Effect of replacement of calcium carbonate by fly ash on processability and thermo-mechanical properties of solid tire middle compounds

Abstract

In this study, as the first step, the effect of partial replacement of CaCO3 with unmodified fly ash on the curing characteristics of the solid tire middle compound and the properties of its vulcanizate was investigated. Fly ash and CaCO3 were first characterized. A series of solid tyre middle compounds with varying CaCO3 / fly ash loading were prepared in a laboratory-scale internal mixer. The total content of non-reinforcement filler was kept constant. Fly ash loading was increased from 0 to 60 pphr intervals with replacing CaCO3. The dispersion level was evaluated using the α view and SEM studies. Curing characteristics of the compounds were evaluated. Filler dispersion levels of the compounds and mechanical, rheological and physical properties of the respective vulcanizates were then focused. The unmodified fly ash filled rubber compound with optimum filler loading was selected based on the above properties. In the second step of the study, the same studies were carried out with a smaller particle size (modified) fly ash filled NR compounds loaded with the selected filer loading. It was shown that dispersion level was reduced with the addition of fly ash. Dispersion was improved with the incorporation of fly ash with reduced particle size and narrow particle size distribution. SEM studies showed a higher tendency of particle agglomeration with increasing loading of fly ash. It was found that MH and ML values of the rubber compounds were deteriorated with the increase of unmodified fly ash loading and the values were improved when fly ash with smaller particle size was used. However, no impact was observed on curing characteristics either with the replacement of CaCO3 with fly ash, it's loading nor their sizes. The hardness of the vulcanizates of the unmodified fly ash incorporated compounds was increased with the increase of fly ash percentage. Tensile strength, tearing strength, elongation at break and modulus showed a general reduction with the increase of unmodified fly ash except for tear strength, which had reduced only up to 45 pphr and shown a slight increase in 60 pphr of fly ash added sample. When the overall performance was considered, rubber compounds and vulcanizates prepared with 30 pphr fly ash loading showed the most comparable properties. Studies carried out in the second stage, it was found that physical properties were improved with the use of fly ash with smaller particle size and narrow particle size distribution (0-53 μm) compared to unmodified fly ash incorporated compounds. Rebound resilience values were reduced with the increase of the fly ash percentage. Dynamic mechanical properties such as heat build-up and blowout time were deteriorated with the addition of unmodified fly ash and results were improved with the use of small particles of fly ash. Tan delta value which depends on loss modulus and storage modulus shows a neutral role. Based on the study, it was concluded that there is a potential to replace 50% w/w (i.e. 30 pphr) of the CaCO3 loading from the fly ash with smaller size particles without a significant adverse effect on the curing, physical, mechanical and rheological properties.