Flame treatment was initially developed in the 1950s to improve the adhesion properties of polyolefin films. Flame treatment typically creates oxidized species on the surface of films, by the formation of hydroxyl, carboxyl and carbonyl functionalities. Treatment (oxidation) depth varies with the substrate type, as does the generation of low molecular weight oxidized material at the surface.
Surface exposure to flame treatment directly modifies the electron distributions and densities of molecules, resulting in oxidation at the polymer surface up to several nanometers deep.
This review aims to provide a summary of developments regarding flame treatment as a valuable technique for improving the surface properties of polymers. In particular, in the first part special focus is on the combustion process and the main process parameters of flame treatments. In the second part, effects due to flame activation processes on polymers are discussed from different points of view (chemical, physical, morphological). Although the flame treatment represents the oldest activation treatment, the optimization of process parameters and the changes in chemistry and morphology of the polymeric materials were investigated in detail only recently.
Key words: FLAME TREATMENT; OXIDATION; POLYETHYLENE; POLYPROPYLENE; SURFACE ACTIVATION; SURFACE FREE ENERGY; WETTABILITY