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The main purposes of filler addition in papermaking are to improve paper properties and reduce cost. The cost reduction is attributed to the low cost of the filler itself and to the energy savings that occur during the papermaking process. In this work, the effects of clay filler addition on the energy savings during the papermaking process, including water drainage, pressing, and drying, were systematically investigated. Experimental results indicated that the addition of filler could dramatically increase the drainage rate and the water removal rates during pressing and drying. With 20% filler addition, the drainage time decreased by 20% compared to the unfilled paper. At a filler content of 23%, the solids content of the handsheets after pressing increased at least 5 absolute points, and the drying rates increased by 20%. All these improvements can offer considerable benefits for paper mills, including enhanced machine speeds and large energy savings. [ABSTRACT FROM AUTHOR]

To increase the filler content in paper without sacrificing paper properties, clay−starch composites, made from a simple precipitation method, were used in papermaking. Compared to untreated clay, the clay−starch composite filled paper improved paper tensile strength up to 100−200%. Contrary to untreated clays that usually reduce the ZDT (z-directional tensile strength) of papers, the clay−starch composite actually increases the ZDT. The significant improvements in the paper strengths are attributed to the formation of a fiber−starch−filler sandwich structure, which avoids direct contact between filler and fiber. The specific shear bond strengths (expressed as specific bond strengths) between fillers and fibers were measured and used as the main variables for the modeling. It was also found that the fiber−fiber specific strength is weaker than the fiber−starch specific bond strength. The tensile strength (expressed as breaking length) was modeled by using a modified Page equation. The experimental results agreed very well with the modeling results. [ABSTRACT FROM AUTHOR]