Enhancing the Fracture Resistance and Impact Toughness of Mechanically Frothed Epoxy Foams with Hollow Elastomeric Microspheres

Nonporous elastomeric particles are often employed to improve the toughness of brittle epoxy foams but this also decreases their compressive strength and stiffness. Herein, a novel strategy utilizing hollow elastomeric microspheres as toughening agent for epoxy foams is presented. The addition of 0.5 wt.% hollow elastomeric microspheres into epoxy foam leads to a 15% increase in critical stress intensity factor (K _1c) to 0.38 MPa m^0.5 and 33% increase in Charpy impact strength (a_cU ) to 1.05 kJ m⁻², respectively, compared to unfilled epoxy foam (K _1c = 0.33 MPa m^0.5 and a_cU  = 0.79 kJ m⁻²). However, a further increase in the hollow elastomeric microsphere concentration to 1.0 wt.% leads to microsphere agglomeration, which reduces both K _1c and a_cU to 0.35 MPa m^0.5 and 0.93 kJ m⁻², respectively. Nevertheless, the added hollow elastomeric microspheres do not lead to a reduction in the quasi-static compressive properties of the epoxy foams.