Surface & Coatings Technology 204 (2009) 635–641

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Protective epoxy dispersion coating materials modified a posteriori withorganophilized montmorillonites

Krzysztof Kowalczyk, Tadeusz Spychaj ⁎West Pomeranian University of Technology, Polymer Institute, ul. Pulaskiego 10, 70-322 Szczecin, Poland

⁎ Corresponding author. Tel.: +48 91 449 4247; fax:E-mail address: Tadeusz.Spychaj@zut.edu.pl (T. Spyc

0257-8972/$ – see front matter © 2009 Elsevier B.V. Aldoi:10.1016/j.surfcoat.2009.08.046

a b s t r a c t

a r t i c l e i n f o

Article history:Received 1 April 2009Accepted in revised form 31 August 2009Available online 8 September 2009

Keywords:Epoxy coatingEpoxy dispersionWater-thinnable coatingNanofillerMontmorilloniteBentonite

Two types of paints (primer and topcoat) and coatings based on epoxy resin dispersions, water solution ofpolyamine hardener and a posteriori introduced four types of organophilized montmorillonite (mMMT)nanofillers: two commercial Nanofil-type (used as powders) and two pilot plant NanoBent-type products (ina powder and water-slurry form) were formulated and investigated. Pulverized organoclays werepreliminarily incorporated (in various doses: 1, 2.5 and 5 wt.%) into the epoxy resin dispersions, filledmainly with iron oxides (primer) or the TiO2/white filler (topcoat) using either a pearl-mill or a dissolver.Water-slurry of semihydrophilic modified montmorillonite was mixed with epoxy resin dispersions in thedissolver. The paints were applied on steel substrate and cured at room temperature. An influence of themethod of introduction, handling form and type of mMMT on properties of epoxy dispersion paints andcoatings has been investigated. In most cases coatings with semihydrophilic NanoBent-type nanofillersexhibited better properties than those with hydrophobic mMMT. Differences of barrier and mechanicalfeatures for primer, topcoat and primer/topcoat (multilayer) coatings based on results of water uptake,relative impedance, adhesion to steel, hardness and abrasion resistance tests, are discussed.

+48 91 449 4685.haj).

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© 2009 Elsevier B.V. All rights reserved.

1. Introduction

In recent years continuous progress of water-thinnable coatingstechnology based on curable synthetic resins has been observed. Themost important reactive binders belong to epoxy resins, which areused as aqueous dispersions or emulsions in anticorrosive paints forsteel substrates. Such coating systems can be obtained by mixingaqueous dispersions/emulsions of solid or liquid epoxy resinscontaining various inert and anticorrosive additives with a properlyselected hardener (mainly based on polyamines) [1,2].

Fillers with nano-sized particles/grains (nanofillers) are relativelyoften applied as components of chemoreactive polymeric composi-tions usually in casting or coating systems. Most of the commerciallyavailable nanoparticles (various metal oxides e.g. Al2O3, TiO2, ZnO,silicas or carbon nanotubes) improve barrier properties, abrasion andscratch resistance, thermal stability as well as UV resistance of curedpaints and varnishes [3–12]. Nanofillers can be incorporated intopowder or liquid coating composition thanks to their: (i) homogeni-zation with a melted binder, e.g. in an extruder (a method noted inliterature as “melt homogenization”), (ii) premixing (and swellingoccasionally) with liquid resin or monomer (“in situ polymerization”)and (iii) milling/high-speed mixing with a coating binder andappropriate solvent(s), e.g. an organic solvent or water (“solvent-

based method”) [13–15]. Nevertheless, the best results were noticedfor coatings based on compositions with separately preparednanofiller slurry (by its milling as well as sonication and optionallylong-lasting swelling in a solvent). In the case of organophilizedmontmorillonites especially designed for water-soluble or water-thinnable binders, stable as well as easy-to-handle water-slurry of ananofiller could be directly prepared during organophilization oflayered aluminosilicates with appropriate ammonium salt [16–18]. Inthis work the effect of a posteriori incorporationmethods of two typesof organophilized montmorillonites (modified by ammonium saltswith different hydrophobicities) in various handling forms into 2 Kepoxy paints has been investigated. These montmorillonites in a formof powders or water-slurry were used for a water-thinnable primerand also a topcoat based on epoxy resin dispersions with a water-soluble amine hardener.

2. Experimental

2.1. Materials

Water-thinnable epoxy paints were based on the followingcomponents:

– CHS-EPOXY 200 V55, water dispersion of a medium molecularweight epoxy resin solution (in amixture of methoxypropanol andmethoxydipropyleneglycol), 56 wt.% of solids, epoxy equivalentweight of solid ca. 490 g/mol (Chemical Works “Spolchemie”,Czech Republic);

636 K. Kowalczyk, T. Spychaj / Surface & Coatings Technology 204 (2009) 635–641

– Telalit 180 (abbreviated to T), water based solution of polyaminecuring agent (50 wt.% solution in water/butylglycol) with anamine value of about 140 mg KOH/g (from “Spolchemie”).

Water-thinnable epoxy primer paint (EP) was prepared by mixing30 wt.% parts of CHS-EPOXY 200 V55 epoxy dispersion and 70 wt.%parts of anticorrosive filler paste (various iron oxides dispersed inwater/cosolvents system; Hegman 6.5) in a dissolver (PS IP, Szczecin,Poland).

Water-thinnable epoxy topcoat paint (ET) was prepared by mixing35.5 wt.% parts of CHS-EPOXY 200 V55 epoxy dispersion and 64.5 wt.%parts of TiO2/white filler paste (Hegman 7) in a dissolver (PS IP).

Four commercial organophilic modified montmorillonites (mMMT)used as coating nanofillers were applied:

– Nanofil 5 (N5), pulverized montmorillonite modified with diocta-decyldimethylammonium chloride, characterized by particle di-ameter about 8 µm and gallery spacing 28 Å [19] (product fromSüd-Chemie/Rockwood Additives Ltd., Germany);

– Nanofil 9 (N9), pulverized montmorillonite modified with benzy-loctadecylammonium salt, powder with particle diameter of about8 µm and gallery spacing 20 Å [19] (from Süd-Chemie/RockwoodAdditives, Germany);

– NanoBent ZS-1 (ZS), montmorillonite modified with laboratoryprepared semihydrophilic ammonium salt bearing long-chainaliphatic and aromatic substituents with several hydroxyl groups,powder with particle diameter of 50 µm and gallery spacing 39 Å[18] (pilot plant product of Z.G.M. Zebiec S.A., Starachowice,Poland);

– NanoBent D-ZS-1 (DZS), water-slurry of NanoBent ZS-1, 37 wt.% ofsolids (obtained from Zebiec S.A.).

The above-mentioned organophilized montmorillonites wereprimarily incorporated into the epoxy paints (EP or ET). Thedispersion process of powder-type mMMTs (N5, N9 and ZS) wascarried out (0.5 h at 25 °C) using a laboratory low-shear pearl-millwith glass pearls ϕ 2.3–2.6 mm (Klaxon, UK). NanoBent D-ZS-1 wasmixed (for 20min) with epoxy paints using a laboratory dissolverwith a heavy-duty dispersion impeller (400 rpm; VMA GetzmannGmbH, Germany). Nanofillers were dosed into the paints in theamount of 1, 2.5 and 5 wt.% (based on the epoxy dispersion/hardenersolids content). For comparison, the epoxy paints without mMMTswere also processed (before mixingwith Telalit 180 hardener) using apearl-mill (paints abbreviated to EP-M/T and ET-M/T, respectively) ora dissolver (EP-D/T, ET-D/T).

Table 1Barrier properties of cured epoxy primer modified with organophilized montmorillonites.

mMMT type mMMT content (wt.%) Coating acronym Water ab

1 day

– 0 EP-M/T3 6.3Nanofil 5 1 EP/T/N5-1 4.0

2.5 EP/T/N5-2.5 5.05 EP/T/N5-5 3.2

Nanofil 9 1 EP/T/N9-1 3.02.5 EP/T/N9-2.5 6.65 EP/T/N9-5 5.2

NanoBent ZS-1 1 EP/T/ZS-1 1.52.5 EP/T/ZS-2.5 2.65 EP/T/ZS-5 5.1

– 0 EP-D/T4 3.5NanoBent D-ZS-1 1 EP/T/DZS-1 2.1

2.5 EP/T/DZS-2.5 1.95 EP/T/DZS-5 4.4

1 — After 1- and 7-day immersion of cured coatings in distilled water; 2 — relative impedanNaCl solution; 3 — coatings based on epoxy component EP processed in pearl-mill; 4 — coa

2.2. Sample preparation

The steel plates were ground with the P-240 type abrasive paperand degreased with acetone and toluene. The substrate panels with adimension of 80×100 mm (for adhesion, hardness and abrasiontests), 50×100 mm (for water uptake and water resistance tests) and100×100 mm (for electrochemical impedance spectroscopy analysis)were used in the experiments.

Epoxy dispersion paints (EP or ET) with or without modifiedmontmorillonites were thinned (after 48 h since processing in apearl-mill or a dissolver) with distilled water (in the amount ofabout 5 wt.% of the total weight of epoxy dispersion/hardenercomposition) and mixed together with T18 hardener for 5min usinga mechanical laboratory stirrer. Then, the primer or topcoat coatingcompositions were filtered and applied with a brush (according tothe Polish Standard PN-C-81514:1979) or a spiral film applicator(150 µm, Unicoater 409, Erichsen GmbH, Germany) on the steelsubstrate and cured at room temperature for 14 days. The four-layersamples for electrochemical impedance spectroscopy (EIS) testswere prepared by applying two layers of each selected primer andtopcoat compositions with a spiral film applicator (100 µm) with24 h painting intervals.

2.3. Test methods

Conventional viscosity tests (flow time according to PN-C-81508:1981, Ford cup ϕ 4 mm, viscosity testing during 2 h with10 min intervals) were performed on liquid coating compositions. Thehardness (PN-EN ISO 2815:2004, Buchholz method; eight measure-ments for each composition), abrasion resistance (PN-C-81516:1976,falling sand abrasion method; five measurements) and distilled wateruptake/resistance (PN-ISO 15184:2001, gravimetric method/visualobservation of samples during 7 days of immersion; three measure-ments) were evaluated on the cured paints. The cross-cut adhesiontests (PN-EN ISO 2409:1999, adhesion to steel substrates, threemeasurements), as well as, the pull-off adhesion tests (PN-EN ISO4624:2004, PHO-4 hydraulic apparatus, Dozafil, Poland; analysis ofEP-type coatings, ten measurements for each composition) were alsoperformed. The thickness of cured films was measured with theelectronic film gauge Byko-test 8500 (BYK-Gardner GmbH, Germany)according to PN-EN ISO 2808. EIS tests were carried out with coatedpanels after 1 h (one-layer coatings with 58–67 µm thickness) or10 min and 24 h (four-layer coating systems; total thickness 186–203 µm) since their exposure to aqueous NaCl solution (3.5 wt.%).Measurements were realized using three coated samples for each

sorption1 (wt.%) Water resistance (days) Relative impedance2 (kΩ/µm)

7 days 2mHz 10 Hz

11.9 1 175 43.36.8 1 0.3 2.28.3 1 54.2 2.35.9 1 2.5 0.78.2 1 1.2 0.7

10.3 1 1.0 1.78.7 1 0.7 3.34.1 1 17.0 5.17.0 1 12.6 6.96.6 1 18.9 9.27.0 1 37.6 1.62.4 2 1.8 3.22.3 2 43.1 5.63.9 2 3.8 1.1

ce values at the selected current frequencies measured after 1 h immersion in 3.5 wt.%tings based on epoxy component EP processed in dissolver.

Fig. 2. Cross-cut adhesion of cured epoxy primers unmodified (a— EP-M/T, b— EP-D/T)andmodifiedwith various amounts of Nanofil 5, Nanofil 9 or NanoBent ZS-1 using pearl-mill, as well as modified with NanoBent D-ZS-1 using dissolver.

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tested composition. A three-electrode glass cell (with 16.6 cm2

surface sample area and equipped with a graphite counter electrodeand a saturated calomel reference electrode) was used inside theFaraday cage. The impedance data (at frequency 0.002–30,000 Hz,100 mV amplitude of sinusoidal voltage) were collected using EIS300software with FAS2 femtostat (Gamry, USA) and analyzed as a relativeimpedance value for 2mHz and 10 Hz (kΩ per 1 µm of cured filmthickness). Thermogravimetric analysis (TGA) was performed on aDerivatograph OD-102 (MoM, Hungary). The samples (400 mg) ofpulverized and sieved topcoat coatings filled with NanoBent D-ZS-1(paints applied on PET film, conditioned for 14 day at roomtemperature and 4 h at 60 °C) were heated to 900 °C at a rate of10 °C/min under air atmosphere. DSC tests were performed at atemperature range of 0–250 °C (10 °C/min) using DSC Q100 apparatus(TA Instruments). X-ray diffraction curves for the above-mentionedsamples were obtained with X'Pert PRO Philips diffractionmeter(Cu Kα, 1.5–10° 2θ) using X'Pert PRO High Score Philips software.

3. Results

3.1. Epoxy primer compositions and coatings

Conventional viscosity values of liquid epoxy primer (EP) com-positions with and without powders as well as water-slurry ofmodified montmorillonites (descriptions and abbreviations of sam-ples according to Table 1) are presented in Fig. 1. Tested paintscontaining Nanofil 5 or Nanofil 9 exhibited significantly longer flowtime than the reference composition EP-M/T (100 s) and systemswiththe other applied nanofillers. Additionally, the viscosity of thesecoating systems depended on the mMMT content and reached thehighest value for compositions filled with Nanofil 9 (e.g. 187 s for EP/T/N9-5). A flow time parameter was only slightly changed after theincorporation of NanoBent ZS-1 (by milling) or NanoBent D-ZS-1 (bymixing in a dissolver) into the liquid coating compositions; viscosityof samples with the mentioned nanofillers was in the range of 92–103 s (EP/T/ZS-series) and 87–89 s [EP/T/DZS-series; reference com-positions EP-D/T (89 s)].

Cured coating compositions filled with Nanofil-type modifiedmontmorillonites as well as both reference samples without mMMTs(EP-M/T, EP-D/T) exhibit the highest cross-cut adhesion value(0°; Fig. 2). Although a 1 wt.% dose of NanoBent ZS-1 or NanoBentD-ZS-1 did not affect cross-cut type adhesion of primer paints tosteel substrates, it has been found that the former parameter was

Fig. 1. Conventional viscosity values (flow time) of epoxy primer compositions un-modified (a — EP-M/T, b — EP-D/T) and modified with various amounts of Nanofil 5,Nanofil 9 or NanoBent ZS-1 using pearl-mill, as well as modified with NanoBent D-ZS-1using dissolver.

substantially decreased in case of samples with a higher content of thementioned nanofillers (up to 4° for EP/T/ZS-5 and up to 5° for EP/T/DZS-5). Pull-off adhesion tests have confirmed unacceptable lowadhesion of paints with 5 wt.% of either NanoBent ZS-1 or NanoBentD-ZS-1 (0 MPa, Fig. 3). On the other hand, comparable adhesionvalues for all samples containing 2.5 wt.% of any organophilizedmontmorillonites (respectively: 2.3–2.7 MPa for EP/T/N-series and2.4–2.6 MPa for paints with NanoBent nanofillers) have been found.Improved pull-off adhesion [in comparison with the respectivereference samples EP-M/T (2.8 MPa) and EP-D/T (3.1 MPa)] wasonly noticed for a paint with the lowest dose of Nanofil 5 (EP/T/N5-1;3.2 MPa). Other samples containing 1 wt.% of mMMTs reached thesame or slightly decreased (2.7 MPa for EP/T/N9-1) values of theconsidered parameter.

Table 1 presents water absorption values and water resistance ofcured epoxyprimers unmodified andwithmodifiedmontmorillonites.In each case (with the exception of EP/T/N9-2.5) coatings withpowdered mMMTs exhibit remarkably lower water uptake valuesthan appropriate reference sample without a nanofiller (EP-M/T,6.3 wt.% ofwater absorption after 1 day of immersion in distilledwaterand 11.9 wt.% of water absorption after 7 days). Although the additionof either Nanofil 5 or Nanofil 9 into the primer paint decreases thevalue of the mentioned parameter down to 3.2/5.9 wt.% (EP/T/N5-5;respectively after 1 and 7 days of immersion) and 3.0/8.2 wt.% (EP/T/N9-1), coatings filled with NanoBent ZS-1 reach the lowest value ofwater uptake (1.5/4.1 wt.%; EP/T/ZS-1). Comparing reference samples

Fig. 3. Pull-off adhesion of cured epoxy primers unmodified (a — EP-M/T, b — EP-D/T)and modified with various amounts of Nanofil 5, Nanofil 9 or NanoBent ZS-1 usingpearl-mill, as well as modified with NanoBent D-ZS-1 using dissolver.

Fig. 4. Conventional viscosity values (flow time) of epoxy topcoat compositions un-modified (a — ET-M/T, b — ET-D/T) and modified with various amounts of Nanofil 5,Nanofil 9 or NanoBent ZS-1 using pearl-mill, as well as modified with NanoBent D-ZS-1using dissolver.

Fig. 6. Hardness of cured epoxy topcoats unmodified (a — ET-M/T, b — ET-D/T) andmodified with various amounts of Nanofil 5, Nanofil 9 or NanoBent ZS-1 using pearl-mill, as well as modified with NanoBent D-ZS-1 using dissolver.

638 K. Kowalczyk, T. Spychaj / Surface & Coatings Technology 204 (2009) 635–641

EP-D/T (based on epoxy dispersion processed in a dissolver) withpaints containing NanoBent D-ZS-1 (water-slurry of NanoBent ZS-1)similar high effectiveness of the mentioned form of a nanofiller wasobserved;water absorption parameterwas decreased from3.5/7.0 wt.%(EP-D/T) down to 1.9/2.3 wt.% for EP/T/DZS-2.5. Nevertheless, onlythat type of tested coatings (i.e. filledwith various amounts ofNanoBentD-ZS-1) reaches 2-day long water resistance. Other samples (i.e. with-out mMMTs and with powdered mMMTs) were already substantiallyblistered after 24 h of immersion in distilled water.

Relative impedance values of cured primers with and withoutorganophilized montmorillonites are shown in Table 1. Based on thedata collected, improved barrier properties for coatings based onpaints filled with 2.5 wt.% of NanoBent D-ZS-1 were only observed (incomparison with appropriate reference coatings); in this case arelative impedance value was increased from 37.6 kΩ/µm (referencesamples EP/D-T) to 43.1 kΩ/µm (at 2mHz; EP/T/DZS-2.5) and from1.6 kΩ/µm up to 5.6 kΩ/µm (at 10 Hz). The other coatings withmMMTs (EP/T/DZS-1 and EP/T/DZS-5) reach low relative impedance,therefore that data can be directly related neither to water absorptionnor to water resistance value of the mentioned samples and referencecoatings EP-D/T (Table 1).

3.2. Epoxy topcoat compositions and coatings

Flow time values of liquid epoxy topcoat (ET) compositions withand without powders or water-slurry of organophilized montmor-

Fig. 5. Cross-cut adhesion of cured epoxy topcoats unmodified (a— ET-M/T, b— ET-D/T)andmodifiedwith various amounts of Nanofil 5, Nanofil 9 or NanoBent ZS-1 using pearl-mill, as well as modified with NanoBent D-ZS-1 using dissolver.

illonites are shown in Fig. 4. In comparison with ET-M/T referencecomposition (flow time 175 s), based on premilled epoxy dispersion,the tested samples with powdered mMMTs represent the followingcorrelation between a nanofiller content and the features mentioned:(i) the highest viscosity of liquid paints with Nanofil 5 is observedfor that with mediummMMT content (217 s for ET/T/N5-2.5), (ii) vis-cosity of compositions slightly increases with the growth of theNanofil 9 content above 2.5 wt.%, and (iii) viscosity of paint withNanoBent ZS-1 jumps up to 205 s, if the smallest dose of thatnanofiller is used. Significantly shorter flow times than for ET-M/Twere noted for compositions with 1 and 5 wt.% of Nanofil 5: (158 and153 s, respectively) and with 5 wt.% of NanoBent ZS-1: 155 s. Similarviscosity values were observed for a composition based on epoxydispersion processed in a dissolver without mMMT (154 s for ET-D/T)and that with a medium content of NanoBent D-ZS-1 (154 s for ET/T/DZS-2.5). The other coating compositions with the water-slurry ofmentioned nanofiller added in an amount 1 or 5 wt.% into the epoxydispersion during mixing in a dissolver — reach the lowestconventional viscosities (140 and 142 s, respectively) as comparedwith the other tested liquid paints (Fig. 4).

The cured coatings with and without Nanofil 5 and Nanofil 9nanofillers adhere very well to steel substrates, i.e. exhibit 0° of cross-cut adhesion (Fig. 5) but all samples with NanoBent ZS-1 indicatesignificantly depreciated cross-cut adhesion values. The highercontent of the nanofiller, the lower the adhesion value. Althoughcompositions filledwith a 5 wt.% content of NanoBent-type nanofillers

Fig. 7. Abrasion resistance of cured epoxy topcoats unmodified (a— ET-M/T, b— ET-D/T)and modified with various amounts of Nanofil 5, Nanofil 9 or NanoBent ZS-1 using pearl-mill, as well as modified with NanoBent D-ZS-1 using dissolver.

Table 2Barrier properties of cured epoxy topcoat modified with organophilized montmorillonites.

mMMT type mMMT content (wt.%) Coating acronym Water absorption1 (wt.%) Water resistance (days) Relative impedance2 (kΩ/µm)

1 day 7 days 2mHz 10 Hz

– 0 ET-M/T3 6.0 11.0 1 18.6 7.6Nanofil 5 1 ET/T/N5-1 6.6 14.2 1 1.9 3.6

2.5 ET/T/N5-2.5 6.2 11.1 1 31.7 20.15 ET/T/N5-5 3.2 6.9 1 103.1 42.0

Nanofil 9 1 ET/T/N9-1 6.7 13.3 1 3.6 2.22.5 ET/T/N9-2.5 6.9 12.3 1 8.0 5.55 ET/T/N9-5 6.8 10.0 1 14.5 9.9

NanoBent ZS-1 1 ET/T/ZS-1 6.6 11.4 1 6.4 7.72.5 ET/T/ZS-2.5 5.3 9.9 1 7.6 8.85 ET/T/ZS-5 3.5 3.6 1 161.1 58.7

– 0 ET-D/T4 5.7 11.7 1 47.6 17.6NanoBent D-ZS-1 1 ET/T/DZS-1 2.7 2.4 1 24.9 17.5

2.5 ET/T/DZS-2.5 3.0 2.9 3 71.5 29.05 ET/T/DZS-5 3.9 4.1 1 42.3 25.1

1 — After 1- and 7-day immersion of cured coatings in distilled water; 2 — relative impedance values at the selected current frequencies measured after 1 h immersion in 3.5 wt.%NaCl solution; 3 — coatings based on epoxy component ET processed in pearl-mill; 4 — coatings based on epoxy component ET processed in dissolver.

Table 4Relative impedance value of cured epoxy primer/epoxy topcoat coating systemmodified with NanoBent D-ZS-1.

639K. Kowalczyk, T. Spychaj / Surface & Coatings Technology 204 (2009) 635–641

exhibit unacceptable adhesion (4° for ET/T/ZS-5 and ET/T/DZS-5),samples with the lowest amount of NanoBent D-ZS-1 (1 wt.%) reachthe best value of the analyzed parameter (0°).

Coatings with 2.5 wt.% of NanoBent ZS-1 powder nanofillerindicate higher hardness: 86 units (Fig. 6) and abrasion resistance:856 g/µm (Fig. 7) than the reference paint ET-M/T without mMMTs:80 units of Buchholz hardness and 817 g/µm of abrasion resistance.However, neither hardness nor abrasion resistance values of thesesamples (ET/T/ZS-2.5) exceed relevant values of ET-D/T referencepaint based on epoxy dispersion premixed in a dissolver, i.e. 87 unitsof hardness and 865 g/µm of abrasion resistance. On the other hand,coatings with 1 wt.% of NanoBent D-ZS-1 exhibit an acceptablehardness value (83 units) and slightly lower attrition (870 g/µm).

The incorporation of NanoBent-type modified montmorilonites –

mainly as water-slurry – into the epoxy topcoat compositiondecreases the water absorption of coatings cured on steel substrates(Table 2). Comparing with both systems without mMMTs, coatingsmodified with NanoBent D-ZS-1 as well as with higher doses ofNanoBent ZS-1 (ET/T/ZS-2.5 and ET/T/ZS-5) have exhibited aremarkably lower water uptake after 1- and 7-day immersion testsin distilled water. Similarly reduced values in a case of samplescontaining Nanofil-type nanofillers have been observed only forcoatings with 5 wt.% of Nanofil 5, i.e. 3.2 wt.% after 1 day and 6.9 wt.%after 7 days of immersion. Additionally, the water absorptionresults for ET/T/N5-5 and ET/T/ZS-5 correlate with relevant relativeimpedance data presented in Table 2 (as compared with base coatingET-M/T).

However, the water absorption of ET/T/DZS-1 coatings wasspectacularly reduced down to the value much less than 3.0 wt.%,whereas the parameter for reference coatings ET-D/T is 5.7 wt.% inmomentary immersion and 11.7 wt.% in long-lasting immersion tests.The highest water resistance (3 days of immersion) was observed forsamples with 2.5 wt.% of NanoBent D-ZS-1. High barrier property ofthese coatings has been confirmed by an electrochemical impedance

Table 3Thermal stability and Tg values of cured epoxy topcoat modified with NanoBent D-ZS-1.

Sample acronym Weight loss temperature (°C) Tg1 (°C)

1 wt.% 2.5 wt.%

ET-D/T 180 270 50.3ET/T/DZS-1 185 263 –

ET/T/DZS-2.5 185 260 47.2ET/T/DZS-5 195 255 15.6NanoBent ZS-1 192 205 –

1 — Glass transition temperature.

spectroscopy test (Table 2). Samples ET/T/DZS-2.5 have reached anevidently higher relative impedance value for two considered currentfrequencies, i.e. 71.5 kΩ/µm at 2mHz and 29 kΩ/µm at 10 Hz, than theunmodified reference coatings ET-D/T (47.6 kΩ/µm at 2mHz and17.6 kΩ/µm at 10 Hz) or other coatings with that nanofiller. Thelowest relative impedance parameters were observed for samplesfilled with 1 wt.% of NanoBent D-ZS-1 (24.9 kΩ/µm at 2mHz and17.5 kΩ/µm at 10 Hz). However, these results of relative impedancedo not correlate with the data of the water absorption test because ET/T/DZS-1 coatings have reached an extremely lowwater uptake but alsolow value of impedance.

Results of thermogravimetric tests for epoxy topcoats withNanoBent D-ZS-1 are presented in Table 3. The temperature for1 wt.% weight loss of samples directly depends on nanofiller contentand increases from 180 °C up to 195 °C for coatings with 5 wt.% ofmMMT. It was found that thermal stability of the modified coatings athigher temperature is deteriorated in comparison with the referenceone. The lowest temperature values for 2.5 wt.% weight loss ofcoatings have been noticed for ET/T/DZS-5 (255 °C).

3.3. Epoxy primer/topcoat coating system

Based on the effects of mechanical and barrier property tests ofepoxy primer and epoxy topcoat paints with and without variousmMMTs, the primer/topcoat coating system filled with a selectedmost effective organophilized montmorillonite has been prepared.Four-layer samples with 2.5 wt.% NanoBent D-ZS-1 denoted as EP/ET/DZS-2.5 consisting of two layers of the primer EP/T/DZS-2.5 and twolayers of the topcoat ET/T/DZS-2.5 as well as four-layer referencesamples EP-D/ET-D based on two layers of EP-D/T and two layers of

Coating system EP-D/ET-D1 EP/ET/DZS-2.52

Immersion time 10 min 24 h 10 min 24 h

Relative impedance3 (kΩ/µm) 2mHz 2210 4.5 1800 22.010 Hz 110 2.1 106 9.1

Relative impedance decrement4

(kΩ/µm)2mHz 2205±413 1778±24010 Hz 108±4 97±5

1 — Based on EP-D/T (primer) and ET-D/T (topcoat); 2 — based on EP/T/DZS-2.5(primer) and ET/T/DZS-2.5 (topcoat); 3 — relative impedance values at the selectedcurrent frequencies measured after 10 min and 24 h immersion in 3.5 wt.% NaClsolution; 4 — decrement of relative impedance values (at the selected currentfrequencies) in relation to measurements after 10 min and 24 h immersion in 3.5 wt.%NaCl solution.

Fig. 8. Impedance curves of cured epoxy primer/topcoat coating systems: unmodifiedEP-D/ET-D (194 µm) and modified with organophilized montmorillonites (EP/ET/DZS-2.5; 196 µm) after 10 min and 24 h immersion in 3.5 wt.% NaCl solution.

Fig. 9. Location scheme of organophilized montmorillonites platelets/grains insidecured dispersion paint: coats with semihydrophilic (a) or hydrophobic mMMT (b).

640 K. Kowalczyk, T. Spychaj / Surface & Coatings Technology 204 (2009) 635–641

ET-D/T were tested using the EIS method. Relative impedance, after10 min and 24 h of immersion in NaCl water solution, and also relativeimpedance decrement values noticed for the analyzed EP/ET coatingsystems are presented in Table 4. Examples of impedance curves fortwo samples are shown in Fig. 8. As it may be seen from Table 4 at thebeginning of the EIS test coatings with 2.5 wt.% of NanoBent D-ZS-1have exhibited a slightly lower relative impedance value (1800 kΩ/µm at 2mHz and 106 kΩ/µm at 10 Hz) than the sample without ananofiller (2210 kΩ/µm at 2mHz and 110 kΩ/µm at 10 Hz). Never-theless, larger relative impedance decrement for data collected after10 min and 24 h of immersion in NaCl electrolyte was observed forreference coatings EP-D/ET-D (Fig. 8 and Table 4). In that case, theanalyzed parameter was spectacularly reduced down to 4.5 kΩ/µm at2mHz and 2.1 kΩ/µm at 10 Hz, whereas a relative impedance value oftested coatings containing NanoBent D-ZS-1 has reached values22 kΩ/µm and 9.1 kΩ/µm, respectively.

4. Discussion

Properties of a liquid as well as cured epoxy paints based on resindispersions with a posteriori added organoclays depend on a form ofapplied nanofillers (powder, water-slurry), their dose and anincorporation method. Nevertheless the type of modified montmor-illonites (type of ammonium salt used for clay organophilization)most evidently affects features of coatings. That has been found in theresults of a comparative analysis of several mechanical as well as

Table 5Influence of organophilized montmorillonites addition on some coating properties.

Paint Coatingproperty

mMMTtype

The highestimprovementindex (%)

mMMTcontent(wt.%)

Epoxy primer Pull-off adhesion Nanofil 5 14 1Water absorption1 NanoBent D-ZS-1 67 2.5Water resistance NanoBent D-ZS-1 – 1–5Relative impedance2 NanoBent D-ZS-1 15 2.5

Epoxy topcoat Hardness NanoBent ZS-1 8 2.5Abrasion resistance NanoBent ZS-1 5 2.5Water absorption1 NanoBent D-ZS-1 80 1Water resistance NanoBent D-ZS-1 – 2.5Relative impedance2 NanoBent ZS-1 866 5Thermal stability NanoBent D-ZS-1 15 3 5

1 — After a 7-day immersion in distilled water; 2 — relative impedance at 2mHz; 3 —

improvement index in (°C).

barrier features of the tested coatings (Table 5). In most cases, coatingcompositions with semihydrophilic NanoBent-type nanofillersreached considerably better properties than those with hydrophobicmontmorillonites, i.e. with Nanofil 5 or Nanofil 9. NanoBent D-ZS-1more effectively enhanced water resistance (relative impedance) andminimized water absorption of EP and ET-type coatings. A decrease inwater uptake: 67% for the primer and 80% for the topcoat was foundwhile pulverized NanoBent ZS-1, added in amount 2.5 wt.%, improvedhardness (8%) and abrasion resistance (5% for topcoat). On the otherhand, an increased adhesion value onto steel substrates has only beenobserved for coatings including Nanofil 5. For samples EP/T/N5-1, thediscussed pull-off adhesion parameterwas upgraded by about 14%, i.e.from 2.8 MPa for EP-M/T up to 3.2 MPa. The observed results i.e.significantly lower adhesion, relatively high mechanical (hardness,abrasion resistance) and barrier properties of samples with eitherNanoBent ZS-1 or NanoBent D-ZS-1 could be connected with specificlocations of such organoclays particles (platelets/grains) inside thecured epoxy coatings. Probably, the mentioned semihydrophilicmontmorillonites – due to the presence of some OH groups in the

Fig. 10. XRD curves of cured epoxy topcoats unmodified (ET-D/T) and modified withorganophilized montmorillonites.

641K. Kowalczyk, T. Spychaj / Surface & Coatings Technology 204 (2009) 635–641

modifier molecules – have been dispersed into separate plateletsduring organophilization treatment and/or high-shear incorporationprocess and more uniformly deposited onto the surface of epoxydispersion particles (Fig. 9, Scheme a). Exfoliation of NanoBent ZS-1platelets cannot be confirmed by X-ray diffraction tests due to thepresence of large amount of inorganic pigments and fillers (TiO2, ironoxides with particle sizes above 12 µm) inside the tested coatings.XRD patterns of topcoats unfilled and filled with the organophilizedmMMT were similar and no extra peaks at low 2θ angle values couldbe observed (Fig. 10). Unfortunately the mMMT platelets distributionin epoxy matrix of coatings, containing the mentioned microsizedadditives cannot be analyzed with transmission electron microscopy.We suppose that monolayers of NanoBent ZS-1 separate and seal eachepoxy semisolid drop, therefore, they affect adhesion of curedcoatings into steel substrates, i.e. disturb “binder–steel” interactionin dispersion paints with higher doses of mMMTs, improve hardnessand abrasion resistance as well as barrier properties of the coatings.On the other hand, hydrophobic platelets of the Nanofil-typemodifiedmontmorillonite were settled (in a form of a scattered multilayerpacket) inside the cured coatings and acted as a conventional fillerwith micrometric grain size (Fig. 9, Scheme b). These organoclays didnot create a uniform barrier monolayer onto epoxy resin particles,thus good adhesion into steel substrates has been observed.

In most cases, the features of the investigated coating composi-tions filled with modified montmorillonites depend on the content oforganoclays in the sample. It is evident for coatings with eitherNanoBent ZS-1 or NanoBent D-ZS-1 but also for samples with Nanofil-type nanofillers. The organophilized aluminosilicates incorporatedinto the paints in the amount of 1–2.5 wt.% improved mostmechanical as well as barrier parameters of the cured coatings,whereas larger doses of mMMTs usually have deteriorated that effect(Figs. 3, 5 and 7). Probably the excess of layered nanofiller grains/platelets located between epoxy resin dispersion particles causedsignificant isolation to each other and disturbed the coalescence aswell as curing process. Themolecules of hardener could not effectivelymigrate into epoxy resin droplets surrounded with layers of mMMTplatelets, they adsorbed onto these platelets (partially neutralizedpolyamine curing agent acts as a co-modifier of mMMT) and thecrosslinking of the binder has not occurred effectively. In such a casethe glass transition temperature (Tg) did not rise during coatingsconditioning and reached lower value (e.g. 15.6 °C for specimen withthe highest amount of NanoBent D-ZS-1; Table 3) comparing to thesample without nanofiller. As a consequence the prepared coatingswith the largest doses of mMMTs were not fully homogeneous and/orcrosslinked and exhibited an unacceptably low adhesion (Figs. 2, 3and 5) as well as degradation of other properties (Figs. 6 and 7).

Modified montmorillonite NanoBent D-ZS-1 affects the thermalstability of epoxy topcoat. Although, that property increases withhigher nanofiller load in coatings, it is significantly improved only attemperatures below 200 °C (Table 3). Weight loss of samplesincreases over that temperature due to limited thermal stability ofthe modified montmorillonite caused by degradation of ammoniumsalt used for organophilization. Powdered NanoBent ZS-1 starts to

decompose in air atmosphere at about 190 °C and it is the highestexploitation temperature for coatings modified with that organoclay.

5. Conclusions

Based on the test results, the following conclusions can be drawnon introduction of organophilized aluminosilicates a posteriori intoepoxy dispersion paints:

– the effectiveness of organophilized montmorillonite in epoxydispersion paints depends on its dosage, modification type (hydro-philicity of ammonium modifier) and incorporation method;

– between investigated nanofiller types water-slurry of semihydro-philic NanoBent ZS-1 is the most suitable modified montmoril-lonite for epoxy dispersion paints cured with polyamine hardener;

– incorporation of NanoBent ZS-1 into epoxy compositions improvestheir hardness and abrasion resistance, barrier properties and alsothermal stability up to 200 °C;

– NanoBent D-ZS-1 should be incorporated into epoxy dispersionpaints (using dissolver) in the amount of 2.5 wt.%. Larger doses oforganophilized nanofiller negatively influence on abrasion resis-tance, barrier properties as well as adhesion of coatings onto steelsubstrates, whereas Nanofil-type organoclays do not significantlyaffect the latter parameter.

Acknowledgements

The project was financed from the European Social Fund, the Statebudget of the Republic of Poland within the framework of IntegratedRegional Operational Programme and Polish Committee for ScientificResearch (project no. 3 T08E 038 30).

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