Self-bonded coconut shell biocomposites for sustainable applications

Abstract

The widespread use of petroleum-based polymers raises environmental concerns due to their non-biodegradability and their retention in ecosystems. Developing sustainable alternatives that balance functionality and eco-friendliness is, therefore, critical. In this study, coconut shell powder (CSP), an abundant agricultural by-product, was employed to fabricate a self-binding, coating-free biocomposite via acetic acid pre-treatment and a simple thermal moulding process. Pre-treatment of CSP with 20 vol% acetic acid effectively loosened the lignocellulosic matrix, enabling reshaping of CSP under thermal compaction at 16 MPa and 150°C for 30 minutes, resulting in intrinsic binding and the in situ formation of a protective carbonised surface layer. Smaller particle sizes further enhanced densification. Under optimised processing parameters, the composite exhibited a maximum compressive strength of 78 N/mm² with a compressive modulus of 1378 MPa. The surface had an average Vickers hardness of 42 HV20. Furthermore, after immersing in water for 24 hours, water absorption plateaued at around 4%. The resulting external binder and coating-free biocomposite shows potential as a sustainable substitute for plastics.