EFFECT OF PARTICLE SIZE OF MAGNESIUM SILICATE FILLER ON PHYSICAL PROPERTIES OF PAPER Vipul Singh Chauhan, 1 Nishi Kant Bhardwaj 1 * and Swapan Kumar Chakrabarti 2 1. Department of Paper Technology, Indian Institute of Technology Roorkee, Saharanpur Campus, Saharanpur 247 001, Uttar Pradesh, India 2. Thapar Centre for Industrial Research & Development, Yamuna Nagar 135 001, Haryana, India Fillers are essential component of printing papers to increase the opacity, brightness, and to improve formation and printing properties. As a very little work has been reported so far on magnesium silicate (talc), the study was conducted with the filler of different particle size for papermaking. The sheets were made in the laboratory with refined mixed hardwood chemical pulp with five grades of talc, ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC) fillers with 15–24% ash level. Apparent density along with tensile, burst, tear index, Z-direction tensile strength (ZDTS) and bending stiffness index were evaluated for talc filled sheets, and compared with GCC and PCC. Physical strength properties of talc filled sheets were decreased at a faster rate on increasing filler loading in paper and decreasing the particle size of the filler. With same type of filler its particle size determines the physical properties of paper. The postulate was not found to be valid for all the three varieties of fillers viz., talc, PCC and GCC. Shape and geometry of the PCC and GCC fillers determine the individual property. Keywords: magnesium silicate, particle size, calcium carbonate, inter-fibre bonding, paper strength INTRODUCTION C onsiderable amount of inorganic mineral fillers is used along with fibres for the production of paper. Fillers are highly desirable in printing papers; these increase the opac- ity, raise the brightness and improve printing properties. The use of fillers is particularly important when opacity is needed at a low-basis weight. It also decreases the energy demand in paper- making process due to lesser usage of fibrous mass per unit weight of paper (Chauhan et al., 2011). The mineral fillers for acid papers are talc, hydrous kaolin, cal- cined kaolin, precipitated silica and silicates and titanium dioxide. For neutral and alkaline papers, talc, hydrous kaolin, calcined kaolin, ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), silica and silicates and titanium dioxide are used. The shape of GCC particles is generally blocky, whereas PCC can be produced in various crystal shapes including scalenohe- dral, rhombic and aragonitic. Mechanically processed pigments like GCC or kaolin usually have wider particle size distribution (PSD) than chemically precipitated products like PCC. However, now-a-days finer grades of GCC are also available commercially and being used for the production of premium grades of paper. The spherical hollow particles of PCC were produced and used as filler in paper to increase the brightness of paper (Enomae and Tsujino, 2004). Talc, a magnesium silicate mineral (Mg 3 Si 4 O 10 -(OH) 2 ) usually occurs in foliated, granular or fibrous form. It is characteristically inert and the softest mineral on earth (Cavanagh and Bates, 1994). Compared to other silicates, talc is relatively hydrophobic due to the oxide surfaces (M¨ alhammar, 1990). The key considerations in filler selection include the effect of the filler on paper quality, raw material costs, machine produc- tivity and chemical consumption. The key pigment properties are brightness and shade, PSD and shape of the particles. Size- dependent effects include light-scattering efficiency, abrasiveness and strength loss. The tendency to weaken paper is proportional to the specific surface area of filler. It is reported that the filler weakens paper through decreasing the inter-fibre bonding; this effect gets increased with the decrease in particle size of filler (Fairchild, 1992; Adams, 1993; Han and Seo, 1997; Krogerus, 1999; Kinoshita et al., 2000). Thick particles have a more dramatic strength-lowering influence than do flat particles (Li et al., 2002). The effect of available surface area of fibres with ∗ Author to whom correspondence may be addressed. E-mail address: nishifpt@iitr.ernet.in Can. J. Chem. Eng. 9999:1–7, 2012 © 2012 Canadian Society for Chemical Engineering DOI 10.1002/cjce.21708 Published online in Wiley Online Library (wileyonlinelibrary.com). | VOLUME 9999, 2012 | | THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING | 1 |