Investigation of thermomechanical one-way and two-way shape memory behaviors of crosslinked poly (ethylene-co-vinyl acetate) / multi-walled carbon nanotube composites

Abstract

Abstract This study systematically investigates the thermomechanical characterization of crosslinked poly(ethylene-co-vinyl acetate) (cEVA) nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs). Through melt-blending and thermo-curing, nanocomposites with 1–5 wt% MWCNTs were synthesized and rigorously evaluated via differential scanning calorimetry, dynamic mechanical analysis, and thermomechanical tests. The nanocomposites exhibit dual-responsive one-way (1 W-SME) and two-way (2 W-SME) shape memory effects under constant stress/strain conditions, driven by crystallization-induced elongation and melting-induced contraction mechanisms, with effective transition temperatures deviating from DSC-measured values due to mechanical loading. Large reversible strains in 2 W-SMEs and good shape fixity/recoverability in 1 W-SMEs were achieved. The study further elucidates the influence of MWCNT content, cooling/heating rates, and external loads on the thermomechanical responses, providing experimental and theoretical foundations for designing programmable actuators and adaptive structures. The integration of nanofiller-mediated crystallization control and thermomechanical coupling mechanisms highlights a novel pathway to tailor high-performance smart materials with predictable recovery and scalability.