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.
To improve the bondability between clay filler and lignocellulosic fiber, Kaolin clay particles were modified using a starch−fatty acid complex method. The coating efficiency of starch on clay particle surfaces was investigated by measuring the dissolved starch in the supernatant. The experimental results indicated that more than 98% of the applied starch was precipitated onto the surface of the filler, and the resulting starch−fatty acid−clay composites had relatively good resistance against moderate shear force. The morphology, particle size, and ζ potential of the starch modified filler were also determined with scanning electron microscopy, Malvern particle size analyzer, and Malvern Zetasizer, respectively. An aqueous slurry of linerboard pulp containing 5−15 wt % modified fillers was used for handsheet preparation, and the effects of the addition of modified filler on the paper properties were studied. At a dosage of 10% of the modified filler (based on filler), the retention of the filler was higher than 75%. The strength properties of paper with starch modified fillers were improved by approximately 15% when compared against those of paper with unmodified fillers.
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