The Changes in Surface Properties of the Calcite Powder with Stearic Acid Treatment

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1 Materials Transactions, Vol. 5, No. 3 (9) pp. 95 to 71 #9 The Japan Institute of Metals EXPRESS REGULR RTICLE The Changes in Surface Properties of the Calcite Powder with Stearic cid Treatment Young-Cheol Yang 1, Soo-Bok Jeong 1; *, Shi-Young Yang, Young-Bae Chae 1 and Hyung-Seok Kim 1 1 Mineral Resources Research Division, Korea Institute of Geoscience & Mineral Resources, Deajeon 35-35, Korea Science Industry Division, Strategy & Industry Bureau, Jeonbuk Provincial Government, Jeonju 5-71, Korea The chemisorption isotherm of stearic acid on a calcite powder was established by calculating the amounts adsorbed using a UV-Visible spectrophotometer. The changes in surface properties of the calcite powder with the surface treatment were examined using contact angle measurements and inverse gas chromatography (IGC) at an infinite dilution. The adsorption of stearic acid was available only at their dilute concentration. The contact angle with water and formamide increased with increasing amount of stearic acid adsorbed on the calcite powder. The adsorption of stearic acid onto the calcite powder surface resulted in a significant decrease in the dispersive component of the surface free energy, S D of calcite powder. The D S value of calcite powder with 9% surface coverage was 7. mjm at 1 C, whereas that of untreated calcite powder was 13.3 mjm. The standard adsorption enthalpy, H values of the non-polar probes (n-alkanes) for stearic acid-treated calcite powder had decreased to almost the heat of liquefaction of the corresponding probes. The specific component of the surface free energy, G SP values of the polar probes for stearic acid-treated calcite powder were lower than those of untreated calcite powder. [doi:1.3/matertrans.mer3] (Received October 17, ; ccepted January 7, 9; Published February 1, 9) Keywords: calcite, stearic acid, inverse gas chromatography (IGC), dispersive component of surface free energy (S D ), standard adsorption enthalpy (H ), specific component of the surface free energy (GSP ) 1. Introduction Calcium carbonate (CaCO 3 ) containing calcite used in this study is the most widely used filler in the plastics, rubber, paper, paint and ink industry. 1) It is usually obtained by grinding a natural mineral or synthetic CaCO 3 prepared by carbonatation of a calcium hydroxide solution. Indeed, the presence of filler enhances some of the technological properties of the resulting filled polymer. However, it very often decreases their impact strength because of agglomeration of filler. ccordingly, before incorporation into plastics, calcite powder is often surface treated in order to facilitate dispersion in the polymer matrix as well as to prevent the loss of mechanical performance. ) When stearic acid is chemisorbed on the calcite powder surface, its adsorption mechanism is not established and its influence on the surface properties of calcite powder is not established quantitatively. Therefore, this paper examined the mechanism of the reaction between calcite powder and stearic acid using a UV-Visible spectrophotometer (UVS) and the changes in surface properties of calcite powder using contact angle and IGC measurement. Inverse gas chromatography (IGC) at infinite dilution conditions be used frequently to determine the surface properties of various solids. 3 ) Some results of an examination of the surface properties of precipitated calcium carbonate using IGC have been published. 7,) In the present study, IGC was used to detect the possible differences in the dispersive component of surface free energy, S D, the standard adsorption enthalpy, H, and the specific component of the surface free energy, G SP,of untreated and stearic acid-treated calcite powder. This paper reports the IGC results from this study. *Corresponding author, sbjeong@kigam.re.kr. Experimental.1 Materials Calcite powder was obtained with particle sizes ranging from.1 to. mm by crushing and grinding natural calcite. Table 1 shows the chemical composition and physical properties of the calcite powder. -propanol (C 3 H 7 OH) was used as the solvent for stearic acid (CH 3 (CH ) 1 COOH), and water and formamide (CH 3 NO) were used to measure the contact angle. homologous series of n-alkanes, hexane (C H 1 ), heptane ( H 1 ), octane ( H 1 ), nonane ( H ) and decane (C 1 H ) were used as the non-polar probes, and chloroform (CHCl 3 ), benzene (C H ), toluene (C H 5 CH 3 ) and p-xylene ( H 1 ) were used as the polar probes for the IGC experiment.. dsorption experiment The experiment designed to modify the calcite powder surface was carried out as follows: solvent (1 ml), stearic acid (various concentration) and calcite powder ( g) were stirred with a magnetic bar stirrer for h. The mixture was then separated into solid and liquid components using a centrifugal separator. The concentration of the separated liquid was determined using a UV-Visible spectrophotometer (UVS). The separated calcite powder was dried for 1 h at 15 C, and used for the contact angle measurement and IGC experiment. The amount of stearic acid adsorbed on the calcite powder and the degree of surface coverage was calculated by the following eqs. (1) and () using the difference in the concentration of stearic acid before and after the adsorption experiment. q ¼ðC i C e ÞV 1 G M ð1þ

2 9 Y.-C. Yang, S.-B. Jeong, S.-Y. Yang, Y.-B. Chae and H.-S. Kim Table 1 Chemical compositions and physical properties of calcite powder. Chemical Ig. CaO MgO SiO l O 3 Fe O 3 K O Na O TiO MnO P O 5 composition loss (mass%) <: Physical properties Max. Min. verage Specific surface verage diameter diameter diameter area pore size. mm.1 mm.1 mm 1.7 m /g nm ¼ðC i C e ÞV a G n ðþ S where q (g/g) is amount of adsorption, is a degree of surface coverage, C i (M) is the concentration of stearic acid in solvent before adsorption experiment, C e (M) is the concentration of stearic acid in the separated solvent after adsorption experiment, V (L) is the volume of solvent, n is vogadro s number, M (g/mol) is the molecular weight of stearic acid, G (g) is the weight of calcite powder used in adsorption experiment, a is cross sectional area of stearic acid (.1 nm ) 9) and S (m /g) is the specific surface area of calcite powder..3 Contact angle measurement The surface energies were readily evaluated on flat surfaces using classical liquid contact angle measurements. The determinations were also performed on powders compressed into discs. Moreover, for solids with high surface energy, it is preferable to use the two liquid technique. 1) However, this method is difficult to apply to agglomerated or compressed calcite particles due to surface hysteresis. 11) Hence, contact angle only was used to illustrate roughly the changes in surface properties of calcite powder when coated with stearic acid. In practice, the discs were prepared by compression under controlled conditions: 1 mg of calcite powder and a pressure 1 9 Pa, in a typical IR die. The contact angle measurements were carried out using a goniometric telescope within 1 seconds after placing a drop of liquid on calcite powder disc.. IGC theory and experimental conditions In IGC under infinite dilution conditions, the retention volume V N can be calculated using the following eq. (3): V N ¼ðt R t ÞjD C ð3þ where t R is the retention time of the probes, t is the zero retention time measured with a nonadsorbing probe such as methane, j is the compressibility factor depending on the pressure at the column inlet and outlet, and D C is the corrected flow rate. In practice, the retention time and retention volume, V N can be determined in a current chromatographic experiment: a larger V N will correspond to a higher affinity of a probe to the chromatographic support. In eq. (3), j was calculated using the following eq. (): 1) j ¼ 1:5 ðp i=p Þ 1 ðp i =p Þ 3 ðþ 1 where p i is the inlet pressure of the carrier gas, and p is the outlet pressure of the carrier gas, which usually equal to atmospheric pressure. For a test substance, the free energy of adsorption, G is the sum of the energies of adsorption attributable to the dispersive and specific interactions. The adsorption of nonpolar probes, such as n-alkanes, occurs through dispersive interactions, whereas, for polar probes, both London and acid-base interactions contribute to G. In this study, the model reported by Donnet et al. was used because the injected probe is in the gas phase. 13) In this model, G is given by the following equations: ½ G Š ¼½ G D Šþ½ GSP Š ð5þ ¼½ þ CŠ ðþ ¼½K ðh S Þ 1= S ðh L Þ 1= L Šþ½ G SP Š ð7þ where G D and GSP are the dispersive and specific components of the free energy of adsorption, respectively. R is the ideal gas constant, T is the absolute temperature and the value of the constant, C depends on an arbitrarily chosen reference state of the adsorbed molecule in eq. (). In eq. (7), K is a constant, h S and h L are the ionization potentials of the interacting materials, and the deformation polarizability of the molecules. Subscripts S and L refer to the solid and liquid phases, respectively. In the case of n-alkanes, G is equal to the free energy of adsorption corresponding to the dispersive interactions only, G D, i.e., ½ GSP Š¼ in eq. (7). The term ½K ðh S Þ 1= S Š is a characteristic of a given solid surface and is related to G D. Consequently, ½ þ CŠ between an adsorbate and an adsorbent is a linear equation of the parameter ½ðh L Þ 1= L Š with a slope of ½K ðh S Þ 1= S Š. Table shows the calculated ½ðh L Þ 1= L Š values of the probes. Polar testing probes e.g. chloroform and benzene have their corresponding ½ G Š values above the reference line. The ½ G SP Š value is determined by the vertical distance between the n-alkane plot and the data for the polar probe of interest. The IGC experimental conditions performed in this study is the following. Since the particle size of the calcite powder was too small to be used as a chromatographic support, calcite powder discs were prepared by compressing the powders in an IR die at a pressure of 1 Pa. The discs were then hand-crushed and sieved to select the fraction of particles with sizes ranging from 5 to 5 mm. Particles of the correct size were introduced into a stainless steel column, which was 5 cm long and 3.17 mm in inner diameter. pproximately 1 g of each sample was used to fill the

3 The Changes in Surface Properties of the Calcite Powder with Stearic cid Treatment 97 Probe Table 1 [Cm V 1 ] chromatographic column. Each column filled with the samples was attached to a gas chromatograph equipped with a highly sensitive flame ionization detector (FID), and then conditioned at C for 15 hours to remove any impurities. The carrier gas was nitrogen (N ) and the flow rate was ml/min. The temperature of the injector and detector is controlled at C. Measurements were carried out between 1 and 1 C. Very small amounts of the probes were injected using the following procedure. Ten to ml of the probe was introduced through a septum into a 1L flask, which was filled with N. Subsequently, approximately.1 ml of the diluted probe was injected into the GC system. The physical and chemical properties of the probes were obtained from the CRC Handbook of chemistry and physics. 1).5 nalysis instruments Fluidized Bed Proposed Jet Mill 1 FG from lpin Co. was used for grinding of calcite, a Mastersizer from Malvern Co. was used for particle size analysis, an SP from Micromeritics Co. was used to determine the specific surface area and average pore size, a MXF-1 XRF purchased from Shimatzu Co. was used for chemical composition analysis, an UVS-5 from Hewlett Packard Co. was used to measure the concentration of liquid, an ERM Contact ngle Meter from ERM Optical Works Co. was used to measure contact angle and an HP 9 GC (gas chromatography) of Hewlett Packard Co. was used for the IGC experiments. 3. Results and Discussion Characteristics of probes. h 1 19 [CV] ðhþ 1= 1 9 [C 3= m V 1= ] n-hexane n-heptane n-octane n-nonane Chloroform Benzene Toluene p-xylene Figure 1 shows the amount of stearic acid adsorbed, which was calculated using eq. (1) as a function of the equilibrium concentrations (C e ) of the solution determined by UVS. The adsorption isotherms indicate a stirring time of, 1 and h, and 1 h aging after h stirring, respectively. When it was stirred for h, the maximum stearic acid adsorption was observed. Satisfactory agreement between the shape of each adsorption isotherm was observed. These adsorption isotherms correspond to a type III isotherm, which was classified by Schay for the adsorption of a nonelectrolytic solution. 15) In Fig. 1, the adsorption of stearic acid on the calcite powder surface was only achieved successfully at low concentrations, and can be explained as follows. 1 1) lcohols form hydrogen bonds, as shown in Fig. (a). Fatty acids only form hydrogen bonds by two molecules, as shown in Fig. (b). fatty acid liquid or solution exists in a state mount of adsorption (mg/g) hrs(s) hrs(s)-1hrs(l) 1hrs(s) hrs(s) s : stirring time l : leaving time. 1 Equilibrium concentration, C e (g/l) Fig. 1 dsorption isotherm of stearic acid on calcite powder, determined from the change in concentration of the solution. Fig. Hydrogen bonds of alcohol and carboxylic acid. of a double molecule but is a single molecule at very low concentrations. In addition, the hydrogen bond of a fatty acid is broken if a temperature is increased. 19) Stearic acid forms hydrogen bond with hydroxyl sites on the surface of calcite powder. If a adsorption is controlled by the polarity of stearic acid and -propanol, 17) stearic acid will be adsorbed on the calcite powder surface because the dipole moment of stearic acid is larger than that of -propanol. 1) However, if the stearic acid concentration is increased sufficiently, a double molecule of stearic acid is formed, e.g. a hydrocarbon chain, in which in both ends of the stearic acid become nonpolar. Eventually, -propanol will be adsorbed preferentially on the calcite powder surface. The amount of stearic acid adsorbed on the calcite powder surface and the degree of surface coverage were calculated by eqs. (1) and (), respectively, using the measured stearic acid concentration before and after the adsorption experiment. Calcite powders with.1,.13,.1,.,.,.3 and.3 mass% of amount adsorbed were used as the

4 9 Y.-C. Yang, S.-B. Jeong, S.-Y. Yang, Y.-B. Chae and H.-S. Kim Table 3 The contact angle of water and formamide on calcite powder with various degree of coverage. Degree of surface Contact angle (degree) coverage Water Formamide 7% % % % % 97 % % G CH - standard samples for the contact angle measurement and IGC experiment. The cross sectional area of stearic acid is.1 nm. 9) ssuming stearic acid is fixed perpendicularly to the calcite powder surface, the above weight percents of stearic acid correspond to 7, 35,, 53, 7, and 9% degree of surface coverage, respectively. Table 3 shows the contact angle with water and formamide on calcite powder with various degree of coverage. The untreated calcite powder was wetted completely with the water and formamide used in the contact angle measurements. This means that the calcite powder surface has high surface energy. The contact angles with water and formamide on calcite powder increased with increasing level of stearic acid adsorption on the calcite powder surface. When the fatty acid was adsorbed as a complete monolayer, the maximum contact angle was 13 for water and 95 for formamide. ) In this study, the contact angles for water and formamide had already reached the maximum value when the degree of surface coverage was %. Therefore, it is considered that an approximately % degree of surface coverage in the point of the surface free energy is similar to a complete monolayer. IGC under infinite dilution conditions was used to determine the S D, H and GSP values of the surface of untreated and stearic acid-treated calcite powder. The dispersive component of the surface free energy, S D, was obtained by injecting a homologous series of n-alkanes into the column and determining their retention characteristics. Dorris and Gray used the incremental amount of free energy of adsorption, which corresponds to the adsorption of a single CH group, G CH, to determine the value of D S :1) D S ¼ 1 CH " # G CH ðþ N a CH where CH is the surface energy of a solid composed solely of -CH - groups, i.e., a surface analogous to polyethylene, N is the vogadro s number, and a CH is the cross sectional area of an adsorbed -CH - group (. nm ). 1) The variation in CH with temperature is given by the following equation: CH ¼ 35: þ :5ð93 TÞ in mjm where T is the temperature in K. Generally, the logarithm of V N varies linearly with the number of carbon atoms of the injected n-alkane. Therefore, it is possible to define the free energy of adsorption, G CH, of a single methylene group, which no longer depends on the arbitrary choice of a reference state: ð9þ Fig. 3 Determination of the G CH G CH ¼ RT ln Vnþ1 N V n N value. ð1þ where R is the ideal gas constant, T is the absolute temperature, and VN nþ1 and VN n are the net retention volumes of n-alkanes with n þ 1 and n carbon atoms, respectively. In the IGC experiment, the retention time and volume are associated with the S D of the solid. This means that ½ Š varies linearly with the number of carbon atoms in the injected n-alkane, as shown in Fig. 3. In Fig. 3, G CH is the slope of the line obtained from eq. (1). Therefore, the S D values of the solid were calculated using eq. (). Figure shows the change in ½ Š at 1 Casa function of the number of carbon atoms in the n-alkanes used to probe the surface properties of the untreated and stearic acid-treated calcite powder samples. Each line indicates the degree of surface coverage of the standard samples. Figure shows that the G CH values decreased with increasing degree of surface coverage. Figure 5 shows the change in S D values, which was calculated using slope of the lines in Fig., as a function of the degree of surface coverage of the untreated and stearic acid-treated calcite powder. It is clear that the S D values decreased with increasing degree of surface coverage. The S D value decreased significantly in case of only 7% surface coverage. The S D value of calcite powder with 9% surface coverage was approximately 9 mjm, which is almost the same as the S D values reported for a solid surface composed solely of alkyl chains (S D ¼ 35 mjm for CH and S D ¼ mjm for CH 3, at C). ) Figures and 7 show the change in ½ Š at various temperatures as a function of the number of carbon atoms in the n-alkanes used to probe the surface properties of the untreated and stearic acid-treated calcite powder, respectively. The treated calcite powder with 9% surface coverage was used to examine the change in S D values at different measuring temperatures. Each line indicates the variation with temperature of the IGC measurements. In Figs. and 7,

5 The Changes in Surface Properties of the Calcite Powder with Stearic cid Treatment Degree of surface coverage % 7 % 35 % % 53 % 7 % % 9 % Untreated calcite powder 1 C 13 C 1 C 15 C 1 C 17 C 1 C Fig. Change in ½ Š of n-alkanes, on untreated and stearic acidtreated calcite powder samples measured at 1 C, as a function of the carbon number Fig. Change in ½ Š of n-alkanes, on the untreated calcite powder measured at various temperatures, as a function of the carbon number. D γ S - (mj m ) Treated calcite powder (9% surface coverage) 1 C 13 C 1 C 15 C 1 C - 17 C Degree of surface coverage (%) Fig. 5 Change in the dispersive component of surface free energy, D S, were measured at 1 C as a function of the degree of surface coverage of the stearic acid-treated calcite powder. the G CH values were calculated from the slope of each line, and the S D values were calculated at various temperatures ranging from 1 to 1 C using eq. (). Table shows the calculated S D values for the untreated and stearic acid-treated calcite powder samples. The S D values decreased with increasing measuring temperature for all samples except for a few cases where S D increased slightly. The D S values of the treated calcite powder with 9% surface coverage were slightly lower than those of polyethylene. This means that the end of stearic acid facing out is CH 3, not CH, when it is adsorbed on the calcite powder surface, because the S D value for CH 3 generally is lower than that for CH at the same temperature. 3) The standard adsorption enthalpy, H, was determined by examining the temperature dependence of ½ Š for the same non-polar probe enables: 1) Fig. 7 Change in ½ Š of n-alkanes, on the stearic acid-treated calcite powder with 9% surface coverage measured at various temperatures, as a function of the carbon number. Table Dispersive components of the surface free energy, S D of untreated and stearic acid-treated calcite powder. Sample S D (mjm ) 1 C 13 C 1 C 15 C 1 C 17 C 1 C Untreated CaCO Treated CaCO 3 (9% of coverage) Linear polyethylene Calculated from Ref. 3). H ¼ R dðln V NÞ ð11þ dð1=tþ where, the H value can be calculated using the slope of the line in the graph of ½ R ln V N Š, as a function of the reciprocal absolute temperature. Figures and 9 show the change in

6 7 Y.-C. Yang, S.-B. Jeong, S.-Y. Yang, Y.-B. Chae and H.-S. Kim 1 3 [ -R ln V N ] (kj mol -1 K -1 ) Untreated calcite powder C H 1 H 1 H 1 H Table 5 The standard adsorption enthalpies, H of n-alkanes on untreated and stearic acid-treated calcite powder. H L (kjmol 1 ) H (kjmol 1 ) Probe (Heat of liquefaction at 5 C) Untreated Treated CaCO 3 CRC PI CaCO 3 (9% of coverage) (at 5 C) C H H H H C 1 H Calculated from Ref. 1). Calculated from Ref. ) [ 1 / T ] (K -1 ) Fig. Change in ½ R ln V N Š as a function of ½1=TŠ (T in K) for n-alkanes adsorbed on the untreated calcite powder. 1 1 Untreated calcite powder nonpolar probes polar probes toluene 1 3 [ -R ln V N ] (kj mol -1 K -1 ) Treated calcite powder (9% surface coverage) H 1 H 1 H C 1 H 1 1 benzene p-xylene chloroform C (hν L ) 1/. α,l.1 9 (C 3/ m V -1/ ) [ 1 / T ] (K -1 ) Fig. 9 Change in ½ R ln V N Š as a function of ½1=TŠ (T in K) for n-alkanes adsorbed on the stearic acid-treated calcite powder with 9% surface coverage. ½ R ln V N Š of n-alkanes as a function of the reciprocal absolute temperature for the untreated and stearic acidtreated calcite powder samples. Each line indicates the change in ½ R ln V N Š of n-alkanes according to the measurement temperature. In Figs. and 9, the H values were calculated using the slope of each line using eq. (11). Table 5 shows the H values of the non-polar probes (n-alkanes) calculated using the above method and the heat of liquefaction of the corresponding probes. 1,) The H value of n- alkanes increased with increasing carbon number of n- alkanes. The H values of n-alkanes for the treated calcite powder with 9% surface coverage were similar to the heat of liquefaction of the corresponding n-alkanes. This means that the interaction between n-alkanes and the treated calcite powder surface was similar to the interaction between n-alkanes. This means that the interaction between n-alkanes and treated calcite powder surface becomes weak because the Fig. 1 Variation of ½ Š as a function of ½ðh L Þ 1= L Š for different probes adsorbed on the surface of untreated calcite powder, measured at 1 C. sites with high surface energy on the calcite powder surface are covered by stearic acid. Figures 1 and 11 show the change in ½ Š as a function of ½ðh L Þ 1= L Š for each probe used to evaluate the G SP of the untreated and stearic acid-treated calcite powder (9% of surface coverage) from eq. (7), respectively. The ½ Š values of the n-alkanes used as the nonpolar probe varied linearly with ½ðh L Þ 1= L Š, and the ½ Š values of the polar probes of interest were above the reference line, as shown in Figs. 1 and 11. The vertical distance between the n-alkane plot and the ½ Š value for the polar probe corresponds to the G SP value. In Fig. 1, the ½ Š of toluene could not be calculated because the retention time of toluene was too long to be measured. The G SP values of the calcite powders were measured at 1 C. Table shows the calculated G SP values. For the calcite powder with 9% of surface coverage, the G SP values of all polar probes were lower than on the untreated calcite powder. It is believed that the alkyl chains of stearic

7 The Changes in Surface Properties of the Calcite Powder with Stearic cid Treatment Treated calcite powder (9% surface coverage) nonpolar probes polar probes chloroform benzene toluene p-xylene surface coverage and IGC measuring temperature. The H values of n-alkanes for the calcite powder with 9% surface coverage decreased and were similar to the heat of liquefaction of the corresponding n-alkanes. The specific component of surface free energy, G SP of the polar probes on the calcite powder with 9% surface coverage decreased. bove conclusions suggest that stearic acid covered the sites with high surface energy on the calcite powder surface. Therefore, treating the calcite powder with stearic acid will reduce the particle-particle interactions and hence facilitate the dispersion of the filler in some matrix. On the other hand, the surface treatment enhances the compatibility between the filler and matrix leading to better mechanical performance of the composite. - acid shield the calcite powder surface, which is in agreement with the conclusion from the contact angle, S D and H values.. Conclusions C 1 1 (hν L ) 1/. α,l.1 9 (C 3/ m V -1/ ) Fig. 11 Variation of ½ Š as a function of ½ðh L Þ 1= L Š for different probes adsorbed on the surface of treated calcite powder, measured at 1 C. Table The specific component of the surface free energy, G SP,of polar probes on calcite powder. G SP,kJmol 1 Polar probes Treated CaCO 3 Untreated CaCO 3 (9% degree of coverage) Chloroform Benzene.. Toluene Too high 7.5 p-xylene Contact angle measurements and a well-established IGC method were used to evaluate the surface properties of untreated and stearic acid-treated calcite powder. When stearic acid from a -propanol solution was adsorbed on the calcite powder surface, adsorption was only achieved quite slowly at low concentrations. The adsorption of stearic acid on the calcite powder surface changed their hydrophilic surface into a hydrophobic surface. The contact angle on the calcite powder surface increased with increasing amount of adsorbed stearic acid. The maximum contact angles were 13 for water and 95 for formamide. These values correspond to the maximum contact angle for the monolayer with CH 3. The stearic acid adsorbed on the calcite powder surface decreased S D value of the calcite powder dramatically (13.3 mjm for untreated calcite powder and 7. mjm for treated calcite powder with 9% surface coverage at 1 C). The S D values decreased with increasing degree of cknowledgement This study was supported by the Energy-Resources Technology Development Program of the Ministry of Knowledge Economy of Korea. REFERENCES 1) D. H. Solomon and D. G. Hawthorne: Chemistry of Pigment and Fillers, (John Willey & Sons 193) p. 9. ) H. S. Katz and J. V. Milewski: Handbook of Fillers and Reinforcements for Plastics, (Litton Educational Publishing Inc. 197) p. 1. 3) H. Balard, M. Sidqi, E. Papirer, J. B. Donnet,. Tuel, H. Hommel and. P. Legrand: Chromatographia 5 (19) ) E. Papirer, H. Balard, Y. Rahmani,. P. Legrand, L. Facchini and H. Hommel: Chromatographia 3 (197) ) M. Sidqi, H. Balard, E. Papirer,. Tuel, H. Hommel and. P. Legrand: Chromatographia 7 (199) ) M. M. Chehimi and E. Pigois-Landureau: J. Mater. Chem. (199) ) D. S. Keller and P. Luner: Coat. Conf. Proc., (TPPI Press, tlanta, 199) p. 39. ) M. Pyda, M. Sidqi, D. S. Keller and P. Luner: TPPI 7 (1993) 79. 9) W. J. Moore: Physical Chemistry, (Prentice-Hall, Inc. 19) p. 7. 1) Z. Kessaissia, E. Papirer and J. B. Donnet: J. Colloid Interface Sci. (191) 5. 11) R. E. Johnson and R. H. Dettre: dv. Chem. Series 3 (m. Chem. Soc. Washington D. C., 19) p ). T. James and. J. P. Martin: J. Biochem. 5 (195) ) J. B. Donnet, S. J. Park and H. Balard: Chromatographia 31 (1991) 3. 1) CRC Handbook of Chemistry and Physics, 9ed., (CRC Press Inc. 199). 15) G. Schay: Surface and Colloid Science, (Wiley-Interscience,, 199) ) S. Sircar, M. B. Rao and T. C. Golden: Elsevier Science B. V. 99 (199) 9. 17) V. Y. Davydov: Elsevier Science B. V. 99 (199) 73. 1) I. Dekany: Elsevier Science B. V. 99 (199) ) S. Glasstone and D. Lewis: Elements of Physical Chemistry, (D. Van Nostrand Co. Inc. 19) 193. ) E. G. Shafrin and W.. Zisman: dv. Chem. Series 3 (m. Chem. Soc. Washington D. C., 19) 15. 1) G. M. Dorris and D. G. Gray: J. Colloid Interface Sci. 77 (19) ) S. Wu: J. Macromol. Sci. Rev. Macromol. Chem. C 1 (197) 1. 3) E. G. Shafrin and W.. Zisman: J. Phys. Chem. (19) 519. ) F. D. Rossini and B. J. Zwolinski: Research Project of merican Petroleum Institute, (Thermodynamic Research Center, Texas Engineering Experiment Station, 19).