Investigation on a Novel Fly Ash Based Calcium ... - ACS Publications

Nov 27, 2012 - Limerick Pulp and Paper Center, University of New Brunswick, Fredericton E3B ... develop new filler or new filler loading technology in...
0 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/IECR

Investigation on a Novel Fly Ash Based Calcium Silicate Filler: Effect of Particle Size on Paper Properties Shunxi Song,*,†,‡ Meiyun Zhang,*,† Zhibin He,‡ Jack Zhe Li,‡,§ and Yonghao Ni‡ †

Shaanxi Province Key Laboratory of Papermaking Technology and Specialty Paper, College of Light Industry and Energy, Shaanxi University of Science & Technology, Xi’an 710021, China ‡ Limerick Pulp and Paper Center, University of New Brunswick, Fredericton E3B 5A3, Canada § Queen’s University, Kingston, Ontario, K7L 3N6, Canada ABSTRACT: Value-added utilization of fly ash has recently gained a strong interest. As a solid waste, fly ash can be used as a paper filler, and the recent innovation on the production of high-brightness fly ash products further facilitated such applications. This work reports the results on using the novel fly ash based fillers in the paper making process, with a focus on the effect of filler particle size. In comparison with ground calcium carbonate (GCC) commonly used as paper fillers, the original fly ash based calcium silicate filler (FACS) has a larger particle size (27.6 μm), a much lower true density (1.3−1.4 g/cm3), a higher specific surface area (121 m2/g), and a similar brightness (91% ISO). FACS exhibits porous, aggregated, and needle-like morphologies based on the results of scanning electron microscope image analysis. Ball milling decreased the particle size, broadened the particle size distribution, and improved the brightness while changing its morphology. The paper bulk increased dramatically when the original FACS was used due to its large particle size and narrow particle size distribution. With ball milling, the paper bulk and porosity decreased with decreasing particle size at the same filler content, while the tensile index increased. In addition, the ball milled FACS-filled paper had better light scattering coefficient and brightness than the GCC-filled paper.

■

INTRODUCTION Mineral fillers, including clay, precipitated calcium carbonate (PCC), and ground calcium carbonate (GCC), are widely used in the papermaking industry as part of paper products.1,2 Substituting some cellulosic pulp fiber with mineral filler is one of the most economical and effective ways to reduce the cost of paper products because inorganic fillers are usually cheaper than pulp fibers.3,4 Additionally, filler enhances some key paper properties, such as bulk, brightness, opacity, smoothness, and printability. However, the use of fillers weakens paper strength due to decreased interfiber hydrogen bonding. The filler average particle size (APS) and particle size distribution (PSD), specific surface area (SSA), morphology, and brightness play an important role in paper properties.5−8 In general, common fillers, such as GCC, have small average particle size, low specific surface area, high brightness, and high density. These characteristics provide some benefits to paper quality. For example, the low APS and the narrow PSD help to improve the light scattering coefficient. Additionally, low specific surface area (SSA) is good for sizing.9 The detrimental effects of particle size on tensile strength are more pronounced at smaller particle size.8,10,11 Due to the requirements of new functions and low cost for paper products, the development of filler engineering becomes an urgent need for the papermaking industry, especially for the new filler with low cost, new functions, and environmental friendliness.12 In recent years, many efforts have been made to develop new filler or new filler loading technology in order to improve the quality of paper production and/or to reduce the production cost. Work done by Zhao et al.13 showed that an innovative starchcoated filler technology can allow at least 5−10% filler content © 2012 American Chemical Society

for lightweight and board grades, and the technology made it possible to use inorganic fillers without negatively affecting paper strength. Similarly, Yoon and Deng14 showed that starch−clay composites can provide a high filler content while preserving tensile strength. Some solid wastes can also be used as potential papermaking fillers. An example is fly ash which is produced from coal-fired power (thermal power) plants. The brightness of fly ash is normally low. Its colors can be ranged from gray to black. Fly ash contains 35−70% SiO2, 15−30% Al2O3, 1−10% CaO, 5− 10% Fe2O3, 1−2% TiO2,15 and small amounts of other oxides such as MgO, Na2O, SO3, P2O5, etc. Its composition depends on the type of coal used and the process of burning. There are more than 1400 coal-fired power plants in China. Official statistics16 showed that in 2010 about 480 million tons of fly ash were generated and the reuse rate of the fly ash was approximately 68%. A large amount of fly ash is deposited by landfills near power plants, which can result in undesired environmental consequences. Therefore, the utilization of fly ash with added value has become a key focus. Currently, fly ash may be used as construction materials, road pavement, agriculture, and sorbent.17 Scientific publications about using fly ash as a paper filler are limited in the literature. Work done by Sinha15 suggested that paper loaded with fly ash with a mean particle size of 19 μm yielded higher printing opacity and tear index, with other properties, such as burst index, tensile index, and smoothness, Received: Revised: Accepted: Published: 16377

October 21, 2012 November 25, 2012 November 27, 2012 November 27, 2012 dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384

Industrial & Engineering Chemistry Research

Article

almost unaffected, in comparison with those of fly ash and kaolin-clay as fillers; however, the brightness of fly-ash-filled paper was significantly lower than that of GCC. The results by Fan and Qian18 indicated that, when fly ash was purified by screening and flotation and subsequently used together with calcium carbonate, the brightness of the filler and filled handsheet can be improved; however, it was still lower than the usual fillers, such as GCC and clay. The low brightness of fly ash is still the main barrier for use as a paper filler. An industrial scale novel calcium silicate was found with high brightness and high light scattering coefficient that was produced from fly ash,19 which was referred to as fly ash based calcium silicate (FACS). The filler was a byproduct of fly ash while the aluminum oxide extraction had been processed. As shown in Scheme 1, in order to extract aluminum oxide in

paper properties was investigated. The results were compared with those of using GCC as the filler.

■

MATERIALS AND METHODS Materials. The pulp fibers used for handsheets in this study were a blend of 25% commercially bleached softwood kraft pulp and 75% bleached hardwood kraft pulp. The softwood pulp and hardwood pulp were refined to 450−500 mL, respectively, using a PFI mill according to TAPPI test method T 248 sp-00. The freeness of the pulp was measured on a Canadian Standard Freeness (CSF) tester following TAPPI test method T 227 om-09. The original FACS filler was supplied by a coal-fired power (thermal power) plant in China and is mainly composed of calcium silicate. The GCC filler was supplied by a paper mill in Shandong province of China. High molecular weight cationic polyacrylamide (CPAM) Percol 182 was provided by Ciba. Methods. Filler Characterization. The particle size and size distribution of filler were measured using a Malvern Mastersizer 2000 particle size analyzer. The brightness of the fillers was tested following T 534 pm-92. The sediment volume and pH of the filler were tested according to the national standard of China of GB/T 19281-2003 and HG/T 23769-2009. Filler specific surface area was determined using the BET method and nitrogen adsorption. The surface morphology of the samples was characterized with a JEOL JSM-6400 scanning electron microscope. The cross sections of the paper sample were characterized with back scattering images (BEI). Samples were carbon coated using an Edwards E306A evaporative golden coater, and analysis conditions used an accelerating voltage of 15 kV. Decreasing Particle Size of Filler. A planetary ball mill PM 100 was used to decrease the filler particle size, and the filler was put into a 250 mL stainless steel vessel. The final average particle size and particle size distribution can be controlled by grinding speed, time, and the number of balls. Approximately 20 g of original FACS was charged to the 250 mL stainless steel vessel with stainless steel balls. The ball milling parameters were shown in Table 1.

Scheme 1. Overview of the FACS Production Process

Table 1. The Parameters for FACS Ball Milling

fly ash, sodium hydroxide was used to react with fly ash and transferred aluminum oxide into its sodium salt. At the same time, silicon oxide also existed as the form of sodium silicate which was then converted to calcium silicate with the addition of calcium hydroxide. Sodium hydroxide was regenerated and recycled to the system. As a byproduct of fly ash, its low production cost and environmental friendliness can enhance its potential for commercialization. Silicate-based fillers are known in the paper industry.20−22 Alderfer and Crawford20 reported a synthetic silica filler that was amorphous and had high brightness (98% ISO). Mathur21 prepared a fibrous calcium silicate hydrate- based filler, which showed better strength and optical properties than common fillers. Amorphous silicate fillers can serve as partial or complete replacements for titanium oxides.22 However, these silicate fillers are more expensive than the common fillers, because they were prepared from sodium silicate or silica-based ore. As mentioned above, the coal-based power generator fly ash contains a great deal of silica which can be used to prepare calcium silicate, as shown in Scheme 1, and the FACS is very cost-effective. In this study, the potential of this novel FACS as a paper filler was evaluated and the effect of particle size on

sample ID

grinding speed (rpm)

grinding time (h)

FACS1 FACS2

100 200

12 2

FACS3

350

2

ball descriptions 2 large balls (Ø20 mm) 10 small balls (Ø10 mm) 10 small balls (Ø10 mm)

Handsheet Preparation and Testing. Similar procedures as reported in the literature23 were followed. The mixed pulp was disintegrated at a consistency of 1.2% and diluted with water to a consistency of 0.3%. Filler slurries were prepared at 10% solid content and subsequently added to pulp slurries. Fillers were added to the fiber furnish at 20, 30, and 40 wt % ratios based on the oven-dried pulp amount. The retention aid (CPAM) was added into fiber furnish at a dosage of 0.05 wt % based on the oven-dried pulp amount. The paper handsheets were made with 60 g/m2 (air-dried) on the laboratory sheet former with different weight percentages of filler. The wet papers were pressed according to TAPPI test method T 205 sp-95 and then air-dried at 25.0 °C and 50% relative humidity for 24 h. The 16378

dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384

Industrial & Engineering Chemistry Research

Article

Table 2. Characteristics of FACS0 and GCC

a

filler

APS (μm)

PSDa

true density (g/cm3)

bulk density (g/cm3)

SSA (m2/g)

brightness (% ISO)

pH

FACS0 GCC

27.6 4.4

1.36 4.30

1.3 2.6−2.9

0.3 1.1

121 2.44

91.5 92.4

9.7 9.2

PSD = (d90 − d10)/d50: the narrower the distribution, the smaller the PSD.

Figure 1. Scanning electron micrographs of filler: GCC (A), original FACS (B, C), FACS 1(D), FACS 2(E), and FACS 3(F).

common filler is in the range 2−15 m2/g. A higher specific surface area is conducive to a higher light scattering coefficient but disrupts interfiber bonding and increases the amount of sizing agent required.21 The brightness of FACS0 is similar to GCC, and so is the pH. It is noted that the FCAS0 has a much higher brightness than that of the usual fly ash (below 30% ISO),15,18 which has an advantage when it is used in the production of high-quality paper. Generally, particle morphology can be divided into two types: discrete and aggregated.22 The morphologies of FACS0 and GCC fillers are shown in Figure 1A−C. GCC, used in this study, exhibits discrete morphology and is blocky in nature. However, there are two types of FACS fillers: (1) needle-like and (2) aggregated particles with a wrinkly porous surface. Air voids always exist in aggregated fillers. Some paper properties can be affected by the air voids, such as opacity and bulk.22 The wrinkly porous surface is responsible for the high specific area. Effect of Ball Milling on Filler Properties. Fillers with large particle size may have a negative effect on the resulting paper properties, including poor smoothness and printability. As noted in Table 2, the original FACS (FACS0) has a larger particle size than GCC. Therefore, we made further effort in decreasing the particle size of FACS by using a ball mill. The APS, PSD, and brightness of milled FACS fillers are shown in Table 3. There was a small increase in the brightness of the FACS filler with decreasing filler particle until the APS was 8.4 μm. However, a further decrease in the APS from 8.4 to 6.5 μm may have occurred due to the metal contamination and/or thermal-induced brightness loss during ball milling.

porosity was measured according to TAPPI test Method T 460 om-96. Other physical properties of handsheets were tested in accordance with TAPPI test Method T220. The filler content was analyzed according to TAPPI test Method T211 om-93.

■

RESULTS AND DISCUSSION Filler Characterization. The characteristics of original FACS (i.e., FACS0) are listed in Table 2; included in the table are also those from GCC, which was used for comparison. FACS0 has a larger particle size (27.6 vs 4.4 μm) and narrower PSD (1.36 vs 4.3) than GCC. The filler PSD has an impact on the physical properties of the resulting paper. A narrow PSD helps to improve optical properties, while a broad PSD has a less negative effect on paper strength due to the fact that particles will pack more tightly.24 Generally, the true density of common fillers, such as PCC, GCC, clay, and talc, is approximately 2.6−2.9 g/cm3. As shown, FACS has a true density of 1.3 g/cm3. For the same filler content and particle size, a higher density helps to increase filler content because the number of particles in the higher density filler is less than the lower density filler. This implies that the interfiber bonding will be affected to a lesser extent if a higher density filler is used. The bulk density depends on filler morphology, APS, and PSD. Fillers with larger particles and narrower PSD usually have lower bulk densities, which is the case for FACS0; on the other hand, the larger filler particles (lower bulk density) can improve the paper bulk and light scattering coefficient. Another important difference of FACS filler from GCC is its specific surface area. Typically, the specific surface area of 16379

dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384

Industrial & Engineering Chemistry Research

Article

in Figure 4, adding FACS fillers helped to improve paper bulk as compared to GCC-filled paper. The bulk of FACS-filled papers was increased as the filler content increased. The bulk of FACS0-filled paper was 1.97 g/cm3 when the filler content was around 15.5% ,which was increased by 41% as compared to the control (without filler, 1.39 g/cm3). In contrast, the bulk of GCC-filled paper was similar to that of the control. Additionally, the bulk of paper filled with FACS decreased as the APS decreased, which supports the conclusion that, for a given filler, paper bulk mainly depends on the particle size of the filler.25 It is well-known that, for a given filler, the particle shape, PSD, and APS can be the determining factors for paper bulk when filler is added to the sheet, while the particle size dominates paper bulk properties at a given particle density.24 The large particles are able to open larger interfiber spaces within the paper,26 which contributes to the improved paper bulk. Additionally, aggregated structure and narrow PSD help to improve paper bulk because they can bring more air voids to the finished sheet as compared to fillers exhibiting discrete morphologies.22 A lower bulk density filler always means more air voids are present in the particles. The aggregated particles, low bulk density, and narrow PSD fillers of the FACS0 are partly responsible for the highest bulk in Figure 4. Ball milling reduced the particle size of FACS filler by breaking the surface morphology, resulting in a broad PSD. That is why the paper bulk decreased along with APS of ball milled samples. The bulk of paper filled with GCC was only slightly changed with the filler content increase due to its very small particle size, and its broad PSD; similar results were reported in the literature.24,26 Paper porosity has a great effect on paper printability, and it affects how thoroughly and quickly inks are absorbed into the paper. The porosity can be measured by either the time required for a given amount of air to pass through a paper sample or the rate of air passage through a sample. Besides pulp furnish and pulp refining conditions, fillers can also have an

Table 3. APS, PSD, and Brightness of Milled FACS Fillers filler ID

FACS 0

FACS 1

FACS 2

FACS 3

average particle size (μm) PSD brightness (% ISO)

27.6 1.36 91.5

12.9 2.11 92.7

8.4 2.35 93.1

6.5 3.48 91.8

The morphologies of FACS filler were also changed during ball milling, as shown in Figure 1D−F. With increasing ball mill intensity (from D to F), the changes in the morphology of FACS included (1) damage to porous structure, (2) large particle breakage, and (3) fragmentation. Consequently, the PSD became broadened. The smallest APS of ball milled FACS filler was around 6.5 μm, and it was difficult to decrease the particle size further because the surface area of FACS was increased as the particle size was so high that it would lead to particle aggregation into larger ones during the dry grinding process. Filler Distribution in Handsheets. The changes in the thickness of paper filled with different types of fillers can be observed from Figure 2. Compared to the control (without filler, Figure 3A), paper with fillers became less dense. It is rather evident that FACS0 has opened the gaps between fibers. The thickness of FACS-filled paper decreased as the particle size decreased, as shown in Figure 2. On the basis of the results in Figure 3, fillers with smaller particle size were more likely to be adsorbed and packed onto the pulp fibers. Moreover, the differences in particle size of FACS and GCC were readily seen. Effect of Particle Size on Paper Properties. Bulk and Porosity. Bulk is one of the most important properties in printing grade paper. Some paper grades, such as copy paper, have fixed dimensions of length, width, and thickness. The cost of paper production will decrease if paper bulk increases because it allows the papermaker to reduce the amount of fiber material in the sheet to maintain a constant thickness. As shown

Figure 2. Scanning electron micrographs of the cross section of handsheets: (A) without filler, (B) with GCC, (C) with FACS 0, (D) with FACS1, (E) with FACS2, and (F) with FACS3. 16380

dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384

Industrial & Engineering Chemistry Research

Article

Figure 3. Scanning electron micrographs of paper handsheets with 40% filler addition: (A) without filler, (B) with GCC, (C) with FACS 0, (D) with FACS 1, (E) with FACS 2, and (F) with FACS 3.

Figure 4. Effect of filler content on the bulk of handsheets. Figure 5. Effect of filler content on the porosity of handsheets.

effect on paper porosity. Paper porosity increases as the APS increases.24 Fillers with broader PSD can decrease the paper porosity because sizes of fillers can fill up the pores with different dimensions. Figure 5 illustrates porosity as a function of filler content in paper. FACS0-filled paper had the highest porosity which may result in higher ink absorbency and increased the risk of show-through and/or strike-through in some processes.24 However, paper with low porosity increases ink holdout and there is an increased risk of smudging in procedures such as folding. The decreased particle size of FACS filler with a broadened PSD caused the decrease in the porosity of FACS-filled paper. The porosity of FACS3-filled paper was lower than that of GCC-filled paper, although FACS3 had a larger APS than GCC, which was due to the fact that FACS3 had a lower density of FACS: a lower density filler had more particles at the same filler content which helped to fill up the pores between the fibers. Strength Properties. Improving paper printability and reducing paper production costs are the two main purposes of filler addition. However, paper strength is compromised by filler addition. As shown in Figure 6A, tensile indices by loading

with different fillers were decreased as the filler content was increased. The highest tensile index was achieved by the GCCfilled paper. The tensile index of filler loaded paper in decreasing order was GCC > FACS3 > FACS0 > FACS2 > FACS1. For ball milled fillers (FACS1, FACS2, and FACS3), the tensile index increased as the APS decreased when the comparison was made at the same filler content. There are two widely accepted reasons for explaining the detrimental effects of filler addition on paper properties:27 (1) the use of fillers in paper reduces the amount of fiber at a given grammage and28 (2) common inorganic fillers produce fiber− air−filler interfaces, which results in decreased hydrogen bonds. Hydrogen bonds in the fiber network are critical for paper tensile strength. Thus, the tensile index of paper decreases with increased filler content. Filler APS and PSD are two essential factors for determining paper tensile strength. For the same variety of filler, small particle size has more detrimental effects on paper tensile index,26,29 while a broad PSD has a less negative effect due to 16381

dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384

Industrial & Engineering Chemistry Research

Article

negative effect on the fiber bonding. These are the explanations that account for the highest tensile index of GCC-filled paper of all filler-filled papers, as observed in Figure 6A. Fillers can be located either on the free fiber surfaces or in the pores formed by the surrounding fibers without any significant effect on the structure of the fibrous network itself.30 Fillers can also be located at the crossings of adjacent fibers, which can cause debonding and significantly reduce the tensile strength. Small particles are more likely adsorbed on the fiber surface and distributed in the crossings of adjacent fibers, resulting in the paper strength being more likely to be negatively affected. Additionally, for a given mass, a lower APS always means more particles existing in paper, causing more interfiber bonds to be destroyed. Both reasons explain why fillers with smaller particle size have more detrimental effects on tensile strength.8,10,11,26,29 The above is responsible for the fact that the tensile index decreased significantly using FACS1 as fillers, rather than FACS0. It was noted that the tensile index increased as the APS decreased from FACS1 to FACS3, which was different from the previous assertion that “smaller particle size has more detrimental effects on tensile strength”. Ball milling has broadened the PSD of FACS while decreasing the particle size, which improves the packing ability of filler particles and makes particles that are likely filled in the pores surrounding the fibers, thus decreasing the paper porosity and improving the tensile index. The presence of silanol in the FACS fillers may yield additional hydrogen bonds. The main composition of FACS is hydrate calcium silicate. Mathur31 reported that, in addition to conventional hydroxyl bonds, silanol bonds might form when silicate fillers are used. For this reason, hydrated calcium silicate is used as a reinforcement filler in silicone rubber.32 As the particle size decreases, the filler specific surface area will increase; thus, more silanol-originated hydrogen bonds will be formed. FACS3 has the better packing ability and more silanol groups, resulting in the higher tensile index than FACS0-filled paper. As illustrated in Figure 6B, the paper bulk decreased as the tensile strength increased, implying that paper bulk was improved by using filler at the expense of interfiber bonding. It was also observed that the paper bulk increased with FACS particle size increasing at a given tensile strength. It is interesting to note that FACS0-filled paper had a higher bulk while sustaining an acceptable tensile index, as shown in Figure 6A and B. This can be attributed to its special morphology, large APS, and low density. Because GCC-filled paper has a higher tensile index whereas a higher bulk can be obtained from using FACS, blending GCC and FACS may be a compromising choice to achieve good bulk and acceptable tensile index. The effect of filler content on tear strength is shown in Figure 6C, and it can be seen that tear strength was decreased as the filler content increased. Tear strength mainly depends on fiber length and fiber bonding.33 These results can be explained by less fibers being available in the sheets. For the ball milled FACS fillers, smaller particles resulted in lower tear strength. The original FACS (FACS0) maintained good tear index and tensile index. The porous morphology of FACS0 may help to increase the friction between fiber and filler, which may result in the higher tear strength compared to other fillers. GCC particle size was the smallest, but the tear index was not the lowest. Geometry, the surface roughness, and anisotropy also play important roles for the changes of tear strength in addition to particle size when comparing different fillers.34,35

Figure 6. Effect of filler particle size on paper strength properties.

the fact that the particles pack more tightly and fill in the pores between the fibers.24 Additionally, filler density can affect paper tensile index by changing the number of particles for a given mass and APS. GCC had the finest particle size but showed the highest tensile index. Although filler particle size has a significant role, it is not the only determining parameter when comparing different varieties of fillers. GCC has the broadest PSD among the fillers in this study, which helps to reduce the detrimental effect. Additionally, GCC has a high density (2.6− 2.9 g/cm3), which is higher than that of FACS (1.3 g/cm3). At constant particle size and filler content, the filler with high density has a lower number of particles, resulting in a less 16382

dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384

Industrial & Engineering Chemistry Research

Article

FACS fillers, because of similar morphology, APS determines the light scattering ability. Consequently, the light scattering coefficient of the fillers increased as the APS decreased for ball milled FACS.

Optical Properties. It can be seen from Figure 7A that paper brightness increased as the filler content increased. The

■

CONCLUSION

■

AUTHOR INFORMATION

As a byproduct of aluminum extraction from fly ash, FACS has some special properties as compared to conventional fillers, such as GCC. Four grades of FACS fillers with different particle sizes were prepared; their characteristics as paper fillers and the effect on the resulting paper properties were determined. The original filler (FACS0) has the characteristics of high surface area, low density, and high brightness. The porous and aggregated morphology can explain its high surface area. At a 15% FCAS0, the paper bulk was about 40% higher than that of the control (no filler addition). Ball milling changed the morphology and particle size distribution while decreasing the particle size. For ball milled FACS, the paper bulk of FACSfilled paper decreased because the particle size of FACS filler decreased, while the paper tensile strength increased. The latter may be explained by the broadened particle size distribution and the presence of its silanol groups. A larger FCAS particle size led to higher tear strength for the FACS-filled paper. FACS3 with an average particle size of 6.5 um gave a reasonable tensile strength and porosity but with decreased tear index. Regarding the optical properties, FACS filler had a similar brightness to GCC. The brightness of paper filled with ball milled FACS was higher than FACS0 and GCC filler. Although FACS0 had a large particle size, the light scattering coefficient was higher than that of GCC-filled paper. This can be attributed to FACS0's porous surface and aggregated morphology. The light scattering coefficient for ball milled samples increased as the particle size decreased. On the basis of the above results, it was concluded that FCAS is a potential paper filler that can impart paper products with good strength, brightness, and opacity. In addition, adapting the filler blending concept by taking advantages of the morphology/characteristics of different sizes of FACS may be of commercial interest.

Figure 7. Effect of filler particle size on paper optical properties.

brightness of FACS-filled paper was in decreasing order of FACS2 > FACS1 > FACS3 > FACS0. The brightness of the fillers was in decreasing order of FACS2, FACS1, FACS3, and FACS0, and the resulting paper brightness followed the same order. Paper opacity mainly depends on the light scattering coefficient. FACS0-filled paper has higher light scattering coefficient than GCC-filled paper at high filler content, as shown in Figure 7B, which is due to the porous structures of the FACS filler. Furthermore, the light scattering coefficient is increased as the particle size is decreased for ball milled samples. For fillers with discrete morphology, decreasing particle size always improves paper scattering as long as the particle size stays above 0.5 μm.26 More particles can be obtained when the particle size decreases for a given filler content; consequently, more filler−air−fiber interfaces will be produced which can be improved by light scattering. Additionally, the air voids in filler with aggregated morphology help to improve light scattering ability. The porous and aggregated structure of FACS0 yielded high surface area, which helped to increase light scattering ability. For the ball milled samples, the porous and aggregated structure was converted to a discrete morphology, which was detrimental to light scattering ability. On the other hand, ball milling increased the number of particles and decreased the particle size, both of which would have a positive effect on the light scattering ability. The two opposite effects may lead to less change in light scattering coefficient for the FACS1-filled paper in comparison with the FACS0-filled paper. For the ball milled

Corresponding Author

*E-mail: [email protected] (S.S.), [email protected] (M.Z.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We acknowledge the financial support from the National Science Foundation of China (Grant No. 31170560), the Graduate Innovation Fund of Shaanxi University of Science and Technology and NSERC For Value Net. We also thank Sandra Riley and Steven Cogswell for their technical assistance.

■

REFERENCES

(1) Shen, J.; Song, Z.; Qian, X.; Ni, Y. A review on use of fillers in cellulosic paper for functional applications. Ind. Eng. Chem. Res. 2011, 50 (2), 661−666. (2) Shen, J.; Song, Z.; Qian, X.; Ni, Y. Carbohydrate-based fillers and pigments for papermaking: A review. Carbohydr. Polym. 2011, 85 (1), 17−22. 16383

dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384

Industrial & Engineering Chemistry Research

Article

(3) Dong, C.; Song, D.; Patterson, T.; Ragauskas, A.; Deng, Y. Energy saving in papermaking through filler addition. Ind. Eng. Chem. Res. 2008, 47 (21), 8430−8435. (4) Chauhan, V. S.; Sharma, A.; Chakrabarti, S. K.; Varadhan, R. Energy savings through increased filler loading in paper. Ippta J. 2011, 23 (3), 171−176. (5) Brown, R. The effect of particle size and shape of paper fillers on paper properties. Wochenbl. Papierfabr. 1983, 111 (20), 737−740. (6) Gill, R.; Scott, W. The relative effects of different calcium carbonate filler pigments on optical properties. Tappi J. 1987, 70 (1), 93−99. (7) Adams, J. M. Particle size and shape effects in materials science: examples from polymer and paper systems. Clay Miner. 1993, 28 (4), 509−530. (8) Han, Y. R.; Seo, Y. B. Effect of Particle Shape and Size of Calcium Carbonate on Physical Properties of Paper. J. Korea TAPPI. 1997, 29 (1), 7−12. (9) Laufmann, M.; Forsblom, M.; Strutz, M.; Yeakey, S. GCC vs. PCC as the primary filler for uncoated and coated wood-free paper. Tappi J. 2000, 83 (5), 76. (10) Kinoshita, N.; Katsuzawa, H.; Nakano, S.; Muramatsu, H.; Suzuki, J.; Ikumi, Y.; Toyotake, Y. Influence of fibre length and filler particle size on pore structure and mechanical strength of fillercontaining paper. Can. J. Chem. Eng. 2000, 78 (5), 974−982. (11) Chauhan, V. S.; Bhardwaj, N. K.; Chakrabarti, S. K. Effect of particle size of magnesium silicate filler on physical properties of paper. Can. J. Chem. Eng. 2012, 9999, 1−7. (12) Shen, J.; Song, Z.; Qian, X.; Liu, W.; Yang, F. Filler engineering for papermaking: comparision with fiber engineering and some important research topics. Bioresources 2010, 5 (2), 510−513. (13) Zhao, Y.; Kim, D.; White, D.; Deng, Y.; Patterson, T.; Jones, P.; Turner, E.; Ragauskas, A. J. Developing a new paradigm for linerboard fillers. Tappi J. 2008, 7 (3), 3−7. (14) Yoon, S. Y.; Deng, Y. Clay-starch composites and their application in papermaking. J. Appl. Polym. Sci. 2006, 100, 1032−1038. (15) Sinha, A. S. K. Effects of pulverized coal fly-ash addition as a wet-end filler in papermaking. Tappi J. 2008, 7 (9), 3−7. (16) http://www.gov.cn/gzdt/2012-03/02/content_2080933.htm. (17) Ferreira, C.; Ribeiro, A.; Ottosen, L. Possible applications for municipal solid waste fly ash. J. Hazard. Mater. 2003, 96 (2−3), 201− 216. (18) Fan, Y.; Qian, X. Study on using fly ash as a papermaking filler. China Pulp Pap. 2012, 31 (4), 22−26. (19) Zhanju Z.; Junmin S.; Huifang C.; Xiaoyun Z.; Yanwu W.; Qiang Y. Tongfang Co., Ltd. Preparation of calcium silicate powder from fly ash with high aluminum content. Chinese Patent 200810112618.1, May 26, 2008. (20) Alderfer, G.; Crawford, R. High-structure amorphous silica pigments in paper. Pigments for Paper; TAPPI Press: Atlanta, GA, 1997. (21) Mathur, V. K. Multi-phase calcium silicate hydrates, methods for their preparation and improved paper and pigment products produced therewith. International patent WO 01/14274 A1, August 26, 1999. (22) Thorn, I.; Au, C. O. Applications of wet-end paper chemistry, 2nd ed.; Springer: New York, 2009. (23) Zhang, H.; He, Z.; Ni, Y. Characteristics of dissolved and colloidal substances in high yield pulp and their impact on filler retention. Appita J. 2007, 60 (5), 390−395. (24) Velho, J. How mineral fillers influence paper properties: some guidelines. Iberoamerican Congress on Pulp and Paper Research, 2002. (25) Brown, R. Particle size, shape and structure of paper fillers and their effect on paper properties. Pap. Technol. 1998, 39 (2), 44−48. (26) Hubbe, M. A.; Gill, R. A. Filler particle shape vs. paper properties - A review. 2004 TAPPI paper summit - spring technical and international environmental conference, 2004, 141−150. (27) Casey, J. P. Pulp and paper chemistry and chemical technology; Light industry press: Beijing, 1988.

(28) Fatehi, P.; McArthur, T.; Xiao, H. Improving the strength of old corrugated carton pulp (OCC) using a dry strength additive. Appita J. 2010, 63 (5), 364−369. (29) Krogerus, B. Fillers and Pigments. Papermaking Chemistry; Fapet Oy: Helsinki, Finland, 1999. (30) Koivunen, K.; Paulapuro, H. Papermaking potential of novel structured PCC fillers with enhanced refractive index. Tappi J. 2010, 9 (1), 4−14. (31) Mathur; Vijay, K. Novel silicate “fibrous fillers” and their application in paper. TAPPI paper summit - spring technical and international environmental conference, 2004. (32) Peng, X.; Gu, S.; Huang, T.; Wang, S. Reinforcement of hydrated calcium silicate powder to silicone rubber. J. Civ. Archit. Environ. Eng. 2010, 32 (5), 109−113. (33) Liu, H.; Chen, Y.; Zhang, H.; Yuan, Z.; Zou, X.; Zhou, Y.; Ni, Y. Increasing the use of high-yield pulp in coated high-quality wood-free papers: from laboratory demonstration to mill trials. Ind. Eng. Chem. Res. 2012, 51, 4240−4246. (34) Li, L.; Collis, A.; Pelton, R. A new analysis of filler effects on paper strength. J. Pulp Pap. Sci. 2002, 28 (8), 267−73. (35) Kamo, K.; Sampson, W. W. Analysis of the influence of filler loading and grammage on bonding. TAPPI/PIMA PaperCon’ 08 Conf., May 4−7, Dallas, TX, 15.

16384

dx.doi.org/10.1021/ie3028813 | Ind. Eng. Chem. Res. 2012, 51, 16377−16384