Isocyanate emission from PUR adhesives: influence of temperature, monomer content, and curing mechanism.
The isocyanate emission potential of polyurethane (PUR) adhesives was evaluated by measuring the area-specific emission rate (SERa;microg m(-2) h(-1)) in a laboratory emission test chamber. The chamber was constructed for the analysis of reactive substances allowing quantitative trapping of all isocyanate monomers emitted from the substrate. Isocyanates were analyzed as their 1-(2-pyridyl)piperazine derivatives by HPLC with fluorescence and UV detection. The influence of temperature, the content of the diisocyanate in the resin, and the system pressure were investigated. These parameter studies gave evidence thatthe diisocyanate emission from the resins is a gas-phase-limited mass transfer. The overall mass-transfer coefficient (beta = Ddelta(-1)) was calculated for HDI and MDI. From the temperature dependence of emission rates, the enthalpies of evaporation for 2,4'-MDI, 4,4'-MDI, and HDI from their resins were determined. The influence of monomer content on SERa followed Henry's and Raoult's laws in the cases of HDI and MDI, respectively, allowing the prediction of emission rates proportional to diisocyanate content. Therefore, from simple parameters such as application temperature and monomer content, isocyanate emission rates can be predicted. Additionally, MDI emission from curing PUR adhesives was studied. These results elucidate the influence of monomer reactivity and curing mechanism on the decrease of MDI emission with time.
Wirts
Martin
M
Fraunhofer Institut für Fertigungstechnik und Angewandte Materialforschung (IFAM), Bremen, Germany. martin@wirts.de
Salthammer
Tunga
T
D000269:Adhesives / Q000737:chemistry*; D004784:Environmental Monitoring; D005544:Forecasting; D005740:Gases / Q000032:analysis; D017953:Isocyanates / Q000032:analysis*; D008956:Models, Chemical; D011140:Polyurethanes / Q000737:chemistry*; D013696:Temperature; D014835:Volatilization
D000269:Adhesives; D005740:Gases; D017953:Isocyanates; D011140:Polyurethanes