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Polyurethane (PU) based composites were prepared by solvent casting techniques using different wt. % (0-5 wt. %) of reduced graphene oxide (RGO) as reinforcement. Nanoindentation study has been carried out on these composite sheets in order to investigate its nano-mechanical properties. Incorporation of different wt. % RGO in PU matrix led to significant increase in the hardness and elastic modulus of the composites. The maximum nanoindentation hardness of 140 MPa for 5.0 wt. % RGO loading was observed as compared to 58.5 MPa for pure PU (an overall improvement of 139 %). The nanoindentation elastic modulus for 5.0 wt % RGO loaded sample was 881.7 MPa as compared to 385.7 MPa for pure PU (an overall improvement of 129 %). The enhancement in the nano-mechanical properties was correlated with spectroscopic and microscopic investigations using Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Due to their excellent nano-mechanical properties, these composites find their usefulness in structural applications such as automobile and wind mill blade industries. These composites can also be used in hard and scratch-less coating on automotive vehicles. The experimental results were in good agreement with theoretical Raman studies of the GO, RGO and RGO-PU composite films were carried out using Renishaw inVia Raman spectrometer, UK with an excitation source of 785 nm. The nanoindentation study was carried out using IBIS-Nanoindentation (M/S Fisher-Cripps Laboratories Pvt. Limited, Australia), equipped with Berkovich indenter and the other details are given elsewhere 28 . The analysis of the functional groups attached to the GO and RGO planes were studied by FTIR (NICOLET 5700) techniques.In order to make the samples for TEM studies, films were grinded to make it thin (~200 µm). Circular slice of 2.3 mm is cut using ultrasonic cutter. The slice is polished and dimple grinded to make it electron transparent (~ 50 nm at centre).Scheme 2: Process for the synthesis formation of stretchable and flexible RGO reinforced PU composites film

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