Applied Materials Today 36 (2024) 102016 Available online 14 December 2023 2352-9407/© 2023 Elsevier Ltd. All rights reserved. Enhancing dynamic energy return and performance of running shoes: Replacing talc with multi-walled carbon nanotubes derived from plastic wastes in midsole foam Boon Peng Chang a , Aleksandr Kashcheev a , Andrei Veksha b , Grzegorz Lisak b, c , Ronn Goei a , Kah Fai Leong d , Alfred ling Yoong Tok a, * , Vitali Lipik a, * a School of Materials Science & Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore b Residues and Resource Reclamation Centre (R3C), Nanyang Environment and Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, Clean Tech One, 637141, Singapore c School of Civil & Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore d School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore A R T I C L E INFO Keywords: Ethylene-vinyl acetate Multi-walled carbon nanotubes Nanocomposite foams Foaming Dynamic impact response Dynamic fatigue ABSTRACT Boosting both the lightweight and rebound of a shoe’s midsole without compromising its durability is regarded as a challenging aspect of developing excellent running shoes. This study explores the replacement of talc, a conventional reinforcing and nucleating agent for polymers, with multi-walled carbon nanotubes (MWCNTs) derived from plastics in the midsole foam of running shoes to enhance lightweight, rebound, and durability. Two types of MWCNTs, non-functionalized and oxygen-functionalized, derived from upcycling mixed plastics were processed with copolymer of ethyl-vinyl acetate (EVA) to create nanocomposite foams. The foam reinforced with non-functionalized MWCNTs exhibited higher dynamic stiffness and similar energy return to oxygen- functionalized MWCNTs. The running shoe prototypes with EVA midsole foam containing 0.5 wt% MWCNTs was 13 % lighter and returned more than 10 % higher energy than the conventional EVA midsole foam with mineral fillers. Additionally, the midsole foam produced from EVA/MWCNTs demonstrated greater flexibility, and durability after 500 km of dynamic impact cycles. The cost difference per pair of running shoe midsole is merely 0.08 USD, considering the exceptional performance of the EVA/MWCNTs midsole as compared to con- ventional mineral filled EVA midsole. These findings indicate the potential for commercializing EVA/MWCNTs nanocomposite foam as a viable option for high-performance running shoe midsoles, offering athletes improved running performance. 1. Introduction Lightweight, responsive, and bouncy polymer foams are highly desirable for running shoe midsole applications. These polymer foams are typically closed cell structures containing gas as a dispersed phase within the polymer. Foamed copolymers of ethylene-vinyl acetate (EVA) and thermoplastic polyurethane (TPU) are two popular materials that are commonly used in footwear. Although the resilience and shock- absorbing properties of these two polymers are great for midsole foam materials, their foam’s responsiveness, density, and rebound are still required improvement for better running performance and durability. The foaming technique and foaming ingredients are the key aspects for tuning the foam’s properties and performance. Running shoes have experienced major developments over the years, from simple designs to a highly dedicated products of today. To date, several strategies of footwear design for midsole technologies have been developed to improve the running endurance and performance of trainers. This in- cludes the boost technology from Adidas, ZoomX foam from Nike, Super DNA foam from Brooks, U4iCX light EVA midsole from Mizuno, and supercritical NITRO foam from PUMA. The interest in the lightweight, comfortable, and improved running performance of footwear for a better exercise experience has increased lately. Polymer nanocomposite foams with the use of various nano- materials are gaining much attention in addressing this context. The * Corresponding authors. E-mail addresses: MIYTok@ntu.edu.sg (A.Y. Tok), Vitali@ntu.edu.sg (V. Lipik). Contents lists available at ScienceDirect Applied Materials Today journal homepage: www.elsevier.com/locate/apmt https://doi.org/10.1016/j.apmt.2023.102016 Received 18 July 2023; Received in revised form 7 November 2023; Accepted 5 December 2023