Photo-thermal actuation of ultra-drawn high-density polyethylene

In this work, the photo-actuation of melt-processed ultra-drawn films based on high-density polyethylene (HDPE), incorporating a light-responsive additive (2-(2H-benzotriazol-2-yl)-4,6-ditertpentylphenol, BZT), is presented. These oriented films exhibits a fast (<1 s) and reversible photo-thermal response upon exposure to ultra-violet (UV) light with a maximum actuation stress of -20 MPa at a strain of 0.1%. Actuation is triggered by light, which is absorbed by the BZT and transferred into heat. The generated heat, in combination with the intrinsic high stiffness (similar to 30 GPa) and negative thermal expansion of these oriented polymer films, induces entropy driven contraction of the macromolecular chains and thus when constrained an actuation stress. The above described set of properties, in combination with the facile, low cost and industrially scalable processing of these actuators makes them suitable for a wide range of potential applications, such as light driven robotics, control devices and functional textiles.