Composite materials exhibit a limited weathering durability, which is attributable to the inherent properties of matrix systems used nowadays, such as epoxy or unsaturated polyesters. The epoxy-based gel coats perform unsatisfactorily outdoors, too. It is thus essential to use aliphatic, non-yellowing polyurethanes (PUR), either as a gel coat or as a coating, for exterior applications like rotor blades or yachts. With its VESTANAT® polyisocyanates, Evonik offers a full range of crosslinkers for light-stable PUR coatings:
HDI-polyisocyanates (VESTANAT HB®, HT) as standard crosslinker, whereas the IPDI trimer (VESTANAT® T 1890) is used to optimize drying and chemical resistance. Special solutions for high-solids formulations are available.