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Efficacy of carbohydrate polymers in filler preflocculation for use in papermaking
⁎Corresponding author. Tel.: +91 1732 292703; fax: +91 1732 292748. bhardwaj@avantharesearch.org (Nishi K. Bhardwaj)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Preflocculation of inorganic fillers added to the paper could improve the inter-fiber bonding and enhance paper strength. Selection of a suitable flocculant and flocculating conditions for improved efficacy of the process is highly desired. The flocculating process conditions such as stirring speed, concentration of filler suspension and retention time were optimized through image analysis of the filler flocs when using cationic starch as flocculant. Two carbohydrate polymers, cationic and amphoteric starch, were used at 0.1%, 0.4% and 0.8% doses for the preflocculation of talc filler under optimized conditions. The colloidal charge and particle size distribution of the native and preflocculated fillers were analyzed. The native and preflocculated fillers were added to bleached mixed hardwood kraft pulp for preparing laboratory handsheets of 60 g/m2 targeting varying ash levels of 15–24%. Various paper properties such as tensile, burst, tear indices, light scattering coefficient, Cobb60 and contact angle were analyzed for the native as well as preflocculated fillers. The median particle size of native filler was 6.0 μm which on preflocculation using 0.8% dosage of cationic and amphoteric starch increased to 12.0 μm and 14.8 μm i.e. 100% and 146% increase in particle size, respectively. The preflocculated filler increased the physical and hydrophobic properties of the sheets as compared with the native filler. The increase in tensile index was about 20% when filler was preflocculated using 0.8% dose of amphoteric starch.
Keywords
Talc
Starch
Preflocculation
Paper properties
Filler retention
Papermaking
1 Introduction
For manufacturing of almost all kinds of writing and printing grade papers, inorganic fillers are used to improve the brightness, opacity, dimensional stability, smoothness and printability of paper. By replacing the expensive cellulosic fiber, it reduces the input fiber, papermaking cost and energy associated with the processing of fibrous raw material. Having no intrinsic bonding propensity with the organic fibers, the addition of inorganic filler in paper also has negative aspects to consider such as it decreases the available surface area of fiber per unit mass of paper, prevents inter-fiber bonding and reduces the paper strength.
Filler preflocculation, prior to its addition to the papermaking slurry, has been showing good results for reducing the negative effect of filler loading on paper strength. It leads to significant improvements in filler retention and inter-fiber bonding in paper. The techniques used by researchers involved the use of inorganic compounds, natural and synthetic polymers, surfactants, emulsions, surface nano-structuring and physical modification (Yan et al., 2005; Zhao et al., 2005; Yoon and Deng, 2006, 2007; Ibrahim et al., 2009; Shen et al., 2009; Song et al., 2009; Fan et al., 2012; Sang et al., 2012; Chauhan and Bhardwaj, 2013a,b, 2014a,b).
Cellulosic fibers used for papermaking are the natural carbohydrate based polymers which are bonded together through the phenomenon of hydrogen (H–O–H) bonding in the presence of water molecules. Other carbohydrate polymer, starch, is a traditional wet-end additive; due to its low cost and ability to increase the inter-fiber bonding in paper, it has been commonly used in papermaking. Being a polymer of D-glucose with α-linkage and having six hydroxyl groups it increases hydrogen bonding in paper. The mechanism of dry strength improvement by wet-end starch is based on inter-fiber bonding. The free glucose hydroxy groups participate in the hydrogen bonding with cellulose molecules of the fiber, which means a chemical hydration of the fiber compound system (Holik, 2006).
As the common fillers are not capable of forming bonds with fibers, filler preflocculation with carbohydrate polymers enhances the compatibility between fillers and fibers, and confers certain beneficial attributes of carbohydrate polymers to fillers (Shen et al., 2010). The cationic starch (CS) has been found highly effective in filler preflocculation, and it can be anchored on the filler surfaces or used to encapsulate the filler particles to enhance fiber–filler bonding and to improve the strength properties of filled papers (Yan et al., 2005; Zhao et al., 2005; Bratskaya et al., 2006; Yoon and Deng, 2006, 2007; Sang et al., 2012; Chauhan and Bhardwaj, 2014a,b).
Mabee and Harvey (2000) showed that the filler preflocculation by starch could increase the ash in paper without affecting the paper properties. The addition of clay mineral modified using starch-fatty acid complex in paper resulted in an increase in tensile strength from 100% to 200% as compared with the native clay (Yoon and Deng, 2006). The modified clay with starch precipitate using ammonium sulfate as a precipitation agent provided relatively large floc size of the filler agglomerates, which were favorable to the development of strength in the filled sheets (Yoon and Deng, 2007).
Zhao et al. (2005) reported that the clay and calcium carbonate filler preflocculated using the starch-gel-coating method could strikingly improve the strength properties of filled papers. Yan et al. (2005) further improved the starch-gel-coating method by cooking unmodified starch separately, and starch coating was conducted by mixing cooked starch with clay slurry, followed by drying and grinding treatments. It avoided the need to dewater the mixture before cooking and significantly improved the strength properties of the filled papers. Ibrahim et al. (2009) modified Egyptian talc using cationic dodecyltrimethylammonium bromide (CDTAB) which enhanced the bonding capacity of talc with fibers, and improved the paper strength.
The increased paper strength through preflocculated filler has been attributed to the reduction of the surface area of preflocculated filler and thus less disruption of fiber–fiber bonding from fillers. However, filler flocs formed through preflocculation with polymers tend to break down under high shear rate. The creation of shear-resistant filler flocs with narrow particle size distribution is perhaps the biggest challenge faced by the paper industry. Therefore, it is of interest to assess the performance of the starches for filler preflocculation.
Plenty of literature is available on the preflocculation of fillers other than talc using CS. Moreover, the efficacy of another carbohydrate polymer, amphoteric starch (AS) which has both cationic and anionic groups, on the preflocculation of talc is rarely investigated. The literature on suitable process conditions for the preflocculation of talc using both CS and AS is also scarce. It was the basis of the present research.
In the separate communications, the authors have reported the effect of preflocculated talc filler of different particle size on various properties of paper. The preflocculated talc using CS and AS enhanced the strength and hydrophobicity of the paper (Chauhan and Bhardwaj, 2013a,b, 2014a,b). In the present work, the process conditions for the preflocculation of talc using CS were optimized. Talc was further preflocculated under optimized process conditions using CS and AS at different doses, and added to pulp for making laboratory sheets. The properties of paper filled with native and preflocculated talcs were compared.
2 Experimental
2.1 Materials
The bleached mixed hardwood kraft pulp consisting of 50% eucalyptus, 35% poplar and 15% bamboo was procured from an integrated paper mill in North India. The commercial grades of talc mineral, cationic starch (CS), amphoteric starch (AS), cationic polyacrylamide (CPAM) of medium to high molecular weight and alkyl ketene dimer (AKD) emulsion were procured from different manufacturers in India. The degree of substitution of CS and AS was 0.02 and 0.04 (0.02 each for cationic and anionic groups), respectively. The doses of CPAM used as retention aid polymer with native and preflocculated talc fillers for getting 15%, 18%, 21% and 24% ash in paper were 200, 200, 240 and 280 g/t on pulp, respectively (Chauhan and Bhardwaj, 2013a, 2013b, 2014a). The AKD emulsion was added at constant dose (0.6%) in pulp slurry for the development of hydrophobicity in paper.
2.2 Methods
The initial freeness of the pulp (620 mL), as measured on Canadian Standard Freeness (CSF) tester following Tappi test method T 227 om-09, was decreased to 430 mL through refining in the PFI mill (Hamjern Maskin a/s, Norway) following Tappi test method T 248 sp-00. Talc filler was characterized for physico-chemical characteristics; colloidal and surface charge, particle size distribution (PSD), and shape. The pH of the filtrate of filler suspension (10% w/v) filtered through a 300 μm screen was measured on pH meter. The colloidal charge of 10% (w/v) slurry of filler was examined on Mutek particle charge detector (PCD 03 pH). The PSD of the filler was measured using Laser scattering particle size distribution analyzer (Horiba LA950S2). The talc filler was wetted with ethanol and then dispersed in deionized water to make 10% (w/v) slurry. The particle shape of the fillers was determined by X-ray diffraction (Bruker AXS, D8 Advance, Switzerland) using Cu Kα radiation. Both the starch powders (1% solids, w/v) were cooked at 95 °C for 20 min prior to their use for preflocculation of filler. The granules of CPAM were added into deionized water at ∼40 °C and agitated at 300 rpm for 30 min to prepare 0.1% (w/v) solution. The anionic charge densities of CPAM, CS and AS, as measured on Mutek particle charge detector (PCD 03 pH), were 1134, 166 and 269 μeq/g, respectively.
2.3 Preflocculation of filler
In the preliminary experiments, the process conditions of filler preflocculation such as stirring speed, retention time and concentration of filler slurry were selected using CS as flocculant through image, colloidal charge and particle size distribution analysis. A dynamic drainage paper chemistry (DDPC) jar was used for filler preflocculation. Filler is supposed to be well dispersed prior to preflocculation and addition to papermaking slurry in order to get its impact on light scattering power of paper. However, as there was no effect of wetting and dispersing chemicals on the light scattering power of either paper or filler (Chauhan and Bhardwaj, 2017), the filler was dispersed in water alone to the required concentration level prior to its preflocculation. In the final experiments, the dose of both CS and AS was varied from 0.1% to 0.8% of the weight of dry filler using the selected process conditions from the previous experiments.
2.3.1 Stirring speed
The 30 g dry talc powder was dispersed separately in 270 mL distilled water using agitator at 2000 rpm for 30 min to make 10% (w/v) concentration. The filler suspension was then transferred to the vessel of DDPC jar. The speed of the propeller shaped stirrer was maintained at 300, 500 and 700 rpm. To the 300 g of the filler suspension in the stirring vessel being agitated gently at 300 rpm, 0.4% (w/w) of the cooked CS based on the dried filler was added while providing the retention time of 5 min. The same amount of CS was used in all preliminary experiments. For the image analysis, the filler suspension was diluted to 0.2% (w/v) with deionized water. The slides were prepared by taking a few drops of filler slurry on the glass slides which were then air-dried. The images were taken on Image analyzer (Axio Scope A1, Carl Zeiss Microimaging GmbH, Gottingen, Germany) in transmittance light mode at 40× magnification.
2.3.2 Filler concentration
To examine the effect of the filler concentration on preflocculation, it was dispersed at different solid contents of 5%, 10%, 20% and 40% (w/v) using agitator at 2000 rpm for 30 min. The CS at a dosage of 0.4% (w/w) was added to all filler suspensions while stirring in DDPC jar at 500 rpm and providing the retention time of 5 min. The image analysis of the preflocculated fillers was done similar to previous case.
2.3.3 Retention time
The CS was added to the 10% (w/v) filler suspension at the same dosage level of 0.4% while stirring at 500 rpm. The retention time for the preflocculation was varied for 1, 2, 5 and 10 min keeping all other conditions constant. The analysis of the preflocculated filler was carried out similar to previous two cases.
2.4 Handsheet preparation and testing
The refined pulp stock was disintegrated at ∼1% consistency for 5 min at 3000 rpm. The pulp slurry was then transferred into a bucket and AKD was added into the pulp slurry with an agitation of 400 rpm followed by native/preflocculated talcs. The pulp stock was then diluted to 0.4% and the CPAM was added as a retention aid polymer. The paper handsheets of 60 g/m2 were prepared as per Tappi test method T 205 sp-02. The ash content in paper was determined at 525 °C as per Tappi test method T 211 om-93. The properties of the sheets were determined after conditioning at constant temperature (23 ± 1 °C) and relative humidity (50 ± 2%) for 24 h. The strength properties of paper such as tensile index, burst index and tear index were determined using Tappi test methods T 494 om-01, T 403 om-97 and T 414 om-98, respectively. The light scattering coefficient was determined on Datacolor Brightness tester using Tappi test method T 425 om-01. The hydrophobicity of paper was measured through Cobb60 and contact angle tests. Cobb60 was measured using Cobb sizing tester as per Tappi test method T 441 om-98. The dynamic contact angle was measured on Kruss drop shape analyzer (model: DSA 10, Kruss) as per Tappi test method T 458 cm-94 at 1 s intervals over a total 60 s. The arithmetic average of all 60 readings of dynamic contact angle values was reported as average contact angle. All experiments were carried out in triplicate and the bars shown in the figures represent the standard deviation on either side of the mean.
3 Results and discussion
3.1 Characteristics of preflocculated filler
The images of filler particles/flocs for the native and preflocculated talc fillers using the cationic starch (CS) dosage of 0.4% at three different stirring levels, 300, 500 and 700 rpm, are shown in Fig. 1. The filler suspension was stirred for 5 min after dosing the starch. The flocs size of the preflocculated filler was decreased on increasing the stirring speed. Similar results have been reported by other researchers (Blanco et al., 2005; Seo et al., 2012). This shows that low stirring conditions do not completely disperse filler flocs and the larger flocs tend to stay undispersed, whereas high stirring conditions disperse the filler flocs more rigorously which may not be desired for papermaking application point of view. The moderate speed of 500 rpm seems to be most effective in terms of filler preflocculation and was used in the further experiments.
Effect of agitator speed during preflocculation of filler (10% w/v) using cationic starch (0.4% dosage) on filler floc size at 5 min retention time, native talc (a), preflocculated talc at 300 rpm (b), 500 rpm (c), and 700 rpm (d).
The effect of filler concentration on the flocs formation during preflocculation of talc filler is shown in Fig. 2. The filler suspension of 5%, 10%, 20% and 40% solids (w/v) was preflocculated using the 0.4% CS at 500 rpm for 5 min. It was observed that the filler suspension of different concentrations behaved differently on preflocculation while keeping other conditions constant. Initially at low filler concentration (5%), the flocs were small and increased on increasing the filler concentration to 10%. Further increasing the solids level to 20% and 40% resulted in improper flocs formation which was possibly due to inadequate mixing of filler particles at higher concentration. The flocs at high filler concentration levels were not uniform. When the mixing is not uniform, some particles are covered with more starch and form large flocs whereas others remain intact together. The similar results were reported elsewhere (Schneider et al., 2002; Seo et al., 2012). Moreover at low talc concentration, there are more possibilities of particles getting covered by starch molecules so that it resists attachment to other particles. This occurrence would be less likely at high talc solids, since multiple collisions would take place before the talc particles could become fully covered. The 10% filler concentration level was observed most accurately among all other studied concentrations; thus, it was used in the further experiments.
Effect of concentration of talc (w/v) during preflocculation of filler using cationic starch (0.4% dosage) on filler floc size at 500 rpm agitator speed and 5 min retention time, 5% (a), 10% (b), 20% (c), and 40% (d).
The effect of retention time during filler preflocculation on the flocs formation is shown in Fig. 3. The filler suspension of 10% solids (w/v) was preflocculated using the 0.4% CS at 500 rpm for different time intervals such as 1, 2, 5 and 10 min. It was observed that the filler floc size was increased on increasing the retention time up to 5 min; thereafter, the flocs were found nonuniform. At high retention time, some of the flocs were dispersed again due to longer interaction time of CS and filler. As discussed earlier, the particles covered with the starch tend to form large flocs and get dispersed into smaller ones after extended stirring. The similar results were reported by Seo et al. (2012). The results suggest that 5 min retention time was sufficient for the preflocculation of filler of 10% solids (w/v) when stirred at 500 rpm. These process conditions were used in the following experiments.
Effect of retention time during preflocculation of filler (10% w/v) using cationic starch (0.4% dosage) on filler floc size at 500 rpm agitator speed, 1 min (a), 2 min (b), 5 min (c), and 10 min (d).
3.2 Characteristics of filler preflocculated using varying dosage of starches
The stirring speed, filler concentration and retention time were maintained as 500 rpm, 10% (w/v) and 5 min, respectively. Fig. 4 shows the images of talc filler preflocculated using freshly cooked starch, CS and AS, at 0.1–0.8% of the weight of dry filler. It was observed that the filler floc size was increased on increasing the dose of flocculant i.e. CS and AS. The floc size of preflocculated filler was comparatively higher and dense with amphoteric starch (AS) due to its both anionic and cationic charges, and higher cationicity than the CS. The medium dosage level of 0.4% was effective with respect to preflocculating the talc fillers and increasing the floc size. The highest dosage of starch used in this study was 0.8% on filler which gave highly dense flocs with both CS and AS.
Images of talc particles at 40× magnification in Image analyzer preflocculated with different dosages (w/v) of cationic starch, 0.1% (a), 0.4% (b), 0.8% (c); and amphoteric starch, 0.1% (d), 0.4% (e), and 0.8% (f).
The increase in particle size of the preflocculated filler on increasing the dosage of flocculant was also confirmed from the results of particle size distribution obtained from the Particle size analyzer (Fig. 5). On preflocculation with either of the flocculating agents, the filler floc size was increased. The median particle size of native talc was 6.0 μm which was increased to 6.7, 9.0 and 12.0 μm on its preflocculation with 0.1%, 0.4% and 0.8% CS, respectively, and 6.8, 9.8 and 14.8 μm on its preflocculation with 0.1%, 0.4% and 0.8% AS, respectively. The increase in the median particle size of talc using CS and AS was up to 100% and 146%, respectively. It indicated that the preflocculation of talc resulted in larger flocs with AS as compared to those with CS.
Particle size distribution of native and preflocculated talc filler.
The effect of the CS and AS on the colloidal charge of preflocculated filler is shown in Table 1. The cationic colloidal charge demand indicated that the native filler was anionic. On filler preflocculation with either of the flocculating agents, the anionicity was decreased. It was observed that the cationic charge demand was decreased with increasing the dosage of CS and AS; the latter one was more effective due to its intrinsic higher cationic colloidal charge.
Native talc
2.1
Preflocculated talc using
CS-0.1%
2.0
0.4%
1.4
0.8%
0.8
AS-0.1%
1.9
0.4%
1.0
0.8%
0.5
3.3 Characteristics of paper filled with preflocculated filler
The ash of paper filled with constant doses of native and preflocculated fillers is shown in Fig. 6. Certain positive effect on the retention of filler in paper was caused by the filler preflocculated with either CS or AS. The ash was increased with the higher dose of starch. The increase in the retention of talc was more with AS as preflocculating agent. Similar findings were reported by Park and Shin (1987) in the context of the preflocculation of talc and GCC with CPAM or CS.
Effect of preflocculated talc filler on ash in paper at different loading levels.
As cellulose and starch are the polymers of D-glucose having three free hydroxyl groups in each molecule extensive hydrogen bonds are formed in association with water molecule. This is the causative factor of inter-fiber bonding which attributes strength in paper. Carbohydrate based polymer such as starch lying on the outer surface of talc during preflocculation can also take part in H-bonding with the hydroxyl groups of cellulosic molecules, forms the bridge in fiber–filler–fiber bond and prevents the fall in paper strength during filler loading.
The effect of preflocculated talc on tensile index of paper made at different ash levels is shown in Fig. 7. The preflocculated filler enhanced the bonding capacity of the filler with fiber, resulting in improved paper strength while increasing the filler retention in comparison to that observed with native filler. The tensile index was increased with the change of dosage of starch for the preflocculation of talc. AS was more effective in improving the tensile index as compared to CS for the same amount of starch addition. With the increase of ash in paper, the rate of reduction in tensile index was comparable in case of native and preflocculated filler using CS. However, filler preflocculated with AS retained the strength in paper and decreased the rate of reduction of tensile index (Δy/Δx), the value of which for native filler, filler preflocculated with 0.1%, 0.4% and 0.8% CS was 0.84, 0.86, 0.92 and 0.97, respectively. The rate of reduction in tensile index for talc preflocculated with 0.1%, 0.4% and 0.8% AS was 0.90, 0.48 and 0.49, respectively. The highest increase in tensile index was obtained with 0.8% AS. At 24% ash level, the tensile index of sheet filled with native filler was 27.6 N m/g which was increased to 27.8, 27.8, 28.2; 28.0, 32.4 and 33.2 N m/g on its preflocculation with 0.1%, 0.4% and 0.8% dosage of CS and AS, respectively. The increase in tensile index of paper was about 20% using 0.8% AS. The difference in the tensile index of filled sheet with native and preflocculated talc was higher when the ash in paper was increased.
Effect of preflocculated talc filler on tensile index of paper at different ash levels.
Similar to the tensile index, the burst index of paper was also increased on loading of preflocculated fillers in paper (Fig. 8). The higher improvement in burst index was observed with filler preflocculated with AS as compared to that with CS. The rate of reduction for native and preflocculated talc filler was comparable. However, the preflocculated talc filler provided higher burst index than that with native talc when compared at a constant ash level. This was applicable for all ash levels.
Effect of preflocculated talc filler on burst index of paper at different ash levels.
As shown in Fig. 9, on the incorporation of preflocculated fillers in paper the tear index was marginally increased. Though the preflocculated filler slightly improved ash in paper, there was no negative effect of the increased ash on tear index of paper. In this case too, AS was little more effective than CS in increasing the tearing strength of paper. The rate of reduction in tear index of paper was comparable for the native and preflocculated fillers (0.07–0.08).
Effect of preflocculated talc filler on tear index of paper at different ash levels.
As shown in Fig. 10, the scattering coefficient of paper filled with native filler was 52.2 and 57.8 m2/kg at 18% and 24% ash levels, respectively. It was comparable with the sheets filled with the same filler preflocculated with lower dose of CS and AS and marginally reduced on increasing their dose. The highest scattering coefficient of paper with preflocculated filler at 18% and 24% levels was 52.5 and 58.5 m2/kg, respectively with 0.1% dosage of AS. The bigger flocs developed due to higher dosage of starch reduced the surface area of both filler and paper network which, in turn, lowered the light scattering in paper. Moreover, starch itself absorbed the light and decreased the specific light scattering in paper.
Effect of preflocculated talc filler on scattering coefficient of paper at different ash levels.
The hydrophobicity of paper filled with preflocculated fillers was little higher than that filled with native filler. It was shown by the decreasing Cobb60 (Fig. 11) and increasing contact angle (Fig. 12). The Cobb60 value of sheet filled with native filler at 18% ash was 27.0 g/m2 which was decreased to 21.7 and 20.8 g/m2 on the preflocculation of filler with 0.8% dosage of CS and AS, respectively. In terms of percentage, the Cobb60 value was decreased up to 23% on loading of preflocculated filler as compared with the native filler. Similarly at 24% ash, the Cobb60 value of sheets was decreased up to 21% on loading of preflocculated filler as compared with the native filler. These results showed that the preflocculated fillers could efficiently decrease the Cobb60 value thus increasing the hydrophobicity of paper. Moreover, the decrease in hydrophobicity due to increasing ash of paper was also prevented to a great extent through filler preflocculation. The filler preflocculation with carbohydrate polymers enhanced the compatibility between fillers and fibers, and conferred certain beneficial attributes to fillers. This is one of the effective ways to control the negative effect of filler loading on hydrophobicity of paper because it increases the size of the particles and the inter-fiber bonding.
Effect of preflocculated talc filler on Cobb60 value of paper at different ash levels.
Effect of preflocculated talc filler on average contact angle of paper at different ash levels.
The increase in the average contact angle value of paper sheet on loading of preflocculated filler has also shown their efficacy in papermaking. The contact angle of filled sheets with native filler at 18% ash was 115.5° which was increased to 119.5° and 120.1° on its preflocculation with 0.8% dosage of CS and AS, respectively. At 24% ash level also the contact angle increased from 109° to 115.5° on loading of preflocculated filler in paper. The enhanced hydrophobicity might be due to (i) very little adsorption of sizing chemicals on the surface of the filler particles as they are covered with the thin film of starch, (ii) available sizing chemicals (alkyl ketene dimer) react with the cellulosic fibers which are also bonded in the close network by the starch granules of the preflocculated filler.
4 Conclusions
At high stirring speed during filler preflocculation, the large flocs were converted to small flocs, whereas at low speed the large flocs were formed. The stirring speed influenced the uniformity of the flocs. The concentration of filler suspension also affected the floc formation. The increase in filler concentration caused inadequate mixing of filler particles and nonuniformity of the flocs. The moderate retention time during filler preflocculation was desired as both low and high retention times disturbed the flocs uniformity. The filler preflocculated with carbohydrate polymers provided paper sheets with higher filler retention, hydrophobicity, tensile and burst indices, and comparable tear index and light scattering coefficient. The filler retention and paper strength increased on increasing the dose of polymer. Between cationic and amphoteric starches, the latter one was more efficient in improving the paper properties.
Acknowledgments
The authors are thankful to Director, Avantha Centre for Industrial Research & Development, Yamuna Nagar, Haryana, India, for providing the facilities to complete this work. The supply of pulp, mineral fillers and other chemicals from various suppliers is also gratefully acknowledged.
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