Multi-functional natural fiber composites using flaxseed and cotton: tailoring acoustic, mechanical, and thermal properties for eco-friendly applications

This study explores the development of polymer composites that are sustainable and reinforced by natural flax and cotton fibers at different weight fractions (5%, 10%, and 15%) to improve their mechanical, acoustic, and thermal properties for environmentally friendly engineering applications. Composites based on flax fiber showed a higher flexural strength of 62 MPa compared to a value of 56 MPa achieved for the cotton fibers when using 15 wt%, showing a better load-bearing capacity. Also, the impact strength from flax improved significantly with flax content and recorded the highest values of 16.5 kJ/m2 at 15 wt%, which is thirty percent higher than the cotton-based composites. It was discovered by acoustic analysis that with the increasing flax fiber amount, the sound absorption coefficient (SAC) can be enhanced to a maximum of 0.19 at high frequencies for 15 wt%, superior to the corresponding cotton composites. It was confirmed through thermal gravimetric analysis that flax fiber composites manifested increased thermal stability compared to their counterparts, where the incipient decomposition mode and greater char residue over 250 °C were delayed. It was attributed to their high content of cellulose and lignin. Further, scanning electron microscopy (SEM) showed higher fiber-matrix interlocking and less porosity at optimal fiber loading, adding to gains in the multifunctional performance. This all-around appraisal places flax fiber ahead as a better natural reinforcement than cotton, a greener substitute for synthetic materials in structural and acoustic insulation. The study offers a balanced way of optimizing mechanical, acoustic, and thermal properties that contribute to developing the next-generation sustainable composites.