Toughening mechanisms of rubber modified thin film epoxy resins

An epoxy terminated polybutadiene (ETPB) was synthesized and utilized to enhance the toughening of an epoxy system, in both bulk and coating states. In the first step, the fracture energy of the modified samples was determined using a single edge notched type specimen in a three point bending (SEN3PB) geometry. The effective toughening mechanisms of bulk epoxy specimens were examined using scanning electron microscopy (SEM). The results showed that plastic void growth, cavitation and shear yielding mechanisms were the main toughening mechanisms of the bulk epoxy systems. In the next step, mechanical properties (i.e. impact resistance, flexibility, cupping resistance and hardness) and adhesion of the thin film specimens were evaluated in accordance to the amount of synthesized ETPB. The results showed that the mechanical properties of the ETPB modified epoxy resins considerably improved. In all cases, it was found that the improvement of the mechanical properties reached a maximum at 7.5 wt.% and then began to decrease with further increase in ETPB content. The effective toughening mechanisms in the modified thin films were also examined using SEM and compared to the bulk types. In contrast to the bulk types, the results showed that crack arresting and shear yielding were active mechanisms in thin films. The contribution of these mechanisms led to the improvement of adhesion and mechanical properties by energy dissipation.

► Toughening mechanisms of bulk rubber modified epoxy resins were studied.
► Effective toughening mechanisms of thin film rubber modified epoxy resins were investigated.
► Investigation of the role of the rubber modification on the mechanical properties of thin films.
► Investigation of the amount of rubber modification on the mechanical properties of the samples.