Effect of free foaming and pre-curing on the thermal, morphological and physical properties of reclaimed tyre rubber foam composites

Abstract Foaming of rubber is a well-known technique and foamed rubber products have found application in various industries including cushioning, heat insulation and sound absorption. In the current study, the foaming of reclaimed tyre rubber (RTR), as an alternative to virgin rubber, is explored. The effect of varying the amounts of waste ethylene vinyl acetate (filler), sodium bicarbonate (blowing agent) and dicumyl peroxide (co-curative) on the RTR properties was studied. Composites formulations were obtained by use of the simplex-lattice mixture design and the samples were prepared by following two foaming techniques namely, prepressing and free foaming. Hardness of free foamed samples was found to be lower than that of prepressed samples, owing to effective foaming and the formation of multiple microcells in the former. An increase in blowing agent content resulted in decreased density and thermal stability of the foamed composites. Dicumyl peroxide caused an increase in density but had no effect on thermal stability. The incorporation of a filler in formulations effected an increase in the gel content and thermal stability of the foams. Free foamed samples exhibited higher shrinkage with an increase in both waste ethylene vinyl acetate and sodium bicarbonate. However, dicumyl peroxide significantly increased the shrinkage of prepressed samples, whereas sodium bicarbonate decreased the gel content and thermal stability of both free foamed and prepressed samples. It is demonstrated in the current work that both foaming processes are applicable for RTR and the choice of the processing method is dependent on the desired properties of the composites.