Improved adhesion for thermoplastic polymers using oxyfluorination
Industrial applications of thermoplastic polymers are often limited by their poor adhesion properties. In this work the effect of surface oxyfluorination on the adhesion properties was investigated for polyethylene (PE), polyoxymethylene (POM), polybutylene terephthalate (PBT) and polyamide 6 (PA6). The adhesive joint strength was quantified using lap-shear tests. These results were correlated with the changes in the chemical composition of the surface, determined by X-ray photoelectron spectroscopy (XPS), in the surface free energy, measured by the contact angle method, and in the topography, using white-light confocal microscopy. The adhesive strength is strongly improved for all four polymers, but the degree of this increase depends on the polymer type. The surface free energy shows a similar trend for all four polymers. A high surface free energy exceeding 50 mN/m was observed after oxy-fluorination, whereby the polar component was strongly predominant. Surface topography measurements show no significant increase of the surface roughness. So the effect of oxyfluorination results primarily in increased wettability and polarity, due to changes of the chemical composition of the surface. XPS measurements confirm the integration of fluorine and oxygen groups in the polymer chain, which correlates with the increased polarity.
Characterization of a non-thermal plasma torch in streamer mode and its effect on polyvinyl chloride and silicone rubber surfaces
Abstract In this study, a non-thermal plasma torch in steamer mode was characterized to apply for surface modification in ambient air. The plasma source is a central rod-ring configuration based on DBD operation. Mixture of Ar/air gases was passed through the hollow Copper rod. A home-built high voltage generator at 18.8 kHz was employed to ignite the plasma. Electrical features of plasma torch were studied and different regions of plasma were examined using optical emission spectroscopy to explore the reactive species that result in efficient treatment. The surfaces of polyvinyl chloride (PVC) and silicone rubber (SIR) films were treated by the cold plasma torch. Contact angle measurement shows the improvement of surface hydrophilicity and wettability. Analysis revealed that the surface energy of the films increases indicating their activation after plasma treatment. This process is attributed to increasing the polar component of the surface energy.
Improved and novel surface fluorinated products
Abstract The use of surface fluorination negates the necessity for using adhesive promoters to achieve adequate paint adhesion on polyolefinic substrates, even for water-based paints. The addition of oxyfluorinated polypropylene (PP) fibres to cementitious mixtures enhances properties like wet and dry crack control, impact resistance, water absorption etc. This is due to the improved adhesion between oxyfluorinated fibres and cement. A new surface fluorination method for high-density polyethylene (HDPE) enhances petrol barrier properties to a permeation rate lower than that of fluoropolymers. To scrub unreacted F 2 and gaseous reaction products like HF formed during the surface fluorination process, the use of wet limestone is suggested.