The local clays used in this study were sourced from two different locations, Nsu in Ehime Mbano Local Government Area and Etiti in Ihitte-Uboma Local Government Area within the South-Eastern region of Nigeria.

The local clays (Nsu and Ihitte-Uboma clays) were hand dug from the deposit area and sundried. Impurities were removed from the clay before crushing. The crushed clay samples were calcined for three hours at the following temperatures 550, 650, 750, 850, and 950˚C respectively and stored for subsequent studies. The clay samples calcined at different temperatures were each sieved to 0.075 mm clay particle size and later, alkyd paint samples were formulated with each calcined clay sample, Table 1. Each of the prepared paint samples was subjected to a drying test, a very important factor driven by trends in modern architectural paints for end consumer which enabled the determination of the optimum calcination temperature of the clays.

The uncalcined clays and extender pigments (calcined clays) were analyzed for major oxides contents using Munipal 4 Energy Dispersive X-ray fluorescence spectrometer (EDXRF). A scanning electron microscope (SEM; JEOL JX 840), a microanalyzer electron probe was also used in this study to estimate the particle shapes of the clays and the extender pigments. The ASTM international standard was used to characterize the extender pigments for specific gravity (ASTM D153-84), oil absorption (ASTM D281- 12), refractive index (ASTM D 1208-96), hydrogen ion concentration (ASTM D 1208- 96), and chemical reactivity (ASTM D34-08).

*P/B = pigment to binder ratio.

The results obtained the from the drying studies of paints formulated with the calcined clays presented in Table 2 show that both Nsu and Ihitte-Uboma clays formulated paints exhibited through-dry times of 210 and 201 min respectively for the formulations with local clays calcined at 850˚C. The surface-dry times of Nsu and Ihitte-Uboma clays formulated paints for clay calcined at 850˚C are 105, and 103 min respectively. Similarly, for the local clays calcined at 950˚C, the surface-dry times of the applied paint samples are 100 and 102 min respectively for Nsu and ihitte-uboma local clays. From energy consumption considerations, a very important factor in the processing industry, since the surface-dry times at 850˚C and 950˚C for the local clays are very similar, the temperature of 850˚C should represent the optimum calcination temperature for the local clays as the paints formulated with the clays calcined at 850˚C had good drying properties. It is important to note that trends in modern architectural paints is driven by two factors, namely, lower volatile organic compound (VOC) emission and, arguably, the most important is the end-consumers who are asking for long lasting, easier to use products that have quicker drying properties.

The particle size distribution (PSD) of the local clays was analyzed using the dry sieving method in accordance with ASTM D422-63. The results show that the greater portion of the clays were of particles less or equal to 0.30 mm and which were found to be the major particles present in the clays as shown in Figure 1. According to British Soil Classification System (BS 5930, 1981), both clays are classified as medium sand under coarse grain soil. Therefore 0.075 mm clay particle size was used in the characterization of the extender pigments and subsequent analysis.

The physical-characterization of the extender pigments are illustrated graphically in

*NC = Nsu clay; IU = Ihitte-Uboma clay; EP = Extender pigment.

Figure 2. The local clays have the following physical properties: pH (5.1 and 4.8), oil absorption (59 and 51), refractive index (1.7 and 2.0) [13] and specific gravity (2.54 and 2.49) respectively for Nsu and Ihitte-Uboma clays. According to US Department of Agriculture on classification of soil pH both clays are strongly acidic in nature. Hare and Beck [14] had reported a pH that ranged from 4.5 - 7 for kaolin. The pH of some extenders are talc 9 - 9.5, commercial whiting 8.74, fly ash 8.15 [15] [16] , and industrial waste clay 7.88 [17] . The oil absorption of extender pigments depends chiefly on the particle size, the surface area of the pigment, with lower particle sizes being associated with increased oil absorption. Oil absorption is the minimum quantity of oil required to convert a given mass of pigment to a coherent uniform paste [18] . The oil absorption value obtained in this study is in agreement with the result obtained by Odozi et al. [15] for Okigwe-Mbano clay (60.0). The high oil absorption recorded for the two local clays is an indication that more base resin may be required in the paint formulation. The oil absorption of some extenders are fly ash 19.0, China clay 30 - 60, barytes 10 - 14, and

talc 25 - 35 [19] . Also other values reported include, calcium carbonate 6 - 30, talc 30 - 45, mica 50 - 70, and kaolin 25 - 50 [15] . The specific gravity values obtained compared to that reported by Hare and Beck [14] for 2.6. Generally, pigments having low specific gravity generally exhibit low settling tendencies, high oil absorptions, and high tinting strengths in paints [20] . The refractive indices of some extenders are: barytes (1.64), commercial whiting (1.58), and talc (1.40) [20] . Others are commercial whiting 1.65, mica 1.59, and kaolin 1.57 [19] . The refractive indices of extenders have great influence on the scattering power of paints. Generally, extenders do not enhance the true opacity or colour of the coating film. The low refractive indices of some extenders are responsible for the poor opacity exhibited in solvent paints [20] . The low specific gravity obtained in this study is an indication that the local clays can be used in high proportions without having any adverse effect in the bulk density of the formulated paint. The specific gravity of some conventional extender pigments are barytes (4.25 - 4.5), china clay (2.6), mica (2.8 - 2.85), talc (2.65), and whiting (2.7) [20] .

The X-ray fluorescence (XRF) determinations on the uncalcined and calcined (850˚C) local clays are presented in Table 3. These data are illustrated graphically in Figure 3. The result indicates the presence of silica (SiO₂) and aluminium oxide (Al₂O₃) in high proportions while the other constituents are present in very small proportions. The SiO₂ content of uncalcined and calcined Nsu clay was found to be lower than that of Ihitte-Uboma clay while the reverse was the case for Al₂O₃ and TiO₂ contents. The Nsu local clay was found to contain 57.52% SiO₂, 25.29% Al₂O₃, and 0.85% TiO₂ while Ihitte-Uboma local clay contained 63.09% SiO₂, 20.90% Al₂O₃, and 0.60% TiO₂ respectively. The high proportion of silica and aluminium oxide in the clays is indicative of the kaolinite nature of the clays and the basis for the type of clay to be used for the production of clay paint [21] . The oxide contents (SiO₂ and Al₂O₃) of the calcined clays were generally found to be higher than the uncalcined clays. The increase in the oxide contents with calcination at high temperature (850˚C) as observed in this study is an indication of more sites for adsorption. The oxide contents (SiO₂ and Al₂O₃) of some

Nigerian clays are Obowo clay 67.08%, 21.6% and Ihitte-Uboma clay 56.4%, 29.3% [12] , Ibere clay 52.06%, 27.87% and Oboroclay 60.21%, 19.05% [22] , Mayo-Belwa clay 59.8%, 7.08% [23] , Omankwo Afikpo clay 87.13%, 6.70%; Okposi clay 53.04%, 19.70% [19] . The presence of the unreacted oxides in the clays in indicative that paint formulated with the clays will function as anti-corrosive paints since the unreactive oxides will slow down the diffusion of corrosive species thereby delaying the phenomenon of corrosion in painted surface [14] .

The effects of heat on the solubility and colour stability of the local clays was studied and was shown in Table 4 and Table 5. The results show that Nsu and Ihitte-Uboma clays were not soluble in methanol, toluene, Ethanol, chloroform, 2-propanol and hydrochloric acid except for the slight solubility of the clays observed in acetic acid.

Generally, the colour of the clays were not affected in the media investigated either in the cold or when heated. However, Nsu and ihitte-Uboma clays exhibited slight colour change in the presence of hydrochloric acid on heating. Therefore, paints formulated with these clays may not be suitable for use in hydrochloric prone environment. The same recommendation applies for the clays in acetic acid (CH₃COOH) prone environments.

The morphology of the clays obtained from scanning electron microscope (SEM) are shown in Figure 4 and Figure 5. The SEM micrograph of uncalcined Nsu clay (Figure 4(a)) shows alternate structures with grains of metallic impurities imbedded in the matrix base in chains of irregular structures. Also, seen in the figure are some dark sec-

tions indicating the presence of carbonaceous materials or cracks within the clay morphology. The SEM micrograph of calcined Nsu clay Figure 4(b) shows the presence of sub-angular platelet with sharp edges of varying sizes. From the SEM analysis studied, the calcined Nsu clay was determined to contain a total of 67 particles (Table 6). The SEM micrograph of uncalcined Ihitte-Ubomaclay in Figure 5(a) shows the presence of uniform texture having more distribution of metal oxides in the matrix in the form of regular shapes rather than elongated chains (of irregular shapes) as present in uncal-

cined Nsu clay. Figure 5(b) is the SEM micrograph of calcined Ihitte-Uboma clay showing the presence of sub-angular platelet with rounded edges of different sizes. The clay was determined to contain a total 53 particles from SEM analysis (Table 7). The particle properties of the clays presented in Table 6 and Table 7 are illustrated graphically in Figure 6 and Figure 7. The figures indicated that the surface area of both clays increased with increases in volume. The particle shape of an extender affects its parking efficiency and the hiding power Ewulonu et al. [12] . The angular-shaped particles observed in this study will contribute to increased paint viscosity due to their low particle-to-particle distance which will restrict the movement of the molecules when used in paint formulation. The plates observed in this study will not only exert reinforcing effects but also reduce the clay’s water and gas permeability. This has the applicability to imparting good anticorrosive properties and special appearances to paints when used in paint formulations. The low aspect ratio (length to diameter ratio) and elongation observed in this study provides a reinforcing layer structure of the clays and has other advantages on the applied paint film durability such as high gloss, high opacity, increased hardness and consequently improved abrasion (crack and scrub) resistance when used in paint formulations.