Surface energy plasma treatment

While polymeric surfaces with relatively high surface energies (e.g. polyimides, ABS, polycarbonate, polyamides) can be adhered to readily without surface treatment, low surface energy polymers such as olefins, silicones, and fluoropolymers require surface treatments to increase the surface energy. Various oxidation techniques (such as flame, corona, plasma treatment, or chromic acid etching) allow strong bonds to be obtained to such polymers. 

Electric discharge (corona, cold plasma) is another method of physical treatment. Corona treatment is one of the most interesting techniques for surface oxidation activation. This process changes the surface energy of the cellulose fibers [28]. In the case of wood surface activation it increases the amount of aldehyde groups [291. 

Some physical techniques can be classified into flame treatments, corona treatments, cold plasma treatments, ultraviolet (UV) treatment, laser treatments, x-ray treatments, electron-beam treatments, ion-beam treatments, and metallization and sputtering, in which corona, plasma, and laser treatments are the most commonly used methods to modify silicone polymers. In the presence of oxygen, high-energy-photon treatment induces the formation of radical sites at surfaces these sites then react with atmospheric oxygen forming oxygenated functions. 

Adhesion or printability of polymeric surfaces, including films, is often promoted by plasma or glow discharge treatment. In particular for apolar (low surface energy) surfaces such as polyolefins this is a commonly applied procedure. As a practical industrial example, the adhesion behaviour of polypropylenes after... 

Hydrophobicity - Before plasma treatment, silica powder is highly hydrophilic and immediately sinks in water. After plasma film deposition, the material floats on water for several hours. A significant reduction in polarity and in surface energy compared to untreated silica is found, down to the range of 28.4-47.7 mJ/m2. The water penetration into powder beds of untreated and plasma-treated silica is shown in Fig. 7. The untreated silica absorbs water very fast, whereas the plasma-treated silicas show a significantly decreased water penetration rate. The lowest rate is found for the polythiophene-coated silica (PTh-silica). 

The reduction in filler-filler interaction due to acetylene-plasma treatment is obviously due to the lower surface energy of the coated carbon black. The carbon black shows an appreciable reduction in surface energy after the plasma treatment, towards the range of the polymer S-SBR. This results in a better wetting of the filler particles by the elastomer [53, 54]. 

Plasma treatment is useful to activate the surface of a certain material. The treatment enhances the adhesion property. Basically, surface activation effects the introduction of chemical functionalities on the polymer surface in order to increase its surface energy. 

Fig. 8.4. Adhesion in the polar portion of the surface energy as a result of plasma treatment by BOPP [7].

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