In this study, the effect of nanodiamond on scratch resistance of an acrylic/melamine clearcoat was studied. Clearcoat is a layer of paint or resin that is applied on top of a car\\\\\\\'s colored base coat. Therefore, it is vital to enhance the resistance of the coating against environmental factors. In order to guarantee an undamaged surface for the lifetime of a product the mechanical propertiesof clearcoat layer can be increased by fillers and additives. Addition of hard particles to polymers to improve their physical and mechanical properties is very common. For this purpose we used detonation nanodiamond (DND) with average particle diameter 4-6nm as filler. To improve dispersion of as-received (AR) DNDs in acrylic, surfaces of AR-DNDs were modified by heat treatment (oxidation) in air (HT) and by oxidation in air followed by functionalization in concentrated oleylamine and thinner. The nanocomposite sprayed on the pre-electro-deposited steel samples. Then samples were scratched under constant loads and speed. The results indicated that the presence of DND promotes scratch resistance of acrylic because of an increase in surface hardness. The identifications and characterizations were investigated by employing many analytical methods such Fourier transform infrared spectroscopy (FTIR) ،Transmission electron microscopy (TEM) ٫Thermo-Gravimetry Analysis (TGA).

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