Carbon nanomaterials as additives to ethylene vinyl acetate copolymer foams for sport footwear applications

Abstract Ethylene vinyl acetate (EVA) copolymer foams with addition of 1.0, 2.5, and 5 wt% of carbon nanomaterials (graphene, graphene oxide, carbon nanotubes, and multiwalled carbon nanotubes) were fabricated. Properties of these foams were compared with reference sample (no additives) and samples containing carbon black. The following properties of these samples were examined: density, compressive stress (50% compression), impact behavior, thermal conductivity, and hydrophobicity. The morphology was studied using scanning electron microscopy. The samples were additionally characterized using thermal gravimetric analysis and differential scanning calorimetry. Increasing weight percentage of carbon‐based additives led to foam structure with lower porosity and higher density. Samples with a higher degree of cross‐linking were less dense (~10%) as compared to the reference sample and also displayed better mechanical and thermal properties. Increasing weight percentages of additives led to higher compressive strength and higher energy absorption. Samples with 5 wt% of additives and increased quantity of cross‐linking agent exhibited great mechanical properties. Despite their lower density, these samples had higher values of compressive stress, 10%–15% higher than those of the reference sample, and higher energy return properties. All samples follow the trend of increasing values of compressive strength with the increase in density, for some samples, this correlation has quasi linear character. The obtained results show that EVA foams with the addition of carbon black, graphene, carbon nanotubes, and multiwalled carbon nanotubes have properties desirable in high‐performance materials for sport footwear soles. Multiwalled carbon nanotube additives could be incorporated at low weight percentages and low degree of crosslinking into EVA matrix to achieve lower density and enhanced energy repulsion and cushioning effects.