Cationic Starch Preflocculated Filler for Improvement in Filler

Jun 27, 2014 - Talc filler preflocculated using 0.1−0.8% dosages of cooked cationic starch based on the dry weight of filler was loaded in paper to ...
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Cationic Starch Preflocculated Filler for Improvement in Filler Bondability and Composite Tensile Index of Paper Vipul Singh Chauhan and Nishi Kant Bhardwaj* Avantha Centre for Industrial Research & Development, Yamuna Nagar 135 001, India ABSTRACT: Inorganic fillers, the second largest component of the papermaking process, have poor bondability with cellulosic fibers, interfere in interfiber bonding, and reduce paper strength. Filler preflocculation/modification is a practical method for enhancing interactions between the filler particles and fibers. This article reports on the effects of filler content and preflocculation on the filler bondability factor calculated based on first-pass ash retention and paper strength properties such as the tensile, Z-direction tensile, and composite tensile indexes. Talc filler preflocculated using 0.1−0.8% dosages of cooked cationic starch based on the dry weight of filler was loaded in paper to obtain varying filler contents of 15−24%. The filler bondability factor (FBF) and various tensile properties of paper were calculated and analyzed for all experiments. FBF and paper strength were reduced with increasing filler content in paper, whereas they were improved upon addition of preflocculated filler in paper. Noticeably, preflocculated filler resulted in increases in FBF and composite tensile index of 13−24% and 7−15%, respectively, at a 24% filler content in paper.

1. INTRODUCTION Cellulosic fibers and mineral fillers are the first and second largest components, respectively, of the papermaking process. From the papermakers’ point of view, increasing filler content is always desired to make the papermaking process costcompetitive. Increased filler loadings in paper also reduce the energy demand in various stages of the papermaking process and improves the optical and printing properties of paper. However, it has negative impact on the interfiber bonding among different layers of the paper sheet and decreases the paper strength, which is more prominent at high filler addition levels. Moreover, beyond a certain addition level, fillers have other disadvantages such as poor filler retention, decreased sizing efficiency and bending stiffness, increased wire abrasion, and dusting during printing.1,2 These are the key factors limiting the filler loading in paper beyond a critical level. Because of the above-mentioned disadvantages of filler addition to paper sheets, researchers have developed several techniques to overcome or alleviate these disadvantages, one of which is filler modification or preflocculation. It has been reported that the addition of preflocculated filler to paper markedly improves filler retention and paper strength while maintaining the functional properties of paper.3−18 This occurs through the improvement of the interaction between filler particles and cellulosic fibers with the aid of chemical additives.3 Various chemicals have been used by researchers for the preflocculation of filler, such as inorganic compounds, natural and synthetic polymers, surfactants, and emulsions. Cellulosic fibers used for papermaking consist of natural carbohydrate polymers. Some other carbohydrate polymers, such as starch, have been reported to be suitable for the preflocculation of filler. Because it is a polymer of glucose similar to cellulose, starch is commonly used as a dry strength additive for papermaking and increases the interfiber bonding in paper.19−21 Starch is highly effective in filler modification. It can be anchored on filler surfaces to enhance filler bondability with fibers and to improve paper strength. It has been extensively © XXXX American Chemical Society

used for the modification of clay and calcium carbonate fillers.8−17 Yoon and Deng used a high dosage of starch for the modification of clay and claimed a 100−200% increase in the tensile strength of paper.8,9 Zhao et al. reported an improvement in paper strength properties such as tensile, tearing, and folding endurance using a starch-gel-coating method.16 The concept of filler preflocculation using cationic and amphoteric starches for papermaking has been reported elsewhere by the authors.22−24 The role of particle size of filler in the development of various paper properties has also been demonstrated.25,26 As discussed earlier, preflocculated filler improves paper strength by enhancing the filler−fiber bondability, and the quantification of this ability will enhance the understanding of the process. Recently, the concept of filler bondability factor (FBF) was proposed by Huang et al., who used FBF in combination with other parameters to evaluate the impact of the filler modification process conditions and retention systems.3 The present article considers the use of cationic starch for the preflocculation of magnesium silicate (talc) filler at different dosages and loadings of preflocculated filler in paper targeting varying ash levels of 15−24%. The aim was to preflocculate the filler with lower dosages of cationic starch and modify the FBF in terms of various tensile strength properties of paper such as the tensile, Z-direction tensile, and composite tensile indexes at different levels of filler content in paper.

2. MATERIALS AND METHODS 2.1. Materials. Fully bleached mixed hardwood kraft pulp composed of 50% eucalyptus, 35% poplar, and 15% bamboo Received: May 17, 2014 Revised: June 27, 2014 Accepted: June 27, 2014

A

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index (CTI), is proposed. CTI provides the tensile strength of paper in all applicable directions. For the present study, CTI was calculated using the equation

was supplied by an integrated paper mill in North India. The pulp was refined in a PFI mill following TAPPI test method T 248 sp-00 to a freeness level of 430 CSF (Canadian standard freeness) before use. Talc filler having a median particle size of 5.4 μm was obtained from a mineral manufacturer in North India. Cationic starch powder with a 0.02−0.025 degree of substitution was also obtained from a chemical manufacturer in North India. It was dissolved in deionized water to a concentration of 1% (w/v) and cooked at 95 °C for 20 min prior to use for the preflocculation of filler. Cationic polyacrylamide (CPAM) of medium to high molecular weight was obtained from a paper chemical manufacturer in India. The granules of CPAM were mixed with deionized water at ∼40 °C in a beaker and agitated at 300 rpm for about 30 min to prepare a 0.1% (w/v) solution. The anionic charge densities of CPAM and cationic starch as measured on a Mutek particle charge detector (PCD 03 pH) were 1134 and 166 μequiv/g, respectively. The dosages of CPAM in pulp were 200, 200, 240, and 280 g/t to obtain filler contents in paper of 15%, 18%, 21%, and 24%, respectively. The dosage levels were optimized separately by the authors and reported elsewhere.25,26 The purpose of increasing the dosage of CPAM was to obtain comparable first-pass ash retention (FPAR) values at all filler contents in paper. 2.2. Preflocculation of Filler. The procedure for the preflocculation of filler was based on a previously published method.22−24 Talc filler with dry weight of 30 g was taken in a 500 mL beaker, and 270 mL of deionized water was poured into the beaker to make a slurry with a 10% (w/v) filler concentration. It was dispersed at 2000 rpm for 30 min. The speed of the agitator was then decreased to 500 rpm before the addition of freshly cooked cationic starch to the filler slurry, and the resulting mixture was stirred for an additional 5 min. The dosage of cationic starch was varied from 0.1% to 0.8% of the dry weight of filler. 2.3. Preparation of Paper Sheets and Determination of Paper Properties. The refined pulp suspension was diluted to a consistency of 1% (w/v) and stirred at 400 rpm. Both native and preflocculated fillers were added separately to the pulp suspension keeping the stirring speed constant and targeting the desired filler content in paper. After a retention time of 1 min, the pulp suspension was diluted to 0.4% consistency, and the desired volume of CPAM was added. Paper sheets with a target grammage of 60 g/m2 were prepared on TAPPI handsheet former, pressed at 345 kPa pressure for 5 and 2 min, and air-dried in accordance with TAPPI test method T 205 sp-02. The properties of the paper sheets were determined after conditioning at constant temperature (23 ± 1 °C) and relative humidity (50 ± 2%) for 24 h. The apparent density of the paper was calculated from the ratio of the grammage to the thickness of the paper. The latter was measured on an L&W micrometer in accordance with TAPPI test method T 411 om97. The tensile index of the paper sheets was determined on an L&W tensile strength tester in accordance with TAPPI test method T 494 om-01. The Z-direction tensile strength (ZDTS) was determined on an L&W ZD tensile tester in accordance with TAPPI test method T 541 om-99. Close relationships between ZDTS and apparent density28 and between ZDTS and tensile strength29 were reported for paper earlier. Moreover, to consider the combined effects of all three directions in the case of commercial papers and two directions in the case of laboratory sheets, a new parameter, namely, composite tensile

composite tensile index [(N·m/g)2 ] =

tensile strength (N/m) × ZDTS (N/m 2) grammage (g/m 2) × apparent density (g/m 3) (1)

× 1000

Ten readings were recorded for each set, and the average value was determined from the measurement of the properties of three sets. All experiments were carried out in triplicate, and the bars shown in the figures represent the standard deviations on either side of the mean. 2.4. Determination of Filler Content, Retention in Paper, and Filler Bondability Factor. The filler content in paper was determined in a muffle furnace at 525 °C in accordance with TAPPI test method T 211 om-93 using the equation filler content in paper (%) =

oven‐dry weight of filler in paper (g) × 100 oven‐dry weight of handsheet (g)

(2)

The first-pass ash retention (FPAR) was calculated based on the filler content in paper using the equation FPAR (%) =

filler content in paper (%) filler added based on pulp and filler (%) × 100

(3)

The filler bondability factor (FBF) was proposed recently to justify the filler modification process and to use broadly for the papermaking process.3 It could provide a comparative analysis for a given filler loading level and different filler contents in paper when the filler was modified using a chemical additive. However, when compared at different filler additions, retentions, and contents in paper, it cannot provide a reasonable understanding of filler bondability in paper. Efforts have been made to calculate FBF using different approaches on the basis of various tensile strengths of paper and filler retentions in paper (i.e., FPAR). FBF has also been calculated using a composite tensile index to obtain a better understanding of filler bondability among different directions and layers of the paper sheet. During the calculation and analysis of FBF, it was observed that the filler retention, rather than the filler content, in paper provides a more precise FBF. Hence, the equation reported earlier by Huang et al.3 was modified slightly for the calculation of FBF on the basis of a given paper strength (either tensile strength, ZDTS, or composite tensile strength) filler bondability factor strength of filled paper = × FPAR (%) strength of unfilled paper

(4)

3. RESULTS AND DISCUSSION 3.1. Effects of Preflocculated Filler on Filler Retention. The filler retention in paper for a given filler addition level should always be as high as possible to decrease the filler loss, back-water turbidity, pollution load, and papermaking cost and to improve the cleanliness of the system. For a native or B

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nonpreflocculated filler of similar shape, the filler retention is directly proportional to the size of filler.25 The effects of filler addition to pulp and preflocculation of filler using different dosages of cationic starch on the filler content in paper are shown in Figure 1. At the same filler

addition level and increasing dosage of cationic starch for filler preflocculation, the filler content in paper increased slightly, demonstrating the efficacy of cationic starch for increasing filler retention in paper. The highest increase in filler content was observed with preflocculated filler using 0.4% cationic starch. An increased dosage of 0.8% cationic starch for the preflocculation of filler had a negative impact on filler content in paper. Overall, the filler content was increased by about 0.2− 0.9 points at all filler levels. When other variables are constant, the filler retention in paper is governed by the characteristics of the filler, namely, its size, shape, surface area, and colloidal charge. The effects of filler addition and preflocculation on first-pass ash retention (FPAR) is shown in Figure 2. When compared at the same filler addition level, FPAR increased with increasing dosage of cationic starch for the preflocculation of filler. This trend was applicable for all filler addition levels used in the present study.

The average FPAR calculated from the mean values obtained at different filler addition levels of native filler was 56.0%. This increased slightly by 1.1 and 1.8 points, that is, 2.0% and 3.2%, with filler preflocculated using 0.1 and 0.4% cationic starch, respectively. Similarly to the case of filler content, FPAR also decreased marginally upon increasing the dosage of cationic starch to 0.8%. 3.2. Effects of Preflocculated Filler on Paper Strength. Tensile index is the maximum tensile force per unit width per unit grammage of paper sheet tested in either machine or crossmachine direction. Paper made on a machine has machine and cross-machine directions and exhibits anisotropic symmetry. A handsheet made in the laboratory does not contain machine and cross-machine directions and exhibits transversely isotropic symmetry. The fibers essentially lie in the plane of the sheet and provide a layered structure, so that the handsheet exhibits the same properties in all directions that lie in the plane of the sheet. In the case of laboratory handsheets, it is assumed that the machine (x) and cross-machine (y) directions lie in the plane of the sheet and that the third (z) direction corresponds to the thickness of the sheet. Thus, tensile strength in laboratory handsheets is basically considered as the combined tensile strength in x−y directions (for correlation with machinemade paper sheets).27 The tensile strength in the thickness direction is determined by the Z-direction tensile strength (ZDTS). It is generally defined as the force required to produce a unit area fracture perpendicular to the plane of the paper sheet and provides an idea of the internal bond strength (cohesive strength) out of the plane of the sheet.27 For the analysis of the combined effects of tensile strength in and out of the plane of the laboratory sheet, a new parameter, composite tensile index (CTI), is proposed. The following section describes the effects of filler content and preflocculation on various properties of paper. 3.2.1. Tensile Index. Our previous study showed that the granules of cationic starch are effectively encapsulated on the surface of filler particles. Compared to native filler, preflocculated filler particles are more firmly adhered to the fiber surface and increase the fiber−filler−fiber bonding in paper.23,24 The effects of preflocculated filler on the tensile index of paper at different filler contents are shown in Figure 3. An increase in the filler content in paper reduced the tensile index of the paper. This was applicable for all filler contents. The tensile

Figure 2. Effects of filler dosage on the first-pass ash retention (FPAR) in paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch (CS).

Figure 3. Effects of filler content in paper on the tensile index of paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch (CS).

Figure 1. Effects of filler dosage on the filler content in paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch (CS).

C

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index of paper made from native filler was reduced from 34.4 to 26.9 N·m/g when the filler content in the paper was increased from 15% to 24%. At same filler content level of 15%, the tensile index was surprisingly increased to 35.0, 35.9, and 36.9 N·m/g upon addition of filler preflocculated using 0.1%, 0.4%, and 0.8% dosages of cationic starch; that is, an increase in tensile index of about 7% was obtained. Similarly, at filler contents of 18%, 21%, and 24%, the increase in tensile index was about 8−12%. These results demonstrate that preflocculated filler improves the bonding capacity of the filler with fiber, resulting in an improvement in tensile index, and indicate the possibility of achieving similar tensile index values for paper using higher amounts of preflocculated filler compared to native filler.23 3.2.2. Z-Direction Tensile Strength. The effects of filler content and preflocculated filler on ZDTS of paper are shown in Figure 4. Similarly to tensile index, ZDTS also decreased

introduced. CTI is based on the tensile strength of paper in all applicable directions. It is calculated by multiplying the tensile strength and ZDTS and dividing by the apparent sheet density, considering that the latter has an impact on interfiber bonding in the fibrous sheets, and further dividing by the grammage of the paper sheets to obtain an index value (please see eq 1 in Materials and Methods). The effects of content and preflocculation of filler on CTI are shown in Figure 5. Similarly

Figure 5. Effects of filler content in paper on the calculated composite tensile index of paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch (CS).

to the previously discussed tensile strength, CTI also decreased with increasing filler content and increased upon addition of preflocculated filler. It increased upon preflocculation to 7%, 9%, 12%, and 15% at filler contents of 15%, 18%, 21%, and 24%, respectively. These results clearly showed that the impact of filler preflocculation was greater at higher filler loading levels, at which the native filler particles had more impaired interfiber bonding in the paper sheet. The present study shows that cationic-starch-preflocculated filler improves the tensile strength of a paper sheet in all directions. 3.2.4. Tensile versus Tear, ZDTS, and CTI Relationships. The effects of filler preflocculation on the tensile−tear relationship at different filler contents in paper are shown in Figure 6. It was observed that, with increasing filler content in

Figure 4. Effects of filler content in paper on the Z-direction tensile strength (ZDTS) of paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch (CS).

with increasing filler content in paper, whereas it increased upon addition of preflocculated filler. The ZDTS values of sheets with native filler at 15%, 18%, 21%, and 24% filler contents were 592, 574, 528, and 502 kPa, respectively. The corresponding ZDTS values obtained with filler preflocculated using 0.8% cationic starch increased to 620, 608, 571, and 547 kPa; that is, 5−9% increases in ZDTS were obtained by loading preflocculated filler in paper. The increases in ZDTS represent improved interfiber and filler−fiber bonding along the thickness direction of the paper. The sheets containing preflocculated filler exhibited higher increases in both tensile index and ZDTS at high filler contents in paper, whereas in the case of native filler, the greater number of filler particles impaired the filler− fiber bonding and had the most negative impact on paper strength. As the amount of starch in the filler increased, the specific bond strength between the fibers and filler increased.8 Similar results on the effects of preflocculated filler on tensile index and ZDTS of paper were reported elsewhere by the authors.23,24 3.2.3. Composite Tensile Index. A close relationship between ZDTS and apparent density of paper sheets was suggested by Koubaa and Koran for hardwood and softwood fibers.28 Similarly, a relationship between ZDTS and the tensile strength of paper was reported by Singh.29 Efforts have been made to verify the two relationships by only one equation, and hence, the new term composite tensile index (CTI) has been

Figure 6. Effects of filler content in paper on the tensile index vs tear index relationship for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch (CS). D

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papermakers in optimizing process variables based on mathematical reasoning. 3.2.5. Effects of Cationic Starch as a Dry Strength Additive and as a Talc Preflocculating Chemical. The effects of cationic starch both as a dry strength additive (i.e., when added to pulp) and as a talc preflocculating agent (i.e., when added to filler) on paper strength were reported elsewhere by the authors.23 For this experiment, the constant dose of talc added to the pulp was 61%. When an equivalent dose of cationic starch (0.5% on pulp), on the basis of 0.8% on talc (used for talc preflocculation), was added to the pulp, it had an impact on the paper properties. As a dry strength additive, the cationic starch was added to the pulp prior to the addition of native talc; a similar dose of about 0.5% based on pulp was added. A more positive effect of starch on paper strength was observed when the starch was used for talc preflocculation than when it was added to the pulp directly. The tensile index and ZDTS were higher even at higher ash content when the starch was added to the talc compared to when it was added to the pulp. 3.3. Effects of Preflocculated Filler on Filler Bondability Factor. The filler bondability factor (FBF) based on the tensile strength of paper was recently introduced.3 It was proposed that, for a given filler addition level, the tensile strength of the filled paper might be indicative of filler bondability, so FBF is calculated based on filler addition and tensile strength. However, the number of filler particles retained in a fibrous matrix will also have an impact on the filler bondability in paper. In this context, FBF is calculated based on the filler retention in paper at varying filler addition levels and dosages of preflocculating chemical (i.e., cationic starch) using various tensile strengths as the measuring parameter for bondability. The amounts of filler addition and filler retention are both important variables for the point of interaction of the preflocculating chemical with filler and the impacts on filler bondability in paper and paper strength. For a given filler, FBF decreases with increasing filler loading in the paper because of the greater number of filler particles in the paper sheet, which will decrease the interaction among fibers. A similar trend was observed when FBF was calculated using the tensile index of paper at different filler contents and dosages of cationic starch (Figure 8). It was observed that FBF has a linear relationship with the dosage of cationic starch used

the paper, the tensile−tear relationship was reduced. However, when preflocculated filler, rather than native filler, was used, the relation shifted toward a higher tensile index, and the tear index increased marginally. This trend was observed at all filler contents in paper. The slope of the linear trend line (not shown in the figure) for the tensile versus tear index relationship for paper having native and preflocculated filler was slightly decreased on increasing the filler content in paper indicating that the effects of filler preflocculation on tear index of paper was slightly reduced on increasing the filler content in paper. Moreover, when the trend of tensile versus tear index relationship at different filler contents was compared, it was observed that the lowest slope (not shown in the figure) was in case of native filler, and the slope was increased on increasing the dosage of cationic starch for filler preflocculation. This showed that the relationship between tensile and tear index could be improved by using preflocculated filler. Likewise, the more positive impact of filler prflocculation on this relationship was at higher filler content in paper when the impairment of interfiber bonding using native filler is the most among all studied filler content levels (Table 1). The improved tensile− tear relationship obtained using preflocculated filler would be helpful in improving machine runnability during commercial papermaking. Table 1. Effects of Filler Preflocculation on the Tensile and Tear Indexes of Paper at Different Filler Contents in Paper tensile index (N·m/g)

tear index (mN·m2/g)

filler content in paper (%)

native filler

filler preflocculated using CS (0.8%)

native filler

filler preflocculated using CS (0.8%)

15 18 21 24

35.2 30.2 28.1 26.9

37.1 32.4 30.2 29.9

4.59 3.94 3.71 3.47

4.64 4.03 3.76 3.50

To analyze the relationships of tensile index with ZDTS and CTI, scattered lines are plotted in Figure 7. The relationship between tensile index and CTI was linear (regression coefficient, R2 = 0.98), whereas that between tensile index and ZDTS is a second-order polynomial with R2 = 1.00. Both curves showed very good relationships among the three tensile properties of paper. These relationships will be useful in providing the basis for further studies and will support

Figure 8. Effects of filler content in paper on the filler bondability factor (FBF) based on the tensile index of paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch.

Figure 7. Relationships of tensile strength with Z-direction tensile strength and composite tensile index of paper for native filler. E

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for the preflocculation of filler (R2 = 0.89−0.93). For same type of filler, the highest FBF was obtained at the lowest filler content of 15%, and FBF then decreased with increasing filler content. This was due to the interaction of a greater number of filler particles with fibers, which impaired the bondability in paper. This finding was applicable not only for native filler but also for filler preflocculated using various dosages of cationic starch. The increase in FBF with filler preflocculated using a 0.8% dosage of cationic starch was about 8−14% at various filler content levels. A higher increase in filler bondability was obtained with a higher dosage of cationic starch. For native filler, the decrease in FBF on increasing the filler content from 15% to 24% was about 21%, which was reduced slightly to 18% with the increased bondability due to filler preflocculation using 0.8% cationic starch. An increase in FBF of about 130% was reported elsewhere using calcium carbonate filler modified with a starch dosage of 20%.3 For sheets prepared in the laboratory, the resultant tensile strength of paper in the plane of the sheet (x and y directions) is given by tensile index values. ZDTS represents the out-ofplane tensile strength in the third (z or thickness) direction. To obtain a better understanding of filler bondability in the thickness direction of paper, FBF was calculated using the ZDTS results for unfilled and filled sheets at different filler addition levels. FBF calculated based on ZDTS exhibited a trend at different filler contents similar to that of FBF based on tensile index (Figure 9); that is, it decreased with increasing

Figure 10. Effects of filler content in paper on the filler bondability factor (FBF) based on the composite tensile index of paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch.

to that of tensile index, but in this case, the R2 value decreased with increasing filler content in paper. This trend was not observed for FBF calculated based on the tensile index of paper. FBF calculated based on CTI presents a comparatively better understanding of filler bondability due to the impact of the composite tensile strength of paper in all directions. The increases in FBF using preflocculated filler at 15%, 18%, 21%, and 24% filler contents were 13%, 14%, 18%, and 24%, respectively, showing that the preflocculating chemical is more effective for filler bondability at higher filler addition levels. The decrease in FBF with increasing filler content from 15% to 24% for native filler was about 35%, which was reduced marginally to 29% with filler preflocculated using 0.8% cationic starch. This result also shows that filler preflocculated using cationic starch helps in retaining paper strength even at high filler contents in paper.

4. CONCLUSIONS The concept of filler bondability based on various tensile strengths of paper, namely, tensile index, Z-direction tensile strength, and composite tensile index, was investigated for native and preflocculated talc filler at different filler contents of 15−24%. Fillers preflocculated using cationic starch dosages of 0.4−0.8% based on the dry weight of filler were found to be suitable for increasing filler retention, paper strength, and filler bondability in paper. The composite tensile index of paper provides a better understanding as compared with other paper strengths. Preflocculated filler resulted in an increase in filler bondability factor calculated based on composite tensile index from 13% to 24% at 15% and 24% filler contents, respectively, demonstrating that the preflocculating chemical is more effective for filler bondability at higher filler addition levels. These results would be useful for papermakers who want to increase the filler content in paper while maintaining the paper strength.

Figure 9. Effects of filler content in paper on the filler bondability factor (FBF) based on the Z-direction tensile strength (ZDTS) of paper for native and preflocculated fillers using 0.1%, 0.4%, and 0.8% dosages of cationic starch.

filler content in paper. In this case, the relationship between FBF and dosage of cationic starch was not linear; rather, it was polynomial (R2 = 0.81−0.98), which was correlated with the relationship of tensile index versus ZDTS (Figure 7). In this case too, a higher increase in filler bondability was obtained with a higher dosage of cationic starch; it was about 7−14%. When the filler content was increased from 15% to 24%, the decrease in FBF for native filler was about 15%, which was reduced slightly to 11% with filler preflocculated using 0.8% cationic starch. The effects of the dosage of cationic starch on FBF calculated based on CTI (i.e., the composite tensile index of paper in and out of the plane of the sheets) at different filler contents in paper are shown in Figure 10. The trend was linear, comparable

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. F

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of cellulose fibers toward high filler technology in papermaking. Ind. Eng. Chem. Res. 2006, 45 (22), 7374−7379. (20) Gaiolas, C.; Mendes, P.; Silva, M. S.; Costa, A. P.; Belgacem, M. N. The role of cationic starch in carbonate-filled papers. Appita J. 2005, 58 (4), 282−287. (21) Mendes, P. M.; Sansana, P.; Silvy, J.; Costa, C. A. V.; Belgacem, M. N. Cationic starch as a dry strength additive for bleached kraft pulps from eucalyptus globules. Appita J. 2001, 54 (3), 281−284. (22) Chauhan, V. S.; Bhardwaj, N. K. Effect of particle size and preflocculation of talc filler on sizing characteristics of paper. Appita J. 2013, 66 (1), 66−72. (23) Chauhan, V. S.; Bhardwaj, N. K. Preflocculated talc using cationic starch for improvement in paper properties. Appita J. 2013, 66 (3), 220−228. (24) Chauhan, V. S.; Bhardwaj, N. K. Enhancing paper properties by preflocculation of talc using amphoteric starch. Nordic Pulp Pap. Res. J. 2013, 28 (2), 248−256. (25) 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. 2013, 91 (5), 855−861. (26) Chauhan, V. S.; Bhardwaj, N. K. Effect of particle size of talc filler on structural and optical properties of paper. Lignocellulose 2012, 1 (3), 241−259. (27) Perkins, R. W., Jr. Models for describing the elastic, viscoelastic, and inelastic mechanical behavior of paper and board. In Handbook of Physical Testing of Paper, 2nd ed.; Mark, R. E.; Habeger, C. C.; Borch, J.; Lyne, M. B., Eds.; Marcel Dekker Inc., New York, 2001; Vol. 1; pp 1−75. (28) Koubba, A.; Koran, Z. Measure of the internal bond strength of paper/board. Tappi J. 1995, 78 (3), 103−111. (29) Singh, S. P. Relationship of z-tensile strength with in-plane strength properties of paper. Indian J. Chem. Technol. 2007, 14 (5), 317−320.

ACKNOWLEDGMENTS The authors are thankful to Director, Avantha Centre for Industrial Research & Development, Yamuna Nagar, India, for providing the facilities to complete the research. The supply of pulp, mineral filler, and other chemicals from various suppliers is also gratefully acknowledged. V.S.C. also acknowledges the support and guidance received from Dr. S. K. Chakrabarti during experimental work.

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dx.doi.org/10.1021/ie502008d | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX