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Malaysian Polymer Journal, Vol. 5, No. 1, p 81-94, 2010 Available online at www.fkkksa.utm.my/mpj

The Use of Some Local Clays in Alkyd Paint Formulations

Isaac Ogbennaya Igwe* and Luvia Uchenna Ezeamaku

Department of Polymer and Textile Engineering, Federal University of Technology, Owerri, Imo State, Nigeria.

ABSTRACT: The use of two local clays, Amankwo Afikpo and Okposi, present in large quantity in Nigeria as extenders at varying concentrations in alkyd paints has been investigated, and compared with a commercial whiting. The results showed that the formulated alkyd paints have good chemical resistance, and no adverse effect on other coating properties such as drying times, dry paint film thickness, etc was found. Similarly, the formulated alkyd paint samples showed no sign of chalking, skinning or settling tendency, and there was no formation of mildew on any of the paint samples. The hardness of the prepared alkyd paint was generally good. The properties of the local clays that contribute to their usefulness as extenders are their chemical inertness, low oil absorption, and specific gravity. Generally, the performances of these local clays are comparable and even better than that of commercial whiting; an indication that these local clays can prove to be suitable substitutes to the imported and more costlier commercial whiting in alkyd paint formulations. Keywords: paint, extenders, clay, coatings, alkyd.

1.0

INTRODUCTION

Extenders, which are sometimes referred to as extender pigments are an integral part of almost all coating formulations. They contribute significantly towards modifying various coating properties such as flow characteristics, gloss, abrasion resistance, settling tendency, etc. Extenders differ from true pigments because they do not impart opacity to the coating. They are particularly transparent in the oil medium. The selection and proper blending of suitable extenders have helped to optimize several engineering properties and the aesthetics of a coating. Extenders, inspite of their widespread use in almost all coatings, and their elevation from "fillers" to "extenders" have received limited attention from research scientists in the field of coating technology. Most of the extenders used in coatings are of mineral origin and require long processing, including grinding, levigation, chemical treatments, etc, from ore to final step, resulting in significant loss of material [1]. These processed extenders are expensive, many are not available locally, and this has led to increases in the cost of the resultant coating products [2]. Recently, paint formulators and technologists have begun to find technically and economically viable extenders for use in coatings, and thus, bring down the cost of painting to acceptable limits. Some of the materials considered for extender purposes are reviewed below. The use of red mud, a by-product of aluminum companies in protective coatings has been reported [3,4]. Several patented processes are available for the treatment of red mud particles for improved properties and for use in concrete formulations [5-8].

*Corresponding author: e-mail: [email protected]

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The utilization of fly ash, a waste by-product of thermal power stations, as an extender in water based coating formulations was reported by Gogte and Agrawal [9]. However, there were certain disadvantages that limited the use of fly ash in water based coatings [10]. The major problem associated with such coatings is their greater tendency towards increasing corrosion of the substrate material owing to the presence of water. The addition of surfactants to reduce the higher surface tension of water led to the formation of films with poorer water resistance. Further investigation on the possibility of using fly ash as an extender in solvent borne coatings for high performance industrial applications was reported by Tiwari and Saxena [11]. The coatings that were developed showed improved corrosion, abrasion and chemical resistance when compared with those of conventional extenders. Youssef [12] reported that when Egyptian dolomite ore was characterized and modified to be used as extenders, promising results were achieved and the films showed high performance as efficient extender pigment for coating applications that can replace satisfactorily prime pigments. Feller and Christian [13] studied the use of precipitated aluminum silicates in coatings and were of the opinion that the high oil absorption of the silicate was not detrimental to the mechanical properties of paints but would rather allow for more efficient utilization of TiO2 pigments in paints. The use and advantage of modified clay to improve dispersion characteristics in solvent based paint was studied by McGuffog [14] who reported that an extender with a finer particle size imparted high gloss and smooth surface finish while the least finer grades imparted thixotropy and sag resistance. Youssef et al. [15] studied the use of waste materials as extenders in coatings. In their evaluation of silica fumes as an extender in surface coatings reported that silica fume can replace satisfactorily the imported diatomaceous silica from the economic and environmental point of view. The use of an indigenous China clay (kaolin) as an extender in alkyd paints was reported by Odozi et al. [16]. Clay obtained from Okigwe ­ Mbano, Nigeria was used in formulating alkyd paints. The performance characteristic of the local clay was reported to be comparable, and even marginally better than that of the imported and commercial China clay. Keeping pace with the technological advances in coatings, the technical demand on extenders has grown tremendously. In a country like Nigeria, the conventional extenders in use in the coatings industry are imported into the country at huge foreign exchange. The local clays that hold potential as extenders in the coatings industry are presently not exploited. It is a matter of concern to the paint formulators and technologists in Nigeria to find technically and economically viable extenders of indigenous origin for use in coatings, and thus, bring down the cost of painting to acceptable limits. Although Nigeria is a rich source of minerals, many of the deposits are yet to be fully exploited. Silica (SiO2), a naturally occurring silicate with potential as an extender in coatings is one of the minerals found in commercial quantity in some parts of the country, but has received little attention in areas of applied research. The present investigation is an attempt in this direction. In this study is reported the utilization of two local clays, Amankwo Afikpo (AA) and Okposi (OK) clays obtained from Ebonyi state, Nigeria as extenders in formulating alkyd paints. In these efforts, the central objectives are (i) to characterize fully the properties of the local clays and (ii) evaluate the properties of paint products obtained using the two local clays as extenders.

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The use of Amankwo Afikpo (AA) and Okposi (OK) clays as extenders in formulating paint products (solvent based) has not been reported in the scientific literature to our knowledge. The Okposi clay is called "Aja Ukpa" in its locality and the clay has many economic values to the people of the locality. The clay is used as lubricant for road construction. It is also used in smoothing local wall (plastering), and for molding local blocks. Amankwo Afikpo clay on the other hand is called "Uroh" or "Uriah" by the people of Afikpo, the host community. The clay is chiefly used in molding pots and bowls by the women of the area. It is important to note that the study [16] on the use of local clay obtained from MbanoOkigwe, Nigeria in formulating alkyd paint was not exhaustive. The clay was analyzed to be aluminum silicate (kaolin). The study was focused on determining the wet properties of the extended paint, leaving thus, important coating properties such as the drying rate, hardness of dried paint films, resistance of dried paint films to chemicals, etc. undetermined. 2.0 Materials and Methods 2.1 Raw Materials The alkyd resin, cobalt, and lead naphthanates used in this study were gifts from Nicen Industries Limited, Osisioma, Abia state, Nigeria. The metal contents of the driers as collected were 36% lead and 12% cobalt. The solvents toluene, xylene , chloroform , 2propanol and butanone were of analytical grades and used without further purifications. The local clays used in this study were Amankwo Afikpo and Okposi clays. They were collected from Afikpo Local Government Area, and Ohazara Local Government Area respectively, all in Ebonyi State, Nigeria. 2.2 Purifications and Determinations on Clay Samples The two local clays (AA and OK) which were hand dug from their respective locations were purified, calcined, and sieved to 0.075 mm mesh size. Wet chemical analysis was used to determine the composition of the clays. The refined and calcined clays were tested for their hydrogen ion concentration using an Abbe's Refractometer, specific gravity(ASTM D183­ 84),and oil absorption (ASTM D 281 ­ 89) respectively, and compared with those of some conventional extenders. The chemical reactivity tests on the clays were carried out using the following media: hydrochloric acid, methanol, toluene, 2-propanol, butanol, chloroform, ethanol, sodium hydroxide, acetic acid, and distilled water respectively. 2.3 Preparations and Determinations on Paint Samples A series of alkyd paint samples were prepared using the Amankwo Afikpo (AA) and Okposi (AA) clays as well as the commercial whiting (CW). A typical formulation used in the preparations of alkyd paint samples is shown in Table 1. The viscosities of the paint samples were determined using the I.C.I. Rotothinner viscometer in accordance to ASTM D 1725 ­ 62 method while the specific gravity was determined using a pycnometer, which is a cup of known accuracy. The paint samples extended with the local clays and commercial whiting were evaluated for their drying times, on mild steel panels (surface dry and dry through), the thickness of dried paint films were measured with a micrometer screw gauge. The resistance to chemical of the dried paint films on mild steel panels were determined in distilled water (48 hr,) 2% H2S04 (24 hr), 2% Na2CO3 (1/2 hr), and 2% NH3 solution (1/2 hr) immersion in that order. The performance of the paint samples was rated according to Muralidharan Nair et al

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[17] as follows: 0(no change), 1(very slight effect), 2(light effect), 3(definite effect), and 4(bad effect). 3. Results and Discussion 3.1. Compositional Analysis of Clays The results of wet chemical analysis of the local clays (AA and OK) are presented in Table 2. The results indicate the presence of 83. 13% silica, 6.7% alumina and 5.3% iron oxide as the major constituents of Amankwo Afikpo clay. Table 1: Formulations of Paint Samples Ingredient (Part by weight) Sample Code CW1 CW2 CW3 CW4 CW5 AA1 AA2 AA3 AA4 AA5 OK1 OK2 OK3 OK4 OK5

Abbreviations: AA = OK = CW =

Alkyd resin 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8 45.8

Xylene 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4

Titanium dioxide 33.7 27.9 22.2 16.5 10.8 33.7 27.9 22.2 16.5 10.8 33.7 27.9 22.2 16.5 10.8

Extender CW 13.1 18.9 24.6 30.3 36.0 AA 13.1 18.9 24.6 30.3 36.0 OK 13.1 18.9 24.6 30.3 36.0

Amankwo Afikpo Clay Okposi Clay Commercial Whiting.

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Table 2: Composition of Extenders Constituents Composition, wt. % Amankwo Commercial Okposi Clay Afikpo Clay Whiting [13] 87.13 53.04 1.50 6.70 5.30 0.01 0.36 0.01 0.11 0.15 0.21 19.70 22.60 0.16 1.90 0.04 0.15 0.86 1.5 0.50 97.50 0.50

Silica Alumina Iron oxide Manganese oxide Magnesium oxide Calcium oxide Sodium oxide Potassium oxide Nitrogen oxide Calcium carbonate Others

Similarly, for Okposi clay, the results indicate the presence of 33.04% silica, 19.7% alumina, and 22.6% iron oxide as the major constituents. The other constituents of these clays are present in smaller proportions (Table 2). The mineral whiting used for comparison contains mainly calcium carborate as the major constituent. The mineral whiting is widely used as an extender especially in solvent borne and industrial and marine coatings and anticorrosive coatings [20]. 3.2 Properties of Local Clays The pH values of Amankwo Afikpo, and Okposi clays are 7.74, and 7.46 respectively. These results indicate that the local clays are alkaline. The pH values of some extenders are Okigwe-Mbano clay 6.0 [16], fly-ash 8-15 [11], and talc 9-9.5 [11]. The refractive index of 10% solution of the local clays determined using an Abbe's refractometer shows that Amankwo Afikpo clay has a refractive index of 1.65, while that of Okposi clay is 1.45. It is important to note that all extenders have refractive indices that fall in the range between 1.45 and 1.65, and which are not markedly different from the values found in most dry paint films (1.45-1.7). Extenders therefore do not give opacity or much colour when they are added to clear coatings. This should be compared to true prime pigments such as TiO2 which has refractive index near 2.75. The refractive indices of some extenders are whiting 1.58, and talc 1.591.64 [11]. The specific gravity of Amankwo Afikpo clay is determined to be 1.54, while that of Okposi clay is 1.65, values which are less than that of whiting (2.8), and many other conventionally used extenders [11]. The above results give the local clays the advantage of being able to be used in higher proportions without any adverse increase in the buck density of the formulations.

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The oil absorption of Amankwo Afikpo determined using the spatula rub out method is 51.50, while that of Okposi clay is 46.50. The oil absorption of commercial whiting is 6-30.0 [11]. The oil absorption of an extender gives directly an idea of the amount of base resin required. Less oil absorption indicates less resin demand without compromising other coating properties. It is important to note that the particle size of both the local clays and commercial whiting was kept the same by sieving them to remove all >0.075 mm particles for the determination of oil absorption. Thus, the difference in the oil absorption values obtained above could be attributed mainly to the differences in the particle shape, and nature of the particle surfaces. The level of oil absorption recorded for the local clays is an indication that more of the local clays can be incorporated as compared to other mineral extenders, and a reduction in the amount of resin required is achieved. The effect of heat on the solubility and colour of the local clays (AA and OK) is presented in Table 3. The results indicate that heat has no effect on the colour of the local clays in the various chemical media studied. Similarly, the clays are not soluble in most of the media examined except for the partial solubility exhibited by Amankwo Afikpo clay in methanol. The above results are indications that Amankwo Afikpo and Okposi clays can be quite stable in the surrounding environment of use. The mineral whiting has been reported to be soluble in dilute mineral, and acetic acids [11]. In the mineral acid, the reaction of nature; C032- + 2H+ H2O + CO2

can be envisaged to be occurring with the evolution of carbon dioxide(CO2). The local clays are thus more stable in dilute hydrochloric and acetic acids than commercial whiting. Table 3: Reactivity Test on Amankwo Afikpo (AA) and Okposi (OK) clays Solvent Hydrochoric acid Methanol Toluene Ethanol Butanol 2-Propanol Chloroform Sodium hydroxide Acetic acid solubility test AA Nil Slightly soluble Nil Soluble Nil Nil Nil Nil Nil OK Nil Nil Nil Nil Nil Nil Nil Nil Nil Colour change AA OK Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil

3.3 Influence of Clay Contents on Alkyd Paint Properties The values of viscosity of Amankwo Afikpo, and Okposi clay formulated alkyd paints in comparison to commercial whiting were determined and illustrated graphically as shown in Figure 1. The viscosity of any coating system is the result of interaction between its various constituents [19]. In the present study, the amount of the local clays was varied without changing the proportion of other ingredients as stated earlier, and this gives an idea of the effect of local clays and whiting on coating viscosity. Small increases in viscosity with

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increasing quantity of commercial whiting are observed in this study. The coating formulations containing the local clays were observed to behave differently: the viscosity of Amankwo Afikpo formulated paints was found to increase with increases in clay content up to 18.9 wt.%, and thereafter decreased with further increases in clay content. The viscosity of the Okposi clay formulated paints on the otherhand showed steady decreases with increasing clay content, and tended to level off at 185 poise at a high clay content (>30.7wt.%). The viscosity of coatings containing commercial whiting was observed in the range, 270- 286 poise. The lower viscosity of the local clay formulated paints is a desirable property though, which can be attributed to the particle shape and size of the local clays. Values of specific gravity of Amankwo Afikpo and Okposi clay formulated alkyd paints in comparison to the commercial whiting are illustrated graphically as shown in Figure 2. Figure 2 shows that specific gravity decreases gradually with increase in clay content for Okposi clay formulated alkyd paint. On the other hand, for Amankwo Afikpo and commercial whiting formulated alkyd paints, the specific gravity was observed to increase with increases in clay content, up to 18.9 wt.% of clay incorporation into the paint, and thereafter decreases with any further increase in clay content. Like was noted for the viscosity of the paint samples, the highest specific gravity obtained for the paint samples can be said to occur at the critical pigment volume concentration of the formulated paint samples for the commercial whiting, and Amankwo Afikpo clay. Tiwari and Saxena [11] in their study on fly ash incorporated alkyd paint found that the specific gravity of formulated alkyd paint increased with increases in fly ash content in the formulated alkyd paint. This finding [11] is in contrast to what is obtained in this study. The specific gravity of the formulated alkyd paints varies from 1.32 to 1.37 for Amankwo Afikpo clay based formulations, 1.36 to 1.42 for Okposi clay based formulations and 1.41 to 1.44 for the commercial whiting. For any clay content incorporated into the paint, the order of specific gravity increase is commercial whiting > Amankwo Afikpo clay > Okposi clay. Obviously, more local clays can be incorporated as compared to commercial whiting.

400

350

Amankwo Afikpo clay Okposi clay Commercial Whiting

Viscosity (poise)

300

250

200

150 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38

Clay Content (wt.%)

Figure 1: Effect of clay content on viscosity of alkyd paint

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1.8

1.7

Amankwo Afikpo Clay Okposi Clay Commercial Whiting

1.6

1.5

Specific Gravity

1.4

1.3

1.2

1.1

1 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38

Clay Content (wt.%)

Figure 2: Effect of clay content on specific gravity of alkyd paint

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The drying properties of the prepared paint samples are illustrated graphically as shown in Figures 3 to 4. Drying times were recorded for surface, and through-drying. Figure 3 shows that the surface drying times for Amankwo Afikpo clay, Okposi clay, and commercial whiting formulated paints are similar. The same observation is also noted for the throughdrying (Figure 4). Thus, the incorporation of the local clays has no adverse effect on the drying properties of the prepared paint samples. No general trend on the effect of clay content on drying of the formulated paint samples is observed in this study. At low extender (13.4 wt. %) and high extender (36.0 wt. %) contents, there are differences between the through-dry periods for the formulated paint samples. The variation of dry paint film thickness with extender contents is illustrated graphically in Figure 5. The clay samples as well as commercial whiting showed similar film thicknesses at the clay contents investigated; an indication that clay contents do not have any appreciable effect on the thickness of the formulated paint samples prepared in this study. Film thicknesses obtained for the local clay formulated paints range from 0.35 to 0.32 mm. This compares with 0.34 to 0.28 mm obtained for commercial whiting based formulations. The film thickness of a coating directly affects its durability. Generally, a film thickness of more than 20 µm performs well as a barrier resistant to weathering [11].

50 Amankwo Afikpo Clay Okposi Clay 45 Commercial Whiting

Surface Dry Time (min.)

40

35

30

25 10 15 20 25 30 35 40

Clay Content (wt.%)

Figure 3: Effect of clay content on surface dry of alkyd paint

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200

Amankwo Afikpo Clay

180

Okposi Clay Commercial Whiting

Through-Dry Time (min.)

160

140

120

100 10 15 20 25 30 35 40

Clay Content (wt.%)

Figure 4: Effect of clay content on through-dry of alkyd paint

0.45

Amankwo Afikpo Clay

0.4

Okposi Clay Commercial Whiting

Film Thickness (mm)

0.35

0.3

0.25

0.2 10 15 20 25 30 35 40

Clay Content (wt.%)

Figure 5: Effect of clay content on film thickness of alkyd paint

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The visual changes that occurred on the paint samples after immersion in distilled water, 2% H2S04, 2% Na2CO3, and 2% NH3 are given in Table 4. Table 4 shows that all the prepared paint samples on mild steel panels have good water resistant property. The performance of Amankwo Afikpo and Okposi clay formulated paint samples is generally good in 2% Na2CO3, and 2% NH3 solution, and this is attributed to the presence of inert oxides in the clay samples. Commercial whiting formulated paint samples performed poorly in 2% Na2CO3, and 2% NH3 solutions as large blisters occurred on the painted panels. The performance of local clay formulated coatings in 2% H2S04 is good, while for whiting based formulations, the dry paint films on the panels were completely detached from the substrate because of the reactivity of commercial whiting. Such poor performance in acidic and basic media by whiting based coating formulations has been reported by Tiwari and Saxena [11]. Thus, the chemical reactivity of whiting due to its decomposition by the mineral acid should restrict its use where high durability against corrosive environment is required. Similarly, the chemical reactivity of commercial whiting is an indication that it cannot be used with pigments or additives which are sensitive to alkaline conditions [20]. Table 4: Media Resistance Tests of prepared paint samples Formulation AA-1 (13.4) AA-2 (18.9) AA-3 (24.6) AA- 4 (30.9) AA-5 (36.0) OK-1 (13.4) OK-2 (18.9) OK-3 (24.6) OK- 4 (30.9) OK-5 (36.0) OK-5 (36.0) CW-1 (13.4) CW-2 (18.9) CW-3 (24.6) CW- 4 (30.9 CW-5 (36.0) Resistance to : Distilled Water 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2% H2SO4 0 0 1 1 1 1 1 0 1 0 0 5 5 5 5 5 2% Na2 CO3 0 1 1 0 0 1 0 0 1 0 0 4 4 4 4 4 2%NH3 1 1 1 1 1 1 1 1 1 1 1 4 4 4 4 4

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Data obtained on adhesion of dry paint films on mild steel panels are plotted against clay contents as shown in Figure 6. The prepared paint samples exhibited good, and similar adhesion properties, and which are in conformity with Nigeria Industrial standard N1S 268, 1989. The adhesion values for the paint samples range from 10 to 16%. Figure 6 also shows that Amankwo Afikpo and commercial whiting have particularly good adhesion property at extender contents of 13.4, and 18.9 wt.% respectively. According to American Society for Testing and materials (ASTM 2197, 1987), adhesion is the state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking action or both. For the most part, paints are removed in service by abrasion, chipping, or scraping off through the use of knives, coins, and other instruments, picking away at exposed edges, etc. None of the formulated alkyd paint samples showed any sign of chalking; an indication that the local clays performed equally well in coatings just like the commercial whiting. It is necessary that a good paint should not chalk. Also, there was no formation of skin on the wet paint samples formulated with the local clays, and commercial whiting. Similarly, none of the paint samples exhibited settling tendencies, and there was no noticeable mildew formation or fungal growth on any of the paint samples within the period of exposure to the environment. These results once again attest to good performances of the local clays in alkyd paint formulations.

22

20

Amankwo Afikpo Clay Okposi Clay Commercial Whitng

18

Adhesion (%)

16

14

12

10

8 10 15 20 25 30 35 40

Clay Content (wt.%)

Figure 6: Effect of clay content on adhesion of alkyd paint

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4.0

CONCLUSION

The present study shows that Amankwo Afikpo, and Okposi clay formulated alkyd paints have good resistance to chemical attack, and the incorporation of the clays into paints has no adverse effect on other coating properties such as the drying times, etc. Generally, the performances of the local clays in coatings are comparable to that of commercial whiting; an indication that these clays can be suitable substitutes to the imported commercial whiting. Other advantages on the use of the local clays in coatings are that the clays are of low cost, indigenously available in abundance, and easy to process. It is important to point out that the present study does not anticipate, nor intend, the total replacement of the conventional extenders now with the local clays. The expectation is that these local clays will develop their own niche in the coatings market in the future. The use of the local clays as sources of extenders to the coatings industry will not only provide a steady source of extenders but can also generate a non-food source of economic development for the farming and rural areas where they are found in abundance. References [1] [2] Morgans., W.M. Outlines of Paint Technology, Edward Arnold, London, 43 - 51, (1990). Prem Kumar, N. ; Sathyanarayana, M.N.; Bala Krishna, R.S.; Shirsalkar, M.N., Sivasamban, M.N. Mahua Oil- Based Resins for the High Temperature Curing of Fly Ash Coatings, Paintindia 34(11), 13-18, (1984). Ramanujam, S. Corrosion and its Prevention, Paintindia,13, 23-27, (1963). Guruviah, S.; Raigopalan, K.S. Effect of the Incorporation of Extenders on the Protective Action of Red Lead, Paintindia, 16, 31-34, (1966). George, W. Germany Patent No. 803360, (1951). Szerecz, J.;Janaszic, F.; Lengyi, B. Hungary Patent No.42116, (1987). Thakur, R.S.; Das, S.N. Red Mud: Analysis and Utilization, Publications and Information Directorate, Wiley Eastern, New Delhi, 195-200, (1994). Ramanujam, S.; Saluja, R.V. Indian Patent No.91431, (1964). Gogte, B.B.; Agrawal, A. Fly Ash Based Coatings, Paintindia, 44(10), 51- 56, (1994).

[3] [4]

[5] [6] [7]

[8] [9]

[10] Wicks, Z.W.; Jones, F.N.I.; Pappas, S.P. Organic Coatings, Science and Technology, Vol.2, Wiley, New York, 208-217, (1992). [11] Tiwari, S.; Saxena, M. Use of Fly Ash in High Performance Industrial Coatings, British Corrosion Journal, 34, 184-191, (1999). [12] Youssef, E. A.M. Characterization, Surface Modification, and Evaluation of Egyptian Dolomite Ore as an Extender Pigment for Paint. Journal of Pigment and Resin Technology, 31(4), 226-233, (2002).

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[13] Feller, A.; Christian, H.D. The Influence of Selected Synthetic Aluminium Silicates on Physiochemical Properties of Emulsion Paints, Polymer Colour Journal, 195 (4484), 26 - 30, (2005). [14] McGuffog, R. The Use and Advantage of Modified Clay in Improving Dispersion in Solvent Based Paints, ECC International Europe, Cornwall, U.K., (1995). [15] Youssef, E.A.M.; Nivin, M.; Abd El-Ghaffar, M.A. Characterisation and Evaluation of Silica Fumes as an Extender Pigment for Surface Coating Application, Journal of Pigment and Resin Technology 27, 88-98, (1998). [16] Odozi, T.O.; Dore, R.; Onu, C.O. Paint Extenders Based Upon an Indigenous Clay, Journal of Nigerian Society of Chemical Engineering, 5(2), 34-40, (1986). [17] Nair, N.M.; Unnikrishnan, K.G.; Unnikrishnan, M.; Nair, C.S. Utilisation of Rubber Seed Oil and Karinnotta Oil for the Preparation of Air- Drying Oil ­ Modified Alkyd Resin, Paintindia, 31(5), 5-9, (1981). [18] Parikh, C. Indian Paints and Extenders, Paintindia 47(5), 65-66, (1997). [19] Nylen, P.; Suderland, E. Modern Surface Coatings, Interscience, London, (1965). [20] Ahmad, J.; Thakkar, B. Selection of Extenders: A Practical Approach, Paintindia, 47(5), 65-66, (1997).

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