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Foulingandstabilityofpolymersandcompositesinmarineenvironment

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IndianInstituteofTechnologyMadras

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International Biodeterioration & Biodegradation 65 (2011) 276e284

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International Biodeterioration & Biodegradation

journal homepage: www.elsevier .com/locate/ ibiod

Fouling and stability of polymers and composites in marine environment

Thangavelu Muthukumar a, Adithan Aravinthan a, Karunamoorthy Lakshmi a, Ramasamy Venkatesan b,Loganathan Vedaprakash b, Mukesh Doble a,*

aDepartment of Biotechnology, Indian Institute of Technology Madras, IIT Campus, Adayar, Chennai 600036, Tamil Nadu, IndiabNational Institute of Ocean Technology, Chennai 600100, India

a r t i c l e i n f o

Article history:Received 31 July 2010Received in revised form22 November 2010Accepted 22 November 2010Available online 28 December 2010

Keywords:Surface energyHardnessBiofoulingTotal suspended solidsFTIRAFM

* Corresponding author. Tel.: þ91 44 2257 4107; faE-mail address: mukeshd@iitm.ac.in (M. Doble).

0964-8305/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.ibiod.2010.11.012

a b s t r a c t

Effect of biofouling on various polymers and composites such as, Polyurethane (PU), Silicone rubber (SR),Polyester (PET), Glass Fiber Reinforced Polymer (GFRP), Carbon fibre Reinforced Plastic (CFRP) andSyntactic foams (SF) deployed for a period of one year in marine waters at a depth of 1 m was studied.These materials find wide marine applications. SR with lowest surface energy was the least fouled.Maximum barnacle attachment was seen on hard surface (GFRP) and minimum on flexible surface (SR).Attachment of barnacles and polychaetes are positively correlated with surface energy. Fouling load ispositively correlated with Surface energy and hardness. The surface energy, hardness and tensilestrength reduced while surface roughness considerably increased during this period. Maximum gravi-metric weight loss was seen in PET (7.49%) followed by PU (4.25%) and minimum in CFRP (0.45%).Maximum thermogravimetric weight loss was observed in PET (73.5% at 400 �C) followed by PU (71.1%)and least in SR (2.4%). Fourier Transform infrared spectrum revealed that carbonyl/oxidation indicesdecreased for PET, GFRP, CFRP, and SR indicating biotic degradation. The same index increased for PUindicating abiotic oxidation.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

The most serious problem faced by the marine industry isbiofouling. All surfaces under aquatic environment gets fouled dueto the attachment of marine flora and fauna. A complex communityofmicroorganisms andmacrofoulants includingbiomacromoleculesare involved during this process. The initial step in this process is theformation of a biofilm which is made up of carbohydrate, proteins,exopolysachrides andmicroorganisms, etc. Due to this, the materialexperience a series of discrete physical, chemical and biologicalchanges (Baier, 1984; Geesey andWhite, 1990; Ford et al., 1991; Gu,2003). The macrofoulants include barnacles, hydroides, algae bryo-zoans,mussels, andpolychaetes,whichattach lateron this biofilmorconditioning film. This film alters the surface characteristics of thebase material (Sudhakar et al., 2007).

Polymers and composites are commonly used in marine applica-tions. Varieties ofmaterialswithdifferent surfaces aredeveloped inanattempt to reduce biofouling and bioadhesion, but still there is a direneed to find a perfect antifouling surface. Baier et al. (1983) reportedthat the surface energy of a material significantly influences the

x: þ91 44 22574102.

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bacterial adhesion process. In previous studies from our lab we haveobserved that surfaceenergyandseasonplaya role in thebiofoulingofsynthetic polymers deployed in tropical marine sea water (Sudhakaret al., 2007; Artham et al., 2008; Artham and Doble, 2009).

Polyurethanes (PU) are a remarkable class of polymers whichexhibit a wide range of mechanical properties, and physicalbehaviour (Hepburn, 1992). These materials find increasing appli-cations at sea. In the fishing industry selectivity grids, oceano-graphic appliances including fenders and tubing on underwatervehicles and underwater antenna protection gears are fabricatedwith PU (Loaec et al., 2006).

Fiber reinforced composite materials have been the alternativesfor metal, steel and wood in many applications because of their lowcost to weight savings, improved life cycle, high specific tensile andcompressive strength, good fatigue and corrosion resistant(Couchman and Mouritz, 2006). Glass Fiber Reinforced Polymer(GFRP) are predominantly used as a light weight material in a widevariety of marine applications including parts in ship, boat, patrolboats, underwater sea pipes and fishing trawlers. Broad scale usageof GFRP is seriously hindered by the lack of experimental data and,understanding of its durability aspects in the marine environment(Apicella et al., 1983; Smith, 1990). Carbon fibre Reinforced Polymer(CFRP) is also used because of its delamination resistant properties.Syntactic foams (SF) because of their buoyancy property are used in

T. Muthukumar et al. / International Biodeterioration & Biodegradation 65 (2011) 276e284 277

boat hulls, deep-sea exploration, and autonomous underwatervehicles.

Polyester resins (PET) are widely used in marine applications,mostly with glass fibers, in reinforced composite structures. Theyhave been used as organic spray coatings to prevent corrosion ofsteel in marine waters (Singh et al., 2007). They are cheap, havegood physical strength, excellent handling characteristics, and highheat resistance and have versatile use. Their curing process andmechanical properties can be changed by modifying the monomerin the polyester chain (Visco et al., 2008).

The present study investigates the role of surface characteristicsof these polymers and composites on the formation of biofilm andbiofouling, and the subsequent changes they undergo when theyare immersed in marine water for 12 months. Biodegradation/biodeterioration of wide range of synthetic polymers (polyolefin,polycarbonate) in field and in lab has been reported (Sudhakaret al., 2007; Artham et al., 2008; Artham and Doble, 2009;Muthukumar et al., 2010). These studies could help in identifyingthe properties of the surface which affect fouling and hence in thelong run help in designing antifouling surfaces. The current studywill also help in ascertaining their stability in such field conditions.

2. Materials and methods

The materials used in this study namely, Polyester [IsopthalicPolyester Resin (PET)], Glass Fiber Reinforced Polymer [Glass FibereChopped Strand Mat (CSM 450); Resin e Isopthalic Polyester Resin(GFRP)], Carbon fibre Reinforced Plastic [Carbon fibre e T 300;Matrix e Epoxy resin LY 556; Hardner e HY 951 (CFRP)], Syntacticfoam [Matrix e Araldite GY 257; Hardner e Arudur HY 951; Filler eGlass Spheres (SF)], except for Polyurethane [Polyether based Poly-urethane (PU)] and Silicone rubber [Polysiloxane Polymer (SR)], arecommerciallyavailable andarepurchased fromIndustrial InsulationsLtd., Chennai-600001, India. They are mainly used in marine appli-cations. Syntactic foamwas obtained fromNIOT, Chennai. They werecut into uniform size (100� 75mm). All materials except for SFwereof 0.3 cm thick, while the latter was 1.4 cm thick. The coupons werecleaned with 70% v/v ethanol and dried in a hot air oven at 50 �C for24h. Theywere left at room temperature andweighedwith SartoriusPrecision balance (Germany).

Dumbbell shaped tensile coupons of dimensions 215 � 12 �3 mm (as per ASTM D256) were prepared and were also subjectedto the same studies. All the samples were deployed in the surfacewaters (at a depth of 1 m) of Bay of Bengal at Ennore Port LimitedChennai, India at a Latitude of 13�1504800 N and a Longitude of 80�

2002800 E. The coupons were tied vertically in a polypropyleneframe. Each frame consisted of all the six materials in triplicate. Theframes were tied to a floating raft made of High Density Poly-ethylene. This study was conducted from July 2008 to July 2009.Each frame was retrieved once every two months for analysis. Thesamples were photographed using a Digital Still Camera (Sony,model No: DSC-H2) immediately after removal from the frames.Similar samples were prepared and were also left undisturbed inthe laboratory which acted as controls.

2.1. Seawater parameters

During the sampling period, temperature, salinity and dissolvedoxygen of the seawaterweremeasured using a pre-calibratedwaterquality monitoring system (Hydrolab, Quanta Instruments, USA).

2.2. Analysis

The biological and physical characterization of the biofilmformed on the material surfaces, namely fouling load, total

suspended solids, carbohydrate, protein, chlorophyll a, ATP(Adenosine triphosphate) and total viable count were measuredonce every two months. It is well documented that these param-eters constitute the biofilm. The change in the physiochemicalproperties of the materials were analysed using a Thermogravi-metric (TG) and differential thermal analyser (TGA), Fouriertransform infra red spectroscopy (FTIR) and Atomic force micros-copy (AFM). The tensile strength, surface energy, and weight loss ofthe samples were also analysed. All analysis was performed intriplicates.

2.3. Biofilm characterization

The polymer coupons were retrieved from the field and carriedto the laboratory in a sampling jar containing 500 ml of 0.2 mm(Millipore) filtered and autoclaved sea water. Total fouling load ofthe sample was calculated by measuring the wet weight of thepolymer without cleaning along with the biofilm, micro and mac-rofoulants. Then the solids deposited on the test coupons werescraped with the seawater using a sterile nylon brush (Bhosle et al.,1989) and stored at �20 �C. The macrofoulants settled on thesurface of the polymers were removed using 10% hydrochloric acidand then the coupons were dried in a hot air oven at 40 �C for 4 h(Artham et al., 2009).

The total suspended solid (TSS) in the biofilm was estimatedfrom the sample based on the method reported by Parsons et al.(1984). A sample of 10 ml was filtered through a pre-weighed GF/C filter (47 mm, 0.22 mm), dried at 100 �C for 1 h and reweighed toget the dry weight of the residual biomass. The amount of chloro-phyll a pigment in the sample represents the quantity of alga andphotosynthetic bacterial growth. 10 ml of the scraped biofilmsuspension was filtered through a pre-weighed GF/C filter paper(47 mm, 0.22 mm). The filtrates with the filter paper were placed ina screw capped centrifuge tube containing 10 ml of 90% acetone forextracting the chlorophyll a (Holm-Hansen et al., 1977; Bhosle,2005). The samples were incubated for 12 h at 4 �C in the darkafter which the absorbance at 630, 645, 665 and 700 nm weremeasured using a UV spectrophotometer (Perkin Elmer, Lambda 35,USA).

For the estimation of ATP (indication of the activity of livebacterial cells), the filtrate was taken in 3 ml of 0.02 M Tris (pH 7.5)buffer and boiled for 10 min, to allow for complete extraction ofATP. It is stored at �20 �C until the analysis was carried out as perthe method suggested by Hamilton and Holm-Hansen (1967). Theamount of ATP was determined based on the firefly biolumines-cence reaction (Hamilton and Holm-Hansen, 1967) with a lumin-ometer (Berthold Detection Systems (GmbH) Sirius LuminometerD-75173, Germany). The concentration of ATPwas determined fromthe RLU (Relative Light Units) values with reference to the ATPstandard.

Total Viable Count (TVC) was estimated from the scraped bio-film by transferring 100 ml of media into a 1 ml micro-centrifugetube and was serially diluted. Around 20 ml of the sample wasplated on the surface of Zobell marine agar (ZMA) and pseudo-monas agar (PS) (Himedia Laboratories Pvt. Ltd Mumbai, India)solidmedia in sterile petridish and incubated at 37 �C for 24 h (Buckand Cleverdon, 1960; Moat and Foster, 1995). Viable colony countswere obtained by appropriately diluting the samples and visuallycounting them by using digital colony counter (Scigenics (India) PvtLtd, Chennai, India).

The total carbohydrate and protein contents in the biofilm wereestimated using phenolesulphuric acid method using glucose asthe standard and Lowry’s methods using crystalline bovine serumalbumin as the standard respectively (Lowry et al., 1951; Duboiset al., 1956).

T. Muthukumar et al. / International Biodeterioration & Biodegradation 65 (2011) 276e284278

2.3.1. MacrofoulantThe macrofoulants namely, barnacle, hydroids and bryozoans

that had adhered on the surfaces were manually counted on threereplicate panels after each exposure intervals.

2.4. Physiochemical characterization

Fourier transform infrared spectroscopy (FTIR) is used todetermine the formation and changes in the functional groups inthe polymers after one year of exposure with respect to the control.The spectra were obtained using a Jasco N4200 (Japan) spectrom-eter by superimposing 32 scans at a resolution of 4 cm�1 in thefrequency range of 4000e5000 cm�1, and calibrated with poly-styrene standard. The keto carbonyl, ester carbonyl, and vinylindices for PU, PET, GFRP and CFRP were calculated using thefollowing formulae.

Keto carbonyl bond index ¼ I1715/I1465

Ester carbonyl bond index ¼ I1740/I1465

Vinyl bond index ¼ I1640/I1465

where intensities at 1740, 1715, 1640 and 1465 cm�1 correspondto ester and keto carbonyl, double bond (vinyl index) and methy-lene bands respectively (Albertsson et al., 1987). Oxidation indexfor silicone rubber was calculated using the ratio of spectral peakheight associated with carbonyl (C]O) degradation product at1735e1745 cm�1 to SieCH3 at 1263 cm�1 (Liu et al., 2005).

2.5. Weight loss

The gravimetric weight loss generally occurs due to degradationor deterioration caused by the growth of micro and macrofoulants

Fig. 1. Effect of biofiouling after one year of deployment in ocean (a) SR (b) PET (c) PU (d) SF (

over the polymer surface, action of extracellular enzymes andmetabolites produced by the organisms, and ocean currents. Thesamples before and after deployment were weighed with anaccurate four digit balance (Sartorius CP64, 0.1 mg accuracy,Germany). The samples removed after one year were cleaned andwashed to remove all the micro and macrofoulants (as mentionedbefore) and then dried before they were weighed.

2.6. Hardness testing

Hardness of the samples were measured with a Barcol hardnesstester (Qualitest, GYZJ 934-1, USA). Measurements were taken atregular distances at least 12 mm from the edge of the specimen and10 mm apart. A minimum of six readings were taken for eachspecimen and the mean was calculated.

2.7. Tensile

The tensile properties of the dumbbell-shaped samples weremeasured as per the ASTM D638 procedure on an Instron machine(No. 4204) at 30 �C, 50% humidity and cross-head speed of 25 mm/min. The impact strength was measured by following the ASTMD256 procedure. The tensile strength and the % elongation of thesamples are estimated from the stressestrain curve by the softwareprovided with the instrument. The values were calculated asaverages over six specimens (Na et al., 2005).

2.8. TGA

Thermogravimetric analysis (TGA) of the samples were recorded(Thermal analyser, model 204, Netzsch, Germany) under nitrogenatmosphere in the temperature range of �50 to 450 �C at a heatingrate of 10 �C/min (Khabbaz et al., 1999).

e) CFRP and (f) GFRP (coupons on the left before immersion and on the right retrieved).

T. Muthukumar et al. / International Biodeterioration & Biodegradation 65 (2011) 276e284 279

2.9. Atomic force microscope

Atomic force microscopy (AFM) is capable of revealing surfacestructures with high spatial resolution. The surface profiles of thesamples were obtained in the contact mode using a piezoelectricscanner atomic force microscope (Shimadzu Corporation, Kyoto,Japan; SPM-9500) with an ADCS controller within an area of20 mm2 with a silicon nitride cantilever.

2.10. Surface energy

Surface energy is a measure of the intermolecular forces at thematerialeair interface. The lowsurface energy solids arenotwettedbyliquids and thus are termed as hydrophobic and as the surface energyof the solid increases it becomes hydrophilic. Surface energy of thepolymers andcompositesweremeasuredusingEasyDropGoniometer(KRUSS, DSA II GmbH, Germany). Two polar liquids namely, Milli-Qwater and formamide and a non-polar liquid namely, diiodomethanewereusedhere.DSA2 softwareprovidedwith the instrumentwas ableto estimate the surface energy based on the Fowke’smethod (Fowkes,1965). Average of five readings is reported here.

Table 1Analysis of biofilm sample from the polymer and composite for a period of one year at E

Name ofPolymers

Total foulingload mg cm�2

TSS � 10�2

mg cm�2Proteinmg cm�2

Carbohydratemg cm�2

Colony form

TVC � 10�3

SRSep 38.73 � 6.82 1.37 � 0.33 0.48 � 0.02 0.22 � 0.03 93.3 � 18Nov 29.07 � 6.78 0.21 � 0.05 0.14 � 0.02 0.15 � 0.02 58.2 � 5.3Jan 42.40 � 27.35 0.74 � 0.02 0.29 � 0.05 0.19 � 0.00 65.0 � 5.6Mar 34.93 � 4.69 0.39 � 0.08 0.55 � 0.26 0.22 � 0.01 123.0 � 4.4May 20.67 � 9.93 0.81 � 0.09 0.94 � 0.24 0.39 � 0.05 195.0 � 27July 36.38 � 0.63 1.22 � 0.12 1.02 � 0.14 0.54 � 0.04 191.7 � 32

PUSep 44.73 � 14.40 1.11 � 0.26 0.46 � 0.05 0.22 � 0.01 55.3 � 8.3Nov 37.07 � 5.13 0.13 � 0.05 0.10 � 0.02 0.08 � 0.03 53.0 � 3.6Jan 50.47 � 7.06 0.77 � 0.05 0.36 � 0.09 0.16 � 0.01 60.3 � 6.5Mar 35.22 � 11.98 0.40 � 0.09 0.68 � 0.23 0.17 � 0.02 142.3 � 45May 41.78 � 21.44 1.08 � 0.11 1.22 � 0.13 0.51 � 0.04 163.3 � 57July 100.58 � 35.18 1.42 � 0.21 1.15 � 0.25 0.48 � 0.02 166.67 � 27

PETSep 72.11 � 24.02 1.89 � 0.45 0.59 � 0.04 0.30 � 0.05 102.0 � 9.2Nov 39.53 � 2.28 0.24 � 0.04 0.16 � 0.02 0.18 � 0.03 58.2 � 6.3Jan 63.09 � 13.02 0.80 � 0.03 0.34 � 0.04 0.22 � 0.04 62.2 � 13Mar 86.73 � 0.10 0.54 � 0.00 0.86 � 0.00 0.27 � 0.00 143.0 � 0.0May 53.67 � 3.30 1.02 � 0.05 1.39 � 0.17 0.56 � 0.10 275.0 � 49July 134.07 � 46.90 1.47 � 0.06 1.25 � 0.03 0.63 � 0.04 290.0 � 43

SFSep 112.04 � 15.82 4.40 � 0.37 0.80 � 0.04 0.38 � 0.02 107.3 � 13Nov 49.91 � 3.48 0.32 � 0.07 0.21 � 0.05 0.16 � 0.00 61.2 � 7.0Jan 144.53 � 44.91 0.85 � 0.04 0.43 � 0.05 0.20 � 0.05 71.3 � 6.3Mar 72.91 � 20.22 0.59 � 0.07 0.72 � 0.15 0.31 � 0.02 144.3 � 32May 125.00 � 21.52 1.51 � 0.16 2.47 � 0.12 0.82 � 0.10 241.67 � 22July 163.80 � 28.26 1.42 � 0.07 1.32 � 0.07 0.67 � 0.02 308.33 � 38

GFRPSep 49.42 � 10.21 2.27 � 0.51 0.76 � 0.08 0.47 � 0.01 112.7 � 5.8Nov 45.42 � 5.51 0.24 � 0.03 0.26 � 0.04 0.24 � 0.04 67.8 � 3.8Jan 78.51 � 48.72 0.80 � 0.04 0.37 � 0.01 0.30 � 0.04 58.8 � 3.4Mar 74.60 � 23.35 0.76 � 0.13 0.78 � 0.22 0.35 � 0.03 122.0 � 29May 64.38 � 9.98 1.17 � 0.09 1.47 � 0.18 0.52 � 0.05 355.0 � 49July 164.62 � 36.25 1.26 � 0.17 0.97 � 0.40 0.51 � 0.10 270.0 � 35

CFRPSep 79.51 � 19.09 2.75 � 0.70 0.78 � 0.02 0.39 � 0.05 104.7 � 9.9Nov 45.00 � 0.01 0.28 � 0.00 0.25 � 0.00 0.20 � 0.02 69.0 � 9.7Jan 116.04 � 45.72 0.81 � 0.05 0.41 � 0.06 0.24 � 0.03 72.2 � 5.3Mar NIL Nil NIL NIL NILMay NIL Nil NIL NIL NILJuly 203.23 � 38.70 1.37 � 0.17 1.13 � 0.04 0.63 � 0.03 297.50 � 10

SReSilicone rubber, PUePolyurethane, PETePolyester, SFeSyntactic foam, GFRPeGlass F

2.11. Correlation study

Correlation between the various biological parameters andsample properties and significance of the measurements werestatistically ascertained with ANOVA using Minitab version 14(Minitab Inc, PA.USA).

3. Results and discussion

3.1. Effect of fouling on polymers

The average temperature, pH, salinity and dissolved oxygen ofthe sea water at Ennore port during the study period were28� 2.04 �C, 8.18� 0.08, 31.60� 3.78 (ppt) and 4.60� 0.39 (mg l�1)respectively. The photographs of the samples immediately onretrieval from the sea water after a period of one year are shown inFig. 1. Presence of macrofoulants on the surface of the samples, areapparent and they became clearer after the removal of the biomass.The predominant macrofoulants observed during this period werebarnacles, hydroids and bryozoans. These macrofoulants were seen

nnore port.

ing unit (CFU/ml) ATP ng/m Chl amg cm�2

Barnaclenumber/plate

Polychaetesnumber/plate

PS

.10 101.3 � 30.0 160.99 � 0.02 0.477 21.7 � 17.60 17.0 � 5.000 37.5 � 2.80 109.46 � 4.34 0.16 1.0 � 1.00 5.0 � 2.000 75.5 � 10.50 138.99 � 10.90 0.367 0.3 � 0.60 00 161.3 � 11.40 168.84 � 28.45 0.452 0 0.3.84 183.3 � 25.20 281.09 � 6.45 0.172 8.7 � 4.00 26.0 � 3.60.15 593.3 � 40.40 321.17 � 17.27 0.54 0.3 � 0.20 4.0 � 2.30

68.3 � 38.8 131.53 � 9.11 1.47 42.0 � 8.5 7.0 � 4.054.8 � 8.3 92.00 � 9.53 0.234 6.0 � 1.0 7.0 � 4.051.7 � 3.2 143.87 � 10.28 0.283 4.0 � 3.0 2.7 � 1.5

.8 138.0 � 21.4 214.20 � 5.80 0.599 2.0 � 2.0 7.3 � 4.9

.95 210.0 � 50.0 328.48 � 2.23 0.552 18.0 � 10.0 35.3 � 10.1

.54 246.7 � 75.1 397.37 � 12.34 0.519 14.3 � 5.9 10.3 � 2.1

172.3 � 19.1 147.04 � 10.77 1.394 17.3 � 11.3 13.7 � 4.267.7 � 7.5 107.67 � 4.38 0.482 5.0 � 1.5 51.3 � 9.2

.5 90.2 � 3.8 155.33 � 12.63 0.413 2.7 � 1.5 2.0 � 1.0168.0 � 0.0 243.73 � 0.0 0.708 0 2.3 � 1.3

.50 620.0 � 0.0 281.09 � 6.45 0.876 9.5 � 5.7 38.5 � 12.0

.59 513.3 � 40.4 409.39 � 7.25 0.6 11.7 � 5.0 5.7 � 2.1

.6 150.0 � 45.8 166.91 � 0.03 2.512 38.3 � 29.5 9.3 � 0.655.3 � 6.5 106.60 � 36.41 0.325 4.3 � 1.0 24.3 � 6.0

137.5 � 6.9 146.55 � 19.33 0.201 7.0 � 3.0 3.0 � 2.6.7 128.3 � 6.7 222.06 � 16.90 0.666 3.3 � 3.1 4.7 � 3.2.55 450.0 � 75.5 313.48 � 47.06 0.299 13.0 � 7.8 17.3 � 13.0.84 696.7 � 168.6 416.51 � 6.91 0.625 17.0 � 3.0 8.7 � 3.8

137.3 � 19.7 156.61 � 25.77 1.593 43.3 � 19.6 36.7 � 3.291.3 � 3.5 137.17 � 10.18 0.614 2.7 � 0.6 44.0 � 16.4

146.0 � 8.8 145.69 � 19.42 0.221 7.0 � 4.6 2.3 � 1.2.6 55.7 � 24.5 199.39 � 41.81 0.806 1.0 � 1.0 10.3 � 7.4.24 870.0 � 43.6 352.09 � 25.17 0.593 13.7 � 7.4 12.7 � 7.3.00 740.0 � 120.0 353.37 � 17.93 0.867 23.7 � 9.1 3.7 � 1.5

96.7 � 14.2 163.50 � 0.03 1.271 44.3 � 19.1 25.0 � 8.782.0 � 6.2 144.61 � 0.00 0.482 3.0 � 0.0 20.0 � 0.0

126.8 � 10.1 158.19 � 7.80 0.211 5.0 � 0.0 3.3 � 0.6NIL NIL NIL NIL NILNIL NIL NIL NIL NIL

.61 965.0 � 106.1 431.41 � 20.89 0.467 17.0 � 5.7 12.5 � 3.5

iber Reinforced Polymer, CFRPeCarbon fibre Reinforced Plastic.

Table 2Physical properties of polymers and composites (control and one year deployed samples).

Name ofthe polymers

Surface energy (mN/m) Root mean squareroughness (nm)

Hardness % Weight loss Mechanical properties

Control After one year

Control One year Control One year Control One year One year Tensilestrength Mpa

% Elongation Tensilestrength Mpa

% Elongation

Silicone rubber 21.43 � 0.15 32.1 � 2.50 168.49 188.97 17.0 � 0.58 15.67 � 0.47 2.91 � 0.05 3.32 � 0.7 203.45 � 2.40 2.33 � 0.9 214.7 � 3.33Polyurethane 36.61 � 0.20 40.5 � 1.52 41.37 181.89 43.2 � 1.58 41.00 � 0.05 4.25 � 0.13 13.58 � 0.12 276.05 � 2.72 11.71 � 0.27 318.55 � 3.16Polyester 34.46 � 0.47 55.59 � 1.33 28.95 102.75 43.6 � 1.30 40.00 � 2.12 7.49 � 0.17 54.29 � 1.62 2.71 � 0.53 46.94 � 1.81 2.14 � 0.47Syntactic foam 38.32 � 0.97 63.61 � 2.31 62.92 317.05 41 � 1.13 34.33 � 0.47 2.14 � 0.52 28 � 0.95 4.5 � 0.39 26.64 � 0.84 2.13 � 0.27GFRP 37.59 � 1.84 54.75 � 2.26 365.9 378.32 47.2 � 1.53 44.00 � 0.70 2.83 � 0.13 147 � 3.46 5.5 � 0.48 119 � 2.39 6.3 � 0.64CFRP 47.63 � 1.37 61.11 � 2.48 324.8 338.12 37 � 1.25 30.00 � 0.02 0.45 � 0.20 e e e e

GFRPeGlass Fiber Reinforced Polymer, CFRPeCarbon fibre Reinforced Plastic.

T. Muthukumar et al. / International Biodeterioration & Biodegradation 65 (2011) 276e284280

to be seasonal. Barnacles and hydroids were generally observedduring September, May and July.

The constituents in the biofilm deposited on the surface of thesamples namely fouling load, proteins, carbohydrates, suspended

Fig. 2. AFM images revealing the surface topography of the polymers and composites befoe-PET, f-CFRP; a1,b1,c1,d1,e1,f1- respective retrieved samples).

solids (TSS), total viable count (colony forming unit CFU), ATP andchlorophyll a measured every alternate month are listed in Table 1.Seasonal effect on biofouling was observed in our current study.Built up of total suspended solids was high in the month of

re and after one year of immersion in marine environment (a-GFRP, b-SR, c-PU, d-SF,

T. Muthukumar et al. / International Biodeterioration & Biodegradation 65 (2011) 276e284 281

September which then decreased in November. It once againincreased during January. Maximum suspended solids wereobserved during the month of September 2008eJuly 2009 (pre-monsoon). An effect of season on the formation of biofilm onpolyolefins and polycarbonate immersed in shallow marine waterhas been previously reported (Sudhakar et al., 2007; Artham et al.,2008). Sudhakar et al. (2007) have reported that the maximumfouling load was seen during the month of August and it variedduring the study period. Attachment and dislodgment of solids onsurface can also lead to varying fouling load, as observed by others(Aziz et al., 2001; Artham and Doble, 2009).

The first set of samples retrieved two months after deploymentindicated that among the six substrates, TSS was highest onsyntactic foam (88 mg cm�2) followed by on CFRP (54.9), GFRP(45.3), PET (37.7), SR (27.4) and PU (22.1). A positive correlation isobserved between surface energy and fouling load (r ¼ 0.93),

Fig. 2. (cont

indicating that hydrophobic materials gets fouled more thanhydrophilic materials. A positive correlation is also observedbetween surface energy and TSS. Adhesion of marine bacterialspecies on different surfaces was investigated by severalresearchers and they concluded that bacterial adhesion is less onlow energy surfaces when compared to adhesion on high energyones. Also they are easy to clean because of weak binding at theinterface (Dexter et al., 1975; Hamza et al., 1977). Kerr and Cowling(2003) suggested that substrates with surface energy between 5and�25mN/mwill haveminimum fouling. In our current studywehave found that the lowest surface energy substrate namely, sili-cone rubber (21.43 mN/m) had lowest fouling. Baier (Hamza et al.,1977; Baier, 1980; Baier et al., 1983) also gave a relationshipbetween surface energy and relative bacterial adhesion. Similarfindings were reported earlier from our lab (Sudhakar et al., 2008).By the end of 12 months, the TSS on all the substrates was almost

inued).

Fig. 3. FTIR of the control and after one year of immersion in marine environment (a)keto carbonyl, (b) ester carbonyl and (c) vinyl bond index.

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the same (28e34 mg cm�2). This indicates that subsequent foulingof surfaces is governed by the initial conditioning film and not onthe initial surface energy of the substrates.

Attachment of macrofoulants such as barnacles was seen moreduring MayeJuly 2009 and hydroids during the monsoon period(November 2009) than any other months. Apart from barnacles andhydroids, other foulants observed includes polychaetes, bryozoansand tube worms. They were not seen in all the samples and theirrelative amount varied from month to month as reported in ourearlier studies on other materials (Sudhakar et al., 2007; Arthamet al., 2008, 2009). Maximum numbers of barnacles were seen onstiff surface such as GFRP (23.7/plate) andminimum number on theflexible surface such as SR (0.3/plate) (see Table 1). Correlationbetween the initial surface properties of the materials and biofilmconstituents are listed in supporting information (Table 1). Surfacehardness seems to affect fouling. Hard surfaces lead to higher bio-film than soft ones (correlation coefficient ¼ 0.68, p < 0.05). Anegative correlation (�0.73) is observed between surface roughnessand TSS, indicating smooth surfaces attract more suspended solidsthan rough ones. A negative correlation was observed betweensurface energy and roughness by us in our earlier field studies withLDPE, HDPE and PC (Sudhakar et al., 2007; Artham et al., 2008;Artham and Doble, 2009) but we did not notice such a relation-ship here. Surface energy and surface hardness seem to positivelyaffect the attachment of barnacles (correlation coefficient of 0.87and 0.79 respectively). Similar results were observed by Becker(1993) on polycarbonate, polytetrafluorethylene (PTFE), and copol-ymers made from PTFE perfluro compounds and by Crisp et al.(1985) on slate. Literature mentions that hard hydrophilic surfacesenhance the attachment of barnacles (Roberts et al., 1991). Surfaceenergy in our study positively affects the attachment of polychaetes.

Biofouling in the marine environment is initially governed bythe surface properties of the material and the bacteria rather thanthe biological processes. These polymers once deployed in themarine are first covered by the conditioning film (Bradshaw et al.,1997; Taylor et al., 1997). This is followed by the attachment ofmacrofoulers. Microfoulers in turn, based on the season, affect theattachment of macrofoulers (DeSouza et al., 2005). The settlementof bryozoans and barnacle on the surface of the polymers differdepending upon the study period (Menon et al., 1977).

Inter correlation between different biofilm constituents namelycarbohydrate, protein, suspended solids, fouling load, TVC and ATPare given in supporting information (Table 2). Protein and TVC,protein and pseudomonas count, ATP and TVC, ATP and pseudo-monas count in the biofilm on all the surfaces are highly correlatedwith each other (correlation coefficient> 0.80). Similar correlationshave been reported earlier by others (D’souza and Bhosle, 2003).

3.2. Effect of fouling on the surface

Table 2, lists the surface roughness, surface energy, hardness,weight loss and tensile strength of all the samples before and afterdeployment for one year. Surface energy in all cases increased(p < 0.001) indicating that they turned relatively hydrophilic. Themaximum increase in the surface energy is mainly attributed topolar groups. Similar findings have been reported by others(Schneider, 1996; Artham et al., 2009) and they attribute thischange to the conditioning film formed on the surface. Maximumgravimetric weight loss was observed in polyester (7.49%) followedby in polyurethane (4.25%). The weight loss is minimal in CFRP(0.45%) indicating that it is stable in marine water. The decrease inweight could be due to the conditioning films, the effect of theextracellular material, the micro and macrofoulants that areattached to the surface. This phenomenon could be termed asa combination of biodegradation and biodeterioration. The tensile

strength and hardness of the samples after one year decreased(p < 0.001) when compared to the control (Table 2), indicating lossof mechanical properties and integrity. Increase in percentageelongation (p < 0.001) indicates increase in stiffness.

Fig. 2 shows the surface topography (AFM image) of the mate-rials before and after one year of deployment in the marine envi-ronment. Roughness of all the surfaces increases after one year(p < 0.001) when compared to the control (Table 2). The maximumincrease was seen in syntactic foam (a difference of 254.13 mm)followed by in polyurethane (140.52 mm) and in polyester(73.80 mm). This may be due to ocean currents and the action ofmicro and macro foulers during this time. Others have alsoobserved that formation of biofilm on the polymers not onlychanges its surface features but also lead to degradation (Cappitelliand Sorlini, 2008; Artham et al., 2009).

T. Muthukumar et al. / International Biodeterioration & Biodegradation 65 (2011) 276e284 283

In thermogravimetric analysis the polymer sample is heated upto 600 �C under nitrogen atmosphere and its weight loss is noted.This method is used to study thermal kinetics of the polymers. Asthe temperature of the sample is increased, the weight of thesample suddenly drops down and finally reaches zero (Thermo-grams are shown in Fig. 1 of supporting information) Polyester(isopthalic polyester resin) showed maximum thermogravimetricweight loss (73.5% at 400 �C) followed by PU (71.1%). GFRP, CFRPand SF showed a TGA weight loss of 58.0, 67.0 and 56.2% respec-tively. Silicone rubber is found to be the most stable material at400 �C and it showed only 2.5% of weight loss when compared tothe control. These results indicate that polyester has undergone themaximum and silicone rubber the minimum biodeterioration inone year.

Fig. 3(aec) shows the carbonyl, ester and vinyl indices for PU,PET, GFRP and CFRP before and after one year of deployment in themarine water. Decrease in carbonyl and ester indices was seen inPET, GFRP and CFRP indicating that they had undergone bioticdegradation. PET showed maximum reduction in its carbonyl andvinyl indices when compared to others (p < 0.001) and alsoexhibited highest gravimetric weight loss. Whereas an increase incarbonyl and ester indices was seen in PU indicate abiotic oxida-tion. Increase in vinyl index was found in all the four materialsprobably due to biotic degradation through Norrish type II mech-anism or through ester formation (Gustavasson et al., 2001). Nosignificant changes were observed in the IR pattern of syntacticfoam. Increase in the absorbance peak at 1000e1130 cm�1 indicatesthe cross linking of silicone rubber, either by stretching vibration ofSieO or SieCH2eSi bonds (Chipara et al., 1999; Gustavasson et al.,2001) (FTIR spectra of all the materials are given in Fig. 1 of sup-porting information). Oxidation index for SR decreased from 2.3 to1.97 after a year, indicating the possibility of biotic degradation.

4. Conclusion

Surface of materials immersed in sea water foul. Biofoulingprocess is a complex phenomenon. Build up of biofilm parameterssuch as TSS, Protein, carbohydrate and TVC were in September,which then decreased in November. It once again increased andreached a maximum in July. The attachments of barnacles werehigher during the months of MayeJuly 2009 and hydroids duringthe monsoon period (November 2009) when compared to othermonths. Biofouling has an effect on the biodegradation and stabilityof polymers. Our current study suggests that the surface properties(roughness, surface energy and hardness) determine the formationof initial biofilm and further biofouling does not seem to depend onthese properties. Initial fouling on the surface is directly propor-tional (positive correlation) to the surface energy. Surface energydecreases with time indicating that surfaces turn relativelyhydrophilic. Once a material is immersed in sea environment, itsphysical and chemical properties change due to adsorption ofmacromolecules and early colonisers. The subsequent attachmentof the colonisers may not depend on the initial physical property ofthe substratum. Biofouling seem to affect the physical andmechanical properties such as gravimetric and thermogravimetricweight losses, tensile strength, surface energy, and hardness of thematerials. FTIR spectrum shows that biotic degradation areobserved in few cases (PET, GFRP and CFRP) and abiotic oxidation inothers (PU). Maximum gravimetric and thermogravimetric weightloss is observed with PET. This study gives ample evidence that theweight loss of the polymers is due to deterioration and degradationof the polymers. Biofouling and attachment of barnacles areminimum on silicone rubber probably because of its flexible nature.On the contrary stiff surface (GFRP) attract more attachment ofbarnacles and polychaetes.

Acknowledgement

We thank Naval Research Board, New Delhi, for providing us thefinancial support. Director of NIOT, Chennai and Sophisticatedanalytical instrument facility, IIT Madras for analytical support andMr. P. Kumar, Department of Metallurgy, IIT Madras for his helpduring the sample collection.

Appendix. Supporting information

Supporting information related to this article can be foundonline at doi:10.1016/j.ibiod.2010.11.012.

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