Peel strength of polyurethanes from oxypropylene polyols. I. Effect of polyol structure and fillers

Abstract

A study has been made of some of the factors that influence the adhesion properties of polyurethane coatings to aluminum. The peel strength (at angles of 180 and 90 degrees) has been plotted against film thickness (from 1.5 to 20 mils) and extrapolated to zero thickness; these intercept values have been found to have more significance than peel strengths at finite thicknesses. It has been found that, for polyether-urethanes prepared from polyoxypropylene glycols and polyols, the peel strength increases with increasing urethane and urea content. It has also been found that peel strength decreases with increasing film rigidity, where rigidity is caused by increasing the crosslinking density or isocyanate/hydroxyl ratio. Fillers play an important role in peel strength; at concentrations up to 15% in the glycol component the adhesion of polyurethanes increases with the addition of iron oxide and calcium carbonate. The use of chromic oxide causes only a decrease in peel strength.