Cryo-Assisted Extrusion Three-Dimensional Printing of Shape Memory Polymer–Graphene Composites

Abstract

A cryo-system-assisted extrusion three-dimensional printing technique has been developed to fabricate Shape Memory Polymer Epoxy (SMPE) thermoset into a near-net shape. With a unique cryogenic sprayer-assisted printing system, it is possible to 3D print “pure” thermoset polymer, otherwise limited to thermoplastic or highly functionalized co-polymeric thermoset systems. The temperature was maintained below 10 °C to immobilize the polymeric chain at the atomic level. Nanoplatelet (GNP) reinforced SMPE ink was synthesized to be compatible with cryo-assisted extrusion 3D printing of shape memory composites. The addition of a mere 0.1 wt% GNP exhibited 15% faster shape recovery due to improved thermal conductivity, evidence of a strong interface between GNP and the polymer matrix. Also, GNP addition imparted a 30% improvement in the ultimate tensile strength and a 17% increase in 3D-printed composites’ elastic modulus. Mechanical testing showed that the addition of 0.1 wt% GNP in SMPE increased the composite's storage modulus by 365% and loss tangent by 66% compared to pure 3D-printed SMPE, indicating enhanced damping characteristics. This study is the first to demonstrate a non-existent 3D printing technology for “pure thermoset” polymers with and without conductive graphene that has the potential to develop an energy-efficient actuation system, passive thermal sensors, and self-deployable communication system structures.