Surface modification of polypropylene film using N2O-containing flames

Contact-angle measurements and X-ray photoelectron spectroscopy (XPS or ESC A) were used to characterize polypropylene (PP) films that were exposed to laminar premixed air:natural gas flames containing small quantities of nitr ous oxide. During combustion, the nitrous oxide generates gas-phase nitroge n oxides that lead to the affixation of nitrogen-containing functional grou ps to the PP surfaces. Treatment of PP in nitrous oxide-containing flames a lso leads to an increase in surface oxidation and markedly improves wettabi lity when compared with standard flame treatments. The chemical form of the nitrogen affixed to the PP surface is strongly dependent on the flame equi valence ratio. Fuel-lean flames tend to affix highly oxidized forms of nitr ogen such as nitrate and nitro groups, while fuel-rich flames tend to affix less-oxidized nitrogen groups such as nitroso, oxime, amide, and amine. A computational model, SPIN, was used to elucidate the chemistry of the flame as it impinges upon the cooled PP surface, The SPIN modeling indicates tha t the principal reactive gas-phase species at or near the PP surface are O- 2, OH, Ii, NO, NO2, HNO, and N2O. A number of possible reactions between th ese species and the PP van account for the formation of the various nitroge n functional groups observed.