By Dan Heberer and David Bareis, Huntsman Polyurethanes
Polyurethanes (PU) are a promising alternative to traditional vinyl ester and epoxy-based matrix systems. They offer the potential of short cycle times, high toughness and exceptional durability. They have not been widely adopted in the past because they suffer from short pot life and gel times.
But by using new catalyst packages, urethane systems can be adjusted to offer unique processing parameters, cure temperatures, cure cycles and physical properties to make it possible to challenge the dominance of incumbent materials.
This paper shows data on resin cure properties and rheology as well as the physical properties and composite production methods that are achievable with urethane materials. It shows that with correct formulation, polyurethane systems can have significant production benefits over traditional epoxy formulations in a wide number of applications.
By modifying compounding parameters and ingredient choices, it is possible to make PU resin systems with glass transition temperatures (Tg)s from 104°C to 225°C, viscosity values as low as 150 cP, and pot-lives of several hours. These urethane resins have outstanding impact strength and are considerably higher than epoxy resins with an equivalent Tg. Advances in urethane formulation and catalysis has greatly expanded the ability to use urethane chemistry for composite applications and processing methods including pultrusion, RTM, resin…