Utilization of high and low calcium oxide fly ashes as the alternative fillers for natural rubber composites: A waste to wealth approach

Recently, fillers from renewable resources or agricultural wastes have been considered as the alternative fillers to reduce the environmental problems. Therefore, utilization of the fly ashes (FA) collected from the electric power plants as the reinforcing filler in natural rubber (NR) composites was carried out and compared these high (HCaO) and low (LCaO) calcium oxides with carbon black (CB). The FA concentration was varied up to an optimum loading of 1000 parts per hundred rubber (phr) by using melt mixing technique. Particle size and chemical composition of HCaO and LCaO were reported and the properties of NR composites in terms of cure characteristics, Payne effect, mechanical and dynamical properties together with morphologies were examined. It was found that the addition of HCaO significantly reduced the vulcanization time of the NR composites, while the one with LCaO provided higher degree of reinforcement efficiency to the NR matrix. It clearly supports the relation of storage modulus as a function of strain sweep and their morphologies, which are the major requirements in case of composites. Upon increasing of FA loading, NR has changed its role from rubber matrix to an adhesive binder and therefore the Young’s modulus was found to be strongly changed. FA can be used to replace CB in NR composites with the composition ratios starting from 1:2–1:6 phr. Although, CB exhibited a slightly better reinforcing effect than FA, based on the lowered glass transition temperature (Tg), Tan delta (Tan δ) exhibited the same elasticity and CB can be replaced in case of several CB-based composites, particularly, the artificial wood, car stopper and tire industries to produce rubber belt and bead. [Display omitted] •Proper ratio of FA and CB using in the NR composites is first established.•Effect of CaO in both FA types is effectively modeled and examined.•Extremely high FA loading of 1000 phr was investigated and characterized.•The results clearly summarized the different reinforcement mechanism.•FA waste can replace several CB applications with competitive FA contents.