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Effects of Grinding Aids Used in Grinding Calcium Carbonate (CaCO 3 ) Filler on the Properties of Water-Based Interior Paints

: Grinding aid chemicals which are used in the grinding of calcium carbonate (CaCO 3 ) to prevent agglomeration are chemisorbed on the surfaces of particles, and the compatibility of them with the solvent, water, or organic resin affects the dispersion of the minerals and ultimately down-stream product properties in consumer industries such as paint, papermaking, and plastic. This study tries to explain the effects of triethanolamine (TEA) and monoethylene glycol (MEG), which are most commonly used as grinding aids, on the behavior of CaCO 3 in water-based paints and on the properties of the paints. The powder properties of CaCO 3 (grain size, color, surface area, oil absorption capacity, zeta potential, etc.) were characterized, and the changes in the can stability, ease of application, and optical properties (gloss, opacity) of the paints were revealed with rheological and optical analysis. It was observed that amine compounds remained in higher amounts on the CaCO 3 surface and created negative results in the paint. On the other hand, glycol compound adhered less on the CaCO 3 surface and affected the properties of the ﬁnal product less than the amine compound. Therefore, CaCO 3 ground without using any chemicals gives the best results in terms of long-term stability, ease of application, and visuality of the paint.


Introduction
In the cement and industrial mineral grinding technologies, liquid grinding aids are used to prevent the coating-effects on grinding media and mill equipment, agglomeration of fine particles, to increase the grinding performance, fineness of the product, and energy efficiency [1,2]. Amine and glycol compounds are the most widely used grinding aids. Triethanolamine (TEA) contains both amine and hydroxyl groups, all of which have the chemical properties of amines and alcohols. Monoethylene glycol (MEG), a polyol compatible with water and numerous organic compounds, contains non-dissociated and hydrophilic hydroxyl groups [3]. Studies involving molecular simulations have shown that the adsorption of grinding aids on the surface of the ground particles happens with their polar parts [4]. Thus, hydrogen bonds and other polar interactions connect the particle surface with the grinding aid functional groups. As a result, an adsorption layer is formed that keeps the particles at a distance where the effect of short-range attractive particle-particle forces is reduced [2]. The adsorption layer decreases the surface energy of the particle, so the agglomeration energy between the particles is strongly reduced during grinding in the mill. However, the performance of the grinding aid depends on both the type and the amount used in the grinding process [5]. Different types and amounts of grinding aids affect the properties of the final products in which the ground particles are used as filler since they are chemisorbed on the fresh surface of particles created by the grinding [6]. The compatibility of the grinding aid grafted on the mineral surface with the solvent, water or organic resin will affect the dispersion of the minerals and ultimately down-stream product properties such as gloss, opacity, viscosity and storage stability in consumer industries such as paint, papermaking, and plastic [3,7].
The driving force for the development of water-borne coatings has been environmental [8]. At the end of the road started in the mid-1960s to reduce volatile organic compounds (VOCs) and toxic chemicals in traditional solvent-based paints, today water-based paints have become the most widely used paints globally [9]. Waterborne paints use water as a solvent, which is cheap and non-toxic to human beings and the environment, making this type of paint one of the ideal choices for paint manufacturing in the modern coating market [10]. However, there are still technical problems in manufacturing water-based paints that can cause aesthetic issues and application disadvantages [11]. Pigment dispersion is one of these problems [7]. The state of the pigment dispersion affects paint properties (gloss, opacity, viscosity, storage stability) [7,12]. The dispersion process involves three major states; (i) wetting of the pigment, (ii) disagglomeration of the pigment assembly by mechanical disruption, and (iii) stabilization of the pigment [7,13]. Wetting of the pigment is one of the most important stages of pigment dispersion. In wetting, pigment is wetted, and the absorbed air on the pigment surface is replaced by an aqueous resin solution [7,12]. Due to water's much higher surface tension, water reducible-paints have more technical problems in wetting than conventional solvent-based paints [7]. It is understood that pigment surface chemistry and wetting characteristics directly affect the most critical properties of paints [7,12,14,15]. After wetting and mechanical disruption, a particle-particle repulsive force must be introduced to achieve stabilization [7,12]. Dispersion stabilization can be achieved by one of the following mechanisms: steric stabilization, electrostatic stabilization [7,12], or electrosteric stabilization, which combines the first two mechanisms [16,17]. Electrosteric stabilization is usually achieved by means of ionic surfactants. Polyelectrolytes bearing a polar head-group capable of forming an electrical double layer and a lipophilic side chain capable of providing steric repulsion can be used for this purpose as polymeric surfactants [17]. As the pigment volume concentration (PVC) values increase, the effects of fillers (pigments) and dispersants on the properties of the paint become more complex.
In this study, the effects of amine and glycol compounds remaining on the surface of the CaCO 3 particles on the properties of high PVC water-based interior paints were investigated. Powder characteristics of CaCO 3 ground using TEA and MEG were determined, and the viscosity, pH, electrokinetic, rheological properties, thinness, gloss, and opacity of water-based interior paints containing these powders as fillers were compared.
The grafting ratio (%) of the grinding aid chemicals on the surfaces of CaCO 3 was calculated after the furnace test. Five grams of CaCO 3 samples were kept at 105 • C for half an hour and dehumidified. Next, we heated the dehumidified coated CaCO 3 samples to 405 • C in a furnace and allowed them to stand at this temperature for 1 h. The weight loss at 405 • C was used to calculate the amount of chemical grafted onto the surface of the micronized CaCO 3 particles.
The particle size distributions of the CaCO 3 powder samples were analyzed using a laser particle size diffraction analyzer (Mastersizer 2000, Malvern Instruments Ltd., Worcestershirecity, UK). The colors of the powders were determined using a color spectrophotometer (Elrepho, DataColor, Trenton, NJ, USA) as defined by the Commission Internationale de l'Eclairage (CIE), L* indicates lightness, a* is the red/green coordinate, and b* is the yellow/blue coordinate [18].
Zeta potential is a physical property that is exhibited by any particle in suspension. The magnitude of the zeta potential indicates the potential stability of the colloidal system [19]. Electrophoretic mobility of the powder and paint samples was measured by a zeta potential measurement system (Zetasizer Nano ZS90, Malvern, UK). The velocity of a particle in a unit electric field is referred to as its electrophoretic mobility [19,20]. Electrophoretic mobility was converted to zeta potential by using Smoluchowski's approximation. The zeta potential values of CaCO 3 powders were measured in triple distilled water at a solid-toliquid ratio of 0.05 gr/100 cc. Powders were measured at equilibrium pH 8.4 after acid/base addition. The zeta potentials of the paints were measured at their inherent pH values.
Brunauer-Emmett-Teller (BET) measurements were used to assess the precise surface areas of the CaCO 3 powders using a surface-area analyzer (Quadrasorb-Evo, Quantachrome, Boynton Beach, FL, USA).
The oil absorption values of the CaCO 3 powder samples were determined according to the ASTM D 281 standard [21]. A stiff, putty-like paste was formed by the dropwise addition of dioctyl phthalate (DOP) oil or linseed (flax) oil to CaCO 3 powder under thorough rubbing with a spatula. The amount of oil required to achieve the desired endpoint was used to calculate the oil absorption value.
Three different paints were prepared using ground calcite without using any grinding aid (UC), ground calcite using TEA (TC), and ground calcite using MEG (MC). All paint components were added in the order in the industrial recipe and mixed with the help of a multipurpose disperser (VBR-12, Yokes, Turkey). The paint is prepared to contain 60% CaCO 3 , 17% binder dispersion, 20% water, and 3% dispersing, anti-foaming, rheological agents. pH measurements of paints were made using a benchtop pH meter (Mettler Toledo, Columbus, OH, USA). Paints were applied with the help of a film applicator to Leneta charts and glass slides, with a thickness of 200 µm. The fineness of the grind of paints was measured using grind gauge (2020, Elcometer, Manchester, UK).
The color values of the paint films in the black and white regions of the Leneta chart were measured as tristimulus values (X, Y, and Z) using a color spectrophotometer (Ci-64, X-rite, MI, USA). The contrast ratio was calculated, which is defined in ASTM D 2805 as the ratio of the reflectance (Y) of a film on a black surface to that of an identical film on a white substrate. Opacity (%) was calculated, which is simply the Contrast Ratio multiplied by 100 to get a percentage, where 100% is complete hiding. Gloss is an essential aspect of our visual perception of objects. The perception of gloss can relate to a product's finish, texture, and how a sample is illuminated and viewed. Surfaces with high reflectance are perceived as glossy, shiny, or lustrous, while less reflective surfaces are perceived as semi-gloss or matt. Glossmeter (Elcometer, Manchester, UK) was used to measure the gloss of paint surfaces using 60 • and 85 • angles. The gloss values were expressed as gloss units (GU).
Rheological measurements were performed using a rotational rheometer (Kinexus Lab+, Netzsch, Germany) and the rSpace software. A parallel plate geometry with a diameter of 20 mm was used. The Viscosity-Shear rate measurements at a specific temperature (25 • C) were conducted with a controlled shear rate from 1 s −1 to 3750 s −1 .
The morphologies of paint films on glass slides were characterized by scanning electron microscopy (SEM, EVO50, Zeiss, Oberkochen, Germany) using a back-scattered electron detector (BSD). The film surfaces were coated with a layer of gold prior to SEM imaging to avoid charging.

Results
The results of the analysis of the CaCO 3 powder samples used as fillers in the paints are given in Table 1. Grain size analyzes show that the powders used are of the same grain size. They have median particle diameters (d50) of about 3 µm and maximum grain sizes (d100) of about 20 µm. The color measurement results show that all CaCO 3 powders used have high lightness with L* values near 100. The a* and b* values both approaching zero shows that CaCO 3 powders contain no red, green, yellow, or blue colors. These color values of CaCO 3 enable the preparation of white paint formulations. Although the grinding aid chemicals did not cause a significant change in the color of the powders, the L value of the powders decreased slightly (Table 1). It was observed that the grinding aids adhere to the surface of the CaCO 3 grains, increasing their surface area but decreasing their oil absorption capacity (Table 1). CaCO 3 powders (TC and MC) obtained from grinding using grinding aid chemicals have higher surface areas than powder ground without using chemicals (UC). It is thought that TEA can bind to the CaCO 3 surface with a physical bond [22] more strongly than MEG. The result of the furnace test also revealed that TEA binds to the CaCO 3 surface in more significant amounts than MEG ( Table 1). The grafting ratio (%) for TC and MC samples was 0.52% and 0.12%, respectively. Considering that 0.7 wt.% of grinding aid chemical is added during grinding, the efficiency of grafting of chemicals on CaCO 3 was calculated after Yang et al. [23] and Ersoy et al. [24]. A total 74.3% and 17.1% grafting efficiencies were calculated for TC and MC, respectively. It is seen that the surface area increases as the amount of grinding aid on CaCO 3 increases. This finding is similar to the results obtained in previous studies [6,[25][26][27]. The fact that CaCO 3 grains show less oil absorption despite their increased surface area can be explained by the surface chemistry change due to the grinding aid chemicals grafted onto the CaCO 3 surfaces. The oil demands of minerals explained by the acid-base interaction are attributed to the acidic or basic functional groups on the mineral surface [28]. It is thought that the chemicals grafted onto the CaCO 3 surface alter the basic sites on the surface and reduce the interaction between the CaCO 3 surface and the acidic groups in the oil molecules.
The effects of the grinding aids on the surface charges of the CaCO 3 particles were revealed as a result of the zeta potential measurements ( Table 1). The zeta potential of the CaCO 3 powder ground without using any chemicals (UC) was measured as 10.3 mV, and the zeta potentials of the CaCO 3 powders with TEA (TC) and MEG (MC) were measured as 0.18 and 0.00, respectively. This change in the surface charges of the CaCO 3 grains indicates the presence of chemicals on the surface, changing the surface properties. In previous studies, it is known that organics adsorbed on the CaCO 3 surface render the surface potential less positive or even negative regardless of their composition and structure [29][30][31][32]. In this study, amine and glycol compounds grafted onto the CaCO 3 surface changed the surface charge of the grain in a more negative direction. Thus, the presence of these compounds on the surface has changed the pH value for CaCO 3 , where the zeta potential is zero (isoelectric point). This shows that the dispersion stability of the colloidal systems (e.g., paints) including UC, TC, and MC can be achieved at different pH values.
The zeta potentials of the paints were measured at their inherent pH values (Table 2). PUC has a higher pH value than other paints. The more acidic character of the PTC and PMC paints can be attributed to the fact that the basic functional groups on the CaCO 3 surface are altered by the grinding-aid chemicals, as discussed above. According to zeta potential theory, the magnitude of the zeta potential indicates the potential stability of the colloidal system. No significant difference was observed in the zeta potentials of the paints at their inherent pH values. However, when evaluated together with all their ingredients as a colloidal system, it was observed that the paints were far from the isoelectric point (zeta potential = 0) at their inherent pH values and were relatively stable. The color values of paint films in the black and white regions of the Leneta chart and the gloss values of the films measured using 60 • and 85 • angles were given in Table 2. According to Master Painters Institute (MPI) standards, all paints have traditional matte finishes with gloss values below 5 at 60 • [33] ( Table 2). The opacity of the paints calculated according to ASTM D 2805 show that TEA and MEG grafted on the CaCO 3 surfaces reduce the hiding power of the paints (Table 2 and Figure 1). Calcite milled without using any chemicals (UC) had better hiding power than calcite milled using chemicals (MC and TC). TEA significantly negatively affected opacity, while MEG had less impact on opacity. Adverse effects of both chemicals were also observed on the gloss of paints ( Table 2). The hiding power represents the ability of the CaCO 3 particles in the paint layer to cover the background light from the matrix.
The zeta potentials of the paints were measured at their inherent pH values (T 2). PUC has a higher pH value than other paints. The more acidic character of the and PMC paints can be attributed to the fact that the basic functional groups on the Ca surface are altered by the grinding-aid chemicals, as discussed above. According to potential theory, the magnitude of the zeta potential indicates the potential stability o colloidal system. No significant difference was observed in the zeta potentials of the p at their inherent pH values. However, when evaluated together with all their ingred as a colloidal system, it was observed that the paints were far from the isoelectric p (zeta potential = 0) at their inherent pH values and were relatively stable. The color values of paint films in the black and white regions of the Leneta chart the gloss values of the films measured using 60° and 85° angles were given in Tab According to Master Painters Institute (MPI) standards, all paints have traditional m finishes with gloss values below 5 at 60° [33] ( Table 2). The opacity of the paints calcu according to ASTM D 2805 show that TEA and MEG grafted on the CaCO3 surfaces re the hiding power of the paints (Table 2 and Figure 1). Calcite milled without using chemicals (UC) had better hiding power than calcite milled using chemicals (MC and TEA significantly negatively affected opacity, while MEG had less impact on opacity verse effects of both chemicals were also observed on the gloss of paints (Table 2). hiding power represents the ability of the CaCO3 particles in the paint layer to cove background light from the matrix.  While the agglomeration of the pigment grains and their poor dispersion in the matrix decreases the hiding power, well-dispersed grains and optimized grain size increase the hiding power of the paint. In this study, no visible signs of agglomeration were observed in the paint films at the macro scale. The fineness of the grind of all paints was measured below 20 µm, consistent with the maximum grain size (d100) of CaCO 3 powders indicating that no agglomeration occurred in paints (Table 2 and Figure 2). Agglomeration was also not observed at micro dimensions in SEM images ( Figure 3). However, in UC, it was observed that the binder material (resin) between the grains was more abundant, the grains were in a binder on the paint film surface, the surface was smoother (Figure 3a), but in TC and MC, the grains were free on the paint film and gave a porous and rough surface appearance (Figure 3b,c). This difference in roughness, which can be observed at the microscale on the surfaces of paint films, is probably one of the crucial reasons affecting the opacity and gloss of the paints [13]. It is seen that UC, in which CaCO 3 grains are observed to be wetted by the binder, has a smoother surface and a higher gloss value than TC and MC. The fact that the binder is not evenly distributed to all particles (pigments) in the paint or cannot wet the pigments causes surface roughness in micro scales and thus a decrease in opacity and gloss [13]. It is thought that this deterioration in the optical properties of the paint is due to the inability of the resin to fully wet CaCO 3 grains due to the chemicals on the surfaces of the grains. Another possibility is the "frozen state" due to post-application water evaporation and coagulation of binder aggregates, which can be observed in high PVC water-borne (acrylic) dispersions as a result of poor stabilization, which can also be caused by poor wetting [11]. This instant "frozen state" limits the mobility of the binder, resulting in poor flow and leveling behavior of the paint.
While the agglomeration of the pigment grains and their poor dispersion in the matrix decreases the hiding power, well-dispersed grains and optimized grain size increase the hiding power of the paint. In this study, no visible signs of agglomeration were observed in the paint films at the macro scale. The fineness of the grind of all paints was measured below 20 μm, consistent with the maximum grain size (d100) of CaCO3 powders indicating that no agglomeration occurred in paints (Table 2 and Figure 2). Agglomeration was also not observed at micro dimensions in SEM images ( Figure 3). However, in UC, it was observed that the binder material (resin) between the grains was more abundant, the grains were in a binder on the paint film surface, the surface was smoother (Figure 3a), but in TC and MC, the grains were free on the paint film and gave a porous and rough surface appearance (Figure 3b,c). This difference in roughness, which can be observed at the microscale on the surfaces of paint films, is probably one of the crucial reasons affecting the opacity and gloss of the paints [13]. It is seen that UC, in which CaCO3 grains are observed to be wetted by the binder, has a smoother surface and a higher gloss value than TC and MC. The fact that the binder is not evenly distributed to all particles (pigments) in the paint or cannot wet the pigments causes surface roughness in micro scales and thus a decrease in opacity and gloss [13]. It is thought that this deterioration in the optical properties of the paint is due to the inability of the resin to fully wet CaCO3 grains due to the chemicals on the surfaces of the grains. Another possibility is the "frozen state" due to post-application water evaporation and coagulation of binder aggregates, which can be observed in high PVC water-borne (acrylic) dispersions as a result of poor stabilization, which can also be caused by poor wetting [11]. This instant "frozen state" limits the mobility of the binder, resulting in poor flow and leveling behavior of the paint. To prevent settling and instability during storage and transport, water-borne dispersion coatings must have high viscosities under low shears. However, they need low viscosities under high shears during application. This behavior is called shear-thinning or pseudo-plasticity [11,34,35]. It was understood from shear rate-dependent viscosity measurements that all the paints prepared in this study showed shear-thinning behavior (Figure 3). The power-law model was fitted to all viscosity curves (R 2 > 0.99) to compare the The power-law model is given by the following mathematical equation [36]: where n is the power-law index, K is the consistency (with the strange units of Pa.sn).
(a) (b) (c) The power-law index (n) gives information about the behavior in the high shear region, that is, shear-thinning and K give information about the behavior in the low shear area, that is, storage or in-can stability [36,37]. Smaller n values indicate more shear-thinning (pseudo-plastic) behavior, while smaller K values indicate lower viscosities in the low shear zone, i.e., low storage stability [37]. The viscosity of high PVC dispersions is To prevent settling and instability during storage and transport, water-borne dispersion coatings must have high viscosities under low shears. However, they need low viscosities under high shears during application. This behavior is called shear-thinning or pseudo-plasticity [11,34,35]. It was understood from shear rate-dependent viscosity measurements that all the paints prepared in this study showed shear-thinning behavior (Figure 3). The power-law model was fitted to all viscosity curves (R 2 > 0.99) to compare the flow properties of the paints quantitatively. The power-law model is given by the following mathematical equation [36]: where n is the power-law index, K is the consistency (with the strange units of Pa.sn). The power-law index (n) gives information about the behavior in the high shear region, that is, shear-thinning and K give information about the behavior in the low shear area, that is, storage or in-can stability [36,37]. Smaller n values indicate more shear-thinning (pseudo-plastic) behavior, while smaller K values indicate lower viscosities in the low shear zone, i.e., low storage stability [37]. The viscosity of high PVC dispersions is more sensitive to small variations in particle properties [38], and these changes are evident with the power-law properties of paints (Table 3). At low shear-rate range (<10 s −1 ), higher viscosity values indicate better in-can stability of PUC with 223.4% and 149.7% higher consistency indexes (K) than PTC and PMC, respectively. PUC seems to have higher dispersion and long-term storage stability than other paints. At a high shear-rate range (>100 s −1 ), PUC has the lowest viscosity suggesting that it is more advantageous in terms of application (painting, brushing, spreading). The particles in the paint are allowed to flow and orientate themselves during application due to the low viscosity behavior in the high shear-rate zone [37]. The more pseudoplastic behavior of PUC has also been seen from the power-law index (n) values (Table 3). PUC has 203.4% and 229.7% lower n values than PTC and PMC, respectively. Although PTC and PMC exhibit similar behavior, PMC appears to be somewhat more pseudo-plastic. At medium shear-rate ranges (10-100 s −1 ), the workability, which indicates the flow behavior during mixing, stirring, pouring, will be more difficult for PUC due to its relatively higher viscosity in this zone (Figure 4). Based on the effects of the grinding agents grafting on the CaCO 3 surface, it can be said that these chemical barriers preventing the wetting of the grains and the homogeneous distribution of the binder increase the grain-grain interaction in the paint. Since the wetting of the grains by the binder, which is the first stage of the dispersion process, is prevented by grinding aid chemicals, the behavior series that started with poor stabilization continued with high viscosity and application difficulties under high shear rates.

Conclusions
The grinding aid chemicals used while grinding to the grain sizes required to be used as a filler mineral adhere to the surface of CaCO3 and affect the properties of the fina products. It was observed that amine compounds, one of these grinding aid chemicals remained in higher amounts on the CaCO3 surface and created negative results in th paint in which CaCO3 was used as a filler. On the other hand, glycol compound adhered less on the CaCO3 surface and affected the properties of the final product less than th amine compound. It has been observed that CaCO3 ground without using any chemical gives the best results in terms of long-term stability, ease of application, and visuality o the paint.
It is thought that the chemicals grafted on the CaCO3 surface during grinding chang the surface chemistry of the CaCO3 grains, alter the functional groups that interact with the binder, and cause poor stabilization and application difficulties due to the lack of ho mogeneous distribution of the binder after poor wetting. Since it has been determined tha grinding aid chemicals affect the behavior of the mineral fillers in the final product, it i understood that the companies producing filler minerals for industries such as paint and plastic need to use grinding aids that improve the properties of the final product. Consid ering that it is not technically possible to achieve effective dry grinding without the use o grinding aids, it is necessary for mineral producers to conduct research and developmen in order to be able to select grinding aids considering the end product properties.

Data Availability Statement:
The data presented in this study are available in article.