Elsevier

Thin Solid Films

Volume 712, 31 October 2020, 138347
Thin Solid Films

Anticorrosion performance of polyvinyl butyral composite coatings improved by polyaniline-multiwalled carbon nanotubes/poly (methylhydrosiloxane)

https://doi.org/10.1016/j.tsf.2020.138347Get rights and content

Highlights

  • Polyaniline-multiwalled carbon nanotubes nanocomposites were prepared.

  • Synthesized nanocomposites were added into poly (vinyl butyral) primer as fillers.

  • Poly (methylhydrosiloxane) was added for better long-term corrosion protection.

  • The best content of nanocomposites for the coating was investigated.

Abstract

Polyaniline-carboxylic multiwalled carbon nanotubes (PANI-CMWCNTs) nanocomposites was prepared by a facile in-situ polymerization. PANI-CMWCNTs nanocomposites were incorporated into polyvinyl butyral (PVB) to prepare a protective coating on AA2024 aluminum substrates using a spin coating method. Besides, Poly (methylhydrosiloxane) (PMHS) was added to increase the crosslinking of the coating and form a hydrophobic surface. Scanning electron microscope, transmission electron microscope, UV–visible spectroscopy and Fourier transform infrared spectrum were used to characterize the morphologies and structures of different composites. The corrosion protection properties were investigated by electrochemical impedance spectroscopy and Tafel polarization in 3.5 wt% NaCl solution. Results showed that the PVB/PANI-CMWCNTs/PMHS composite coating exhibited remarkably enhanced anticorrosion properties, the corrosion current density (Icorr) of the coating decreased to 0.039 μA•cm−2, and the impedance value (|Z|0.01Hz) of the coating significantly improved compared with bare aluminum and exceeded 107 Ω•cm2, and the long-term corrosion resistance of the coating could last for over 60 days. The anticorrosive efficiency of PVB coating was promoted and an idea for the preparation of environmentally friendly coatings was proposed.

Introduction

Aluminum is the most widely used metal after steel and it is highly valued in the development of marine resources on an expanding scale owing to its low density, high strength, excellent thermal and electrical conductivity [1, 2]. Compared with steel and other metals, aluminum alloy has better corrosion resistance with the formation of an oxide film in a short time, which still cannot meet the need of the usage in marine environment due to the existence of various corrosive ions [3]. Different strategies have been developed to reduce the economic losses caused by metal corrosion, including metal surface modification represented by physical/chemical vapor deposition [4, 5] and electroplating [6], corrosion inhibitor [7], and coating protection [8], [9], [10]. Among them, organic coatings are widely used because of its simple construction and low cost compared with other anticorrosion methods. However, most solvents used for preparation of coatings are volatile and toxic, so for a long time, researchers have been committed to develop methods for facile preparation of coatings with low Volatile Organic Compounds contents.

Polyvinyl butyral (PVB) is getting more attention in the preparation of anticorrosive coatings with its excellent mechanical strength, biocompatibility, as well as good solubility in alcohol [11, 12]. Zhu et al. [13] combined PVB and graphene oxide for the preparation of anti-corrosion coatings on Aluminum alloys. Niratiwongkorn et al. [14] prepared Self-healing PVB based coatings by incorporating polypyrrole-carbon black composite as an inhibiting pigment. Mahmoudian et al. [15] studied the influence of polypyrrole/TiO2 nanocomposites with different morphologies to the anticorrosion performance of PVB coatings on mild steel. All these works showed the bright application prospects of PVB in metal protection.

Usually, different kinds of fillers are added into organic coatings to improve the corrosion resistance of the latter. Polyaniline (PANI) is an important conductive polymer with the advantages of environmental stability, easy synthesis and low cost [16, 17].And it has become one of the most widely used nanofillers that could enhance the mechanical, physical, and chemical properties of coatings due to its synergistic effect [18]. PANI has three different forms, completely reduced leucoemeraldine base, half-oxidized emeraldine base, and completely oxidized pernigraniline base. The reversible transformation of three different state of PANI forms a passive and protective metal oxide layer, which will slow down the corrosion process [19]. A lot of efforts have been made to combine PANI with other inorganic materials in order to acquire better properties. Wang et al. [20] prepared Nb doped TiO2 nanofibers/PANI composite coating by electropolymerization on 316 stainless steel for better corrosion resistance. Lei et al. [21] grafted PANI onto graphene surface which was incorporated into zinc-rich epoxy primers and exhibited extraordinary anticorrosion performance. In recent years, carbon nanotubes (CNTs) have attracted much attention due to their excellent electrical conductivity and mechanical properties [22]. There are plenty of studies discussed the application of PANI/CNTs composites in supercapacitors [23, 24] and cells [25], but reports about its application in anticorrosive coatings are relatively rare.

For a long time, silane compound has always attracted much attention of researchers in the field of hydrophobic surface preparation [26], [27], [28]. And Poly (methylhydrosiloxane) (PMHS) was widely used because due to its low surface energy and molecular structure containing large amounts of methyl [29, 30]. Moreover, the active Si-H bond on the is favorable for the crosslinking reaction with other compounds. Liu et al. [31] prepared a nanofilament coating on the surface iron sheet by PMHS modified geopolymer layer. And Lin et al. [32] use PMHS as surface modifier to prepare highly hydrophobic wood with anti-fouling properties. While the application of PMHS in the preparation of anticorrosion coating is rarely reported.

In this work, we proposed a facile synthetic method of polyaniline-carboxylic multiwalled carbon nanotubes (PANI-CMWCNTs) composites, which was used as nanofiller incorporated into PVB primers to investigate the anticorrosion performance of the coatings on AA2024 aluminum substrates. Ethanol is selected as solvent for PVB and the prepared coating will be environment-friendly. Meanwhile, Poly (methylhydrosiloxane) (PMHS) was introduced to modify the hydrophobicity and enhance the cross-linking degree of the coatings. The corrosion resistance of the coating was characterized by electrochemical impedance spectroscopy (EIS) and Tafel polarization curve in 3.5 wt% NaCl solution with a three-electrode system. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR) and UV–visible spectrum was combined to investigate the corrosion mechanism of the coatings.

Section snippets

Materials

Carboxylic multiwalled carbon nanotubes (CMWCNTs) (Purity>95%, ID: 5–10 nm, OD: 10–20 nm, length: 10–30 μm, -COOH: ~2 wt%) and Dodecylbenzenesulfonic acid (DBSA) (90%) was purchased from Shanghai Macklin Biochemical Co., Ltd. Polyvinyl butyral (PVB) (Aviation grade), aniline (AR), ammonium persulfate (APS) (AR), HCl (AR, 37%) and acetone (AR) were provided by Sinopharm Chemical Reagent Co., Ltd. Poly (methylhydrosiloxane) (PMHS) (Viscosity: 15–40 mPa.s (20 °C)) was obtained from Aladdin

Morphology analysis of nanocomposites

Fig. 2(a) shows the SEM morphology of PANI, which is in a state of aggregation due to the inter chain H-bonding between amine and imine [16]. This kind of agglomeration may be unfavorable to the dispersion of Polyaniline in the coating. It can be seen from Fig. 2(b) that CMWCNTs show typical tubular morphology and are entangled with each other, the diameter of CMWCNTs is about 15–20 nm. Fig. 2(c) and (d) are the SEM and TEM images of PANI-CMWCNTs nanocomposites, CMWCNTs are covered with PANI

Conclusions

In this paper, PANI-CMWCNTs nanocomposite was prepared by in-situ polymerization and introduced into PVB coating, also PMHS was added to form a hydrophobic surface that the long-term anticorrosion performance of composite coating got further improved. Different methods were used to characterize the coating, and the anticorrosion abilities was investigated by electrochemical measurement techniques including EIS and Tafel polarization in 3.5 wt% NaCl solution. All the results showed that as

CRediT authorship contribution statement

Anhang Li: Conceptualization, Investigation, Methodology, Formal analysis, Validation, Writing - original draft. Min Sun: Software, Formal analysis, Writing - review & editing. Zhidong Ma: Software, Formal analysis, Writing - review & editing. Sifan Chen: Writing - review & editing. Guiyu Zhu: Methodology, Writing - review & editing. Yue Zhang: Methodology, Supervision, Project administration, Funding acquisition. Wei Wang: Supervision, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was sponsored by National Nature Science Foundation of China (51972289 and 51572248).

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