Surface modification of polypropylene film by exposure to laminar, premixed methane-air flames

The flame treatment of polypropylene film was investigated through experimental and numerical studies. Two process parameters, flame equivalence ratio and burner-to-film separation distance, were varied, and the extent of surface treatment was quantified through wettability tests and oxygen-to-carbon atomic ratios obtained from X-ray photoelectron spectroscopy. These results were compared with numerical simulations using the nonreacting Fluent fluid-dynamics software and the one-dimensional PREMIX chemical kinetics code. Excellent agreement was found between the experiments and the modeling, with optimal treatment occurring at a flame equivalence ratio of 0.93 and a separation distance of 2 mm. A correlation between the film wettability and the concentrations of O and OH radicals was observed. The mechanism of surface oxidation by flame treatment probably involves polymer-radical formation by O and OH, followed by rapid reaction of the polymer radicals with O, OH, and O-2.