Sol–gel derived hybrid coatings for the improvement of scratch resistance of polyethylene

Organic–inorganic hybrid materials were prepared through the sol–gel approach starting from tetraethoxysilane (TEOS), as silica precursor, and triethoxysilane terminated polymers; before gelling the solutions were applied to polyethylene (PE) films and slabs by spin-coating, without any previous surface pre-treatment of the substrate, and finally the coatings were thermally cured at 60 °C for 24 h. Among the various polymers used to prepare the coatings, only polyethylene-b-poly(ethylene glycol) copolymers gave good results in terms of adhesion to the PE substrates, and hybrid coatings with different organic–inorganic ratios were prepared. As suggested by visual inspection and SEM investigation, and confirmed by the critical loads derived from scratch tests, a good adhesion of the coating to the PE substrates was obtained, probably due to the presence of PE segments in the organic phase of the coating. Transparency as well as SEM and DSC data were in agreement with the formation of a nanostructured hybrid coating, with a high level of interpenetration between organic and inorganic domains. It was also observed that these hybrid coatings are able to improve significantly the scratch resistance and slightly increase the wettability with respect to uncoated PE. This approach to the surface-properties modification of PE appears as a simple and convenient method for the functionalization of PE substrates.