Morphology, reversible phase crystallization, and thermal sensitive shape memory effect of cellulose whisker/SMPU nano-composites

To investigate the morphology, crystallization properties of reversible phase and thermal sensitive shape memory properties of CW/SMPU (Cellulose Whisker/Shape Memory Polyurethane) nano-composite, the CW/SMPU nano-composite having CW contents of 0.1-3.8 wt % were prepared. SEM investigation showed the evolution of reversible phase morphology from spherolite crystallization structure to uniform matrix with tiny CW aggregates with the addition of CW into the SMPU matrix. DSC and isothermal crystallization kinetic method revealed the effect of CW on crystallization properties of reversible phase and fixed phase, suggesting that the effect of CW on the crystallization of hard segment phase is not comparable with thermal history; the more CW causes the higher crystallization rate of reversible phase; the crystallization mechanism of reversible phase in nano-composite gradually evolves to heterogeneous nucleation and crystal growth in two dimensions with the increase of CW content; the excellent nucleation effect of CW for the reversible phase leads to the drop of activity energy from 134.1 kJ/mol (N-0), to 95.1 kJ/mol (N-4). Cyclic tensile tests illustrate the addition of CW content can engender rapid shape fixity ability after a relative short cooling time; the shape fixity ratio of nano-composite and the control sample after sufficient cooling all can be identically high.