Flame retardant and Moisture Adsorption Behaviour of Kenaf/Flax/Coconut-Shell Biochar Based Hybrid Composites

^{1,3,4 & 5} Department of Mechanical Engineering, School of Engineering, Mohan Babu University, Tirupati- 517 102, Andhra Pradesh, India.
² Department of Mechanical Engineering, University Centre for Research and Development, Chandigarh University, Gharuan, Mohali-140 413, Punjab, India.
⁶ Department of Mechanical Engineering, Suguna College of Engineering, Coimbatore- 641 014, Tamil Nadu, India.

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 3 March 2026

Abstract

This study examined the effects of biochar produced from coconut shells on the moisture absorption and flammability of flax and kenaf bio-composite epoxy hybrid. Three types of composites were developed using hand lay-up and compression molding for composites A, B, and C (2, 4, and 6 wt% biochar, respectively). Moisture absorption test, limiting oxygen index (LOI) test, vertical burning (UL-94) test, and cone burn test were performed on the composites. It was found that with each addition of biochar, composite C (6 wt% biochar) exhibited the greatest improvement in flame-retardant capability, with an LOI of 27.5%, a char yield rated as UL-94 V-0, and better performance in other comparative tests, including lower peak heat release and longer time to ignition. The C-type biochar reduced moisture absorption to the greatest extent due to the combined effect of complex diffusion pathways and improved matrix adhesion. The addition of 6 wt% biochar from coconut shells to sustainable multifunctional natural fiber composites increased fire resistance and moisture absorption durability.