Microflames for the surface treatment of polymers

Polyethylene (PE) films were treated with flame pulses for a confined activation of the surface. Acetylene, ethene, and butane were used in various mixing ratios with oxygen. The gas mixture was fed through a 0.5 mm stainless steel capillary, which was placed close to the surface of the film. An electrical spark was used to ignite the gas. A single flame pulse suffices to oxidize the polymer surface to an oxygen concentration of 26 at% (XPS). The profile of the oxygen concentration was analyzed by XPS and revealed full width at half maximum values down to 2.8 mm. The treatment of pieces of sintered PE powder (nominal pore size, 80 µm) showed that the surface oxidation penetrates several millimeters into the pore system. Microflames can efficiently activate a polymer surface. With a capillary feeding the burning gas mixture to the surface, the oxidation can be confined to spots and lines (full width at half maximum [FWHM] as small as 2.8 mm). A single flame pulse results in an oxygen concentration at a polyethylene (PE) surface of well above 20 at%.