Development of high performance two-way shape memory zinc dimethacrylate/ethylene vinyl acetate composite fibers for building flexible yarn actuators

Soft and flexible mechanical actuators capable of demonstrating large deformations and outputting stress spontaneously in responding to external environmental stimuli have been becoming a research focal point in the field of smart biomimetic systems and devices. Here, a novel twisted yarn actuator consisting of shape memory zinc dimethacrylate/ethylene vinyl acetate (ZDMA/EVA) composite fibers has been created following a four-step fabrication protocol including two-roll milling, melt-spinning, ultraviolet crosslinking, and twisting procedures. The obtained ZDMA/EVA composite fibers demonstrate excellent thermomechanical coupling effect and superior thermal/mechanical stability. In specific, the twisted yarn actuators present strong two-way shape memory capability (up to 8% reversible tensile stroke) and outstanding recovery stress (1.63–1.82 MPa). Notably, this composite yarn actuator (in diameters of 438–719 μm) is able to afford tension loads about 2300 times heavier than its own weight, reaching 7.76% reversible strain and exhibiting an exceptional energy density of 210 J/kg that is 26 times higher than the typical skeletal muscles. In addition, the optimal yarn actuator displays an ultimate rotation speed and rotational energy density of 15456 rpm/m and 5439 J/kg, respectively. This experimental study presents a facile, low-cost, and environmental-friendly manufacturing approach of developing high performance composite fiber-based yarn actuators.