Ameliorating properties of castor oil based polyurethane hybrid nanocomposites via synergistic addition of graphene and cellulose nanofibers

Castor oil based polyurethanes were reinforced with cellulose nanofibers derived from hemp and graphene nanosheets to yield hybrid nanocomposites using ultrasonication coupled with high shear homogenization. Morphology of nanocomposites assessed using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) elucidated 3D network of CNFs and GNS in polyurethane matrix. The paramount properties were obtained with equal amounts of CNFs and GNS attributed to higher degree of crystallinity. Thermal stability was evaluated using Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC), which exhibited a substantial increase in peak degradation temperature by 24 °C and glass transition temperature by 36 °C, with mere addition of 1% CNFs and GNS each. The mechanical properties improved by more than 400% attributed to the presence of interconnecting network of GNS and CNFs, initiating enhanced interactions amongst polymer and nanofillers, established by X-Ray photoelectron spectroscopy (XPS). Strong intermolecular bonding between the fillers and the polymer matrix reduced the phase separation, facilitating migration of soft segments to the surface increasing the water contact angle by 32°. The decrease in surface energy and work of adhesion contributed to hydrophobicity of nanocomposites. The improved properties of hybrid nanocomposites ascertain their potential applications in protective coatings and automobile parts..