Adhesion properties of polyamide-6 fibres treated by dielectric barrier discharge

The adhesion properties of polyamide-6 fibres are improved by dielectric barrier discharge (DBD) treatment in helium at atmospheric pressure. These properties are usually expressed by means of the adhesion work, the surface energy and its polar and dispersive components, the polarity etc. Since the calculation of these quantities requires measurement of the contact angles between a liquid drop and the fibres, we use here a theoretical method that allows calculating the contact angle on cylindrical surfaces using measurable geometrical dimensions of the drop. Also, an experimental arrangement for contact angle measurement, based on the image-processing system, is described and the quantities related to the adhesion properties are estimated. The adhesion work, the surface energy and the surface polarity are increased after treatment, demonstrating the efficiency of the DBD technique in improving the adhesion properties of the polymer fibres. Moreover, AFM topography images show modifications at the micro and nanostructure level, relevant to enhanced adhesion. Microparticles and oligomers are removed from the treated fibres, leaving a cleaner and smoother surface at the microscale. Furthermore, a new structure is observed at the nanoscale, with an increased roughness and a larger surface area, favouring the adsorption. The AFM phase images confirm the cleaning of the fibre surface and also a better compositional homogeneity after DBD treatment.