Effect of free foaming and pre-curing on the thermal, morphological and physical properties of reclaimed tyre rubber foam composites Mapoloko Mpho Phiri * , Motshabi Alinah Sibeko, Mohau Justice Phiri, Shanganyane Percy Hlangothi Centre for Rubber Science & Technology, Department of Chemistry, Nelson Mandela University, Port Elizabeth, South Africa article info Article history: Received 25 June 2018 Received in revised form 30 January 2019 Accepted 5 February 2019 Available online 6 February 2019 Keywords: Foamed composites Waste EVA filler Dual-curing Reclaimed tyre rubber composites Mixture design Shrinkage 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 ob- tained 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. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction Waste management protocol advocates for recycling and re-use of waste materials through conversion into value-added products (CIWMB, 2003). Two of the industries producing the most solid waste are the tyre and shoe industries due to waste generated on the production line and at the end of the useful life of the products. The disposal of solid waste generated from these industries has become a global concern because of the crosslinks formed during their compounding processes, which inhibits both environmental and bio-degradation upon disposal (European-Commission, 2008). In the case of tyres, the problem is exacerbated by the use of sta- bilizers and additives during compounding, making tyres more stable under different environmental conditions. There have been countless studies dealing with the re-use of waste produced by each of these industries. Waste tyres have been recycled in the form of rubber crumbs for use in various applications such as, as a filler in lightweight construction applications (Herrera-Sosa et al., 2015). For example, rubber crumbs modified asphalt/bitumen was found to have improved resistance to permanent deformation at elevated temperatures and cracking resistance at low temperatures when rubber crumbs were added to the hot aggregate prior to bitumen (dry process). This also decreased stability and flow of the asphalt upon blending with the waste tyre rubber crumbs (Tai Nguyen and Nhan Tran, 2018). For further reading, a review by (Lo Presti, 2013) is recommended. Crumbs have been used as fillers in thermoplastic matrices (Montagna and Santana, 2012), and as an infill in artificial turf fields (Peterson et al., 2018). The waste tyre rubber crumbs use as fillers in foamed composites have been shown to aid in the foaming process of foamed portland cement (Eiras et al., 2014), foamed polyurethane (Zhang et al., 2013), and foamed low density polyethylene (Zhu et al., 2011). Another method of recycling waste rubber material, which has * Corresponding author. E-mail address: s218213956@mandela.ac.za (M.M. Phiri). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro https://doi.org/10.1016/j.jclepro.2019.02.051 0959-6526/© 2019 Elsevier Ltd. All rights reserved. Journal of Cleaner Production 218 (2019) 665e672