Structure, viscoelastic properties and damping mechanisms of reactive butadiene-nitrile rubber/epoxy polymer blends

Carboxyl-terminated butadiene acrylonitrile (CTBN) rubber/ epoxy (diglycidyl ether of bisphenol-A) / diamino diphenyl methane polymer blends with 60 wt% of CTBN were formulated to evaluate the viscoelasticity and the damping properties. When the blend resins had micro-phase separated morphologies composed of epoxy-rich dispersed phases larger than 500 nm in diameter surrounded by a rubber-rich continuous phase, the loss factors (eta) of the steel laminates adhered with the resin significantly depended on the environmental temperature and the resonant frequencies. The resins with epoxy-rich phases smaller than 200 urn in diameter had broad glass-transition temperature range that resulted in the high loss factor (eta > 0.1) of the steel laminates in the broad temperature range. Inhomogeneous nano-gel structures with 20 similar to 30 nm sizes were observed in more compatible resins by scanning probe microscopy, although appreciable micro-phase separation was detected by none of SEM and TEM. Pulse NMR suggested that the fraction of interfacial phase in the resins increased with increasing the compatibility of the blends. The large interfacial phase in the inhomogeneous nano-gel structures seems to play an important role in the damping mechanisms.