Fly Ash from Lignite Combustion as a Filler for Rubber Mixes. Part I: Physical Valorization of Fly Ash

Abstract

The potential use of fly ash (FA) originating from lignite combustion at the Belchatow Power Plant (Poland) as filler for rubber mixes was evaluated. Samples of fly ash collected from heaps created in different years were compared according to their chemical and phase composition, particle size distribution, and morphology. The sieve fractionation of fly ash results in size fractions of different chemical structures, phase compositions, and morphologies, reflected in changes to their specific surface area, surface energy, and activity in rubber mixes. Fractionation turned out to be more effective than grinding from the point of view of using ash as a filler for rubber mixes, because it results in higher specific surface area (SSA) and chemical composition differentiation. Carbon black can be replaced by up to 40% by weight with the fly ash fraction (FFA) of dimensions below 125 µm, without any significant deterioration in the mechanical properties of styrene butadiene rubber (SBR) vulcanizates filled with 50 phr of active carbon black (N 220). Despite the larger fly ash fraction of grain dimensions in the range between 125 and 250 µm presenting the highest specific surface area, the particle size adversely affects its strengthening effect in rubber. Taking into account all the tests performed, ranging from morphology, Payne effect and bound rubber, to mechanical and abrasion tests, the highest potential effectivity is presented by a sample containing 30 phr of N 220 and 20 phr of FFA of grain sizes from 63 to 125 µm. The obtained results indicate that fractionation seems to be an effective physical method of fly ash valorization.

Fly Ash from Lignite Combustion as a Filler for Rubber Mixes—Part II: Chemical Valorisation of Fly Ash

“…In this sense, there are many scientific papers devoted to the modification of fly ash and its use as a carbon black substitute. The novelty of the proposed approach to FA valorization is based on the fact of the existence of significant differences in the chemical and phase composition between its fractions, confirmed in our previous work [ 28 ]. In this paper, we decided to check the efficiency of silanization in relation to selected ash fractions and its impact on the mechanical properties of rubber with their participation.…”

“…The selection of silane binders was guided by the possibility of a chemical reaction between the functional groups present on the surface of various ash fractions, determined on the basis of their phase analysis [ 28 ] as well as their ability to participate in rubber crosslinking.…”

“…Fly ash A (sample collected in 2017) was selected for further research, due to the higher content of its silicon compounds and theoretically better potential to be a reinforcing filler. This type of fly ash was characterized and investigated for rubber reinforcement in our previous study [ 28 ]. Fractionation of the fly ash was performed using a laboratory sieve shaker LPzE-3e (MULTISERW-Morek Ltd., Brzeźnica, Poland), operating with 0.250, 0.125, and 0.063 mm sieves.…”

“…The measurement error was calculated using the Student’s t -test for α = 0.005. Based on the results of the first part of the publication [ 28 ], it turns out that the best results were obtained for ashes of small and medium grain size: FA < 0.063 mm, 0.063 < FA < 0.125 mm, and 0.125 < FA < 0.250 mm. They have been selected to evaluate the effectiveness of various silane binders in rubber mixes.…”

“…The first part of the work [ 28 ] concerned the use of various ash fractions as a filler for rubber mixtures. A different chemical and phase composition of FA fractions with different grain sizes was found and their influence on the properties of rubber mixtures with their participation was investigated.…”