The polymers PET, PA6, PVDF, HD-PE, and PP are activated by a commercially available plasma jet system at atmospheric pressure to improve adhesive bondability. The adhesion properties of the activated surfaces are evaluated by lap shear tests. The results are correlated with the surface properties that are investigated by XPS, AFM, and contact angle measurements. In addition the influence of operational parameters of the plasma treatment is studied. The activated samples exhibit a substantially increased bonding strength. The improvement can be related to an increase of oxygen concentration, and to changes of the topology of the substrate surface induced by the thermal component of the plasma. The most influential parameters in the plasma treatment are the distance between substrate and nozzle exit and the treatment time.

Polymeric hard/soft combinations consisting of a rigid, thermoplastic substrate and an elastomeric component offer many advantages for plastic parts in industry. Manufactured in one step by multi-component injection moulding, the strength of the thermoplastics can be combined with sealing, damping or haptic properties of an elastomer. Bonds of self-adhesive liquid silicone rubber (LSR) on high performance thermoplastics such as polyetheretherketone (PEEK) or polyphenylene sulphide (PPS) are especially interesting e.g. for medical applications due to their outstanding resistance properties. To ensure good adhesion between the two components, surface treatments from an atmospheric pressure plasma jet (APPJ) and a Pyrosil^® flame are applied. Chemical changes on the thermoplastic surfaces are verified by water contact angle measurement (CA) and X-ray photoelectron spectroscopy (XPS). Plasma treatment causes a decline in water contact angle, indicating the formation of functional groups, especially –OH, on the surface. XPS measurements confirm the increase of oxygen on the surface. Thus, the number of functional groups on the thermoplastic surface is enlarged by plasma treatment, leading to stronger bonding to the organofunctional silanes of the self-adhesive silicone rubber. A thin layer of silanol groups is created by the Pyrosil^® flame on the thermoplastic substrates, which could be verified by XPS. A hydrophilic behaviour of the coated surface is noticed. Both surface modification methods lead to enhanced adhesion properties of self-adhesive LSR on thermoplastic surfaces. This is confirmed by 90°- peel tests of the injection-moulded composites leading to an increase in peel force by the applied surface modification techniques.

Improvement of paint adhesion to aluminium surfaces is one of the main challenges in many industrial applications. In this paper, we introduce the atmospheric pressure air plasma jet as an appropriate candidate for preparation of 5052 aluminium surface alloy to improve paint adhesion in the industrial level. The employed plasma jet can promote paint adhesion to aluminium surface at the treatment velocity of 2 m/min and plasma size of 10 mm. Based on the cross-cut test, adhesion of polyurethane paint to the surface greatly increases from 1B to 5B level due to the plasma treatment. According to the results, the surface wettability increases under the influence of the plasma treatment so that water droplet contact angle reduces from 79.0°±2.0°–27.5°±2.0° after the treatment. Dyne test ink also denotes the increment of surface energy to the greater than 72 mN/m. Besides, we employ various analytical methods to investigate the physical and chemical changes arise from the plasma processing to the surface. Atomic force microscopy (AFM) results show a twofold increase in the roughness parameters of plasma treated surface which can result in a stronger paint and surface interlocking. Chemical analysis of the surface reveals that plasma treatment of the aluminium surface leads to the surface cleaning and formation of hydrophilic functional groups that attract much more water towards the surface and improves the paint adhesion.

Polar and dispersion surface free energy (SFE) can be determined with the Owens-Wendt method. Thereby, contact angles (CAs) of at least two liquids with known surface tension (ST) components are measured. The ST components can either be determined through experiment or drawn from literature. However, it is important to know how big the difference is between SFE component values that have been calculated with experimentally-determined ST values or values derived from literature. In this study, STs of different test liquids were analyzed by Pendant Drop method and the components by CA measurement on a non-polar surface. CAs on different polymer surfaces were measured to calculate SFE components with the Owens-Wendt method. The calculations conducted were either based on experimentally-determined ST parts or different sets of values found in the literature. The findings of the survey show that, depending on the set of literature values used, the SFE results deviate significantly from the values obtained from experiment. Expressing this deviation in figures, in extreme cases the polar part differs for some polymers by -100% to +100%, with the dispersion component spanning -50% to +43%. In comparison, the expected relative uncertainties exhibited by the experimentally-determined ST values are about 15% for the polar and approximately 5% for the dispersion SFE part. Hence, the results show that the SFE uncertainty can be reduced significantly by means of analyzing the ST parts experimentally.

Effect of the electron radiation generated by a high-voltage linear accelerator on the wettability, contact angle and surface free energy (SFE) of a biaxially oriented polypropylene (BOPP) film was studied. Radiation doses of 25, 50, 100, 250, and 500kGy were used. Water, glycerol, formamide, diiodomethane, and α-bromonaphthalene were applied as measuring liquids. The calculations of SFE were made with the methods of Owens–Wendt and van Oss–Chaudhury–Good, using the results of measurements of the contact angle with various sets of the measuring liquids. Wettability tests were also performed. It was found that the contact angle decreased with the rising radiation dose for all the measuring liquids and the shapes of these dependences were similar to one another. However, significant quantitative differences were observed. The largest changes in the contact angle were detected in the dose range of up to 100kGy. The SFE values when measured with different methods and various measuring liquids differed generally in the whole range of the applied doses. Therefore, the surface free energy cannot be accepted as an absolute measure of the thermodynamic state of the surface layer of a radiation-modified BOPP film. Its values can be compared with one another only when they were determined with the same method and same measuring or standard liquids.

In the gas flame treatment of low surface free energy (SE) substrates, such as high-density polyethylene (HDPE), problems might arise from under or over flaming, oxygen concentration differences in and around of the flame, etc. Consequently, in printing applications, the possible variation of induced SE existing on the surface, could cause distortion on printed letters. In this research, a new method based on the wetting and spreading phenomena was developed to display and study details of the SE variation on HDPE flame treated substrates. It was an easy and quick method. Results showed good agreements with previous works done on the flame treatment characteristics. The optimal flaming was achieved, while the substrate surface had been positioned about 10 to 12 mm below the tip of the flame's blue part. Also when the flaming speed had been controlled about 80 mm/s. Results from the adhesion strength test supported the optimum situations found previously by others. It was hoped that this new method could also be capable of estimating the critical SE of solid surfaces in future works.