Advanced use of waste rubber and fly ash to ensure an efficient circular economy

Abstract

The manufacture of high-performance products that have in their structure both rubber waste and fly ash represents the objective of the research which is a common one with that of the international community, in order to be able to ensure an efficient circular economy for the waste. Research has focused on the creation of new composite materials that contain as large amounts of fly ash as possible, respectively materials obtained from the processing of rubber waste. Thus, during the research, the use of a fairly large proportion of fly ash (30 phr), but also reclaimed rubber (25 phr) and rubber powder with size 80–100 µm (15 phr) was considered. The new composite materials were tested from several points of view, with the aim of determining their properties, but also the possibilities of use in different applications. Thus, the microscopic structure (SEM) was analyzed to observe how the connections between fly ash and rubber are made, but also how they behave in thermal shocks, the evolution of hardness, respectively the adhesion of dirt particles on the surface of the samples. The tests performed have shown that by using a KWQ coupling agent, a fairly homogeneous structure of the materials can be obtained, with a very good incorporation of the fly ash into the rubber matrix. It has also been demonstrated that by using fly ash in combination with reclaimed rubber or rubber powder, a very good topography of the surface layer of the samples can be obtained, which prevents dust from adhering to the surfaces of products containing a large amount of fly ash or regenerated rubber. It is noteworthy that composite materials containing a large amount of fly ash (FA) and regenerated rubber retain their properties very well after applying an aging process. Thus, the use of FA and regenerated rubber allows to obtain composite materials that have an aging elasticity loss of only 0.4% compared to rubber without FA, when this loss of elasticity was 25.5%. At the same time, the use of a suitable coupling agent allows the creation of new materials that have a fairly high hardness, without the addition of fly ash and regenerated rubber causing a large reduction in hardness. It is noteworthy that the reduction in hardness was very low, from 790ShA for the rubber without fly ash to 740ShA for the rubber containing FA. The rubber mixtures used in the research were also subjected to a TGA-DTGA analysis demonstrating that the addition of an optimal amount of FA ensures a weight loss comparable to that of rubber mixtures that do not contain FA. Thus, it was demonstrated that an efficient circular economy can be ensured for waste from rubber products as well as for FA.