The degradation of mechanical properties due to stress concentration caused by retained acetone in epoxy nanocomposites

Abstract

Multi-layered graphene (MLG)–epoxy nanocomposites of three different types were produced using the solution casting technique with MLG dispersed in three different mediums; acetone (MA), an epoxy (ME), and a hardener (MH). In the case of MLG dispersed in the hardener (MH), the maximum increases in tensile and flexural properties, fracture toughness, and microhardness were observed at 0.3 wt% of MLG. The Young's modulus increased from 610 MPa to 758 MPa (24% increase) and the tensile strength increased from 46 MPa to 60 MPa (31% increase). The fracture toughness (K_1C) increased from 0.8 MPa m^1/2 to 1.1 MPa m^1/2 (29% increase) and the Charpy impact toughness increased from 0.85 kJ m⁻² to 1.61 kJ m⁻² (89% increase). An increase in the storage modulus and glass transition temperature (T_g) was also observed which is attributed to the high stiffness and restriction of polymer chains. Also, if the acetone is not completely removed, the products would have porosity which acts as a stress concentrator and significantly degrades the mechanical properties of the nanocomposites.