Green Eugenol Oligomers as Corrosion Inhibitors for Carbon Steel in 1M HCl

Furtado, Luana B.; Nascimento, Rafaela C.; Guimarães, Maria José O. C.; Brasil, Simone L. D. C.; Barra, Sergio H. R.

doi:10.1590/1980-5373-MR-2022-0012

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Articles • Mat. Res. 25 • 2022 • https://doi.org/10.1590/1980-5373-MR-2022-0012 copy

Green Eugenol Oligomers as Corrosion Inhibitors for Carbon Steel in 1M HCl

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

This study investigated the corrosion inhibition of polyeugenol on API P110 in 1 M HCl. Its monomer – eugenol – is obtained from clove and cinnamon, making the oligomer environmentally friendly. The influence of molecular weight and polymerization degree was evaluated by increasing the polymerization initiator/monomer ratio. This enabled the polymerization of three different oligomers (P10, P20 and P30), which were characterized by Fourier-transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H-NMR), thermogravimetric analysis (TGA/DTG), and size exclusion chromatography techniques. The inhibition performance of polyeugenol was determined by weight loss (WL) and electrochemical tests to assess the influence of structural differences. WL indicated that the oligomer with the lowest polymerization degree (P10) exhibited greater efficiency (82-84%) due to more uniform surface coverage. Electrochemical tests confirmed polyeugenol as a mixed inhibitor. Energy-dispersive X-ray spectroscopy (EDX) calculations indicated the presence of an organic layer covering the steel surface.

Keywords:
Polymeric inhibitor; Weight loss; Green corrosion inhibitor; Electrochemical measurements

Oligomer	Initiator (g)/monomer (g)	M_n	M_w	Degree of polymerization	PDI
P10	0.10	416	743	4.5	1.78
P20	0.20	466	885	5.4	1.89
P30	0.30	504	930	5.7	1.84

Inhibitor	Concentration (%v/v)	Corrosion rate (mm/y)	Inhibition efficiency (%)
Blank	0.0	69.98±4.38	-
P10	0.5	15.70±0.84	77.24±0.99
	2.0	13.03±1.22	81.11±1.50
	3.5	11.82±1.20	82.86±1.52
	5.0	10.82±1.34	84.32±1.64
P20	0.5	21.33±0.24	69.08±0.25
	2.0	16.89±0.73	75.51±0.84
	3.5	15.18±1.34	78.00±1.59
	5.0	15.46±0.94	77.59±1.12
P30	0.5	19.56±1.04	71.65±1.13
	2.0	16.43±0.91	76.18±1.05
	3.5	14.01±0.40	79.69±0.49
	5.0	15.23±0.83	77.92±0.98

Inhibitor	Langmuir				Temkin		El Awady		Frumkin
Inhibitor	K_ads (L mg^-1)	R²	Slope	-ΔG_ads (kJ mol^-1)	R²	Slope	R²	Slope	R²	Slope
P10	11.2360	0.9998	1.1737	25.8193	0.9950	-13.8020	0.9880	0.1941	0.9974	17.146
P20	10.7991	0.9999	1.2667	25.7095	0.9531	-9.8443	0.9598	0.2057	0.9709	12.6750
P30	15.6986	0.9994	1.2615	26.7452	0.8685	-11.3630	0.8631	0.1724	0.9145	14.300

Test	E_a (kJ mol^-1)	R²
Blank	55.31	0.9888
P10	49.94	0.9937
P20	50.56	0.9965
P30	54.53	0.9995

Oligomer		LPR			PDP
Oligomer	Rp (Ω cm^-2)	Standard deviation (%)	R²	IE_LPR (%)	Ecorr (mV)	\|βc\| (mV/dec)	βa (mV/dec)	I_corr (µA/cm²)	IE_PDP (%)
Blank	38.78	8.83	0.9999	-	504.30	48.5	20.28	42.52	-
P10	102.67	9.64	0.9971	62.23	458.46	25.67	21.62	10.98	74.18
P20	87.90	4.85	0.9960	55.88	464.92	37.34	15.21	13.48	68.30
P30	67.06	6.39	0.9967	42.18	468.85	33.20	14.48	13.79	67.57

Test	Element	%Mass	C/Fe (%)	O/Fe (%)
Blank	Fe	90.55	7.74	2.69
	C	7.01
	O	2.44
P10	Fe	24.11	243.92	66.19
	C	58.81
	O	15.96
	Cl	1.12

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