Preparation of shape memory polyurethane composite materials by grafting PCL onto CNFs with different carboxyl content

Abstract This study describes the preparation of cellulose nanofibers (CNFs) with varying amounts of carboxyl groups from rice straw pulp using the TEMPO/NaBr/NaClO oxidation system. The resulting CNFs were found to be in the form of nanofibers with an average diameter of 6 nm and an average length of 160 nm. To further enhance their properties, the CNFs were grafted with polycaprolactone (PCL) to create CNFs-g-PCL, which was then blended with shape memory polyurethane (SMPU) to produce CNFs-g-PCL/SMPU composites. It was observed that as the carboxyl content in CNFs increased from 0.35 to 1.14 mmol/g, the graft ratio of PCL on CNFs decreased from 24.6 to 10.7%. Consequently, the hydrophobicity of the grafted product (CNFs-g-PCL) also decreased. When 10% CNFs-g-PCL was added to the SMPU matrix, the elastic modulus and tensile stress of the resulting composite were both higher than those of the pure SMPU, increasing by up to 54.4% and 67.3%, respectively. Additionally, the shape retention and shape recovery rates of the composite remained stable after addition of CNFs-g-PCL. In conclusion, incorporating CNFs-g-PCL into SMPU can improve its mechanical properties while maintaining its shape memory properties. Graphical abstract