Page 104 - Handbook of Adhesion Promoters

6.4 Modification by epoxy group 97

Figure 6.3. Schematic illustration of the epoxy coating chemical bonding with the steel substrate modified by gra-
phene oxide coating. [Adapted, by permission, from Parhizkar, N; Shahrabi, T; Ramezanzadeh, B, Corrosion Sci.,
in press, 2017.]
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chemical resistance properties. Their applications include electronics, construction, and
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aerospace industries. The adhesion to glass increased with increasing epoxy group con-
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tent. The bonding between the epoxy and carboxyl groups resulted in a delayed degrada-
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tion of the cured adhesive.
The epoxy-silane hybrid coatings were investigated for their anti-corrosion perfor-
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mance and adhesion on galvanized steel. Alkoxy, epoxy, amine, and thiol group-contain-
ing silanes were selected to study the role of functionality on the performance of the
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hybrid coating. The aminosilane showed superior performance. The addition of 1-
3 wt% silane into epoxy polymer backbone caused improvement in both anti-corrosive
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performance and adhesion strength.
The loss of adhesion of thin epoxy coatings is directly provoked by the arrival of
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water at the interface. In the thicker coating, some adhesion loss is caused by the pres-
ence of internal stress present because of difference in expansion and contraction of metal
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substrates and epoxy.
The addition of 1,4-butanediol to a bisphenol-F epoxy resin cured with 4-methyl-2-
phenyl imidazole led to a decrease in the modulus and glass transition temperature, which
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resulted in lower residual stresses. The addition of 1,4-butanediol increased moisture
uptake by the resin, which is associated with an increase in the free volume of the epoxy. 27
Even with greater moisture uptake, the addition of 1,4-butanediol to the epoxy increased