improvement of acrylic-urethane paint adhesion to pp-epdm...

Scientia Iranica C (2020) 27(3), 1253{1263

Sharif University of TechnologyScientia Iranica

Transactions C: Chemistry and Chemical Engineeringhttp://scientiairanica.sharif.edu

Improvement of acrylic-urethane paint adhesion toPP-EPDM surface by mediated electrochemicaloxidation

Sh. Mokhtari, F. Mohammadi�, and M. Nekoomanesh HaghighiIran Polymer and Petrochemical Institute, Tehran, P.O. Box 14965/115, Iran.

Received 12 May 2019; received in revised form 2 November 2019; accepted 22 February 2020

KEYWORDSPP-EPDM bumper;MEO by Ag (II);Adhesionimprovement.

Abstract. Adhesion improvement of acrylic-urethane paint on bumper surface made ofpolypropylene/ethylene-propylene-diene monomer was investigated in the long term afterelectrochemical treatment by 2N nitric acid and 0.6M silver (II)-nitrate/2N nitric acid.The stability of electrochemically treated samples was examined at di�erent aging timesby ATR and SEM. The results were also compared to those of untreated and ame-treatedsamples. Accelerated UV weathering analysis and morphological study by SEM con�rmedthe e�ectiveness of the Ag (II) treatment technique in the long term, particularly at thecurvature of the bumper. For the Ag (II)-treated samples, increase in adhesion strengthwas sustained even after 650 hours of exposure to UV irradiation in wet conditions beforebonding. In addition, the stability of the Ag (II)-treated surface was maintained for atleast three months. In the case of the ame-treated surface, hydrophobic recovery duringaging in the environment was found to reduce the polarity of the PP-EPDM surface. Thepull-o� test showed that Ag (II) treatment could enhance the adhesion strength of theacrylic-urethane coating onto PP-EPDM in comparison with the aming method by 20.7%.Moreover, the results of zeta potential analysis for Ag (II) treated blend showed a typicalacidic surface.

© 2020 Sharif University of Technology. All rights reserved.

1. Introduction

A major problem with utilizing polypropylene (PP),widely used as the main body of auto bumpers, is itsnon-polar surface, which in turn, makes its wettingproperty and paint adhesion poor in quality [1,2].Di�erent surface modi�cation techniques have beenapplied to improve the wetting characteristics of

*. Corresponding author. Tel.: +98 21 48662455;Fax: +98 21 44580192E-mail address: [email protected] (F. Mohammadi)

doi: 10.24200/sci.2020.53396.3220

such non-polar plastics. These include chemicaltreatment by environmentally hazardous chemicalssuch as trichloroethylene [3], corona discharge withhigh frequency and voltage [4,5], plasma treatment invacuum [6,7], air plasma [8,9], ame treatment withlittle prospect for irregular shapes [10,11], and recentlyproposed mediated electrochemical treatment [12,13].Among these techniques, the boosting electrochemicaltreatment is considered to be an e�ective method toamplify the surface energy of the plastics and improvetheir adhesion to other layers. Polyole�n is amongthe most regularly surface-modi�ed polymers for thispurpose. Brewis et al. [3,14,15] investigated the pos-sibility of applying electrochemical techniques for the

1254 Sh. Mokhtari et al./Scientia Iranica, Transactions C: Chemistry and ... 27 (2020) 1253{1263

modi�cation of polyole�n such as PP and polyethylene(PE) over the last decade. They found that themediated electrochemical treatment was more e�cientin terms of joint strength for PE than PP. Their resultsalso revealed that the concentration of oxygen formedon PP surface was limited to about 4 atom% [16]. Wehave also recently reported the e�ectiveness of Medi-ated Electrochemical Oxidation (MEO) by Ag (II) ionsas a substitute for the conventional ame-treatmenttechnique for the modi�cation of PP/EPDM bumper.Initial results show that MEO by Ag (II) o�ers anattractive opportunity for increasing surface polarityof non-polar polymer alloys [17]. It has recently beenreported that surface modi�cation of some rubbers,e.g., BR, NR, and EPDM by MEO, improves theirsurface characteristics for compatibility with othermaterials in blending [18{20]. Electrochemical surfacemodi�cation of the non-polar plastics such as PE, PP,and PS [3], rubbers such as BR and NR [14], SBR [15],and BR-clay nanocomposite [18] has already beenreported in the literature. However, the surface agingand adhesion strength of electrochemically modi�edpolymers have yet to be addressed. To obtain a deeperunderstanding of Ag (II) treatment on the chemicaland physical nature of the surface, aging and adhesionstrength of PP-EPDM blend were thus studied afterexposure to an accelerated UV irradiation test in a wetcondition. Since surface properties may change withtime upon storage in atmospheric conditions, chemicalchanges in the PP-EPDM surface have also beentracked for three months. Aging study was followedby ATR, EDX, and contact angle measurements. Theresults were also compared to those of the untreatedand ame-treated PP-EPDM sheets.

A growing desire to minimize painting of auto-motive parts is increasing the necessity for reliablepredictions of weathering performance. AcceleratedUV weathering analysis is a useful technique thatprovides relatively quick responses to color change andsurface resistance after exposure to heat, cold, UV,moisture, and high temperature. This technique is vitalto examine any possible damage to the treated surface

caused by sunlight, rain, and moisture, particularly atthe curvature of bumpers. Therefore, all PP-EPDMsamples were initially coated with the same acrylic-urethane paint. Then, accelerated UV weathering andsurface characterization techniques were employed toinvestigate the e�ectiveness of Ag (II) treatment. Thestudy of the low accessible area of PP-EPDM bumperwas our main interest.

2. Experimental

2.1. MaterialsSilver (I)-nitrate and nitric acid were obtainedfrom Sigma-Aldrich and Merck Inc., respectively.PP-EPDM bumper plates (polypropylene/ethylene-propylene-diene monomer blend) with a thickness of3.0 mm were supplied by Kimia Baspar Company, Iran.The blend weight formulations were: 76% PP, 19%EPDM, and 5% talc-�lled and other additives such asNano and carbon black. The melt ow index of PP at230�C was 12 g/10 min. It has a density of 0.9 g/cm3.The EPDM contains 57 wt% of ethylene and 4.5wt%of ethylidene norbornene. It has a Mooney viscosity(MU1+4 at 125�C) rate of 77.

The curvature area of the bumper was cut intosmall pieces (2 � 2 cm2) and cleaned in 2-propanolaccording to the factory procedure. The paint includedthermoplastic acrylic (Trade number: PL 2181) andacrylic-urethane (Trade number: PL 7040) purchasedfrom Goharfam Co., Iran as the primer and the basecoat, respectively. The thickness of the paint includingthe primer and base coats was 35 �m.

2.2. Treatment techniquesThe electro-oxidation of Ag (I) in an electro-membranecell was performed using IrO2/Ti DSA anode, Ti cath-ode, and Ag/AgCl reference electrode. The anolyteincluded AgNO3 in 7 N HNO3 media and catholyte in-cluded HNO3 8 N (Figure 1). Na�on® 115 membranewas employed as a separator. Constant cell voltage(2.2{2.8 V) was applied to the cell during electrolysis byPGSTAT30 system (Eco Chemie Autolab) which �tted

Figure 1. Schematic diagram of the electro-membrane cell used in this study [19].

Sh. Mokhtari et al./Scientia Iranica, Transactions C: Chemistry and ... 27 (2020) 1253{1263 1255

with the General Purpose Electrochemical Software(GPES). After cleaning the samples with a 2-propanolsolution, the electrochemical treatment with dilutenitric acid (2N) or in the presence of Ag (II) ionsunder optimum conditions obtained previously [21] wascarried out in an electro-membrane cell.

The pieces of bumper sheet were placed in theanolyte adjacent to the anode at the contact time of 5to 15 min.

Fuel for ame treatment was butane (C4H10), andair/fuel-ratio was 22/1. Flame gun height was about25{250 mm. For ame treatment, a gas burner waspassed at 3 cm above the PP-EPDM sheets at a speedof ame set at 400 mm/s. The operating condition for

ame treatment was �xed according to the proceduredescribed by [22].

2.3. Test methods2.3.1. Atomic Force Microscopy (AFM)A commercial AFM (Dualscope/Rasterscope C26,DME, Herlev, Denmark) was carried out for examiningthe surface topography and roughness of di�erenttreated samples in various scan areas. All analyseswere performed at room temperature with a relativehumidity rate of 50%. The roughness parameters se-lected as the maximum height and the RMS data weredetermined using average of surface height values. TheAFM measurements were achieved in three di�erentplaces for each blend.

2.3.2. IR-ATR absorption spectroscopyIR-ATR technique was employed to characterize thechemical structure of the samples. The spectral reso-lution of ATR/FTIR spectrophotometer (Equinox 55,Bruker, Germany) was 4 cm�1. Wave numbers rangingfrom 400 to 4000 cm�1 were recorded as a function oftransmittance.

2.3.3. Scanning Electron Microscopy (SEM)Surface morphology of the samples was examined bySEM (Brno, Czech Republic) which worked in thesecondary electron mode at 20 kV.

2.3.4. Energy dispersive X-ray analyses (EDXA)Oxygen-element mapping was also used by SEMequipped with energy dispersive X-ray analysis(EDXA). The sheets were mapped in the secondaryelectron mode at 10 kV.

2.3.5. UV accelerated analysisUV accelerated analysis was carried out according toASTM D4587-11 for testing automotive coating. Ac-cording to this test method, the ability to paint sampleswith di�erent treatments is compared with that withthe untreated sample. In this way, one can investigatehow a painted sample may resist deterioration in termsof physical and optical properties caused by exposure tolight, heat, and moisture. The experimental conditionswere set according to the procedure described in ASTMD4587-11, as mentioned in Table 1.

2.3.6. Contact angle measurementThe surface wettability of the PP-EPDM blend samplewas determined by static contact angle measurements(error � 5%) with sessile drop technique using thesurface energy evaluation system (KRUSS G10, Ger-many) [14,17]. The measurements of the water contactangles (error � 5%) were also performed using distilledwater at 10 di�erent positions. For reproducibilitycon�rmation, each liquid probe was carried out �vetimes, the mean value of which was reported.

2.3.7. Zeta potential measurementsThe zeta potential (isoelectric point: IEP) of di�erenttreated PP-EPDM samples was measured in the pHrange of 3{12 using Electro kinetic analyzer (EKASurPass-type A, Anton Paar GmbH, Graz, Austria).The EKA system is composed of an automatic pHtitrator with an evaluation software program and atemperature sensor.

2.3.8. Pull-o� testPull-o� adhesion test was performed according toASTM D5179. To carry out pull-o� tests, aluminumdollies adhered to the surface of the coated samplesand, then, were left for at least 24 h to be fully cured.Afterward, by a 5 kN universal testing machine, the�xture was strained at a rate of 1 mm/min until theadhered dollies were removed from the substrate withthe maximum recorded load. Finally, the force trendsversus extension were recorded by the tensile machine.For each mode, six replicated samples were performedand, then, the mean values were reported.

Table 1. UV-condensation exposure test.

Cycle description 340 nm irradiance Black paneltemperature

Relativehumidity

Typical uses

8 hUV,

4 h condensation,

repeated continuously

0.83 W/(m2.nm) dark

period

70� 2:5�C50� 2:5�C

50� 5% Automotivecoatings


3. Results and discussions

3.1. Chemical structure of surface agingSurface micro hardness of the electrochemically treatedPP-EPDM samples was investigated, and the resultswere compared to those of the untreated sample. Acomparison of the surface topography of the untreatedand Ag (II)-treated samples clearly shows the etchingability of the electrochemical treatment technique (seeFigure 2 and Table 2.). The untreated sample hasa comparatively smoother surface, whereas the Ag(II)-treated sample shows a uniform chemically etchedsurface, leading to a considerable change in topographyby treatment. Rq is characterized by a value of136 for the Ag (II) compared to 139 nm for theuntreated sample. Surface roughness in the Ag (II)-treated sample has slightly increased mainly due tothe enhanced e�ective surface area and the formationof more edge sites, leading to the higher adsorptionof the polar groups on these active sites and a bettermechanical interlocking.

The ATR absorption on the surface layer of thePP-EPDM sheets before bonding with the paint wasmeasured one day after electrochemical treatment byAg (II) ions and then again after three months. Theresults, which have been compared to those of theuntreated PP-EPDM samples, are depicted in Figure 3.As evident, on the surface of the treated sample byAg (II) in comparison with the untreated sheet, anew absorption peak within the wavelength range of1650 to 1660 cm�1 has appeared after 1 day, which isattributed to the polar carbonyl groups in an oxidizing

Figure 2. Atomic Force Microscopy (AFM) images ofPP-EPDM blend samples: (a) Untreated and (b)electrochemically treated by Ag (II).

medium [23,24]. Besides, a strong wide absorptionband for the Ag (II)-treated surface is observed atabout 3080 to 3685 cm�1, which may be associatedwith the presence of both hydroxyl and carboxylgroups [6]. However, a decrease in the intensity of thebands at 3485 cm�1 after 3-month storage is observed.The strong and intense peak at about 1665 cm�1indicates the presence of a carboxylic acid or carbonylgroup after 1 day and 3-month storage periods for theAg (II)-treated samples. This means that the newactive sites are perhaps associated with the surfaceetching caused by the electrochemical treatment [17].

In addition, the intensive absorption peaks at1261, 1041, and 1099 cm�1 are noticeable, particu-larly after 1-day storage, which is attributed to -C-O stretching bands and the formation of ester bandswithin the wave number range of 900 to 1300 cm�1 [25].During the �rst 3 months, the peak intensities forAg (II)-treated sample decreased quite slowly. Thereason for oxidizing the surface properties after ambientaging may be the reactive unsaturation and oxidizedhydrocarbons in the absorption band range of 1650 and3300 cm�1 [16,25].

Figure 4 depicts surface oxygen content obtainedfrom EDX spectra of the untreated PP-EPDM sheetbefore bonding with the paint compared to the elec-trochemically treated samples by Ag (II), nitric acid(2N), and ame at di�erent aging times. As seenearlier, various oxygen-containing functional groups

Figure 3. ATR-IR spectra of Ag (II) treated PP-EPDMsample in comparison with the untreated one at di�erentaging times.

Table 2. The roughness parameters for PP-EPDM untreated and electrochemically treated samples.

Samples Untreated Electrochemicallytreated by Ag (II)

Root-mean square roughness (Rq: nm) 136� 1 139� 0:9Mean square roughness (Ra: nm) 91� 1:1 98� 0:7Sdq 0.28 0.27


appeared particularly on the surface of the Ag (II)-treated sample, leading to the signi�cant enhancementof oxygen content (18.28%) in comparison with theuntreated (5.7%) and ame-treated (10.05%) samplesafter one-day storage time. However, prolonging stor-age time to three months caused a slight decrease inthe introduced polar groups containing oxygen. Thepresence of surface functional groups is more distinctfor the electrochemically treated samples, particularlyfor the one modi�ed by Ag (II).

Although the oxygen content for the ame-treatedsample has somewhat increased, the surface exhibitsrather more changes upon aging. As is evident, the oxy-gen content of the ame-treated sample decreased morethan those of the electrochemically treated ones afterthree months. It appears that once treated by Ag (II)ions, PP-EPDM surface will have a more stable surface,which is favorable in the long term due to measuredoxygen content and characterized functional groups.

The e�ect of electrochemical treatment on the

wettability of the PP-EPDM surface before bondingwith the paint was also investigated, and the resultswere compared to those of the untreated and ame-treated samples. The results of contact angle mea-surements at di�erent ambient aging times were thusobtained and depicted in Figure 5. As observed earlier,the contact angle of the ame-treated sample decreasedmore than that of the untreated one; however, inthe course of aging, contact angle increased againsigni�cantly. This may be caused by the reorientationof functional groups into the surface layer of the blendsheet [17]. The treatment of PP-EPDM surface byelectrochemical technique, particularly for the Ag (II)-treated samples, resulted in a considerable decrease inthe water contact angle so that the long-term agingcould not cause a signi�cant loss in wettability. Thisobservation strongly suggests that the wettability orcontact angle on the Ag (II)-treated PP-EPDM sampleappears not time dependent. The results also suggestthat Ag (II) treatment may lead to proper surface etch-

Figure 4. Surface oxygen content of PP-EPDM sheets treated by di�erent techniques as a function of aging time.

Figure 5. Water contact angle for PP-EPDM samples treated by di�erent techniques as a function of aging time.


ing and possibly long-term adhesion strength, whichwill be discussed in the next section.

3.2. UV accelerated analysisAs found earlier [17], the electrochemical pretreatmentcould create polar groups on a polymeric surface,leading to increased surface energy. Consequently,the wettability and adhesion of the paint to thepolymeric surfaces have improved through polar-polarinteractions. However, there can be two more potentialproblems. First is the aging problem in atmosphericconditions, as discussed in the previous section. Thesecond one is adhesion failure in a real environmentunder wet conditions, light exposure, and so on. There-fore, by means of UV accelerated analysis, the adheringsystem between the primer coat and the surface-treatedPP-EPDM by di�erent methods in the curvature areawas evaluated using strong UV irradiation in a wetenvironment. The results were also compared to thoseof the untreated sample. For rapid acceleration ofthe tests, UV-B test method was used according toASTM D4587-11, which accelerated the degradationprocess. Figure 5 shows di�erent treated samplesparticularly in the curvature area, which were coatedby the same thermoplastic acrylic and acrylic-urethaneas the primer and base coats, respectively. Accordingto Figure 6(a), the surface of all samples includingthose painted before UV exposure is visually detectfree. The UV analysis results after 90 hours (Fig-ure 6(b)) showed that there was much more yellowingresistance against color change during the exposure inthe electrochemically treated samples (3 and 4) thanthe untreated or the ame-treated ones (1 and 2).This e�ect is more distinct upon increasing the UVaccelerated time so that after 160 and 650 hours ofUV radiation (B) (weathering) (Figure 6(c) and (d)),the Ag (II) treatment can help attenuate the colorchange (sample c). Since the same coating was appliedto the surface of each sample with uniform thickness(35 microns), di�erent outcomes may be attributed tothe surface chemistry and type of modi�cation. Itappears that in accelerated conditions, gas di�usionby O2, nitrogen, and SO2 occurs easier and fasterfrom surface to depth. Further, the chemical reactionbetween aromatic rings at the interface of the substrateand base coat occurred as a result of chromophoricreactions, which is the main cause of discoloration[26,27]. Apparently, on the untreated surface, dueto insu�cient mechanical interlocking between surfaceand base coat, more discoloration is observed.

These observations are in good agreement withearlier studies for polyurethane degradation after UVirradiation. Yousif et al. [28] recently considered thesurface degradation of polymers by exposure to UVirradiation. They reported that UV irradiation causedoxidative degradation that produced free radical and

Figure 6. UV accelerated test for acrylic-urethanecoating according to ASTM D4587-11 on the PP-EPDMsamples treated by di�erent methods: (a) Before UVexposure, (b) after 90 hr of UV exposure, (c) after 160 hrof UV exposure, and (d) after 650 hr of UV exposureanalysis.

caused the deterioration of mechanical properties, thusleading to the production of useless materials. Whena polymer is subjected to UV irradiation, it under-goes rapid yellowing. Many factors are responsiblefor the discoloration of polymeric materials such asinternal and external impurities, which may containchromophoric groups. Similarly, Rosu et al. [28] inves-tigated the yellowing of polyurethane as a result of UVirradiation. Based on their results, the photochemicaldegradation of polyurethane is associated with thescission of the urethane group, and these reactionsare combined with the yellowing of the polyurethanesurface. It was concluded that, after UV irradiation,the oxidation of the central methylene group withquinone formation caused yellowing as a result ofchromophoric reactions.

3.3. Adhesion strength of surface in thecurvature area after UV accelerated bySEM

After the removal of the coated PP-EPDM samplesfrom accelerated environmental conditions, SEM im-


ages were taken to investigate the strength of junctionsbetween the curvature surface and the primer. Thus,all samples were cut cross-section in liquid nitrogen,and the junction between surface and primer coatingwas evaluated at di�erent magni�cations. Figure 7shows the untreated PP-EPDM surface junction withacrylic urethane coating after 650 hours of exposure tothe UV accelerated conditions at two magni�cations of500 and 1000 times. As is evident, a noticeable sepa-ration with a thickness rate of 5.69 micron can be seenin large areas at the junction coating on the surface.This induces no appropriate strength on the untreatedsurface after exposure to UV accelerated conditions.

Cross-sectional view of the SEM micrographsfor the acrylic-urethane coating on the ame-treatedsample after 650 hours of UV exposure at di�erentmagni�cations is shown in Figure 8. As is obvious,there is better strength at the interface between thePP-EPDM surface and the primer coating, thougha gap with 550 nm thickness shows the lack ofappropriate strength in this junction. These resultsreveal that the bond between the primer and the

ame-treated surface is highly vulnerable to moistureattack and gas di�usion.

Figure 9 illustrates SEM micrographs at the cross-section of the Ag (II)-treated sample after exposure to

Figure 7. Cross-sectional view of the SEM micrographs (magni�cations 500� and 1000�) for the acrylic-urethane coatingon the untreated PP-EPDM sample after 650 hours of exposure to accelerated conditions (surface thickness: 34.81 �m).

Figure 8. Cross-sectional view of the SEM micrographs (magni�cations 700� and 20000�) of the acrylic-urethanecoating on the ame-treated PP-EPDM sample after 650 hours of exposure to UV accelerated conditions (surfacethickness: 34.78 �m).


UV accelerated conditions for 650 hours. Evidently,at the junction of primer coating, even at the highzoom level measured by SEM (20000 X), there isno groove and connection between the substrate andcoating, which is detectable only by changing thecolor (the darker: surface and transparent: coating).This is one piece of evidence for the considerablemechanical strength endurance after 650-hour exposureto accelerated environmental conditions.

Cross-sectional view of the SEM image for thenitric acid treated PP-EPDM sample under conditionssimilar to those of the other samples is also shown in

Figure 10. Obviously, the bond between the coatingand the HNO3-treated surface is highly invulnerableso that, even at the highest magni�cation, no grooveor hole can be diagnosed. These observations revealedthat by electrochemical treatment, a higher degreeof interfacial interaction formed between the primerand the treated surface, leading to mechanicalinterlocking as a driving force for improved adhesionstrength [17]. In fact, the adhesion strength on theelectrochemically-treated samples did not declineby aging, indicating that these samples had a quitestable surface. Since polar surfaces have inherently

Figure 9. Cross-sectional view of the SEM micrographs (magni�cations 700� and 20000�) for the acrylic-urethanecoating on the Ag(II) treated sample after 650 hours of exposure to UV accelerated conditions (surface thickness:34.81 �m).

Figure 10. Cross-sectional view of SEM micrographs (magni�cations 700� and 20000�) for acrylic-urethane coating onthe nitric acid treated sample after 650 hours of exposure to the accelerated conditions (surface thickness: 34.81 �m).


hydrophilic nature, water molecules can easilypenetrate into the interface and disturb the adhesionbetween the treated surface and the paint.

Besides, after applying electrochemical treatment,especially by Ag (II), the chance for gas di�usionby gases such as O2, nitrogen, and SO2 as wellas moisture di�usion from surface to depth is mini-mized. As a result, there is a remote possibility forcreating chromophores as the main cause of discol-oration.

There is a good correlation between the result ofcross-sectional view of the SEM image and UV accel-erated analysis performed according to ASTM D4587-11, as shown in Figure 6(a){(d), because increase inthe yellowing of the polyurethane surface is due tothe presence of groove or hole at the interface of thesubstrate and base coat. On the other hand, the higherthe separation at the junction coating to the surface,the higher the chance for gas di�usion from surface todepth, which leads to color change during the exposureto UV irradiation.

These results fully comply with those obtainedfor adhesion strength of coating on the same treatedsamples, as evident in Figure 11. According toFigure 11(a), the trend of coating adhesion failureafter electrochemical treatments by Ag (II) is ratherdi�erent from that of the ame treatment method.

Figure 11. The pull-o� adhesion test: (a) Adhesionstrength vs. extension and (b) bar chart with standarddeviation for di�erent treated blends.

Figure 12. Zeta potential analysis of di�erent treatedPP-EPDM blends.

The fracture of the �lms in Ag (II)-treated samplesoccurs at higher extensions and forces than that inthe ame-treated sample. Figure 11(b) solely comparesthe maximum adhesion strength for these samples. Asobserved earlier, the highest adhesion strength of theacrylic-urethane coating onto the PP-EPDM samplecorresponds to the Ag (II)-treated sample, which hasbeen enhanced ten times more than the untreated PP-EPDM sample.

Zeta potential measurement was performed to de-termine the isoelectric point (IEP) and surface chargeproperties such as functional sites. The variations inzeta potential with pH for the untreated and electro-chemically treated samples are depicted in Figure 12.As is clear, the �-pH plot of the untreated PP-EPDMsurface is a curve with no plateau, which is a typicalcharacteristic of a non-polar surface due to the lackof functional groups. However, after performing ametreatment, S-shaped curves were attained and theirIEPs shifted to higher pH values. Flame treatmentalso changed the acidity and basicity of the surface.In the case of the Ag (II)-treated sample, a shift ofIEP to a lower pH is detected as compared to theuntreated sample. This is a typical graph for acidicsurfaces because of the curve IEP shifting to lower pHvalues. Moreover, in this case, increase in negativezeta potential with a speci�c pH may result fromthe adsorption of OH� ion on the surface as well asdissociation of acidic groups.

4. Conclusions

The e�ect of electrochemical treatment on the adhesionof acrylic-urethane paint onto a PP-EPDM bumperwas investigated in the long term by ATR, SEM,and accelerated UV weathering analysis along withSEM study. Aging of the Ag (II) treated PP-EPDMsample did not lead to a signi�cant change in thesurface properties. Accelerated UV weathering analysis


con�rmed the e�ectiveness of the Ag (II) treatmentin the long term, particularly at curvature and low-access area of the bumper. Accelerated UV analysisrevealed that, after exposure to wet conditions, unlikethe untreated and ame-treated PP-EPDM samples,the adhesion strengths for the Ag (II)-treated sampleremained almost intact. In fact, the aging of Ag(II)-treated surface after three months did not leadto signi�cant surface changes. In the case of ame-treated surface, however, hydrophobic recovery duringaging in the environment reduced the polarity of thePP-EPDM surface layer. Finally, MEO by Ag (II)considerably improved surface adhesion strength of theacrylic-urethane coating onto the PP-EPDM comparedto the conventional ame-treatment by 20.7%. Zetapotential measurements for Ag (II) treated blends alsoproved acidic surface of functional surface sites.

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20. Ronagh-Baghbani, M., Naderi, G., and Mohammadi,F. \Surface characterization of polybutadiene andnatural rubbers oxidized by silver (II)", Soft Materials,14(3), pp. 187{198 (2016).

21. Mokhtari, Sh., Mohammadi, F., and Nekoomanesh,M. \E�ect of process parameters on the concentration,current e�ciency and energy consumption of electro-generated silver (II)", Chemical Papers, 69(9), pp.1219{1230 (2015).


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Biographies

Shahrnaz Mokhtari is a Researcher of Chemical En-gineering at the Petrochemicals Synthesis Department,Iran Polymer and Petrochemical Institute (IPPI),

Tehran, Iran. He received the BSc and MSc degreesin Petrochemical Engineering from Tehran University,Tehran, Iran in 2001 and 2007, respectively, and PhDdegree in Polymer Engineering from Iran Polymer andPetrochemical Institute in 2015. His main area ofinterest includes mediated electrochemical oxidationof polymers and hydrocarbons, electro-membrane pro-cess, and gas conversion process.

Fereidoon Mohammadi is an Associate Professor ofChemical Engineering at the Petrochemicals SynthesisDepartment, Iran Polymer and Petrochemical Institute(IPPI), Tehran, Iran. He received BSc degree inPetrochemical Engineering from Amirkabir Universityof Technology, Tehran, Iran in 1988. Then, he obtainedMSc and PhD degrees in Chemical Engineering fromUniversity of New South Wales Sydney/Australia in1993 and 1997, respectively. His main area of in-terest includes mediated electrochemical oxidation ofpolymers and hydrocarbons, ion exchange membranefabrication and recycling, electromembrane processsuch as PEM fuel cell, chlor-alkali, and Ionic polymer-metal composite.

Mehdi Nekoomanesh Haghighi is a Full Professorspecializing in Chemistry at Polymerization Engineer-ing Department, Iran Polymer and Petrochemical In-stitute (IPPI), Tehran, Iran. He received BSc degreefrom Pars College, Tehran, Iran in 1981; MSc degreefrom UMIST in 1987, and PhD degree from ManchesterUniversity in 1991. His main area of interest includescoordination polymerization of ole�ns, polymerization& characterization of styrenic polymers, reactions ofpolymers, and characterization of polymers.

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