weathering resistance of opaque pvdf-acrylic coatings applied on wood substrates

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ARTICLE IN PRESS Model

OC-2897; No. of Pages 8

Progress in Organic Coatings xxx (2012) xxx– xxx

Contents lists available at SciVerse ScienceDirect

Progress in Organic Coatings

jou rn al h om epage: www.elsev ier .com/ locate /porgcoat

eathering resistance of opaque PVDF-acrylic coatings applied on woodubstrates

éronic Landry1, Pierre Blanchet ∗

PInnovations Wood Products Division, 319 rue Franquet, Quebec City, Quebec, G1P 4R4, Canada

r t i c l e i n f o

rticle history:eceived 12 September 2011eceived in revised form 3 May 2012ccepted 13 June 2012vailable online xxx

a b s t r a c t

PVDF-acrylic opaque coating systems were applied onto two different wood species; Black spruce andWhite pine. Weathering resistance of these products was compared to the one of industrial water-basedacrylic coatings used for exterior siding. ATR-FTIR results have shown that the PVDF portion of the coatingsresist easily to the UV light, even at the extreme surface. At the opposite, the acrylic portion of the coatingswas strongly affected by the UV light. This degradation has led to significant color change. Contact angleswere also measured before and after the accelerated aging test in order to assess the recoatability of

eywords:luoropolymerxterior wood coatingsrchitectural coatingsolyvinylidene fluorideeathering resistance

these coatings. Wettability was found to be slightly lower for the PVDF-acrylic coatings. The morphologyof the different coating systems was finally assessed. Results have shown that the PVDF-acrylic coatingsare strongly affected by the White pine resin exudation.

© 2012 Elsevier B.V. All rights reserved.

ltraviolet resistance

. Introduction

Opaque coatings, even if they hide the wood texture and color,re often used to protect exterior woodworks against UV light,oisture and oxidation. Pigments can absorb UV light, limiting

he wood photodegradation. On the other hand, pigments andesins are also prone to chemical degradation. The most commonndustrial wood coatings for exterior wood sidings and shinglesre nowadays water-based acrylics. These coatings are relativelyheap; they present good mechanical properties as well as a gooddhesion on most wood substrates. Unfortunately, acrylic coat-ngs also present some major drawbacks. When exposed to UVight, acrylics coatings undergo significant discoloration and chalk-ng. Acrylics contain esters and possibly other functional groupsensitive to both photochemical degradation and other types ofegradation such as hydrolysis [10].

Polymers containing high fluorine content show a greater chem-cal inertness than most resins, including acrylics. Their bondtrength (C–F) stabilized the structure decreasing the chemicalegradation, i.e. scission of the polymer chains, scission of end

Please cite this article in press as: V. Landry, P. Blanchet, Weathering resiProg. Org. Coat. (2012), http://dx.doi.org/10.1016/j.porgcoat.2012.06.004

hains, etc [1]. For this particular reason, fluoropolymers are nowa-ays used in many industrial sectors, including the coatings.

∗ Corresponding author. Tel.: +1 418 781 6731; fax: +1 418 659 2922.E-mail address: [email protected] (P. Blanchet).

1 Tel.: +1 418 781 6725; fax: +1 418 659 2922.

300-9440/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.porgcoat.2012.06.004

Over the last decades, fluoropolymers have gained in impor-tance in the architectural coating market, mostly because of theirgood resistance to UVA, UVB and to corrosive chemical agents [7].For these reasons, they are often the coatings of choice to passhighly demanding architectural specifications such as those of theAmerican Architectural Manufacturers Association (AAMA), AAMA605.2 and AAMA 2605.2 [9]. Fluoropolymer coatings have beenholding up on metal buildings for more than 30 years of contin-uous exposure in South Florida showing minimal gloss and colorchange [8]. Until now, the use of these polymers was limited toheat-sensitive substrate, but new developments, such as water-based emulsions, allow the preparation of fluoropolymer coatingsfor exterior wood products [3].

Polyvinylidene fluoride (PVDF), which is one of two fluo-ropolymers with the fluoroethylene alkyl vinyl ether alternatecopolymer (FEVE) frequently used in the coating market, showsbetter mechanical properties than the majority of other fluoropoly-mers. It is also melt-processable and less expensive than mostfluoropolymers [6]. However, PVDF emulsions are costly comparedto acrylics. For this reason, their utilization needs to be kept as lowas possible in order, for the wood industries, to keep being costcompetitive.

The objectives of this study were to study the weathering resis-tance of opaque PVDF-acrylic coatings applied on wood substrates

stance of opaque PVDF-acrylic coatings applied on wood substrates,

and to compare them with water-based acrylics. Several PVDF-acrylic systems were prepared in order to determine if PVDF needsto be employ in each coating layers of a system in order to benefitfrom it.

dx.doi.org/10.1016/j.porgcoat.2012.06.004


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https://www.researchgate.net/publication/44494014_Fluorine_in_organic_chemistry_R_D_Chambers?el=1_x_8&enrichId=rgreq-67b2ac9ddfb9726038bcaac1775567d8&enrichSource=Y292ZXJQYWdlOzI3MTU2MDc0NTtBUzoyNjQ4ODc5MTgxMzMyNTFAMTQ0MDE2NTYxMDA0Mg==

https://www.researchgate.net/publication/228984259_The_effect_of_fluoropolymer_architecture_on_the_exterior_weathering_of_coatings?el=1_x_8&enrichId=rgreq-67b2ac9ddfb9726038bcaac1775567d8&enrichSource=Y292ZXJQYWdlOzI3MTU2MDc0NTtBUzoyNjQ4ODc5MTgxMzMyNTFAMTQ0MDE2NTYxMDA0Mg==

https://www.researchgate.net/publication/285932729_Fluorinated_Coatings_and_Finishes_Handbook?el=1_x_8&enrichId=rgreq-67b2ac9ddfb9726038bcaac1775567d8&enrichSource=Y292ZXJQYWdlOzI3MTU2MDc0NTtBUzoyNjQ4ODc5MTgxMzMyNTFAMTQ0MDE2NTYxMDA0Mg==

https://www.researchgate.net/publication/284248978_Fluorine_in_Organic_Chemistry?el=1_x_8&enrichId=rgreq-67b2ac9ddfb9726038bcaac1775567d8&enrichSource=Y292ZXJQYWdlOzI3MTU2MDc0NTtBUzoyNjQ4ODc5MTgxMzMyNTFAMTQ0MDE2NTYxMDA0Mg==

ARTICLE IN PRESSG Model

POC-2897; No. of Pages 8

2 V. Landry, P. Blanchet / Progress in Organic Coatings xxx (2012) xxx– xxx

Table 1Description of the coating systems prepared.

Systems First coat Second coat Third coat

1 Innocryl Innocryl No2 Innocryl PVDF-acrylics No3 Innocryl PVDF-acrylics PVDF-acrylics4 PVDF-acrylics PVDF-acrylics No

2

2

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2

2

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Table 2Parameters used for the accelerated aging tests.

Exposure time (h) 2000Filter Direct exposure, daylight (Boro–Boro)Irradiance (W/m2/nm) 0.35Wavelength (nm) 340Step 1 102 min of light, 50% HR, 63 ◦C (black

temperature panel)

2.2.5. Contact angle measurementsContact angle experiments were performed on the acrylic and

. Materials and methods

.1. Materials

Four coating systems were compared in this study. Table 1resents the systems prepared. The first system (System 1) isomposed of 2 coats of the exterior acrylic coating Innocryl fromociété Laurentide, Canada. Innocryl is a water-based acrylic coat-ng formulated especially for exterior wood siding. It contains UVbsorbers that allow good color retention by minimizing the degra-ation of the wood by ultraviolet radiation. The solid content is 33%y weight. The second system (System 2) is also composed of 2oats, the first coat is one of the Innocryl and the second one is aVDF-acrylic coating. The third system (System 3) is composed ofhree coats: one coat of Innocryl and two coats of PVDF-acrylics. Theast system (System 4) is composed of two coats of PVDF-acrylics.he PVDF-acrylic coating was prepared from a Kynar emulsionKynar Aquatec). The ratio PVDF/acrylic was 70%. The solid con-ent is 33 wt.% Innocryl and the PVDF-acrylic coatings used werepaque (dark green). Green color was selected as it often lead toignificant color change under UV. Phthalocyanide green pigmentas used in acrylic and PVDF-acrylic formulations.

Coatings were applied onto two wood species to assess thempact of the substrate on the color change and the general coat-ng performance. Planed White pine (Pinus strobus L.) and brushedlack spruce (Picea mariana, Mill), two Canadian wood species,ere selected for this study as they are often used in the manu-

acture of exterior wood products. The test panels selected containound knots but they were free of cracks, blue staining and anyther apparent defects. Coatings were applied with an Airmix sprayun from Kremlin, United States, except for the first coat on thelack spruce test panels that was applied by brushing. The rough-ess of the Black spruce test panels being very high, brushing wassed to ensure that coating was applied evenly. The wet film thick-ess of each coat was 100 �m. Coatings were dried by means of

Sunkiss Thermoreactor infrared oven from Ayotte Techno-Gaz,anada.

.2. Methods

.2.1. Accelerated aging testWeathering is mainly caused by deteriorating agents such as

olar radiation, temperature and humidity. Solar radiation is by farhe main cause of coating degradation as it heats the coating andnitiates the photochemical degradation of the polymer. As nat-ral weathering is a long and slow process, artificial acceleratedeathering experiments were performed to assess color retention

nd chalk performance of the coatings. The equipment used for theccelerated aging test is the Ci3000+ Weather-Ometer from Atlasaterials Testing Solutions, United States. Tests were performed in

he spirit of ASTM G155 test method, Standard Practice for Operat-ng Xenon Arc Light Apparatus for Exposure of non-metallic Substrates,


ycle 1. The parameters that were used in Accelerated Aging Tests arehown in Table 2.

Step 2 18 min of light, direct water spray

2.2.2. Color measurementsColor measurements were performed with a color-guide 45/0

from BYK-Gardner (400 to 700 nm, illuminant D65). The CIELABcolor scale was used for these measurements. Three basics coordi-nates (L*, a* and b*) were determined for each sample before theaccelerated aging test and after 24, 48, 72, 240, 800, 1100 and 2000 hof artificial weathering. Delta values (�L*, �a* and �b*) were cal-culated for each coordinate. Tests were performed according toASTM standard D 2244.

2.2.3. X-ray photoelectron spectroscopyX-ray photoelectron spectroscopy (XPS) was used to study the

chemical composition of the extreme surface, which means approx-imately the first 10 nm. XPS spectra of acrylic and PVDF-acryliccoatings applied on White pine, after and before the acceler-ated weathering experiments, were recorded. The extreme surfaceof the samples was analyzed. To do so, coating was removedfrom the samples by using a razor blade. The experiments wereperformed with a XPS instrument (AXIS-ULTRA) from KRATOS(UK). It has 3 communicating chambers: the analysis chambercomprising the ESCA analyzer, the preparation chamber and theintroduction chamber. Base pressure in the analysis chamber is5 × 10−10 Torr. X-ray source is a monochromatic Al source operatedat 300 W.

Survey scans are recorded with a pass energy of 160 eV and astep size of 1 eV; survey scans are used for elemental analysis andapparent concentrations calculations. C1s and O1s detailed highresolution spectra are recorded at 10 or 20 eV pass energy and stepsize of 0.025 eV or 0.050 eV. High energy resolution spectra are usedfor chemical analysis. In this project, carbon, fluorine and oxygenhigh resolution spectra were recorded.

Calculation of the apparent relative atomic concentrationsis performed with the software provided with the instrumentor with the software CasaXPS based on well known princi-ples found in standard textbooks and using sensitivity factorspertinent to the operating conditions of the spectrometer. Theconcentrations obtained are named “apparent” because the calcu-lation is made assuming that the analyzed volume (here roughly800 �m × 400 �m × 5 nm) is homogenous in composition, whichis generally not the case, especially for samples contaminated byatmospheric species or coated with very thin films or clusters.

2.2.4. Fourier transform infrared spectroscopyATR-FTIR spectroscopy was performed to study the degrada-

tion of the two coating systems after the artificial weatheringexperiments. ATR-FTIR spectra were recorded using the Tensor 37spectrophotometer from Bruker (United States). The surface of thecoatings was analyzed by removing then with a razor blade fromthe wood samples. Five spectra were recorded for each sample. Theparameters were used for these analyses are shown in Table 3.


PVDF-acrylic systems, before and after the accelerated aging test.Contact angle can be described as the angle formed at the air–liquid




V. Landry, P. Blanchet / Progress in Organic Coatings xxx (2012) xxx– xxx 3

Table 3Parameters used for the infrared spectroscopy experiments.

Resolution 4 cm−1

Sample scan time 1 minBackground scan time 2 minAperture 6 mmScanner velocity 10 kHzAcquisition mode Double sided/forward–backwardPhase resolution 32

itti

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-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

2000150010005000

Del

taL

Hours (h)

System 1 (Acrylic)

System 2System 3System 4

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

2000150010005000

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System 1 (Acrylic)

System 2System 3System 4

Phase correction mode MertzApodization function Blackman–Harris 3-TermZero-filling factor 2

nterface and the liquid–substrate interface. The more important ishe contact angle, the lower is the wettability. The liquid used forhe wettability tests was demineralized water. The equipment useds the FTA 200 from First Ten Angstroms, United States.

.2.6. Scanning electron microscopyScanning electron microscopy experiments were performed

sing a JEOL JSM6360LV model, United States. A gold layer of0–15 nm was deposited on the samples. The voltage used for thesexperiments was 30 kV.

.2.7. 3D-profilometryA 3D profilometer from Bruker, the ContourGT-K1, was used

o study the roughness and the morphology of the coatings. Thisquipment uses light interferometry to capture surface rough-ess down to 130 nm high, until steps around 1 mm high. TheontourGT-K1 is delivered with a dual-LED light source, a focusodule controlled by computer and a measure table that can be

ilted or moved to ensure a greater precision and allow more sam-le geometries. The tests were performed using the VSI (verticalcanning interferometry) along with the Remove Tilt filter that com-ares every point to its neighbors and provides a 3D picture of theample free of tilt influence.

The 3D-profilometer was also used to measure the scratch resis-ance of the coatings. The scratch test was divided in two steps. Therst step was the scratch itself, performed with a Taber Multifin-er Scratch/Mar Tester. A weight of 20 N was applied on a 0.7 mmiameter tip. After applying the tip on the sample, a pneumaticable performed the scratch at a speed of 10 cm/s. The test was per-ormed back and forth. Depth and width of the scratches were then

easured with the 3D profilometer.

. Results and discussion

.1. Color measurements

Fig. 1 presents the change of �L* for the different systems arepplied on (a) White pine and (b) Black spruce after the weatheringnalysis. The curve in black represents the acrylic system. Duringhe first part of the test (0–1000 h) the acrylic and the three PVDF-crylic systems were found to perform in a similar way. For thehite pine samples, at approximately 800 h, the curves separated.

he slope of the acrylic curve is significantly higher than the one ofhe three PVDF-acrylic systems, revealing that the change in light-ess in the second part of the test (last 1000 h) is more significant forhe acrylic system (more than the double). For the PVDF-acrylic sys-ems (red, blue and green curves), curves almost reached a plateaut 1000 h, which means that not much change can be observed after000 h. Similar results were found for the Black spruce samples,lthough lightness changes were found to be less important than


or the White pine samples. One hypothesis that could explain thishenomenon is the presence of different wood extractives in Blackpruce and White pine. For both substrates, the System 4, whichs the one without any pure acrylic layers, seems to protect more

Fig. 1. Change in lightness (�L) of the acrylic PVDF-acrylic coatings applied (a) onWhite pine and (b) on Black spruce.

efficiently the wood. This effect seems to be more pronounced onBlack Spruce. In fact, the lightness change is less important for thesamples prepared with this system.

�a* results are presented in Fig. 2, a* is the green and red chro-matic component. The results obtained are similar for both woodspecies. Acrylic system show more significant delta a* changescompared to the three PVDF-acrylic systems. For the White pinesamples the delta a* after 2000 h is significantly lower for the PVDF-acrylic coatings than for the acrylic system. For the Black sprucepanels, PVDF-acrylic systems present curves having slope near 0,which means that between 1000 and 2000 h, there is almost nochange. It is different for the acrylic system curve as the delta a*significantly changes in the second part of the test.

�b* results over exposure time are shown in Fig. 3. White pineand Black spruce samples were found to give different results. Forthe White pine panels, all systems lead to a negative delta b. Thedecrease is very significant for the first part of the test, then thecurve is going up, leading to a lower delta b* in absolute value.Acrylic and PVDF-acrylics systems performed in a similar way butthe changes are more important for the acrylic system. On Blackspruce panels, acrylic and PVDF-acrylic coatings were found to per-form in a different way. The delta b* found for the acrylic systemis negative while the one found for the PVDF-acrylic systems arepositive. Delta b* variation was found to be small after 2000 h.

Finally, the delta E curves in function of the exposure time arepresented in Fig. 4. Delta E represents the total color change, which


means that it includes the delta L*, a* and b*. The main conclu-sions that can be obtained from these curves are that PVDF-acrylicsystems perform better than the acrylic system, especially in the






(a)

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0.0

0.5

1.0

1.5

2.0

2.5

3.0

2000150010005000

Del

taa

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Syst em 1 (Ac rylic )

Syst em 2Syst em 3Syst em 4

(b)

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-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 50 0 100 0 150 0 200 0

Del

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Syst em 2

Syst em 3

Syst em 4

Fig. 2. Change in delta a* of the acrylic and PVDF-acrylic coatings applied (a) onWhite pine and (b) on Black spruce.

(a)

(b)

-2.0

-1.5

-1.0

-0.5

0.0

0.5

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0 50 0 100 0 150 0 200 0

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Hours (h)



-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 50 0 100 0 150 0 200 0

Del

tab

Hours (h)

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Fig. 3. Change in delta b* of the acrylic and PVDF-acrylic coatings applied (a) onWhite pine and (b) on Black spruce.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

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2.0

2.5

3.0

3.5

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Hours (h)



(a)

(b)

Fig. 4. Change in delta E* of the acrylic and PVDF-acrylic coatings applied (a) onWhite pine and (b) on Black spruce.

second part of the test (last 1000 h). Furthermore, color changesare less important on Black spruce than on White pine.

3.2. ATR-FTIR

ATR-FTIR experiments were performed in order to study thechemical degradation of the acrylic (Fig. 5) and PVDF-acrylic (Fig. 6)systems caused by the UV exposure. Only the first PVDF-acrylic sys-tem is represented in Fig. 6 as they all lead to similar results. Themain changes that can be observed here are the formation of a broadpeak above 3000 cm−1 [4]. This can be related to the formationof hydroxyl bonds during the degradation of the acrylic resin. Thestretching of the ether from the ester group of the acrylic resin at1143 cm−1 was also found to be strongly affected, more importantlyfor the acrylic resin. The carbonyl elongation peak at 1727 cm−1 wasalso found to decrease importantly after UV exposure. From theseresults, it is possible to conclude that the acrylic resin of these sys-tems undergo important degradation when expose to UV light, asall the peaks listed are associated with the acrylic resin. The PVDFresin was found to be more resistant to photochemical degrada-tion. The band at 874 cm−1, assigned to the CH2 rocking vibrationof PVDF, remains of the same intensity after the weathering test. Itshows that PVDF is highly stable compared to the acrylic resin. Away of comparing the stability of the two resins is to measure theratio between the intensity of the band at 874 cm−1 and the one at1727 cm−1, before and after the accelerated weathering test [5]. Theband at 874 cm−1 is related to the PVDF and the one at 1727 cm−1


to the acrylic resin. These results are presented in Table 4. Theseresults suggest that the acrylic portion of the spectrum do not sus-tain very well the UV exposure. In fact, the ratios were found toincrease significantly after the UV exposure, meaning that the ester





Fig. 5. Infrared spectra of the acrylic system before and after the weathering experiment.

stem

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ptTt

TRt

Fig. 6. Infrared spectra of the PVDF-acrylic sy

roups of the acrylic resin undergo chemical degradation. The PVDFortion of these coatings on the other hand seems to sustain the UVxposure efficiently.

Similar ratios were found for the Black spruce and White pine


anels, revealing that the difference in color changes between thewo species are not only related to the acrylic degradation extent.he wood specie used is also a factor to consider when interpretinghe color change results.

able 4atio between the intensity of the band at 874 cm−1 and the one at 1727 cm−1 ofhe Systems 2–4.

Systems Black spruce White pine

Before After Before After

System 2 0.40 0.94 0.47 0.83System 3 0.56 1.03 0.46 0.89System 4 0.44 0.96 0.43 1.03

before and after the weathering experiment.

3.3. X-ray photoelectron spectroscopy

XPS measurements were performed in order to study the effectof the UV exposure on the chemical composition of the extremesurface. Sodium, iron, nitrogen, calcium, potassium, aluminum andsulfur were found in low concentration (<2%). These elements comefrom the surfactant, UV absorbers, pigments, etc. Silicon was foundin more important concentration (<6%) as silica was used as a mat-ting agent. Table 5 presents the atomic percentages of the threemain elements found in the coatings (fluorine, carbon and oxygen)measured before and after the UV exposition. Changes in elementalcomposition are not negligible. Enrichment in oxygen was found,impoverishment in carbon and mixed results for the fluorine. Fig. 7presents the high resolution spectrum of the PVDF-acrylic coat-


ings (Fluoro-acrylic System 1) before and after the weatheringexperiments. This spectrum was decomposed in three peaks repre-senting the different fluorine species. There are no new componentsformed during the UV exposition, more over the proportion of the





Table 5Atomic percentage of the oxygen, carbon and fluorine before and after the weathering experiments.

Elements Acrylic Fluoro-acrylic System 1 Fluoro-acrylic System 2 Fluoro-acrylic System 3

Before After Before After Before After Before After

Oxygen 21.64 34.18 19.65 26.96 16.22 20.38 16.86 17.71Carbon 72.89 50.87 63.97 47.86 63.92 61.75 66.64 56.10Fluorine 0 0 10.60 13.96 16.92 9.55 13.03 18.78

Laboratoire d'analyse de surface-CERPIC-Université Laval

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Name

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Binding Energy (eV)

Laboratoire d'analyse de surface-CERPIC-Université Laval

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Name

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Binding Energy (eV)

before

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Similar surfactant was used for the acrylic and PVDF-acrylic for-mulations. No matter the reasons, these experiments revealed thatthe recoatability of both systems becomes more difficult after theUV exposure, although the difference was negligible.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

Conta

ct angle

(°)

Acrylic System - before

PVDF-acrylic System 1 - before

Acrylic System - after

PVDF-acrylic System 1 - after

Fig. 7. High resolution fluorine spectra (a)

ifferent components does not seem to change much. It is thusossible to conclude that the PVDF portion of the coating does noteem to be affected by the UV exposure. The acrylic resin, on thether hand, was strongly affected, no matter if it was used alone aren combination with PVDF. Enrichment in oxygen (only presents incrylic resin) observed support this affirmation. Carbon and oxygenpectra were found to change more importantly than the ones ofuorine. It was shown in the literature that surfactants can migrateo the surface during the weathering experiments and affect theurface properties [2]. Even if the same surfactant was used for allhe formulations, no further analysis are presented on the C and Oetailed XPS spectra.

.4. Contact angles

Wettability experiments were also performed for opaqueoatings. Fig. 8 shows the results obtained. The acrylic system wet-ability did not change significantly after the UV exposure. In fact,he wettability decreases only slightly. For the PVDF-acrylic sys-em, the wettability before the UV exposure is comparable to the


ne of the acrylic system. After the UV exposure, the wettability islightly lower, as for the acrylic system. Two reasons could explainhis result. UV rays could have damaged the surface of the coat-ng slightly or the surfactant could have migrated to the surface.

and (b) after the weathering experiments.


50403020100

Time (s)

Fig. 8. Contact angle curves for the acrylic and PVDF-acrylic systems, before andafter the weathering experiments.





crylic

3

wst

Scwrw

Fig. 9. 3-D profilometry pictures (a) and (b) for the PVDF-a

.5. 3D-profilometry and scanning electron microscopy

Profilometry and scanning electron microscopy experimentsere performed in order to study the morphology of the opaque

ystems. Figs. 9 and 10 present the images obtained from theseechniques.

Fig. 9 presents the results obtained for the System 3 and theystem 4 applied on White pine panels. As it is possible to see,


oatings failures are present all over the surface. These featuresere present before and after the weathering experiments, which

eveals that these failures are not associated to the acceleratedeathering experiments. In fact, these features were noticeable

Fig. 10. Scanning electron microscopy of the PVDF

Systems 2 and 4; (c) and (d) for the PVDF-acrylic System 3.

right after the drying in the infrared oven. These failures werenot observed on Black spruce panels. White pine contains a highconcentration of resin. Resin exudation could help creating thesedefects as it will create pressure on the coating. The morphology aswell as the roughness of the acrylic and PVDF-acrylic coatings werenot found to change much during the UV exposure.

Fig. 10 presents similar patterns than Fig. 9. In Fig. 10(a), it ispossible to see a round at the center of the star-shaped defect, which


suggests that some kind of extractives, coming from the White pine,tries to pass through the coating film when the sample is heated.The coating failure seems to start from this point, and then migratesthrough the surface. To confirm that these defects could be created

-acrylic Systems 1 (a and b) and 3 (c and d).


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sintes

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ARTICLEOC-2897; No. of Pages 8

V. Landry, P. Blanchet / Progress i

y resin exudation, they were placed in an oven at 180 ◦C for 2 hnd it was found that high resin concentration at this place areesponsible for this phenomenon. These results revealed that theVDF-acrylic formulations are not flexible enough to sustain theesin exudation. Lowering the PVDF concentration could help tomprove the flexibility and prevent the formation of the defectsreated by the resin exudation.

. Conclusion

The objectives of this study were to improve the weatheringesistance of opaque exterior acrylic coatings and see if the naturef the wood specie influences the performance of the PVDF-acrylicoatings.

The results obtained in this study have shown that PVDFignificantly improved the weatherability of opaque exterior coat-ngs. ATR-FTIR and XPS experiments have shown that PVDF isot affected by the UV exposure. At the opposite, the degrada-ion of the acrylic resin was found to be important, which couldxplain why significant color changes are observed for the acrylicystem.

The nature of the substrate was not found to change signifi-


antly the weatherability of the PVDF-acrylic systems, althoughome changes were observed. Color measurements and the mor-hology of the coatings were found to be the main differencesetween the Black spruce and the White pine samples. Star-shaped

[

PRESSnic Coatings xxx (2012) xxx– xxx

coatings failures were observed for the White pine samples andthey were found to be created by the resin exudation or extractivemigration.

Three different PVDF-acrylic coating systems were prepared inthis study. The results have shown that systems with more thanone PVDF-acrylic coats do not seem to perform in a better waythan the system with only one coat of this coating. This means thatPVDF-acrylic coating could be use only as the top coat, limiting thedegradation of the entire system as well as the costs.

References

[1] Anonymous, Introduction to Fluoropolymers, Zeus Technical Whitepaper(2006) 1–9.

[2] C. Arnold, G. Klein, M. Maaloum, M. Ernstsson, A. Larsson, P. Marie, Y. Holl,Colloids Surf. A: Physicochem. Eng. Aspects 374 (2011) 58–68.

[3] D.R. Chambers, Fluorine in Organic Chemistry, Blackwell Publishing Ltd, Oxford,UK, 2004.

[4] B. Forsthuber, G. Grull, Polym. Degrad. Stab. 95 (2010) 746–755.[5] X. Gu, C. Michaels, D. Nguyen, Y. Jean, J. Martin, T. Nguyen, Appl. Surf. Sci. 252

(2006) 5168–5181.[6] L.W. McKeen, Fluorinated Coatings and Finishes Handbook, William Andrew

Publishing, Norwich, 2006.[7] L. Sung, S. Vicini, D. Ho, L. Hedhli, C. Olmstead, K. Wood, Polymer 45 (2004)

6639–6646.


[8] K.A. Wood, C. Cypcar, L. Hedhli, J. Fluorine Chem. 104 (2000) 63–71.[9] K. Wood, A. Tanaka, M. Zheng, D. Garcia, 70% PVDF coatings for highly weather-

able architectural coatings, Polymer, (n.d.).10] K. Wood, Effect of fluoropolymer architecture on the exterior weathering of

coatings, in: XXVI FATIPEC Congress, Dresden, 2002.








weathering resistance of opaque pvdf-acrylic coatings applied on wood substrates

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