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Journal of Membrane Science 365 (2010) 180–187

Contents lists available at ScienceDirect

Journal of Membrane Science

journa l homepage: www.e lsev ier .com/ locate /memsci

hthalate doped PVC membranes for the inhibition of fouling

ames Chapmana, Antoin Lawlora, Emma Weirb, Brid Quiltyb, Fiona Regana,∗

National Centre for Sensor Research, School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, IrelandSchool of Biotechnology, Dublin City University, Dublin, Ireland

r t i c l e i n f o

rticle history:eceived 9 May 2010eceived in revised form 5 August 2010ccepted 3 September 2010vailable online 21 September 2010

eywords:VChthalate

a b s t r a c t

Four phthalate plasticizers, each with different structural characteristics were assessed within a poly(vinylchloride) (PVC) matrix for their potential as an antifouling material. The materials containedphthalic ester compounds: dimethyl phthalate (DMP), diethyl phthalate (DEP), butyloctyl phthalate (BOP)and di-(2-ethylhexyl) phthalate (DEHP) and were prepared at 5% w/v concentration. The phthalates allpossess the same phthalic ester C6H4COCO moiety with structural differences of chain length and branch-ing across the four plasticizer compounds. This poses a question as to whether alkyl chain length doesaffect microorganism attachment and subsequent fouling. In order to determine the antifouling capacityof the materials, the polymer coatings underwent a series of analyses for biomass determination, bio-

iofoulinglasticizer

logical assessment, glycocalyx production, contact angle determination, surface roughness using atomicforce microscopy (AFM) and topological characterisation through scanning electron microscopy (SEM).It was found that using a 7-day fresh water tank study, the increased branched and longer chain phthalicesters, in DEHP and BOP gave rise to better antifouling performance. A pure culture study involvingthe test membranes in Staphylococcus aureus and Escherichia coli cell suspensions, displayed less cellu-lar attachment on the DEHP and BOP doped PVC matrices, once again showing potential in preventing

iofou

cellular attachment and b

. Introduction

The term ‘biofouling’ refers to the undesired accumulation ofio-molecules, cells and organisms upon an immersed substrateften resulting in a negative or adverse output [1,2]. The totalrocess presents deleterious effects, prevailing as, but not limitedo; turbulent drag on ships (thus increasing fuel consumption),ipeline biofilm build-up (causing inefficiency on dynamics orow) or compromised outputs (on deployed field sensors) [3–6].he need and requirement for antifouling surfaces therefore playsn important role in reducing concurrent problems and costs thatre associated through biofouling [7,8].

The biofouling sequence comprises of four main stages; adsorp-ion of a conditioning layer, adhesion of microorganisms and cells,rowth of a biofilm and a macrofouling stage. The initial biofilm for-ation is often the precursor for successive fouling of organisms

nd can be influenced by specific chemical, physical and biologi-al factors [9–14]. Once organisms have established on the surface,ensing chemicals are released to entice further colonisation [15].his problem has stimulated coatings to be designed to counteract

∗ Corresponding author. Tel.: +353 0 17005765.E-mail addresses: jchapman.dcu@gmail.com (J. Chapman),

ona.regan@mail.dcu.ie (F. Regan).

376-7388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.memsci.2010.09.003

ling.© 2010 Elsevier B.V. All rights reserved.

biofouling and therefore fundamental understanding and techno-logical improvements are a major objective in antifouling systems.Recently, polymers have become suitable doping matrices for thebasis of antifouling systems and have presented as promising incoating design [16–18]. Substantial work has been carried out onthe use of polydimethylsiloxane (PDMS) [19], zwitterionic poly-mers [20] and even polyvinyl chloride (PVC) as a doping matrix forbiocidal agents [12]. The most widely used of these polymers indaily life is PVC, and is more than often doped with plasticizers togive pliable material property [21], and this forms the impetus forthe study presented in this paper. Within this study, four phthalicacid ester derived plasticizers were selected each with varyingdegrees of molecular variation, Fig. 1. This formed the premisewhether each plasticizer would have a different effect when dopedinto PVC in impacting levels of fouling. To the best of the author’sknowledge, no other research has been reported using PVC dopedphthalates in an antifouling approach. A freshwater study, range ofcharacterisation experiments and fouling assays permitted in theinterrogation of each phthalate doped PVC membrane. Pure culturestudies were then performed to further analyse cellular attach-

ment to each test, resulting in some promise of phthalate dopedPVC membranes having antifouling capability. The results obtained,show promise that the novel plasticized membranes, with oppor-tunity for use in optically clear-based systems show antifoulingcapabilities.

J. Chapman et al. / Journal of Membrane Science 365 (2010) 180–187 181

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ig. 1. Molecular structures of phthalic acid esters used in the study, from L → R: Dnd diethyl phthalate (DEP).

. Materials and methods

.1. Reagents

Plasticizers shown in Table 1 were all obtained from Scientificolymer Products Inc©, Ontario. PVC and tetrahydrofuran (THF)as purchased from Sigma Aldrich, Ireland and was used without

urther processing. HPLC grade water was obtained (from Labscan,reland), absolute ethanol (from Cooley Distillery, Co., Louth, Ire-and), chloroform (from Fisher Scientific, Ireland), glacial acetic acidAGB Scientific, Ireland), toluidine blue (Avonchem LTD, UK), sterileutrient broth (Oxoid), sterile phosphate buffer pH 7.2 and acridinerange (Sigma Aldrich, Ireland).

.2. PVC thin films

A polymeric solution of phthalate doped plasticized PVC wasreated for each phthalic acid ester. This was achieved by adding 5%/v PVC and 5% w/v phthalic acid ester to each PVC polymeric solu-

ion in THF. The polymeric solutions were then individually coatedn to pre-cleaned glass coupons (3 × 1′ ′, Sigma Aldrich, Ireland)sing a spin coating method described later. The glass couponsere pre-cleaned with acetone submerged in an ultrasonic bath

or 15 min. They were then wiped clean with fibre-free wipes thatad previously been soaked in the solvent.

Using a spin-coater (Chemat Technology), the phthalate dopedVC polymeric solutions were spin coated on to glass coupons using1000 rpm for 3 s followed by a gradient ramp of 3500 rpm for

5 s programme. All polymer thin films were optically clear and

ere measured by UV–visible spectrophotometry (UV–vis) in range

f 200–800 nm using air as a reference. The thin films all showedut-off in optical transmission at wavelengths between 350 and00 nm.

able 1howing plasticizer data information, inclusive of surface roughness and contactngles.

Name Acronym Surfaceroughness (Ra)

Contact angle (◦)

n = 9 ± 1 SD n = 9 ± 1 SD

Butyloctyl phthalate BOP 77.167 ± 1.37 90.76 ± 0.13Dimethyl phthalate DMP 35.139 ± 2.93 81.11 ± 0.17Diethyl phthalate DEP 32.139 ± 2.10 83.33 ± 0.21Di-(2-ethylhexyl) phthalate DEHP 154.32 ± 3.21 92.84 ± 0.12uPVC (no plasticizer) uPVC 37.69 ± 1.66 86.51 ± 0.13

hylhexyl) phthalate (DEHP), butyloctyl phthalate (BOP), dimethyl phthalate (DMP)

2.3. Laboratory tank setup

The phthalate doped PVC thin films were exposed to freshwatersampled from the River Tolka, Dublin, Ireland for 7 d. The materialswere left in a flow-though tank system (240 L at a flow of 250 mL/s).The average temperature for the study was 16.3 ◦C, the concentra-tion of chlorophyll a was between 4 and 2 �g/L−1, pH was foundto be 7.6 on average and dissolved oxygen (DO) at 8 ppm In thisstudy no attempts were made to identify species present in theriver sample as previously documented by Vachee et al. [22].

2.4. Thin film characterisation

2.4.1. HydrophobicityContact angle measurements were taken using a sessile drop

method (Artray and Navitar camera with FTA32 video 2.0 datalog software). Measurements were taken through the analysis ofsitting drops upon the phthalate doped PVC thin films throughautomatic drops of HPLC grade water (n = 10), with a range of10–2000 mN/m, resolution 0.2% and accuracy ±1%. The drop wasreleased from a 25 gauge 10 mL hypodermic needle where allcontact angles are quoted in degrees (◦) where each sample wasphotographed for each polymer treatment at room temperature,Fig. 2.

2.4.2. Surface roughnessAFM examinations were performed with a commercial AFM

(Dimension 3100 AFM using a Nanoscope IIIa controller, equippedwith a phase imaging extender Digital Instruments); this wasoperated in tapping-mode atomic force microscope (TM-AFM),using standard silicon tips (Tap300, Budget Sensors, Romania) with42 N/m nominal spring constant and 330 kHz nominal resonancefrequency. All images were recorded in air at room temperature ata scan speed of 1–2 Hz. The background slope was resolved usingfirst or second order polynomial functions. No further filtering wasperformed.

2.4.3. Plasticizer availabilityDetermination of plasticizer availability was carried out using

a Perkin–Elmer FTIR (GX FTIR) instrument (Fig. 6). The phthalicacid ester doped samples were scanned (16 scans/min at 0.5 cm−2)

with a reference background of PVC in order to isolate plasticizerbands. Samples were then immersed in ultra-pure water over 1week to ascertain the plasticizer leaching effects from the inter-nal PVC thin film matrix by the monitoring of the characteristicIR-bands. Temperatures remained constant (20 ◦C) that were as

182 J. Chapman et al. / Journal of Membrane Science 365 (2010) 180–187

of the

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Fig. 2. Contact angle measurements taken

lose to the tank study as possible, replicating as close to theonditions as possible. A weight study was performed in tandemn order to ascertain the level of weight attributed to plasticizeross, which was then deducted from the overall mass contained inection 3.1.1.

.5. Mass assessment

Each polymer sample was weighed before and after immersionnto the tanks to ascertain any changes in mass (% mass change).amples, following exposure, were then rinsed with Milli-Q watero ensure un-adhered material was removed, such as particulate

atter, and allowed to dry until the weight remained constant. Aubtraction of weight of the glass slide with phthalic ester dopedVC thin film per sample before and after was carried out and thensubtraction of plasticizer loss (where data was obtained from

he IR leaching data) was factored giving a mean mass increaseesult.

.6. Glycocalyx (slime test)

Glycocalyx production was evaluated using a series of fixationnd staining techniques. Slime production was measured on theest material that was attached to the polymer surface only. Thelides were washed twice with 1 mL of sterile Milli-Q water prioro staining. The slime was initially reacted with Carnoy’s solutionabsolute ethanol (Cooley Distillery, Co., Louth, Ireland), chloroformFisher Scientific, Ireland) and glacial acetic acid (AGB Scientific,reland) in a 6:3:1 ratio) for a 30 min period. The solution was thenecanted and a 0/1% toluidine blue (Avonchem LTD, UK) was addedo stain the biofilm present on the polymers for 1 h. The excess stain

as decanted off and the polymers were rinsed twice with Milli-Qater (3 mL). NaOH (0.2 M) was added and heated to 85 ◦C for 1 h.

ach sample was allowed to cool to room temperature and opticalensity was measured at 590 nm (Cary 50 UV-visible spectropho-ometer) [23].

4 phthalic acid ester doped PVC thin films.

2.7. Thin film fouling characterisation

Surface analysis of adhered microorganisms and cells of thewashed thin film samples were carried out using a HitachiS3400 scanning electron microscope (SEM). Accelerating voltagesof 5–15 keV with secondary electron (SE) detection was used,varying the working distances from 5 to 10 mm. Samples wereprepared (n = 9), by cutting 2 mm × 2 mm samples, peeling themfrom the glass substrates and then attaching them to carbonSEM tabs.

2.8. Pure culture assay of Gram positive and Gram negativemicroorganisms

Sterile nutrient broth (Oxoid) was inoculated with a singlecolony of either Escherichia coli (ATCC 25925) or Staphylococcusaureus sp. And incubated at 37 ◦C overnight in an orbital shaker(Gallenkamp). The culture was then placed in sterile centrifugetubes and centrifuged (Eppendorf 5810R) at 5000 rpm for 10 minat 25 ◦C. The supernatant was removed and the cell pellet resus-pended in sterile Ringers solution (Oxoid) and centrifuged at5000 rpm for 10 min at 25 ◦C, and repeated to remove any remain-ing broth. The cell pellet was finally suspended in Ringers solutionand adjusted until an optical density of 0.1 AU at 600 nm wasachieved – giving a cell suspension of approximately 108 cells permL.

S. aureus (Gram positive) and E. coli (Gram negative) were chosento conduct the pure culture studies as they are typically used toassess bacterial adhesion on modified polymeric surfaces [24–26].The test materials were sterilized (germicidal Ultra-Violet light, 1 h)in order to prevent side polymerisation and degradation reactions,after which levels of bacterial adhesion were evaluated.

The test materials were removed by sterile forceps from cul-ture and rinsed twice with sterile phosphate buffer pH 7.2 (SigmaAldrich, Ireland), then stained with 0.1% (w/v) acridine orange(Sigma Aldrich, Ireland) for 2 min and rinsed with the buffer whencomplete. Imaging was performed on a Leica microscope with mag-

mbrane Science 365 (2010) 180–187 183

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shown that staining glycocalyx with the use of radiolabelled bac-teria can show microorganism involvement upon a substrate [29].Mass is clearly affected by the levels of slime produced across theplasticized PVC thin films and this, to the author’s knowledge, is thefirst time slime and mass have been shown in tandem to confirm

J. Chapman et al. / Journal of Me

ifications of 63 times. The images were analysed using Image Joftware and plugins [27]. To analyse the images random grid ref-rence numbers were obtained and using 10 grid references cellsontained in each reference were then counted and recorded.

.9. Statistical analysis of pure culture assay

Images were processed by Image J software, where bacterialells were counted from randomly chosen grid positions. Theverages were obtained and processed. Statistical analysis wasonducted on the values obtained from the adhered bacterial cellounts. Analysis was performed with SPSS (version 15) statisti-al software. The non-parametric Kruskal–Wallis test was used tossess the data obtained from both bacterial species.

. Results and discussion

.1. Fouling assays

.1.1. Mass analysisA series of mass measurements were taken across each of the

hthalate doped membranes to ascertain the levels of fouling uponach of the thin PVC films. Mass measurements were monitoredefore and after the 7 days for each of the thin films giving a massertaining to fouling activity of both physical and biological activ-

ties. Fig. 3 shows the average mass increase of each phthalic acidster doped PVC thin film, which clearly shows that DEHP (0.22%)nd BOP (0.35%) are outperforming DEP (1.34%), DMP (1.33%) andhe unplasticized PVC (uPVC) control.

.1.2. Glycocalyx (slime test)Fig. 4 shows the results of the slime test performed on the thin

lms after a 7-day freshwater tank test. Slime is the term used toepict exopolymeric substances (EPS) in particular, glycocalyx thatome microorganisms secrete after settling on a substrate [28].n the cases of DEHP (0.02 AU) and BOP (0.03 AU) less slime haseen detected in comparison to DEP (0.05 AU) and DMP (0.055 AU)espectively. This shows that toluidine blue is showing significantlyower concentrations and thus lower absorbance values in DEHPnd BOP. These low responses have been reflected in the biomass

esults (Fig. 3) where DEHP and BOP both perform in a similar man-er. Statistical analysis (ANOVA F = 44.74, p = 0.05) suggests thathere is a clear difference between the levels of microorganism par-icipation on the surface of DEHP and BOP when compared to thePVC control. The remaining two plasticized PVC membranes DEP

ig. 3. Percentage mass increases of the control and 4 phthalic acid ester doped PVChin film coatings (n = 9 ± 1 SD).

Fig. 4. Absorbance readings taken across the phthalic acid ester doped PVC thinfilms illustrating the levels of slime attributed to microorganism attachment.

and DMP both show a result double to that of the other two plas-ticizers indicating that higher levels of slime have been producedupon these thin films. In the same manner, Van Pett et al. have

Fig. 5. Graph showing pure culture cell counts for E. coli and S. aureus for thephthalic acid ester doped and uPVC blank (n = 9 ± 1 SD). For the statistical analysisof E. coli (DEHP = 0, BOP = 0, DEP = 0.004, DMP = 0) and S. aureus (DEHP = 0, BOP = 0,DEP = 0.524, DMP = 0.563) compared to the uPVC blank.

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84 J. Chapman et al. / Journal of Me

ass linked to slime production upon plasticized materials. Slime,n this result, has been attributed to surface roughness along withydrophobicity. Other factors can are also involved, one of which

s surface charge. Surface charge could also be speculative in whyicroorganisms have preferentially produced increased slime lev-

ls on DMP and DEP. It is well known that plasticizers when dopednto PVC produce a net negative charge across the surface.

.1.3. Pure culture studies using Gram negative and Gramositive bacteria

Fig. 5 shows a study to assess bacterial attachment on the dif-erent plasticized materials and was carried out using S. aureus and. coli in multiple studies in which bacterial attachment to poly-eric substances was assessed [24–26]. E. coli is regularly found inater bodies contaminated with untreated human and agricultural

ewage [30,31], while S. aureus is commonly used in challengingurfaces frequently associated with nosocomial infections [30,32].

Adhered microorganisms were observed by epifluorescencemaging, where S. aureus and E. coli were counted by cell attach-

ent per cm2 following immersion in a cell suspension for 1 h.t was found that BOP and DEHP plasticized polymers prevent

icroorganism attachment by up to 45% compared to the uPVControl. It is noted from the study that both branched plasticiz-rs, BOP and DEHP performed well in preventing adhesion of the

wo species compared to the other test polymers. A reduction in. aureus cellular adhesion of 45% and 42% respectively for theEHP and BOP plasticized membranes was achieved compared to

he uPVC control. E. coli cells displayed a greater aversion to thelasticized polymer coatings with a noticeable reduction in set-

Fig. 6. IR absorbance measurements of phthalic acid ester both before and after a 7-d

ne Science 365 (2010) 180–187

tlement, reflected in all tests. Mirroring previous results, DEHP andBOP demonstrated the most promise as an antifouling coating, pre-senting little or no E. coli adhesion. The E. coli (Gram-negative)result is particularly significant, given that Rheinheimer consid-ers that the predominant bacteria in most waters is Gram-negative[33]. This demonstrates that DEHP and BOP plasticized PVC offersa potentially, genuine solution to biofouling of sensors and sen-sor housing equipment. It is important to note that S. aureus had10 times more adsorption on the PVC thin films compared to E.coli. This can be explained due to the overall surface charge ofPVC and plasticizers having a net negative charge [34]. The liter-ature reports that bacteria have net negative zeta potentials [35]when in specific conditions. This could indicate that E. coli does notachieve the same preferential settlement due to other factors (i.e.,van der Waals forces), in the settlement process as highlighted in[36].

Statistical analysis was conducted on the values obtained fromcounting the adhered bacterial cells. Analysis was performed withSPSS software (version 15) statistical software. The non-parametricKruskal–Wallis test was used to assess the data obtained from bothbacterial species. E. coli and S. aureus output analysis showed statis-tical significance, as both p values were 0.00 (p < 0.05). This showsthat significant difference is seen between the plasticized polymersand the respective organisms investigated. Further statistical anal-

ysis was performed using a Mann–Whitney test, which assessesthe non-parametric independent samples. Here, the uPVC controlis compared to the other independent samples and their signifi-cance indicates is there is an effect of the plasticized PVC comparedto the uPVC control. The E. coli exposed samples displayed signifi-

ay water study, the total % plasticizer loss from each PVC thin film (n = 3, %RSD).

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J. Chapman et al. / Journal of Me

ant difference in all plasticized PVC samples compared to the uPVControl, all p values were below 0.05. The S. aureus adhesion valueso the plasticized polymers DEHP and BOP both showed significantifference with respect to the uPVC control (p < 0.05). However,he DEP and DMP plasticized membranes were not significantlyifferent to the uPVC control, which is indicated in Fig. 5, display-

ng S. aureus cells per cm2. This is concurrent with other physicalharacterisation methods discussed.

.2. Availability of plasticizer

PVC falls into a group pertaining to a matrix that has biocideelease attributes after the incorporation of the antimicrobialgent into a host polymeric matrix, in this study, plasticizers. Thehthalic acid esters contained within the PVC matrix are thereforeble to leach. This proves to be beneficial for the material regardingts antifouling capacity [37], and has been probed in this work usingTIR analyses. The plasticizers have characteristic bands that areisted and shown in Fig. 3. In this study, the same membranes weremmersed in water for a 7-day period and each phthalic acid ester

as then measured for absorbance before and after which gave anndication of the rate of biocidal activity. Each phthalate had the fol-owing IR-bands monitored ϑC O stretching (1727 cm−1), CH2CH3ibration (1291 cm−1, 1128 cm−1), C–Cl (1076 cm−1, and 976 cm−1)hich relate to phthalic acid esters in the PVC matrix [38].

DEHP (29.45%) leached significantly lower than the other plas-icizers. This is attributed to more branching within the moleculehus making it more difficult for the plasticizer to move through theolymer links [39]. From the study it was found that DEP (63.17%)nd DMP (75.89%) showed significantly more plasticizer loss from

he matrix when exposed to water. It was also found that these

embranes also showed significantly higher levels of biologicalttachment of microorganisms in both the slime and mass results,s shown in Figs. 3 and 4. Staples et al. [40] have reported that DMPnd DEP showed significantly less toxicity in biological assays when

Fig. 7. Scanning electron micrographs depicting fouling across eac

e Science 365 (2010) 180–187 185

compared to DEHP and BOP when using pure cultures of algae, pro-tozoa and other microorganisms Fig. 6. They determined that inorder to get LC50 for some microorganisms the following concen-trations were required: DEP (137 mg/L), DMP (537 mg/L), BOP N/Aand DEHP (25 mg/L) [41,42]. This is within good agreement of theresults that have been shown in this study. Where DEHP and BOPhave given greater biocidal impact on the levels of fouling observedin each assay. The PVC matrix offers a slow release biocidal matrixwith each plasticizer in the PVC matrix showing clear evidence thatthe phthalic acid esters are available to microorganisms that settleon the surface when compared to the undoped blank. Definitiveproof lies with each plasticizer giving a range of biocidal effectsfrom matrix to matrix.

3.3. Thin film surface characteristics

A series of surface roughness measurements were taken usingAFM measurements thus investigating the surface that microor-ganisms involved in the biofouling process, come up against.Surface roughness varied across each different plasticizer dopedPVC matrix. In each case Ra corresponds to the mean surface rough-ness as seen in Table 1.

DEHP (Ra 154.32 nm) shows roughness 5 times greater than theuPVC blank, DEP and DMP. The higher surface roughness observedin DEHP and BOP doped materials are hindering the level of foulingreflected in both the biomass and slime results, similar findingswere reported by others [43]. Chae et al. attributed high sur-face roughness values to increase hydrophobicity and subsequenthigher levels of fouling, this is indeed reflected in this study [44].The contact angles for DEP (83.33◦) and DMP (81.11◦) was found to

be significantly less than DEHP (92.84◦) and BOP (90.76◦), suggest-ing that the more hydrophobic the material is, the less attachmentand has been reported abundantly by others [45,46]. Scanning elec-tron microscopy, Fig. 7, was used to characterise levels of foulingupon each of the test polymers.

h of the membranes (a) DEHP, (b) DEP, (c) BOP and (d) DMP.

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86 J. Chapman et al. / Journal of Me

It was noted that smoother morphologies experienced in thePVC control, DEP and DMP all showed increased levels of fouling,hereas the rougher surfaces DEHP and BOP did not. Lopez-Llorca

t al. used SEM to characterise biofouling of polymer membranesolely [47], in a degradation study. In the same manner as this study,olino et al. used SEM to characterise diatom attachment and slime

roduction on materials [48].

.4. Plasticizer molecular properties

It was found that the structure of each phthalic acid estermpacted upon both the PVC structural characteristics and theegree of microorganism attachment. Although all the plasticizersave the same C6H4COCO moiety they are all structurally differ-nt. DEHP and BOP have higher degrees of branching within theolecule whereas DEP and DMP exist as shorter alkyl chain moi-

ties. The polarity of DEHP is somewhat dissipated through theolecule as summarised by Togashi and Matsuaga [49]. DEP andMP do not have the same level of induction and therefore could

dentify reasons as to why (i) the level of leaching has been moreapid from the polymer and (ii) why we have seen different lev-ls of fouling attributed to biocidal activity of the plasticizer. Asentioned previously DEHP and BOP are more toxic to organisms

ompared with DEP and DMP, thus re-enforcing the results shownn this study.

. Conclusions

The aim of this study was to demonstrate if molecular structuresf phthalic acid esters when incorporated into a PVC matrix wouldive different responses to the fouling assays implemented herein.t was found that plasticizers do indeed present different results

hen presented in a PVC matrix. The doping of these plasticizersrings about different physical opportunities for physical and bio-

ogical phenomena. The plasticizers investigated: DEHP, BOP, DMPnd DEP allow fouling but to different degrees. It was found thatigher branching and longer alkyl chain moieties upon two of thelasticizer molecules (DEHP and BOP) gave opposite scale results inhysical characterisation when compared to smaller chain lengthlasticizer molecules (DMP and DEP), and have consequently given

nteresting responses to the fouling assays herein. The work high-ights that if more branched plasticizers are incorporated in theVC matrix, different surface roughness values are achieved, whenompared to the less branched molecules. It was found that DEHPnd BOP changed the hydrophobicity (surface energy interactionith water) and thus presents a concept that organic, inorganic andicroorganism involvement is somewhat different when compar-

ng to DMP and DEP plasticized PVC thin films.Hydrophobicity and surface roughness can be linked with

ach other illustrating that heterogeneous wetting may be impor-ant in preventing fouling across the phthalate doped thin films.hrough AFM, surface roughness was performed showing thatigher surface roughness actively prevents fouling in this study.ydrophobicity has also shown to be influential in this body ofork, where, higher responses in DEHP and BOP have given less

ouling levels across all assays shown in this body of work.Adhesion of both pure culture bacterial species showed signif-

cant reduction on the phthalic acid ester doped polymers, whereEHP and BOP performed more favourably compared with DMPnd DEP. E. coli gave particularly less attachment on all surfaces.

owever, S. aureus displayed limited attachment on DEHP and BOPlasticized thin films.

Overall, DEHP and BOP have shown the most promise as anntifouling coating when introduced into a freshwater system asresented in these results. The work presented, to the author’s

[

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ne Science 365 (2010) 180–187

knowledge, uses phthalates doped into PVC as a means for the pre-vention of fouling (something that has been overlooked in polymerresearch). The aim of this study was to investigate the effective-ness of phthalic acid esters in the prevention of fouling, somethingwhich has been achieved.

Acknowledgements

The work would like to thank The Questor Centre, Belfast for thefinancial support and Emma Weir for her work on Epifluorescence.

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