Contact-angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated biaxially oriented polypropylene (PP) films. While the surface of PP treated in a fuel-lean flame is highly oxidized, no water soluble low-molecular-weight oxidized material (LMWOM) is formed by the flame treatment. A new computational model, SPIN, was used to determine the chemical composition of the impinging flames used to modify the PP The SPIN model indicates that the species primarily responsible for the surface oxidation of the PP are OH, HO2, H2O2, and O-2. Because the concentration of atomic O in the flame is low, there is little scission of the PP chains and no formation of LMWOM. AFM indicates that a 'nodular' surface topography is generated during the flame oxidation of the PP. The surface topographical features generated by flame treatment are probably the result of the agglomeration of intermediate-molecular-weight materials.

This study focuses on the key parameters that enhance the stability of ribbon burners used in various industrial processes, characterizing the flame environment and flow regimes that the burner creates under changing operating conditions. The research includes the exploration of ribbon-pack configurations in order to define the effects of separation distance and port arrangement on flame stability and thermal and fluid flow. Flow visualization studies reveal that burners having a 1.5–2.0mm division between rows appear to be the most stable. More than four rows of ports in the ribbon-pack are required to resist entrainment of ambient air as a result of impinging surface motion. The flame environment created by the ribbon burner experiences higher levels of mixing, at a lower Reynolds number in comparison to a single non-reacting jet due to combustion-induced turbulence and jet interaction. Under these high flow velocity conditions there is little entrainment of ambient air along the impingement surface and a very stable flame environment is created.

This article focuses on recent advances in the understanding of industrial gas burners. Ribbon burners have been chosen as the focus of the review because of the advantages presented by the burner arrangement and burner performance. The ribbon burner configuration, because of its ability to provide large flame surface and flame stabilization, has a large range of stability as flow rate, equivalence ratio and reactant gas composition are varied. Discussed in detail is the application of ribbon burners in the surface modification, or flame treatment, of polymer films to increase the wettability of a polymer surface. Optimum treatment requires a spatially homogeneous post-flame reaction zone even with burners up to 3m in length. For methane/air flames, the optimum equivalence ratio is near 0.93 where the active oxidizing-species concentration near the surface is a maximum. Chemical kinetic models of the impinging flame and surface oxidation chemistry of a polymer film are also discussed. The model predictions are in good qualitative agreement with the available understanding of the flame variables affecting surface treatment and the expected oxidized species on the polymer surface.

A cross-web non-uniformity ('laning') in the flame surface modification of polypropylene (PP) film was investigated using flame temperature measurements and Wilhelmy plate force measurements. To associate the cross-web non-uniformity in the flame treatment with specific features of the flame supported on an industrial 4-port ribbon burner, the temperature and force measurements were registered to a specific burner port. The Wilhelmy force measurements show that the upstream pair of ribbon-burner ports causes a slightly greater treatment of the PP surface than the corresponding downstream pair of ports. The average temperature experienced by the PP as the film traverses through the flame is noticeably higher along the down-web line of the upstream burner ports as compared with a line passing through the downstream pair. This greater average temperature correlates to an exposure to a greater concentration of the active species, such as OH radicals, that cause the surface oxidation of the PP.

The flame treatment of polypropylene (PP) film involves the use of impinging, conical flames to oxidize the surface of the PP. Depending on treatment conditions, the PP film can be exposed to an inhomogeneous environment because of the conical shape of the flames. This environment can lead to cross-web variations, or 'lanes', in the wettability of the film. We have developed a simple method to quantify these non-uniformities using the information provided by the Wilhelmy plate technique of dynamic contact angle measurement. Both surface-averaged and spatially resolved surface-energy data can be obtained by this technique. In the case of our PP film, the spatial non-uniformities were found to be caused by variations in surface chemistry, not topography. These nonuniformities are not observed on untreated PP. Use of this method enables a quantitative evaluation of the effects of flame-treatment process variables on treatment uniformity.

The comparison of corona-treated and flame-treated polypropylene (PP) films provides insight into the mechanism of these surface-oxidation processes. Atomic force microscopy (AFM), contact-angle measurements, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize surface-treated biaxially oriented PP. While both processes oxidize the PP surface, corona treatment leads to the formation of water-soluble low-molecular-weight oxidized materials (LMWOM), while flame treatment does not. Computational modeling of the gas-phase chemistry in an air corona was performed using a zero-dimensional plasma-chemistry model. The modeling results indicate that the ratio of O to OH is much higher in a corona discharge than in a flame. Chain scission and the formation of LMWOM are associated with reactions involving O atoms. The higher ratios of O to OH in a corona are more conducive to LMWOM production. Surface-oxidized PP exhibits considerable thermodynamic contact-angle hysteresis that is primarily caused by microscopic chemical heterogeneity.