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High performance at a low cost Blending seed oil-modified polyesters with MF resins for high quality industrial coatings. The short oil polyester (alkyd) from Mesua Ferrea L. seed oil provides a way to utilize a sustainable resource as a binder for coatings by suitable blending with melamine formaldehyde resin. Polyester and MF resins have excellent compatibility. A blend of 60:40 ratio of polyester and MF resin gives optimum performance. Nandini Dutta, Niranjan Karak, Swapan K. Dolui. Vegetable oil-modified polyester (alkyd) resins have been widely used in coatings, for example for architectural and industrial uses and as an ink vehicle [1]. Their varied structures and properties as well as low cost [3-7] give them a significant role as a binder [2] . However, they have low alkali resistance, a long drying time, especially for non-drying vegetable oils, moderate adhesion and low hardness. Thus, a strong demand exists to improve these characteristics. Blending makes it possible Since oil-modified polyester resins have very good compatibility with a wide range of coatings resins [1, 8], the limitations may be improved by blending them with suitable materials such as epoxy resins, silicon resins, amino resins, nitrocellulose, etc. Among these, melamine formaldehyde (MF) resin is one of the important raw materials in the surface-coating industry. It enables coatings with high performance in hardness, chemical resistance, scratch hardness, colour retention, durability, good electrical insulation property, thermostability and so on, to be made. [9]. However, alone it forms very hard, brittle coatings with poor adhesion after baking. [10]. Therefore, it is always used together with resins with a flexible backbone containing polar groups [11, 12]. Since oil-modified polyesters exhibit high flexibility due to the presence of long linear hydrocarbon chain in their structure, their combination with MF resin can result in a film with good flexibility as well as good chemical resistance, hardness, thermal stability, etc. The cross-linking reactions take place by heating, using acid catalyst or both [13, 14]. Improvements in the coating properties of polyester resins of different vegetable oils by blending with MF resin have already been looked at [15-19]. Also, our laboratory recently worked on the improvement of Mesua ferrea L. seed oil-modified polyester resins by blending with commercial bisphenol-A based epoxy resin [20]. Furthermore, we have studied the morphology, thermostability, chemical resistance and coating performance of the blends of short oil polyester resin with MF resin at different weight ratios. Experimental The materials used came from various sources. The Mesua ferrea L. seed oil was purified before use. The phthalic anhydride from S.D.Fine Chem., the glycerol from Merck, the lead monoxide from Loba Chemie and the p-toluene sulfonic acid from BDH, England were used as received. Berger Paint India Ltd., Kolkata made the partially N-butylated melamine-formaldehyde resin available free of charge. The sample was used as received. The oil-modified polyester resin was prepared by the alcoholysis process, which has been mentioned before [24], using the following formulation: oil: 80 g glycerol: 41.40 g

phthalic anhydride: 89.93 g litharge: 0.12 g Once the desired acid value of 30mg KOH/g had been reached, the reaction mixture was cooled to 120°C and diluted to about 60% solid content with xylene. The blends of above polyester and MF resins were prepared at different weight ratios (Table 1) with 0.5% by weight of a 2% w/v acetone solution of p-toluene sulfonic acid. After hand stirring for 10-15 minutes, each blend was applied uniformly as a thin film on different substrates for different tests and cured at 120°C for one hour. A wide range of instruments and test methods was used. (Table 2) Resin characteristics The characteristics of the resins, their curing properties, morphology, thermal properties, performance characteristics and chemical resistance were investigated. The various physical properties are set out in Table 3. We saw that this short oil polyester resin (oil length 40%) showed moderate acid value, which indicated its moderate reactivity for the paint, coating and matrix for FRP composite applications. The comparatively low iodine value of the resin and its high saponification value are both due to the short oil length of the resin and non-drying nature of the oil. A high molecular weight gave the resin its higher viscosity. The relatively low polydispersity index and higher weight average molecular weight indicate that the resin has good mechanical properties. The relatively high hydroxyl value indicates that the resin interacts well with MF resin. The IR spectra of the oil-modified polyester resin show the presence of important linkages such as -OH, -COOR, -C=Cand other characteristics peaks [24]. The IR data of the MF resin indicates the presence of different linkages such as C-N, N-H, -N-CH2-OR, etc. [25, 26]. A complex curing mechanism The curing mechanism of the conventional oil-modified polyester and MF resin is complex due to a large number of functionalities such as -OH, -OR, -COOR, -COOH, -NH, -NH 2, etc. This makes a variety of reactions possible [25, 27, and 28]. The principal reaction takes place between the alkoxymethyl or methylol group of the amino resin and the hydroxyl group of the polyester resin. This leads to the formation of ether linkages. These reactions are supported by FTIR. The FTIR spectrum of each blend was measured before and after curing. Before curing, the spectra showed a broad peak (Figure 1) at 3435 - 3360 cm-1 , due to the overlapping of the bands of the -OH group of the polyester resin and the -OH and/or -NH group of the MF resin. After curing the blends at 120°C for one hour, the peak becomes sharper. This indicates the involvement of the -OH group of the polyester and MF resin and -NH group of the MF resin in the cross-linking reaction. The FTIR spectra of the blends after curing showed the formation of ether, methylene and ester linkages during the cross-linking process (Figure 1). Both good compatibility ... Looking at the morphology, the ability to produce blends with an improved combination of properties of the individual components depends on the degree of compatibility of the system. All the blends (P-80, P-60, P-50, P-20) showed very clear and homogeneous micrographs in the SEM study (Figure 2). A comparison of the micrographs of the cured blends with those of pure melamine-formaldehyde resin

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(P-0) showed that these blends were compatible in any proportion and there was no phase separation. This is mainly due to the different functionalities of the resins involved in the cross-linking reaction making a single phase system possible. The better dispersion of the blend components may also be due to the good compatibility of the aromatic moieties present in both the resins, as well as the polar-polar and H-bonding interaction between the resins. ...and thermal properties The cured blends P-80, P-60, P-50 and P-20 as well as P-0 (100% MF resin) have good thermal stability under the nitrogen atmosphere. The thermal stability improves with the increasing amount of MF resin (Figure 3). This may be because a higher concentration of MF resin favours self-polymerization [29]. This in turn increases the cross-linking density by the formation of a dense three-dimensional network made possible by the branch structure of the MF resin. Also, as the MF level increases in the blend, the amount of thermostable triazine moiety increases, which further enhances the thermal stability of the matrix. Furthermore, the blends degrade by a single-step pattern with the char residues 1.46%, 4.31%, 3.45%, 6.8% and 16.73% at 713.740C for the blends P-80, P-60, P-50, P-20 and P-0 (100% MF resin) respectively. MF level is critical to cured film performance The cured-film performance characteristics of the blends are summarized in Table 4. - Gloss improves with an increasing level of MF resin due to its higher clarity [30] compared to polyesters. A report elsewhere [16] supports this. - A higher level of MF resin decreases the flexibility of the cured blend. The higher melamine concentration in the blend probably leads to more self-polymerization, resulting in higher degree of cross-linking. This in turn increases the hardness of the network, giving higher pencil hardness [16] in the blends. This greater hardness is also due to more rigid triazine moiety in the matrix as the MF resin content in the blends increases. - Initially, the impact resistance of the blends climbs with the increasing amount of MF resin, but at a certain level, it starts to decrease. This initial increase may due to improved strength properties as the cross-link density goes up. But at a certain point, the decrease of impact resistance, due to the higher value of MF, increases the brittleness of the network and causes a decrease in adhesion. - The adhesive strength of the blends goes down with the increase of MF resin. This is because the amount of free polar groups such as -OH and -COOH groups decreases with higher cross-linking. Also as the amount of polyester resin increases, transetherification will be preferred to a self-condensation reaction. More flexible ether linkages are formed, which facilitate the diffusion of the resin in the substrate and hence increase the adhesive strength [31]. Sensitivity to chemicals The qualitative results of chemical resistance are shown in Table 5. Coated plates of the blends are unaffected after immersion for four days in water and aqueous salt solution, but slightly affected by aqueous solutions of H2SO4, HCl and CH3COOH. As the MF resin content in the blends increases, acid resistance goes down. This may be due to the reaction of stronger acids such as H2SO4 or HCl with the -NH group of the MF resin. However, alkali resistance improves with the increase of MF resin due to less alkali-hydrolysable ester groups and the more stable triazine moiety in the blends.

Acknowledgements The authors wish to thanks to UGC, New Delhi for their financial support of the work [Grant No. F.14-40/2003(SR)]. Authors are thankful to Berger Paint India Ltd., Kolkata for supplying MF resin for this purpose free-of-charge, National Testing House, Guwahati for their help with the instruments and to Mr. R.K. Sharmah, Jubiliant Organosis, New Delhi for the GPC analysis. References [1] V.D. Athawale, A. V.Chamankar, Eur Coat J 11 (2000) 57-64. [2] S. Paul, Surface Coatings Science & Technology. 2nd edition, New York: Wiley; 1997 [3] V.D. Athawale, K.R. Joshi, Paintindia LI (2001) 47-50. [4] M.N. Narkhede, J Colour Society 30 (1991) 2-10. [5] H. Hintze-Bruning, Ind Crops & Products 1 (1993) 89-99. [6] A.R.C. Reddy, Paintindia LIII (2001) 53-56. [7] V.C. Malshe, M. Sikchi, Basic of Paint Technology. Part I, 1st edition, UICT, Matunga, Mumbai. [8] V.D. Athawale, A.V. Chamankar, M. Athawale, Paintindia L (2000) 39-44. [9] J.A. Brydson, Plastics Materials, fifth edition 1989, Butterworth-Heinemann Ltd. [10] B. Golding, Polymers and Resins, Van Nostrand Company, New York, 1959. [11] J. Ott, Resins for Coatings. Chemistry, Properties and Applications, Edited by Dieter Stoye and Werner Freitag. Hanser publishers, New York 1996. [12] Encyclopedia of Polymer Science and Engineering, Vol.3, Wiley Interscience Publication. [13 K. Holmberg, J Oil Col Chem Assoc 61 (1978) 356-358. [14] K. Holmberg, J Oil Col Chem Assoc 61 (1978) 359-361. [15] P. Kalenda, A. Kalendova, Surface Coat Intern 12 (1995) 508-511. [16] N.A. Ghanem, F.F.Abd El-Mohsen, S.El-Zayyat, J Oil Col Chem. Assoc 60 (1977) 58-64. [17] E.J.W. Vogelzang, J Oil Col Chem Assoc 46 (1963) 89-117. [18] L. Kovacs, D. Charlesworth, J Oil Col Chem Assoc 46 (1963) 47-50. [19] D. Stoye, J. Dörffel, in Organic Coatings Science & Technology, edited by G. D. Parfilt and Angelas V. Patsis, Vol.6. (1984) [20] N. Dutta, N. Karak, S.K. Dolui, J Appl Polym Sci, (Accepted). [21] Oil and Colour Chemist's Association of Australia, Surface Coatings. Vol.1, London: Chapman & Hall; 1981. [22] Indian Standard, Methods of Sampling and Test for Paints, varnishes and Related Products 101 ( Part 5/ Sec2)-1988, Clause no. 2. [23] Indian Standard, Methods of Sampling and Test for Paints, varnishes and Related Products 101( Part 4/ Sec 4)-1988, Clause no. 2. [24] N. Dutta, N. Karak, S.K. Dolui, Prog Org Coat 49 (2004) 146-152. [25] S.N. Gan, B.Y. Tan, J Appl Polym Sci 80 (2001) 2309-2315. [26] J.R. Dyer, Application of Absorption Spectroscopy of Organic Compounds, Prentice Hall of India, New Delhi, 1991. [27] R.C. Wilson, W.F. Pfohl, Vib Spectros 23 (2000) 13-22. [28] V. Vargha, G. Kiss, J Therm Anal Cal 76 (2004) 295-306. [29] C.S.D. Diakoumakos, F.K.N. Jones, H.N. Ye, W.C. Shen, J Appl Polym Sci 83 (2002) 1317-1333. [30] G.Odian, Principles of Polymerization John Wiley and Sons, New York 1991.

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[31] S.Ahmed, S.M. Ashraf, E. Sharmin, M. Nazir and M. Alam, Prog Org Coat 52 (2005) 85-91. Results at a glance - A short oil polyester resin has been prepared from Mesua Ferrea L. seed oil, a sustainable resource. - The resin was blended with commercially available partially n-butylated melamine-formaldehyde (MF) resin at different ratios to investigate their performance characteristics as coating materials. - The pencil hardness, flexibility, impact resistance, adhesive strength, gloss and chemical resistance in different chemical media of the blends were looked at. - The blends with higher content of MF resin exhibit good thermal stability, alkali resistance, gloss and pencil hardness. But the blends with higher polyester content exhibit better flexibility, adhesion and acid resistance. - Optimum performance was achieved with a 60:40 (polyester: MF). - The work showed that suitable blending of a raw material from a sustainable resource with synthetic materials can produce high performance industrial coatings. The authors: -> Nandini Dutta, M.Sc. (Polym. Sci.), has been working on the development of polyester resins from renewable resources and their utilization since 2000. She will soon submit her Ph.D. thesis and has published four research papers in reputed international journals. -> Niranjan Karak, Ph. D. Reader, has been working on polymer science and technology since 1990 and published 24 papers in national and international journals. -> Swapan K. Dolui, Ph.D. Professor, Dean School of Science and Technology, has been working on various fields of polymer science and technology for the last 20 years and published 45 papers in national and international journals.

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Figure 1: FTIR spectra of the blends before (representative one) and after curing (P-80, P-60, P-50, P-20 and P-0).

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P-0.

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P-20.

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P-50.

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P-60.

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P-80. Figure 2:The SEM micrographs of the blends (P-80, P-60, P-50, P-20 and P-0).

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Figure 3. TGA the rmograms of the blends (P-80, P-60, P-50, P-20 and P-0).

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