimental determination of these constants for PUR hotmelts is carried out using a new laboratory cell whose entire surface can be heated. This minimises the undervaluation of emissions caused by irreversible adsorption effects on the cell walls. Prediction of the room air concentrations of monomeric isocyanates is not possible by simply extrapolation of the laboratory cell results. The use of statistical experimental planning allowed the key factors influencing the expected air concentrations to be determined for defined workplaces. In particular, it was found that reducing the residual monomer content of the adhesives being used reduces the risk of elevated concentrations of airborne monomeric isocyanates at the workplace.