Send Orders for Reprints to
[email protected] Current Bionanotechnology, 2015, 1, 00-00
1
Studies on Biocide Encapsulated Zeolite-epoxy Nano Hybrid Coatings on Mild Steel Palanivelu Saravanan1,2, Sridhar Aparna2, Srinivasan Ananda Kumar2*and Dhanapal Duraibabu2 1 2
Department of Chemistry, St. Joseph’s college of engineering, Chennai 600 119, Tamil Nadu, India; Department of Chemistry, Anna University, Chennai 600 025, Tamil Nadu, India Abstract: The present study aims at the fabrication of diglycidyl ethers of bisphenol-A (DGEBA) modified with effective low cost as well as less toxic antifoulants viz., benzoic acid (BA) and sodium benzoate (SB), which are encapsulated into nano-hybrid containers as matrix materials that could be utilized for marine coatings. These two antifoulants were incorporated into epoxy antifouling (AF) coatings separately in the amount of (1, 3, 5, 7 and 10 wt. %) to investigate their corrosion resistant behaviour and antifouling capabilities. Corrosion rate of 3 wt. % SB incorporated epoxy AF coating P. Saravanan was determined to be much lower than that of 3 wt. % BA incorporated epoxy AF coating. A direct relationship between the corrosion rate, antifouling nature, antibacterial behaviour and toxicity was observed by electrochemical impedance spectroscopy, salt spray test, static immersion study, antibacterial test and acute toxicity tests. The SB encapsulated coating with 3 wt. % loading exhibits enhanced antifouling and corrosion resistance performance, while AF coatings contains 5 wt. % loading of BA showed a marked reduction in fouling attachment than other coating compositions.
Keywords: Antifouling paint, barnacle, biocide, epoxy resin, nano-hybrid containers, mild steel, salt spray. INTRODUCTION The gradual deterioration of metals by electrochemical reaction with the environment is termed as corrosion, which yields metal oxides or metal salts. The corrosion exhibits adverse effect to a greater extent on the physical, chemical and mechanical properties of the substrate. It is a prevailing problem in many industries such as fertilizer, marine, chemical plants, petrochemicals etc. This issue is world-wide and has a remarkable impact on financial status of global economy. Along with corrosion, bio-fouling is an omnipresent problem, which severely affects the economies of the chemical and marine industries. Biofouling takes place when organisms accumulate and grow on surfaces of structures immersed in water [1, 2]. Biofouling is seen in many gadgets such as surgical equipment, medical implant biomaterial, biosensor, textile and food packaging material [3]. In context of ships, bio-fouling causes an increase in hull roughness that decreases the drag speed, because of which 40% extra fuel is consumed [4]. Decrease in ship speed and increased fuel consumption lead to emission of the green-house gases like CO2 and NOx [5]. Bio-fouling can be efficiently controlled using antifouling (AF) paints. Generally used biocides are heavy metal compound such as tri-butyl tin oxide (TBT), which gets released from the coating and restrains the attachment of microorganism. Unfortunately, most of the heavy metals are highly toxic against non-targeted marine *Address correspondence to this author at the Department of Chemistry, Anna University, Chennai 600 025, Tamilnadu, Índia; Tel: +91 222358661; E-mail:
[email protected]
2213-5294/15 $58.00+.00
organisms [6, 7]. Due to their toxic behavior, the usage of TBT was banned by IMO (International Maritime Organization) since January 2003 and had insisted the removal of TBT coated AF paintings by 2008 [8]. Therefore, considerable efforts have been made in search of non-toxic AF paints. Benzoic acid (BA) and sodium benzoate (SB) appear to be the safe chemicals used in food preservation and antimicrobial agents. The permissible daily intake of BA has been set at 5 mg kg-1 body weight by the Food and Agriculture Organization/World Health Organization [9]. They are widely used in acidic foods and beverages to delay the yeast spoilage. In USA, BA and SB are permitted up to a maximum level of 0.1% and are recognized as safe chemicals in their permitted limits [10]. In Europe, depending on the food BA and SB are permitted as food preservatives at various limits [11]. Owing to their non-toxic nature, low cost and accessibility BA and SB appear as attractive biocidal systems to be inculcated into AF coatings as eco-friendly alternatives [12]. Anti-fouling compounds inhibit the growth of microbes by inhibiting the bio-chemical reaction involved in cell adhesion to the substrate. In citric acid cycle, BA restricts oxidative phosphorylation in yeast and bacteria by controlling acetic acid metabolism by deactivating the core enzyme responsible for that metabolism, thus acting as an effective antimicrobial agent [13]. Recent study on BA over the antimicrobial mechanism has revealed that the BA varies the pH of the cells leading to the lysis of the cell organelles [14, 15]. Hence, BA exhibits non-toxicity and is being effective over a wide range of microbes. The salt form of BA, such as SB is even more effective AF agent compared to BA. The mode of action of SB was not precisely studied com© 2015 Bentham Science Publishers
2 Current Bionanotechnology, 2015, Vol. 1, No. 1
Table 1.
Saravanan et al.
Chemical composition of MS.
Metal Composition
C
Si
Mn
P
S
Cr
Ti
Ni
Al
Co
Nb
Fe
Weight (%)
0.033
0.005
0.235
0.011
0.005
0.046
0.003
0.043
0.073
0.007
0.005
balance
Table 2.
Nomenclature of coating systems and their physical, chemical and solvent resistance. Composition (wt. %)
Group
Group 1
Group 2
Coated
Physical properties
BA loaded zeolite
SB loaded zeolite
5%NaCl b (cm/yr)
5% H2SO4
5% NaOH
Panels
Epoxy/Pigment and hardener
C1
99
1
x
100
5B
±0.86
±0.99
±1.17
>27
C2
97
3
x
100
5B
A
B
B
>27
C3
95
5
x
100
5B
A
A
A
>27
C4
93
7
x
100
5B
A
B
C
>27
C5
90
10
x
100
4B
±0.76
±0.87
±0.90
>27
C6
99
X
1
100
5B
±0.62
±0.77
± 0.94
>27
C7
97
X
3
100
5B
A
A
A
>27
C8
95
X
5
100
5B
A
B
B
>27
C9
93
X
7
100
5B
A
B
B
>27
C10
90
X
10
100
4B
±0.53
±0.64
±0.88
>27
Thickness
Cross cut
Chemical and solvent resistance
b
(cm/yr)
b
Acetone a (DRs)
(cm/yr)
Film appearance: A-no effect; B-slight loss of gloss, film intact; C- loss of gloss, film intact; D-blistering a DRs: film appearance affected after specified double rubs. b cm/yr: corrosion rate.
pared to BA, but the studies made by Vetere V et al., indicated that the freely floating benzoate anion in water is important for the AF properties of SB, and that the AF mechanism of SB is similar to BA in some aspects [16]. However, studies have shown that SB encapsulated paint has successfully inhibited the microorganism attachments in marine environment [17]. The AF properties of BA and SB could make them suitable to incorporate into AF coatings. Mild steel (MS) is commonly used in construction, production of vessels and utensils due to its flexibility and low cost, which undergo the problem of corrosion and fouling as mentioned earlier. Therefore many efforts have been taken in the direction to prevent the surface degradation due to corrosion and fouling. In this work, the reinforcing effect of BA and SB loaded zeolite (nano container) with epoxy resin against corrosion and fouling has been studied extensively. Applications of zeolite as corrosion resistant [18] and AF coating [19] on MS have been reported recently. In another work, silver and zinc /zeolite complex have been reported as Anticorrosion coating material. The main focus of this work is to obtain BA or SB incorporated epoxy coatings with minimum changes in bulk and surface properties of the resin and also attaining a tolerable leaching such that the AF paint is capable of preventing microbial attachment for a prolonged period of time. The different coating systems formulated in our present work were investigated using Fourier transform infra-red (FTIR) spectra, electrochemical impedance, salt-
spray test, field exposure study, acute toxicity test and antimicrobial test. The mechanical properties of the BA and SB reinforced epoxy coatings were determined by cross-cut adhesion test. MATERIALS AND METHOD Materials DGEBA, Aradur HY951 curing agent (Huntsman), Silica powders, red iron oxide pigment, Aminopropyltriethoxysilane, BA and SB (Aldrich Chemicals), zeolite (Alfa Aesar Ltd), Dimethyl formamide (DMF), tetrahydrofuran (THF), acetone and toluene (SISCO Research Laboratories) were used for the study. Five different coatings were prepared and coated on MS specimens (whose composition given in Table 1) were used for the study. The acronym of different coating systems is discussed in Table 2. Preparation and Testing of Coatings The uncoated MS panels were subjected to 100 psi pressure of sand blasting through a nozzle to get an apt crevice. The sand particles measuring 82 mesh were used in this study. A distance of 2 feet was maintained between the specimen and the blaster. For conditioning purpose the panels were stored in desiccators. The coatings were applied over the MS plates (70 mm x 50 mm x 1 mm) manually us-
Studies on Biocide Encapsulated Zeolite-epoxy Nano Hybrid Coatings
ing a bar coater for various analyses like salt spray, static immersion and anti-microbial analysis. The coated panels were then cured for 3 days at room temperature and then stored in desiccators over a week before the analysis. The coating thickness was maintained at 100 µm. The panels were sealed using an epoxy adhesive to an extent of 0.5-0.8 cm from the edges for further analyses. Synthesis of BA-MCM-41 and SB-MCM-41 with Aminopropyltriethoxysilane and Epoxy Material In order to remove the moisture content, zeolite material was dried at 150 °C in a hot air oven and then, it was subjected to encapsulation of biocide, which is elaborately discussed by Ananda Kumar and Savitha for a book chapter contribution which was published besides the work reported by Thierry Azais et al., for loading of biocides in an encapsulant. The appropriate ratio of BA (10 g) and zeolite (20 g) were mixed with water to get in solution form and stirred for 8h at room temperature to load the BA into zeolite (2.3 nm). The solid wastes were filtered using Buckner flask [20]. About 1:1 ratio of biocides loaded zeolite and BA loaded zeolite was reacted with aminopropyltriethoxysilane in the presence of toluene at 60 °C and then reacted with DGEBA in the stoichiometric ratio. Then the reaction mixture was
Fig. (1). Synthesis of biocide loaded epoxy resin.
Current Bionanotechnology, 2015, Vol. 1, No. 1
3
treated with acetone at 40 °C in the presence of Nitrogen gas by stirring 2–3 h continuously. The synthesis of biocide loaded epoxy resin is shown in Fig. (1). The procedure for sample curing is as follows: stoichiometric amount of red iron oxide pigment, silica powder, leveling agent GLP503A were mixed together and powdered, followed by sifting through 200 mesh screen in an oil bath (50- 70 °C) [21]. Then ultra-sonication for 8- 12 h was done to disperse the BA/SB uniformly within the epoxy resin and to fabricate AF coating, stoichiometric amount of hardener was added to the resin. Similar procedure was followed for other coating formulations with different ratios of BA and SB (1, 3, 5, 7 and 10 wt. %). The synthesized AF paint was applied on MS plates to a thickness of 100 µm using a bar-coater. The schematic representation of replicated treatment of biocide loaded AF coating is shown in Fig. (2). TEST PROCEDURES Spectroscopy Characterization The spectroscopy characterization using FTIR spectrophotometer (PerkinElmer 1750) determines the chemical structure of epoxy/BA and epoxy/SB AF coatings. The spectra of epoxy AF paint cured with Aradur HY951 were ob-
4 Current Bionanotechnology, 2015, Vol. 1, No. 1
Saravanan et al.
Fig. (2). Schematic representation replicated treatment of biocide loaded AF coatings.
served by grinding a small part of cured resin in a mortar to make it a fine powder, and later mixed it with potassium bromide, and pressed to form a pellet to take the spectrum [22]. Cross-cut Adhesion Test The cross-cut adhesion test was done by making square boxes of 1 mm2 which was used as test specimen. The edges of the boxes were covered using a cello tape. Cross-cut adhesion was carried out according to the standard method of ASTM 3359-83B and the results were tabulated in Table 2 [23]. Chemical Resistance and Solvent Resistance Analysis Corrosion test was performed by dipping coated and uncoated specimens in plastic jars containing 5% NaCl, acid (10 wt. % HCl), alkali and (5 wt. % NaOH) for 196 h, maintained at room temperature. The coated panels were evaluated visually for blisters, cracks and degree of adhesion [24]. Acetone double rub test was carried over the coated epoxy/MS panels to test the solvent resistance using the standard method of ASTM D 4752 [25]. Salt Spray Analysis The salt spray analysis was carried out on the coated MS panels of 70 mm × 50 mm × 1 mm with diagonal cuts on coated panels. This analysis was used to mimic the oce-
anic environment where the MS panels were exposed as per the standard of ASTM B 117. The salt spray solution was made with 3.5% NaCl solution maintained at a pH of 6.9, spraying air pressure maintained at 15 psi. The temperature of the chamber was maintained between 31°C to 33°C and sprayed continuously for a time period of 1200 hrs. The panels were scratched for a width of 200 µm and 40 mm in length for the analysis. The panels were examined visually to detect the rust formation on coated surface and the images were taken using an Olympus 4XWIDE digital camera [26-28]. Electrochemical Impedance Spectroscopy (EIS) After immersing the samples for a period of 30 days in 3.5% NaCl solution, the Bode plots for both the coating systems were analyzed. A three electrode corrosion cell was used to carry out the EIS measurements using an ACM electrochemical impedance analyzer (Gill AC Serial No. 1634Sequencer Version 4). A SCE, Pt foil was used as reference and counter electrode respectively. MS substrates of 3 cm x 1.4 cm x 1cm dimensions were used for EIS experiments. The 3.5% NaCl solution was used as electrolyte. 1cm2 area of the uncoated MS, epoxy/ BA and epoxy/ SB coated MS was dipped into the electrolyte. Remaining area was masked by using insulating cellophane tape. In EIS analysis, 10 mV amplitude AC signal and a frequency range of 10kHz to 0.1 Hz at OCP (open circuit potential) were applied to the coated MS panels. The charge transfer resistance (Rct) and the dou-
Studies on Biocide Encapsulated Zeolite-epoxy Nano Hybrid Coatings
Current Bionanotechnology, 2015, Vol. 1, No. 1
ble layer capacitance (Cdl) values were calculated from the impedance plots [29, 30].
average weight of 2.8 g were used in the test. Approximately 10 organisms were transferred to each jar. Plastic jars were filled with 50000 ppm paint leachate suspension at the range of pH 7-8 and exposure with a light dark cycle of 120 h at room temperature. Dead and immobile fish were counted after 120 h.
Potentiodynamic Polarization Measurement After immersing the samples for a period of 30 days in 3.5% NaCl solution, the polarization responses of the coated MS panels were studied. The Tafel polarization potential was tested at OCP at a scan rate of 0.5 mV /Sec from -250 mV to +250 mV. The obtained anodic and cathodic polarization curves were used to identify the Tafel regions and extrapolated to get corrosion potential (Ecorr) and corrosion rate (Icorr) in mm per year [31]. All measurements were taken at room temperature (25± 2°C) and the resultant data was examined using the ZSimpWin software [32-37].
Antimicrobial Test The antibacterial activities of samples namely MS, neat epoxy, coating ‘C3’ and ‘C7’ were tested by an inhibition zone method. In this method Escherichia coli (ATCC 8739) was taken as the test bacterium. 100 ml Muller Hinton broth, 200 ml Muller Hinton agar, Petri dish, and the samples were autoclaved at 121 °C, 15 psi for 15 min. A hoop of the bacterial culture was separated from fresh colonies into 100 ml Muller Hinton culture medium containing agar. The culture was let to grow until the O.D reached 0.2 at 600 nm (OD of 0.2 corresponding to a concentration of 108 CFU ml-1 of medium). Then it was applied uniformly on separate agar plates using germ-free cotton pads. The coated MS panels and uncoated control were placed in the culture swabbed petriplate in such a way that the coating and culture were in contact. The formation of clear zone was checked after 24 h. The appearance of zone around the steel panels was recorded as an inhibition against the microbial species. The entire experiments were conducted in a laminar hood to prevent any contamination [40].
Static Immersion Test Epoxy coated MS panels were used for the AF study. Bay of Bengal, on the East Coast Road in Chennai, India was selected to carry out the study. The coated MS panels were immersed at a depth of 3 m in the backwaters bank. Properly supported Nylon ropes were used to hang the systems vertically in a secluded area for 12 months. Every system was examined in triplicate, under the same conditions. The panels were taken out and the accumulation of corrosion associated fouling growth was observed. The coating systems were carefully examined for the identification of fouling organisms. The fouling organisms accumulated on the surface of coated panels were then, detached using a brush without affecting the specimen for SEM analysis [38].
Scanning Electron Microscope Analysis (SEM) The panels were prepared using the standard specimen preparation technique. The analysis was carried out using SEM (LEO 1455VP). The coated panels were viewed after suspending in the oceanic environment for both corrosion and fouling resistance after 12 months period.
Leaching and Acute Toxicity Study Leaching was performed in natural sea water (NSW). Three replicates were made of each epoxy coating ‘C3’ (5 Wt. %) and ‘C7’ (3 Wt. %). The painted MS were dropped in 1 litre of NSW for 1h to remove the paint flakes. The painted MS plates were transferred to beakers, which were previously autoclaved and covered to avert evaporation and development of microbes. The conical flasks were kept on a shaking table (30 rpm) for simulating water movement at room temperature over a period of 14 days. This leaching period was selected as per the permitted biocide release rate from paints, after 14 days. Leachates for chemical analysis were collected in acid rinsed bottles.
RESULT AND DISCUSSION Structural Characterization of AF Coatings Figs. (3a and b) depict the FT-IR spectrum of the BA and SB loaded zeolite with the following characteristic peaks. From Table 3 the presence of the Si-OH, Si-O-Si and –OH was confirmed. These peaks confirm the functional groups present in APTES Figs. (3a and b) which in turn confirm the loading of the AF loaded Zeolite with the epoxy [41].
ASTM E729 was followed to perform the Aquatic toxicity test [39]. Aquatic freshly hatched Juvenile fishes with a)
5
b)
Fig. (3). (a) FTIR spectrum of epoxy/BA AF coatings (b) FTIR spectrum of epoxy /SB AF coatings.
6 Current Bionanotechnology, 2015, Vol. 1, No. 1
Table 3.
Saravanan et al.
Characteristic FT-IR peaks. Sl. No.
Wave number (cm-1)
Inference
1
946
Si-OH group
2
1088 to 1223
Si-O-Si
3
3425 to 3500
-OH group
4
1260
Si-C group
5
1110
Si-OC 2H5
6
2800 to 2965
Alkyl group
7
3400
Amine
8
3300-3500
-OH group
9
2800-2900
Alkyl group
10
910-950
Epoxy
Cross-cut Analysis of AF Coatings The adhesion property depends on the nature of substrate-coating system. The result of adhesion test of coatings containing BA and SB is discussed in Table 2. From the test, it was observed that edges of cuts were smooth in all systems except ‘C5’ (10 Wt. % of BA) and ‘C10’ (10 Wt. % of SB) in which small flakes of coating was detached at intersections during cross-cut adhesion test (3-4 in numbers). The results indicated that the adhesion strength of highly loaded BA and SB epoxy coatings were poor than other coatings [42]. The reason for the adhesion offered by epoxy/BA and epoxy/SB AF coatings may be due to the surface functionalized nanozeolites that excellently disperse and adhere strongly with the epoxy AF paint formulation offering defect free coating. Analysis of Chemical Resistance of AF coatings Corrosion accelerates under acidic/alkaline conditions. As shown in Table 2, the major weight loss was found in NaOH medium, but the rate of weight loss was found to increase with the increase in the concentration of SB in Epoxy/SB system. Compared to NaOH medium, the weight loss in acid medium was very low even when the edges were not sealed, which indicated that there was no direct contact between the surface and the medium. Table 2 shows the rate of corrosion for a year at different concentration of epoxy/BA and epoxy/SB systems. MS panels were then immersed in brine, H2SO4 and NaOH solutions for 196 h. From Table 2, it can be concluded that the rate of corrosion is minimum for NaCl medium and maximum for NaOH medium. In nature, the epoxy and SB act as corrosion inhibitors. With an increase in the loading percentage of SB/BA from 1Wt. % to 10 Wt.%, the corrosion resistance for H2SO4, NaCl and NaOH solution had increased, and the corrosion resistance reached a maximum value i.e minimum corrosion rate in NaCl solution possessing remark ‘A’. Analysis of Acetone Double Rub Test of AF Coatings The use of Ketone is generally used to deduce the solvent resistance. Acetone is used in this test. Along with immer-
sion test, solvent resistance can also be deduced by solvent rub rest. The end of the test is marked by either disruption or removal of the coating films from the MS panels. Greater the cross-linking better will be the coating characteristics ideally necessary for corrosion resistance, as the acetone cannot permeate through the 3-dimensional network. Even after 27 double rubs, it was found that all epoxy/SB and epoxy/BA AF had no defect on the surface indicating their solvent resistance property over neat epoxy. Evaluation of Corrosion Resistance by Potentiodynamic Polarization Studies on AF Coatings Potentiodynamic polarization curves for MS in 3.5% NaCl with and without epoxy/SB AF coatings are illustrated in Fig. (4a). When compared with the uncoated MS panels, it was evident that the polarization curves of MS coated with epoxy gave improved potential shifts nearer to noble metal values. The polarization variables such as Icorr and Ecorr obtained from anodic and cathodic curves by extrapolation of Tafel lines are discussed in Table 4. It is observed that the Ecorr values decreased considerably for MS coatings ‘C3’, ‘C4’, ‘C5’,‘C2’ and ‘C1’. This result clearly shows that the cathodic and anodic reactions are controlled by the coated MS panels. The rate of corrosion of uncoated MS was found to be 1. 029 ×10-1 mm/y and it minimized with ‘C3’ to a decreased value of 3.850 ×10-5 mm/y which is higher than the other coatings ‘C1’, ‘C2’, ‘C4’ and ‘C5’ whose values are 1.384×10-2, 1.228×10-3, 3.043×10-3 and 1.812×10-3 respectively. Moreover, the CR of ‘C3’ has the least corrosion rate among all formulations used in our present study. Hence it may be concluded that the contact between the metal and the electrolyte is restricted by the coatings applied over MS panels. The maximum restriction was shown by ‘C3’ whereas the minimum was seen in system ‘C1’. This may be due to the even distribution of 5 wt% BA within the epoxy coating of ‘C3’, which offers barrier effect by interconnecting more molecules leading to a defect free coating. BA showed large crystal formation in the bulk of the matrix on solvent evaporation. The fast corrosion of BA/epoxy coating
Studies on Biocide Encapsulated Zeolite-epoxy Nano Hybrid Coatings
Current Bionanotechnology, 2015, Vol. 1, No. 1
7
Fig. (4). (a) Polarization response of different epoxy/BA AF coatings after 30 days in 3.5% NaCl. (b) Polarization response of different epoxy/SB AF coatings after 30 days in 3.5% NaCl. Table 4.
Data resulted from polarization studies after 30 days of immersion in NaCl.
Group
Group 1
Group 2
Coated panels
Ecorr (mV)
Icorr (mA/cm2 )
CR (mm/y)
C1
-375
1.200 ˟ 10-3
1.384 ˟ 10-2
C2
-275
3.330 ˟ 10-5
1.228 ˟ 10-3
C3
-150
9.450 ˟ 10-5
3.850 ˟ 10-5
C4
-290
2.148 ˟ 10-4
3.043 ˟ 10-3
C5
-315
1.710 ˟ 10-4
1.812 ˟ 10-3
C6
-370
1.791 ˟ 10-3
2.076 ˟ 10-2
C7
-200
8.087 ˟ 10-4
9.372 ˟ 10-4
C8
-270
1.392 ˟ 10-4
1.613 ˟ 10-3
C9
-250
1.242 ˟ 10-3
1.440 ˟ 10-2
C10
-300
2.111 ˟ 10-4
2.446 ˟ 10-3
may be due to the formation of large crystals as discussed in [43, 44]. Potentiodynamic polarization curves for MS in 3.5% NaCl with and without epoxy/SB AF coatings is illustrated in Fig. (4b). When compared with the uncoated MS panels, it was evident that the polarization curves of MS coated with epoxy gave improved potential shifts nearer to noble metal values. The polarization variables such as Icorr and Ecorr obtained from anodic and cathodic curves by extrapolation of Tafel lines are discussed in Table 4. It is observed that the Ecorr values decreased considerably for MS coatings ‘C6’, ‘C7’, ‘C8’, ‘C9’, and ‘C10’. This result clearly shows that coatings over MS act like inhibitors. The rate of corrosion of uncoated MS was found to be 1. 029 ×10-1 mm/y and it minimized with ‘C7’ to a decreased value of 9.372 ×10-4 mm/y which is higher than the other coatings‘C6’, ‘C8’, ‘C9’ and ‘C10’ whose values are 2.076 ×10-2, 1.613 ×10-3, 1.440 ×10-2, 2.446 ×10-3 respectively. Moreover, the CR of ‘C7’ has the minimum corrosion rate among all formulations used in our present study. Hence it may be concluded that the contact between the metal and the electrolyte is restricted by the
coatings applied over MS panels. The maximum restriction was shown by ‘C7’ whereas the minimum was seen in system ‘C6’. This may be due to the even distribution of 3wt% SB within the epoxy coating of ‘C7’, which offers barrier effect by small particle size giving a defectless coating. SB, on the other hand, exhibited lower and controllable corrosion rate thus acting as a corrosion inhibitor. Evaluation of Corrosion Resistance by EIS on AF Coatings EIS is used for evaluating the corrosion resistance property of various epoxy coatings. Where RP is the pore resistance of the coatings, RS is the electrolyte resistance, Rct is the charge transfer resistance, Ccoat is the coating capacitance, Z is the impedance and Cdl is the double layer capacitance. The Rct and Cdl for different wt. % of BA containing epoxy with curing agent coated over MS suspended in 3. 5% NaCl are consolidated in Table 5. The impedance plots of ‘C3’ showed capacitive behavior with very high resistance of 5.256×10-7 ohm cm2 . Fig. (5) shows a Bode
8 Current Bionanotechnology, 2015, Vol. 1, No. 1
Table 5. Group
Group 1
Group 2
Saravanan et al.
Data resulted from impedance studies after 30 days of immersion in NaCl. Coated Panels
Impedance (ohm.cm2)
Charge Transfer Resistance (Ohm.cm2)
Protection Efficiency (%)
C1
107
1.193×103
95.92
C2
107
1.292×103
96.28
C3
10
8
1.152×10
5
99.95
C4
10
8
7.870×10
4
99.93
C5
107
7.407×103
99.35
C6
10
7
2.283×10
3
97.89
C7
10
8
5.110×10
4
99.90
C8
108
1.164×104
99.58
C9
10
7
3.482×10
3
98.61
10
7
2.724×10
3
98.23
C10
plot of the different coatings with the epoxy/BA on MS in a 3.5% NaCl solution. The charge transfer resistance of ‘C1’, ‘C2’, ‘C4’ and ‘C5’ combinations in 3.5 % NaCl decreased by 1 to 3 folds at the end immersion and the Cdl has increased by 1 fold. Nevertheless in case of ‘C3’ epoxy/BA coating the variation in Rct and Cdl is higher with slight difference when compared with other coating’s results. Initially Cdl increases with the immersion time and then reaches equilibrium since the water absorption becomes constant even with further increase in immersion time. Tiny-cell formation occurs at the MS/Epoxy interface, due to the porous nature of the coatings [45]. As the immersion time increases, diffusion process gets established due to the of corrosion products buildup at the MS/Epoxy interface. But in the case of ‘C3’ with BA, the compactness of crosslinked epoxy/BA coating structure contributed corrosion resistance. Apparently, it was difficult for the chloride and the water ions to penetrate the coating. The EIS also supported the ‘C3’ system which is void free with better compactness. The lower moisture content also indicates the pore free structure which contributes for a more secured system in a corrosive medium [46]. The protection efficiency of the coating has been calculated from the results
of the Rct measurement: Rct and Rct(C) are the charge transfer resistance values in the absence and presence of polymer coatings. The protection efficiency of coating ‘C1’, ‘C2’, ‘C3’, ‘C4’, and ‘C5’ is as same as that of EIS and is consolidated in Table 5. Fig. (6) shows Bode plot of the various coatings with the epoxy/SB on MS in a 3.5% NaCl solution. The charge transfer resistance of ‘C6’, ‘C8’, ‘C9’ and ‘C10’ combinations in 3. 5 % NaCl decreases by 1 to 3 times at the end of test, the Cdl increases by 1 fold. Nevertheless in case of ‘C7’ epoxy/SB coating the variation in Rct and Cdl are higher with slight difference when compared with other coatings results. As the immersion days progress, the values of Cdl and Rct also change. Usually Cdl increases with the increase in immersion days, and then reaches equilibrium as the water absorption becomes constant.
Fig. (6). Bode plot of different epoxy/SB AF coatings after 30 days in 3.5% NaCl.
Salt Spray Test Results of AF Coatings
Fig. (5). Bode plot of different epoxy/BA AF coatings after 30 days in 3.5% NaCl.
The AF coated panels were prone to crisscross scratches with a cutter in order to make the base metal exposed to the continuous 3.5% NaCl salt fog chamber. The 1200 h salt spray test results go well with the EIS results. The results of the salt spray test are schematically shown in Fig. (7a
Studies on Biocide Encapsulated Zeolite-epoxy Nano Hybrid Coatings
Current Bionanotechnology, 2015, Vol. 1, No. 1
9
Fig. (7). (a) Photograph of different epoxy/BA AF coatings after 1200h in 3.5% NaCl (b) Photograph of different epoxy/SB AF coatings after 1200h in 3.5% NaCl. Table 6. Group
Group 1
Group 2
Results of salt spray test after 1200 hours exposure of 3.5 % NaCl. Coated Panels
Observation After 1200h
C1
light brown rust on top right along the scribes, rust creep 2mm along scribes
C2
light brown rust on top right along the scribes, rust creep 1mm along scribes
C3
no light brown rust along the scribes, no rust creep
C4
light brown rust on top right and left along the scribes, rust creep 1mm along scribes
C5
light brown rust along the scribes, rust creep 2 mm along scribes
C6
light brown rust along the scribes, rust creep 3 mm along scribes
C7
no light brown rust along the scribes, no rust creep
C8
light brown rust along the scribes, rust creep 2 mm along scribes
C9
light brown rust along the scribes, rust creep 1 mm along scribes
C10
light brown rust along the scribes, rust creep 2 mm along scribes
and b). ‘C3’ and ‘C7 showed excellent corrosion resistance with no corrosion products over the surface of the unscratched area as similar to the EIS results. Coating ‘C1’ and ‘C6’ containing 1 wt. % BA and SB respectively offered poor corrosion resistance than the other eight coatings (‘C2’, ‘C3’, ‘C4’, ‘C5’) and (‘C6’, ‘C8’, ‘C9’, ‘C10’) respectively. Table 6 shows the observations made for the groups 1 and 2 after 1200 h of salt-spray test. The firmly adhered films over the MS showed corrosion resistance and no coating defects were found over the surface of the panels [47-49]. Except for ‘C1’ and ‘C6’, other panels showed excellent results even after 1200 h of saltspray exposure of the cross-cut. Hence, coatings‘C1’ (1wt. % BA) and ‘C6’ (1wt. % SB) exhibited poor salt-spray resistance.
Static Immersion Test Result of AF Coatings AF behavior of coatings was studied by immersing the epoxy coated panels in the ocean for a one year time period at Chennai (Muttukadu boat house), Tamil Nadu, East coast of India. Photographs of the ‘C1’, ‘C2’, ‘C3’, ‘C4’ and ‘C5’ systems with fouling are illustrated in Fig 8a. Fouling photos of replicates of coating system ‘C3’ and ‘C7’ and their results are given in Fig. (8b). It was observed that the accumulation of microbes was more on‘C1’, followed by ‘C2’, ‘C5’ and ‘C4’respectively. Similarly, the intensity of microbes attached to ‘C3’ and ‘C4’ was much minimized than other coatings. Among the coated panels, ‘C3’ (5 wt. % BA) showed minimum fouling organisms on its surface than ‘C4’ indicating its outstanding AF property. The enhanced anti-
10 Current Bionanotechnology, 2015, Vol. 1, No. 1
Saravanan et al.
a)
b)
Fig. (8). (a) Photograph of coating panels after 12th month’s immersion in seawater (b) Replicate photograph of ‘C3’ and ‘C7’coating panels.
fouling activity shown by ‘C3’ may be due to the optimized coating formulation. It is observed that the AF efficiency of the epoxy coatings improved by adding 3 wt. % of SB (‘C7’) and then decreased with (‘C8’) 5wt. %, (‘C9’) 7wt. % and (‘C10’) 10 wt. %. Good dispersion of SB is seen in 3 wt. % (‘C7’), offers excellent antifouling property. With the increase in the SB concentration above 3 wt%, pore formation is seen in the coatings. This may be due to the uneven distribution of SB at higher loading concentration. This porous nature of the coating films from ‘C8’ to ‘C10’ helps the development of fouling organisms, thus possessing lower AF properties than ‘C7’. The fouling community distribution pattern and biomass on coated specimen for different wt. %
of BA/SB loaded zeolite containing epoxy with hardener coated over MS immersed in sea water are consolidated in Table 7. Analysis of Acute Toxicity Test of AF Coatings During the period of exposure, the temperature of water was maintained at 23 ± 2 °C. The pH was maintained at 7.5–8.4 and dissolved oxygen content of the NSW was maintained at 5.10 mg/L. The number of deceased fishes was recorded at an interval of 12 h and was isolated instantaneously to avoid pollution of NSW solutions. The outcome of the acute oral toxicity test after 120 h shows
Studies on Biocide Encapsulated Zeolite-epoxy Nano Hybrid Coatings
Table 7.
Current Bionanotechnology, 2015, Vol. 1, No. 1
11
Fouling community distribution pattern and biomass on coated panels (Before immersion all coated panels weight ± 25.89g/dm2). Observation After 1 Year
Group
Group 1
Group 2
Coated Panels Community
Population Intensity
Wet Weight (g/dm2)
C1
Oyster, Barnacle
Dense
± 35.38
C2
Oyster, Barnacle
Dense
± 32.20
C3
Barnacle
Sparse
± 28.95
C4
Oyster, Ascidians
Scattered
± 29.81
C5
Bryozoans, Mollusk
Dense
± 36.27
C6
Oyster, Ascidians
Dense
± 31.43
C7
Green algae
Sparse
± 26.62
C8
Bryozoans, Ascidians
Scattered
± 32.55
C9
Mollusk, Green algae
Scattered
± 34.87
C10
Oyster, Barnacle
Dense
± 34.22
that LC50 > 50,000 ppm, which supports the fact that the oceanic environment will not get polluted, if this coating film is immersed in sea. This is due to the nontoxic nature of BA/SB AF agents. Table 2 shows that the epoxy film synthesized in this study has exceptional corrosion resistance and adhesion properties, which make it an able material that can be used as high performance coating. All results support this novel AF coating towards industrial application. Analysis of Antimicrobial Test of AF Coatings BA and SB salts are commonly used as food, cosmetic preservatives [50], beverages, fruit products, sauces and condiments, preferably in a range below pH = 4.5. The average concentrations allowed in food in different countries are between 0.15 % and 0.25 %. Using these properties, we
were further interested in extending our work towards antibacterial investigations of biocide loaded zeolite epoxy AF paint formulation which could act as an effective antibacterial coating. Hence, an investigation was under taken to study and compare the antibacterial activity of epoxy/BA, epoxy/SB and neat epoxy coatings. In the results, Fig. (9) shows the coating ‘C3’ (5 wt.%) and ‘C7’ (3 wt.%) having greater zone of inhibition compared to control (MS) and neat epoxy shows there is no zone of inhibition indicating their inferior bacterial resistance. It could be concluded that the epoxy/BA and epoxy/SB coated sample exhibit effective antibacterial activity. Antibacterial activity of coating ‘C3’ and ‘C7’ may be attributed to the better dispersion and subsequent compatibility exhibited by BA/SB with the epoxy matrix. This subsequently leads to seepage of cell constituents and therefore cell death.
Fig. (9). Antibacterial test against Escherichia coli bacteria: (a) control MS, (b) neat epoxy, (c) coating ‘C3’ and (d) Coating ‘C7’.
12 Current Bionanotechnology, 2015, Vol. 1, No. 1
Saravanan et al.
Fig. (10). SEM images of panels ‘C3’ and ‘C7’ after immersion in seawater.
Analysis of SEM Results Fig. (10) illustrates the surface morphologies of coated panels ‘C3’ and ‘C7’ which were obtained after immersing the panels in sea for fouling study. Through SEM results we can note that the intensity of fouling organisms were minimum on panel ‘C3’ and ‘C7’ with BA and SB respectively. This might be due to the antifouling activity of the optimized coating formulations of ‘C3’ and ‘C7’ than the other concentration. CONCLUSION Both low toxic biocides BA and SB of varying compositions (1, 3, 5, 7 and 10 wt. %) were separately incorporated into epoxy resin via nano-zeolite encapsultant to fabricate AF coatings. Coatings formulated with varied concentration of SB from 1 to 3 wt. % were found to offer excellent corrosion and fouling resistance, above which their coating performance becomes worse. Similar observation was made in the case of 5 wt. % concentration BA coatings, which showed best results of corrosion and fouling resistance. Beyond which the coating’s performance declined. Both BA and SB loaded epoxy coatings had a controlled leaching of their constituents to the corrosion and fouling environment with respect to time. However, SB loaded coating exhibited improved corrosion resistance than BA incorporated coatings indicating its excellent corrosion resistance. Although the toxicity of SB is 4 to 5 folds lower than the commonly used AF agents such as
TBT and SeaNine 211, SB incorporated coatings exhibited enhanced AF behavior when compared to epoxy coatings containing BA. The promising AF results of SB incorporated coatings coupled with the simplicity suggest that SB would be an eco-friendly alternative to the currently used toxic biocides in AF applications. The data resulted from corrosion and field exposure studies clearly indicate that the (3 wt. %) optimum use of low toxic SB in coating formulations could offer superior corrosion resistance and AF efficiency than the other coatings that are currently used for the same purpose. CONFLICT OF INTEREST The authors confirm that this article content has no conflict of interest. ACKNOWLEDGEMENTS Instrumentation facility provided under FIST-DST and DRS-UGC to Department of Chemistry, Anna University, Chennai are gratefully acknowledged. Mr. P. Saravanan like to thank the management of St. Joseph’s college of engineering, Chennai for the infrastructure and moral support. REFERENCES [1] [2]
Evans LV, Clarkson N. Antifouling strategies in the marine environment. J Appl Bacteriol 1993; 74: 119–129. Abdulhadi A, Al-Juhni, Bi-min Zhang Newby. Incorporation of benzoic acid andsodium benzoate into silicone coatings and subse-
Studies on Biocide Encapsulated Zeolite-epoxy Nano Hybrid Coatings
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11] [12]
[13] [14] [15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
quent leaching of thecompound from the incorporated coatings. Prog Org Coat 2006; 56: 135–145. Banerjee I, Pangule RC, Kane RS. Antifouling coatings: Recent developments in the design of surfaces that prevent fouling by proteins, bacteria, and marine organisms. Adv Mater 2011; 23: 690718. Shan C, JiaDao W, HaoSheng C, DaRong C. Progress of marine biofouling and antifouling technologies. Chin Sci Bull 2011; 56: 592-612. Khan MY, Agarwal H, Ranganathan S, Welch WA, Miller W, Cocker DR. Greenhouse gas and criteria emission benefits through reduction of vessel speed at sea. Environ Sci Tech 2012; 46: 12600-12607. Axiak V, Vella AJ, Agius D, Bonnici P, Cassar G, Cassone R, et al. Evaluation of environmental levels and biological impact of TBT in Malta (central Mediterranean). Sci Total Environ 2000; 258: 89– 97. Haslbeck E, Kavanagh CJ, Shin HW, Banta WC, Song P, Loeb GI. Minimum effective release rate of antifoulants: measurement of the effect of TBT and zosteric acid on hard fouling. Biofouling 1996; 10: 175–186. Champ MA. Review of organotin regulatory strategies, pending actions, related costs and benefits. Sci Total Environ 2000; 258: 21–71. JECFA. Evaluation of certain food additives and contaminants twenty seventh report of the joint FAO/WHO Expert Committee on Food Additives. World Health Organization Technical Report Series no. 696, Geneva 1983. Anon. Code of federal regulations, United States: US food and drug administration. Title 21, Section 1977/1988; 184.1021 and 184.1733. Anon. EC Directive 95/2/EC: Food additives other than colours and sweeteners. OJ 1995; 61: 1–40. Haque H, Cutright TJ. Effectiveness of sodium benzoate and benzoic acid as freshwater low toxicity antifoulants when dispersed in solution and entrapped in silicone coatings. Biofouling 2005; 21: 109–119. Lueck E. Benzoic acid in antimicrobial food additives: Characteristics, uses, effects, Springer-Verlag. Berlin, 1980; 210–217. Chapman JS. Biocide resistance mechanisms. Int Biodet Biodeg 2003; 51: 133–138. Eklund T. The effect of sorbic acid and esters of p-hydroxybenzoic acid on the proton motive force in Escherichia coli membrane vesicles. J Gen Microbiol 1985; 131: 73–76. Vetere V, Perez M, Garcia M, Deya M, Stupak M, Del Amo B. A non-toxic antifouling compound for marine paints. Surf Coat Int 1999; 12: 586–589. Stupak ME, Garcia MT, Perez MC. Non-toxic alternative compounds for marine antifouling paints. Int Biodet Biodeg 2003; 52: 49–52. Pande HB, Parikh PA. Novel Application of ZSM-5 Zeolite: Corrosion-resistant coating in chemical process industry. J Mater Eng Perform 2013; 22: 190-199. Katariya MN, Jana AK, Parikh PA. Corrosion inhibition effectiveness of zeolite ZSM-5 coating on mild steel against various organic acids and its antimicrobial activity. J Ind Eng Chem 2013; 19: 286– 291. Thierry A, Geoffrey H, Sandrine Q, Guillaume L, Florence B. Solution state NMR techniques applied to solid state samples: characterization of benzoic acid confined in MCM-41. J Phys Chem C 2010; 114: 8884–8891. Charnay C, Bégu S, Tourné-Péteilh C, Nicole L, Lerner DA, Devoisselle JM. Inclusion of ibuprofen in mesoporous templated silica: drug loading and release property. Eur J Pharm Biopharm 2004; 57: 533–540. Dharmendra Kumar Shukla, Subramanyam, Kasisomayajula V, Venkitanarayanan Parameswaran. Epoxy composites using functionalized alumina platelets as reinforcements. Compos Sci Tech 2001; 68: 3055–3063. ISO 2409. Paints and Varnishes—Cross Cut Test for Films 2007.
Current Bionanotechnology, 2015, Vol. 1, No. 1 [24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35] [36]
[37] [38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
13
Ayman M, Ahmed F, Kafrawy EI, Morsy H, Abdel-Azim A. New epoxy resins based on recycled poly (ethylene terephthalate) as organic coatings. Prog Org Coat 2007; 58: 13–22. Sharif A, Naqvi F, Eram S, Kanak LV. Development of amine–acid cured Annona squamosa oil epoxy anticorrosive polymeric coatings. Prog Org Coat 2006; 55: 268-275. Ananda Kumar S, Balakrishnan T, Alagar M, Denchev Z. Development and characterization of silicone/phosphorus modified epoxy materials and their application as anticorrosion and antifouling coatings. Prog Org Coat 2006; 55: 207–217. Berndt M, Berndt CC, Cramer SD, Covino BS. Corrosion - fundamentals, testing and protection, ASM Handbook, ASM International, Materials Park 2003; 13A: 803-813. Bagherzadeh MR, Mahdavi F. Preparation of epoxy–clay nanocomposite and investigation on its anti-corrosive behavior in epoxy coating. Prog Org Coat 2007; 60: 117–120. Ananda Kumar S, Sankara Narayanan TSN. Thermal properties of siliconized epoxy interpenetrating coatings. Prog Org Coat 2002; 45: 323–330. Sankara Narayanan TSN, Subbaiyan M. Evaluation of phosphate coatings by electrochemical impedance spectroscopy. Met. Finish 1994; 92: 33–36. Dong CF, Sheng H, An YH, Li XG, Xiao K, Cheng YF. Corrosion of 7A04 aluminum alloy under defected epoxy coating studied by localized electrochemical impedance spectroscopy. Prog Org Coat 2010; 67: 269–273. Sinebryukhov SL, Gnedenkov AS, Mashtalyar DV, Gnedenkov SV. PEO-coating/substrate interface investigation by localised electrochemical impedance spectroscopy. Surf Coat Technol 2010; 205: 1697–1701. Pebere N, Picaud T, Duprat M, Dabosi F. Evaluation of corrosion performance of coated steel by the impedance technique. Corros Sci 1989; 29: 1073–1086. Mansfeld F. Use of electrochemical impedance spectroscopy for the study of corrosion protection by polymer coatings. J Appl Electrochem 1995; 25: 187–202. Okazaki Y. Effect of friction on anodic polarization properties of metallic biomaterials. Biomaterials, 2002; 23: 2071–2077. Louis Floyd F, Avudiappan, S, Gibson J, Mehta B, Smith P, Provder T, et al. Using electrochemical impedance spectroscopy to predict the corrosion resistance of unexposed coated metal panels. Prog Org Coat 2009; 66: 8–34. Holland RI. Corrosion testing by potentiodynamic polarization in various electrolytes. Dent Mater 1992; 8: 241–245. Ananda Kumar S, Sasi Kumar A. Studies on novel silicone/phosphorus/sulphur containing nano-hybrid epoxy anticorrosive and antifouling coatings. Prog Org Coat 2010; 68: 189–200. ASTM E729. Standard Guide for Conducting Acute Toxicity Tests on Test Materials with Fishes, Macroinvertebrates, and Amphibians 2007. Duraibabu D, Ganeshbabu T, Manjumeena R, Ananda Kumar S, Priya Dasan. Unique coating formulation for corrosion and microbial prevention of mild steel. Prog Org Coat 2014; 77: 657-664. Ananda Kumar S, Savitha R. Protective coatings: Novel nanohybrid coatings for corrosion and fouling prevention. Wiley online Library 2011; pp.355-392. Ramezanzadeh B, Attar MM, Farzam M. Effect of ZnO nanoparticles on the thermal and mechanical properties of epoxy-based nanocomposites. J Therm Anal and Calorim 2011; 103: 731-739. Selvaraj R, Selvaraj M, Iyer SV. Studies on the evaluation of the performance of organic coatings used for the prevention of corrosion of steel rebars in concrete structures. Prog Org Coat 2009; 64; 454-459. Ayman MA, Abdou MI, Abdel A, Elsayed A, Mohamed E. New bisphenol novolac epoxy resins for marine primer steel coating applications. Prog Org Coat 2008; 63: 372-376. Arthananareeswari M, Sankara Narayanan TSN, Kamaraj P, Tamilselvi M. Polarization and impedance studies on zinc phosphate coating developed using galvanic coupling. J Coat Technol Res 2012; 9: 39-46.
14 Current Bionanotechnology, 2015, Vol. 1, No. 1 [46]
[47]
[48]
Saravanan et al.
Ayman MA, Shanker NO, Abdou MI, Abdelfatah M. Synthesis and characterization of high thermally stable poly(Schiff) epoxy coatings. Prog Org Coat 2006; 56: 91-99. Ananda Kumar S, Alagar M, Mohan V. Studies on corrosionresistant behavior of siliconized epoxy interpenetrating coatings over mild steel surface by electrochemical methods. JMEPEG 2002; 11: 123-129. Ananda Kumar S, Alagar M, Mohan V. Assessment of corrosionresistance of siliconised epoxy coatings by potentiodynamic polarisation method. Surf Coating Int B Coating Trans 2001; 84: 43-48.
Received: October 31, 2014
[49]
[50]
Pedro de LN, Alexsander PA, Walney SA. Study of the anticorrosive behaviour of epoxy binders containing non-toxic inorganic corrosion inhibitor pigments. Prog Org Coat 2008; 62: 344-350. Wibbertmann A, Kielhorn J, Koennecker G. World Health Organization: Proceedings of International Programme on Chemical Safety, Benzoic acid and Sodium benzoate. Concise international chemical assessment document No. 26. Geneva 2000.
Revised: February 25, 2015
Accepted: March 04, 2015
