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The deterioration of coatings by microbiological attack takes place directly or indirectly as a result of metabolic activity of microorganisms. The most severe bacterial corrosion occurs due to presence of sulphate reducing bacteria (SRB), as these produce hydrogen sulphide, leading to formation of metal sulphides and sulphates. Such type of microbiological corrosion can be controlled by incorporating suitable biocide in the coating. The objective of this study was to simulate such microbiological corrosion phenomena in the laboratory and observe its effect on the coating performance. In the present work, experiments were conducted to assess the antibacterial property of epoxy based anticorrosive coatings, with and without of biocide, by exposing them to SRB culture under anaerobic condition. Coal tar epoxy (CTE)-polyamide coating system which is known for superior antibacterial properties was selected as benchmark. The SRB effectiveness was evaluated by the formation of zone of inhibition in nutrient agar and visual observation. The surface morphology of coatings before and after exposure was analysed by scanning electron microscopy (SEM). The anticorrosive property of these coatings under SRB exposure was also monitored by measuring impedance of the coating by electrochemical impedance spectroscopy (EIS). The loss in adhesion after exposure was also measured for all the coatings.

Coal tar epoxy (CTE) coating system has been widely used for protection of steel structures under atmospheric, buried and immersion conditions because of their low water vapour permeability, high electrolyte resistance and good antibacterial properties. However, coal tar has been classified as carcinogen, mutagen and toxic for reproduction (CMR) as per International guideline (REACH, IARC and GS 11). It is now banned in the developed nations like US, Europe, Japan, etc. As the use of coal tar is being restricted, there is an urgent need to formulate a coal tar free epoxy product for corrosion protection of structures. In the present study, alternative approaches have been proposed to replace coal tar such as bitumen (BIT), hydrocarbon resin (HR), flexibilizer (FL) and curing agents like polyamide (PAD) or polyamine (PAM). Four different coal tar free formulations were formulated separately by using these approaches. The standard CTE and coal tar free epoxy compositions were evaluated for mechanical properties such as elongation at break, tensile strength, adhesion strength and resistance to abrasion, impact and flexibility. The resistance to corrosion of optimized composition (epoxy-HR-FL-PAD-PAM) and coal tar epoxy coating was evaluated by exposing to different environments. The corrosion resistance property was also evaluated by cathodic disbondment and electrochemical impedance spectroscopy (EIS) technique. Results indicate that epoxy-hydrocarbon resin-flexibilizer composition cured with blend of polyamide and polyamine has comparable mechanical and corrosion protection properties to that of standard CTE.

To study the effect of pigmentation on mechanical and anticorrosive properties of thermally sprayable ethylene vinyl acetate (EVA)/polyethylene (PE) and ethylene vinyl alcohol (EVAl)/PE coatings, red iron oxide (RIO) and titanium dioxide (TiO 2 ) pigments at varying concentration (10, 20 and 30%) were mixed using internal mixer. Pigmented compositions were characterized for mechanical properties and water vapor transmission rate (WVTR). These compositions were applied on grit blasted mild steel surface by flame spray technique and coated specimens were evaluated for adhesion strength, abrasion resistance and resistance to corrosion by exposing them in different environments. The corrosion resistance of pigmented composition was also studied by electrochemical impedance spectroscopy (EIS) technique.

Application of thermally sprayable polymeric coating is one of the methods for protection of mild steel against corrosion. In the present study, grafting of low density polyethylene (LOPE) was carried out with maleic acid at different concentrations (3, 5, 8 and 10%, w/v) using gamma-irradiation technique. LOPE, gamma-irradiated LOPE and grafted LDPE (LDPE-g-MAc) were characterized by chemical method, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and melt flow index (MFI). Grafted LDPE was pigmented with nanoclay (NC) at varying concentrations (1, 2, 3 and 4 wt.%) using melt mixing method. Pigmented compositions were evaluated for their mechanical properties and dispersion characteristics using X-ray diffraction (XRD). LDPE-g-MAc/nanocomposite with 3 wt.% nanoclay showed superior mechanical properties and maximum d-spacing value. This composition was applied on grit blasted mild steel specimens by flame spray technique and evaluated for adhesion strength, abrasion resistance and resistance to corrosion in different exposure conditions. Electrochemical Impedance Spectroscopy (EIS) technique was also employed to study the corrosion resistance behavior of the nanocomposite coating. (C) 2011 Elsevier B.V. All rights reserved.

Application of polymeric coatings is one of the methods for protection of mild steel against corrosion. In the present work, blends of different grades of ethylene vinyl acetate (EVA) with varying vinyl acetate (VAc) content viz. 18%, 28%, 40% and hydrolyzed EVA i.e., ethylene vinyl alcohol (EVAl) with low density polyethylene (PE) have been used as binder for development of anticorrosive coating. The blend compositions were characterized using differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and melt flow index (MFI) techniques for determination of melting point, degradation temperature and flow behavior respectively. The blend compositions were applied on grit blasted mild steel specimens by flame spray technique and the coated specimens were evaluated for their resistance to corrosion in salt spray, humidity and seawater. EVA/PE based compositions showed superior resistance to corrosion compared to EVAl/PE based compositions in all exposure conditions after 8 weeks. The corrosion resistance of blend compositions was also studied by electrochemical impedance spectroscopy (EIS) technique. The results indicate that EVA/PE coatings have better resistance to corrosion than EVAl/PE coatings.

Dispersion of nanoclay (NC) in polymer blend system is governed by the sequence of addition of different ingredients. In the present work nanoclay was added in different sequences to blend composition such as ethylene vinyl acetate (EVA)/low density polyethylene (LDPE) and ethylene vinyl alcohol (EVAl)/LDPE in internal mixer to get nanocomposite. It was found that sequential addition of individual polymers and nanoclay influenced mechanical properties of resulting composites. Blending sequence of PE/NC/EVA and PE/NC/EVAl gave best mechanical properties. After optimization of addition sequence, concentration of nanoclay was varied from 1 to 8% by weight in the polymer blend. The resulting composites were evaluated in terms of their mechanical properties, dispersion characteristics (XRD), water vapor transmission rate (WVTR) and water absorption (Wa). Nanocomposite containing EVA/LDPE blend with 4% nanoclay showed optimum properties. The optimized composition was applied on grit blasted mild steel specimens by flame spray technique. The coated specimens were evaluated for adhesion strength, abrasion resistance and resistance to corrosion properties.

Ethylene vinyl acetate (EVA) copolymer with varying vinyl acetate (VAc) content, viz. 18%, 28% and 40% has been hydrolyzed using alcoholic NaOH solution. Fourier Transform Infrared Spectroscopy (FTIR) analyses of hydrolyzed polymer showed the presence of both OH group and acetate group indicating that the EVA has been partially hydrolyzed. Differential Scanning Calorimeter (DSC) and Thermo Gravimetric Analyzer (TGA) of EVA and hydrolyzed EVA showed large difference in melting and decomposition temperature, respectively. Hydrolyzed EVA showed higher tensile strength and elongation at break compared to corresponding EVA. Blends of different grades of EVA and ethylene vinyl alcohol (EVAl) with low density polyethylene (LDPE) were applied on grit blasted mild steel surface by flame spray technique. FTIR analysis of blends before and after coating showed no degradation during flame spray. Measurement of adhesion strength of these coating showed that adhesion strength increased on hydrolysis of EVA.

Application of organic coatings is one of the methods for protection of mild steel against corrosion. In the present work, low-density polyethylene (LDPE) has been used as binder for development of anticorrosive coating. Since non-polar characteristics of LDPE make its adhesion poor to most substrates, polar groups have been introduced in LDPE by grafting maleic acid (MAc) using reactive extrusion method. Grafted LDPE was characterized by chemical method, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), wide angle X-ray scattering (WAXS) and melt flow index (MFI). Grafted LDPE was pigmented with different pigments such as red iron oxide, micaceous iron oxide (MIO), titanium dioxide (TiO2) and aluminium at three concentrations (i.e., 20, 30 and 40%). These compositions were applied on grit blasted mild steel specimen by flame spray technique. The coated specimens were evaluated for adhesion strength and resistance to corrosion in salt spray, humidity and seawater. Red iron oxide-based composition showed better adhesion and corrosion resistance compared to other compositions. Subsequently, corrosion resistance of red iron oxide-based compositions was studied by electrochemical impedance spectroscopy (EIS). The modified LDPE coating containing 30% red iron oxide showed higher resistance to corrosion compared to 20 and 40% red iron oxide-based compositions., © Elsevier

Low density polyethylene (LDPE) coatings are being used in an ever growing range of applications. However, non-polar characteristics of LDPE make its adhesion poor to metal substrate and so become less suitable for anticorrosive coating application. An anticorrosive coating can therefore be developed if LDPE is modified with requisite polar groups. In the present work, a polar group has been introduced in polyethylene matrix by grafting maleic acid. Grafted LDPE was characterized by chemical method, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), melt flow index (MFI), particle size analysis and hot stage optical microscopy. The presence of carbonyl peak of high intensity, high acid value and low melt flow index value confirmed grafting of maleic acid on LDPE. Change in crystallization behaviour of LDPE has been noticed after grafting. Grafted LDPE was applied on grit blasted mild steel surface by flame spray technique and adhesion study showed improved adhesion of grafted LDPE than LDPE. The coated panels were evaluated for resistance to corrosion in salt spray, humidity cabinet and seawater. The corrosion resistance of modified LDPE was also studied by AC Impedance technique. Grafted LDPE showed satisfactory corrosion resistance. Grafted LDPE was pigmented with red iron oxide and pigmented composition has shown improved resistance to corrosion in laboratory tests., © Elsevier

Grafting of maleic acid (MAc) on low density polyethylene (LDPE) was carried out using γ-irradiation technique. Preactivation method was used for grafting and a maximum grafting of 2.4% was obtained. Grafted polymer(LDPE-g-MAc) was characterized by chemical method, Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermo-Gravimetric Analysis (TGA), Melt Flow Index (MFI), Tensile Property Measurement, Particle Size Analysis, and Hot Stage Optical Microscopy. Presence of carbonyl peak of high intensity, high acid value, and low melt flow index value confirmed grafting of MAc on LDPE. A marginal change in thermal and mechanical properties of LDPE was observed after grafting. Change in crystallization behavior of LDPE has been noticed after grafting. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2802–2807, 2004