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Progress in Organic Coatings 60 (2007) 117–120

Preparation of epoxy–clay nanocomposite and investigationon its anti-corrosive behavior in epoxy coating

M.R. Bagherzadeh ∗, F. MahdaviCoating Research Center, Research Institute of Petroleum Industry, N.I.O.C, Tehran, Iran

Received 22 November 2006; received in revised form 4 June 2007; accepted 9 July 2007

bstract

An epoxy–clay nanocomposite was synthesized using a quaternary ammonium-modified montmorillonite clay and diglycidyl ether of bisphenol(DGEBA) type epoxy resin, in order to produce anti-corrosive epoxy coating. Anti-corrosive properties of the nanocomposite were investigated

sing salt spray and electrochemical impedance spectroscopy (EIS) methods. The results showed an improvement in the barrier and anti-corrosiveharacteristics of epoxy-based nanocomposite coating and a decrease in water uptake in comparison with pure epoxy coating. Wide-angle X-ray

iffraction (WAXD) patterns and transmission electron microscopy (TEM) analysis showed that the interlayer spacing of clays increased afterddition of epoxy resin along with applying shear force and ultrasound sonicator. The best performance of this coating was achieved at 3 andwt.% clay concentration.2007 Elsevier B.V. All rights reserved.

eywords: Nanocomposite; Epoxy coating; Nanoclay; Water uptake; Barrier; EIS

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. Introduction

Polymer–clay nanocomposites (PCNs) are compounds inhich nanoclay particles are distributed in a polymer matrix.

n recent years, such substances have attracted interest in engi-eering and scientific aspects of coating due to their excellentroperties, such as high-dimensional stability, heat deflectionemperature, reduced gas permeability, optical clarity, flameetardancy and enhanced mechanical properties [1,2].

The barrier, adhesion and inhibiting features have an impor-ant role in lifetime of coatings. The strength of coating/metalystem is in proportion with contact time of system with theorrosive medium, changes in adhesion, barrier and inhibitingroperties. Aging and diffusion of corrosive agents such as H2O,2 and H+ into coating/substrate interface can lead to blister-

ng, reduce stability of the adhesion bond, increase the speed ofathodic reaction and degradation of coating and substrate [3].

Recently many efforts have been done to improve anti-orrosive properties of epoxy coatings such as: modifyingormulation of organic epoxy resins through introduction of

∗ Corresponding author. Tel.: +98 21 55901078; fax: +98 21 55901078.E-mail address: Bagherzadehmr@ripi.ir (M.R. Bagherzadeh).

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300-9440/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.porgcoat.2007.07.011

ilane-coupling agents, preparation of epoxy–siloxane hybridinders or other methods such as decrease in coating/membraneermeability of aggressive species [4].

Yasmin et al. [5], Becker et al. [6] and Kim et al. [7]ave studied the mechanical, barrier and molecular permeabilityroperties of epoxy–clay nanocomposites. Good anti-corrosiveroperties of epoxy–clay nanocomposites and their reducedases and moisture permeabilities are the aspects which makehem attractive in order to produce protective coatings.

All types of layered silicates such as smectite, montmo-illonite and saponite are the effective and reinforcing agentsn making polymer clay composites. Pristine-layered silicates,hich contain layered Na+ or K+ ions, are only miscible withydrophilic polymers. Through ion-exchange reactions withationic surfactants layered silicates render miscible with otherolymers. Cations reduce the surface energy of the organic hostnd improve wetting characteristics of polymer, resulting in aarger interlayer spacing.

Several types of morphologies may occur when the poly-er is mixed with layered silicates: (a) conventional composites

b) intercalated nanocomposites and (c) exfoliated nanocompos-tes. Their differences can be related to the polymer permeationetween clay layers and dispersion uniformity of silicate sheetsn polymer matrix. The high aspect ratio of silicate layers plays

1 ess in Organic Coatings 60 (2007) 117–120

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investigated. Table 1 shows the results of adhesion tests forprepared nanocomposite coatings and the sample with no claycontent. These results show that the adhesion does not vary

18 M.R. Bagherzadeh, F. Mahdavi / Progr

n important role in production of anti-corrosive coating systems1,7,8]. In this study an epoxy–clay nanocomposite coating wasynthesized and its anti-corrosive properties were investigatedsing salt spray and EIS test methods.

. Experimental

.1. Materials

The nanoclay used in this study was a modified montmo-illonite with commercial grade of cloisite 30B®, obtainedrom Southern Clay Products. The diglycidyl ether of bisphe-ol A (DGEBA) epoxy resin (Araldite Razeen LR-2257)nd polyamide hardener (Aradure43SBD) was purchased fromuntsman Corporation.

.2. Preparation of epoxy–clay nanocomposite coating

The desired amount of resin and nanoclay were mixedogether. The mixing process was performed in an oil bath50–70 ◦C). Then the mixture was subjected to sonication for–12 h. For fabrication of nanocoating after addition of somedditives to epoxy–clay mixture, the stoichiometric amount ofhe hardener was added to mixture. By this method, three sam-les containing different amounts of clay (1, 3, and 5 wt.%) wererepared.

.3. Surface preparation and applying the coating

The metallic panels were sandblasted using ASTM D7055nd then the nanocoatings were applied by spray on metallicanels. The panels were dried at 23 ◦C for 1 week. The dry filmhickness was 60 ± 5 �m.

.4. Characterization

Wide-angle X-ray diffraction (WAXD) was used to evalu-te degree of exfoliation and d-spacing between clay platelets.he WAXD study was performed with Philips PW 1840. Trans-ission electron microscopy was used for distinguishing the

ispersion of platelets in polymer matrix using Philips CM00-FEG. Adhesion and salt spray tests were performed withRICHSEN equipments in accordance with ASTM D3359 andSTM B117. Electrochemical impedance spectroscopy (EIS)

est was performed with EG&G equipment.

. Results and discussion

.1. TEM and WAXD analysis

The WAXD patterns of cloisite 30B®, pure epoxy,poxy–organoclay mixture and epoxy–clay nanocomposite arehown in Fig. 1. The patterns show a characteristic diffraction

eak at 18 A for pure cloisite 30B and a peak with d-spacing of6.8 A for epoxy–organoclay mixture. The increase of the basalpacing of clay platelets indicates that intercalation occurrednd epoxy resin diffused into galleries. After mixing resin and

ig. 1. WAXD patterns of cloisite 30B, epoxy–organoclay, epoxy–clayanocomposite and pure epoxy.

rganoclay, the clay attracts polar epoxy molecules due to itsigh surface energy. Also the presence of alkyl ammoniumations with the strong polarity of the N–H groups in the primarynd secondary amines catalyze the epoxy homopolymerization9–11].

When the hardener was mixed with epoxy–organoclay mix-ure the peak shifted to the lower angle with d-spacing of 40.7 A,gain indicating an increase in spacing of clay platelets. Theppropriate balance between inter- and extra-gallery reactions,ogether with the resin and amine diffusion, are the key fac-ors to control the organoclay exfoliation [12]. TEM imagef epoxy–clay nanocomposite, indicate 3–4 nm gallery spacingFig. 2), and demonstrates that an intercalated nanocompositeas been formed.

.2. Adhesion analysis

Adhesion of coating films on metallic substrates was also

Fig. 2. TEM image of epoxy–clay nanocomposite.

M.R. Bagherzadeh, F. Mahdavi / Progress in

Table 1Adhesion results of epoxy–clay nanocomposite coatings with varying clay con-tents using ASTM D3359

Clay concentration (wt.%) Result

– 5B1 5B35

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ith increase in clay concentration and all of the samples showxcellent adhesion.

.3. Salt spray testing

Salt spray test method was used to evaluate performancef the epoxy–clay nanocomposite coatings using ASTM B117.able 2 shows the results of salt spray tests.

Last studies show that the water permeability in the com-ounds with a less powder volume due to decrease in the networkensity results in the swelling of the coating film, whereas theater permeability in the compounds with a higher powder vol-me performs through forming holes on the surface of coating

lm as well as extending water distribution highways [13]. How-ver, the results of present work confirm that increase in the clayoncentration leads to reduction of degradation and blisteringensity. This property is one of the remarkable advantages of

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able 2alt spray results of epoxy–clay nanocomposites with varying clay contents in accord

Clay concentration (wt.%) Results

– A lot of small blisters were observed on the surfacewater penetration from the tracks was about 1 mm

1 Some small blisters were observed on the surface (3 There was no blister and water penetration5 There was no blister and water penetration

ig. 3. The surface aspect of the samples containing different amounts of clay afterwt.% clay concentration.

Organic Coatings 60 (2007) 117–120 119

sing nanoclay particles. The aspects of the surface samples arehown in Fig. 3, indicating excellent anti-corrosive feature of Cnd D samples in contrast with the A sample which does notontain any organoclay.

.4. Electrochemical impedance spectroscopy testing (EIS)

EIS measurements of each sample were conducted over a fre-uency range of 105 down to 10−2 Hz using a 10 mV amplitude.he electrical capacitance of the coating (C), resistance polar-

zation (R) and water uptake values were evaluated from theode curves and log|Z| values. Table 3 shows the log|Z| values.

The water uptake values of samples shown in Table 4 andig. 4 obtained from Brasher–Kingsbury equation:

ater uptake = log(Ct/C0)

log 80

here Ct is the electrical capacitance of the coating during time of immersion, C0 the electrical capacitance of the coatingefore immersion [14]. These results indicate that water uptakef nanocoatings decreases as the clay concentration increases. Inhe sample with no clay content the water uptake is three times

ore than the nanocoating containing 1 wt.% of clay.In the coating with no clay content, the free volume of poly-

eric matrix is higher than in nanocomposite coating, so theggressive compounds can diffuse through microvoids easily.

ance with ASTM D 714

(Blister size No. 8, Medium). There was trace of rust under the blisters, and

Blister size No. 6, Few), but there was trace of rust under the blisters

exposing to salt spray for 500 h. (A) 0 wt.%, (B) 1 wt.%, (C) 3 wt.%, and (D)

120 M.R. Bagherzadeh, F. Mahdavi / Progress in

Table 3log|Z| values of nanocomposite coatings with different amounts of clay

Clay concentration (wt.%) log|Z| (t = 0) log|Z| (t = 500 h)

– 5.64 2.981 7.54 6.843 9.26 9.205 9.36 9.33

Table 4water uptake values of nanocomposite coatings with varying clay contents after500 h exposure to salt spray

Clay concentration (wt.%) Water uptake

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ig. 4. The variation of water uptake as a function of clay content wt.% foranocomposite coatings containing different concentration of organoclay.

he salt spray and EIS results indicate that degradation in sampleithout any clay is more than for other samples, so incorporationf clay platelets into epoxy matrix results in decrease of waterermeability for nanocomposite coating.

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Organic Coatings 60 (2007) 117–120

Nanocomposite coating with 1 wt.% clay loading showsbout 70% reduction in water uptake. The salt spray and EISesults show that the barrier properties increase as the clay con-entration increases, so there is a significant difference betweennti-corrosive properties of nanocomposite coatings with 1 andwt.% clay content. The best performance of the coating waschieved at 3 and 5 wt.% clay concentrations.

. Conclusion

Incorporating nanoclay particles into organic coatingsmproves the anti-corrosive properties of coatings. As thelay loading increases the barrier and anti-corrosive propertiesncrease, so in this work the best anti-corrosive performance ofoatings was obtained at 3 and 5 wt.% clay concentrations. TheIS results with 3 and 5 wt.% clay concentration samples were

elatively similar but using 3 wt.% is economically preferred.

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