USE OF LIQUID MDI PRODUCTS FOR POLYURETHANE REACTIVE HOT-MELT RESINS

Reactive hot-melt resins typically consist of pure MDI (methylenediphe nyl diisocyanate) prepolymers of adipate-based polyester polyols. Thes e materials are solids at room temperature and thus harder to process than liquids. This study evaluates the effectiveness of liquid version s of MDI for reactive hot melts. Pure (close to 100% p,p') MDI served as the control, and two liquid formulations-MDI containing 50% o,p' is omer, MDI containing carbodiimide adduct-were tested for rheological p roperties, peel strength, cure rate, melt point, open time, and long-t erm stability. The liquid formulations were comparable with the pure M DI control in all physical and thermal properties, with the following exceptions. The MDI with 50% o,p' had a lower melt viscosity and cure rate, but it also showed an increase in shelf and pot stability. The a dduct-modified MDI showed a moderate increase in melt viscosity and 15 -min peel strength, increased hardness, and significantly improved she lf stability.