Improved Adhesion of TiO2 -Based Multilayer Coating on HDPE and Characterization of Photocatalysis

Multilayered photocatalytic TiO₂-based coating was prepared by spin coating on a high-density polyethylene (HDPE) substrate. The multilayered coating consisted of a polyurethane (PU) barrier layer and two layers of TiO₂ nanoparticles bound with PU. The adhesion between the HDPE substrate and protective PU coating was enhanced by oxygen plasma treatment of the substrate. The improved adhesion contributed to the photocatalytic degradation of palmitic acid. Long-term activity of the photocatalytic coating in degradation of palmitic acid under UV illumination was followed by FTIR-ATR. The catalytic activity of the coating was maintained in three identical cycles where palmitic acid was added and UV-irradiated for 6 h. According to FTIR measurements, the palmitic acid was almost completely decomposed after 6 h, but gas chromatography (GC) analysis showed total decomposition to require 12 h UV illumination (∼ 97% of palmitic acid decomposed in 12 h). Study of the degradation of palmitic acid by GC as a function of time indicated that the degradation kinetics was pseudofirst order, and the rate constant obtained was 0.31 h⁻¹.