Graphene Foam Reinforced Shape Memory Polymer Epoxy Composites

Abstract

Shape memory polymer (SMP) epoxy has received growing interest due to its facile processing, low density, and high recoverable strain. Despite these positive attributes, SMP epoxy has drawbacks such as slow recovery rate, and inferior mechanical properties. The slow recovery rate restricts the use of SMP epoxy as a functional structure. The aim of the present work is to explore the capabilities of three-dimensional (3D) graphene foam (GrF) and graphene nanoplatelet (GNP) as reinforcements in SMP epoxy to overcome their slow recovery and improve the mechanical properties. GrF and GNP based SMP epoxy composites are fabricated by mold-casting approach and 3D printing techniques, respectively. They are investigated for their thermal, shape recovery, and mechanical behaviors. 0.13 wt.% GrF addition results in 19% increase in the glass transition temperature (Tg) of mold-cast SMP epoxy. GrF-based SMP epoxy composite displays thermal conductivity of 0.296 W mk-1 at 70oC, which is 57% greater than that of SMP epoxy. The addition of GrF results in excellent thermal and electrical conductivity of SMP epoxy by providing a continuous network of graphene for phonon and electron flow, respectively. Thus, thermal and electrical stimulation are employed to actuate shape recovery in GrF-reinforced SMP epoxy composite. Maximum shape recovery ratio is achieved for thermally actuated GrF-based SMP epoxy composite with a 23% improvement in the recovery rate. GrF addition transforms a non-electrically conductive SMP epoxy to an electrically conductive polymer. Moreover, 0.5 wt.% GrF integration enhances tensile strength and elastic modulus of SMP epoxy by 6% and 20%, respectively which is attributed to excellent stress transfer from matrix to GrF reinforcement. Damping behavior of of SMP epoxy -0.5 wt.% GrF is also improved by 180%, respectively. SMP epoxy-GNP composite is successfully 3D printed using a slurry-based extrusion technique. 3D printed composites exhibit complete shape recovery. A mere 0.1 wt.% GNP addition resulted in enhanced tensile strength (30%) and elastic modulus (17%). Damping behavior of 3D printed of SMP epoxy-GNP composite is also improved by 50% (below its Tg) as compared to 3D printed SMP epoxy. This study demonstrates that graphene-based reinforcement endow SMP epoxy with multifunctional capabilities; thereby paving the way for a new generation of advanced shape memory polymer composite, finding potential applications in electro-mechanical systems, micro-robots and morphing wing of an aircraft.