Achieving shape memory: Reversible behaviors of cellulose-PU blends in wet-dry cycles

Shape memory effect (SME) was achieved for cellulose-polyurethane (PU) blends of different compositions in wet-dry cycles, featuring that the amorphous cellulose and the PU content served as the fixing phase and the recovery phase, respectively. The dependence on the compositions of the fixity ratio and the recovery ratio was quantitatively measured by tensile tests. The morphological and thermal properties of the blends were further investigated by scanning electron microscopy and thermogravimetric analysis. The storage modulus of the blends varied reversibly in the wet-dry cycles, as determined by dynamic mechanical analysis. Furthermore, the microstructure of the blends reversibly changed correspondingly, as determined by wide-angle X-ray scattering diffraction and Fourier transform infrared. It was predicted that the reversible transition in different amorphous cellulose structures triggered by water led to the reversible variation in modulus as well as the wet-dry SME of the blends.