Sports shoe maker adopts cellulose nanofiber-reinforced compound in midsole

Wood pulp-derived cellulose nanofibers (CNFs) are five time lighter than steel and exhibit five times the strength of the latter. Research and development efforts into their use as reinforcing agents for thermoplastics have been active for many years in Japan and these efforts now appear to be bearing fruit.

Leading Japanese sports shoe manufacturer Asics is one of the early adopters of a CNF-reinforced compound, sourcing Starcel material from compounder Seiko PMC, also based in Japan, for use in its Gel-Kayano 25 running shoe. Asics blends the Starcel compound with its FlyteFoam Lyte thermoplastic polyamide (TPA) elastomer to improving durability by around 7% and strength by approximately 20%, as well as enhance the cushioning effect. FlyteFoam Lyte is 55% lighter than the ethylene-vinyl acetate (EVA) resin normally used in sports shoe midsoles.

Starcel technology was developed at Seiko PMC based on work conducted as part of a Japanese Government-funded project at coordinated by the New Energy and Industrial Technology Development Organization (NEDO). In October 2014, Seiko PMC started up a pilot plant in Ibaraki Prefecture for the production of CNF-reinforced composite materials based on polypropylene (PP), polyethylene (PE), and other resins. Capacity was expanded to a commercial scale of around 200 tonnes/year (70 tonnes/year of CNF) at the end of 2017.