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Journal of Adhesion Science and Technology
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/tast20
An easy route for preparation of carboxylic acid
and urea functional block copolymer as corrosion
inhibitor
Ahmet Ince, Ilayda Koramaz, Ertuğrul Kaya & Bunyamin Karagoz
To cite this article: Ahmet Ince, Ilayda Koramaz, Ertuğrul Kaya & Bunyamin Karagoz (2023): An
easy route for preparation of carboxylic acid and urea functional block copolymer as corrosion
inhibitor, Journal of Adhesion Science and Technology, DOI: 10.1080/01694243.2023.2240593
To link to this article: https://doi.org/10.1080/01694243.2023.2240593
Published online: 07 Aug 2023.
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An easy route for preparation of carboxylic acid and urea
functional block copolymer as corrosion inhibitor
Ahmet Ince
a
, Ilayda Koramaz
a
, Ertu
grul Kaya
b,c
and
Bunyamin Karagoz
a
a
Department of Chemistry, Istanbul Technical University, Istanbul, Turkey;
b
3-S Engineering
Consultation Industry and Commerce Incorporated Company, D€
uzce, Turkey;
c
Department of
Mechanical Engineering, Faculty of Engineering, Corrosion Research Laboratory, D€
uzce University,
D€
uzce, Turkey
ABSTRACT
A novel POEGMA-b-(PMEEU-co-PMAA) (poly(oligo(ethylene glycol)
methacrylate)-b-poly((methacrylamidoethyl) ethylene urea)-co-pol-
y(methacrylic acid) block copolymer has been synthesized by
RAFT polymerization as a corrosion inhibitor. Structural character-
ization of the block copolymer was done by FTIR,
13
C NMR and
1
H NMR spectroscopic techniques. The carboxylic acid and cyclic
urea units on the block copolymer exert a synergistic effect on
corrosion inhibition through chelating of the metal ions or
adsorption to the metal surface. Corrosion inhibition of SAE 1012
carbon steel in a 1 M HCl medium has been investigated in the
presence of 5 mM polymer using both experimental (electrochem-
ical impedance spectroscopy, Tafel polarization (TP), weight loss)
and theoretical approaches. Also, SAE 1012 carbon steel surface
morphology changes were followed by energy dispersive X-ray
spectroscopy and scanning electron microscopy. Electrochemical
techniques indicated that the presence of PMEEU-co-PMAA seg-
ments of the polymer in the acid solution inhibits corrosion of
SAE 1012 carbon steel. The inhibition efficiency of the polymer
was found to be about 85%. According to TP studies, PMEEU-co-
PMAA segment acts as a mixed type corrosion inhibitor. The
adsorption of PMEEU-co-PMAA molecules onto the metal surface
follows Langmuir adsorption isotherm. The K
ads
value calculated
from the equilibrium constant of the adsorption process reflects a
strong interaction. SEM and EDAX studies provide evidence of
PMEEU-co-PMAA adsorption on the metal surface.
ARTICLE HISTORY
Received 13 March 2023
Revised 19 June 2023
Accepted 9 July 2023
KEYWORDS
Acid corrosion; multi-
functional block copolymer;
carbon steel; corrosion
inhibitor; RAFT
polymerization
1. Introduction
Acid especially aqueous HCl treatment is generally applied to metal surfaces for chem-
ical cleaning, descaling, picking, and similar purposes [1–5]. This process increases
the existing corrosion problems that become unbearable in the industry [6–8]. On
the other hand, unfortunately acidic cleaning is absolutely necessary as it removes the
CONTACT Bunyamin Karagoz karagozb@itu.edu.tr Department of Chemistry, Istanbul Technical University,
34469 Istanbul, Turkey.
ß2023 Informa UK Limited, trading as Taylor & Francis Group
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY
https://doi.org/10.1080/01694243.2023.2240593
impurities and metal oxide layer on the applied surface [9]. In order to prevent or
minimize the metal loss in this aggressive and intense process or condition, some
corrosion inhibitor additives are needed and have vital importance, and are widely
used in industry [10–17] to reduce the cost of corrosion in industrial settings, par-
ticularly in acidic environments [3,18,19]. In this context, there appear many studies
in the literature that organic compounds containing heteroatoms such as O, N, S
and P work with high efficiency in corrosion inhibition [20,21]. One of the good
studies on the inhibition of C38 steel corrosion in hydrochloric acid was carried out
by the Ould Abdelwedoud et al. using N-propargyl saccharin (NPS) as an inhibitor.
NPS has been shown to act as a mixed inhibitor reducing both anodic and cathodic
current densities and improving the charge transfer resistance of C38 steel by
increasing the thickness of the protective layer as the inhibitor concentration
increases [3]. Among the small molecule-based corrosion inhibitors, polymer-based
ones offer many opportunities for tailoring the polymer backbone with the desired
functional groups [22]. The design of the polymer can be easily adjusted by attaining
different functional segments onto the polymer chain by directly using functional
monomers or post-modification [23]. In theoretical aspect, strong ion chelating
groups such as carboxylic acid and amino groups (tertiary amines, urea and amide),
etc. provide high corrosion inhibition rates due to the easy interaction of the applied
metal surfaces [24–26]. In his review, Umoren demonstrated that polymers, particu-
larly those that are water-soluble, exhibit significant effectiveness as corrosion inhibi-
tors across various aqueous environments [27]. The inhibition mechanism of
polymers primarily relies on adsorption and is influenced by several factors such as
the type of metal, physicochemical properties of the molecule (including functional
groups, steric factors, aromaticity at the donor atom, and orbital character of electron
donation), as well as the electronic structure of the molecules. Essentially, the effect-
iveness of polymers as corrosion inhibitors depends not only on the characteristics of
the surrounding environment, the nature of the metal surface, and the electrochem-
ical potential at the interface, but also on the structure of the inhibitor itself. This
encompasses the number of active adsorption centers in the molecule, their charge
density, molecular size, mode of adsorption, formation of metallic complexes, and
the projected area of the inhibitor on the metal surface [27]. In their review, Fathima
Sabirneeza et al. explored the key factors that influence the corrosion inhibitor per-
formance of polymeric compounds on metals in different corrosive environments
[28]. The enhanced effectiveness of a polymeric corrosion inhibitor can be attributed
to its larger size and a higher number of functional anchoring groups. These anchor-
ing groups facilitate the easy adsorption of polymers onto the metal surface, covering
a significantly larger area compared to corresponding monomers. The corrosion miti-
gating properties of the polymers are influenced by various factors, including
molecular size, weight, composition, and the nature of the anchoring groups.
Additionally, the performance of the inhibitor is influenced by solution pH, concen-
tration, exposure time, and temperature [28].
In this regard, Cao et al. designed a novel kind of core cross-linked assemblies
formed from a ‘semi-amphiphilic’block copolymer, poly(syringaldehyde methacryl-
ate)-block-poly(dopamine methacrylate-co-methyl methacrylate-co-styrene), hosted for
2 A. INCE ET AL.
anti-corrosive and corrosion detection molecules that have been shown to effectively
detect and prevent corrosion in steel. These assemblies were differed from traditional
core cross-linked micelles, as they were formed in organic resin rather than water
and were pH-responsive with good stability. In this study, the controlled release of
corrosion inhibitors was also demonstrated through changes in coating resistance and
the expansion of the capacitor ring [22]. Another work done by Benchikh et al. via
pre-formed poly(methoxyaniline-co-orthotoluidine) copolymer through chemical oxi-
dative polymerization was examined as a corrosion inhibitor for carbon steel in a 3%
NaCl solution using potentiodynamic polarization and electrochemical impedance
spectroscopy (EIS) techniques. The results indicated that the copolymer acted as an
effective corrosion inhibitor, with the inhibition process attributed to the formation
of an adsorbed film on the metal surface [29]. Dwivedi et al. have studied aniline for-
maldehyde (AF) copolymer as a corrosion inhibitor with 93.44% inhibitor efficiency
for mild steel in 0.5 N hydrochloric acid. The mechanism of inhibition occurs
through molecular adsorption, where the compound regulates anodic and cathodic
reactions in acidic solutions. Besides, the presence of a quaternary amine group in
the structure contributes to the chain extension of the polymer through molecular
repulsion, thereby increasing the adsorption efficiency [30]. Moreover, polymer-based
corrosion inhibitors have many other advantages against small organic molecule
inhibitors, such as the ability to form multilayer films on metal surfaces, a higher
number of adsorption sites, and better temperature resistance [31,32]. Chen et al.
studied poly(maleic acid-co-N-[3-(dimethylamino)propyl]-methacrylamide) (PMD) as
a corrosion inhibitor on Q235 carbon steel in a neutral medium. Results revealed that
PMD exhibited a high corrosion inhibition efficiency (IE) of 90.1% at a dosage of
200 mg/L, and acted as an anodic-type inhibitor by forming an adsorption polymer
film on the metal surface [32].
Herein, a new POEGMA-b-(PMEEU-co-PMAA) (poly(oligo(ethylene glycol) meth-
acrylate)-b-poly((methacrylamidoethyl) ethylene urea)-co-poly(methacrylic acid) block
copolymer was prepared as a corrosion inhibitor. This totally hydrophilic block
copolymer consisting of carboxylic acid, cyclic urea and oligo(ethylene glycol) pen-
dant groups was consciously tailored. In this design, carboxylic acid moieties act as
strong-chelating units and cyclic urea segments have either chelating ability with
metal ions or film forming (or adsorption ability on metal surfaces) ability via strong
hydrogen bonding (seconder forces, van der Waals forces) with the metal surfaces.
On the other hand, poly(oligo-ethylene methacrylate) block prevents the precipitation
of the polymer in aqueous media during these metal ion/surface interaction. All these
features may inhibit scale formation and make the polymeric material as a potential
candidate for scale and corrosion inhibitor.
2. Experimental
2.1. Materials
Oligo(ethylene glycol) methacrylate (OEGMA, Aldrich, St. Louis, MO) was used as
received. 2,2-Azobis(isobutyronitrile) (AIBN, Fluka, Buchs, Switzerland, 98%) was puri-
fied by recrystallization from methanol. Acetonitrile was obtained from Merck
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 3
(Kenilworth, NJ); 4-cyanopentanoic acid dithiobenzoate was obtained from CPADB,
Aldrich (St. Louis, MO); diethyl ether was obtained from ISOLAB (Eschau, Germany);
and petroleum spirit (boiling range of 40–60 C) was obtained from Merck
(Kenilworth, NJ). SIPOMER WAM II (50% N-(2-methacrylamidoethyl) ethylene urea þ
25% methacrylic acid þ25% water, w:w:w) was obtained from Solvay (Brussels,
Belgium), and potassium persulfate was obtained from Sigma (St. Louis, MO).
2.2. Instrumentation
1
H NMR and
13
C NMR spectra of POEGMA Macro-CTA and POEGMA-b-(PMEEU-
co-PMAA) block copolymer were recorded at room temperature at 500 MHz on
Agilent VNMRS NMR Spectrometer. Tetramethyl silane (TMS, Si(CH
3
)
4
) was used as
an internal standard, and the solutions of the polymers were prepared in deuterated
chloroform CDCl
3
and DMSO-d
6
. FTIR spectra were recorded on a Perkin Elmer
FTIR Spectrum One spectrometer. Gel permeation chromatography (GPC) measure-
ments for obtaining the average molecular weight and PDI of the homo and block
copolymer were done with an Agilent instrument (model 1100, Santa Clara, CA) with
a pump, refractive index and UV detectors and four Waters Styragel columns (HR
5E, HR 4E, HR 3, HR 2) (4.6 mm internal diameter, 300 mm length, packed with
5lm particles). THF was applied as an eluent solvent with 0.3 mL/min flow rate at
30 C. The molecular weights (M
n
and M
w
) of the polymers were determined by
using linear polystyrene (PS) standards (Polymer Laboratories, Lewiston, ME).
2.3. Synthesis of POEGMA Macro-CTA
POEGMA was synthesized by RAFT polymerization as given in the literature [33]. For
this purpose, a simple polymerization reaction was carried out with
OEGMA:CTA:AIBN ¼1:0.02:0.0025 feed molar ratios. Based on these ratios,
410
2
mol (12 g) OEGMA, 8 10
4
mol (0.224 g) CPADB, 1 10
4
mol
(1.64 10
2
g) AIBN and 50mL acetonitrile were mixed in a round bottom flask
under N
2
atmosphere and sealed with a rubber septum. Then, the reaction mixture was
saturated with continuous nitrogen flow for 30 min in ice-bath. The polymerization
reaction was carried out for 8 h at 70 C. Then, reaction mixture was cooled rapidly
and precipitated in 50 mL diethyl ether and petroleum spirit (boiling range of 40–
60 C) mixture (1:1, v/v) and dried under vacuum at room temperature (Figure 1).
2.4. Synthesis of POEGMA-b-(PMEEU-co-PMAA)
POEGMA-b-(PMEEU-co-PMAA) block copolymer was prepared by using RAFT poly-
merization. In a typical chain extension procedure, 10
4
mol (0.68 g) POEGMA,
8.63 10
3
mol (1.7 g) N-(2-methacrylamidoethyl) ethylene urea and
9.88 10
3
mol (0.85 g) methacrylic acid were added to 5 mL distilled water in a
vial. The monomers feed weight ratios were arranged POEGMA:N-[2-methacrylox-
yethyl] ethylene urea:methacrylic acid ¼1:2.5:1.25 and macro-CTA to initiator molar
ratio was arranged POEGMA:K
2
S
2
O
8
¼1:0.25. Then, the reaction mixture was
4 A. INCE ET AL.
saturated under continuous nitrogen flow for 20 min in ice-bath. And then
2.5 10
5
mol K
2
S
2
O
8
(6.76 10
3
g) was added to the reaction mixture and the
solution was continued to saturate with continuous nitrogen flow for 10 min in ice-
bath. Polymerization reaction was carried out in an oil bath at 70 C and stirred over-
night. Then, the reaction mixture was cooled and purified with distilled water by
using a dialysis membrane with 3500 cut-offs (Figure 2).
2.5. Corrosion inhibition studies
The chemical composition of SAE 1012 carbon steel is given in the study in the lit-
erature [17]. For the electrochemical experiments, the SAE 1012 carbon steel was pre-
pared after mechanical cutting with a surface area of 0.79 cm
2
. The samples of SAE
1012 carbon steel were abraded with different grades of SiC paper. Then, they were
mechanically polished with diamond paste, rinsed in deionized water, and dried with
a compressed air stream. The metal sheet was divided into coupons measuring
33cm
2
for weight loss analysis. The samples underwent mechanical abrasion using
emery papers of varying grit sizes, ranging from #800 to #2000. Subsequently, they
were rinsed under flowing water, cleaned with acetone to remove any grease, and
dried using warm air. Finally, the samples were stored in a desiccator until further
use [34]. SAE 1012 carbon steel samples were suspended using a hook inside a reac-
tion vessel containing 100 mL of the specific solution being studied, such as a 1 M
HCl solution or an acid solution with varying concentrations of PMEEU-co-PMAA
copolymer. Before immersing the samples in the solution, their initial weights were
recorded. After a 24-hour immersion period, the specimens were carefully removed
and washed under running water, followed by rinsing with ethanol. Subsequently, the
samples were dried using warm air. The final weights of the samples were then
Figure 1. Preparation of POEGMA Macro-CTA.
Figure 2. Preparation of POEGMA-b-(PMEEU-co-PMAA).
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 5
recorded. The weight loss (g) was calculated as the difference between the initial
weight and the final weight of the samples [34–36]. The electrochemical tests were
performed by Gamry Potentiostat/Galvanostat/ZRA (Interface 1010 E) instrument
(Philadelphia, PA) that was used with a conventional for EIS experiments. A triple
electrode system was used for the experiments. SAE 1012 carbon steel samples as
working electrode, a saturated Ag/AgCl electrode was used as reference electrode, a
platinum electrode as counter electrode. The EIS measurements were carried out at a
frequency of 100 kHz to 0.1 Hz and the amplitude signal was 10 mV peak-to-peak.
The impedance analysis was done using ZsimpWin 3.21 software. Tafel polarization
(TP) experiments were scanned in the range of 250 to þ250 mV with the reference
to corrosion potential using a constant sweep rate of 1 mV/s. Analysis of the polariza-
tion curves was accomplished using the Gamry Echem Analyst program. The surface
morphology changes of the SAE 1012 carbon steel were tested in 1 M HCl solution
with one-hour interaction via SEM model Quanta FEG 250 coupled with EDAX
probe (accelerating voltage 20 keV) to determine the composition.
3. Results and discussion
3.1. Preparation of POEGMA-b-(PMEEU-co-PMAA) block copolymer
The block copolymer was prepared by RAFT polymerization technique. Initially,
POEGMA macro-CTA was synthesized with a 60% of polymerization yield to avoid
the diminishing of the active end-group. Then, chain extension of the macro-CTA
was achieved in the presence of MEEU and MAA monomers. Herein, the block
copolymer consisting of double functional groups was designed consciously to attain
better corrosion inhibition ability of the polymer. In this perspective, the carboxylic
acid units on the polymer worked as chelating units to the metal ions on the metal
plate. On the other hand, urea units interacted strongly with the surface of the metal
plate and covered the surface. In both cases, the polymer behaved as a perfect corro-
sion inhibitor agent.
Structural characterization of POEGMA macro-CTA and POEGMA-b-(PMEEU-co-
PMAA) block copolymer was carried out via
1
H NMR measurements. The character-
istic peaks of POEGMA homopolymer were assigned in the NMR spectrum as given
in Figure 3. In this spectrum, the aromatic protons belonging to the RAFT agents
appeared between 7.9 and 7.4 ppm, and methylene protons tethered to the ester group
were observed at 4.0 ppm clearly as expected. After chain extension reaction, new
peaks belonging to the carboxylic acid proton came from PMAA segment and sec-
onder amine proton belonging to the cyclic urea group were appeared at 12.25 and
6.3 ppm, respectively. The other proton peaks came from the second block were men-
tioned in the spectrum. Thus, the success of the formation of homo and block
copolymers was proved by the NMR results.
In addition to
1
H NMR,
13
C NMR characterization was done for POEGMA-b-
(PMEEU-co-PMAA) block copolymer. The characteristic peaks of the block copoly-
mer were assigned in the
13
C NMR spectrum as given in Figure 4. According to the
spectrum, carbonyl carbons of ester groups in the polymer were observed at 178 ppm,
whereas carbonyl carbons of carboxylic acid and cyclic urea appeared at 182 and
6 A. INCE ET AL.
164 ppm, respectively. All the pendant methyl groups directly attached to the back-
bone of the polymer were seen at around 17 ppm, and the –CH
2
–groups on the
backbone of the polymer were appeared at 58 ppm. On the other hand, the naked
–C–groups on the backbone of the block copolymer were spotted at around 38 ppm.
Moreover, the peaks belonging to –CH
2
groups in the cyclic urea ring were observed
at around 38 ppm and 45 ppm. The other peaks, which are not mentioned, are
assigned in Figure 4.
In the FT-IR spectrum of POEGMA (Figure 5), characteristic methacrylate ester
carbonyl (C═O) stretching vibration peak and etheric (–C–O–C–) stretching vibra-
tion peak appear at 1700 cm
1
and 1100 cm
1
, respectively. After the block copoly-
merization of POEGMA homopolymer, two new peaks appeared at 3500–3250 cm
1
and 1650 cm
1
. The broad stretching vibration peak belonging to the seconder amine
(–N–H) on urea group and the carboxylic acid –O–H group at 3500–3250 cm
1
proved the chain extension reaction. In addition, the bending vibration peak at
1650 cm
1
came from pendant cyclic urea groups on PMEEU segments on the block
Figure 3.
1
H NMR spectrum of POEGMA Macro-CTA (in CDCl
3
) and POEGMA-b-(PMEEU-co-PMAA)
block copolymer (in DMSO-d
6
).
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 7
copolymer. Overall, these peaks indicated that the RAFT polymerization of
POEGMA-b-(PMEEU-co-PMAA) was successful.
3.2. Electrochemical impedance spectroscopy measurements
The block copolymer POEGMA-b-(PMEU-co-PMAA) has been observed to readily
soluble in 1 M HCl. The corrosion protection behavior of POEGMA-b-(PMEEU-co-
PMAA) block copolymer with various concentrations was determined in 1 M HCl
solution of SAE 1012 carbon steel with one-hour interaction at 25 C by EIS method.
The Nyquist diagram was obtained by the EIS method as a result of the addition of
POEGMA-b-(PMEEU-co-PMAA) block copolymer into 1 M HCl solution at different
concentrations as shown in Figure 6(a). A semicircular-like shape was observed in
1 M HCl medium at high frequency from the Nyquist representative spectra (Figure
6(a))[37]. This behavior was a characteristic of the corrosion process controlled by
charge transfer [38]. The Nyquist diagrams showed that the blank system retained its
shape compared with the POEGMA-b-(PMEEU-co-PMAA) one. The observed aug-
mentation in the magnitude of the curve, as a function of the concentration of
POEGMA-b-(PMEEU-co-PMAA) block copolymer, elucidated the corrosion inhibi-
tory capability of the block copolymer [24]. This proportional increase of the semi-
circle curves with the inhibitor concentration indicated that the desired inhibition
rate could be achieved with the regulated block copolymer concentration. PMEEU-co-
PMAA segments on the block copolymer might have adsorbed either chelating or
hydrogen bonding on the metal surface by carboxylic and cyclic urea units and in
Figure 4.
13
C NMR spectrum of POEGMA Macro-CTA (in CDCl
3
) and POEGMA-b-(PMEEU-co-PMAA)
block copolymer (in DMSO-d
6
).
8 A. INCE ET AL.
this case cover the reaction sites, delaying charge transfer. The phenomenon of
imperfection of semicircles is included in the literature as a frequency dispersion of
interfacial impedance [39]. The factors leading to this phenomenon can be listed as
follows: (i) surface roughness of the working electrode, (ii) heterogeneity of the work-
ing electrode, (iii) impurities in the metal structure and working medium, (iv) grain
boundaries, (v) layer formation on the surface, and (vi) adsorption of corrosion prod-
ucts or inhibitors on the surface [2,17,39,40].
The Bode modulus (Figure 6(b)) is compatible with the Nyquist spectra. As the
amount of inhibitor increases, the impedance moves in the nobler direction indicat-
ing effective corrosion inhibition at higher inhibitor concentrations. The phase angles
(Figure 6(c)) move toward 75at each concentration, so that possible diffusion is
ruled out [24].
Analysis of Nyquist spectra was performed using an R(QR) equivalent circuit
(Figure 6(d)) to obtain quantitative information on the corrosion of SAE 1012 carbon
steel studied in a 1 M HCl environment and the degree of inhibition by the synthe-
sized POEGMA-b-(PMEEU-co-PMAA) polymer. ZSimpWin 3.21 program was used
for the analysis. The Chi-square value serves as an indicator of the discrepancy
between the measured data and the fitted results, with a lower v
2
value indicating a
higher degree of fitting quality. The calculated electrochemical impedance parameters
Figure 5. FTIR spectra of the POEGMA Macro-CTA and POEGMA-b-(PMEEU-co-PMAA).
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 9
are given in Table 1. As can be seen from the table, the R
s
value does not exceed
1.18 Xcm
2
in 1 M HCl acidic medium and this is reported as a negligible value in
the literature [37]. The value of the nparameter approached one inferring depending
on the increase of the inhibitor concentration. This suggests that the substrate surface
behaves capacitively [35,41]. The R
ct
values for the medium with the inhibitor added
Figure 6. Electrochemical impedance spectra of (a) Nyquist, (b) Bode modulus and (c) Bode phase
angle (d) equivalent circuit representations for SAE 1012 carbon steel in 1 M HCl solution in the
absence and presence of PMEEU-co-PMAA at different concentrations.
Table 1. Electrochemical impedance parameters for SAE 1012 carbon steel in 1 M HCl solution in
the presence and absence of PMEEU-co-PMAA different concentrations.
Inhibitor concentration R
s
(Xcm
2
)
CPE
R
ct
(Xcm
2
) IE (%) Chi-squareY
0
(X
1
s
2
cm
2
)n,0n1
Blank 1.12 0.000253 0.68 99.10 –9.960E–4
1 mM PMEEU-co-PMAA 1.15 0.000105 0.71 275.80 64.0 9.321E–4
2 mM PMEEU-co-PMAA 1.18 0.000093 0.72 353.90 71.9 9.804E–4
3 mM PMEEU-co-PMAA 1.18 0.000081 0.74 499.55 80.2 8.554E–4
4 mM PMEEU-co-PMAA 1.18 0.000079 0.76 588.90 83.2 9.112E–4
5 mM PMEEU-co-PMAA 1.17 0.000067 0.84 708.98 86.0 7.854 E–4
10 A. INCE ET AL.
are higher than for the medium without the inhibitor, and an increasing in the
inhibitor concentration causes this value to increase even more. The C
dl
values show
an opposite behavior to the R
ct
values. This shows that the retardation of corrosion
of SAE 1012 carbon steel in 1 M HCl environment is due to the adsorption of
POEGMA-b-(PMEEU-co-PMAA) block copolymer and the protective layer grows
with increasing inhibitor concentration [22,25,42]. This observation is consistent with
the experimental results (Table 1). Table 1 presents the measured values of R
s
, which
represents the solution resistance of SAE 1012 carbon steel in a 1 M HCl solution,
measured as 1.12 X.cm
2
. In comparison, for solutions containing the synthesized
POEGMA-b-(PMEEU-co-PMAA) copolymer, both R
s
and R
ct
values are lower, while
the Qvalue of the stationary phase element is higher. As the concentration of
POEGMA-b-(PMEEU-co-PMAA) in the solution medium increases, there is an
increase in both R
s
and R
ct
values, and a decrease in the Qvalue. In the absence of
POEGMA-b-(PMEEU-co-PMAA), the R
ct
value for the 1 M HCl solution is
99.1 X.cm
2
, and the Qvalue is measured as 0.000253 X
1
s
2
cm
2
. However, when
1 mM of POEGMA-b-(PMEEU-co-PMAA) is added to the 1 M HCl solution, the R
s
and R
ct
values increase to 1.15 X.cm
2
and 275.8 X.cm
2
, respectively, while the Qvalue
decreases to 0.000105 X
1
s
2
cm
2
. Similarly, when 5 mM of POEGMA-b-(PMEEU-
co-PMAA) inhibitor is added to the 1 M HCl solution, the R
s
and R
ct
values increase
to 1.17 X.cm
2
and 708.98 X.cm
2
, respectively, while the Qvalue decreases to
0.000067 X
1
s
2
cm
2
. While the %g
EIS
for the highest inhibitor concentration
studied was 86.0% in the HCl solution.
The POEGMA-b-(PMEEU-co-PMAA) block copolymers possess a significant num-
ber of pi bonds and the coexistence of nitrogen and sulfur elements, which play a
crucial role in preventing the corrosion of iron in corrosive environments. The pres-
ence of delocalized pi electrons facilitates the formation of coordination bonds with
the iron surface. In an acidic medium, iron carries a negative charge, and the pres-
ence of nitrogen and sulfur acts as anchoring units, allowing the polymer chain to
attach to the surface [43]. The bulky nature of the polymers leads to the formation of
a cluster network on the iron surface, resulting in stronger anchoring and a better
coverage of the surface, ultimately enhancing the IE [43,44].
3.3. Tafel polarization studies
Figure 7 shows the TP curves of SAE 1012 carbon steel at 25 C in 1 M HCl solution
with and without POEGMA-b-(PMEEU-co-PMAA) block copolymer at different con-
centrations. Tafel electrochemical parameters associated with these curves are given
in Table 2. The %g
TP
value given in the table was calculated using the following
equation [35]:
%gTP ¼Icorr Blank
ðÞ
Icorr Inh
ðÞ
Icorr ðBlankÞ
(1)
In Figure 7, the block copolymer is shown to affect both anodic oxidation and
cathodic hydrogen reduction. The displacement of E
corr
by the inhibitor is minimal
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 11
compared to E
corr
from material without inhibitor addition, suggesting that the
PMEEU-co-PMAA segments on the block copolymer play a role as a mixed-type
inhibitor in the corrosion protection process.
The inclusion of the POEGMA-b-(PMEEU-co-PMAA) block copolymer hindered
the acid attack on the SAE 1012 carbon steel. When comparing the values in both
scenarios, it was observed that increasing the inhibitor concentration consistently
decreased both anodic and cathodic current densities [44]. This finding indicates that
the POEGMA-b-(PMEEU-co-PMAA) block copolymer functions as a mixed-type
inhibitor. The E
corr
values showed minimal changes, suggesting that the additives pri-
marily acted as a mixed inhibitor, effectively slowing down the rates of cathodic
hydrogen evolution and anodic dissolution of SAE 1012 carbon steel [36]. The cath-
odic and anodic Tafel slopes were noticeably altered by the inhibitor concentrations.
This observation strongly suggests that the inhibitor effectively regulated both cath-
odic and anodic reactions, indicating its behavior as a mixed-type inhibitor. The
Figure 7. Tafel polarization plots for SAE 1012 carbon steel in 1 M HCl solution in the absence
and presence of PMEEU-co-PMAA at different concentrations.
Table 2. Tafel polarization parameters for SAE 1012 carbon steel in 1 M HCl solution in the pres-
ence and absence of PMEEU-co-PMAA different concentrations.
Inhibitor concentration b
a
(mV/Dec) b
c
(mV/Dec) E
corr
(mV/Ag/AgCl) I
corr
(mA/cm2) CR (mmpy) IE (%)
Blank 86.3 141.0 365 271 11.4 –
1 mM PMEEU-co-PMAA 53.4 117.5 342 85.9 3.9 68.3
2 mM PMEEU-co-PMAA 57.3 115.1 341 77.9 2.9 71.3
3 mM PMEEU-co-PMAA 57.8 120.8 325 48.2 1.8 82.2
4 mM PMEEU-co-PMAA 56.1 118.5 332 42.1 1.6 84.5
5 mM PMEEU-co-PMAA 60.9 133.2 313 39.7 1.3 85.4
12 A. INCE ET AL.
difference in b
a
and b
c
values is also in the low ranges. According to the literature,
such a small change is an indication of the unchanged cathodic and anodic reaction
mechanism [25].
The results in Table 2 show that the addition of the block copolymer to the acidic
solution significantly suppresses the corrosion current density of the metal. The add-
ition of 1 mM POEGMA-b-(PMEEU-co-PMAA) block copolymer reduced I
corr
from
271 lA/cm
2
to 85.9 lA/cm
2
, indicating 68.3% protection of the metal surface. It was
found that the block copolymer provided 71.3%, 82.2%, 84.5% and 85.4% protection
on the metal surface when the concentrations were increased by 2 mM, 3 mM, 4 mM
and 5 mM, respectively. These results, which are in good agreement with the EIS
results, reflect the effectiveness of the block copolymer inhibitor in retarding the cor-
rosion of SAE 1012 carbon steel in a very aggressive environment.
3.4. Effect of temperature and weight loss
Table 3 presents the results of weight loss measurements conducted on SAE 1012 car-
bon steel samples immersed in 1 M HCl, both with and without the presence of
POEGMA-b-(PMEEU-co-PMAA) block copolymers. These conditions included both
the absence and presence of different concentrations of PMEEU-co-PMAA copoly-
mers at temperatures of 25 C and 60 C. The equations used for calculating the cor-
rosion rate (mm/yr) and percentage IE can be found in Yadav et al. [45]. Based on
the results, it is evident that the weight loss and corrosion rate of the metal specimens
significantly decrease in the presence of POEGMA-b-(PMEEU-co-PMAA) block
copolymers in the acidic environment.
The effect of temperature on the corrosion behavior of SAE 1012 carbon steel was
investigated in the presence of PMEEU-co-PMAA copolymer, and the results are pre-
sented. The IE was observed to increase up to 60 C, indicating the stability of the
polymer composite and the adsorbed film at these temperatures. While physical
adsorption occurs at room temperature, at higher temperatures, chemical interactions
develop between the adsorbed polymer and the SAE 1012 carbon steel. The max-
imum IE was found to be 88.01% at 40 C and 79.43% at 60 C for the optimal con-
centration of PMEEU-co-PMAA copolymer. However, as the temperature increased,
the adsorption of the inhibitor on the metal surface weakened. Additionally, at higher
temperatures, the equilibrium shifted towards desorption, as the rate of the desorp-
tion process exceeded that of adsorption at these temperatures [44,46].
Table 3. Calculated values of weight loss, corrosion rate, and percentage inhibition for SAE 1012
carbon steel in 1 M HCl solutions in the absence and presence of different concentrations of
PMEEU-co-PMAA copolymers at 25 C and 60 C.
Inhibitor concentration
25 C60
C25
C60
C25
C60
C
Weight loss (g) v(mm y
–1
)%g
Blank 1.012 10.753 52.179 555.379 ––
1 mM PMEEU-co-PMAA 0.370 6.967 19.115 360.092 64.26 35.21
2 mM PMEEU-co-PMAA 0.272 4.553 13.949 235.067 73.16 57.66
3 mM PMEEU-co-PMAA 0.212 3.401 10.849 175.655 79.10 68.37
4 mM PMEEU-co-PMAA 0.151 2.632 7.750 135.874 85.06 75.52
5 mM PMEEU-co-PMAA 0.121 2.212 6.199 114.176 88.01 79.43
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 13
The effectiveness of POEGMA-b-(PMEEU-co-PMAA) block copolymers as corro-
sion inhibitors in an HCl environment is influenced by the concentration of the poly-
mer and the temperature of the system. Higher concentrations of the polymer
demonstrate better retarding effects on the dissolution of SAE 1012 carbon steel com-
pared to lower concentrations. Additionally, the polymer exhibits superior corrosion
inhibition at lower temperatures. These findings are evident from the results pre-
sented in Table 3. The presence of Cl
–
ions plays a crucial role in the corrosion
resistance of the steel [45,47]. Experimental evidence suggests that in strong acid solu-
tions, the steel surface acquires a net positive charge, and Cl
–
ions specifically adsorb
onto the charged steel surface [34]. The adsorption of Cl
–
ions leads to an excess of
electrons, resulting in a negatively charged metal surface. Due to their smaller size,
Cl
–
ions have a higher replenishing power [43,48]. The functional groups present in
POEGMA-b-(PMEEU-co-PMAA) block copolymers, such as C═O, C═N, N═O, and
aromatic rings, contain hydroxyl (–OH) and carboxyl (–COOH) groups. In strong
acid solutions, the carbonyl oxygen (C═O) is protonated, causing the POEGMA-b-
(PMEEU-co-PMAA) block copolymer to exist as polycations [48]. These polycations
can adsorb onto the recharged steel surface through electrostatic attraction. The pres-
ence of Cl
–
ions, which replenish the steel surface, may induce a greater adsorption
of POEGMA-b-(PMEEU-co-PMAA) block copolymer polycations.
3.5. Adsorption isotherm
The adsorption isotherm provides information about the interaction between organic
corrosion inhibitors and metal surfaces in general [49]. Decontamination is a method
that involves the adsorption of contaminants onto surfaces to remove them. These
interactions can occur through physical adsorption, chemical adsorption, or a com-
bination of both mechanisms [17,49]. Equation (2) was deduced based on the pre-
sumptions that the adsorbed species exhibit monolayer formation on the metal
surface and that these species do not exhibit mutual interactions [17,49]. When the
adsorption process adheres to the assumption of non-interplay among the adsorbed
species, the slope of the ratio C/hplotted against Cis equal to unity. Figure 8 illus-
trates the Langmuir plots depicting the adsorption behavior of the POEGMA-b-
(PMEEU-co-PMAA) block copolymer onto the surface of SAE 1012 carbon steel in
HCl solutions at a temperature of 25 C. In the following equations, Cis the concen-
tration of the block copolymer, his the surface coating value, Kads is the equilibrium
constant of the adsorption process, DG
ads refers to the free energy of adsorption, Ris
the universal gas constant, Tis the thermodynamic temperature and 55:5 is the
numerical value of the molar concentration of water in mol/L [50,51].
C
h¼1
Kads
þC(2)
DG
ads ¼RTlnðKads 55:5Þ(3)
14 A. INCE ET AL.
Figure 8 shows C=hversus Cfor the adsorption of PMEEU-co-PMAA molecules
on the surface of SAE 1012 carbon steel at 25 C. The graphs are linear and the R
2
values are approximately one. This shows that the adsorption of POEGMA-b-
(PMEEU-co-PMAA) block copolymer on the surface of SAE 1012 carbon steel follows
Langmuir’s isotherm model [49–51]. Monolayer adsorption exists when the slope of
the Langmuir graph is equal to one. As shown in Table 4 and Figure 8, the slope is
close to one and PMEEU-co-PMAA is assumed to form a single-layer film on the
metal surface [49,50]. The high Kads value (Table 4) indicates a strong interaction
between the block copolymer and SAE 1012 carbon steel.
A review of the literature shows that there is a relationship between DG
ads and
inhibitor adsorption [52–55]. The DG
ads value for physical adsorption is about
20 kJ/mol or less, the DG
ads value for chemical adsorption is about 40 kJ/mol or
more, and the DG
ads value for mixed adsorption is between physical and chemical
adsorption [24,54]. Based on the obtained intermediate value of DG
ads, it suggests
that the interaction between POEGMA-b-(PMEU-co-PMAA) and SAE 1012 carbon
steel involves both physical and chemisorption processes. It is important to note that
the assumption underlying the calculation of DG
ads, which assumes that h¼IE/100,
may not always be valid, as demonstrated by Walczak et al. [56]. Therefore, the
accuracy of the calculated DG
ads may be questionable. Consequently, DG
ads alone may
not serve as a reliable criterion for distinguishing between chemisorption and physi-
sorption, as recently discussed by Kokalj [57]. A glance at Table 4 shows that the
DG
ads value of the block copolymer falls into the category of mixed adsorption. The
PMEEU-co-PMAA segments on the block copolymer contain the secondary amine
Figure 8. Langmuir adsorption isotherms for PMEEU-co-PMAA in 1 M HCl at 25 C from TP and EIS
measurements.
Table 4. The adsorption measurements for PMEEU-co-PMAA on the SAE 1012 carbon steel surface
in 1 M HCl solution.
Technique Kads ðL=molÞDG
ads ðkJ=molÞ
EIS 1060.12 27.97
TP 1488.44 28.25
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 15
(–N–H) on urea group and carbonyl functional groups. These groups are protonated
as PMEEU-co-PMAA
þ
in 1 M HCl medium of the block copolymer. Literature
reports that the surface of SAE 1012 carbon steel acquires a positive charge in a 1 M
HCl environment and chloride ions are adsorbed on the surface [17]. In this case,
excessive negative charges are expected on the surface, facilitating the adsorption of
cationic charges [55]. The DG
ads value calculated for the block copolymer shows that
physical adsorption mechanisms occur on the surface of SAE 1012 carbon steel.
There may be a donor–acceptor interaction between the p-electrons of C═O, C═N,
N═O and the aromatic rings in the PMEEU-co-PMAA segments and the empty 3D-
orbital of Fe. In this case, chemical adsorption occurs.
3.6. SEM and EDAX studies
The SEM images of the SAE 1012 carbon steel surface after EIS experiments in 1 M
HCl solution are shown in Figure 9.Figure 9(a) shows wear due to the sanding pro-
cess, but the metal surface is smooth. In Figure 9(b), severe deformation occurred
when the metal was exposed to the acid solution. Numerous pits of different sizes
can be seen on the metal surface. In Figure 9(c), the pits formed on the surfaces are
closed and the inhibitor molecules are adsorbed on the surface.
The chemical composition of the surfaces of the metals in Figure 9 was studied
using EDAX and these data are shown in Table 5. The major elements detected on
the uncorroded surface include C (2.1%), Si (0.3%), Cr (0.55%), Mn (1.08%), and Fe
(95.97%). The percentages of Mn and Fe decreased to 0.46% and 43.16%, respectively,
Figure 9. SEM images showing the surface morphology of the SAE 1012 carbon steel sample (a)
before immersion in 1 M HCl solution (b) after immersion in 1 M HCl solution, (c) containing 5 mM
PMEEU-co-PMAA.
16 A. INCE ET AL.
on the surface exposed to 1 M HCl in an environment without inhibitors, which can
be attributed to the coating of the surface with corrosion products. The elements O
(38.12%) and Cl (15.58%) were detected on the surface due to corrosion. It has been
reported that the corrosion product formed when the carbon steel is immersed in
HCl solution is mainly a mixture of chloride and oxide [38]. When 5 mM block
copolymer was added to the medium, it was seen that Fe and Mn increased up to
86.9% and 0.72%, respectively. On the other hand, a decrease of 4.87% and 4.56%
was observed in O and Cl atoms.
4. Conclusions
In this study, a multi-functional POEGMA-b-(PMEEU-co-PMAA) block copolymer
was synthesized and its corrosion inhibitor ability was investigated. The cyclic-urea
and carboxylic acid functional block copolymer was tested in 1 M HCl solution as an
inhibitor against the corrosion of SAE 1012 carbon steel. In electrochemical tests, cor-
rosion protection of SAE 1012 carbon steel in a 1 M HCl environment with the block
copolymer at different concentrations was proved. When the concentration of the
block copolymer was increased to 5 mM, the corrosion resistance of the metal
increased from 99.1 Xcm
2
to 708.98 Xcm
2
. The POEGMA-b-(PMEEU-co-PMAA)
block copolymer acted as a mixed-type corrosion inhibitor and adsorbed on SAE
1012 carbon steel via a mixed adsorption mechanism. The adsorption of the block
copolymer onto the metal surface obeys Langmuir’s adsorption isotherm. The K
ads
value calculated from the equilibrium constant of the adsorption process reflects a
strong interaction as expected. SEM and EDAX studies also proved the block copoly-
mer adsorption on the metal surface. Overall, the multi-functional block copolymer is
a promising candidate as a corrosion inhibitor for formulations that can be used in
acidic environments.
Acknowledgements
This work was supported by the Research Fund of the Istanbul Technical University (BAP
Project Number: 39921).
Disclosure statement
No potential conflict of interest of interest was reported by the author(s).
Funding
This work was supported by the Research Fund of the Istanbul Technical University (BAP
Project Number: 39921).
Table 5. EDAX analysis results of SAE 1012 carbon steel in 1 M HCl solution.
Fe O C Cl Mn Cr Si N
Before experiment 95.97 –2.1 1.08 0.55 0.3 –
After immersion in 1 M HCl solution 43.16 38.12 2.05 15.58 0.46 0.38 0.25 –
5 mM PMEEU-co-PMAA 86.90 4.60 2.15 4.56 0.72 0.53 0.27 0.27
JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY 17
ORCID
Ahmet Ince http://orcid.org/0000-0002-4111-1327
Ilayda Koramaz http://orcid.org/0009-0003-8392-9738
Ertu
grul Kaya http://orcid.org/0000-0003-1579-6411
Bunyamin Karagoz http://orcid.org/0000-0003-1191-218X
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