A Review on Use of Fillers in Cellulosic Paper for ... - ACS Publications

Dec 20, 2010 - UniVersity, Harbin 150040, China, Institute of Chemical Industry of ... Centre, UniVersity of New Brunswick, Fredericton, NB, Canada, E...
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Ind. Eng. Chem. Res. 2011, 50, 661–666

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A Review on Use of Fillers in Cellulosic Paper for Functional Applications Jing Shen,† Zhanqian Song,‡ Xueren Qian,*,† and Yonghao Ni§ Key Laboratory of Bio-based Material Science and Technology of Ministry of Education, Northeast Forestry UniVersity, Harbin 150040, China, Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry, Nanjing 210042, China, and Department of Chemical Engineering & Limerick Pulp and Paper Centre, UniVersity of New Brunswick, Fredericton, NB, Canada, E3B 5A3

In this review paper, the use of inorganic fillers in cellulosic paper with some unique functions, such as magnetic, photocatalytic, flame retardant, antibacterial, deodorizing, electrically conductive, and thermal buffering properties, is highlighted. Notably, fillers and cellulosic pulp fibers can sometimes exhibit synergic effects on special applications, such as photocatalysis. The methods associated with the use of fillers can include direct wet end addition, lumen loading, in situ synthesis of filler particles in the presence of cellulosic pulp fibers, formation of fiber/filler composites, and surface filling. Also, regardless of the end uses of the paper products, the general methods for modifying fillers or the papers with fillers can reasonably include nanoengineering, chemical modification, surface encapsulation, mechanical modification, and formation of filler-based composites, etc. The use of cellulosic fibers as carriers of these inorganic fillers for specific functions can create more opportunities for using abundant cellulosic fiber material. Introduction In the production of traditional printing/writing paper grades, filler addition either at the wet-end or surface application is now a very common practice. Usually, the benefits associated with the use of fillers that are attractive to the paper industry mainly include cost and energy savings,1-3 improvement in optical properties, sheet formation, dimensional stability, printability, and writability of cellulosic paper,2-6 and increased furnish drainage rate, machine speed, and productivities.1,7 The use of fillers for traditional printing/writing papers has been reviewed by others.8-11 Different from the traditional applications, the use of fillers in a cellulosic paper network can deliver some unique functions so that cellulosic paper products can be used for special functions. These include magnetic, photocatalytic, flame retardant, antibacterial, electro-conductive, deodorizing, and thermal buffering properties. These applications can be of critical importance in light of bioeconomy due to the fact that lignocellulosic material is the most abundant natural resource and cellulosic paper is biodegradable. The following review is focused on these unique functions. Magnetic Property Imparting magnetic property to cellulosic paper may make it suitable for important applications, such as information storage or security paper.12,13 The magnetic fillers may include maghemite, magnetite, chromium dioxide, and cobalt-doped oxides.12 In addition to such methods as surface coating of cellulosic paper with magnetic particles,14 the addition of fillers at the wet web during the paper formation process can also be used for the preparation of magnetic paper. The relevant methods of using fillers are as follows. Direct Wet End Addition. The direct wet end addition of magnetic filler particles to confer magnetic properties to * To whom correspondence should be addressed. E-mail: [email protected]. † Northeast Forestry University. ‡ Chinese Academy of Forestry. § University of New Brunswick.

cellulosic paper, i.e., interstitial loading of ferrite between fibers to create bulk magnetism, is possible.15,16 However, this method has been rarely reported in the literature (only limited to a few patents). Magnetic filler particles adsorbed on external fiber surfaces can decrease the interfiber bonding. Also, poor filler to cellulosic fiber bonding interaction can result in rob-off losses of fillers, yielding a dirty product.12 On the other hand, it is expected that with the addition of strength additives, the effect of using magnetic fillers on the strength properties of cellulosic papers containing magnetic fillers can be minimized so that it would be able to meet the specific requirements for the unique applications. Lumen Loading. For lumen loading by sufficient mixing of the aqueous mixture containing pulp fibers and magnetic particles, filler particles such as magnetite or maghemite can be introduced into the lumens of the fibers while leaving most of the external surfaces of fibers free from these filler particles,17,18 and the modified fibers can be subsequently used for the preparation of magnetic paper. It has been reported that cationic polyelectrolytes, such as polyethylenimine (PEI), can be used as an excellent retention aid to improve the retention of filler particles inside the lumens of fibers.19-21 Compared with the direct wet end addition of magnetic filler particles, the lumen loading method has the advantage of decreasing the detrimental effects of filler addition on paper strength. The use of cationic starch as a dry strength agent in papermaking of fibers with their lumens loaded with magnetic filler particles has been reported to be capable of further improving the paper strength; however, cationic starch may disturb the location and distribution of magnetic fillers, and some of the magnetic particles can be displaced from the fiber lumens and pit apertures.22 In Situ Synthesis of Magnetic Particles. In situ synthesis of magnetic filler particles in the presence of cellulosic fibers can be used for the preparation of magnetic paper,17,23-30 and this process generally gives rise to the formation of magnetic filler particles between or inside the cellulosic fibers.87 By applying the in situ synthesis procedure, magnetic filler particles can be introduced into the lumens and cell walls of pulp fibers. Marchessault et al.12 patented a method for the preparation of magnetic fibers by generating magnetic particles in situ in paper-

10.1021/ie1021078  2011 American Chemical Society Published on Web 12/20/2010

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forming fibers that contained ionic groups effective for ion exchange with ferrous ions. The ion exchange between the sodium ions and the ferrous ions can be readily achieved in an aqueous ferrous salt solution (e.g., aqueous ferrous chloride); also, the addition of a stochiometric amount of aqueous sodium hydroxide solution precipitates ferrous hydroxide, which is further oxidized to magnetic particles of iron oxide by bubbling oxygen through the gel matrix. Carrazana-Garcia et al.23 evaluated the influence of fibers during the synthesis of crystals and aggregates of ferrites in the presence of oxygen, and the results on the magnetic, morphological, and structural properties of the magnetic paper and the ferrite particles were reported. However, these methods include the oxidation reactions in fiber suspensions as a result of the incorporation of oxygen, and some nonmagnetic iron oxy-hydroxides can be produced, which may detrimentally affect the magnetic property of the paper.24 The in situ synthesis of magnetic filler particles in the absence of oxygen was proposed, and the method of coprecipitation has been reported.24 Compared with lumen loading by mixing the aqueous mixture containing pulp fibers and magnetic particles, the in situ synthesis method may allow better dispersion, greater uniformity, and a better control of the magnetic property of the paper.23,31,32 The in situ synthesis method produces magnetic filler particles incorporated into the lumens, cell walls, and the surface of cellulosic fibers. Fiber Nanocoating. Fiber nanocoating is associated with the coating of pulp fibers with nanostructured materials. Recently, Small and Johnston33 reported this interesting concept for the use of filler particles to confer magnetic property to paper that is different from the direct wet end addition. The process included three steps:33 (1) synthesis of magnetite (Fe3O4) nanoparticles with ammonia and FeCl2 · 4H2O as the starting materials; (2) adding nanoparticles to the suspension of pulp fibers, followed by vigorous stirring, filtering, and washing; and (3) sonication of the coated fibers to remove any loosely bound nanoparticles. This concept can be considered as fiber nanocoating, and it was hypothesized by Small and Johnston to have the advantages of preserving the inherent properties of the fiber (e.g., tensile strength and flexibility).33 Among the above approaches for the preparation of magnetic paper, lumen loading and in situ synthesis of magnetic filler particles in the presence of cellulosic fibers can be advantageous in terms of minimizing the loss of mechanical strength of the fiber networks in comparison with the direct wet end addition procedure. The lumen loading approach can also improve the retention of the inorganic fillers. The in situ approach offers greater control of both the magnetic property and the variety of magnetic particles that can be incorporated into the final product, although it can make the fiber walls less conformable so that the interfiber bonding potential may be decreased. The nano coating approach (coating fibers with nanomagnetic fillers) can preserve the inherent properties of pulp fibers, and can give high efficiency associated with the use of fillers, i.e., the required amount of retained fillers in the fiber matrix might be relatively low, as nanoparticles are expected to be highly efficient in covering the fiber surfaces. Further work regarding the use of fillers to confer magnetic property to cellulosic paper is still much needed in the future, and some technological barriers (such as the detrimental effect of using fillers on paper strength or operational difficulties in implementation) may need more

explorations, and the feasibility and potential of relevant technologies for commercialization must be evaluated. Photocatalytic Property The development of cellulose-based photocatalytic paper has been the interest of many researchers in the past few years, with potential applications such as toxin passivation, deodorizing, disinfection, and environmental purifications.34-36 The available methods regarding the use of photocatalytic fillers for the preparation of photocatalytic paper can be divided into two different groups. For the first group of methods, cellulosic pulp fibers are retained in the sheets as important components useful for photocatalytic applications.37 For the second group of methods, although cellulosic pulp fibers are used as indispensable components for the formation of paper sheets by a papermaking technique, the cellulose-based sheets are ignited at very high temperature (e.g., 700 °C) to remove the organic components, and the resultant products are paper-like materials without cellulosic characteristics.38-40 Although the two groups of methods are both very important, the second group of methods is not described in detail here as this review article is focused on paper products with cellulosic characteristics. Titanium dioxide can exhibit encouraging photocatalytic property at certain conditions.41 In the paper industry, titanium dioxide is usually used to improve the opacity and brightness of paper products; however, its application is normally limited to high-value-added printing paper grades, as its cost is much higher in comparison with the conventional fillers such as clay and calcium carbonate. The methods regarding the use of titanium dioxide for the preparation of photocatalytic paper can include both wet end filling35 and surface coating of paper.42 Pelton et al.34 gave a very systematic review of photocatalytic paper from colloidal titanium dioxide, and different methods for the preparation of photocatalytic paper such as wet end addition of fillers, were reviewed in detail. Photocatalytic paper has also been reviewed by others.43,44 Matsubara et al.45 found that the photocatalytic efficiency (as evaluated by measuring the decomposition of gaseous acetaldehyde under illumination from a weak UV light source, i.e., 0.08 mW cm-2) of the titanium-dioxide-containing paper was higher than that of Degussa P-25, one of the most efficient commercial titanium dioxide powders, indicating that paper can serve as a good supporting or anchoring matrix for highly efficient titanium dioxide photocatalysts. For cellulose-based photocatalytic paper, the cellulosic fiber matrix can be easily damaged by photocatalysis.45 Therefore, the inhibition of photocatalytic decomposition of cellulosic fibers is necessary. Iguchi et al.46 investigated the preparation of photocatalytic paper using commercial titanium dioxide, softwood bleached kraft pulp fibers, ceramic fibers, and retention agents (polydiallyldimethylammonium chloride and anionic polyacrylamide). Ceramic fibers can serve as good supports or matrixes for photocatalytic titanium dioxide particles, and the paper samples were found to have both excellent physical durability and VOC (volatile organic component) photodecomposition performance.46 Obviously, cellulosic fibers can be protected by supporting titanium dioxide particles on ceramic fibers. The photoactive titanium dioxide particles were considered to be preferentially immobilized on the inorganic fibers and incorporated into the layered pulp fiber network out of contact with the organic pulp matrix, resulting in high durability.37 It was also found that, compared with powdery titanium dioxide and pulp/titanium dioxide mixture (not in paper form), the titanium-dioxide-filled photocatalytic paper decomposed

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gaseous acetaldehyde more effectively under UV irradiation presumably due to its unique voids of the sheet; the photodecomposition efficiency was affected by the void structure of the photocatalyst paper, and the initial degradation rate of acetaldehyde increased with an increase in the total pore volume of the paper.37 Thus, under certain conditions, cellulosic pulp fibers used for the preparation of photocatalytic paper can enhance the photocatalytic property of titanium dioxide, i.e., titanium dioxide particles and cellulosic fibers can give interestingly synergic effects on photocatalysis. The retention of titanium dioxide during the paper formation process is usually a critical issue. For this reason, the preparation of photocatalytic paper involved the use of retention agents. Although the flocculation of titanium dioxide particles to form large aggregates may not be desirable, the use of retention agents can be regarded as an important aspect of potential practical applications. The microparticle retention systems can decrease the size of particle aggregates and give a more uniform sheet. Quite interestingly, zeolite-based microparticle system is not only an excellent retention enhancer for titanium dioxide, but also an important promoter for photocatalytic efficiency.35 The use of titanium dioxide/zeolite composite filler (obtained by thoroughly mixing natural zeolite with as-prepared titania sol followed by evaporation, drying, and high-temperature postcalcination treatments) for the preparation of photocatalytic paper has been found to be much more beneficial to the enhancement of photocatalytic property of the paper, for example, for toluene removal.47 The functioning mechanisms associated with the resultant photocatalytic paper can include (1) confinement of organic contaminant in microvoids between fiber networks; (2) the further adsorption of organic contaminates onto zeolite; and (3) subsequent photodecomposition of adsorbate by TiO2 nanoparticles.47 In addition to the direct wet end addition of commercially available or as-prepared titanium dioxide (annealed at high temperature) to confer photocatalytic property to cellulosic paper, dipping cellulosic fibers in nanosol (prepared by mixing titanium tetraisopropoxide with acidic water containing nitric acid) followed by such treatments as pressing, air drying, rinsing (with sodium carbonate solution and water), and hydrothermal treatment at 97 °C, was reported by Daoud et al.48 By applying such a process, photocatalytic titanium dioxide particles were coated on the cellulosic fiber surfaces, which can potentially be suitable for the preparation of photocatalytic paper with antibacterial property. Among the systems/methods reported in the literature regarding the photocatalytic paper/fillers composites, it appears that titanium dioxide is a preferred type of filler because of commercial availability, wet-end compatibility, and also its good optical properties. Although there have been many scientific publications regarding the use of filler particles to confer photocatalytic property to cellulosic paper in recent years, more research would be needed to address, for example: • Shortened lifetime of the cellulosic paper due to the photocatalytic decomposition of cellulosic fibers • Limited use under high moisture conditions due to the hydrophilic nature of cellulosic fibers.

The antibacterial property is much desired for many paper grades, such as office paper, tissue paper, medical packaging paper, and food packaging paper. For the preparation of antibacterial paper, the possible methods mainly include (1) direct wet end addition of antibacterial agents,55 (2) surface coating,56 and (3) impregnation (a material with antibacterial property is made to permeate the fiber structure, rather than merely coat on the surface).55 Both organic and inorganic antibacterial agents have been reported to be suitable for the preparation of antibacterial paper.57-59 As a matter of fact, micro-organisms can grow easily on soft and moist organic masses, whereas it would be more difficult on mineral filler surfaces. Patel gave a very detailed review of the developments in antibacterial paper.57 A vermiculite exchanged with Ag- or Cu- antibacterial ions, multifunctional materials derived from clay minerals and other inorganic materials based on cation exchange reaction and surface modification, and specifically intercalated montmorillonite, saponite, and goethite, can potentially be used as fillers for the antibacterial purpose, as discussed by Patel. Yang et al.56 patented a method for the preparation of antibacterial paper by wet end addition of silver-loaded zeolite filler. Recently, the use of Mg(OH)2 nanoparticles or tetrapod-like zinc oxide whiskers as fillers to confer antibacterial property to cellulosic paper has been reported.60,61 The use of photocatalytic titanium dioxide as a filler can also provide antibacterial property under specified conditions.34 The use of photocatalytic titanium dioxide filler for antibacterial purposes can have another benefit, that is, the optical properties, such as brightness/whiteness of the paper, can also be improved.

Flame Retardant Property

Electrically Conductive Property

For many commercial products such as paper, furniture, and cloth, flame retardant property is much desired in their specific applications. The general principle of methods capable of conferring flame retardant property to cellulosic paper is to

Cellulose-based electrically conductive materials have been an active research area, and they have potential applications such as antistatic and electromagnetic shielding, electrical resistive heating, and energy storage.62-64 The induction of

prevent paper from bursting into flames upon exposure to a high temperature.49 Many types of inorganic fillers have been found to be suitable for this purpose. These fillers are usually inorganic hydrates, and their use can be achieved by the direct wet end addition or fiber loading. For example, in addition to its contribution to paper brightness and ink receptivity, aluminum trihydrate can be a flame retardant for paper, and its effect on flame retardancy can be explained by the 35% of bound water based on the material weight.50 Take et al.51 patented the method of using both calcium silicate and aluminum hydroxide as fillers by following the direct wet end addition procedure for the preparation of nonflammable paper. The use of Mg-Al Hydrotalcites for the preparation of flame retardant paper has been experimented, and both direct wet end addition of Mg-Al hydrotalcites and in situ synthesis of Mg-Al hydrotalcites in the presence of pulp fibers were reported.52,53 Also, the use of other fillers in papermaking such as Mg(OH)2 nanobelts with very high aspect ratios54 can be expected to provide flame retardant property. As flame retardant fillers are usually hydrates, they are often considered to have good dispersibility in the papermaking system. In practical applications, the selection of fillers for the preparation of flame retardant paper depended on a number of parameters, such as the required degree of flame retardance, filler retention and drainage, and cost-effectiveness. Antibacterial Property

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electrical conductivity to cellulosic paper can be achieved by the use of electrically conductive materials or their precursors. The methods capable of fulfilling the purpose can include such aspects as in situ synthesis of conductive materials in the presence of paper sheet or fibers,64-66 surface coating of cellulosic paper,67 electroless plating,68 and use of specialty fibers.69 In addition to the above methods, the use of fillers can also be possible. Electrically conductive fillers or fillers coated with electrically conductive materials have been used to confer electrical conductivity to cellulosic paper. These fillers include the following. • Carbon black or carbon nanotube: It was reported to produce carbon black filled paper for packaging or as an intelligent substrate for electronic sensors design.70 However, due to the weak bonding of carbon black with pulp fibers, such a process may have the issue of carbon black particles easily removed from the paper surface. Anderson et al.71 reported the use of single-walled carbon nanotubes as fillers to produce electrically conductive paper with both good electrical conductivity and flame retardancy. Agarwal et al.72 reported a method of composite nanocoating of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) and aqueous dispersion of carbon nanotubes on lignocellulose wood microfibers to make conductive microfibers and paper sheets. The presence of the sulfonic groups on the coating layer can presumably improve the retention of the carbon nanotubes, but of course increase the production cost. • Indium tin oxide (ITO): Based on the layer-by-layer (LBL) assembly of conductive indium tin oxide (ITO) nanofiller particles and polyelectrolytes onto wood fibers, the preparation of electrically conductive paper with excellent properties was possible.73 • Clay modified with conductive polymer: By surface coating of kaolin clay with conductive polymer, it is possible to produce electrically conductive paper by wet end addition of the modified filler particles.74,75 Burridge et al.76 coated kaolin clay with the conducting polymers including polypyrrole and polyaniline, and the polymer spheres were found to be fused together in a continuous sheet to coat the clay platelets in their entirety. Due to the fact that surface coating of fillers would require less material (thus, less conductive polymers, which are usually more expensive than cellulosic fibers), it is expected that at the same amount of conductive polymer used, a higher conductivity can be achieved by using the conductive fillers following the surface coating method. Similarly, to achieve the same electroconductivity, using the conductive fillers by following the surface coating method would require less conductive polymers that are expensive. Therefore, the production cost of the electroconductive paper composite based on the conductive fillers via a surface coating process would be less than that based on the wet-end process. Deodorizing Property Paper with deodorizing properties can be suitable for such important applications as food packaging and smell deodorizing. It can be made by coating and/or impregnating cellulosic paper sheet using deodorizing ions (e.g., iron ion).77,78 It is also possible to confer deodorizing property to cellulosic paper by using fillers, but there are only limited reports of this in the literature. The use of photocatalytic titanium dioxide fillers at the wet end of the papermaking process can provide deodorizing property under certain conditions, as discussed in

the earlier section. The use of calcium phosphate filler in cellulosic paper for the deodorizing property was first patented by Tsuru et al.,79 and in a recent patent Dai and Gao80 reported the wet end addition of porous calcium phosphate in combination with wet strength agent, cationic polyacrylamide, and silica-aluminum microparticles for the same purpose. Since zeolite can be used in paper coating to provide cellulosic paper with deodorizing property,81 its use as a filler material in cellulosic paper might also be expected to be possible. On the other hand, the commercial potential of these technologies would depend heavily on the product/process economics. Other Special Properties In addition to those properties discussed above, the use of fillers can also provide other special functions. The heat insulation property, much desired for such applications as food packaging, can be conferred to cellulosic paper by in situ precipitation of aluminum silicate in the presence of pulp fibers.82 By coating cellulosic pulp fibers with ZnS nanocrystal fillers doped with Mn2+ and Cu2+, followed by the use of the composites for the wet web formation of paper, the resultant paper can exhibit photoluminescent property.83 By fixing dyes to the surface of fillers (such as calcium carbonate) with coupling agent, the modified colored fillers can provide the selected coloring in the paper product, which has better property in comparison with the conventional method of direct wet end addition of dyes.84 Quite interestingly, nanostructured calcium silicate, which was prepared from synthetic nanostructured calcium silicate and alkaline phase change material, can provide thermal buffering functions to cellulosic paper.85,86 With the development of the paper industry and other relevant industries, the special properties that can be conferred to cellulosic paper by using fillers seem more and more diversified. It is likely that the concept of using fillers for the purpose of providing cellulosic paper with unique functions will lead to more active research and development, therefore, some unique products will ultimately enter into the market place. Concluding Remarks The use of fillers can lead to cellulosic fiber/paper products with special properties or functions. These special properties or functions can include magnetic, photocatalytic, flame retardant, antibacterial, electrically conductive, deodorizing, and thermal buffering properties. The relevant methods can include the following: (1) fillers either in powder form or in slurry form directly added to the furnish system containing cellulosic pulp fibers before the wet web formation of paper; (2) fillers introduced into the lumens of cellulosic pulp fibers under strong mechanical forces (agitation); (3) in situ synthesis of filler particles in the presence of cellulosic pulp fibers, and the filler particles introduced into the cell walls and/or lumens of fibers, as well as onto the fiber surfaces; (4) fillers fixed/adhered to the surface of cellulosic pulp fibers to form fiber/filler composites; (5) fillers used on the paper surface by surface application methods, such as coating. Also, regardless of the end-use application, based on the publications regarding fillers for papermaking available in the literature, the relevant methods for modifying fillers or the papers with fillers can reasonably include nanoengineering, chemical modification, surface encapsulation, mechanical modification, and formation of fillerbased composites, etc. In specified applications, fillers can be pretreated or modified before the wet end addition.

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The use of fillers provides an effective way to functionalize paper, and it is also an indispensable way to foster the development of a “smart paper” industry. It is noted that in some cases, for example, for the photocatalytic property of the cellulosic fiber/filler composites, cellulosic paper can act as both supporting material and performance-enhancer. Also, there are a number of novel technologies emerging, such as coating of cellulosic pulp fibers with nanofillers (also referred to as fiber nanocoating). Further scientific and technological development in this area will potentially provide new concepts, new strategies, new cellulosic paper products, and new possibilities. However, some important issues associated with the use of fillers, such as filler retention, filler dispersing, solubility of the filler in the aqueous papermaking system, paper strength, distribution of filler particles within the fibrous matrix, cost-effectiveness, and commercialization feasibility should always be taken into comprehensive consideration. Acknowledgment We acknowledge support from the Fundamental Research Funds (DL09BB07) for the Central Universities of China, Foundation (11533009) of the Education Department of Heilongjiang Province of China, and Canada Research Chairs Program. We also thank the reviewers for their valuable comments and suggestions which helped in improving the quality of the paper. Literature Cited (1) Dong, C.; Song, D.; Patterson, T.; Ragauskas, A.; Deng, Y. Energy saving in papermaking through filler addition. Ind. Eng. Chem. Res. 2008, 47, 8430–8435. (2) Gill, R. A. Fillers for papermaking. Retrieved Oct. 17, 2009. URL: http://www.specialtyminerals.com/fileadmin/user_upload/smi/Publications/ S-PA-AT-PB-42.pdf. (3) Song, D.; Dong, C.; Ragauskas, A. J.; Deng, Y. Filler modification engineering for improved paper properties and papermaking process. TAPPI 2nd Annual PaperCon’09 Conference - Solutions for a Changing World, 2009. (4) Laufmann, M. Fillers for paper: A global view. PTS-Seminar Wet End Operations-Vorga¨nge in der Siebpartie, 1998. Retrieved Jun. 6, 2010. URL: http://www.omya.de/web/omya_at.nsf/Attachments/ DC167D8418BDC7D4C1256B6D0045017B/$FILE/Omyape1.pdf. (5) Nelson, K.; Deng, Y. Effect of polycrystalline structure of TiO2 particles on the light scattering efficiency. J. Colloid Interface Sci. 2008, 319, 130–139. (6) Hubbe, M. A.; Pawlak, J. J.; Koukoulas, A. A. Paper’s appearance: A review. BioRes. 2008, 3, 627–665. (7) Ragauskas, A. J.; Deng, Y.; Jones, P.; White, D. Modified Fillers for Enhanced Paper Performance. Retrieved Mar. 11, 2010. URL: http:// www.ipst.gatech.edu/faculty_new/faculty_bios/ragauskas/posters/ 0501011_Modified%20Filler.pdf. (8) Beazley, K. M. Fillers - A Brief chronological review. Pap. Technol. 1985, 26 (6), 266–268. (9) Hubbe, M. A.; Gill, R. A. Filler particle shape vs. paper properties - A review. Proceedings from TAPPI Paper Summit - Spring Technical and International EnVironmental Conference 2004, 141–150. (10) Wilson, I. Fillers and coating pigments for papermakers. Retrieved Oct. 10, 2010. URL: http://wakaolin.com/Website%20pdfs/ IRW%20PAPER%20PIGMENTS%20%20SME%202006.pdf. (11) Laufmann, M. Fillers for paper: A global review. PTS-Seminar on Wet End Operations - Vorga¨nge in der Siebpartie, 1998. (12) Marchessault, R. H.; Rioux, P.; Ricard, S. Preparation and synthesis of magnetic fibers. U.S. Patent 5143583, 1992. (13) Marchessault, R. H.; Rioux, P.; Raymond, L. Magnetic cellulose fibres and paper: Preparation, processing and properties. Polymer 1992, 33, 4024–4028. (14) Liu, Q. Paper with magnetic property and its manufacture method. Chinese Patent 1125797, 1996. (15) Iwasaki, S.; Nagasawa, O.; Takano, T.; Matsumoto, S. Magnet paper sheet and a method for manufacturing the same. U.S. Patent 4234378, 1980.

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ReceiVed for reView September 13, 2010 ReVised manuscript receiVed November 18, 2010 Accepted November 29, 2010 IE1021078