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Electron beam processed plasticized epoxy coatings for surface protection
Materials Chemistry and Physics 130 (2011) 237–242
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Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Electron beam processed plasticized epoxy coatings for surface protection Mervat S. Ibrahim a , Heba A. Mohamed b,∗ , Nadia G. Kandile c , Hossam M. Said a , Issa M. Mohamed a a
National Center for Radiation Research and Technology, Nasr City, Egypt National Research Center, Dokki, Egypt c University College for Girls, Ain Shams University, Egypt b
a r t i c l e
i n f o
Article history: Received 5 December 2010 Received in revised form 14 June 2011 Accepted 18 June 2011 Keywords: Electron beam Corrosion Inhibitor Mild steel
a b s t r a c t Epoxy acrylate oligomer (EA) was plasticized by adding different plasticizers such as epoxidized soybean oil, glycerol and castor oil and cured by electron beam (EB). Different irradiation doses (1, 2.5 and 5 Mrad pass−1 ) were used in the curing process. The effect of both different irradiation doses and plasticizers on the end use performance properties of epoxy acrylate coating namely, pencil hardness, bending test, adhesion test, acid and alkali resistance test were studied. It was observed that incorporation of castor oil in epoxy acrylate diluted by 1,6-hexanediol diacrylate (HD) monomer with a ratio (EA 70%, HD 20%, castor oil 10%) under 1 Mrad pass−1 irradiation dose improved the physical, chemical and mechanical properties of cured films than the other plasticizer. Sunflower free fatty acid was epoxidized in situ under well established conditions. The epoxidized sunflower free fatty acids (ESFA) were subjected to react with aniline in sealed ampoules under inert atmosphere at 140 ◦ C. The produced adducts were added at different concentrations to epoxy acrylate coatings under certain EB irradiation dose and then evaluated as corrosion inhibitors for carbon steel surfaces in terms of weight loss measurements and corrosion resistance tests. It was found that, addition of 0.4 g of aniline adduct to 100 g epoxy acrylate formula may give the best corrosion protection for carbon steel and compete the commercial corrosion inhibitor efficiency with the same concentration. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Thermal curing processes of solvent-based coatings creates environmental pollution by emitting large amount of volatile organic compounds (VOC) and other hazardous air pollutants (HAP) into the atmosphere [1–4]. As environmental and public health concerns have become major issues in the coating processes, the radiation curing process has been found to be an effective alternative to solvent borne technology in the coating industry. Radiation curing is a polymerization/cross-linking process, initiated by highenergy radiation, to convert a reactive liquid chemical system into a non-tacky solid cross-linked network at room temperature with virtually zero emission of VOC or HAP since these systems are one hundred percent reactive and usually contain no solvents. EB curing of resins containing acrylate end groups have been the subject of interest of many research groups recently because of mainly two reasons [5]. The first is the benefit offered by the EB curing process and second is a wide range of properties achieved by proper selection and combinations of the oligomers [6,7]. Epoxy acrylates and urethane acrylate resins, in particular, have been the backbone of
∗ Corresponding author. Tel.: +20 101557520; fax: +20 225203197. E-mail addresses: [email protected], [email protected] (H.A. Mohamed). 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.06.033
radiation and electron beam cured coatings for over 20 years. Both the resins have their distinct properties [8]. The use of corrosion inhibitors is one of the most practical methods for protection against metallic corrosion. In general, organic compounds, such as amines, acetylenic alcohols, and heterocyclic compounds, have been in use as corrosion inhibitors in industrial applications [9–12]. Some workers, prepared efficient corrosion inhibitors by the reaction of the epoxidized linseed oil free fatty acids with different aliphatic amines and p-substituted anilines [13]. The protection against corrosion imparted by epoxy paints modified by the addition of polyaniline emeraldine salt and polypyrrole composite with carbon black as additives of an epoxy paint coating were studied [14,15]. The addition of polyaniline corrosions has better efficiency in protection against corrosion than spinel-type pigments alone in the solvent-based alkyd resin [16]. The reaction product of epoxidized soy bean oil with sulfur compounds were used as good corrosion inhibitors in varnish based on Alkyd resin [17]. Also they could be emulsified and applied with emulsion polymers in water based paints [18]. The objective of the work is to use low viscosity plasticizers to adjust and regulate the application viscosity of epoxy acrylate oligomers for better applicability of the coating and to study the effect of irradiation doses and plasticizers concentration on end use performance properties of epoxy acrylate coatings. Also,
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M.S. Ibrahim et al. / Materials Chemistry and Physics 130 (2011) 237–242 Table 1 The physical, mechanical and chemical properties of epoxy acrylate cured films without any additives.
Fig. 1. Chemical structure of epoxy acrylate oligomer.
preparation and evaluation of epoxidized free fatty acid/aniline adduct as corrosion inhibitor in epoxy acrylate formulations to protect carbon steel is another target. 2. Materials and experimental techniques 2.1. Materials
Test
Formulation composition (%) EA/HD 80/20
Irradiation dose (Mrad pass−1 ) Hardnessa Adhesionb Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
1 7H 3B Not pass v.g. v.g. v.g.
2.5 9H 4B Not pass v.g. v.g. v.g.
5.0 9H 4B Not pass v.g. v.g. v.g.
a Lead pencils supplied with the unit, softest to hardest, are as follows: 9B, 8B, 7B, 6B, 5B, 4B, 3B, 2B, B, HB, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H. b The adhesion of the cured films decreases in the following descending order: 5B > 4B > 3B > 2B > B > 0B.
All the used chemicals are originally pure and no further purification is carried out. EBECRYL 604 (Epoxy acrylate oligomer consisting of 80% of bisphenol A epoxy diacrylate diluted with 20% of 1,6-hexanediol diacrylate) was obtained from Cytec Surface Specialties (Drogenbos, Belgium) and represented in Fig. 1. Inert plasticizers (Castor oil, epoxidized soybean oil and glycerol) were used for plasticization of epoxy acrylate oligomer for curable coating formulations. Castor oil was delivered from paint and chemical industry (PACHIN), Egypt, with molecular weight 933 and its molecular formula C57 H104 O9 . Epoxidized soybean oil was delivered from Paint and Chemical Industry (PACHIN), Egypt. Its molecular weight is 1000 and its molecular formula is C57 H106 O10 . Glycerol was supplied by El Naser Pharmaceutical Chemical Co., Egypt. Its molecular weight is 92.09 and molecular formula is C3 H5 (OH)3 . Sunflower oil free fatty acid with iodine value of 130–150 was used and supplied by Paint and Chemical Industry (PACHIN), Egypt. Dowex 50W-8X (20–50 mech) is a sulphonated poly(styrene/divinyl benzene) copolymer, dark yellow solid particles and product of Dow Chemicals Ltd., England. Aniline was supplied from Aldrich Co. Ltd., Germany. Commercial inhibitor was delivered from Petrolite Ltd., England under trade name EPRI 523.
2.2.6. Testing and evaluation The formulated epoxy coatings were tested and evaluated in absence and presence of the prepared epoxydized sun flower free fatty acid/aniline adduct (EP-SF–An) as corrosion inhibitor, according to well-known standard methods. Steel panel surface was prepared before coatings applications according to ASTM D 609-52. Dry film hardness was measured using Wolff-Wilborn pencil hardness tester according to ASTM D 3363. Bending test was done by mandrels of 2 mm according to ASTM D 1737-73. Film adhesion was measured according to DIN 53 151. Corrosion scratch test of coated carbon steel (5 cm × 7 cm) was determined after 28 days immersion in artificial seawater (27.26 g sodium chloride, 3.51 g magnesium chloride, 1.84 g magnesium sulfate, 0.69 g potassium chloride, 0.11 g sodium bicarbonate, 0.09 g potassium bromide and 1.29 g calcium sulfate), according to ASTM D 1654. Blister resistance test was determined according to ASTM D 714. Steel rusting was determined according to ASTM D 610. Weight loss measurements of 3 cm × 3 cm dimension coated steel panels were determined according to ASTM D 2688. Alkali resistance test in solution of 5% NaOH was determined according to ASTM D 1647. Acid resistance test in solution of 5% HCl was determined according to ASTM B 287.
2.2. Techniques 2.2.1. Preparation of epoxidized sunflower free fatty acid Sunflower free fatty acids were epoxidized in situ under well-established conditions [19]. 0.238 mole of sunflower oil free fatty acids was mixed with the 1.14 mole of acetic acid (one mole/double bond) and 50 g of catalyst (Dowex 50W-8X) was added together with 100 ml benzene. The flask is heated by means of temperature controlled water bath. A moderate regular stirring is applied during the preparation. When the temperature of the reaction reaches 70 ◦ C, hydrogen peroxide (3.6 moles) is added dropwise within 2 h. After about 4 h, the reaction mixture is separated by separating funnel to get rid off the water layer. The oil layer was washed several times with warm distilled water till acid free and finally dried under reduced pressure at 40 ◦ C. 2.2.2. Determination of oxirane oxygen content [20] A sample of 0.5 g was accurately weighed into 50 ml flask, dissolved in 5 ml benzene or chlorobenzene and 5 drops of crystal violet indicator were added. The sample was stirred and titrated against 0.1 N HBr in glacial acetic acid solution till bluish green end point. The oxirane oxygen content was determined using equation below: Oxirane oxygen content (%) =
L × N × 1.6 W
where L is the volume of HBr solution, N is the normality of HBr solution, and W is the weight of the sample. 2.2.3. Preparation of corrosion inhibitor Aniline was mixed with epoxidized sunflower free fatty acid in stoichiometric amounts, i.e. one mole aniline per each epoxy group and one mole aniline per each carboxylic group. The reactions were carried out in sealed ampoules and at 130 ◦ C. 2.2.4. Fourier transform infrared (FTIR) spectrometry ATI Mattson, Genesis series, Fourier transform infrared spectrometry was used. 2.2.5. Electron beam irradiation Energy1.5 MeV, power 37.5 kW, beam current 25 mA and scan width variable up to 90 cm. The formulations were applied as a thin film on different substrates such as glass, tin metal and carbon steel metal by using film applicator (100 m thickness) and were exposed to 1 Mrad pass−1 , 2.5 Mrad pass−1 and 5 Mrad pass−1 doses of electron beam radiation.
3. Results and discussion Many attempts have been made to cure the epoxy-acrylate (EA) oligomer and 1,6-hexanediol diacrylate (HD) monomer with ratio (80%:20%) respectively without any additives under different irradiation doses (1 Mrad pass−1 , 2.5 Mrad pass−1 and 5 Mrad pass−1 ). As shown in Table 1 it is found that, all cured films are very hard and their hardness increase with increasing of irradiation doses and this may be due to the formation of high degree of cross linking density. On the other hand, the flexibility of all cured films is very bad and they fail to pass bending test. However, the cured films give the accepted adhesion and pass the chemical tests (acid, alkali, and water resistance tests) under different irradiation doses. However, their film flexibility can be modified by adding non-reactive plasticizer such as natural oils, polyesters and polymerizable celluloses [21]. Epoxy acrylate resins generally are high viscosity reactive oligomers due to the strong hydrogen bonding through secondary hydroxyl groups and produce hard, glossy and chemical resistance coating. Due to rigid and brittle nature, epoxy resins exhibit low toughness, and poor wear and crack resistance in a real application. To overcome these problems, a considerable amount of work has been carried out in the direction of toughening epoxies, with some research focused on introducing rubbery and flexible components into epoxy networks in an appropriate ratio [22]. The aim of this work is to optimize the percent of different types of plasticizer and select the suitable irradiation dose for curing the epoxy acrylate coatings formulations. Also it is interesting to choose the best plasticized epoxy acrylate formula and improve its corrosion inhibition efficiency by different concentrations of the prepared epoxydized sun flower free fatty acid/aniline adduct (EPSF–An). A comparative study with commercial organic corrosion inhibitor is our aim to make this work applicable in the industrial field.
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Table 2 The physical, mechanical and chemical properties of cured films of series A. Test
Formulation composition (%) EA/HD/Glycerol 75/20/5 −1
Irradiation dose (Mrad pass Hardness Adhesion Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
)
1.0 4H B Not pass v.g. v.g. v.g.
2.5 5H 2B Not pass v.g. v.g. v.g.
EA/HD/Glycerol 70/20/10 5.0 7H 2B Not pass v.g. v.g. v.g.
1.0 4H B Not pass v.g. v.g. v.g.
2.5 5H B Not pass v.g. v.g. v.g.
EA/HD/Glycerol 65/20/15 5.0 7H 2B Not pass v.g. v.g. v.g.
1.0 4H 0B Not pass v.g. v.g. v.g.
2.5 5H 0B Not pass v.g. v.g. v.g.
5.0 7H B Not pass v.g. v.g. v.g.
Table 3 The physical, mechanical and chemical properties of cured films of series B. Test
Formulation composition (%) EA/HD/ESOL 75/20/5
Irradiation dose (Mrad pass−1 ) Hardness Adhesion Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
1.0 5H B Not pass v.g. v.g. v.g.
2.5 6H B Not pass v.g. v.g. v.g.
EA/HD/ESOL 70/20/10 5.0 8H 2B Not pass v.g. v.g. v.g.
3.1. Coating formulations containing different plasticizers This part consists of three series of different epoxy acrylate coating formulations (A, B, and C). Each series includes three coating formulations which cured under different irradiation doses. The percent of epoxy acrylate oligomer for each coating series in this group is varied from 75% to 65%. Also, the plasticizer percent for each coating series in this group is varied from 5% to 15%, by increasing of 5%. The difunctional monomer (1,6-hexanediol diacrylate) which used as a thinner for the viscosity of oligomer has the same percent (20%) in all above mentioned series. In addition to blank formula without any plasticization, a series of formulations containing different plasticizers namely (A) for glycerol, (B) for epoxidized soybean oil and (C) for castor oil are prepared and their properties are mentioned in Tables 1, 2, 3 and 4, respectively. With respect to series (A) and (B) which contain glycerol and epoxidized soybean oil as plasticizers, respectively. It is clear that, hardness of cured films increase by increasing the irradiation dose, due to the formation of high degree of crosslinking density and make the cured films harder. It is found that the cured films fail to pass the bending test for all formulations. Moreover, the cured films in all formulations have a bad adhesion but they have good chemical resistance (acid, alkali, and water media) without considerable defects. On the other hand, the formulations composition, physical, mechanical and chemical test results of the cured films of series (C) which contain a castor oil as plasticizer are shown in Table 4. They show good hardness and moderate adhesion in all formulations
1.0 5H 0B Not pass v.g. v.g. v.g.
2.5 6H 0B Not pass v.g. v.g. v.g.
EA/HD/ESOL 65/20/15 5.0 8H B Not pass v.g. v.g. v.g.
1.0 5H 0B Not pass v.g. v.g. v.g.
2.5 6H B Not pass v.g. v.g. v.g.
5.0 8H B Not pass v.g. v.g. v.g.
except the formulation containing EA 70%, HD 20%, and castor oil 10% under1 Mrad pass−1 irradiation dose which gave the best adhesion and passed bending test due to the formation of low degree of crosslinking density that makes the cured films more elastic. Moreover, all coating films of this series were successfully passed the chemical tests including acid, alkali, and water resistance tests. Based on physical, mechanical and chemical tests, it can be concluded that, formulated coatings with EA 70%, HD 20%, and castor oil 10% and cured under1 Mrad pass−1 irradiation dose, show the best properties compared with other formulations. This may be due to saturated long chain of castor oil plays important rule in plasticization of epoxy acrylate oligomer. So it is interesting to apply this formula in anticorrosive coating for mild steel and improve its corrosion inhibition efficiency by prepared epoxidized free fatty acid/anline adduct. 3.2. Preparation of epoxidized sunflower free fatty acid/anline adduct Sunflower free fatty acid was epoxidized by preparing peracetic acid in situ process using Dowex 50W-8X as a catalyst. The oxirane oxygen content of the prepared epoxidized sunflower free fatty acid was measured volumetrically by titration against HBr in glacial acetic acid solution and it was found to be 5%. Fig. 2 represents the difference between the IR spectrum of the sunflower free fatty acid and its epoxidized. The IR spectrum of epoxidized free fatty acid shows a very characteristic band of the epoxy group, which appears at 824 cm−1 and characteristic band of
Table 4 The physical, mechanical and chemical properties of cured films of series C. Test
Formulation composition (%)
Irradiation dose (Mrad pass−1 ) Hardness Adhesion Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
1.0 4H 3B Pass v.g. v.g. v.g.
EA/HD/Castor oil 75/20/5 2.5 5H 3B Not pass v.g. v.g. v.g.
EA/HD/Castor oil 70/20/10 5.0 6H 4B Not pass v.g. v.g. v.g.
1.0 4H 4B Pass v.g. v.g. v.g.
2.5 5H 4B Not pass v.g. v.g. v.g.
EA/HD/Castor oil 65/20/15 5.0 6H 5B Not pass v.g. v.g. v.g.
1.0 4H 3B Pass v.g. v.g. v.g.
2.5 5H 3B Not pass v.g. v.g. v.g.
5.0 6H 4B Not pass v.g. v.g. v.g.
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Table 5 Coating formulations by adding aniline adduct as corrosion inhibitor. Composition
Epoxy acrylate (%) 1,6-Hexanediol diacrylate (%) Castor oil (%) EP-SF–An (g)
Formula no. Blank
Formulations
S1
S2
S3
S4
S5
S6
70 20 10 0.2
70 20 10 0.4
70 20 10 0.6
70 20 10 0.8
70 20 10 1.0
70 20 10 –
In addition, another a bending band near 1560 cm−1 due to secondary N–H, C C band at 1600 and 1500 and C–H band of aromatic ring at 3030. These observations indicate that the epoxy/amine reaction has taken place successfully.
Fig. 2. IR-spectra of sunflower free fatty acid, its epoxidized sunflower free fatty acid and aniline adduct.
C–O group appears at 1160 cm−1 . Also this figure reveals disappearance of the characteristic bands of the sunflower free fatty acid (i.e. C C band at 1630 cm−1 ). The carboxylic acid group exhibits two bands, a strong band at 1740 cm−1 due to C O group and broad band at 3475 cm−1 due to O–H group. Also, there is a strong band at 2940 cm−1 due to aliphatic C–H attached to the carboxylic group. The produced epoxidized sunflower free fatty acid was allowed to react with aniline stiochiometrically (one mole aniline per each epoxy group and one mole aniline per each carboxylic group). The reaction was carried out in sealed ampoules under inert nitrogen atmosphere at 130 ◦ C for 3 h. IR spectra of aniline adducts, which is shown in Fig. 2, prove that all epoxy groups of the epoxidized sunflower free fatty acids were consumed during the reaction with aniline, where the bands of the epoxy group, which appear at 824 cm−1 has completely diminished.
3.2.1. Evaluation of epoxidized sunflower free fatty acid/aniline adduct (EP-SF–An) as corrosion inhibitor Six formulations based on plasticized epoxy acrylate, containing regular increments of 0.2 g EP-SF–An adduct have been prepared, taking formula S1 as reference (blank), as shown in Table 5. Radiation dose (1 Mrad pass−1 ) and all formulation characteristics were kept constant to clarify the inhibitive effect of the tested aniline adduct. Physical, mechanical and chemical properties of the cured films are represented in Table 6. It was noticed from this table that, all properties do not affect significantly on addition of the prepared EP-SF–An adduct. The cured films of the investigated formulations showed high adhesion to steel panels. All the mechanical properties such as hardness and bending are reasonable. In addition, acid, alkali, and water do not affect all cured films, which provide a distinguished chemical resistance of the cured films. Corrosion test results of steel panels under cured films, after 28 days immersion in artificial seawater, can be seen in Table 7 and Fig. 3. It is clear that addition of the prepared amine adduct (EP-SF–An) improves corrosion resistance up to 0.4 g EP-SF–An/100 g of acrylate resin formulation. At this concentration (0.4 g of EP-SF–An), formula no. S3, the best corrosion protection to carbon steel, where no sign of blisters in the cured film (rating 10), a slight degree of corrosion have been observed under the cured film (rating 8), and the adhesion of cured film at the scribe is acceptable (rating 9). Beyond this concentration, corrosion starts to appear again with some loss of adhesion of cured films around the scribe. This may be referred to the polarity of EP-SF–An and its adsorption on the steel panels through lone pair of electrons on the nitrogen atom of the amino group also the aromaticity of the adduct gives extra protection to steel substrate by chemisorption mechanism [23,24]. On the other hand at high concentration more than 0.4 g of EPSF–An corrosion inhibition decreases due to random distribution of the prepared adducts which may bloom to the surface and attract the water molecule to cured film through its hydrophilic groups.
Table 6 Physical, mechanical and chemical properties of cured films. Test
Formula no. Blank
Adhesion Hardness Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
Formulations
S1
S2
S3
S4
S5
S6
4B 4H Pass v.g. v.g. v.g.
4B 4H Pass v.g. v.g. v.g.
4B 4H Pass v.g. v.g. v.g.
4B 4H Pass v.g. v.g. v.g.
4B 3H Pass v.g. v.g. v.g.
4B 3H Pass v.g. v.g. v.g.
M.S. Ibrahim et al. / Materials Chemistry and Physics 130 (2011) 237–242
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Table 7 Corrosion resistance tests of coated steel panels of. Test
Formula no.
Degree of rustinga Degree of blisteringb Failure at scribec a b c
Blank
Formulations
S1
S2
S3
S4
S5
S6
4 2F 7
6 10 9
8 10 9
8 10 8
7 2M 7
5 2M 8
It is rating of rust as area percentage; it is graded on a scale from 10 to 0, where 10 < 0.01% and 0, greater than 50%. It is graded on a scale from 10 to 0, where 10 no blistering and 0 for largest blisters and frequency denoted by F, M, MD, and D (few, medium, medium dense and dense). It is rating of corrosion or losing of paint extending from the scribe; it is graded on a scale from 10, no creepage to 0, >16 mm.
Fig. 3. Corrosion of metal plates under cured films.
The weight loss measurements of coated metal plates are represented graphically in Fig. 4 after 60 days of immersion in artificial seawater. The results go hand in hand with the corrosion resistance tests results and confirm that, formula no. S3, which contains 0.4 g of EP-SF–An adduct have the minimum weigh loss value (0.333 mg cm−2 ) among the other formulations. This concentration of aniline adduct can protect mild steel panel and give the lowest corrosion rate. 3.3. Comparative study between the prepared aniline adduct and a commercial inhibitor in curable coating formulations It is interesting to study the inhibition efficiency of the aniline adduct as corrosion inhibitor at its optimum concentration with a commercial inhibitor and under the same EB dose (1 Mrad pass−1 ), and correlates a suitable relation between them. Estimating from weight loss measurements [17], the percentage of inhibition efficiency (I, %) can be measured according to the following equation:
I (%) =
Wo − Wi × 100 Wo
Fig. 4. Variation of weight loss values of coated metal plates with immersion time in artificial seawater.
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Table 8 Corrosion inhibition efficiency of the prepared aniline adduct and commercial inhibitor.
on plasticization of epoxy acrylate with castor oil and addition of EP-SF–An adduct as corrosion inhibitor.
Adduct type
Concentration Corrosion inhibition efficiency (%)
References
EP-SF–p-An Commercial inhibitor
50.8 51.8
[1] W. Shao-Bing, D.S. Mark, J. Coat. Technol. 70 (887) (1998) 53. [2] Guide to Cleaner Technologies: Organic Coating Replacements, United States Environmental Protection Agency, Cincinnati, OH, September 1994. [3] J.T. Kunjappu, Paint Coat. Ind. (October) (2000) 164. [4] D. Patel, N.R. Kondekar, Paint India (June) (2002) 35. [5] B. Defoort, G. Lopitaux, X. Coqueret, G. Larnac, J.M. Dupillier, Macromol. Chem. Phys. 202 (2001) 3149. [6] C.S.B. Ruiz, L.D.B. Machado, E.S. Pino, M.H.O. Sampa, Radiat. Phys. Chem. 63 (2002) 481. [7] H. Xiancong, S. Meiwu, Z. Guotai, Z. Hong, H. Xiaopeng, Z. Chunlan, Radiat. Phys. Chem. 77 (2008) 643. [8] C. Decker, Prog. Polym. Sci. 21 (1996) 593. [9] A.Y. El-Etre, M. Abdallah, Corros. Sci. 42 (2000) 731. [10] H. Shokry, M. Yuasa, I. Sekine, R.M. Issa, H.Y. El-Baradie, G.K. Gomma, Corros. Sci. 40 (1998) 2143. [11] H.A. Mohamed, B.M. Badran, H.A. Aglan, J. Appl. Polym. Sci. 80 (2001) 269–286. [12] H.A. Mohamed, B.M. Badran, J. Appl. Polym. Sci. 115 (2010) 174–184. [13] B.M. Badran, S.M. El-Sawy, A.A. El-Sanabary, Pigment Resin Technol. 23 (5) (1994) 10–16. [14] E. Armelin, C. Alemán, J.I. Iribarren, Prog. Org. Coat. 65 (2009) 88–93. [15] E. Armeline, F. Liesa, X. Ramis, J.I. Iribarren, C. Aleman, Corros. Sci. 50 (3) (2008) 721–728. [16] J. Brodinová, J. Stejskal, A. Kalendová, J. Phys. Chem. Solids 68 (2007) 1091–1095. [17] H.A. Mohamed, Corros. Eng. Sci. Technol. 45 (4) (2010) 262–267. [18] H.A. Mohamed, B.M. Badran, A.A. Farag, J. Appl. Polym. Sci. 117 (2010) 1270–1278. [19] B.M. Badran, N.A. Ghanem, F.M. EL-Mehelmy, J. Oil Colour Chem. Assoc. 59 (1976) 291. [20] A. Durbetaki, J. Anal. Chem. 28 (1956) 2000. [21] A. Mejiritski, T. Marino, V. Lungu, D. Martin, D. Neckers, US Patent 6,211,262 (2001). [22] V. Kumar, Y.K. Bhardwaj, N.K. Goel, S. Francis, K.S.S. Sarma, K.A. Dubey, C.V. Chaudhari, S. Sabharwal, Surf. Coat. Technol. 202 (2008) 5202– 5209. [23] F. Bentiss, M. Traisnel, M. Lagrenée, J. Appl. Electrochem. 31 (2001) 41–47. [24] E.A. Noor, Corros. Sci. 47 (2005) 33–55.
where Wo and Wi are the weight loss values in the absence and in the presence of inhibitor after 60 days, respectively. Table 8 indicates corrosion inhibition efficiency of the aniline adduct at optimum concentration (0.4 g) and commercial inhibitor in cured films with the same concentration. According to the previous results, it may conclude that, the corrosion protection of carbon steel of the prepared aniline adduct have nearly inhibitive efficiency to commercial inhibitor in curable coating formulations. 4. Conclusions Based on the previous investigations, it can be concluded that, the coatings which formulated with EA 70%, HD 20%, and castor oil 10% under 1 Mrad pass−1 irradiation dose show the best adhesion and passed bending tests. The prepared EP-SF–An adduct improve anti-corrosion properties of coatings without any significant effect on physical, mechanical and chemical properties of the cured film. The optimum amount of aniline adduct as corrosion inhibitor was found to be 0.4 g for 100 g of coating formulation. On the other hand, the corrosion inhibition efficiency of the prepared adduct compete the commercial efficiency. Friendly to environment anti-corrosive coating and free from any heavy metal or volatile organic compound was prepared based
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Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Electron beam processed plasticized epoxy coatings for surface protection Mervat S. Ibrahim a , Heba A. Mohamed b,∗ , Nadia G. Kandile c , Hossam M. Said a , Issa M. Mohamed a a
National Center for Radiation Research and Technology, Nasr City, Egypt National Research Center, Dokki, Egypt c University College for Girls, Ain Shams University, Egypt b
a r t i c l e
i n f o
Article history: Received 5 December 2010 Received in revised form 14 June 2011 Accepted 18 June 2011 Keywords: Electron beam Corrosion Inhibitor Mild steel
a b s t r a c t Epoxy acrylate oligomer (EA) was plasticized by adding different plasticizers such as epoxidized soybean oil, glycerol and castor oil and cured by electron beam (EB). Different irradiation doses (1, 2.5 and 5 Mrad pass−1 ) were used in the curing process. The effect of both different irradiation doses and plasticizers on the end use performance properties of epoxy acrylate coating namely, pencil hardness, bending test, adhesion test, acid and alkali resistance test were studied. It was observed that incorporation of castor oil in epoxy acrylate diluted by 1,6-hexanediol diacrylate (HD) monomer with a ratio (EA 70%, HD 20%, castor oil 10%) under 1 Mrad pass−1 irradiation dose improved the physical, chemical and mechanical properties of cured films than the other plasticizer. Sunflower free fatty acid was epoxidized in situ under well established conditions. The epoxidized sunflower free fatty acids (ESFA) were subjected to react with aniline in sealed ampoules under inert atmosphere at 140 ◦ C. The produced adducts were added at different concentrations to epoxy acrylate coatings under certain EB irradiation dose and then evaluated as corrosion inhibitors for carbon steel surfaces in terms of weight loss measurements and corrosion resistance tests. It was found that, addition of 0.4 g of aniline adduct to 100 g epoxy acrylate formula may give the best corrosion protection for carbon steel and compete the commercial corrosion inhibitor efficiency with the same concentration. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Thermal curing processes of solvent-based coatings creates environmental pollution by emitting large amount of volatile organic compounds (VOC) and other hazardous air pollutants (HAP) into the atmosphere [1–4]. As environmental and public health concerns have become major issues in the coating processes, the radiation curing process has been found to be an effective alternative to solvent borne technology in the coating industry. Radiation curing is a polymerization/cross-linking process, initiated by highenergy radiation, to convert a reactive liquid chemical system into a non-tacky solid cross-linked network at room temperature with virtually zero emission of VOC or HAP since these systems are one hundred percent reactive and usually contain no solvents. EB curing of resins containing acrylate end groups have been the subject of interest of many research groups recently because of mainly two reasons [5]. The first is the benefit offered by the EB curing process and second is a wide range of properties achieved by proper selection and combinations of the oligomers [6,7]. Epoxy acrylates and urethane acrylate resins, in particular, have been the backbone of
∗ Corresponding author. Tel.: +20 101557520; fax: +20 225203197. E-mail addresses: [email protected], [email protected] (H.A. Mohamed). 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.06.033
radiation and electron beam cured coatings for over 20 years. Both the resins have their distinct properties [8]. The use of corrosion inhibitors is one of the most practical methods for protection against metallic corrosion. In general, organic compounds, such as amines, acetylenic alcohols, and heterocyclic compounds, have been in use as corrosion inhibitors in industrial applications [9–12]. Some workers, prepared efficient corrosion inhibitors by the reaction of the epoxidized linseed oil free fatty acids with different aliphatic amines and p-substituted anilines [13]. The protection against corrosion imparted by epoxy paints modified by the addition of polyaniline emeraldine salt and polypyrrole composite with carbon black as additives of an epoxy paint coating were studied [14,15]. The addition of polyaniline corrosions has better efficiency in protection against corrosion than spinel-type pigments alone in the solvent-based alkyd resin [16]. The reaction product of epoxidized soy bean oil with sulfur compounds were used as good corrosion inhibitors in varnish based on Alkyd resin [17]. Also they could be emulsified and applied with emulsion polymers in water based paints [18]. The objective of the work is to use low viscosity plasticizers to adjust and regulate the application viscosity of epoxy acrylate oligomers for better applicability of the coating and to study the effect of irradiation doses and plasticizers concentration on end use performance properties of epoxy acrylate coatings. Also,
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Fig. 1. Chemical structure of epoxy acrylate oligomer.
preparation and evaluation of epoxidized free fatty acid/aniline adduct as corrosion inhibitor in epoxy acrylate formulations to protect carbon steel is another target. 2. Materials and experimental techniques 2.1. Materials
Test
Formulation composition (%) EA/HD 80/20
Irradiation dose (Mrad pass−1 ) Hardnessa Adhesionb Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
1 7H 3B Not pass v.g. v.g. v.g.
2.5 9H 4B Not pass v.g. v.g. v.g.
5.0 9H 4B Not pass v.g. v.g. v.g.
a Lead pencils supplied with the unit, softest to hardest, are as follows: 9B, 8B, 7B, 6B, 5B, 4B, 3B, 2B, B, HB, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H. b The adhesion of the cured films decreases in the following descending order: 5B > 4B > 3B > 2B > B > 0B.
All the used chemicals are originally pure and no further purification is carried out. EBECRYL 604 (Epoxy acrylate oligomer consisting of 80% of bisphenol A epoxy diacrylate diluted with 20% of 1,6-hexanediol diacrylate) was obtained from Cytec Surface Specialties (Drogenbos, Belgium) and represented in Fig. 1. Inert plasticizers (Castor oil, epoxidized soybean oil and glycerol) were used for plasticization of epoxy acrylate oligomer for curable coating formulations. Castor oil was delivered from paint and chemical industry (PACHIN), Egypt, with molecular weight 933 and its molecular formula C57 H104 O9 . Epoxidized soybean oil was delivered from Paint and Chemical Industry (PACHIN), Egypt. Its molecular weight is 1000 and its molecular formula is C57 H106 O10 . Glycerol was supplied by El Naser Pharmaceutical Chemical Co., Egypt. Its molecular weight is 92.09 and molecular formula is C3 H5 (OH)3 . Sunflower oil free fatty acid with iodine value of 130–150 was used and supplied by Paint and Chemical Industry (PACHIN), Egypt. Dowex 50W-8X (20–50 mech) is a sulphonated poly(styrene/divinyl benzene) copolymer, dark yellow solid particles and product of Dow Chemicals Ltd., England. Aniline was supplied from Aldrich Co. Ltd., Germany. Commercial inhibitor was delivered from Petrolite Ltd., England under trade name EPRI 523.
2.2.6. Testing and evaluation The formulated epoxy coatings were tested and evaluated in absence and presence of the prepared epoxydized sun flower free fatty acid/aniline adduct (EP-SF–An) as corrosion inhibitor, according to well-known standard methods. Steel panel surface was prepared before coatings applications according to ASTM D 609-52. Dry film hardness was measured using Wolff-Wilborn pencil hardness tester according to ASTM D 3363. Bending test was done by mandrels of 2 mm according to ASTM D 1737-73. Film adhesion was measured according to DIN 53 151. Corrosion scratch test of coated carbon steel (5 cm × 7 cm) was determined after 28 days immersion in artificial seawater (27.26 g sodium chloride, 3.51 g magnesium chloride, 1.84 g magnesium sulfate, 0.69 g potassium chloride, 0.11 g sodium bicarbonate, 0.09 g potassium bromide and 1.29 g calcium sulfate), according to ASTM D 1654. Blister resistance test was determined according to ASTM D 714. Steel rusting was determined according to ASTM D 610. Weight loss measurements of 3 cm × 3 cm dimension coated steel panels were determined according to ASTM D 2688. Alkali resistance test in solution of 5% NaOH was determined according to ASTM D 1647. Acid resistance test in solution of 5% HCl was determined according to ASTM B 287.
2.2. Techniques 2.2.1. Preparation of epoxidized sunflower free fatty acid Sunflower free fatty acids were epoxidized in situ under well-established conditions [19]. 0.238 mole of sunflower oil free fatty acids was mixed with the 1.14 mole of acetic acid (one mole/double bond) and 50 g of catalyst (Dowex 50W-8X) was added together with 100 ml benzene. The flask is heated by means of temperature controlled water bath. A moderate regular stirring is applied during the preparation. When the temperature of the reaction reaches 70 ◦ C, hydrogen peroxide (3.6 moles) is added dropwise within 2 h. After about 4 h, the reaction mixture is separated by separating funnel to get rid off the water layer. The oil layer was washed several times with warm distilled water till acid free and finally dried under reduced pressure at 40 ◦ C. 2.2.2. Determination of oxirane oxygen content [20] A sample of 0.5 g was accurately weighed into 50 ml flask, dissolved in 5 ml benzene or chlorobenzene and 5 drops of crystal violet indicator were added. The sample was stirred and titrated against 0.1 N HBr in glacial acetic acid solution till bluish green end point. The oxirane oxygen content was determined using equation below: Oxirane oxygen content (%) =
L × N × 1.6 W
where L is the volume of HBr solution, N is the normality of HBr solution, and W is the weight of the sample. 2.2.3. Preparation of corrosion inhibitor Aniline was mixed with epoxidized sunflower free fatty acid in stoichiometric amounts, i.e. one mole aniline per each epoxy group and one mole aniline per each carboxylic group. The reactions were carried out in sealed ampoules and at 130 ◦ C. 2.2.4. Fourier transform infrared (FTIR) spectrometry ATI Mattson, Genesis series, Fourier transform infrared spectrometry was used. 2.2.5. Electron beam irradiation Energy1.5 MeV, power 37.5 kW, beam current 25 mA and scan width variable up to 90 cm. The formulations were applied as a thin film on different substrates such as glass, tin metal and carbon steel metal by using film applicator (100 m thickness) and were exposed to 1 Mrad pass−1 , 2.5 Mrad pass−1 and 5 Mrad pass−1 doses of electron beam radiation.
3. Results and discussion Many attempts have been made to cure the epoxy-acrylate (EA) oligomer and 1,6-hexanediol diacrylate (HD) monomer with ratio (80%:20%) respectively without any additives under different irradiation doses (1 Mrad pass−1 , 2.5 Mrad pass−1 and 5 Mrad pass−1 ). As shown in Table 1 it is found that, all cured films are very hard and their hardness increase with increasing of irradiation doses and this may be due to the formation of high degree of cross linking density. On the other hand, the flexibility of all cured films is very bad and they fail to pass bending test. However, the cured films give the accepted adhesion and pass the chemical tests (acid, alkali, and water resistance tests) under different irradiation doses. However, their film flexibility can be modified by adding non-reactive plasticizer such as natural oils, polyesters and polymerizable celluloses [21]. Epoxy acrylate resins generally are high viscosity reactive oligomers due to the strong hydrogen bonding through secondary hydroxyl groups and produce hard, glossy and chemical resistance coating. Due to rigid and brittle nature, epoxy resins exhibit low toughness, and poor wear and crack resistance in a real application. To overcome these problems, a considerable amount of work has been carried out in the direction of toughening epoxies, with some research focused on introducing rubbery and flexible components into epoxy networks in an appropriate ratio [22]. The aim of this work is to optimize the percent of different types of plasticizer and select the suitable irradiation dose for curing the epoxy acrylate coatings formulations. Also it is interesting to choose the best plasticized epoxy acrylate formula and improve its corrosion inhibition efficiency by different concentrations of the prepared epoxydized sun flower free fatty acid/aniline adduct (EPSF–An). A comparative study with commercial organic corrosion inhibitor is our aim to make this work applicable in the industrial field.
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Table 2 The physical, mechanical and chemical properties of cured films of series A. Test
Formulation composition (%) EA/HD/Glycerol 75/20/5 −1
Irradiation dose (Mrad pass Hardness Adhesion Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
)
1.0 4H B Not pass v.g. v.g. v.g.
2.5 5H 2B Not pass v.g. v.g. v.g.
EA/HD/Glycerol 70/20/10 5.0 7H 2B Not pass v.g. v.g. v.g.
1.0 4H B Not pass v.g. v.g. v.g.
2.5 5H B Not pass v.g. v.g. v.g.
EA/HD/Glycerol 65/20/15 5.0 7H 2B Not pass v.g. v.g. v.g.
1.0 4H 0B Not pass v.g. v.g. v.g.
2.5 5H 0B Not pass v.g. v.g. v.g.
5.0 7H B Not pass v.g. v.g. v.g.
Table 3 The physical, mechanical and chemical properties of cured films of series B. Test
Formulation composition (%) EA/HD/ESOL 75/20/5
Irradiation dose (Mrad pass−1 ) Hardness Adhesion Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
1.0 5H B Not pass v.g. v.g. v.g.
2.5 6H B Not pass v.g. v.g. v.g.
EA/HD/ESOL 70/20/10 5.0 8H 2B Not pass v.g. v.g. v.g.
3.1. Coating formulations containing different plasticizers This part consists of three series of different epoxy acrylate coating formulations (A, B, and C). Each series includes three coating formulations which cured under different irradiation doses. The percent of epoxy acrylate oligomer for each coating series in this group is varied from 75% to 65%. Also, the plasticizer percent for each coating series in this group is varied from 5% to 15%, by increasing of 5%. The difunctional monomer (1,6-hexanediol diacrylate) which used as a thinner for the viscosity of oligomer has the same percent (20%) in all above mentioned series. In addition to blank formula without any plasticization, a series of formulations containing different plasticizers namely (A) for glycerol, (B) for epoxidized soybean oil and (C) for castor oil are prepared and their properties are mentioned in Tables 1, 2, 3 and 4, respectively. With respect to series (A) and (B) which contain glycerol and epoxidized soybean oil as plasticizers, respectively. It is clear that, hardness of cured films increase by increasing the irradiation dose, due to the formation of high degree of crosslinking density and make the cured films harder. It is found that the cured films fail to pass the bending test for all formulations. Moreover, the cured films in all formulations have a bad adhesion but they have good chemical resistance (acid, alkali, and water media) without considerable defects. On the other hand, the formulations composition, physical, mechanical and chemical test results of the cured films of series (C) which contain a castor oil as plasticizer are shown in Table 4. They show good hardness and moderate adhesion in all formulations
1.0 5H 0B Not pass v.g. v.g. v.g.
2.5 6H 0B Not pass v.g. v.g. v.g.
EA/HD/ESOL 65/20/15 5.0 8H B Not pass v.g. v.g. v.g.
1.0 5H 0B Not pass v.g. v.g. v.g.
2.5 6H B Not pass v.g. v.g. v.g.
5.0 8H B Not pass v.g. v.g. v.g.
except the formulation containing EA 70%, HD 20%, and castor oil 10% under1 Mrad pass−1 irradiation dose which gave the best adhesion and passed bending test due to the formation of low degree of crosslinking density that makes the cured films more elastic. Moreover, all coating films of this series were successfully passed the chemical tests including acid, alkali, and water resistance tests. Based on physical, mechanical and chemical tests, it can be concluded that, formulated coatings with EA 70%, HD 20%, and castor oil 10% and cured under1 Mrad pass−1 irradiation dose, show the best properties compared with other formulations. This may be due to saturated long chain of castor oil plays important rule in plasticization of epoxy acrylate oligomer. So it is interesting to apply this formula in anticorrosive coating for mild steel and improve its corrosion inhibition efficiency by prepared epoxidized free fatty acid/anline adduct. 3.2. Preparation of epoxidized sunflower free fatty acid/anline adduct Sunflower free fatty acid was epoxidized by preparing peracetic acid in situ process using Dowex 50W-8X as a catalyst. The oxirane oxygen content of the prepared epoxidized sunflower free fatty acid was measured volumetrically by titration against HBr in glacial acetic acid solution and it was found to be 5%. Fig. 2 represents the difference between the IR spectrum of the sunflower free fatty acid and its epoxidized. The IR spectrum of epoxidized free fatty acid shows a very characteristic band of the epoxy group, which appears at 824 cm−1 and characteristic band of
Table 4 The physical, mechanical and chemical properties of cured films of series C. Test
Formulation composition (%)
Irradiation dose (Mrad pass−1 ) Hardness Adhesion Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
1.0 4H 3B Pass v.g. v.g. v.g.
EA/HD/Castor oil 75/20/5 2.5 5H 3B Not pass v.g. v.g. v.g.
EA/HD/Castor oil 70/20/10 5.0 6H 4B Not pass v.g. v.g. v.g.
1.0 4H 4B Pass v.g. v.g. v.g.
2.5 5H 4B Not pass v.g. v.g. v.g.
EA/HD/Castor oil 65/20/15 5.0 6H 5B Not pass v.g. v.g. v.g.
1.0 4H 3B Pass v.g. v.g. v.g.
2.5 5H 3B Not pass v.g. v.g. v.g.
5.0 6H 4B Not pass v.g. v.g. v.g.
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Table 5 Coating formulations by adding aniline adduct as corrosion inhibitor. Composition
Epoxy acrylate (%) 1,6-Hexanediol diacrylate (%) Castor oil (%) EP-SF–An (g)
Formula no. Blank
Formulations
S1
S2
S3
S4
S5
S6
70 20 10 0.2
70 20 10 0.4
70 20 10 0.6
70 20 10 0.8
70 20 10 1.0
70 20 10 –
In addition, another a bending band near 1560 cm−1 due to secondary N–H, C C band at 1600 and 1500 and C–H band of aromatic ring at 3030. These observations indicate that the epoxy/amine reaction has taken place successfully.
Fig. 2. IR-spectra of sunflower free fatty acid, its epoxidized sunflower free fatty acid and aniline adduct.
C–O group appears at 1160 cm−1 . Also this figure reveals disappearance of the characteristic bands of the sunflower free fatty acid (i.e. C C band at 1630 cm−1 ). The carboxylic acid group exhibits two bands, a strong band at 1740 cm−1 due to C O group and broad band at 3475 cm−1 due to O–H group. Also, there is a strong band at 2940 cm−1 due to aliphatic C–H attached to the carboxylic group. The produced epoxidized sunflower free fatty acid was allowed to react with aniline stiochiometrically (one mole aniline per each epoxy group and one mole aniline per each carboxylic group). The reaction was carried out in sealed ampoules under inert nitrogen atmosphere at 130 ◦ C for 3 h. IR spectra of aniline adducts, which is shown in Fig. 2, prove that all epoxy groups of the epoxidized sunflower free fatty acids were consumed during the reaction with aniline, where the bands of the epoxy group, which appear at 824 cm−1 has completely diminished.
3.2.1. Evaluation of epoxidized sunflower free fatty acid/aniline adduct (EP-SF–An) as corrosion inhibitor Six formulations based on plasticized epoxy acrylate, containing regular increments of 0.2 g EP-SF–An adduct have been prepared, taking formula S1 as reference (blank), as shown in Table 5. Radiation dose (1 Mrad pass−1 ) and all formulation characteristics were kept constant to clarify the inhibitive effect of the tested aniline adduct. Physical, mechanical and chemical properties of the cured films are represented in Table 6. It was noticed from this table that, all properties do not affect significantly on addition of the prepared EP-SF–An adduct. The cured films of the investigated formulations showed high adhesion to steel panels. All the mechanical properties such as hardness and bending are reasonable. In addition, acid, alkali, and water do not affect all cured films, which provide a distinguished chemical resistance of the cured films. Corrosion test results of steel panels under cured films, after 28 days immersion in artificial seawater, can be seen in Table 7 and Fig. 3. It is clear that addition of the prepared amine adduct (EP-SF–An) improves corrosion resistance up to 0.4 g EP-SF–An/100 g of acrylate resin formulation. At this concentration (0.4 g of EP-SF–An), formula no. S3, the best corrosion protection to carbon steel, where no sign of blisters in the cured film (rating 10), a slight degree of corrosion have been observed under the cured film (rating 8), and the adhesion of cured film at the scribe is acceptable (rating 9). Beyond this concentration, corrosion starts to appear again with some loss of adhesion of cured films around the scribe. This may be referred to the polarity of EP-SF–An and its adsorption on the steel panels through lone pair of electrons on the nitrogen atom of the amino group also the aromaticity of the adduct gives extra protection to steel substrate by chemisorption mechanism [23,24]. On the other hand at high concentration more than 0.4 g of EPSF–An corrosion inhibition decreases due to random distribution of the prepared adducts which may bloom to the surface and attract the water molecule to cured film through its hydrophilic groups.
Table 6 Physical, mechanical and chemical properties of cured films. Test
Formula no. Blank
Adhesion Hardness Bending (2 mm mandrel) Acid resistance Alkali resistance Water resistance
Formulations
S1
S2
S3
S4
S5
S6
4B 4H Pass v.g. v.g. v.g.
4B 4H Pass v.g. v.g. v.g.
4B 4H Pass v.g. v.g. v.g.
4B 4H Pass v.g. v.g. v.g.
4B 3H Pass v.g. v.g. v.g.
4B 3H Pass v.g. v.g. v.g.
M.S. Ibrahim et al. / Materials Chemistry and Physics 130 (2011) 237–242
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Table 7 Corrosion resistance tests of coated steel panels of. Test
Formula no.
Degree of rustinga Degree of blisteringb Failure at scribec a b c
Blank
Formulations
S1
S2
S3
S4
S5
S6
4 2F 7
6 10 9
8 10 9
8 10 8
7 2M 7
5 2M 8
It is rating of rust as area percentage; it is graded on a scale from 10 to 0, where 10 < 0.01% and 0, greater than 50%. It is graded on a scale from 10 to 0, where 10 no blistering and 0 for largest blisters and frequency denoted by F, M, MD, and D (few, medium, medium dense and dense). It is rating of corrosion or losing of paint extending from the scribe; it is graded on a scale from 10, no creepage to 0, >16 mm.
Fig. 3. Corrosion of metal plates under cured films.
The weight loss measurements of coated metal plates are represented graphically in Fig. 4 after 60 days of immersion in artificial seawater. The results go hand in hand with the corrosion resistance tests results and confirm that, formula no. S3, which contains 0.4 g of EP-SF–An adduct have the minimum weigh loss value (0.333 mg cm−2 ) among the other formulations. This concentration of aniline adduct can protect mild steel panel and give the lowest corrosion rate. 3.3. Comparative study between the prepared aniline adduct and a commercial inhibitor in curable coating formulations It is interesting to study the inhibition efficiency of the aniline adduct as corrosion inhibitor at its optimum concentration with a commercial inhibitor and under the same EB dose (1 Mrad pass−1 ), and correlates a suitable relation between them. Estimating from weight loss measurements [17], the percentage of inhibition efficiency (I, %) can be measured according to the following equation:
I (%) =
Wo − Wi × 100 Wo
Fig. 4. Variation of weight loss values of coated metal plates with immersion time in artificial seawater.
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Table 8 Corrosion inhibition efficiency of the prepared aniline adduct and commercial inhibitor.
on plasticization of epoxy acrylate with castor oil and addition of EP-SF–An adduct as corrosion inhibitor.
Adduct type
Concentration Corrosion inhibition efficiency (%)
References
EP-SF–p-An Commercial inhibitor
50.8 51.8
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where Wo and Wi are the weight loss values in the absence and in the presence of inhibitor after 60 days, respectively. Table 8 indicates corrosion inhibition efficiency of the aniline adduct at optimum concentration (0.4 g) and commercial inhibitor in cured films with the same concentration. According to the previous results, it may conclude that, the corrosion protection of carbon steel of the prepared aniline adduct have nearly inhibitive efficiency to commercial inhibitor in curable coating formulations. 4. Conclusions Based on the previous investigations, it can be concluded that, the coatings which formulated with EA 70%, HD 20%, and castor oil 10% under 1 Mrad pass−1 irradiation dose show the best adhesion and passed bending tests. The prepared EP-SF–An adduct improve anti-corrosion properties of coatings without any significant effect on physical, mechanical and chemical properties of the cured film. The optimum amount of aniline adduct as corrosion inhibitor was found to be 0.4 g for 100 g of coating formulation. On the other hand, the corrosion inhibition efficiency of the prepared adduct compete the commercial efficiency. Friendly to environment anti-corrosive coating and free from any heavy metal or volatile organic compound was prepared based