Utilizing spent coffee grounds as a bio-based source for natural rubber: An alternative to synthetic leather

Over 6 million tons of spent coffee grounds (SCG) are generated annually worldwide, contributing to methane emissions and landfill pollution. This study demonstrates the use of recycled SCG as a bio-additive in natural rubber (NR) to create a sustainable alternative to bovine and synthetic leather. The developed NR-SCG composite mimics bovine leather in appearance and demonstrated superior mechanical properties, including isotropic tensile strength with less than 5.00% variation across directions, while bovine and synthetic leather showed that of 39.45% and 44.52%, respectively. This uniformity enables pattern pieces to be oriented in any direction, providing improved utilization efficiency, reduced waste, and enhanced design flexibility for complex geometries. The composite also demonstrated soil burial biodegradation within 2 months. The carbon footprint assessment revealed that NR composite with SCG 25 parts by weight per hundred parts of rubber (NR-SCG25) has a significantly lower carbon footprint of 3.22 kgCO 2 eq/m 2 , approximately 5.3 times lower than bovine leather and 4.9 times lower than polyurethane leather. This innovation offers an eco-friendly and high-performance material for sustainable design.