Fly ash based composite fillers modified by carbonation and the properties of filled paper

With the major crystal phases of gehlenite, anhydrite and calcite in high whiteness, original fly ash (OFA) was considered as a kind of possible paper filler. But the high solubility, broad size distribution and some doped chromophoric particles restrain the substitutability of traditional fillers. There was an exciting whiteness improvement of more than 50% by precipitating thin calcium carbonate layers on the surface of OFA particles in a Ca (OH)2-H2O-CO2-Fly Ash system, to obtain the fly ash based composite fillers. The composite fillers modified from different size OFA were filled into handsheets, and the filling performances were evaluated and compared with ground calcium carbonate (GCC). Relatively, smaller particles whose volume average size was less than 28.6 produced an efficient coating after modification, especially the 9.88 m OFA particles, on which the thickness of modified layers could reach 1.61 μm. Papers filled with efficiently coated composite fillers showed higher opacity and bulk, better tensile and bursting strength, but were a little worse in the property of whiteness. Due to the special structure of surface calcium carbonate layers produced by heterogeneous nucleation and crystal growth through carbonation, fly ash based composite fillers exhibited an obvious potential for replacing GCC without considering whiteness. © 2017 De Gruyter Open Ltd. All rights reserved.