Study on Chemical Bonding Between Epoxy Coating and Metal Substrate Using γ-Aminopropyltrimethoxysilaneto Modify Epoxy Resin Molecule

doi:10.11900/0412.1961.2018.00121

Acta Metall Sin

2019, Vol. 55

Issue (2): 238-248 DOI: 10.11900/0412.1961.2018.00121

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Study on Chemical Bonding Between Epoxy Coating and Metal Substrate Using γ-Aminopropyltrimethoxysilaneto Modify Epoxy Resin Molecule

Fachun CAO^1,², Hang WU³(

), Yange YANG^1,⁴(

), Jingyi CAO⁴, Tao ZHANG^1,³, Fuhui WANG³

1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
3 School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
4 Navy Coating Analysis and Test Center, Beijing 102442, China

Cite this article:

Fachun CAO, Hang WU, Yange YANG, Jingyi CAO, Tao ZHANG, Fuhui WANG. Study on Chemical Bonding Between Epoxy Coating and Metal Substrate Using γ-Aminopropyltrimethoxysilaneto Modify Epoxy Resin Molecule. Acta Metall Sin, 2019, 55(2): 238-248.

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Abstract

Epoxy coatings are widely used to protect metals from corrosion in ocean engineering and process industries. It has been proved that the adhesion between epoxy coating and metal is a key factor that affects their service life of the coating. However, interface between epoxy coating and metal substrate is usually combined by weak van der Waals force or secondary bond, which limits the protective performance of coatings. This work aims to translate the interface state from the physical adsorption to chemical bonding so as to increase the service life of epoxy coating. A kind of reactive resin γ-APS/EP with hydrolysis characteristic was prepared using γ-aminopropyltrimethoxysilane (γ-APS), and used as a coating filler with different contents of 0.5%~10%. Both dry and wet adhesion strength of epoxy coatings with different contents of γ-APS/EP were examined, the resistance to aggressive medium of epoxy varied with the contents of γ-APS/EP was evaluated by water absorption measurement, and the structure and composition of the coating/metal systems were characterized by using SEM, XPS, DSC and FTIR. The results showed that amino groups in γ-APS/EP disappeared and methoxysilyl groups (Si—O—CH₃) were remained after the synthesis process. Adhesion strength of the epoxy coating with metal substrate was significantly enhanced by introducing γ-APS/EP. Moreover, the dry adhesion strength of epoxy coating with 3%γ-APS/EP reached the maximum value of 12.4 MPa, which was twice the strength of pure epoxy, and was decreased with the content of γ-APS/EP further increasing. Meanwhile, wet interface adhesion strength of epoxy coating with 3%γ-APS/EP was still kept about 7.4 MPa after 900 h immersion in 3.5%NaCl, more than three times of pure epoxy coating. And also, epoxy coating with 3%γ-APS/EP showed the best performance with lower saturated water absorption. The chemical bonding can be obtained by the generation of oxane on the interface resulting from the reaction between the synthesized reactive resin and the hydroxyl on the metal surface after the reactive resin was added in the epoxy resin. Furthermore, the content of γ-APS/EP affected the number of chemical bonds at the interface, the hydrophilicity and the bulk density of coating. Finally, an interfacial chemical bonding mechanism was proposed.

Key words: epoxy coating γ-aminopropyltrimethoxysilane; chemical bonding

Received: 30 March 2018

ZTFLH:

TQ632.4

Fund: Supported by National Natural Science Foundation of China (No.51401217) and China Postdoctoral Science Foundation (No.2017M613383)

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	Fachun CAO
	Hang WU
	Yange YANG
	Jingyi CAO
	Tao ZHANG
	Fuhui WANG

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https://www.ams.org.cn/EN/10.11900/0412.1961.2018.00121 OR https://www.ams.org.cn/EN/Y2019/V55/I2/238

Fig.1 FTIR spectra of epoxy resin, γ-APS and γ-APS/EP

Fig.2 Schematic of γ-APS/EP preparation

Fig.3 Dry adhesion strength and de-adhered ratio of coatings as a function of the content of γ-APS/EP

Fig.4 SEM images in back scattered mode of pure epoxy (a) and 3%γ-APS/EP (b) after dry adhesion tests

Fig.5 XPS spectra of pure epoxy (a~c) and 3%γ-APS/EP (d~f) samples after dry adhesion test(a, d) survey (b, e) O1s (c, f) Si2p

Table 1 XPS binding energy assignments and full width at half maximum (FWHM)

Fig.6 Wet adhesion strengths of pure epoxy, 3%γ-APS/EP and 10%γ-APS/EP coatings on Q235 panels as a function of immersion time in 3.5%NaCl solution

Fig.7 Surface morphologies of Q235 samples after 900 h wet adhesion strength test(a) pure epoxy (b) 3%γ-APS/EP (c) 10%γ-APS/EP

Fig.8 Time dependence of water absorption for pure epoxy, 3%γ-APS/EP and 10%γ-APS/EP

Table 2 Water absorptions of epoxy coatings with different immersion time

Fig.9 DSC curves of pure epoxy (a), 3%γ-APS/EP (b), 10%γ-APS/EP (c) and corresponding glass transition temperature (T_g) (d)

Fig.10 Cross-sectional SEM images of pure epoxy (a, b), 3%γ-APS/EP (c, d) and 10%γ-APS/EP (e, f) coatings before (a, c, e) and after (b, d, f) 900 h immersion in 3.5%NaCl solution

Fig.11 SEM-EDS analysis of 10%γ-APS/EP coating

Fig.12 Cross-sectional morphology of 10% g-APS/EP and the corresponding EDS mappings

Fig.13 Mechanism of γ-APS/EP action

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