Nano-clay filled polyester coatings

G

P

N

DD

AA

KNpram

1

acSbandasaSunbfinbtlfitd

n

0h

ARTICLE IN PRESS Model

OC-3145; No. of Pages 6

Progress in Organic Coatings xxx (2013) xxx– xxx

Contents lists available at SciVerse ScienceDirect

Progress in Organic Coatings

jou rn al hom ep age: www.elsev ier .com/ locate /porgcoat

ano-clay filled polyester coatings

. Bellisario ∗, F. Quadrini, L. Santoepartment of Industrial Engineering, via del Politecnico, 1, 00133 Rome, Italy

a r t i c l e i n f o

rticle history:vailable online xxx

eywords:ano-composite

a b s t r a c t

Polyester composite coatings were produced by mixing un-saturated polyester (HP) resin and function-alized montmorillonite (MMT) powder. The effect of the mixing conditions on the final performances ofthe composite coatings was accurately evaluated: samples were produced with different MMT contents(up to 5 wt%) and stirring time (up to 1200 min). Rheological analyses of the un-catalyzed resin matrix

olyester coatingsheological propertiesdhesion and wear resistanceontmorillonite

were performed as well as tribological and scratch tests of coatings. Results show the strong effect ofthe mixing time on the performance of the MMT filled coatings. This effect is never negligible and canovercome the effect of the MMT content. After 20 h mixing, a 1 wt% filled mixture reaches a viscositysimilar to a 5 wt% mixture after 30 min. By increasing the resin viscosity, the resulting coating thicknessincreases as well and this effect seems to dominate the tribological behavior of coatings rather than it’sfilling. Best results were obtained with low mixing times and filler contents.

. Introduction

New coating solutions with high strength and durability arelways required for industrial applications: polymer matrix nano-omposites are good candidates for high performance coatings.everal fillers and matrices are commercially available and cane selected in dependence of the specific use and their mutualffinity. Structural and functional properties such as strength, hard-ess, adhesion, gloss, impact [1], gas transport [2] can be tailoredepending on the filler–matrix combination. However, developing

nano-composite coating is a very complex task due to several rea-ons: difficulties in nano-filler exfoliation, high processing times,nd need of defining and optimizing a proper coating technology.ome technological solutions seem to be easier as in the case ofnsaturated polyester (UP) resin with nano-fillers. In particular,ano-montmorillonite (MMT) is a cheap reinforcement which cane functionalized before its mixed with a polyester matrix. Nano-llers can be added into the un-cured liquid resin and the partialano-particle exfoliation can be obtained by mechanical mixingefore adding the resin catalyzer. In facts, nano-filler exfoliation ishe main problem to face to obtain high material performances withow filler content. Despite the simplicity of this process, nano-claylled polyesters is rarely used for coatings and additional scien-ific information on their process conditions or performances are

Please cite this article in press as: D. Bellisario, et al., Nahttp://dx.doi.org/10.1016/j.porgcoat.2013.05.030

eemed necessary.Several data are present in the scientific literature about bulk

ano-composites. In 2006, Jawahar et al. studied the tribological

∗ Corresponding author.E-mail address: [email protected] (D. Bellisario).

300-9440/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.porgcoat.2013.05.030

© 2013 Elsevier B.V. All rights reserved.

behavior of clay–thermoset polyester nano-composites: compos-ites were prepared by changing the filler content from 1 wt% to5 wt% [3]. They measured the highest wear resistance and the leastfriction coefficient for clay content of 3 wt%, with an 85% improve-ment in wear strength in comparison with the unfilled resin. In2008, Jo et al. discussed the positive effect of the nano-MMT rein-force on the UP resin also in terms of mechanical and thermalproperties. In these studies, the effect of the resin-filler mixing con-ditions on the final performances of the nano-composite was notstudied although the definition of a correct mixing phase is nottrivial [4].

In 2007, Swain and Isayev investigated rheology, structureand properties of high density polyethylene/organo–clay nano-composites. In order to enhance the mixing phase, they proposedthe modification of a single screw extruder by integrating an ultra-sound die operating at various amplitudes [5]. Mechanical testswere used to evaluate the effect of the nano-clay filler as wellas in a study of Kim et al. (2009) who investigated the effectof modified carbon nano-tubes in a matrix of thermotropic liq-uid crystal polyester [6]. In the latter case, dynamic mechanicalanalyses (DMA) were also used: the combination of mechanicaltesting and DMA analysis seems to be appropriate to investigatethe filler–resin interaction. Unfortunately, thermoplastic nano-composites are prepared by means of melt blending and resultscannot be extended to the case of liquid state processes.

More recently (2011), Rozman et al. have measured the ten-sile properties of kenaf/UP composites with the addition of MMT:

no-clay filled polyester coatings, Prog. Org. Coat. (2013),

kenaf filler loading allowed reducing matrix material whereas theMMT content led to higher mechanical properties [7]. A similarpositive effect would be expected also in the case of coatings. In2008, Kowalczyk and Spychai studied epoxy coatings with modified

dx.doi.org/10.1016/j.porgcoat.2013.05.030


http://www.sciencedirect.com/science/journal/03009440

http://www.elsevier.com/locate/porgcoat

mailto:[email protected]


ING Model

P

2 Organ

MaTebsant[

eahp2d

vpntdfp1ccbroacmam

cBtafthf

2

2

imMT(s1aa

2

w

ARTICLEOC-3145; No. of Pages 6

D. Bellisario et al. / Progress in

MT, in the amount of 2.5 wt% and 5 wt%: hardness, scratch andbrasion strength were positively affected by the nano-filler [8].he same nano-composite coating was also investigated by Davoodt al. (2010) who introduced organo-clay up to 4 wt% and obtainedest results for 3 wt% filled coatings [9]. They took care of the disper-ion process which was performed by means of high-shear mixingnd ultrasonication. In epoxy coatings, nano-MMT can improveot only wear resistance, which is correlated with scratch resis-ance [10], but also additional performances such as anti-corrosion11,12].

Dealing with UP resins, interesting results were obtained by Seet al. in 2009 [13], who proposed a novel nano-gelcoat for marinepplication, and very recently by Piazza et al. in 2012 [14], whoave defined a polyester-based powder coating with MMT nano-articles. In the latter case, in order to improve the filler dispersion,

wt% and 4 wt% MMT was inserted in the polyester resin matrixuring the powder coating formulation.

The combination of MMT nano-fillers and UP resin seems to beery interesting for coatings, but it has not yet fully investigated. Inrevious work, the authors prepared polyester–montmorilloniteano-composite coatings by the in situ intercalative polymeriza-ion method [15]. Coatings were deposited on aluminum and highensity polyethylene substrates by the spin coating method. Aast fabrication procedure was utilized as 1 h was sufficient torepare each coated sample. The nano-clay content ranged from

wt% to 5 wt%. Mechanical tests were performed on the nano-omposite coatings by macro-indentation and an increase in theoating strength was measured up to 3 wt% nano-clay content foroth substrates. The choice of a fast fabrication procedure waselated to industrial need of reducing production times. By meansf the same procedure, thick films were also prepared for DMAnalyses [16]. The final films had a thickness of 250 �m and a nano-lay content ranging from 0 wt% to 10 wt%. The maximum in theechanical performance was obtained at a clay content of 1 wt%

t which an increase of about 55% for the storage modulus waseasured in comparison with the unfilled resin.Thanks to these studies, the authors evaluated the complex

orrelation between the filler dispersion and the coating process.y improving the filler dispersion, resin mobility reduces both inhe un-cured and in the cured state. The latter effect is positives higher mechanical and surface properties are expected but theormer effect is negative as the resin viscosity increases affectinghe coating process. Therefore, in the current study, the authorsave investigated the effect of the mixing time on the final per-

ormances of MMT filled polyester coatings.

. Materials and methods

.1. Materials

Composite samples and coatings were fabricated by dispers-ng a nano-clay powder into an un-saturated polyester resin. The

ontmorillonite nano-filler was Dellite 43B (by Laviosa Chimicaineraria) which is derived from especially purified natural MMT.

he nano-clay was modified with a quaternary ammonium saltdimethyl benzylhydrogenated tallow ammonium). The particleize, in dry conditions, was about 7–9 nm with a bulk density of.6 g/cm3. The resin matrix was un-saturated polyester for marinepplications (by 3C, Italy). Resin cure was achieved after the cat-lyzation with methylethylketone (2 wt%).


.2. Coating deposition

The procedure for the nano-composite coating fabricationas accurately defined: the clay powder was poured into the

PRESSic Coatings xxx (2013) xxx– xxx

un-catalyzed polyester resin and the mixture was stirred by a mag-netic stirrer for different mixing times (0 min, 5 min, 30 min, 60 minand 1200 min). During mixing, the un-cured resin was kept in asealed container to avoid styrene evacuation. The filler content waschanged between 0 wt% and 5 wt%. After stirring, the catalyst wasadded and mixed for the following 30 s.

For coatings, a drop of the catalyzed mixture was dripped by astepper on the substrate to coat and spun by a spin-coater. Alu-minum square samples (20 mm × 20 mm × 1 mm) were used assupports after cleaning. A two stage spinning process was appliedto allow a uniform thickness of the coating. In the first stage, aspeed of 1000 rpm was applied for 3 s. In the second stage a higherspeed (2500 rpm) was used for 5 s. Coatings were cured in a stovefor 30 min at the temperature of 80 ◦C. Finally, the samples wereleft to cool and settle down at room temperature for 24 h beforetesting.

2.3. Rheology

The un-cured resin mixtures after different mixing times weretested with a rotational rheometer (AR 2000ex by TA instruments).Stationary tests were carried out to evaluate the effect of the mix-ing time on the rheological behavior of un-cured composites. Testswere conducted at a fixed shear rate of 10 rad/s, a temperature of30 ◦C, after a 1 min pre-shear at 1 rad/s, and for a time of 5 min.

2.4. Surface characterization

The morphology of the coatings was investigated by means of acontact gauge Taylor Hobson Surface Topography System (TalySurfCLI 2000, Taylor Hobson, Leicester, UK), using the inductive gaugewith a resolution range from 9.1 nm to 511 �m. For each sample,the surface morphology was analyzed by recording 1000 patterns,6 mm spaced along the x axis and 3 mm along the y axis, so as tocover an area wide enough to be representative of the entire sur-face structure. The coatings were located under the gauge and themeasurement area was placed at the center of the sample.

2.5. Scratch tests

Scratch tests were performed by using a Micro-Combi Tester(CSM Instruments, Peseaux, Switzerland). Spherical tip micro-contact indenters (Rounded Conical Rockwell C diamond indenter,with 200 �m tip radius) were used in progressive mode (track3 mm, scratch speed 1 mm/min, load from 100 mN to 30 N) atroom temperature (20 ◦C) and 40% RH. Scratches were repli-cated to ensure data repeatability: the minimum distance betweenscratches was 4 mm.

During the scratch test, the indenter first profiled the surfacewith a very small load (pre-scan, at 100 mN). Then, the indenterwent back to the starting location and produced the track (loadedscan, at 100 mN).

Normal and tangential forces were on-line monitored duringthe test. Besides, during the pre-scan, the system software storedthe starting surface profile, which was finally subtracted from theloaded scratch scan profile to determine the depth of surface pen-etration (dp). After the loaded scan, a post-scan with a very smallload was carried out to get an estimate of the magnitude of theresidual scratch ditch (dr) and the extent of immediate recovery(dp−dr). Being the distance between the indenter and the evalu-ation unit measured in terms of the movement of the translationtable, positional values of load and penetration could be addressed


to the residual deformation at the same position.Lastly, using the integrated microscope of the scratch tester

machine and the related software it was possible to generate adetailed panoramic view of each entire scratch. These images were


ARTICLE IN PRESSG Model

POC-3145; No. of Pages 6

D. Bellisario et al. / Progress in Organic Coatings xxx (2013) xxx– xxx 3

Fd

us

2

e(iHacwam

3

3

tftitemMiqnfi

Ft

composite coatings with 1 wt% MMT content and in Fig. 5b for the

ig. 1. Shear viscosity as a function of the time for a mixing time of 5 min and twoifferent MMT contents.

sed to study magnitude and shape of residual deformation aftercratch tests.

.6. Reciprocating tribometer

Tribological behavior of MMT nano-composite coatings wasvaluated by using a reciprocating-type ball-on-flat tribometerCSM Instruments) with a counter-body spherical pin (6 mmn diameter) made of 100Cr6 (manufacturer nominal hardness:V = 7 GPa). Sliding tests were performed in room conditions (20 ◦Cnd 40% RH) without lubricant. The slide-way and the samples wereleaned with isopropanol. Two different vertical loads of 2 N and 5 Nere used at a sliding speed of 0.0566 m/s, an amplitude of 6 mm

nd a total sliding distance of 50 m. The friction coefficient wasonitored during the tests.

. Results and discussion

.1. Rheology

Rheological tests were done to measure the shear viscosity ofhe composite mixtures with time. A comparison between two dif-erent mixture compositions is reported in Fig. 1 for the mixingime of 5 min. Higher MMT contents lead to higher shear viscos-ty because of the interaction between the MMT aggregates andhe resin matrix. By increasing the time, the shear viscosity gen-rally decreases due to the molecular orientation of the polymerolecules. Instead, an increase is observed for the case of the 5 wt%MT filled mixture. Due to the partial MMT exfoliation, stronger


nteractions between resin and filler take place with the conse-uence of the reduction of molecular mobility. Higher times areecessary for the 1 wt% MMT filled mixture because of the lowerller content. In fact, Fig. 2 shows the comparison of the shear

ig. 2. Shear viscosity as a function of the time, the MMT content, and the mixingime.

Fig. 3. Shear viscosity for all the tested mixtures.

tests for all the other mixing times. A shear viscosity increase isbarely visible after 1200 min (20 h) mixing for the 1 wt% filled sam-ple whereas after this time an almost constant value is observedfor the 5 wt% filled mixture.

A last comparison is given in Fig. 3 where the shear viscosityvalue at test end is reported.

In the case of 5 wt% MMT content, the viscosity continuouslyincreases with mixing time. At lower MMT contents, the effect ofthe mixing time is appreciable only after long mixing periods.

The increase of the shear viscosity is surely a direct measure ofthe dispersion efficiency of the stirring process. From this point ofview high viscosities should be preferred. Unfortunately, high vis-cosities lead to problems during coating application because of thedifficulty in realizing a homogenous resin layer over the substrate.Apart from the resin flow, reducing molecular mobility affects resinpolymerization during cure.

3.2. Scratch tests and surface characterization

Fig. 4 summarizes the thickness measurements taken on com-posite coatings after curing. Basically, the composite coatings witha stirring time of 1200 min were too thick, and for this reason theyshould be considered as unacceptable (being the thickness mag-nitude one order higher than the others). The remaining coatingsshowed a thickness value in the range of 62–83 �m. In order toevaluate the surface morphology, a series of three profiles, each6 mm long, was measured for each sample.

The average profile of each sample is reported in Fig. 5a for the


5 wt%. The profiles of the composite coating with a mixing time of1200 min are very irregular. Samples with high MMT content have a

Fig. 4. Coating thickness for all the coatings.




4 D. Bellisario et al. / Progress in Organic Coatings xxx (2013) xxx– xxx

F5

mAoAt

fseaAsit

F(

ig. 5. Surface profiles of coatings with different MMT content: (a) 1 wt% and (b) wt%.

ore irregular surface morphology characterized by larger waves.t lower filler percentage, samples are more leveled mainly becausef the greater flow of the resin mixture during the coating process.ccordingly, good or poor leveling can be certainly correlated to

he viscosity trend.A preliminary evaluation of the adhesion behavior of the dif-

erent composite coatings was made by means of progressive loadcratch tests. The samples with a mixing time of 1200 min werexcluded due to their higher thicknesses which invalidate thebility of the test in evaluating the coating–substrate adhesion.


ccordingly, progressive load scratch tests were carried out totudy the load dependent deformation response of the compos-te coatings to a continuous range of loads. Fig. 6a and b reporthe trends of the penetration depth and the residual depth vs. the

ig. 6. Penetration and residual depth trends during progressive load scratch tests:a) 1 wt% and (b) 5 wt%.

Fig. 7. Micrographs of the scratch patterns.

scratch length. The penetration depth increases with scratch length,with discontinuities which correspond to the start of the coatingfailure. Maximum penetration depths in the range of 140–160 �mwere achieved during the tests, therefore the scratching indentercame in contact with the underlying metal substrate, being thecoating thickness in the range of 65–75 �m.

At low scratch loads (<10 N), coatings with a mixing time of60 min for both MMT contents show the least penetration resis-tance. At higher loads (>10 N), all the samples show an increasingtrend of the penetration depth and the complete failure of the coat-ing (Fig. 7). The samples with a mixing time of 5 min showed higher


coating strengths. In terms of filler effect, it was possible to observethat composite coatings with 1 wt% MMT content presented abetter adhesive behavior if compared with the 5 wt% filled sam-ples. Furthermore, their residual scratch patterns (i.e. the scratch




D. Bellisario et al. / Progress in Organic Coatings xxx (2013) xxx– xxx 5

p(

o

tbo

3

ctsfa

irdssc

F(

Fig. 10. Friction coefficient from sliding tests at the normal load of 5 N and differentMMT content: (a) 1 wt% and (b) 5 wt%.

Fig. 8. Thickness and normal force at failure for all the coatings.

attern after the release of the scratch loads) are definitely less deepas shown in Fig. 6a).

Fig. 8 reports the thickness of the composite coating as a functionf the value of the normal force at which the coating breaks.

There is a direct correlation between the two values: the higherhe thickness of the coating, the higher the normal force required toreak it. Moreover, the effect of coating thickness seems to prevailn the effect of the filler content in the experimented ranges.

.3. Reciprocating tribometer

Fig. 9a and b show the friction behavior of the compositeoatings with a vertical load of 2 N. Whatever the MMT content orhe stirring time, the trends of the friction coefficient are nearly theame: In particular, at first the friction coefficient increases veryast by increasing the sliding distance and, then, approaches ansymptotic values.

The coating material is thus characterized by an initial running-n period, during which the coefficient of friction is progressivelyising, followed by a steady-state region, starting from 2 m sliding


istance. Friction stabilizes to a nearly constant value (∼0.7) withmall changes. Increasing the vertical load at 5 N (Fig. 10), the curveshow a sudden change in the friction coefficient in corresponding tooating failure. This occurrence was observed only with a vertical

ig. 9. Friction at the normal load of 2 N and different MMT content: (a) 1 wt% andb) 5 wt%.

Fig. 11. Average friction coefficient and distance at rupture from sliding tests at thenormal load of 5 N.

load of 5 N and underlines a greater wear resistance of the coat-ing with a higher percentage of MMT. Fig. 11 reports the averagefriction coefficient in the steady-state region related to the slidingdistance at which the composite coating breaks. The sliding dis-tance of failure seems to be not directly related to the value of thefriction coefficient.

Generally, a better behavior of composite coatings with a MMTcontent of 1 wt% and 5 wt%, and a mixing time of 5 min was shown.In particular, the highest performances were measured for 5 wt%filled samples (Fig. 8) but the effect of the mixing time seems tobe stronger than the effect of the filler content. This effect is prob-ably related to the higher coating thickness rather than the resinstrengthening.

4. Conclusions

MMT filled polyester coatings can show interesting propertiesbut it is very important to control the coating process in detail.


A proper mixing process is mandatory to obtain high propertieswithout affecting the film deposition. The effect of the mixing timecan be comparable with the effect of the MMT content. Increasing


ING Model

P

6 Organ

mt

R[

[

[

[

[

[15] C. Lucignano, F. Quadrini, Instrumented flat indentation on polyester nanocom-

ARTICLEOC-3145; No. of Pages 6

D. Bellisario et al. / Progress in

ixing time, the resin viscosity increases as well and it is difficulto produce thin coatings.

eferences

[1] D. Is in, N. Kayaman-Apohan, A. Güngör, Preparation and characterization ofUV-curable epoxy/silica nanocomposite coatings, Prog. Org. Coat. 65 (4) (2009)477–483.

[2] M. Spirkova, J. Brus, L. Brozova, A. Strachota, J. Baldrian, M. Urbanova, J. Kotek,B. Strachotova, M. Slouf, A view from inside onto the surface of self-assemblednanocomposite coatings, Prog. Org. Coat. 61 (2–4) (2008) 145–155.

[3] P. Jawahar, R. Gnanamoorthy, M. Balasubramanian, Tribological behaviour ofclay–thermoset polyester nanocomposites, Wear 261 (7/8) (2006) 835–840.

[4] B.W. Jo, S.K. Park, D.K. Kim, Mechanical properties of nano-MMT reinforcedpolymer composites and polymer concrete, Adv. Mater. Res. 22 (2008) 14–20.

[5] S.K. Swain, A.I. Isayev, Effect of ultrasound on HDPE/clay nanocomposites: rhe-ology, structure and properties, Polymer 48 (2007) 281–289.

[6] K.Y. Kim, D.K. Kim, S.H. Kim, Effect of modified carbon nanotube on physi-cal properties of thermotropic liquid crystal polyester nanocomposites, Eur.Polym. J. 45 (2009) 316–324.


[7] H.D. Rozman, L. Muse, A.A. Azniwati, A.R. Rozyanty, Tensile properties ofkenaf/unsaturated polyester composites filled with a montmorillonite filler,J. Appl. Polym. Sci. 219 (2011) 2549–2553.

[8] K. Kowalczyk, T. Spycal, Epoxy coatings with modified montmorillonites, Prog.Org. Coat. 62 (4) (2008) 425–429.

[

PRESSic Coatings xxx (2013) xxx– xxx

[9] Z. Davood, S.A. Asghar, S. Faharad, G.M. Moazzami, K.S. Mahmoud, The impact oforganoclay on the physical and mechanical properties of epoxy-clay nanocom-posito, J. Macromol. Sci. B: Phys. 49 (2010) 960–969.

10] Y. Bautista, J. Gonzalez, J. Gilabert, M.J. Ibanez, V. Sanz, Correlation between thewear resistance, and the scratch resistance, for nanocomposite coatings, Prog.Org. Coat. 70 (4) (2011) 178–185.

11] M.R. Bagherzadeh, T. Mousavinejad, Preparation and investigation of anti-corrosion properties of the water-based epoxy-clay nanocoating modified byNa+-MMT and Cloisite 30B”, Prog. Org. Coat. 74 (3) (2012) 589–595 (to bepublished).

12] M.G. Hosseini, M. Raghibi-Boroujeni, I. Ahadzadeh, R. Najjar, M.S. Seyed Dor-raji, Effect of polypyrrole–montmorillonite nanocomposites powder additionon corrosion performance of epoxy coatings on Al 5000”, Prog. Org. Coat. 66 (3)(2009) 321–327.

13] S.C. See, Z.Y. Zhang, M.O.W. Richardson, A study of water absorption character-istics of a novel nano-gelcoat for marine application, Prog. Org. Coat. 65 (2009)169–174.

14] D. Piazza, D.S. Silveira, N.P. Lorandi, E.J. Birriel, L.C. Scienza, A.J. Zattera,Polyester-based powder coatings with montmorillonite nanoparticles appliedon carbon steel, Prog. Org. Coat. 73 (2012) 42–46.


posite coatings, Int. J. Surf. Sci. Eng. 2 (2008) 409–418.16] C. Lucignano, F. Quadrini, L. Santo, Dynamic mechanical performances of

polyester-clay nanocomposite thick films, J. Compos. Mater. 42 (2008)2841–2852.


http://refhub.elsevier.com/S0300-9440(13)00149-5/sbref0005






























































































































































































































































































































































































































































Documents

Nano-clay filled polyester coatings