- Email: [email protected]
Modification of nanometer calcium carbonate for water-borne architectural coatings
JOURNAL OF CHINA UNIVERSITY OF
MINING & TECHNOLOGY J China Univ Mining & Technol 18 (2008) 0076–0081 www.elsevier.com/locate/jcumt
Modification of nanometer calcium carbonate for water-borne architectural coatings WANG Xun-qiu, JIANG Deng-gao School of Chemical Engineering, Zhengzhou University, Zhengzhou, Henan 450002, China
Abstract: A kind of modifier was synthesized to modify the surface of nanometer calcium carbonate (abbreviated as nano-CaCO3), which is used in architectural coatings. The modification technology of the nano-CaCO3 was studied through orthogonal experimental methods. The factors studied were rotation speed, modifier dosage, emulsification temperature, emulsification time and heat aging time after emulsification. Optimized conditions for modification of the surface were: rotation speed 16000 r/min; modifier dosage 3%; emulsification temperature 75 °C; emulsification time 60 min and aging time 40 min. The modified nano-CaCO3 was also studied by size-distribution measurements, transmission electron microscopy, infrared spectroscopy and thermal analysis. The results show that the size distribution of the modified nano-CaCO3 is uniform and that there are chemi-sorption and physi-sorption between the nano-CaCO3 and the modifier. Compared to traditional architectural coatings without nano-CaCO3, the nanometer composite coatings are obviously improved in respect to dirt resistance, scrub resistance, thixotropy, water resistance, alkalinity resistance and aging resistance. Key words: nanometer calcium carbonate; surface modification; modifier; architectural coatings
1
Introduction
Nanometer calcium carbonate, having a particle size between 1–100 nm, is an important engineering material that has been developed in the 1980s. The super fine nano-CaCO3 particles have a large surface compared to the volume of the crystals. The large number of unsatisfied valencies at the surface results in a “small size” effect and a “surface effect” that ordinary calcium carbonate does not have. Therefore, compounding nano-CaCO3 into architectural coatings might greatly improve the property of architectural coatings, and greatly broaden the application of nano-CaCO3. However, because of the high surface polarity and high surface energy, many things could absorb on the surface of the nano-CaCO3 particles. The particles could also agglomerate and form bigger particles, which could make the nano-CaCO3 lose its special properties and weaken the coating performance. In order to improve how nano-CaCO3 particles disperse in the coating solutions and to increase the nano-particle binding force to other components, it is necessary to modify the surface[1–3]. This will reduce the surface energy of the granules to enhance granule-emulsion affinity and to weaken the polarity of the granule surface. Received 20 September 2007; accepted 20 October 2007 Corresponding author. Tel: +86-13938508357, E-mail address: [email protected]
Therefore, a kind of modifier was synthesized to treat nano-CaCO3 used in architectural coatings. The effect of the surface modification was evaluated by determining the particle size and the settlement percentage. These parameters were also measured to optimize the modification treatment conditions[4–5]. Then nanometer-composite architectural coatings were prepared and the mechanism by which the nano-CaCO3 was modified was studied by infrared spectral and thermal analysis.
2
Experimental
2.1 Materials Nano-CaCO3 suspension (7.76%) was provided by Anhui Chaodong Nanometer Material Science and Technology Co., Ltd.; Butyl acrylate (BA, 99.5%), Acrylic acid (AA, 99.9%), Benzoyl peroxide (BPO, 95.0%) and Triethylamine (TEA, 99.9%) were purchased from Shanghai Shengyu Chemical Industry Co., Ltd.; Ethylene glycol ethyl ether (EE, 99.5%) was obtained from Jiangsu Ruijia Chemistry Co., Ltd. 2.2 Methods 1) Synthesis of modifier 73.125 g of butyl acrylate (BA), 39.375 g of acrylic
WANG Xun-qiu et al
Modification of nanometer calcium carbonate for water-borne architectural coatings
77
acid (AA), 0.675 g of benzoyl peroxide (BPO) and 360 g ethylene glycol ethyl ether (EE) were added to a 1000 mL three-necked flask. The mixture was stirred while continuously adding drop wise mixture I (a mixture of 73.125 g BA, 39.375 g AA, 0.675 g BPO and 90 g EE) over a period of 4 h at a temperature between (104–108) °C. The solution was then kept at this temperature for 1 h. Next, mixture II (a mixture of 0.45 g BPO and 9 g EE) was added drop wise to the solution over an hour and a half. The solution was then kept stirring for an additional 2 h at a temperature of (104–108) °C. Finally, the solution was cooled to room temperature and triethylamine (TEA) was added to neutralize the solution. 2) Optimizing the modification conditions A 1000 mL flask containing 800 g of nano-CaCO3 suspension was placed into a constant-temperature water bath. The suspension was stirred until reaching the designated temperature for that particular trial. Then a certain amount of modifier (based on the experimental plan) was added and the suspension was emulsified for a particular period of time using an emulsifier (WL750CY, Shanghai Weiyu Mechanical and Electrical Making Co., Ltd.) at some specified rotation speed. After emulsification stirring was maintained at 2000–3000 r/min, at the same
temperature, for certain period of time appropriate for that trial. The suspension was cooled to room temperature and a sample was taken and diluted to about 0.01% nano-CaCO3 to test the granule size-distribution of the nano-CaCO3 using a particle size analyzer (Zetasizer 3000HSA, England Malvin Instrument Co., Ltd.). Finally, the suspension was filtered to get a filter cake of modified nano-CaCO3 (the content of water in the cake is about 35%) and the settlement percentage was measured. 3) Testing the settlement percentage A specified quantity of nano-CaCO3 filter cake containing 1.0 g of CaCO3 was weighed and put into a 20 mL ground measuring cylinder along with some water. The solution was mixed to uniform consistency and allowed to stand at room temperature for seven days. The sediment after seven days was weighed to get the percentage settled.
The infrared spectrogram of the modifier was obtained using an FTIR-8700 (Japan Shimadzu Corporation). A representative spectrum is shown in Fig. 1.
of NH+ appear between 2686.6 cm–1, 2495.7 cm–1 and 2362.6 cm–1; the strong absorption from the stretching vibration of -COO- appears at 1732.0 cm–1; the stretching vibration absorption peaks of C=O and
3 3.1
Results and discussion Modifier
The modifier was synthesized following the reaction:
appear at 1255.6 cm–1 and -O-C- in –1 1166.9 cm ; the absorption peaks from C-C appear at 1118.6 cm–1 and 1066.6 cm–1 (Fig. 1) [6]. All these are the characteristic peaks of an amine salt of the acrylic acid ester synthesized in this experiment. 3.2 Orthogonal experiments
Fig. 1
Infrared spectrogram of the modifier
The symmetrical and asymmetrical stretching and the bending mode absorption peaks of the -CH2 group appear at 2873.7 cm–1, 2935.5 cm–1 and 1454.2 cm–1, respectively. The stretching and bending absorption peaks for -CH3 appear at 2960.5 cm–1 and 1394.4 cm–1; the stretching vibration multi-absorption peaks
A Taguchi L16(45) orthogonal design was used to study the effect of different factors on the surface modification of nano-CaCO3. The predictors were rotation speed, modifier dosage, emulsification temperature, emulsification time and the time allowed for aging after emulsification. An optimum set of conditions for performing the modification were obtained. The design and the results, of the orthogonal experiments are shown in Table 1.
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Journal of China University of Mining & Technology
Table 1 Code
Emulsification time (min)
Vol.18 No.1
Design and results of an L16(45) orthogonal experiment
Rotation speed (r/min)
Modifier dosage (%)
Emulsification temperature (°C)
Aging time (min)
Average granule diameter (nm)
7d settlement percentage (%)
W-C1
30(I)
8000(,)
1 (I)
85(I)
20(I)
637.4
30.29
W-C2
30(I)
12000(II)
2 (II)
75(II)
40(II)
452.1
20.56
W-C3
30(I)
16000(III)
3 (III)
65(III)
60(III)
287.9
13.18
W-C4
30(I)
18000(IV)
4 (IV)
55(IV)
80(IV)
594.3
28.79
W-C5
60(II)
8000(I)
2 (II)
65(III)
80(IV)
387.6
18.36
W-C6
60(II)
12000(II)
1 (I)
55(IV)
60(III)
502.9
25.17
W-C7
60(II)
16000(III)
4 (IV)
85(I)
40(II)
256.7
12.78
W-C8
60(II)
18000(IV)
3 (III)
75(II)
20(I)
168.1
4.36
W-C9
90(III)
8000(I)
3 (III)
55(IV)
40(II)
339.8
15.48
W-C10
90(III)
12000(II)
4 (IV)
65(III)
20(I)
412.5
19.05
W-C11
90(III)
16000(III)
1 (I)
75(II)
80(IV)
326.7
15.43
W-C12
90(III)
18000(IV)
2 (II)
85(I)
60(III)
487.3
23.10
W-C13
120(IV)
8000(I)
4 (IV)
75(II)
60(III)
356.0
15.78
W-C14
120(IV)
12000(II)
3 (III)
85(I)
80(IV)
300.1
14.23
W-C15
120(IV)
16000(III)
2 (II)
55(IV)
20(I)
567.2
27.18
W-C16
120(IV)
18000(IV)
1 (I)
65(III)
40(II)
428.7
19.35
6505.3
303.09
∑ĉ ∑Ċ ∑ċ ∑Č Range
1971.7 1315.3 1566.3 1652.0 656.4
1681.5 1302.9 1516.7 2004.2 701.3
1785.2 1477.3 1634.1 1608.7 307.9
80.40 56.13 69.94 96.62 40.49
80.88 68.17 77.23 76.81 12.71
Average granule diameter (nm) 1720.8 1667.6 1438.5 1678.4 282.3
1895.7 1894.2 1095.9 1619.5 799.8
Settlement percentage (%) ∑ĉ ∑Ċ ∑ċ ∑Č Range
92.82 60.67 73.06 76.54 32.15
79.91 79.01 68.57 75.60 11.34
90.24 89.20 47.25 76.40 42.99
Note: The modifier dosage is weight percentage based on nano-CaCO3.
From Table 1, it can be seen that the experiment with an emulsification time of 60 min, a rotation speed of 16000 r/min, a modifier dosage of 3%, an emulsification temperature of 75 °C and the aging time of 40 min had the lowest average granule diameter and settlement percentage: this is the optimized technological condition. Furthermore, variation analysis showed that modifier dosage had the biggest influence, emulsification time and emulsification temperature had the next largest effect while aging time and rotation speed had the smallest influence. The average granule diameter and the settlement percentage of the modified nano-CaCO3 decrease as the dosage of modifier increases. The average granule diameter and the settlement percentage are the smallest when the modifier dosage is 3%. As the dosage increases by more than 3%, the average granule diameter and the settlement percentage of the modified nano-CaCO3 both increase. This is because surface modification of the nano-CaCO3 is incomplete for low modifier dosage. When the modifier dosage is more than 3%, the surface adsorption on the nano-CaCO3 becomes saturated and excess modifier causes agglomeration, which results
in an increase in the average granule diameter and in the settlement percentage. The average granule diameter and settlement percentage of the modified nano-CaCO3 decrease with an increase in emulsification temperature or emulsification time. When the emulsification temperature is higher than 75 °C, or the emulsification time exceeds 60 min, the average granule diameter and settlement percentage increase. This is because the nano-CaCO3 does not have sufficient contact with the modifier at short time, so adsorption is not complete and surface modification is unsatisfactory. Furthermore, if the emulsification temperature is too low, the rate of reaction at the surface decreases, which would require longer contact time to complete reaction. When the emulsification temperature is higher than 75 °C, or the emulsification time exceeds 60 min, the opportunity for collision and agglomeration of the granules increases. This causes an increase in average granule diameter and settlement percentage. 3.3
Granule-size distribution and TEM analysis
A suspension of nano-CaCO3 that had been prepared under the optimized conditions was
WANG Xun-qiu et al
Modification of nanometer calcium carbonate for water-borne architectural coatings
measured using a particle size analyzer, at 25 °C. The average granule diameter was 105.8 nm (while the unmodified nano-CaCO3 was 936.7 nm), and the polydispersity coefficient was 0.29 (while the unmodified nano-CaCO3 had a polydispersity of 1.0). The granule-size distribution is shown in Fig. 2. A filter cake of modified nano-CaCO3 was dried in vacuum and tested for specific surface area: the value found was 32.9 m2/g (while the unmodified nano-CaCO3 had a specific area of 23.5 m2/g). Transmission electron microscopy using a JEOL JEM2010 (Japan JEOL Corporation) gave the results shown in the photograph reproduced in Fig. 3.
(a) Unmodified nano-CaCO3
Fig. 3
79
(b) Modified nano-CaCO3
TEM photograph of unmodified and modified nano-CaCO3
It can be seen from Fig. 2 that the granule size of the modified nano-CaCO3 is uniformly distributed and well dispersed with little agglomeration. From Fig. 3, except for a small part of the modified nano-CaCO3 granules, most granules are separated with a clear boundary and circumscribed space around them, which means that the modification of nano-CaCO3 is successful. 3.4 Infrared spectral analysis
Fig. 2
Granule size distribution of modified nano-CaCO3
Infrared spectra of both unmodified and modified nano-CaCO3, which was obtained after the filter cake was soaked in 80 °C water and washed five times and then dried, is shown in Fig. 4.
(a) Unmodified nano-CaCO3
Fig. 4
From Fig. 4a, it can be seen that the unmodified nano-CaCO3 absorption peaks appear at 713.6, 875.6, 1,450, 1795.6 and 2513.1 cm–1. These are characteristic absorption peaks of calcite calcium carbonate[7–8]. In Fig. 4b peaks at 2871.8, 2923.9, 2962.4, 1728.6, 1704.9, 1267.1, 1166.8, 1114.8, 1082.0 and 1029.9 cm–1 are visible: these are characteristic peaks of the modifier used in the experiment. This indicates that the modifier has bound onto the surface of the nano-CaCO3 granules to achieve modification. 3.5
(b) Modified nano-CaCO3
Infrared spectrogram of the unmodified and modified nano-CaCO3
Thermal analysis
Fig. 5 shows the results of differential thermal analysis of unmodified and modified nano-CaCO3. Curve (b) in Fig. 5 shows the data from the modified nano-CaCO 3 . Results from washed nano-CaCO 3 obtained by soaking the filter cake at 80 °C in hot water, washing five times and drying are shown as trace (c) in Fig. 5. The unmodified nano-CaCO3 gave the trace labeled (a) in Fig. 5. The heating rate of the
Fig. 5
Thermal analysis curves of unmodified and modified nano-CaCO3
thermal analyzer was 10 K/min under a N2 atmosphere. The analyzer was made by German Netzsch Corporation. All three nano-CaCO3 samples begin to decompose at about 600 °C, the maximum decomposition temperature is about 750 °C. At 500 °C, taking unmodified nano-CaCO3 as the standard, the
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Journal of China University of Mining & Technology
modified nano-CaCO3 has lost 3.01% of its weight. The washed, modified nano-CaCO3 has lost 1.72% of its weight. This weight loss happens because of modifier decomposition. Therefore, there exists physical sorption and chemical sorption between the nano-CaCO3 and the modifier. 3.6 Mechanism of the modification reaction
Fig. 6
3.7
There are few differences between architectural coatings without nano-CaCO3 and architectural coatings containing 3%–4% modified nano-CaCO3 as far as appearance, architectural performance, membrane appearance, drying time and resistance to freezing and thawing are concerned: both formulations can meet the national standard requirements[10]. However, compared to traditional architectural coatings without nano-CaCO3, architectural coatings containing nano-CaCO3 are greatly improved in dirt resistance, scrub resistance, water resistance, alkalinity resistance and aging resistance. Scrub resistance was especially improved, by about 75600 times (Table 2). Considering all the architectural coatings that failed to meet qualifications posted by the State Quality Inspection Administration General on March, 2005, the most common reason for failure is due to scrub resistance. About 17% of all market products had this problem. Therefore, it is of very great importance to improve the scrub resistance of architectural coatings by compounding nano-CaCO3 into them. Main performance index of coatings
Item
In Fig. 4b stretching vibration absorption peaks from hydrogen bonds, OH…O, appear at 2500–3500 cm–1 and a strong absorption peak from RCOOCa appears at 1620 cm–1[9]. This indicates that the modifier binds with hydroxyls on the surface of the CaCO3 granule. The process by which this happens is shown in Fig. 6.
Modification mechanism of nano-CaCO3
Application of modified nano-CaCO3 in water-borne architectural coatings
Table 2
Vol.18 No.1
With modified Without Test methods nano-CaCO3 nano-CaCO3
Dirt resistance (%)
5.81
3.89
GB/T9780-1988
Scrub resistance (Times)
3000
75600
GB/T9266-1988
Water resistance, normal maximal time (h)
120
2050
GB/T1733-1993
Alkali resistance, normal maximal time (h)
60
600
GB/T9265-1988
UV-light resistance (45 h), loss of gloss (%)
43.8
18.6
GB/T1766-1995
4
Conclusions
1) A kind of amine salt of an acrylic acid ester was synthesized for application with nano-CaCO3 in water-borne architectural coatings. 2) The rotation speed of factors, modifier dosage, emulsification temperature, emulsification time and aging time influenced the surface modification of nano-CaCO3. These factors were studied through orthogonal experiments to find optimized conditions to prepare material suitable for modifying nanoCaCO3 dispersed in water. 3) The modified nano-CaCO3 was obtained directly by filtration which not only avoided agglomeration of nanometer granules but also makes it easy to disperse the powder when it is time to use it. 4) TEM and particle size analysis show that the granule-size distribution of modified nano-CaCO3 is uniform with an average granule diameter of 105.8 nm. The infrared spectra and thermal analysis show that chemical sorption and physical sorption occurr between nano-CaCO3 and the modifier. 5) Compared with traditional architectural coatings without nano-CaCO3, the nano-CaCO3 composite coatings are greatly improved in dirt resistance, scrub resistance, water resistance, alkalinity resistance and aging resistance; the scrub resistance was improved by 75600 times.
References [1]
[2]
Fekete E, Pukánszky B, Tóth A, et al. Surface modification and characterization of particulate mineral fillers. Journal of Colloid and Interface Science, 1990, 135(1): 200–208. Wang X Q, Jiang D G, Zhao W L, et al. Surface modification of nano-CaCO3 & its application in
WANG Xun-qiu et al
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Modification of nanometer calcium carbonate for water-borne architectural coatings
architectural coatings. Non-Metallic Mines, 2005(1): 7–9. (In Chinese) Jeanett G, Carmen A, Miren I, et al. Effects of coupling agents on mechanical and morphological behavior of the PP/HDPE blend with two different CaCO3. European Polymer Journal, 2002, 38(12): 2465–2475. Kunio E. Interactions between surfactants and particles: dispersion, surface modification, and adsolubilization. Journal of Colloid and Interface Science, 2001, 241(1): 1–17. Chen J F, He T B, Wu W, et al. Adsorption of sodium salt of poly(acrylic)acid (PAANa) on nano-sized CaCO3 and dispersion of nano-sized CaCO3 in water. Colloids and Surfaces A: Physicochem Eng Aspects, 2004, 232(2–3): 163–168.
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[6]
Socrates G. Infrared Characteristic Group Frequencies. New York: John Wiley & Sons, 1981. [7] Wu W, Lu S C. Mechano-chemical surface modification of calcium carbonate particles by polymer grafting. Powder Technology, 2003, 137(1–2): 41–48. [8] Kim D S, Lee C K. Surface modification of precipitated calcium carbonate using aqueous fluosilicic acid. Applied Surface Science, 2002, 202(1–2): 15–23. [9] Socrates G. Infrared Characteristic Group Frequencies. Great Britain: Stonebridge Press, 1980. [10] Wang X Q, Jiang D G, Zhao W L, et al. Study on application of nanometer calcium carbonate in exterior architectural coatings. Journal of Building Materials, 2005, 8(5): 547–552. (In Chinese)
(Continued from page 66)
References [1]
[2]
[3]
[4]
[5]
Bai J B, Hou C J.Control principle of surrounding rocks in deep roadway and its application. Journal of China University of Mining & Technology, 2006, 35(2): 145– 148. (In Chinese) He M C, Jing H H, Sun X M. Research progress of soft rock engineering geomechanics in China coal mine. Journal of Engineering Geology, 2000, 8(1): 46–62. (In Chinese) Zhao G T. Tunnel Country Rock Deforming Regularity and Its Control Research in Soft-Rock Tunnel [Ph.D. dissertation]. Xuzhou: China University of Mining and Technology, 1992. (In Chinese) He Y N, Han L J, Shao P, et al. Some problems of rock mechanics for roadways stability in depth. Journal of China University of Mining & Technology, 2006, 35(3): 288–295. (In Chinese) Peng S P, Wang X L, Liu X W. Research on reological characteristics of rock in the weak coal-bearing strata.
Journal of China Coal Society, 2001, 26(2): 149–152. (In Chinese) [6] Duan Q Q, Liu C P, Ju Y, et al. Fractal effects on subcritical crack growth of concrete. Journal of China University of Mining & Technology, 2006, 35(1): 70–74. (In Chinese) [7] Huang C K. Steel Fiber Concrete Structure. Beijing: Mechanism Industry Publishing House, 2004. (In Chinese) [8] Gao D Y. Steel Fiber Concrete Design and Application. Beijing: China Construction Industry Publishing House, 2002. (In Chinese) [9] Zhou H W, Xie H P. Support technique of steel fiber shotcrete for soft rock tunnel at great depth. Journal of Engineering Geology, 2001, 9(4): 393–398. (In Chinese) [10] Li Y Q, Shen L J. Research and development of steel fiber concrete in shaft and chamber engineering. Mining & Metallurgy, 2006, 6(2): 5–8. (In Chinese)
MINING & TECHNOLOGY J China Univ Mining & Technol 18 (2008) 0076–0081 www.elsevier.com/locate/jcumt
Modification of nanometer calcium carbonate for water-borne architectural coatings WANG Xun-qiu, JIANG Deng-gao School of Chemical Engineering, Zhengzhou University, Zhengzhou, Henan 450002, China
Abstract: A kind of modifier was synthesized to modify the surface of nanometer calcium carbonate (abbreviated as nano-CaCO3), which is used in architectural coatings. The modification technology of the nano-CaCO3 was studied through orthogonal experimental methods. The factors studied were rotation speed, modifier dosage, emulsification temperature, emulsification time and heat aging time after emulsification. Optimized conditions for modification of the surface were: rotation speed 16000 r/min; modifier dosage 3%; emulsification temperature 75 °C; emulsification time 60 min and aging time 40 min. The modified nano-CaCO3 was also studied by size-distribution measurements, transmission electron microscopy, infrared spectroscopy and thermal analysis. The results show that the size distribution of the modified nano-CaCO3 is uniform and that there are chemi-sorption and physi-sorption between the nano-CaCO3 and the modifier. Compared to traditional architectural coatings without nano-CaCO3, the nanometer composite coatings are obviously improved in respect to dirt resistance, scrub resistance, thixotropy, water resistance, alkalinity resistance and aging resistance. Key words: nanometer calcium carbonate; surface modification; modifier; architectural coatings
1
Introduction
Nanometer calcium carbonate, having a particle size between 1–100 nm, is an important engineering material that has been developed in the 1980s. The super fine nano-CaCO3 particles have a large surface compared to the volume of the crystals. The large number of unsatisfied valencies at the surface results in a “small size” effect and a “surface effect” that ordinary calcium carbonate does not have. Therefore, compounding nano-CaCO3 into architectural coatings might greatly improve the property of architectural coatings, and greatly broaden the application of nano-CaCO3. However, because of the high surface polarity and high surface energy, many things could absorb on the surface of the nano-CaCO3 particles. The particles could also agglomerate and form bigger particles, which could make the nano-CaCO3 lose its special properties and weaken the coating performance. In order to improve how nano-CaCO3 particles disperse in the coating solutions and to increase the nano-particle binding force to other components, it is necessary to modify the surface[1–3]. This will reduce the surface energy of the granules to enhance granule-emulsion affinity and to weaken the polarity of the granule surface. Received 20 September 2007; accepted 20 October 2007 Corresponding author. Tel: +86-13938508357, E-mail address: [email protected]
Therefore, a kind of modifier was synthesized to treat nano-CaCO3 used in architectural coatings. The effect of the surface modification was evaluated by determining the particle size and the settlement percentage. These parameters were also measured to optimize the modification treatment conditions[4–5]. Then nanometer-composite architectural coatings were prepared and the mechanism by which the nano-CaCO3 was modified was studied by infrared spectral and thermal analysis.
2
Experimental
2.1 Materials Nano-CaCO3 suspension (7.76%) was provided by Anhui Chaodong Nanometer Material Science and Technology Co., Ltd.; Butyl acrylate (BA, 99.5%), Acrylic acid (AA, 99.9%), Benzoyl peroxide (BPO, 95.0%) and Triethylamine (TEA, 99.9%) were purchased from Shanghai Shengyu Chemical Industry Co., Ltd.; Ethylene glycol ethyl ether (EE, 99.5%) was obtained from Jiangsu Ruijia Chemistry Co., Ltd. 2.2 Methods 1) Synthesis of modifier 73.125 g of butyl acrylate (BA), 39.375 g of acrylic
WANG Xun-qiu et al
Modification of nanometer calcium carbonate for water-borne architectural coatings
77
acid (AA), 0.675 g of benzoyl peroxide (BPO) and 360 g ethylene glycol ethyl ether (EE) were added to a 1000 mL three-necked flask. The mixture was stirred while continuously adding drop wise mixture I (a mixture of 73.125 g BA, 39.375 g AA, 0.675 g BPO and 90 g EE) over a period of 4 h at a temperature between (104–108) °C. The solution was then kept at this temperature for 1 h. Next, mixture II (a mixture of 0.45 g BPO and 9 g EE) was added drop wise to the solution over an hour and a half. The solution was then kept stirring for an additional 2 h at a temperature of (104–108) °C. Finally, the solution was cooled to room temperature and triethylamine (TEA) was added to neutralize the solution. 2) Optimizing the modification conditions A 1000 mL flask containing 800 g of nano-CaCO3 suspension was placed into a constant-temperature water bath. The suspension was stirred until reaching the designated temperature for that particular trial. Then a certain amount of modifier (based on the experimental plan) was added and the suspension was emulsified for a particular period of time using an emulsifier (WL750CY, Shanghai Weiyu Mechanical and Electrical Making Co., Ltd.) at some specified rotation speed. After emulsification stirring was maintained at 2000–3000 r/min, at the same
temperature, for certain period of time appropriate for that trial. The suspension was cooled to room temperature and a sample was taken and diluted to about 0.01% nano-CaCO3 to test the granule size-distribution of the nano-CaCO3 using a particle size analyzer (Zetasizer 3000HSA, England Malvin Instrument Co., Ltd.). Finally, the suspension was filtered to get a filter cake of modified nano-CaCO3 (the content of water in the cake is about 35%) and the settlement percentage was measured. 3) Testing the settlement percentage A specified quantity of nano-CaCO3 filter cake containing 1.0 g of CaCO3 was weighed and put into a 20 mL ground measuring cylinder along with some water. The solution was mixed to uniform consistency and allowed to stand at room temperature for seven days. The sediment after seven days was weighed to get the percentage settled.
The infrared spectrogram of the modifier was obtained using an FTIR-8700 (Japan Shimadzu Corporation). A representative spectrum is shown in Fig. 1.
of NH+ appear between 2686.6 cm–1, 2495.7 cm–1 and 2362.6 cm–1; the strong absorption from the stretching vibration of -COO- appears at 1732.0 cm–1; the stretching vibration absorption peaks of C=O and
3 3.1
Results and discussion Modifier
The modifier was synthesized following the reaction:
appear at 1255.6 cm–1 and -O-C- in –1 1166.9 cm ; the absorption peaks from C-C appear at 1118.6 cm–1 and 1066.6 cm–1 (Fig. 1) [6]. All these are the characteristic peaks of an amine salt of the acrylic acid ester synthesized in this experiment. 3.2 Orthogonal experiments
Fig. 1
Infrared spectrogram of the modifier
The symmetrical and asymmetrical stretching and the bending mode absorption peaks of the -CH2 group appear at 2873.7 cm–1, 2935.5 cm–1 and 1454.2 cm–1, respectively. The stretching and bending absorption peaks for -CH3 appear at 2960.5 cm–1 and 1394.4 cm–1; the stretching vibration multi-absorption peaks
A Taguchi L16(45) orthogonal design was used to study the effect of different factors on the surface modification of nano-CaCO3. The predictors were rotation speed, modifier dosage, emulsification temperature, emulsification time and the time allowed for aging after emulsification. An optimum set of conditions for performing the modification were obtained. The design and the results, of the orthogonal experiments are shown in Table 1.
78
Journal of China University of Mining & Technology
Table 1 Code
Emulsification time (min)
Vol.18 No.1
Design and results of an L16(45) orthogonal experiment
Rotation speed (r/min)
Modifier dosage (%)
Emulsification temperature (°C)
Aging time (min)
Average granule diameter (nm)
7d settlement percentage (%)
W-C1
30(I)
8000(,)
1 (I)
85(I)
20(I)
637.4
30.29
W-C2
30(I)
12000(II)
2 (II)
75(II)
40(II)
452.1
20.56
W-C3
30(I)
16000(III)
3 (III)
65(III)
60(III)
287.9
13.18
W-C4
30(I)
18000(IV)
4 (IV)
55(IV)
80(IV)
594.3
28.79
W-C5
60(II)
8000(I)
2 (II)
65(III)
80(IV)
387.6
18.36
W-C6
60(II)
12000(II)
1 (I)
55(IV)
60(III)
502.9
25.17
W-C7
60(II)
16000(III)
4 (IV)
85(I)
40(II)
256.7
12.78
W-C8
60(II)
18000(IV)
3 (III)
75(II)
20(I)
168.1
4.36
W-C9
90(III)
8000(I)
3 (III)
55(IV)
40(II)
339.8
15.48
W-C10
90(III)
12000(II)
4 (IV)
65(III)
20(I)
412.5
19.05
W-C11
90(III)
16000(III)
1 (I)
75(II)
80(IV)
326.7
15.43
W-C12
90(III)
18000(IV)
2 (II)
85(I)
60(III)
487.3
23.10
W-C13
120(IV)
8000(I)
4 (IV)
75(II)
60(III)
356.0
15.78
W-C14
120(IV)
12000(II)
3 (III)
85(I)
80(IV)
300.1
14.23
W-C15
120(IV)
16000(III)
2 (II)
55(IV)
20(I)
567.2
27.18
W-C16
120(IV)
18000(IV)
1 (I)
65(III)
40(II)
428.7
19.35
6505.3
303.09
∑ĉ ∑Ċ ∑ċ ∑Č Range
1971.7 1315.3 1566.3 1652.0 656.4
1681.5 1302.9 1516.7 2004.2 701.3
1785.2 1477.3 1634.1 1608.7 307.9
80.40 56.13 69.94 96.62 40.49
80.88 68.17 77.23 76.81 12.71
Average granule diameter (nm) 1720.8 1667.6 1438.5 1678.4 282.3
1895.7 1894.2 1095.9 1619.5 799.8
Settlement percentage (%) ∑ĉ ∑Ċ ∑ċ ∑Č Range
92.82 60.67 73.06 76.54 32.15
79.91 79.01 68.57 75.60 11.34
90.24 89.20 47.25 76.40 42.99
Note: The modifier dosage is weight percentage based on nano-CaCO3.
From Table 1, it can be seen that the experiment with an emulsification time of 60 min, a rotation speed of 16000 r/min, a modifier dosage of 3%, an emulsification temperature of 75 °C and the aging time of 40 min had the lowest average granule diameter and settlement percentage: this is the optimized technological condition. Furthermore, variation analysis showed that modifier dosage had the biggest influence, emulsification time and emulsification temperature had the next largest effect while aging time and rotation speed had the smallest influence. The average granule diameter and the settlement percentage of the modified nano-CaCO3 decrease as the dosage of modifier increases. The average granule diameter and the settlement percentage are the smallest when the modifier dosage is 3%. As the dosage increases by more than 3%, the average granule diameter and the settlement percentage of the modified nano-CaCO3 both increase. This is because surface modification of the nano-CaCO3 is incomplete for low modifier dosage. When the modifier dosage is more than 3%, the surface adsorption on the nano-CaCO3 becomes saturated and excess modifier causes agglomeration, which results
in an increase in the average granule diameter and in the settlement percentage. The average granule diameter and settlement percentage of the modified nano-CaCO3 decrease with an increase in emulsification temperature or emulsification time. When the emulsification temperature is higher than 75 °C, or the emulsification time exceeds 60 min, the average granule diameter and settlement percentage increase. This is because the nano-CaCO3 does not have sufficient contact with the modifier at short time, so adsorption is not complete and surface modification is unsatisfactory. Furthermore, if the emulsification temperature is too low, the rate of reaction at the surface decreases, which would require longer contact time to complete reaction. When the emulsification temperature is higher than 75 °C, or the emulsification time exceeds 60 min, the opportunity for collision and agglomeration of the granules increases. This causes an increase in average granule diameter and settlement percentage. 3.3
Granule-size distribution and TEM analysis
A suspension of nano-CaCO3 that had been prepared under the optimized conditions was
WANG Xun-qiu et al
Modification of nanometer calcium carbonate for water-borne architectural coatings
measured using a particle size analyzer, at 25 °C. The average granule diameter was 105.8 nm (while the unmodified nano-CaCO3 was 936.7 nm), and the polydispersity coefficient was 0.29 (while the unmodified nano-CaCO3 had a polydispersity of 1.0). The granule-size distribution is shown in Fig. 2. A filter cake of modified nano-CaCO3 was dried in vacuum and tested for specific surface area: the value found was 32.9 m2/g (while the unmodified nano-CaCO3 had a specific area of 23.5 m2/g). Transmission electron microscopy using a JEOL JEM2010 (Japan JEOL Corporation) gave the results shown in the photograph reproduced in Fig. 3.
(a) Unmodified nano-CaCO3
Fig. 3
79
(b) Modified nano-CaCO3
TEM photograph of unmodified and modified nano-CaCO3
It can be seen from Fig. 2 that the granule size of the modified nano-CaCO3 is uniformly distributed and well dispersed with little agglomeration. From Fig. 3, except for a small part of the modified nano-CaCO3 granules, most granules are separated with a clear boundary and circumscribed space around them, which means that the modification of nano-CaCO3 is successful. 3.4 Infrared spectral analysis
Fig. 2
Granule size distribution of modified nano-CaCO3
Infrared spectra of both unmodified and modified nano-CaCO3, which was obtained after the filter cake was soaked in 80 °C water and washed five times and then dried, is shown in Fig. 4.
(a) Unmodified nano-CaCO3
Fig. 4
From Fig. 4a, it can be seen that the unmodified nano-CaCO3 absorption peaks appear at 713.6, 875.6, 1,450, 1795.6 and 2513.1 cm–1. These are characteristic absorption peaks of calcite calcium carbonate[7–8]. In Fig. 4b peaks at 2871.8, 2923.9, 2962.4, 1728.6, 1704.9, 1267.1, 1166.8, 1114.8, 1082.0 and 1029.9 cm–1 are visible: these are characteristic peaks of the modifier used in the experiment. This indicates that the modifier has bound onto the surface of the nano-CaCO3 granules to achieve modification. 3.5
(b) Modified nano-CaCO3
Infrared spectrogram of the unmodified and modified nano-CaCO3
Thermal analysis
Fig. 5 shows the results of differential thermal analysis of unmodified and modified nano-CaCO3. Curve (b) in Fig. 5 shows the data from the modified nano-CaCO 3 . Results from washed nano-CaCO 3 obtained by soaking the filter cake at 80 °C in hot water, washing five times and drying are shown as trace (c) in Fig. 5. The unmodified nano-CaCO3 gave the trace labeled (a) in Fig. 5. The heating rate of the
Fig. 5
Thermal analysis curves of unmodified and modified nano-CaCO3
thermal analyzer was 10 K/min under a N2 atmosphere. The analyzer was made by German Netzsch Corporation. All three nano-CaCO3 samples begin to decompose at about 600 °C, the maximum decomposition temperature is about 750 °C. At 500 °C, taking unmodified nano-CaCO3 as the standard, the
80
Journal of China University of Mining & Technology
modified nano-CaCO3 has lost 3.01% of its weight. The washed, modified nano-CaCO3 has lost 1.72% of its weight. This weight loss happens because of modifier decomposition. Therefore, there exists physical sorption and chemical sorption between the nano-CaCO3 and the modifier. 3.6 Mechanism of the modification reaction
Fig. 6
3.7
There are few differences between architectural coatings without nano-CaCO3 and architectural coatings containing 3%–4% modified nano-CaCO3 as far as appearance, architectural performance, membrane appearance, drying time and resistance to freezing and thawing are concerned: both formulations can meet the national standard requirements[10]. However, compared to traditional architectural coatings without nano-CaCO3, architectural coatings containing nano-CaCO3 are greatly improved in dirt resistance, scrub resistance, water resistance, alkalinity resistance and aging resistance. Scrub resistance was especially improved, by about 75600 times (Table 2). Considering all the architectural coatings that failed to meet qualifications posted by the State Quality Inspection Administration General on March, 2005, the most common reason for failure is due to scrub resistance. About 17% of all market products had this problem. Therefore, it is of very great importance to improve the scrub resistance of architectural coatings by compounding nano-CaCO3 into them. Main performance index of coatings
Item
In Fig. 4b stretching vibration absorption peaks from hydrogen bonds, OH…O, appear at 2500–3500 cm–1 and a strong absorption peak from RCOOCa appears at 1620 cm–1[9]. This indicates that the modifier binds with hydroxyls on the surface of the CaCO3 granule. The process by which this happens is shown in Fig. 6.
Modification mechanism of nano-CaCO3
Application of modified nano-CaCO3 in water-borne architectural coatings
Table 2
Vol.18 No.1
With modified Without Test methods nano-CaCO3 nano-CaCO3
Dirt resistance (%)
5.81
3.89
GB/T9780-1988
Scrub resistance (Times)
3000
75600
GB/T9266-1988
Water resistance, normal maximal time (h)
120
2050
GB/T1733-1993
Alkali resistance, normal maximal time (h)
60
600
GB/T9265-1988
UV-light resistance (45 h), loss of gloss (%)
43.8
18.6
GB/T1766-1995
4
Conclusions
1) A kind of amine salt of an acrylic acid ester was synthesized for application with nano-CaCO3 in water-borne architectural coatings. 2) The rotation speed of factors, modifier dosage, emulsification temperature, emulsification time and aging time influenced the surface modification of nano-CaCO3. These factors were studied through orthogonal experiments to find optimized conditions to prepare material suitable for modifying nanoCaCO3 dispersed in water. 3) The modified nano-CaCO3 was obtained directly by filtration which not only avoided agglomeration of nanometer granules but also makes it easy to disperse the powder when it is time to use it. 4) TEM and particle size analysis show that the granule-size distribution of modified nano-CaCO3 is uniform with an average granule diameter of 105.8 nm. The infrared spectra and thermal analysis show that chemical sorption and physical sorption occurr between nano-CaCO3 and the modifier. 5) Compared with traditional architectural coatings without nano-CaCO3, the nano-CaCO3 composite coatings are greatly improved in dirt resistance, scrub resistance, water resistance, alkalinity resistance and aging resistance; the scrub resistance was improved by 75600 times.
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