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Techniques & Testing

Corona and atmospheric air plasma treatment
Photo-oxidation
Light stabiliser system
Fourier transform infrared spectroscopy (FTIR)
Light microscopy
Artificial light ageing
Consolidants and application methods
Cross-cut tape test
Burst test
Making a dummy and testing consolidant application methods
Results and conclusion
Polypropylene test samples (24 × 8 cm) of white PP fabric, rough transparent PP film (4 micrometre), smooth transparent PP film (13 micrometre) and grey-coloured PP film (18 micrometre) were corona or atmospheric plasma treated, consolidated and artificially light aged. During ageing, at different intervals, test samples were examined to detect changes in visual and mechanical characteristics. Test samples were therefore observed using light microscopy (LM) and submitted to burst testing and cross-cut testing.

To record the changes in chemical microstructure occurring during the ageing process (build up of carbonyl, hydroxyl functions during photo-oxidation) of PP, fourier transform infrared spectroscopy (FTIR) spectra were taken at different intervals.

Results of the sample testing were summarised in two tables (series 1 and 2)
Table 1 PP test samples first series
Table 2 PP test samples second series
Surface activity (wettability)

Why is the adhesive bonding of polymers so difficult? The minimal requirement for a good adhesive bond is high surface energy (high wettability).

Wetting of different fluids - A shows a fluid with very little wetting (hydrophobic), while C shows a fluid with more wetting (hydrophilic). A has a large contact angle, and C has a small contact angle.
The contact angle is the angle at which the liquid–vapour interface meets the solid–liquid interface. The contact angle is determined by the resultant between adhesive and cohesive forces. As the tendency of a drop to spread out over a flat, solid surface increases, the contact angle decreases. Thus, the contact angle provides an inverse measure of wettability. Source and for more information: http://en.wikipedia.org/wiki/Wetting

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Contact angle measurements
The PP test samples were characterised prior to and after corona and plasma treatment by means of water contact angle measurements. Advancing water contact angles were measured at room temperature with a Krüss DSA-10MK2 drop shape analysis system. The drop size was 0.5 microlitre which was kept constant for all measurements. All angles reported are averages over three separately prepared samples, while on each sample three droplets, placed at different positions, were measured. A sample table moves the sample to the right position. Single or double dosing systems deposit the drop on the surface. Illumination and image zoom ensure optimal drop presentation. The camera records the digital image and allows perfect drop shape analysis. Contact angle and surface free energy can be calculated by software. 
 
Contact angle measurements were performed following atmospheric plasma treatments on PP both on smooth and rough film surfaces. The surface hydrophilicity is clearly improved with the irradiation time of corona or plasma treatment. PP is a hydrophobic polymer with a water contact angle of about 80 degrees. Upon pretreatment with corona or plasma, the water contact angle of the PP decreases considerably and the most hydrophilic surface was obtained after 20 seconds of irradiation, when a visible improvement of the adhesion of water droplets was also observed. However, as no significant differences in contact angle values were obtained when treating the test samples for 15 or 20 seconds, an irradiation of 15 seconds is recommended in order to prevent surface deterioration. The small water droplets on non-treated PP were unable to remain on the surface after tilting the PP at an angle of 90 degrees, however after plasma or corona treatment at 20 mm either for 15 or 20 seconds, the water adhered to the textile and could only be removed by shaking.
 
Corona and atmospheric air plasma treatment
Photo-oxidation
Light stabiliser system
Fourier transform infrared spectroscopy (FTIR)
Light microscopy
Artificial light ageing
Consolidants and application methods
Cross-cut tape test
Burst test
Making a dummy and testing consolidant application methods
Results and conclusion