Effects of N-alkylation on anticorrosion performance of doped polyaniline/epoxy coating

doi:10.1016/j.jmst.2019.06.012

Abstract

Abstract:

N-alkylation of sulfosalicylic acid-doped polyaniline (PANI-SSA) was used to promote the anticorrosion performance of PANI-SSA/epoxy coating for 5083 Al alloy. PANI-SSA was modified with C₅H₁₁Br and C₁₂H₂₅Br in polar solvents IPA (isopropanol) and DMF (dimethylformamide), and then characterized by FTIR, XPS and sedimentation experiments. Results showed that alkanes were successfully linked onto the PANI-SSA chains. The compatibility between N-alkylated PANI-SSA and epoxy/xylene solution was improved. SEM results proved a better dispersion performance of N-alkylated PANI-SSA in epoxy coatings, with less holes and aggregations. Corrosion protection of the epoxy coatings incorporating PANI-SSA and N-alkylated PANI-SSA on 5083 Al alloy was studied by EIS and adhesion measurements in 3.5% NaCl solution. It turned out that the epoxy coating including C₁₂H₂₅Br-modified PANI-SSA in DMF has yielded the highest values of impedance modulus and best protective properties.

Key words: Polyaniline, Coating, Modification, Al alloy, Anticorrosive property

Suyun Liu, Li Liu, Ying Li, Fuhui Wang. Effects of N-alkylation on anticorrosion performance of doped polyaniline/epoxy coating[J]. J. Mater. Sci. Technol., 2020, 39: 48-55.

Figures/Tables 13

Table 1 Chemical composition (wt%) of 5083 Al alloy.

Si	Fe	Cu	Mn	Mg	Cr	Ni	Zn	Al
0.12	0.25	0.1	0.55	4.46	0.07	0.05	0.05	Bal.

Fig. 1. FTIR spectra of PANI-SSA (sulfosalicylic acid doped polyaniline) before and after treatment with 10 vol.% C5H11Br and C12H25Br in IPA (isopropanol) and DMF (dimethylformamide) solution for 24 h, respectively.

Fig. 2. Reaction scheme of the N-alkylation of PANI-SSA.

Fig. 3. Digital photographs of PANI-SSA and N-alkylated PANI-SSA dispersion in epoxy/xylene solution: (a) PANI-SSA; (b) C5-IPA (modified PANI-SSA by C5H11Br in IPA); (c) C5-DMF (modified PANI-SSA by C5H11Br in DMF); (d) C12-IPA (modified PANI-SSA by C12H25Br in IPA); (e) C12-DMF (modified PANI-SSA by C12H25Br in DMF) for different settling time.

Table 2 Compositions of different state of N in PANI-SSA (sulfosalicylic acid doped polyaniline) and N-alkylated PANI-SSA calculated from N 1s spectra of XPS results.

Fillers	N state
Fillers	=N-/N	-NH-/N	N⁺/N
PANI-SSA	44.8%	55.2%	--
C₅-IPA	36.6%	42.6%	20.8%
C₁₂-DMF	30.2%	29.9%	39.9%
C₁₂-IPA	33.9%	47.2%	18.9%
C₅-DMF	32.3%	35.4%	32.3%

Table 3 Water absorption (mass%) for PANI-SSA/epoxy coatings, C5-DMF/epoxy coating and C12-DMF/epoxy coating at different time intervals in 3.5% NaCl solution.

Coatings	Immersion time
Coatings	6 h	24 h	96 h	144 h	360 h
PANI-SSA/epoxy coating	1.89%	3.26%	5.14%	5.38%	5.32%
C₅-DMF/epoxy coating	1.59%	2.62%	4.53%	4.58%	4.66%
C₁₂-DMF/epoxy coating	1.27%	2.24%	3.67%	3.87%	3.85%

Fig. 4. XPS spectra for (a) PANI-SSA, and N-alkylated PANI-SSA, (b) C5-IPA, (c) C12-DMF, (d) C12-IPA and (e) C5-DMF fillers.

Fig. 5. SEM surface morphologies of (a) PANI-SSA/epoxy, (b) C5-DMF/epoxy and (c) C12-DMF/epoxy coatings surface.

Fig. 6. SEM cross-sectional morphologies of (a) PANI-SSA/epoxy, (b) C5-DMF/epoxy, (c) C12-DMF/epoxy coatings and the corresponding partial magnification of (d) PANI-SSA/epoxy, (e) C5-DMF/epoxy, and (f) C12-DMF/epoxy coatings.

Fig. 7. Water absorption and the corresponding average diffusion velocity curve for the three kind of coatings on different immersion time in 3.5% NaCl solution.

Fig. 8. EIS spectra and the corresponding equivalent electrical circuit of the three coatings system for different immersion periods in 3.5% NaCl solution (with fitting error). Nyquist diagrams: (a) PANI-SSA/epoxy; (c) C5-DMF/epoxy; (e) C12-DMF/epoxy coatings; Bode plots: (b) PANI-SSA/epoxy; (d) C5-DMF/epoxy; (f) C12-DMF/epoxy coatings.

Fig. 9. |Z|0.01Hz as a function of the immersion time for PANI-SSA/epoxy, C5-DMF/epoxy and C12-DMF/epoxy coatings in 3.5% NaCl solution.

Fig. 10. Wet adhesion results and the corresponding digital photograph showing corrosion morphologies of (a) PANI-SSA/epoxy, (b) C5-DMF/epoxy and (c) C12-DMF/epoxy coatings after 30 d immersion in 3.5% NaCl solution.

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