Firdous Habib and Madhu Bajpai
Keywords: Novolac Epoxy, Epoxy Acrylate, Acrylation, Silicone Acrylate, UV-Curing
Abstract:
Polymeric materials are exposed to high temperatures that results in lowering of the film integrity. A blend of an epoxy resin with the silicone acrylate resin was developed to provide high heat resistance UV cured coatings. Earlier siliconized epoxy coatings had been developed by conventional curing. But due to environmental awareness, high productivity rate, low process costs and energy saving UV curable coatings are enjoying considerable growth. Thermally stable UV cured coatings used in the present study was developed from silicone acrylate and epoxy acrylate resin with different diluents and photoinitiator. Such coatings provide higher thermal stability (4200C). In addition, such coatings can also be obtained by using functional amino silanes. The resin developed provides a simple and practical solution to improve heat resistance along with physical and chemical corrosion resistance of the UV cured coatings. The purpose of this research paper is to develop UV curable heat resistant coatings by the combination of inorganic and organic polymer, taking epoxy acrylate as a base resin.
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ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 UV-Curing of Heat and Corrosion Resistant Siliconized Epoxy Resin Firdous Habib1 Department of Oil & Paint Technology at Harcourt Butler Technological Institute (HBTI) Kanpur Madhu Bajpai Department of Oil & Paint Technology at Harcourt Butler Technological Institute (HBTI) Kanpur © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 Abstract Polymeric materials are exposed to high temperatures that results in lowering of the film integrity. A blend of an epoxy resin with the silicone acrylate resin was developed to provide high heat resistance UV cured coatings. Earlier siliconized epoxy coatings had been developed by conventional curing. But due to environmental awareness, high productivity rate, low process costs and energy saving UV curable coatings are enjoying considerable growth. Thermally stable UV cured coatings used in the present study was developed from silicone acrylate and epoxy acrylate resin with different diluents and photoinitiator. Such coatings provide higher thermal stability (4200C). In addition, such coatings can also be obtained by using functional amino silanes. The resin developed provides a simple and practical solution to improve heat resistance along with physical and chemical corrosion resistance of the UV cured coatings. The purpose of this research paper is to develop UV curable heat resistant coatings by the combination of inorganic and organic polymer, taking epoxy acrylate as a base resin. Key Words: - Novolac Epoxy, Epoxy Acrylate, Acrylation, Silicone Acrylate, UV-Curing Paper Type - Research Paper 1 Corresponding author; E-mail- firdaus24@gmail.com © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 1. Introduction Epoxy resin belongs to second group or thermosetting family. Epoxy resin holds pride position among the resins used in coating industry. They may be used for coating without modification or they may be esterified with acrylic acid or methacrylic acid [1,2]. Epoxy resins are characterised by low shrinkage, ease of cure and processing, excellent moisture, solvent and chemical resistance and good adhesive strength. However their shortcomings are low fracture energy, low thermal stability, low pigment holding ability, poor hydrophobicity, weathering and impact strength which restrict their wide application in the field of coatings and paints. To improve these properties a second component such as rubber, amino terminated butadiene nitrile rubber, polyurethane, silicone and some other thermoplastics are added as modifiers for epoxy resin .Silicone is considered to be one of the suitable modifiers for epoxy resin, owing to its superior thermal and thermo-oxidative stability, excellent moisture resistance, partial ionic nature, low surface energy, good flame retardancy and free rotations of chains about Si-O bonds, good hydrophobicity, compressivity and doping action [3-5]. Structural materials have limitations for use at high temperature due to oxidation chemical reaction and corrosion therefore to provide improved reliability at high operating temperature, high heat and corrosion-resistant protective coatings are used. Epoxy silicone based coatings have high thermal stability, excellent adhesion, good flexibility and improved acid and solvent © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 resistance compared to conventional epoxy coatings. In past heat resistant siliconized epoxy coating had been developed by conventional curing. Conventional organic protective coatings fail due to carbonization and evolution of aggressive gases. Such films age rapidly at elevated temperature (>1000C) and exhibits loss of flexibility, elasticity, adhesion and protective value. In general, physical properties of highly desirable heat resistant coatings have a high glass transition temperature (>2500C) and a high decomposition temperature (>4000C) [6]. Recently heat resistant UV-curable coatings have enjoyed considerable growth due to environmental awareness and increased productivity compared to traditional method of curing [7,8]. In contrast the usage of UV curing can cut process costs, decrease pollution and save energy [9-14]. Novolac acrylate provides a higher aromatic content and more crosslink sites in the pendent positions along the backbone of molecules than conventional epoxies [15]. Further its blending with silicone acrylate enhances the thermal stability thus giving high heat resistance coating. The utility of silicon-based coatings has evolved from specialty high performance applications into broad usage throughout the coatings industry. In the present study a thermally stable, UV curable, epoxy coating has been developed by the combination of silicone based inorganic and organic polymer. It has been observed that use of silicone invariably enhances the thermal stability, resistance towards chemical corrosion of the epoxy coating. Besides thermal stability silicone provides better flexibility and gloss to coatings. © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 2. Experimental 2.1 Materials Make Epoxy novolac/cresol resin Synthesized in Laboratory Acrylate novolac/cresol resin Synthesized in Laboratory Acrylated Silicone Resin Synthesized in Laboratory Epicholorohydrin (ECH) E. Merck Acrylic Acid E.Merck Hydroquinone (HQ) E.Merck Trimethylolpropane triacrylate (TMPTA) Aldrich Pentaerythritol triacrylate (PETA) Aldrich 1,6 Hexanediol diacrylate (HDDA) Flucka 2,2-Diethoxyacetophenon Flucka 2.2. Method 2.2.1 Synthesis of novolac/cresol resin Novolac resin was prepared by condensation reaction between phenol / cresol and formaldehyde in acidic condition. Initially phenol / cresol (1 mole) with some quantity of water was taken in three neck flask. The pH was adjusted to 0.5 with sulphuric acid (used as catalyst) and the contents were heated to 900C with constant stirring. The required amount (0.5mole) of formaldehyde (37% formaline solution) was added over a period of 3 hours through a dropping funnel, and stirring was continued for an additional 30 minutes, water was then removed under vacuum.(Figure.1) © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 OH OH CH 2 OH H2SO4 + HCHO pH 0.5, 90 °C Novolac Resin Phenol Figure. 1 Synthesis of novolac resin 2.2.2 Synthesis of epoxy novolac/cresol resin Laboratory prepared epoxy novolac / cresol resin (1 mole) was reacted with epichlorohydrine (10 mole) at 1100C and 40% sodium hydroxide solution was added gradually to the reactants over a period of 3 hours through a dropping funnel. After completion of reaction, salt (NaCl) was removed by washing with hot water and then water was removed through vacuum distillation.(Figure.2) OH OH CH2 Cl-CH2-CH-CH2 + CH H2 C 110 °C O ECH Novolac Resin H2 C NaOH O O H 2C CH2 HC CH2 O O n Epoxy Novolac Resin Figure. 2. Synthesis of epoxy novolac resin © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 2.2.3. Synthesis of novolac/cresol acrylate resin Acrylation of above prepared epoxy resin was carried out by using 1:0.9 molar ratios of epoxide and acrylic acid in presence of triethylamine as catalyst (1 Phr) and hydroquinone (200 ppm) as inhibitor. The extent of reaction was determined by calculating the acid value [16] at definite time intervals.(Figure.3) H 2C CH2 CH O CH2 O CH2 HC O CH2 O + CH2=CH COOH Triethylamine HQ 90 °C Acrylic Acid Epoxy Novolac Resin H2C CH C O O CH2 CH CH2 n O CH2 O CH2 CH CH2 OH OH O C CH CH2 O n Novolac Acrylate Resin Figure. 3. Synthesis of novolac acrylate resin 2.2.4. Synthesis of silicone acrylate resin Acrylated silicone resin was prepared by the reaction of methylhydrogendimethyl siloxane with ally methyl acrylate in presence of H2PtCl6 (catalyst) at room temperature. Prepared resin was characterised by IR. (Si O Si, 1040-1070cm-1, Si Me, 1261 cm-1) (Figure.4) © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 Me O Si CH3 Me O H Si + O H2 C Me C submitted 24 August 2009 CH3 C O O C allymethyl acrylate CH2 Room temperature H2PtCl6 Methylhydrogen dimethyl Siloxane CH3 CH3 H2 C C COO CH 2 O Me CH2 Si O Me Si O Me Silicone acrylate Figure. 4. Synthesis of silicone acrylate resin 2.2.5. Characteristics of epoxy novolac/cresol resin The epoxide equivalent weight of the prepared epoxy novolac resin (NE) was determined by pyridinium chloride method. Spectral analysis of this resin was done by IR to confirm the presence of epoxy group. Specific gravity was determined by hydrometer while viscosity of the epoxy novolac resin was determined by Brookfield Viscometer (ASTM-1824-66) in methyl ethyl ketone. (Table I). © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 Resin Code Epoxy Novolac Resin Cresol Epoxy Resin submitted 24 August 2009 NE Sp.Gravity @250C 1.148 Viscosity @ 250C 11500 Epoxide eq. Wt. 185 CE 1.142 10500 180 Solubility Alcohols, dioxane, ketone, ester Alcohols, dioxane, ketone, ester NE- Epoxy novolac resin CE- Cresol epoxy resin Table I. Coding and characterization of epoxy novolac resin 2.2.6. Characterization of acrylated resin Prepared acrylate resins i.e. novolac acrylate (NA) and cresol acrylate (CA) were analyzed by IR spectroscopy to confirm the acrylation process of the epoxy which is due to the carbonyl group of ester formed during the acrylation of epoxy resin. Viscosity of resin is determined by brookfield viscometer (ASTM-D1824-66). The color of the resin was determined by gardener color standard using ASTM-D 1544. While the refractive index was determined by abbe – refractometer. (Table II). © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 Resin Code Refractive index Viscosity @ 600C Novolac Acrylate NA 1.534 18000 Color (Gardner) 3G CA 1.521 16000 2G Resin Cresol Acrylate Resin NA- Novolac acrylate resin CA- Cresol acrylate resin Table II. Coding and characterization of epoxy acrylate resin 2.2.7. Determination of acid value The acid value of the prepared acrylate resin was determined with respect to time until the resin had an acid value of about 6 mg KOH/g resin [17] (Table III). S.No 1 2 3 4 5 6 7 8 9 10 11 Reaction Time 0 30 60 90 120 150 180 210 240 270 300 Acid Value (mgKOH/g solid) CA 120.0 84.0 66.4 50.9 38.0 28.7 21.6 14.0 9.1 6.0 - NA 120.0 92.0 78.2 65.0 53.6 44.02 35.5 28.1 22.9 16.6 6.2 Table III. Acid value and reaction time of different acrylate resin © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 2.2.8. Determination of degree of polymerization The number average degree of polymerization Xn is the total number of molecules initially present divided by the total number of polymer molecules and was calculated (Table IV) using following expression, 1+ r Xn = 1+ r ─ 2rp Where r is the stoichiometric imbalance ratio and p the extent of reaction. S.No 1 2 3 4 5 6 7 8 9 10 Reaction Time (min.) 30 60 90 120 150 180 210 240 270 300 Degree Of Polymerization (Xn) CA 1.27 1.49 1.77 2.13 2.48 3.05 3.69 4.48 5.39 6.78 NA 1.39 1.74 2.20 2.80 3.50 4.48 6.00 7.78 10.00 - Table IV. Degree of polymerization with time for different epoxy acrylates © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 2.2.9. Preparation of test samples The prepared acrylate resins (NA and CA) were mixed with calculated amount of reactive diluents (Table V) i.e. TMPTA, DETA, and HDDA, along with silicone acrylate resin and photoinitiators. The films were applied on the mild steel and glass panels with the film applicator of approximate 15µm film, the coated panels were then exposed to UV-lamp of 80 W/cm for curing. The panels were evaluated for various film characteristics. S.No. Ingredients 1. 2. 3. 4. 5. 6. 7. Samples (by part) I II III NA 4 4 4 CA SA 0.5 0.7 0.9 TMPTA 1.7 1.7 1.7 HDDA 1.7 1.7 1.7 PETA 1.9 1.7 1.5 DEAP .2 .2 .2 NA = Novolac Acrylate Resin CA = Cresol acrylate Resin SA = Silicone Acrylate Resin TMPTA = Trimethylolpropane triacrylate HDDA = 1,6- Hexane diol diacrylate PETA = Pentaerythritol triacrylate DEAP = 2,2- Diethoxyacetophenone IV 4 0.5 1.7 1.7 1.9 .2 V 4 0.7 1.7 1.7 1,7 .2 VI 4 0.9 1.7 1.7 1.5 .2 Table V. Formulation of coatings with silicone compound © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 2.2.10. Volume 12, Preprint 39 submitted 24 August 2009 Thermogravimetric analysis Thermogravimetric analysis of the samples were carried out (on TGA V5.1A DuPont 2100 by heating at the rate of 200C)/min) to study the thermal behavior of the coatings. 3. Results and discussion Table I. shows the coding and characterization of different epoxy resins. The resin epoxy novolac (NE) has epoxide equivalent weight 185, highly viscous and pale yellow in color. Cresol epoxy novolac resin (CE) has epoxide equivalent weight of 180, is highly viscous but slightly less than NE and light yellow in color. Table II. shows the coding and characterization of different acrylate resin. The novolac acrylate resin (NA) is highly viscous and yellow in color as compared to cresol acrylate resin (CA), which is slightly less viscous and yellow in color. Table III. shows the change in acid value of different acrylate resin with the reaction time. It is apparent form the table that the acid value decreases with the reaction time. The time required for product having desired acid value (≤6.0 KOH/gm. solid) was 270 and 300 min. for CA and NA respectively. Table IV. gives data showing the change in number average degree polymerization (Xn) with time for different acrylate resins CA and NA. It can be seen from the table that the degree of polymerization was low at the initial stage of reaction (<50per cent conversion), whereas sharp increase is observed above 85 percent conversion. © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 Figure.6 illustrates the change in acid value with reaction time for all the samples. It is apparent from the plot that the decrease in acid value in the initial stages of reaction is not linear. This is because of the higher concentration of reactive sites and greater possibility of association of acid and epoxide groups. The linearity of the plot in higher conversion region is 70% and above (taking the decrease in acid value from the initial value as a measure of conversion) reveals that the reactivity of functional group is independent of molecular size which is characteristic of such esterification reaction. 120 110 102 Le gand 96 CA NA 90 Acidvalue mg KOH/g solid 84 78 72 66 60 54 48 42 36 30 24 18 12 6 0 30 60 90 120 150 180 210 240 270 300 330 Time (min) Figure 6. Drop in acid value with time © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 Figure 7 & 8 shows the I.R. graph of epoxy novolac resin and cresol epoxy resin NE and CE. A prominent band is observed at 940 cm-1, 933 cm-1 in NE and CE which shows the presence of oxirane rings in all epoxy resins. Figure 7. IR Spectrum of epoxy novolac resin (NE) Figure 8. IR Spectrum of cresol epoxy resin (CE) The I.R. graph of epoxy acrylates shown in figure 9&10 of NA and CA exhibits band in the region of 1775 cm-1 and 1750 cm-1which confirms the presence of ester linkages. The epoxy bands are not so prominent in these graphs due to the opening of oxirane ring during the process of acrylation. A band corresponding to acrylol double bond appeared at 1610 cm-1 and 1615 cm-1 for acrylate resin NA and CA and a broad band near 3454 cm-1shows the presence of – OH group. © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 Figure 9. IR graph of novolac acrylate resin (NA) Figure 10. IR graph of cresol acrylate resin (CA) 3.1. Coating composition Table V shows coating composition of different acrylate resin with acrylated silicone resin having same photoinitiator (2,2-diethoxy acetophenone) and reactive diluents and all films are cured within 20 seconds by UV radiation. 3.2. Mechanical properties of cured films The coated tin, mild steel and glass panels were subjected to following performance test by BIS-101 specifications. © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 3.3. Volume 12, Preprint 39 submitted 24 August 2009 Flexibility The flexibility of the coated films was determined with the help of ¼” mandrel. The coated tin panels were bend to 1800 by using mandrel (Sheen Instrument Limited, England) all the samples passed flexibility test, sample no. III and VI exhibit highest flexibility because they contain higher percentage of silicon compounds as compared to others (Table VI). 3.4. Scratch hardness Hardness is the resistance of a material to indentation of scratching. The most widely used hardness test for coatings are scratch hardness. Load bearing capacity of the films was measured by using scratch hardness tester (ASTM D 5178, Sheen Instrument Limited, England). The panels were loaded with different weights until a clear scratch showing the bare metal surface was seen, scratch hardness of sample no. III and VI with higher percentage of silicon compound were higher. (Table VI). 3.5. Gloss After watching the sample from different angles it has been observed that all the samples possess excellent gloss. (Table VI) 3.6. Pencil hardness In this test sample strip is drawn under a pencil (for example one with changeable 0.5 mm flattened leads) until a hardness grade is reached which will scratch the surface. The hardness value of coating is then assigned as H, 2H, 3H etc. which therefore signifies the hardness grade. Different pencils of different © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 grades have been used and found that samples III and VI passes maximum extent of hardness due to higher percentage of silicone (Table VI) S.No Sample No. 1 2 3 4 5 6 I II III IV V VI Scratch Hardness (gm) 1,700 1,750 1,800 1,700 1,750 1,800 Pencil Flexibility Gloss (%) Hardness (1/4” Mandrel) 4h 4h 5h 4h 4h 5h Pass Pass Pass Pass Pass Pass 92-95 92-97 100 92-95 92-97 100 Table VI. Mechanical properties of UV cured siliconized epoxy resin 4. Corrosion resistance properties of cured films against various chemicals To evaluate the overall performance of the coatings, the coated films were exposed to various acids, alkalis and water. The coated panels were sealed from three sides by using molten paraffin wax before dipping in various chemicals. 4.1. Resistance to acids Sulfuric acid, hydrochloric acid and acetic acid were dissolved in water to make solution of 5 % and 10% concentration on a weight per volume basis. The coated panels were then dipped in these acid solutions for 108 hours to check their corrosion against various acids. Samples which possess high percentage of silicone compound show better resistance against the acid corrosion. (Table VII). © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 S.No Sample No. submitted 24 August 2009 1 I Acetic acid 5% 10% 5 4 Sulfuric acid 5% 10% 4 3 Hydrochloric acid 5% 10% 5 5 2 II 5 5 5 4 5 4 3 III 5 5 5 5 5 5 4 5 IV V 5 5 5 5 5 4 4 5 5 4 4 4 6 VI 5 5 5 5 5 5 5- Film Unaffected 4= Loss in Gloss 3= Blistering in films Table VII. Resistance of UV cured siliconized epoxy resin towards acids 4.2. Resistance to distilled water and saline water Coated cured panels were dipped in distill water and saline water at ambient temperature for 108 hours. The panels were observed for a visible change in the same condition. All the samples exhibit excellent corrosion resistance against distilled and saline water. (Table VIII). © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 S.No Sample No. 1 I 2 II 3 III 4 IV 5 V 6 VI 5 = Film unaffected submitted 24 August 2009 Distilled Water 5 5 5 5 5 5 Saline Water 5 5 5 5 5 5 Table VIII. Resistance of UV cured siliconized epoxy resin towards distilled and saline water 4.3. Resistance to alkali To check the alkali resistance of the samples coated glass panels were placed in 5% and 10% solution of NaOH and NH4OH for 108 hrs on a weight per volume basis. All the samples exhibit good corrosion resistance towards the alkali except few showing loss in gloss in NaOH solution. (Table IX). S.No Sample No. 1 I Sodium Hydroxide 5% 10% 5 4 Ammonium Hydroxide 5% 10% 5 5 2 II 5 5 5 5 3 III 5 5 5 5 4 5 IV V 5 5 5 4 5 5 5 5 6 VI 5 5 5 5 5- Film Unaffected 4= Loss in Gloss 3= Blistering in films Table IX. Resistance of UV cured siliconized epoxy resin towards alkali © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 5. TGA analysis Activation energy (E) for the thermal decomposition of the UV-cured epoxy has been evaluated from the dynamic thermograms. The fractional decomposition (α) for the respective temperature has been calculated from TGA graph (Figure. 11). Higher value of activation energy in the system may be due to the presence of (silicon in the resin) polynuclearity in the resin. High activation energy for the decomposition of system leads to better thermal stability of the compounds [18,19]. 00 Sample No. =I = II = III = IV =V = VI 95 85 Weight (%) 75 65 55 45 35 50 100 150 200 250 300 350 400 450 500 550 Temp erature (ºC) Figure 11. Thermogravimetric graph © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 6. CONCLUSION The thermal stability of the epoxy resin increases i.e. to about 4200C with the higher content of silicone. The increased activation energy with respect to increase in silicon compound up to certain level indicates a more thermally stable cresol novolac epoxy resin system. Chemical corrosion resistance of the composition has also shown improvement while mechanical properties like scratch hardness and flexibility have given satisfactory results. This type of UV cured coatings may be recommended for their applications in moderately stringent environment and under moderately high temperature applications where thermal stability is the main concern. © 2009 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ISSN 1466-8858 Volume 12, Preprint 39 submitted 24 August 2009 References [1] ‘Recent developments in epoxy resin and curing agents’, D. Helfand, J.Coating technology, 68, pp73-79,1997. [2] ‘A novel water born epoxy resin emulsion’, A.Wegmann, J. Coating Technology, 65, pp27-34, 1993. [3] ‘Synthesis characterization and development of high performance siloxane modified epoxy paints’ , S. 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