Toughening of epoxy-amine resin systems for VARTM and filament winding applications

Filament wound composite tanks for the storage of compressed gas generally exhibit brittle behavior and low fracture toughness. For relatively small diameter tanks, this results in the need for additional over-wrap thickness to survive the high-speed projectile penetration (i.e., gunfire) test than would be needed to meet burst test requirements alone. The objective of this work is to evaluate methods for toughening epoxy/amine resin systems for use in the fabrication of compressed gas storage tanks as well as many other VARTM and filament winding applications. The epoxy used in this work is diglycidyl ether of bisphenol F (Epon 862) and the amine is diethyltoluene diamine (Epicure-W). Three approaches will be used to toughen this resin system. The first approach involves rubber modification of the resin using acrylonitrile-butadiene based modifiers containing end groups that react into the systems. These include materials like carboxyl and amine terminated liquid rubbers as well as adducts of these rubbers with epoxies. The solubility of the rubber with the resin is an important requirement for toughening. Initial results indicate that rubber modifiers with increased acrylonitrile content are more soluble with the resin. The second approach to toughening utilizes a thermoplastic as a toughening agent. In this work we investigate the use of polysulfone for this purpose with the expectation that a fully soluble system can be obtained that will phase separate upon cure. The third method of toughening employs core-shell particles as toughening agents. These particles are being investigated with respect to variables such as particle size, particle Tg, and particle functionality (carboxyl or epoxy). This study will compare processing behavior and final performance characteristics of the toughened resin systems.