Dual-Triggered and Thermally Reconfigurable Shape Memory Graphene-Vitrimer Composites

Abstract

Conventional thermoset shape memory polymers can maintain a stable permanent shape, but the intrinsically chemical cross-linking leads to shape that cannot be altered. In this paper, we prepared shape memory graphene-vitrimer composites whose shape can be randomly changed via dynamic covalent transesterification reaction. Consecutive shape memory cycles indicate stable shape memory with undetected strain shift and constant shape fixity and recovery values (Rf > 99%, Rr > 98%). Quantitative characterization of shape reconfiguration by dynamic mechanical thermal analysis (DMA) shows prime reconfigurable behavior with shape retention ratio of 100%. Thus, the arbitrary 2D or 3D newly permanent shape can be easily obtained from a simple plain sample by facile thermal treatment at 200 °C above transesterification temperature (Tv). Besides, it is found that graphene-vitrimers show a ductile fracture in tensile test with a large breaking strain and classical yield phenomenon because of the well-dispersed graphene sheets in the vitrimer that endow effective stress transfer. As the graphene loading increases from 0% to 1%, the yield strength and breaking stain increase from 12.0 MPa and 6% to 22.9 MPa and 44%, respectively. In addition, graphene also serves as energy convertor to convert near-infrared (NIR) irradiation into thermal energy to induce a helix shape sample that is recovered totally within 80 s sequent NIR irradiation. These dual-triggered and reconfigurable shape memory graphene-vitrimers are expected to significantly simplify processing of complex shape and broaden the applications of shape memory polymers.

Ultra‐Fast Microwave Assisted Self‐Healing of Covalent Adaptive Polyurethane Networks with Carbon Nanotubes

“…CNTs have been successfully used to assist self‐healing of vitrimers through near infrared absorption. The CNT loading used in this study is the lowest by comparison with data reported in literature . In addition, the dual exchange reactions in this vitrimer system allowed for better recovery of mechanical properties.…”

“…In this case, organoaniline absorbed NIR and produced the required heat for self‐healing. Due to the high NIR absorbance capability of nanotubes and graphene nanoplatelets, they are used in vitrimers to generate the heat required for activation of the exchange reactions. Using small amounts of carbon nanotubes or graphene nanoplatelets decreased the healing time significantly.…”

Dynamic Covalent Chemistry at Interfaces: Development of Tougher, Healable Composites through Stress Relaxation at the Resin–Silica Nanoparticles Interface

“…Also, transesterification-based shape memory composites based on graphene-filled vitrimers were prepared. [35] However, all of these approaches implement the DCC throughout the resin and fail to implement the desired DCC at the polymer–matrix interface where stress is concentrated, contributing to composite failure.…”

Vitrimerization: A Novel Concept to Reprocess and Recycle Thermoset Waste via Dynamic Chemistry

“…Vitrimers belong to the second category of CANs in which the crosslinking bonds have an associative nature resulting in the ability of the material to change its topology via exchange reactions. These reactions normally are triggered by heat, which causes the gradual decrease in system viscosity with increasing temperature and provides malleability to the network.…”

“…Since vitrimerization also allows for the processing of a thermoset just like a thermoplastic, it affords the unique advantage of incorporating fillers into the thermoset network during recycling to compensate for the drop in mechanical properties due to the catalyst. The addition of fillers to enhance the properties of vitrimers has already been studied extensively . Just as an example, 10 wt% of highly branched carbon nanotubes with a diameter of 7–9 nm known as carbon nanostructures (CNS) were extruded along with the vitrimerized PU samples with the same parameters mentioned above and tested for mechanical properties as can be seen in Figure c.…”