No abstract

It is well recognized globally that the footwear industry contributes to a large waste stream throughout its life cycle. This article reviews the literature pertaining to the life cycle of footwear products and their End-of-Life (EoL) management strategies. The review discusses critical aspects of the footwear industry, commencing with a background on the growth and consumption of footwear products across the globe. The review provides an overview of the environmental impacts of different footwear materials across their life cycles. In this regard, leather materials are given intense focus due to their poor environmental performance. The review further examines proactive and reactive approaches to footwear waste management, whilst additionally exploring the challenges facing EoL footwear recovery. Finally, pyrolysis is examined as a thermochemical treatment process with value due to its potential to recover materials from post-consumer footwear. The significant findings in this review paper are as follows: (a) leather footwear materials have the most detrimental environmental impacts across their life cycle; (b) there is limited scientific literature on thermochemical processes (particularly pyrolysis) as waste recovery options for post-consumer footwear; and (c) several challenges face the recovery of post-consumer footwear products, including inefficient reverse logistics, mixed product recycling and difficulties establishing a value recovery chain. This review paper recommends further research on pyrolysis as a potential post-consumer footwear recovery option. Exploring the viability of new avenues for footwear waste recovery is significant due to its potential to divert this waste stream from landfills and allow a progression toward a more circular economy.

Majority of post-consumer leather footwear currently ends up in landfill sites with adverse environmental impacts. Current waste recovery options have proven largely unsuccessful in minimizing this waste stream. This study investigates whether leather from post-consumer footwear can be pyrolyzed using gram-scale (fixed-bed) and microgram-scale (TGA) pyrolysis reactors. The investigation was conducted using final pyrolysis process temperatures between 450 and 650 °C and solid residence times of 5 to 15 minutes. The purpose of the experiments was to assess the waste recovery potential of leather pyrolysis products for valuable chemicals. The pyrolysis product fractions (solid, liquid, and gas) distribution were investigated, optimal pyrolysis conditions presented, and the product fractions characterized for their elemental and chemical composition using ultimate and GC-MS analysis. The distribution of the product fractions proved leather footwear pyrolysis was viable under the given conditions. The completion of leather footwear pyrolysis was evident at 650°C since the solid yield reached a constant value of approximately 25 wt.%. The liquid fraction was maximized within the temperature range of 550-650°C (Max= 54 wt.%), suggesting optimal pyrolysis conditions within this range. The higher heating values (HHVs) of the pyrolysis leather oil (33.6 MJ/kg) and char (25.6 MJ/kg) suggested their potential application for energy or fuel. The liquid fraction comprised predominantly of nitrogen derivatives and potential applications areas include use in the production of fertilizers, chemical feedstocks, or the pharmaceutical industry. This study proved that leather from post-consumer footwear can be pyrolyzed and provided valuable insight into its characterization and potential applications areas.