Polymer foam that provides good support with high energy return (low energy loss) is desirable for sport footwear to improve running performance. Ethylene-vinyl acetate copolymer (EVA) foam is commonly used in the midsole of running shoes. However, EVA foam exhibits low mechanical properties. Conventional mineral fillers are usually employed to improve EVA’s mechanical performance, but the energy return is sacrificed. Here, we produced nanocomposite foams from EVA and multi-walled carbon nanotubes (CNT) using a chemical foaming process. Two kinds of CNT derived from the upcycling of commodity plastics were prepared through a catalytic chemical vapor deposition process and used as reinforcing and nucleating agents. Our results show that EVA foam incorporated with oxygenated CNT (O-CNT) demonstrated a more pronounced improvement of physical, mechanical, and dynamic impact response properties than acid-purified CNT (A-CNT). When CNT with weight percentage as low as 0.5 wt% was added to the nanocomposites, the physical properties, abrasion resistance, compressive strength, dynamic stiffness, and rebound performance of the EVA foams were improved significantly. Unlike the conventional EVA formulation filled with talc mineral fillers, the incorporation of CNT does not compromise the energy return of the EVA foam. From the long-cycle dynamic fatigue test, the CNT/EVA foam displays greater properties retention as compared to the talc/EVA foam. This work demonstrates a good balanced of mechanical-energy return properties of EVA nanocomposite foam with very low CNT content, which presents promising opportunities for lightweight–high rebound midsoles for running shoes.
Samples of ethylene vinyl acetate (EVA) co‐polymer foams in form of plates and industrial outsoles of prototyped sport shoes containing 0% (reference), 2.5%, and 5.0 weight % (wt%) of hollow glass microspheres (HGM) were made. The goal was to study the influence of HGM on properties of EVA foam in laboratory conditions followed by the industrial trial, where the most promising laboratory result was applied. The physical properties of samples and behavior of material under dynamic load were examined. EVA foams with HGM filler demonstrated that they have better ability to reduce impact peak force and increase absorb impact impulse compared to the reference foam without HGM. Addition of 5.0 wt% of HGM in laboratory foam increased its absorbed impact pulse by two‐fold. Meanwhile for industrial prototype outsoles, the impact peak force was reduced by 5%–7% in walking simulated conditions and by 11% in case of simulated running. It is also observed that, addition of 5.0 wt% of HGM in EVA foam increased its abrasion resistance by three times, which generally helps to increase the lifetime of sport footwear. Under dynamic load, samples with the addition of HGM behave interestingly and result shows a small decrease in energy return (7%) which is logical, because this composite tends to absorb energy and not return it. Samples with 2.5 wt% HGM are stiffer than reference until 40% compression deformation, but beyond that point it becomes softer, and better absorbs impact energy than reference. Outsole with 2.5% of HGM in EVA outsole increased resistance of shoe at lateral bending of 50% and 20% rise of resistance was found at medial twist. Impact absorption and flexibility resistance are useful for protection against impact which are also helpful to prevent sport injuries. The obtained results show the addition of HGMs which are cheap by‐products in several technologies brings improvement to properties of EVA foams which is the most common materials for the sport footwear industry.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.