Synthesis and Characterization of Poly(urethane-ether azomethine) Fatty Amide Based Corrosion Resistant Coatings from Pongamia glabra Oil: An Eco-Friendly Approach

Article abstract of DOI:10.1155/2016/5623126

A novel attempt has been made to incorporate azomethine group in the backbone of polyurethane ether Pongamia oil fatty amide. The overall reaction was carried out in different steps like preparation of N,N-bis(2-hydroxyethyl) Pongamia glabra oil fatty ami

Full text of DOI:10.1155/2016/5623126

Hindawi Publishing Corporation
Journal of Chemistry
Volume 2016, Article ID 5623126, 10 pages
http://dx.doi.org/10.1155/2016/5623126
Research Article
Synthesis and Characterization of Poly(urethane-ether
azomethine) Fatty Amide Based Corrosion Resistant Coatings
from Pongamia glabra Oil: An Eco-Friendly Approach
Manawwer Alam,1 Naser M. Alandis,2 Naushad Ahmad,2 and Mu Naushad2
1Research Center, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
2Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
Correspondence should be addressed to Manawwer Alam; malamiitd@gmail.com
Received 16 January 2016; Revised 24 March 2016; Accepted 30 March 2016
Academic Editor: Carola Esposito Corcione
Copyright © 2016 Manawwer Alam et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
A novel attempt has been made to incorporate azomethine group in the backbone of polyurethane ether Pongamia oil fatty amide.
e overall reaction was carried out in different steps like preparation of N,N-bis(2-hydroxyethyl) Pongamia glabra oil fatty amide,
poly(ether fatty amide), and poly(urethane-ether) fatty amide. e hydroxyl terminated Schiff base, ethane 1,2-di(azomethine)
bisphenol, reacts with fatty amide diol and is further treated with toluylene 2,4-diisocynate (TDI) to form poly(urethane-ether
azomethine) fatty amide (PUEAF). ese synthesized resins were characterized by FT IR, 1H NMR, and 13C NMR spectroscopic
techniques. Molecular weight of PUEAF resin was measured by gel permeation chromatography (GPC), coating was made on
mild steel strips, and evaluating their physicochemical and physicomechanical analysis was carried out by standard methods.
e PUEAF25 coating showed highest scratch hardness (2.5 kg), gloss (90) at 45∘, pencil hardness (4H), and impact resistance
(150 lb/inch). Atomic force microscopy (AFM) and differential scanning calorimetry (DSC)/thermogravimetric analysis (TGA)
were used to determine the topography and thermal behavior of PUEAF. Corrosion studies of PUEAF coated mild steel were used
in different corrosive media (3.5 wt% HCl, 5 wt% NaCl, and tap water) at room temperature using potentiodynamic polarization
technique. e results of this study showed that PUEAF coatings exhibit good physicomechanical, anticorrosive properties and get
application up to 180∘C.
1. Introduction
polyetheramide, polyurethane, polyester, polyepoxy, and pol-
yamine amide in combination with commercial polymers
such as polyvinyl alcohol, polystyrene, polymethylmeth-
acrylate, and polyurethane [11–15]. VO such as linseed,
Pongamia, olive, castor, Jatropha, soybean, Mesua ferrea,
cotton seed, neem (Azadirachta indica), tung, corn, and
Annona squamosa are used for the production of polymeric
coatings [16–23]. e utilization of VO has attracted great
attention in both scientific and industrial applications due
to easy availability, environmental friendliness, low volatile
organic matter, and cost-effectiveness [24–27].
Organic coatings are widely used for protection of mild steel
against corrodents and to provide aesthetic appeal. Various
types of polymeric organic coatings from different renewable
resources like lignin, cellulose, vegetable oils [VO], and others
are used to protect mild steel [1–4]. To further improve
coating performance, inorganic moieties are incorporated
into organic polymer coatings yielding hybrids [5, 6]. Hybrid
coatings show excellent mechanical properties, hardness,
wear resistance, and chemical stability against solar radiations
and pollutants in atmosphere [7], ofen good hydrophobicity
[8], and transparency [9]. Hybrid coatings have also shown
antibacterial and antifungal behavior [10].
Schiff base (azomethine) also called imine (-C=N-) has
nitrogen; it is basic and exhibits pi-acceptor properties. Imine
group possesses excellent donor properties and is used as
ligands, enzymatic intermediates in coordination chemistry
VO are one of the most important renewable resources for
production of polymeric materials like alkyd, polyesteramide,

2
Journal of Chemistry
and biochemistry, respectively. Schiff base compounds are
corrosion resistant antimicrobial with good thermal proper-
ties [28, 29]. e main drawbacks of Schiff base polymers
are brittleness and lack of toughness [30–32]. Keeping in
mind these properties, we introduced azomethine group in
oil fatty amide through ether linkage and further modified by
urethane. us, the approach is synergistic benefitting both
the constituents and rendering a corrosion resistant coating
material.
2.4. Synthesis of Poly(ether azomethine fatty amide) (PEAF).
HEFA (3.60 g), EAB (2.50 g), and 100 mL xylene were taken in
a four-necked conical flask with Dean Stark trap, thermome-
ter, nitrogen inlet, and stirrer and heated up to 180∘C, for
2 h under continuous stirring. e procedure followed was
according to our earlier reported paper [17].
2.5. Synthesis of Poly(urethane-ether azomethine fatty amide)
(PUEAF). PEAF and TDI (20, 25, 30 wt%) along with xylene
were placed in four-necked conical flask fitted with con-
denser, nitrogen inlet, thermometer, and stirrer. e reaction
was carried out under stirring at 120∘C, till the completion of
the reaction.
e goal of present study is the development of new
poly(urethane-ether azomethine) fatty amide (PUEAF)
hybrid from seed oil of Pongamia glabra, by the introduction
of inorganic Schiff base moiety. e synthesis of PUEAF
hybrid is divided into four steps: (i) synthesis of ethane
1,2-di(azomethine) bisphenol (EAB), (ii) synthesis of N,N-
bis(2-hydroxyethyl) Pongamia glabra oil fatty amide (HEFA),
(iii) synthesis of poly(ether azomethine) fatty amide (PEAF),
and (iv) synthesis of poly(urethane-ether azomethine) fatty
amide (PUEAF). e products obtained in each step were
2.6. Methods. HEFA, PEAF, and PUEAF resins were evalu-
ated by spectroscopic techniques such as FT IR, 1H NMR, and
13C NMR. FT IR spectra of HEFA, PEAF, and PUEAF resins
were taken on FT IR spectrometer, Spectrum 100, Perkin
1
Elmer, USA. H and 13C NMR spectrum were recorded on
1
characterized by FT IR, H NMR, and 13C NMR spectro-
Jeol DPX 400 MHz using deuterated chloroform/dimethyl
sulphoxide as solvents and tetramethylsilane as an internal
standard. ermal analysis of PUEAF resin was carried out by
thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) (Model TGA/DSC 1, Mettler Toledo AG,
Analytical CH-8603, Schwerzenbach, Switzerland) in nitro-
gen atmosphere, from 40∘C to 350∘C for DSC and from 25∘C
to 800∘C for TGA with heating rate of 10∘C/min. Molecular
weight (Mw and Mn) of PUEAF resin was investigated by
GPC (HT-GPC Module 350 A, Viscotek, Houston, TX, USA).
THF was used as eluent at a flow rate 1.0 mL/min and instru-
ment was calibrated with polystyrene standard. Topography
of PUEAF coated panels was measured by Atomic Force
Microscope (AFM) in noncontact mode, Model TriA SPM,
APE Research, s.r.l. Area Science Park, Basovizza 34149,
Trieste, Italy. AFM was equipped with a piezoelectric scanner
and HQ:CSC17 Cantilevers (Mikro Masch D35578, Wetzlar,
Germany). Cantilevers have been used with Cr-Au/Pt coated
tip, length 450 5 ꢀm, width 50 3 ꢀm, thickness 2.0 0.5 ꢀm,
force constant 0.06–0.40 N/m, and resonance frequency 10–
17 kHz.
scopy. e physicochemical characterization of PUEAF resin
was carried out by standard methods. PUEAF were applied as
coatings on mild steel panels for physicomechanical analysis.
e thermal stability of PUEAF resins was investigated by
thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC). e corrosion resistance performance of
PUEAF was investigated by potentiodynamic polarization
measurements at ambient temperature.
2. Materials and Methods
2.1. Materials. Pongamia glabra oil was extracted from
seeds through Soxhlet apparatus using petroleum ether (BP
60–80∘C) and characterized by Gas Liquid Chromatog-
raphy (Perkin Elmer Model 716, USA) with FID detec-
tor [19, 33]. Diethanolamine (Riedel-de Haen, Germany),
petroleum ether, sodium methoxide, methanol, xylene,
ethylene diamine (BDH Chemicals, Ltd., Poole, England),
4-hydroxybenzaldehyde (Koch-Light Laboratories, Coin-
brook Bucks, England), and toluylene 2,4-diisocynate (Acros
Organic, USA) were used as received. Mild steel panels
(99.51% Fe, 0.34% Mn, 0.10% C, and 0.05% P) were purchased
from Fancy Steel Company, Tianjin, China.
2.7. Preparation and Testing of Coatings. 40% solutions of
PUEAF resins in xylene were applied by dip method on
commercial mild steel strips with standard sizes (70 ×
25 × 1 mm) for analysis, cured at ambient temperature and
atmosphere. e PUEAF coating curing occurred by evapo-
ration of solvent, reaction free isocynates with moisture, and
autooxidation. PUEAF coated strips were tested for impact
resistance (IS: 101 part 5/sec 3, 1988), scratch hardness (BS
3900), and salt spray test (ASTM D1654). ickness of coat-
ings was measured by Elcometer Coating ickness Gauge
(Model 456; Elcometer Instruments, Manchester, UK). Gloss
of coatings was measured by gloss meter (Model RSPT20;
digital instruments, Santa Barba, CA, USA). Adhesion test
was carried out (ASTM D3359-02) by cross hatch adhesion
tester consisting of 11 with 1 mm spacing of blades. e test
was carried out by pressing and passing the adhesion tester on
coated panel into two directions at right angle to each other.
e square adhesive tape was adhered over panel and afer 5
2.2. Synthesis of Ethane 1,2-Di(azomethine) Bisphenol (EAB).
4-Hydroxybenzaldehyde (2.44 g, 0.02 mol) was dissolved in
50 mL of methanol and ethylene diamine (0.60 g, 0.01 mol)
was added. e reaction mixture was refluxed for 6 hours
at 60∘C with continuous stirring. e colour of solutions
changed from wine red to dark red afer addition of ethylene
diamine. e reaction was monitored by TLC. Afer com-
pletion of reaction, methanol was removed through vacuum
evaporator and distilled water was added to obtain precipitate
of EAB. EAB was washed with diethyl ether several times and
dried in vacuum oven.
2.3. Synthesis of N,N-Bis(2-hydroxyethyl) Pongamia glabra Oil
Fatty Amide (HEFA). HEFA was synthesized according to
previously reported method [17, 34].

Journal of Chemistry
3
minutes removed sharply. e adhesion of film was measured
from number of squares detached with tape. e results
were obtained by comparing number of squares detached by
peeling off the adhesive tape with number of squares that
stayed on sheets. In flexibility test, the coated mild steel strips
were bent, this tested ability of coating to resist cracking
when elongated. Flexibility of coated panels was verified on a
conical mandrel tester (ASTM D3281-84). While performing
assessment, the mandrel was free to rotate on its axis, and
then coated samples were kept in between revolving axes.
e lever of conical mandrel was lowered in a perpendicular
direction to obtain specific angles. e pencil hardness of
coated panel was observed by pencil hardness tester (Wolff-
Wilborn Tester, Sheen Instruments, England). In this test,
pencils having different types (9B, 8B, 7B, 6B, 5B, 4B, 3B, 2B,
B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, and 9H) from
sofer (darker) to hard (lighter) grade were used to move over
surface of coated panel from a distance of 6 mm at fixed angle
(45∘) by using standard holder. Force (7.5 N) was applied to
the pencil, moving it over surface of examination of the panel,
at fixed angle. e coated panels were checked for scratches
on the film. e same process was repeated with pencil of
upper grade of hardness as long as film was not scratched.
e pencil hardness of the coating corresponds to the highest
degree of hardness which the coating resists without being
scratched.
2 HO
CHO +
H2N
NH2
Ethylene diamine
4-Hydroxybenzaldehyde
HO
N
N
OH
Ethane 1,2-di(azomethine) bisphenol
Scheme 1: Synthesis of ethane 1,2-di(azomethine) bisphenol (EAB).
Corrosion resistance studies of PUEAF coated mild steel
strips were accomplished using Gill AC (ACM Instruments,
Cumbria, England, UK). e inhibition efficiency of dif-
ferent PUEAF coated panels was evaluated in relation to
bare mild steel. For this study potentiodynamic polarization
curves were prepared by polarizing the working electrode
at 250 mV in relation to corrosion potential at a scanning
rate of 5 mV/s. e exposed surface area of working electrode
was 1 cm2 in 250 mL volume of solution. e electrochemical
circuit was completed with platinum counter electrode and
calomel reference electrode. Polarization resistance, corro-
sion current, corrosion potential (open circuit potential), and
Tafel constant (ꢁꢀ, ꢁꢁ) values curve were calculated by extrap-
olating the linear portion of the curve. All measurements
were accomplished in triplicate form in different corrosive
media like 3.5% HCl, 5.0% NaCl, and tap water (Cl− ion
164 ppm) [5].
Figure 1: 1H NMR spectra of EAB.
3. Results and Discussion
Figure 2: 13C NMR spectra of EAB.
Schemes 1, 2, and 3 show synthesis of EAB, PEAF, and
PUEAF, respectively. EAB was synthesized by chemical reac-
tion between 4-hydroxybenzaldehyde and ethylene diamine.
Synthesis of PEAF was carried out from the reaction of HEPA
with EAB and further treated with TDI to form PUEAF
hybrids. e chemical reactions were ascertained with help
of FT IR, 1H NMR, and 13C NMR spectroscopy.
ppm): 5.351 (-OH); 8.742 (-CH=N-, azomethine); 6.850–7.781,
(-CH-, aromatic); 3.003 (-CH -, aliphatic) (Figure 1). 13C
2
NMR (DMSO-d6, ꢂ ppm): 161.159 (-CH=N-); 115.508, 126.672,
129.567 (-CH-, aromatic); 61.652 (-CH - aliphatic) (Figure 2),
2
melting point 148∘−C1.
3.1. Spectral Analysis
PEAF. FT IR (cm ): 3454 (OH); 2953 (-CH - asymmetri-
2
EAB. FT IR (KBr, cm−1): 3456 (OH); 2938 (-CH - asym-
cal); 2854 (-CH - symmetrical); 3007 (-CH=CH-); 1628 (-
2
2
metrical); 2854 (-CH - symmetrical); 1628 (-CH=N-); 1278
CH=N-); 1617 (C=O, amide); 1461 (C-N, amide); 1278 (-O-
2
1
1
(-O-Ar); 778, 790 (aromatic ring). H NMR (DMSO-d6, ꢂ
Ar); 1520, 1464, 771, 734 (aromatic ring). H NMR (CDCl3,

4
Journal of Chemistry
OH
HO
OH
OH
N
C
+
O
N
C
N
C
C
C
H
H
H2 H2
R
HEFA
Ethane 1,2-di(azomethine) bisphenol
Δ
−H2O
O
OH
OH
O
N
C
R
N
C
R
O
O
N
C
N
C
C
C
H
H
H2 H2
n
Poly(ether azomethine) fatty amide
Scheme 2: Synthesis of PEAF.
O
O-H
O
OH
N
N
C
R
O
C
R
O
N
N
n
NCO
Δ
O
NCO
TDI
O
O
NH
O
HO
N
N
O
C
R
O
C
R
N
N
NCO
m
Poly(urethane-ether azomethine) fatty amide
Scheme 3: Synthesis of PUEAF.
1
ꢂ ppm): 0.825–0.860 (-CH ); 1.217–1.265 (-CH -); 1.965–
742 (aromatic ring). H NMR (CDCl3, ꢂ ppm): 0.817–0.868
3
2
2.001 (-CH -, attached double bond); 2.310 (CH between
(-CH ); 1.237–1.276 (-CH -); 1.955–2.101 (-CH -, attached
2
2
3
2
2
double bond); 2.780 (CH attached to amide CO) 3.523–3.570
double bond); 2.325 (CH between double bond); 2.681
2
2
(-CH OH); 3.728–3.741 (-CH - attached amide nitrogen);
(CH attached to amide CO) 3.503–3.521 (-CH OH); 3.718–
2
2
2
2
4.164 (-CH attached O); 4.702 (-CH OH); 5.291–5.305 (-
3.721 (-CH - attached amide nitrogen); 4.204 (-CH attached
2
2
2
2
CH=CH-); 6.82–6.84, 7.528 (aromatic ring); 8.713 (CH=N,
O); 4.682 (-CH OH); 5.301–5.325 (-CH=CH-); 6.80–6.84
2
azomethine) (Figure 3). 13C NMR (CDCl3, ꢂ ppm): 14.066 (-
(aromatic ring); 7.96 (-NH, urethane) 8.752 (CH=N, azome-
thine) (Figure 5). 13C NMR (CDCl3, ꢂ ppm): 14.043 (-
CH ); 21.239–29.658 (-CH -); 32.852 (-CH attached amide
CH ); 22.630–29.719 (-CH -); 31.852 (-CH attached amide
3
2
2
carbonyl); 54.096 (-CH - attached to nitrogen); 63.451 (-
2
3
2
2
CH attached to O); 115.131, 129.954, 154.976 (aromatic ring);
carbonyl); 58.234 (-CH - attached to nitrogen); 64.032 (-
2
2
163.652 (-CH=N-); −171 6.453 (C=O, amide) (Figure 4).
CH attached to O); 115.232, 129.817, 155.823 (aromatic ring);
2
161.582 (C=O, urethane); 164.252 (-CH=N-); 177.452 (C=O,
amide) (Figure 6).
PUEAF. FT IR (cm ): 3320 (OH); 2958 (-CH - asymmetri-
2
cal); 2856 (-CH - symmetrical); 3010 (-CH=CH-); 2270 (-
PEAF spectra show the presence of the absorption bands
2
typical for those present in FTIR, H NMR, and 13C NMR
1
NCO free), 1625 (-CH=N-); 1615 (C=O, amide); 1466 (C-N,
amide); 1711 (NH, urethane); 1270 (-O-Ar); 1526, 1466, 775,
of HEFA [17, 34]. Additional peaks appear for aromatic ring

Journal of Chemistry
5
Figure 5: 1H NMR spectra of PUEAF25.
Figure 3: 1H NMR spectra of PEAF.
Figure 6: 13C NMR spectra of PUEAF25.
Figure 4: 13C NMR spectra of PEAF.
PEAF. During urethane formation, hydroxyl value decreases
as some terminal hydroxyl group of PEAF gets consumed
by the addition reaction between the hydroxyl groups and
free -NCO groups of TDI. PUEAF resin was found solu-
ble in acetylacetone, tetrahydrofuran, formamide, dimethyl
formamide, benzene, ethylene glycol dimethyl ether, xylene,
ethyl methyl ketone, diethyl ether, acetone, dichloromethane,
ethyl acetate, toluene, and carbon tetrachloride and insoluble
in acetonitrile, methanol, ethanol, and water, partially soluble
in n-hexane. e solubility results of PUEAF resin can be
ascribed to dense and polar nature of the resin [15].
and azomethine group conferred by EAB. e absorption
bands for -OH show slight depression relative to HEFA, due
to consumption of -OH during the reaction.
Similarly, spectra of PUEAF show the presence of aro-
matic ring and azomethine group as in PEAF. Additional
absorption bands occur due the presence of -NH(-C=O)-
O- and free -NCO of urethane, formed by chemical reaction
between free -OH of PEAF and -NCO of TDI. Molecular
weight of PUEAF25 was observed to be 7267 (Mw) and 4762
(Mn) with PDI 1.526.
3.3. Physicomechanical Properties of Coating. PUEAF coat-
ings dried within 25–30 minutes at ambient temperature.
PUEAF coatings with minor content of TDI take more time
to dry as compared to higher content. is can be accredited
to good affinity of -NCO groups to undergo chemical reaction
with free -OH group, thus facilitating curing of PUEAF resins
at room temperature. When increasing the loading of TDI,
PUEAF resins attain higher cross-link density, which also
accelerates fast drying at ambient temperature. e optimum
cross-linking is achieved in case of 25 wt% loading of TDI
in PUEAF resin, which is responsible for the shortest curing
3.2. Physicochemical Analysis. e physicochemical analysis
was carried out by standard methods [35]. e results indicate
that hydroxyl value (HV) and iodine value (IV) decrease from
HEFA (HV = 8.2, IV = 85) to PUEAF (HV = 5.1, IV = 54) and
subsequently PUEAF20 (HV = 3.3, IV = 27), PUEAF25 (HV =
2.3, IV = 24), and PUEAF30 (HV = 2.0, IV = 17). ese trends
suggest consumption of hydroxyl value of HEFA and EAB
during the condensation reaction between hydroxyl groups
in presence of acid catalyst, resulting in the formation of

6
Journal of Chemistry
Table 1: Physicomechanical characterization of PUEAF coatings.
−200
−300
−400
−500
−600
−700
−800
Resin code∗
PUEAF20
88
PUEAF25
90
PUEAF30
97
Gloss at 45∘
Scratch hardness (kg)
Pencil hardness
Bend test (1/8 inch)
1.9
1H
Passes
2.5
4H
Passes
2.3
3H
Passes
∗
Last numeral digit indicates the loading of TDI in PUEAF resins.
0
−200
−400
−600
−800
10−6 10−5 10−4 10−3 10−2 10−1
100
101
Current (mA/cm2)
PUEAF30
PUEAF25
PUEAF20
MS
Figure 8: Tafel plots of bare MS and PUEAF coated MS in 5% NaCl
solution.
10−5
10−4
Current (mA/cm2)
PUEAF20
MS
10−3
10−2
10−1
polarization curve showed that PUEAF film causes a positive
displacement in the corrosion potential, relative to the value
of bare MS. is positive displacement for PUEAF coating
was higher than bare MS and the shif in the corrosion
potential confirms the protection of metal surface. Tafel mea-
surement evidently displays that a substantial reduction in
PUEAF30
PUEAF25
Figure 7: Tafel plots of bare MS and PUEAF coated MS in tap water.
corrosion rate occurs for PUEAF30 coated coating (1.524ꢃ −
03 mm/year) with respect to bare MS (8.350ꢃ−01 mm/year).
is reduction was due to protective effect of PUEAF film on
MS. Tafel curves of PUEAF coated MS and bare MS in 5 wt%
NaCl solution were shown in Figure 8 and their corrosion
parameters were listed in Table 2. Corrosion current density,
corrosion rate, and linear polarization resistance of PUEAF
coated samples were significantly changed from bare MS to
PUEAF30 coated mild steel in NaCl solution. is change
could be attributed to the protection behavior of PUEAF
polymer coating on MS. It suggests that corrosion protective
nature of PUEAF film acts as chemical barrier to mild steel
[36]. Figure 9 indicates Tafel curve in 3.5% HCl solution;
PUEAF coated mild steel possesses lower corrosion potential
than bare MS. From Table 2 it is clear that corrosion potential
of PUEAF coated panels increases significantly and reduces
the corrosion current density. ese results support that
PUEAF coating maybe acts as protective layer for corrosive
ions on mild steel and improves the corrosion performance.
e Tafel curves exhibit that PUEAF film causes a positive
movement in corrosion potential compared to bare MS.
Furthermore, Tafel analysis showed a substantial reduction
in corrosion rate for PUEAF30 coated (5.537ꢃ−04 mm/year)
with respect to bare MS (11.861 mm/year). Overall, it was sug-
time for PUEAF25. ickness of coatings was found as 80
5
microns.
Table 1 indicates that scratch hardness increases up to
PUEAF25 and afer that decreases as the additional NCO
groups of TDI provide too much cross-linking. All the coat-
ings passed 100% impact (150 lb/inch), bending (1/8 inch),
and crosscut adhesion test, which showed good interface
between substrate and coatings due to the presence of polar
groups like azomethine, carbonyl, hydroxyl, and urethane
in polymeric chain. PUEAF coating showed gloss values
88, 90, and 97 at 45∘ and passed pencil hardness maxi-
mum 4H showing good interaction between substrate and
coatings.
3.4. Potentiodynamic Studies. e protective properties of
PUEAF coated mild steel (MS) in different corrosive media
such as tap water (72 h), NaCl (60 h), and HCl (120 h) were
assessed by potentiodynamic polarization curve. e Tafel
polarization curves (Figure 7) for different compositions
such as PUEAF20, PUEAF25, and PUEAF30 coatings were
conducted in tap water. Table 2 exemplifies the corrosion
rates from bare MS to coated MS with PUEAF20, PUEAF25,
and PUEAF30 and their values were 8.350ꢃ − 01, 6.044ꢃ −
gested that PUEAF30 layer would act as corrosion protection
and decrease in the rate of corrosion.
03, 2.222ꢃ − 03, and 1.524ꢃ − 03 mm/y, respectively. In
the case of PEAF resin, afer increasing the loading of TDI
such as PUEAF20, PUEAF25, and PUEAF30 corrosion rate
decreases in tap water. ese results indicate that PUEAF
can act as a protective layer on bare MS in tap water and
improve the whole anticorrosion performance. e Tafel
e values of polarization resistance (ꢄꢂ) were carried
out using linear polarization resistance (LPR) and the results
were summarized in Table 2. It was observed that higher
ꢄꢂ values were observed in the case of coated MS when
compared with bare MS. PUEAF30 coatings act as protective

Journal of Chemistry
7
Table 2: Corrosion parameter for PUEAF coated and bare MS in different corrosive media.
LPR (ꢄꢂ)
ꢃ
ꢁꢀ
ꢁꢁ
ꢅ
Corrosion
corr
(mV)
corr
Resin code
Medium
mV/dec
mV/dec
(mA/cm2)
rate (mm/y)
KOhm⋅cm2
0.0788
19.412
MS
Tap water
Tap water
Tap water
Tap water
5.0% NaCl
5.0% NaCl
5.0% NaCl
5.0% NaCl
3.5% HCl
3.5% HCl
3.5% HCl
3.5% HCl
−478.89
−323.13
−219.65
−168.25
−535.78
−430.28
−422.85
−370.79
−432.80
−512.70
−460.91
−325.06
19.894
44.111
37.354
49.314
28.050
40.320
31.920
30.023
26.596
26.108
59.161
7.166ꢃ − 02
5.215ꢃ − 04
1.920ꢃ − 04
1.315ꢃ − 04
1.441ꢃ − 01
2.148ꢃ − 03
2.653ꢃ − 04
4.200ꢃ − 05
1.023
8.350ꢃ − 01
6.044ꢃ − 03
2.222ꢃ − 03
1.524ꢃ − 03
1.670
PUEAF20
PUEAF25
PUEAF30
MS
PUEAF20
PUEAF25
PUEAF30
MS
34.356
41.370
18.287
30.045
29.029
19.809
36.334
39.124
83.472
15.634
34.963
67.512
00.035
03.039
22.743
116.59
00.010
00.465
03.020
81.561
2.489ꢃ − 02
3.075ꢃ − 03
4.868ꢃ − 04
11.861
PUEAF20
PUEAF25
PUEAF30
63.157
85.546
25.544
2.226ꢃ − 02
6.083ꢃ − 03
4.777ꢃ − 05
2.618ꢃ − 02
7.050ꢃ − 02
5.537ꢃ − 04
few white spots detected indicated degradation of PUEAF25
coating matrix which is possible due to change in chemical
composition of PUEAF25 coating, due to interaction with
corrosive ions. AFM topography clearly informs about the
surface texture of exposed PUEAF25 coating. e change in
surface roughness value of exposed PUEAF25 coating shows
resistance to salt spray test. A root-mean-squared (RMS)
roughness of PUEAF25 coating before exposure 12.54 nm and
afer exposure 21.72 nm was obtained within the scanning
area of 10 ꢀm × 10 ꢀm, while the coating with salt spray expo-
sure is much rougher as shown in Figure 10(b). Comparison
of RMS values indicates that surface texture of PUEAF25
matrix is affected afer exposure to the saline environment.
−200
−300
−400
−500
−600
−700
10−6 10−5 10−4 10−3 10−2 10−1 100
101
Current (mA/cm2)
3.6. ermal Analysis. e TGA thermogram (Figure 11) of
PUEAF coatings reveals that at initial stages loss of trapped
moisture and evaporation of the entrapped solvent occur that
is observed in TGA up to 350∘C, which is in direct correlation
with DTG, corresponding to approximately 20 wt% loss. In
DSC thermogram, the same temperature range, these events
can be observed as two endothermic peaks, starting from
125∘C to 220∘C and centered at 165∘C, and another one start-
ing from 222 to 320 centered at 270∘C correlated with melting
of the resins. Beyond this temperature, the ramp in TGA
thermogram suggests that the sample undergoes melting
followed by decomposition (the degradation of amide bond,
aromatic ring, and aliphatic chain). Polyurethanes generally
exhibit low thermal stability (up to 150∘C) due to the presence
of labile urethane groups. Here, a relatively higher thermal
stability can be attributed to the formation of hybrid coatings
containing azomethine group.
TGA was carried out on cured coatings of PUEAF. In
DSC thermogram (Figure 12), a sharp peak indicates melting;
however, here we do not observe any sharp peak; rather we
observe broad endotherms, so at this temperature we cannot
say that the resin is melting. e ramp in initial stages in
TGA thermogram suggests that the events occurring can be
the loss of moisture or entrapped solvent. e free -NCO
and -NH-COO- groups in polyurethanes are very likely to
PUEAF30
PUEAF25
PUEAF20
MS
Figure 9: Tafel plots of bare MS and PUEAF coated MS in 3.5% HCl
solution.
barrier for corrosive ions as correlated with the corrosion test
performance.
3.5. Topography Studies. e performance of polymeric coat-
ings is tested whether it is capable of withstanding the outer
environmental effect on exposure and by examination of
corrosion resistance of coatings [37], PUEAF25 coating was
exposed to enhanced salt spray, to find out the defects such as
pin holes and pores expected to form during curing process.
Figures 10(a) and 10(b) are topographs of PUEAF25 coated
sample before exposure to salt spray. It can be seen that
PUEAF25 coating shows uniformity without any pin hole,
indicating excellent film formation without any air trap. e
percentage of rusting and blistering for PUEAF25 coated
samples afer 240 h of exposure in salt spray chamber was
investigated. PUEAF25 coating (Figures 10(a) and 10(b))
shows that it is free from rust and blister on coating surface. A

8
Journal of Chemistry
1,13ꢀm
1,13ꢀm
1,18ꢀm
0,00ꢀm
0,00ꢀm
1,64ꢀm
0,00ꢀm
1,64ꢀm
(a)
1,6ꢀm
0,0ꢀm
0,00ꢀm
0,00ꢀm
(b)
Figure 10: (a) AFM topographic images of unexposed PUEAF25 coating surface. (b) AFM topographic image afer exposed PUEAF25 coating
surface in salt spray chamber.
0.00
100
80
−2.00
−2.25
−2.50
−2.75
−3.00
−3.25
−0.05
−0.10
−0.15
−0.20
60
40
20
100 200 300 400 500 600 700 800
Temperature (∘C)
Figure 11: TGA/DTG thermogram of PUEAF25.
50
100
150
200
250
300
Temperature (∘C)
interact with moisture or even traces of water. us, the
entrapped moisture and solvent (xylene) is expected to be
evaporated at this stage in TGA thermogram. e melting
Figure 12: DSC thermogram of PUEAF25.

Journal of Chemistry
9
is expected to occur beyond 320∘C. us, thermal analysis
suggests that the coatings can be safely used up to 180∘C.
Engineering B: Solid-State Materials for Advanced Technology,
vol. 178, no. 19, pp. 1339–1346, 2013.
[11] M. Alam and N. M. Alandis, “Corn oil based poly(ether
amide urethane) coating material-synthesis, characterization
and coating properties,” Industrial Crops and Products, vol. 57,
pp. 17–28, 2014.
[12] J. Argyropoulos, P. Popa, G. Spilman, D. Bhattacharjee, and W.
Koonce, “Seed oil based polyester polyols for coatings,” Journal
of Coatings Technology Research, vol. 6, no. 4, pp. 501–508, 2009.
[13] M. Alam, A. R. Ray, S. M. Ashraf, and S. Ahmad, “Synthesis,
characterization and performance of amine modified linseed
oil fatty amide coatings,” Journal of the American Oil Chemists’
Society, vol. 86, no. 6, pp. 573–580, 2009.
[14] R. Wang and T. P. Schuman, “Vegetable oil-derived epoxy
monomers and polymer blends: a comparative study with
review,” eXPRESS Polymer Letters, vol. 7, no. 3, pp. 272–292,
2013.
4. Conclusions
Schiff base modified Pongamia glabra oil fatty amide diol
based polyurethane exhibited an enhancement in drying
properties. A unique combination of azomethine, amide,
ether, and urethane in PUEAF hybrid resin improves the
scratch hardness, flexibility, gloss, and anticorrosion perfor-
mance. ermal studies reveal that PUEAF25 can be safely
used up to 180∘C. e approach provides an alternative
method for the utilization of nonedible Pongamia glabra oil as
a corrosion protective hybrid and an environmental friendly
coating material.
Competing Interests
[15] Y. Xu, Z. Petrovic, S. Das, and G. L. Wilkes, “Morphology and
properties of thermoplastic polyurethanes with dangling chains
in ricinoleate-based sof segments,” Polymer, vol. 49, no. 19, pp.
4248–4258, 2008.
e authors declare that they have no competing interests.
Acknowledgments
[16] E. Sharmin, O. U. Rahman, F. Zafar, D. Akram, M. Alam, and
S. Ahmad, “Linseed oil polyol/ZnO bionanocomposite towards
mechanically robust, thermally stable, hydrophobic coatings: a
novel synergistic approach utilising a sustainable resource,” RSC
Advances, vol. 5, no. 59, pp. 47928–47944, 2015.
[17] M. Alam and N. M. Alandis, “Development of poly(urethane
esteramide) coatings from Pongamia glabra oil as anticorrosive
applications,” International Journal of Polymer Analysis and
Characterization, vol. 20, no. 4, pp. 330–343, 2015.
e project was supported by King Saud University, Deanship
of Scientific Research, College of Science Research Center.
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