Page 73 - Handbook of Adhesion Promoters

66 Substrates - Surface Condition and Treat-

Figure 4.13. Transmission electron micrograph of (a) oxide layer (110,000×, 100 kV) and electron diffraction
pattern; (b) bulk polymeric (380,000×, 100 kV) and electron diffraction pattern; (c) positions of three points in
which semi-quantitative analysis was carried out. [Adapted, by permission, from Mazzola, L; Bemporad, E; Car-
assiti, F, Appl. Surf. Sci., 257, 6, 2148-58, 2011.]
mine the exact thickness of the polymeric material influenced by the flame treatment. 31
Using optimized process parameters, the flame treatment improved the surface free energy
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by more than 48% as compared to the untreated sample of PP. The polar component of
2 31
the surface free energy grew from 0.76 to 17.55 mJ/m . The treated sample exhibited a
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porous region of 6.5 µm in depth as determined by microscopy. The elevated concentra-
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tions of oxygen were present up to 400 nm below the surface (Figure 4.12). Figure 4.13a
shows an oxidized zone of 290 nm in thickness, a little transition zone of 130 nm in thick-
ness in which the diffusive effects are present (diffusive zone) and a remaining zone is a
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unoxidized material. The unoxidized bulk polymer (Figure 4.13b) is formed of amor-
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phous domains. There are fewer amorphous domains in the diffusive zone and they com-
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pletely disappear in the oxidized zone.
4.2.6 CORONA DISCHARGE
A corona discharge is an electrical discharge possible because of the ionization of air sur-
rounding a conductor that is electrically charged. The corona treatment is frequently used
for polypropylene, PVC, PET, polyethylene, metallized surfaces, paper, and paperboard
stock. Electric cables, automotive components, 3D parts, medical devices, pipes & tubes,
board & foam, domestic appliances, extruded profiles are some components that are pro-
cessed with corona.
Polyvinylidene fluoride films were treated by the corona discharge coupling tech-
nique to enhance the interfacial adhesion of PVDF-PVC films with alkyl methacrylate
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monomers used as coupling agents. The contact angle decreased with an increasing