Studies on silicone-acrylic hybrid aqueous dispersions and corresponding silicone-acrylic nanopowders designed for modification of powder coatings and plastics Part II - Effect of modification with silicone-acrylic nanopowders and of composition of silicone resin contained in those nanopowders on properties of epoxy-polyester and polyester powder coatings

Epoxy-polyester and polyester coatings were modified with 3% of NP-DASI "nanopowders" consisting of core-shell nanoparticles having silicone resin of very low glass transition temperature (T-g) in the core and poly(methyl methacrylate) of high T-g in the shell. The nanopowders were obtained through spray drying of corresponding aqueous dispersions with core-shell particle structure which were synthesized in a process of emulsion polymerization of methyl methacrylate monomer in aqueous dispersions of silicone resins with different compositions resulting from different compositions of silicone monomers used for their synthesis. A designed experiment was conducted where the effect of composition of silicone resin on the properties of cured coatings was studied. It was confirmed that modification with that "nanopowder" significantly affected the properties of cured coatings, in particular impact resistance and cupping as well as surface properties. Regarding mechanical properties the influence of modification with "nanopowder" was generally more distinct for epoxy-polyester coatings than for polyester coatings. Specifically, great increase in impact and cupping resistance was observed for modified coatings and was explained by absorption of mechanical stresses by particles of low modulus silicone resin which were released from core-shell nanoparticles in the process of curing of the coatings. Other mechanical properties of cured modified and unmodified coatings (abrasion resistance, hardness, scratch resistance, elasticity and adhesion to steel) as well as appearance of the coatings (gloss and whiteness) did not differ much. Water resistance and salt fog resistance were slightly better for modified coatings. Testing the surface properties of modified coatings by XPS and AFM revealed the presence of silicone resin on coating surface what was reflected in higher contact angle and lower SFE as compared to unmodified coatings. That phenomenon was explained by migration of silicone resin to the coating surface. (C) 2014 Elsevier B.V. All rights reserved.