The 3rd International Symposium on Nanocellulosic Materials (3rd ISNCM)

   Shape memory polymer is a kind of smart material with great potential and has been extensively studied in recent years. However, it is difficult to achieve both superior mechanical properties and response sensitivity, besides cost of shape memory materials limit the application. A new biomimetic, stimuli-responsive polymer nanocomposite, which filled with natural cellulose nanofibrillated fibers exhibiting excellent mechanical properties and meanwhile displaying pH and temperature activated shape memory effect, was investigated. This material was produced by introducing Phosphorylated Cellulose nanofibrils (PCNFs) into a rubbery polyurethane (PU) matrix, and composite film were subsequently prepared by solidifying in a Teflon mold. The composite maintains the pH-responsive effect as a result of the percolation network of phosphorylated cellulose nanofibrils which can reversible hydrogen bonding with polyurethane, and simultaneously, possessing thermal-responsive effect originated in the polyurethane matrix. Fourier transform infrared spectroscopy was used to confirm the synthesis process. The tensile tests demonstrated the good mechanical properties of the materials with a tensile modulus and tensile strength at room temperature. The pH-activated properties greatly affected by the pH-value of the polymer percolation network were investigated using differential scanning calorimetry and X ray diffraction.

   The pH reversible hydrogen bonding network serve as a reversible phase, and the cross-linked cellulose percolation network serve as a fixing phase. It is shown that this material can be processed into temporary shape under the optimum conditions at pH 11 and recover to its initial shape at pH 1. The recovery ratio and the fixity ratio were 99.5±0.5% and 97.8±1.1%, respectively. Furthermore, this composite showed triple-shape memory effect. The deformation rate can reach 200% by applying stress and stretching to the material in the thermal environment. After lowering the temperature, the shape quickly retracted to the initial state, completing a cycle within milliseconds, under the effect of temperature induction, the material can achieve 99% shape memory performance, and can stretch more than 300 times of its own load. After several tests, it is found that the material has good fatigue resistance, and the fixed rate and recovery rate are stable at 95% after six cycle tests. Because the good degradability and biocompatibility of this material, it has a high biomimetic potential for medical application.