Polymeric Shape Memory Nanocomposites with Heterogeneous Twin Switches

A novel smart nanocomposite featuring a heterogeneous-twin-switch shape memory effect using cellulose-whiskers as reinforcement and segmented shape-memory-polyurethane as matrix is reported. The composite maintains the thermal-induced shape switchable effect originally existing in the polymer matrix and simultaneously possesses water-induced shape memory effect due to the percolation network of the cellulose whiskers whose hydrogen bonding can be regulated by water reversibly. The composite is capable of fixing the total temporary shape (shape A) through cooling and drying after the extension in a warm water condition. Reversibly, the extended composite partially recovers to the temporary shape (shape B) triggered by thermal stimuli solely and consequently from there to the original shape (shape C) triggered by thermal and water stimulus. This is a new strategy to combine two different types of switches into one material and the responsiveness of the composite is different from the conventional ones being able to response to one external stimulus only. This study gives a new mechanism of developing multi-responsive and multi-shape change materials and is believed to have enormous potential in applications where multi-shape changes responding to different stimulus are required.