Role of surface active additives on reduction of surface free energy and enhancing the mechanical Attributes of easy-to-clean automotive clearcoats: Investigating resistance against simulated tree gum

The objective of this work is enhancing the clearcoat resistance against simulated tree gum (Arabic gum) using surface active additives including hydroxyl-functional polydimethyl siloxane (PDMS) and hydroxyl-functional silicone polyacrylate which are able to reduce gum adhesion to the clearcoat surface by reducing its surface free energy and work of adhesion. Using a contact angle measuring device, the surface free energy, contact angle and work of adhesion were obtained. The mechanical and structural properties of the clearcoats were studied by tensile test, dynamic mechanical thermal analysis (DMTA) and Fourier transform Infrared spectroscopy (FT-IR). Results showed that both additives enhanced the clearcoat easy-to-clean properties and reduced work of adhesion and surface free energy. The decrease in surface free energy and work of adhesion was more pronounced in presence of hydroxyl-functional polydimethyl siloxane. It was found that polydimethyl siloxane could produce contact angles much greater than silicone polyacrylate. Both additives increased clearcoat cross-linking density and toughness by participating in curing reaction. Results showed that the increase in cross-linking density and toughness was more effective when polydimethyl siloxane based additive was used. Results also revealed that additives could significantly improved the clearcoat resistance against Arabic gum by reducing gum adhesion to the surface. Both number of cracks and etched areas were reduced in presence of the additives especially in presence of polydimethyl siloxane. Both the chemical structure and functionality of the additives were found influential parameters which could alter the clearcoat surface cleanability and biological resistance against simulated tree gum.