Water Journal : Water Journal March 2011
refereed paper sewer processes water MARCH 2011 77 the tortuosity provided by the filler. Lu and Mai (Lu et al. 2005) proposed the following simple tortuosity model: (3) Examination of our results, however, show the diffusion coefficients are lowest when the concentration of filler is low (~12%) and highest when the filler concentrations are high (>40%) (see Figure 6). This appears to contradict the tortuosity model proposed by Lu and Mai (Lu et al. 2005) This effect is most prominent as the coating thickness increases, which could suggest issues with filler dispersion. Intuitively increasing the concentration of the filler should provide a greater barrier to acid permeation. However, substantially increasing the concentration of the filler could induce the clustering of the filler and, in effect, increase the overall particle size and reduce tortuosity (see coatings A and D in Figure 2). The effect of the shape or the aspect ratio on the diffusion coefficient was not evident in this study; however, it is clear the reduced particle size of the filler resulted in lower acid permeability (see Figure 7). Conclusions The following conclusions were derived from this study: I. The tortuosity of composite epoxy coatings was imposed by polymer alignment and filler properties including filler size, dispersion and concentration. II. Thicker coatings did not necessarily provide greater protection. The alignment of the polymer chains, which lent itself to greater tortuosity, appeared to control the permeation through the coating. Greater chain alignment was characteristic of thinner coatings and this affected higher tortuosity and lower acid permeability. III. The filler concentration in effect provided greater tortuosity. However, there was a limit to the concentration that would promote an effective barrier. Increasing the concentration of the filler promoted greater clustering, which appears to have resulted in larger particle size and reduced tortuosity. I V. There was little evidence of the effect of the shape or aspect ratio of the filler. However, reducing the particle size of the filler was found to significantly reduce the permeability of sulfuric acid. Acknowledgements The authors would like to acknowledge H Mineyama, WH Cheung and J Shi from the School of Chemical and Biomolecular Engineering, University of Sydney, who performed the experiments and analytical testing of the samples for this study (email: firstname.lastname@example.org; email@example.com, firstname.lastname@example.org). The Authors Dr Marjorie Valix is Associate Professor at the School of Chemical and Biomolecular Engineering, University of Sydney (email: email@example.com). Dr Heri Bustamante is Project Manager at Science & Technology (Sydney Water), PO Box 399, Parramatta, NSW 2124 (email: Heri. Bustamante@sydneywater.com.au). References Alexandre B, Langevin D, Mederic P, Aubry T, Couderc H, Nguyen QT, Saiter A & Marais S (2009): Water barrier properties of polyamide 12/montmorillonite nanocomposite membranes: Structure and volume fraction effects. Journal of Membrane Science 328: 186-204. ASTM, ASTM G62-07 (1998): Standard Test Methods for Holiday Detection in Pipeline Coatings. Aviam O, Bar-Nes G, Zeiri Y & Sivan A (2004): Accelerated biodegradation of cement by sulfur-oxidising bacteria as a bioassay for evaluating immobilisation of low-level radioactive waste. Applied and Environmental Microbiology 70: 6031-6036. Crank J (1956): The mathematics of diffusion: Oxford, Clarendon. Herrera-Alonso J M, Marand E, Little JC & Cox SS (2009): Transport properties in polyurethane/ clay nanocomposites as barrier materials: Effect of processing conditions. Journal of Membrane Science 337: 208-214. Isoda S, Shimada H, Kochi M & Kambe H (1981): Molecular aggregation of solid aromatic polymers: Small-angle X-ray-scattering from aromatic polyimide film. Journal of Polymer Science Part B-Polymer Physics 19: 1293- 1312. Liu J, Vipulanandan C (2003): Modeling water and acid transport through coated cement concrete. ASCE Journal of Engineering Mechanics 129: 426-437. Liu J & Vipulanandan C (2004): Long-term performance of epoxy coated clay bricks in acid. Journal of Materials in Civil Engineering 16: 349-355. Liu W, Hoa S & Pugh M (2008): Water uptake of epoxy-clay nanocomposites: Model development. Composites Science and Technology 68: 156-163. Lu CS & Mai YW (2005): Influence of aspect ratio on barrier properties of polymer-clay nanocomposites. Physical Review Letters 95. Lu CS & Mai YW (2007): Permeability modelling of polymer-layered silicate nanocomposites. Composites Science and Technology 67: 2895- 2902. Mensitieri G, Delnobile MA, Monetta T, Nicodemo L & Bellucci F (1994): The effect of film thickness on oxygen sorption and transport in dry and water-saturated Kapton® polyimide. Journal of Membrane Science 89: 131-141. Nixon R (1997): Future Material Selection Guidelines for Coatings on Concrete for Changing Exposure Conditions in Large Municipal Waste Water Collection/Treatment Systems. Corrosion 97 Paper 379. Pongjanyakul T & Puttipipatkhachorn S (2008): Alginate-magnesium aluminum silicate composite films: Effect of film thickness on physical characteristics and permeability. International Journal of Pharmaceutics 346: 1-9. Ray SS & Okamoto M (2003): Polymer/layered silicate nanocomposites: A review from preparation to processing. Progress in Polymer Science 28: 1539-1641. Sand W & Bock E (1991): Biodeterioration of Mineral Materials by Microorganisms -- Biogenic and Nitric-Acid Corrosion of Concrete and Natural Stone. Geomicrobiology Journal 9: 129-138,. Sroog CE (1991): Polyimides. Progress in Polymer Science 16: 561-694. Sun LY, Boo WJ, Clearfield A, Sue HJ & Pham HQ (2008): Barrier properties of model epoxy nanocomposites. Journal of Membrane Science 318: 129-136,. Yamanaka T, Aso I, Togashi S, Tanigawa M, Shoji K, Watanabe T, Watanabe N, Maki K & Suzuki H (2002): Corrosion by bacteria of concrete in sewerage systems and inhibitory effects of formates on their growth. Water Research 36: 2636-2642. Yang DK, Koros WJ, Hopfenberg HB & Stannett VT (1986): The effects of morphology and hygrothermal aging on water sorption and transport in Kapton polyimide. Journal of Applied Polymer Science 31: 1619-1629.
Water Journal April 2011