Effects of pulverized coal fly-ash addition as a wet-end filler in papermaking

This experimental study is based on the innovative idea of using pulverized coal fly ash as a wetend filler in papermaking. This is the first evaluation of the possible use of fly ash in the paper industry. Coal-based thermal power plants throughout the world are generating fly ash as a solid waste product. The constituents of fly ash can be used effectively in papermaking. Fly ash has a wide variation in particle size, which ranges from a few micrometers to one hundred micrometers. Fly ash acts as an inert material in acidic, neutral, and alkaline papermaking processes. Its physical properties such as bulk density (800–980 kg/m3), porosity (45%–57%), and surface area (0.138–2.3076 m2/g) make it suitable for use as a paper filler. Fly ash obtained from thermal power plants using pulverized coal was fractionated by a vibratory-sieve stack. The fine fraction with a particle size below 38 micrometers was used to study its effect on the important mechanical-strength and optical properties of paper. The effects of fly ash addition on these properties were compared with those of kaolin clay. Paper opacity was found to be much higher with fly ash as a filler, whereas brightness decreased as the filler percentage increased. Mechanical strength properties of the paper samples with fly ash as filler were superior to those with kaolin clay.