Introducing cyano-functionalized multiwalled carbon nanotubes to improve corrosion resistance and mechanical performance of poly(arylene ether nitrile) coating

https://doi.org/10.1016/j.surfcoat.2021.128058Get rights and content

Highlights

  • PEN was applied as protective coating on metallic substrate for the first time.

  • Dispersion of MWCNTs in PEN is notably enhanced via the cyanogen modification.

  • The corrosion resistance of MWCNTs-CN/PEN composite coating enhanced sharply.

  • The mechanical properties of MWCNTs-CN/PEN composite coating increased obviously.

Abstract

Seeking high-performance coating with long service life to protect metallic substrates under complex corrosion environment has attracted abundant attention in modern industry. In this work, poly(arylene ether nitrile) (PEN) was applied as protective coating on metallic substrates for the first time, and the cyano- functionalized multiwalled carbon nanotubes (MWCNTs-CN) was introduced to further enhance the corrosion resistance and mechanical performance of the PEN coating. Electrochemical results demonstrated that the MWCNTs-CN incorporated composite coating possessed outstanding corrosion resistance that the |Z|0.01Hz remained 196.9 MΩ cm2 after 100 days' immersion process in 3.5 wt% NaCl solution, which was 2 orders of magnitude higher than the pure PEN coating. Besides, an evident improvement was investigated from the tensile strength of MWCNTs-CN/PEN coatings, which showed an increment about 20.1% of tensile strength was gained when 1 wt% of MWCNTs-CN was introduced. Benefiting from these advantages, this work is expected to provide a novel insight in high-performance protective coating.

Graphical abstract

The well-dispersed MWCNT-CN fillers are successfully fabricated through the decomposition of AIBN, which significantly enhances the corrosion resistance and mechanical performance of PEN coating.

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Introduction

In contemporary society, industries are regarded as the cornerstone to enormously promote the economic development [1]. To support rapid development of the industries such as petrochemicals, agriculture, automobiles and ships worldwide, metallic facilities are widely used due to their numerous merits [2], [3], [4]. Nonetheless, the frustrating fact is that metals are eroded inevitably by corrosive substances including O2, H2O and ions as the service life extends, leading to the nasty industrial accidents and countless property losses [5], [6]. Thus, seeking for effective and practical approaches to prevent or retard the occurrence of metal corrosion is of vital importance.

Polymer coatings are deemed as one of the most effective and convenient methods to protect metal substrates against complex corrosive environment [7], [8]. Recently, epoxy coatings stand out as corrosion protection from numerous alternative polymer coatings, benefitting from its advantages such as great chemical resistance to severe condition, satisfying mechanical performance, strong adhesion to substrates and fair price [9], [10], [11], [12]. However, the existence of polar epoxide groups in epoxy resins would strongly interact towards water and other organic solvents, which expedites the adsorption process of corrosive solution [13]. Furthermore, micro porosities and cavities are inevitably formed in epoxy coating structure through the curing process. Under this circumstance, the adsorbed corrosive solutions could penetrate to the metal substrates more conveniently through these micro channels, descending the permeability of epoxy system [14]. As the consequence, the epoxy coatings suffer from rapid decline in barrier and mechanical performance with a short exposure time to corrosive environment, resulting in undesirable corrosion protection period [15], [16]. Therefore, exploring for durable polymeric coatings with better overall performance has become an urgent goal for researchers to achieve.

To date, an engineering polymer called poly(arylene ether nitrile) (PEN) has arisen increasing interest in extensive fields [17], [18], [19]. Ascribing to its high molecular weight, rigid backbone structure of benzene ring and controllable branch chains, PEN possess preponderances of superior resistance to corrosion and radiation, high endurance to heat as well as outstanding mechanical strength [20], [21], [22]. Further researches proved that with the polar nitrile groups could notably improve the adhesion of PEN with various substrates through interaction between nitrile and other chemical groups. Additionally, nitrile groups can also act as extra crosslinking site to generate denser structure [23], [24]. Inspired by the characteristics, it's speculated that PEN can be applied as a promising polymer barrier coating to protect metals against harsh corrosion condition.

As is shown by previous reports, the nanofillers can serve as ebullient candidates to reinforce the mechanical and barrier properties of polymer coatings ulteriorly [25], [26], [27], [28], [29]. Among various available nanofillers, multiwalled carbon nanotubes (MWCNTs) trigger intense attention in strengthening polymer coatings' mechanical and corrosion properties, because of its unique characteristic including great chemical resistance, ultrahigh aspect ratio and mechanical stability [30], [31], [32]. However, MWCNTs show chemical inertness and will restack in a short dispersion period within solution and coating matrix via π-π interaction and Van der Waals force [33], [34]. This unsatisfactory compatibility between MWCNTs and PEN matrix would eventually lead to the decline of barrier effect and corrosion resistant properties. As a countermeasure, covalent surface modification methods provide an efficient approach to ameliorate the chemical inertness of MWCNTs [35]. With polar functional groups attached to the surface of MWCNTs, the dispersibility and the compatibility with organic polymer coatings could be improved prominently, which may dramatically expand the application prospects of MWCNTs [36]. For example, Zhong et.al [37] functionalized multiwalled carbon nanotube (MWNT) with acylate groups through different in situ polymerization methods, providing better dispersibility and interfacial compatibility between MWNT and PEN resin. The results firmly confirmed that the acylate functionalized MWNT distinctly enhanced the mechanical performance and thermal resistance of PEN films. However, no research explored the corrosion mitigation of PEN coating containing cyanogen functionalized multiwalled carbon nanotubes.

In this work, through the decomposition of azodiisobutyronitrile (AIBN), carbon radicals containing cyano groups were covalently grafted onto MWCNTs to give cyano-functionalized multi-walled carbon nanotubes (MWCNTs-CN). Compared with the original MWCNTs, the cyano groups attached to MWCNTs-CN improves the interface compatibility between MWCNTs-CN and PEN, and can be cross-linked with phthalonitrile group in PEN matrix under thermal treatment to obtain a denser structure. As the result, corrosion protection properties and mechanical strength of PEN composite coatings gain prominent improvement. Besides, the enhanced corrosion mitigation mechanism was probed in detail.

Section snippets

Materials

2,6-Dichlorobenzonitrile (DCBN), 4-nitrophthalonitrile (4-NPh) were obtained from Heowns Biochem Co. Ltd. with technical grade and used without any purification. Hydroquinone (HQ, 99%) were purchased from Tianjin Bodi Chemical Co. Ltd. Azodiisobutyronitrile (AIBN) and biphenyl (BP, 99.5%) were obtained from Sigma-Aldrich. Multiwalled carbon nanotubes (MWCNTs, diameter: 3–15 nm, length: 1–15 μm) was purchased from Shenzhen Suiheng Technology Co. Ltd. N-methylpyrrolidone (NMP, 99%), dimethyl

Characterization of PEN

The 1H NMR spectrum of PEN was illustrated in Fig. 4. It could be observed that the peaks of all chemical shifts (δ) ranged from 6.5 ppm to 8.0 ppm, identifying that all hydrogens were attached on the benzene rings. The signals centered at δ of 7.24 ppm, 7.42 ppm and 7.73 ppm were attributed to the typical absorption peaks of three different hydrogens on the phthalonitrile groups. Due to the fact that phthalonitrile groups were merely used as capping group, the intensity of these signals was

Conclusion

In conclusion, MWCNT fillers were functionalized with cyano groups through free radical fragments generated from decomposition of AIBN to successfully fabricating MWCNTs-CN. Then neat PEN coating, MWCNTs/PEN coating and MWCNTs-CN/PEN coating were prepared, respectively. After introduction of MWCNTs-CN, the corresponding coating and composite film showed remarkable improvement in impact resistance and tensile strength. From EIS measurement and neutral salt spray test, MWCNTs-CN was demonstrated

CRediT authorship contribution statement

Yunqing Xia: Conceptualization, Investigation, Validation, Writing - original draft, Writing - review & editing, Formal analysis. Yi He, Xiaobo Liu: Supervision, Conceptualization, Funding acquisition, Methodology, Writing - review & editing. Lifen Tong, Guo Lin, Zhongxiang Bai: Validation, Investigation, Formal analysis, Resources. Shuai Zhang: Writing - review & editing. Shuning Liu: Data curation, Formal analysis.

Declaration of competing interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (52073039, 51773028, 51903029, 21805027 and 51803020), International Science and Technology Cooperation Project (52011530027), the Fundamental Research Funds for the Central Universities (ZYGX2019J026), Major Special Projects of Sichuan Province (2020YFG0270, 2020ZDZX0020, 2019ZDZX0027 and 2019ZDZX0016), and Sichuan Science and Technology Program (2019YJ0197, 2020YFG0100, and 2019YFG0056).

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