Co-extruded multilayer shape memory materials: Nano-scale phenomena

Shape memory polymers (SMPs), which demonstrate the ability to possess multiple shapes, are traditionally produced from copolymers and recently from blends. These materials often have phase separated morphologies that possess domain sizes on either the nano- or micro-scale. The observed properties, specifically the shape memory behavior, can be significantly altered by a change in the domain size; however, doing this often requires modification to the materials or material production process. Forced assembly multilayer co-extrusion was used to produce shape memory materials with a continuous layered structure that can be easily tailored to cover layer thicknesses ranging from the nano- to the micro-scale. Upon decreasing the layer thickness of polyurethane/polycaprolactone (PU/PCL) layered films, improvement in the shape fixity and recovery ratios tracked with layer thickness. The improvement in properties was attributed to a change in the PCL crystal orientation from randomly oriented in microlayers to in-plane lamella orientation in nanolayers.