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BY 4.0 license Open Access Published by De Gruyter Open Access August 11, 2022

Rapeseed oil-based hippurate amide nanocomposite coating material for anticorrosive and antibacterial applications

  • Manawwer Alam EMAIL logo , Mukhtar Ahmed , Mohammad Altaf and Fohad Mabood Husain
From the journal Open Chemistry


Industrial crops and products have proved to be an excellent alternative to petro-based chemicals. Vegetable oils are rich in functional groups that can be transformed into monomers and polymers with applications such as biodiesel, lubricants, inks, coatings, and paints. This study describes the synthesis of rapeseed oil (RO)-based esteramide for the first time. The reaction was carried out by amidation of RO, producing diol fatty amide (N,N-bis(2-hydroxyethyl) RO fatty amide), followed by its esterification reaction with hippuric acid, resulting in RO-based hippurate amide (ROHA). Fourier-transform infrared spectroscopy and nuclear magnetic resonance confirmed the introduction of amide and ester moieties in ROHA. ROHA was further reinforced with silver nanoparticles (SNPs) to develop corrosion-protective nanocomposite coatings. ROHA/SNP coatings were scratch-resistant, impact-resistant, and flexible and showed good corrosion resistance performance toward 3.5 w/w% NaCl medium, with adequate corrosion protection efficiency, and antimicrobial behavior against Staphylococcus aureus, Chromobacterium violaceum, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. ROHA/SNP coatings can be safely used up to 250°C.

1 Introduction

The hazards and expenses associated with petro-based chemicals have motivated researchers to substitute sustainable resource-based raw materials for the synthesis of monomers and polymers. Due to their rich functional attributes, vegetable oils (VOs), such as linseed, soybean, castor, and jatropha, among others, are utilized extensively as a sustainable alternative in the form of epoxies, polyesters, diols, polyols, polyurethanes, alkyds, and polyesteramide (PEA) resins [1,2,3,4,5]. Rapeseed oil (RO) is rich in oleic acid and can be transformed into epoxies, polyols, polyurethanes, and alkyds [6,7,8,9,10,11,12]. VO-based PEA resin is prepared by an esterification reaction between an amide diol (obtained by amidation of VO) and a carboxylic acid. While amide diols are derived from VO, a sustainable resource, carboxylic acids are generally synthetic in origin. Recently, PEA has been synthesized using lactic acid, tartaric acid, citric acid, gallic acid, and others that are obtained from natural resources [13,14,15,16,17].

Hippuric acid (HA; N-benzoyl glycine), a conjugation product of phenolic acid and glycine, is an important gut microbial co-metabolite found in urine [18]. HA is used as a biomarker for occupational exposure to toluene and styrene, which are widely used in plastics, rubbers, paints, glues, and other manufacturing units. HA is classified as a uremic toxin and a compound of pharmacological interest [19,20,21,22,23]. Methyl hippurate, an HA derivative, has been used as an antifungal compound [24]. In studies based on clinical data, another HA derivative, methenamine hippurate, has been shown to prevent recurrent urinary tract infections [25,26]. Some HA derivatives have shown promising antibacterial, antifungal, and antiretroviral potential [27,28].

In this study, novel esteramide resin has been prepared from RO-based diol and HA. RO esteramide resin was formulated into corrosion-protective nanocomposite coatings by reinforcement with biosynthesized silver nanoparticles (SNPs). The coatings were postcured by thermal polymerization via heat curing and later subjected to physicomechanical and anticorrosive performance evaluation. Our studies confirmed that these esteramide coatings performed well as protective coatings.

2 Materials and methods

RO, diethanolamine, sodium metal, methanol, sodium chloride (Winlab Limited, Berkshire, UK), and HA (Aldrich Chemical Company Inc., Milwaukee, USA) were used as received. SNPs were biosynthesized in an aqueous extract of Leucaena leucocephala leaves with 0.01 M silver nitrate precursor at room temperature, as reported in our previously published article [29].

2.1 Synthesis of N,N-bis(2-hydroxyethyl) RO fatty amide (HERA)

HERA was prepared according to our previously published article using RO, sodium methoxide, and diethanolamine as starting materials. After washing the final product with NaCl solution, pure HERA was obtained [29].

2.2 Synthesis of RO-based hippurate amide (ROHA) and ROHA/SNP nanocomposite

HERA (1 mol) and HA (1 mol) were taken in a four-necked, flat-bottomed conical flask equipped with a nitrogen inlet tube and thermometer. The contents were placed on a magnetic stirrer and vigorously stirred, followed by an increase in temperature up to 140°C and maintained for 6 h, after which the heating was turned off while stirring continued for an additional 30 min. The reaction was monitored by recording Fourier-transform infrared (FTIR) spectra and determining the acid value (AV) at regular intervals of time. The formation of ROHA was confirmed by the desired low AV and the appearance of characteristic absorption bands in the FTIR spectrum.

SNP (1%w/w) was added to ROHA, and the contents were thoroughly stirred for 60 min to obtain ROHA/SNP nanocomposite.

2.3 Preparation of ROHA and ROHA/SNP nanocomposite coatings

The mild steel/carbon steel panels of standard sizes (composition: Fe, 99.51%; Mn, 0.34%; C, 0.10%; and P, 0.05%) were first polished with silicon carbide papers of different grades, then washed with double distilled water, methanol, and acetone, degreased, and dried for application of coating material. ROHA and ROHA/SNP were diluted with toluene 40% (w/w) and were applied by brush on mild steel panels of standard sizes (70 mm × 25 mm × 1 mm and 25 mm × 25 mm × 1 mm) for evaluation of their physicomechanical performance, gloss measurements, and corrosion tests in 3.5% (w/w) NaCl medium. Another set of circular panels (diameter 1 cm and thickness 150 μm) was prepared for scanning electron microscopy (SEM) analysis. The coated panels were placed in a hot air oven at different temperatures and time periods to optimize the baking temperature and time, which was found to be 180°C for 4 h.

2.4 Characterization

The structural elucidation of ROHA and ROHA/SNP was carried out by FTIR (Spectrum 100 FTIR spectrophotometer; Perkin Elmer Cetus Instruments, Norwalk, CT, USA) and nuclear magnetic resonance (NMR; 1H NMR and 13C NMR; JEOL DPX400MHz, Japan) using deuterated chloroform and dimethyl sulfoxide as solvents and tetramethylsilane as internal standard. Thermal stability of ROHA and ROHA/SNP was assessed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC; Mettler Toledo AG, Analytical CH-8603, Schwerzenbach, Switzerland). The morphology was studied by transmission electron microscopy (TEM; JEM-2100F; JEOL, Tozakishima, Japan), SEM (JSM-7600F; JEOL, Japan), and energy-dispersive X-ray spectroscopy (EDX; Oxford, UK; AV [ASTM D555-61]). To quantify the surface and functional groups of developed materials, an XPS spectrometer (JPS-9030; JEOL, Japan) was used with a MgKα (1253.6 eV) X-ray source at 10 mA and 12 kV in ultrahigh vacuum (<10−7 Pa). Thickness measurements (ASTM D1186-B) of coatings were taken with an Elcometer (Model 345; Elcometer Instrument Ltd, Manchester, UK). Scratch hardness (BS 3900), pencil hardness test (ASTM D3363-05), crosshatch (ASTM D3359-02), impact test (IS 101: Part 5: Section 1: 1988), bend test (ASTM D3281-84), gloss (Gloss meter, Model: KSJ MG6-F1; KSJ Photoelectrical Instruments Co., Ltd, Quanzhou, China), and contact angle measurements (CAM200 Attention goniometer) were performed by standard methods.

For the corrosion resistance test, the specimens were used as working electrodes. An exposed surface area of 1.0 cm2 was fixed by PortHoles electrochemical sample mask, with Pt electrode as a counter electrode and 3 M KCl-filled Ag electrode as a reference electrode (Autolab potentiostat/galvanostat, PGSTAT204-FRA32, with NOVA 2.1 software; Metrohm Autolab B.V., Kanaalweg 29-G, 3526KM, Utrecht, Switzerland).

Antimicrobial activity: Microbial strains: A total of five microbial strains were used in this study, viz., Staphylococcus aureus ATCC 29213 (Gram-positive), Chromobacterium violaceum ATCC 12472, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 (Gram-negative), and Candida albicans ATCC 10231 (fungi). C. albicans was cultured in potato dextrose broth, while all other bacteria were cultured in nutrient broth. The antibacterial activity was determined using an agar well diffusion assay on Mueller–Hinton Agar (MHA) plates. On MHA medium, 100 µL of 0.5 McFarland standardized bacterial inoculum was swabbed. The wells of 8 mm in diameter were then drilled into the medium using a sterile cork borer. A total of 100 µL of the test material were transferred into separate wells, and the plates were incubated at 37°C for 24 h. In the case of the film, a section of 1 cm2 was cut and placed on the MHA plates. After incubation, the plates were observed for the presence of a clear zone of inhibition around the well, indicating antibacterial activity, and zone size was measured in mm. The doxycycline (10 µg/disc) and nystatin (100 units/disc) served as positive controls for bacterial and fungal strains, respectively. The assay to determine the minimum inhibition concentration (MIC) was performed using micro-broth dilution with concentrations ranging from 256 to 0.0625 µg/ml, as described earlier [29].

3 Results and discussion

The hydroxyl groups of HERA reacted with the carboxylic groups of HA to form ROHA (Scheme 1), which was then reinforced with SNP to form the ROHA/SNP nanocomposite. ROHA and ROHA/SNP turned into a hard, flexibility retentive, and well-adhered coating after curing. The reaction was carried out without the use of any solvent, and the raw materials used, such as RO and HA, were biobased. The nanofiller SNP for reinforcement was biosynthesized by the green route [29].

Scheme 1 
               Synthesis of RO-based hippurate amide (ROHA).
Scheme 1

Synthesis of RO-based hippurate amide (ROHA).

3.1 Spectral analysis

FTIR (υ, cm −1 ): FTIR spectra of RO and HERA have been reported earlier [35].

ROHA (Figure 1) shows absorption bands at: 3,324 (–OH str, broad); 3,062 (–C–H str aromatic ring: Ar); 3,006 (C═C); 2,854–2,925 (–CH3, –CH2 stretching); 1,738 (>C═O ester str); 1,642 (>C═O amide); 1,465–1,403 (–CH3, –CH2 bending); 1,297–1,115 (–(C═O)–O–C str); 1,578, 716, and 693 (Ar–C═C–H); 1,029–1,078 (–C–O str of –C–O–H); and 801–928 (–O–H bending vibrations), as typical for the functional groups present in VO-based PEA. The broadband for the hydroxyl group supports that some of the hydroxyl groups in ROHA are not undergoing esterification reaction with carboxylic groups of HA and occur as hydrogen-bonded –OH groups.

Figure 1 
                  FTIR spectra of ROHA and ROHA/SNP nanocomposite.
Figure 1

FTIR spectra of ROHA and ROHA/SNP nanocomposite.

ROHA/SNP (Figure 1) also reveals the presence of the aforementioned absorption bands, wherein some of the absorption bands exhibit a slight shift in values, such as –OH (3,335), 1,310–1,115 (–(C═O)–O–C str), and –O–H bending vibrations (795–930), due to interactions with SNP.

1 H NMR (DMSO- d 6 , δ , ppm)ROHA: 8.97–9.03 (–COOH); 8.48–8.59 (–NHHA); 7.41–7.84 (aromatic ring protons); 5.86 (–OH); 5.25 (–CH═CH–); 4.06–4.27 (–CH 2–O–C(═O)–); 3.82–3.98 (–CH2HA); 3.56–3.62 (–N–CH 2–CH2–O–C(═O)–); 3.345–3.47 (–N–CH 2–CH2–OH); 3.05–3.09 (–N–CH2–CH 2–OH); 2.71 (–CH═CH–CH 2–CH═CH–); 2.31–2.45 (–CH 2–C(═O)–N–); 1.17–2.21(–CH 2–); and 0.79–0.86 (–CH 3) (Figure 2).

Figure 2 
                     1H NMR spectra of ROHA.
Figure 2

1H NMR spectra of ROHA.

13 C NMR (DMSO- d 6 , δ , ppm)ROHA: 174.67 (>N–C═O); 172.20–172.81 (>C═Oester); 166.23–166.77 (>NH–C═OHA); 127.28–127.97, 128.37, 131.29–131.61, and 133.66–134.25 (carbons ArHA); 41.03–42.24 (–CH2HA); 129.60–129.73 (–CH═CH–); 58.84–59.02 (>N–CH2 CH2–OH); 49.24–49.58 (>N–CH2CH2–OH); 22.13–33.93 (CH2chain); and 13.96 (–CH3) (Figure 3).

Figure 3 
                     13C NMR spectra of ROHA.
Figure 3

13C NMR spectra of ROHA.

The spectral analysis thus confirmed the reaction of HA with HERA, forming ROHA.

3.2 Morphology and hydrophobicity

TEM micrograph (Figure 4) of ROHA/SNP showed that SNPs were well-dispersed in ROHA; however, SNPs have been sheathed by the matrix. SEM micrograph (Figure 5a) of ROHA/SNP showed uniform distribution of SNP in ROHA matrix, with no pinholes or cracks. EDX (Figure 5b) peaks pertaining to Ag (1.19%), C (58.29%), N (21.31%), and O (19.21%) are evident and confirm the presence of Ag in ROHA/SNP.

Figure 4 
                  TEM micrograph of ROHA/SNP nanocomposite.
Figure 4

TEM micrograph of ROHA/SNP nanocomposite.

Figure 5 
                  SEM–EDX micrograph of ROHA/SNP nanocomposite coating.
Figure 5

SEM–EDX micrograph of ROHA/SNP nanocomposite coating.

It is very important to evaluate the hydrophobicity of coatings as it plays a crucial role in determining their corrosion protection performance. The contact angle values (Figure 6) were found to be 80o and 86o for ROHA and ROHA/SNP, respectively. The contact angle value increased by the dispersion of SNP in ROHA, which supported the improved hydrophobicity of ROHA/SNP compared to the plain ROHA. Thus, the dispersion of SNP in the ROHA matrix improved the hydrophobicity of ROHA/SNP coating.

Figure 6 
                  Hydrophobicity evaluation of ROHA (a) and ROHA/SNP nanocomposite (b) by contact angle measurements.
Figure 6

Hydrophobicity evaluation of ROHA (a) and ROHA/SNP nanocomposite (b) by contact angle measurements.

3.3 XPS analysis

XPS analysis was employed to elucidate the surface composition of the ROHA/SNP nanocomposite. The deconvoluted peaks of ROHA/SNP, C1s, N1s, O1s, and Ag3d are shown in Figure 7. The peaks for carbons (283.12 [C═C], 284.29 [C–C], 285.00 [C–N], 286.06 [C–O], and 287.68 [C═O]), nitrogens (399.13 [N–H] and 400.00 [N–C]), oxygens (531.40 [C═O] and 532.19 [C–O]), and silver (Ag3d5/2 [367.97] and Ag3d3/2 [374.20]) with respective binding energies supported the structure of ROHA/SNP nanocomposite [30,31].

Figure 7 
                  XPS of ROHA/SNP nanocomposite.
Figure 7

XPS of ROHA/SNP nanocomposite.

3.4 Coating properties

3.4.1 Physicomechanical properties

After curing at the required temperature and for a desirable period of time, hard and glossy coatings were obtained with a thickness of 125 microns. Both ROHA and ROHA/SNP coatings showed good scratch hardness, pencil hardness, and cross-hatch test results, as well as impact resistance and bend tests. The scratch hardness, cross hatch, pencil hardness, and gloss values increased with the dispersion of SNP in ROHA/SNP compared to ROHA (Table 1).

Table 1

Physicomechanical properties of ROHA and ROHA/SNP nanocomposite coatings

Properties ROHA ROHA/SNP
Scratch hardness (kg) 2.8 3.1
Cross hatch (%) 95 100
Pencil hardness 2H 3H
Gloss at 60o 85 90

3.4.2 Corrosion resistance performance Electrochemical impedance studies (EIS)

Nyquist plots of ROHA and ROHA/SNP were obtained at various immersion time periods (1, 4, 7, 10, 13, 16, and 19 days) in 3.5 wt% NaCl solution. As illustrated, the EIS plots of ROHA and ROHA/SNP nanocomposite coatings after the specific period of immersion displayed a one-time constant equivalent circuit model presented in Figure 8, displaying electrolyte resistance (R s), coating capacitance (C c), and coating resistance (R c). As can be seen in Table 2, the pure ROHA and ROHA/SNP coatings reveal that with an increased period of immersion, the solution resistance and coating resistance decrease because corrosive ions can gradually infiltrate via pores and capillary of the nanocomposite coating to adhere to the surface metal. Nyquist plots of ROHA and ROHA/SNP coatings showed similar behavior in terms of R s, R c, and C c. Furthermore, it could be seen that the arc frequencies decreased with time, which indicated an increase in corrosion. It can be due to the generation of pores in the nanocomposite coating or an increase in the exposed area of the existing pores.

Figure 8 
                        EIS (a) and Bodetheta (b) spectra of ROHA coating.
Figure 8

EIS (a) and Bodetheta (b) spectra of ROHA coating.

Table 2

EIS parameters of ROHA coatings in 3.5w/w% NaCl at room temperature

Immersion times (days) Solution resistance, R s (Ω) Coating resistance, R c (MΩ) Coating capacitance, C c (pF) OCP (V) χ 2
1 291 2.59 117 –0.193 1.85
4 283 1.43 119 –0.394 1.12
7 279 1.32 122 –0.403 1.69
10 271 1.26 127 –0.405 1.95
13 264 1.19 133 –0.406 1.13
16 260 1.09 135 –0.413 1.80
19 232 1.02 138 –0.418 1.95
EIS parameters of ROHA/SNP in 3.5w/w% NaCl at room temperature
Immersion times (days) Solution resistance, R s (Ω) Coating resistance, R c (MΩ) Coating capacitance, C c (pF) OCP (V) χ 2
1 281 9.13 109 –0.554 1.67
4 278 8.69 112 –0.550 1.91
7 277 8.54 115 –0.544 1.65
10 261 8.30 120 –0.528 1.59
13 247 8.08 121 –0.464 1.73
16 233 7.56 126 –0.454 1.82
19 220 7.06 130 –0.083 1.39

Impedance responses of ROHA/SNP (Figure 9) show one capacitive arc found at the period of immersion, demonstrating an intact coating with a good barrier against water, oxygen, and corrosive ions. With increasing times of immersion, the resistance of the coating decreases. As shown in the figures, at initial exposure times, the resistance values of ROHA and ROHA/SNP coatings were 2.59 and 9.13 MΩ, correspondingly, which is approximately four times greater than pure ROHA coating. ROHA coating systems showed a one-time constant value even after 19 days of exposure time, which was characterized by a single capacitive loop that described the resistance of coatings. Consequently, the electrochemical behavior of ROHA/SNP coatings could be well inferred by the equivalent circuit model, shown in Figure 8, during all exposure periods. Since all observed impedance values for ROHA/SNP were higher than the plain ROHA coating, it seemed that ROHA/SNP coating showed higher barrier properties due to fine dispersion of SNP.

Figure 9 
                        EIS (a) and Bodetheta (b) spectra of ROHA/SNP nanocomposite coating.
Figure 9

EIS (a) and Bodetheta (b) spectra of ROHA/SNP nanocomposite coating. Coating resistance

As shown in Table 2, the incorporation of SNP into ROHA matrix generally improved Rc, irrespective of pure ROHA. This trend can be observed during all immersion periods in 3.5% (w/w) NaCl media. ROHA/SNP coating possesses Rc values (9.13 MΩ) four times greater than pure ROHA coating (2.59 MΩ) after 19 days of exposure time. Table 2 shows that Rc of ROHA/SNP decreased with increased immersion time and reached its lowest value after 19 days. Hence, the coating resistance, which is responsible for the presence of ions serving as charge carriers in the coating, decreased with increased immersion times due to the penetration of ions through pores and capillary channels of nanocomposite coating. It appeared that there were no pathways for corrosive ion transport when the coating resistance was high. The presence of SNP induced more hydrophobicity to the ROHA matrix, which had otherwise resulted in diminished coating performance due to water diffusion and ion transfer to the bare metal. Such nanosized silver particles occupy the superfine pores of the organic matrix, resulting in increased Rc. In addition, an amalgamation of SNP into ROHA improved the barrier properties of the resultant nanocomposite coating as these nanoparticles acted as hindrances against the diffusion of water and corrosive ions [32]. Open circuit potential (OCP)

OCP of ROHA and ROHA/SNP was observed during various periods (1, 4, 7, 10, 13, 16, and 19 days) of immersion in 3.5 wt% NaCl electrolyte (Table 2). As shown, both coatings had a negative charge when exposed to electrolyte during their respective periods of immersion. Negative OCP showed that the oxygen and water molecules could reach the metal substrate and then cathodic and anodic reactions happened, creating OH and Fe2+ at the interface between nanocomposite coating and substrate. The organic coatings acted selectively to infuse ionic species; hence, the negative charge of ROHA and ROHA/SNP nanocomposite coatings designates these films as permeable to Fe2+ ions with reverse charge. The concentration of OH ions increased at the interface, which led to the creation of a passive layer on the substrate. As the time of exposure increased, Cl ions had a slower diffusion rate compared to OH ions that could reach the interface and repassivation happened [33]; then ROHA coating showed increase in the negative values of OCP with time. In the case of ROHA/SNP coating, nanosized silver particles occupied the pores present in the nanocomposite organic matrix and improved the crosslink density, resulting in a lower diffusion rate of corrosive ions and a lower value of OCP. OCP data were completely consistent with those observed for coating resistance. ROHA/SNP showed better anticorrosive performance as compared to ROHA.

3.5 TGA

DSC thermograms (Figure 10) of ROHA and ROHA/SNP showed two endothermic events at 150–200°C (centered at 175°C) and 300–350°C (centered at 325°C). TGA thermogram (Figure 11a) showed that 5 wt% loss occurred at 278 and 300°C in ROHA and ROHA/SNP, which supported the safe use of ROHA and ROHA/SNP up to 250°C. 25 wt%, 50 wt%, and 80% losses occurred at 328 and 328, 370 and 384, and 560 and 540°C in ROHA and ROHA/SNP, respectively. Until 500°C, both ROHA and ROHA/SNP showed variation in degradation pattern; however, beyond 500°C, the degradation ramp is the same in the case of both ROHA and ROHA/SNP. Differential thermogravimetric (DTG) thermograms (Figure 11b) of ROHA and ROHA/SNP exhibit endothermic events occurring from 250 to 500°C, corresponding to the degradation stages in TGA, which are distinct in DTG but appear somewhat merged with no clear-cut demarcation in TGA. The improved thermal stability of ROHA/SNP over ROHA is attributed to the dispersion of SNP in the matrix of the former [29].

Figure 10 
                  DSC thermogram of ROHA and ROHA/SNP nanocomposite.
Figure 10

DSC thermogram of ROHA and ROHA/SNP nanocomposite.

Figure 11 
                  TGA (a)/DTG (b) thermogram of ROHA and ROHA/SNP nanocomposite.
Figure 11

TGA (a)/DTG (b) thermogram of ROHA and ROHA/SNP nanocomposite.

3.6 Antimicrobial activity

The antibacterial activity of the synthesized test samples was determined against four bacterial strains and a solitary strain of C. albicans and recorded according to their respective zones of inhibition of antimicrobial activity and MIC values (Figure S1). SNP, a known metal with antimicrobial properties, demonstrated inhibition zones ranging from 13 to 16 mm (data not shown) against the test bacteria and fungi. Higher zones of inhibition were observed in the case of ROHA/SNP as compared to ROHA (Figure S1). ROHA demonstrated 15, 14, 16, 13, and 14 mm halo zones of inhibition against S. aureus, C. violaceum, E. coli, P. aeruginosa, and C. albicans, respectively. Furthermore, ROHA/SNP showed (Figure S2) comparatively enhanced antimicrobial activity against all the test pathogens as compared to ROHA (evident from zones of inhibition) with zone diameter ranging from 16 to 23 mm.

The pronounced antibacterial activity of the synthesized sample could be attributed to the large surface area possessed by nanosized SNP, which supports increased surface contact with pathogens. Furthermore, Ag is a known antimicrobial metal and may induce the production of intracellular ROS that overpowers the antioxidant system of the microbes, leading to oxidative stress and eventually cell death. We observed higher MIC values for S. aureus, which was found to be the least sensitive to the action of ROHA/SNP. This could plausibly be due to the difference in the make-up of the cell walls of Gram-positive and Gram-negative bacteria. The cell wall of Gram-positive bacteria (S. aureus) is composed of thickening peptidoglycan and possesses a negative charge on the surface due to the presence of teichoic acid, which is more sensitive to metal ions with a positive charge [34].

4 Conclusions

In this study, RO esteramide was synthesized without any organic solvent and reinforced with SNP. The esteramide resin was derived from biobased raw materials, i.e., RO and HA, and the SNP nanofiller was biosynthesized through green route using a plant extract. The coatings showed good physicomechanical and corrosion protection performance in saline medium and antimicrobial behavior against a number of microbes, such as S. aureus, C. violaceum, E. coli, P. aeruginosa, and C. albicans. With the dispersion of SNP, hydrophobicity, scratch resistance, and thermal stability of coatings were found to improve, as evident by higher contact angle (86o), scratch hardness (3.1 kg) values, and higher degradation temperatures of the nanocomposite relative to the plain esteramide coating. The coatings can be safely employed up to 250°C. The approach provides an excellent example of value-addition to an industrial crop for utilization as nanocomposite corrosion protective coatings.


The authors are grateful to the Researchers Supporting Project number (RSP-2021/113), King Saud University, Riyadh, Saudi Arabia for the support.

  1. Funding information: This research was funded by Researchers Supporting Project number (RSP-2021/113).

  2. Author contributions: Manawwer Alam: writing – original draft, methodology, project administration; resources, Mukhtar Ahmed: formal analysis, writing – review and editing, Mohammad Altaf: formal analysis, Fohad Mabood Husain: formal analysis, writing – review and editing.

  3. Conflict of interest: The authors state no conflict of interest.

  4. Ethical approval: The conducted research is not related to either human or animal use.


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Received: 2022-04-28
Revised: 2022-06-23
Accepted: 2022-07-09
Published Online: 2022-08-11

© 2022 Manawwer Alam et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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