Polylactic Acid ( PLA )/Flax/Phenolic Nonwoven Composite: Synergistic Enhancement of Flame Retardancy and Mechanical Properties

ABSTRACT This work demonstrates the development and characterization of phenolic fiber‐reinforced polylactic acid (PLA)/flax nonwoven composites, aiming to achieve synergistic improvements in both flame‐retardant and mechanical properties. The composites were fabricated using nonwoven technology, followed by hot pressing with a fixed PLA content (60 wt.%) and varying flax/phenolic fiber content ratios: 60/40 (PLA/Flax), 60/35/5 (PLA/Flax/Phenolic fiber), 60/30/10, 60/25/15, and 60/20/20. The results demonstrated synergistic enhancement in flame‐retardant and mechanical properties with up to 15% phenolic fiber content. Among all the samples, the composition 60/25/15 exhibits the highest mechanical properties, including tensile strength (44.1 MPa), bending strength (113.2 MPa), reduced peak heat release rate (pHRR), and total heat release rate (THR), with reductions of 25.9% and 22.2%, respectively. Dynamic mechanical analysis (DMA) showed a significant enhancement in storage modulus ( G ′) and reduction in tan δ, indicating reduced mobility of the polymer by incorporation of phenolic fibers in PLA/flax composites. The improvement of char residue with the incorporation of phenolic content plays a significant role in enhancing thermal stability. These findings demonstrate that thermosetting phenolic fiber can be effectively incorporated into PLA/flax composites, resulting in synergistic improvements in flame‐retardant, mechanical, and thermal properties, making them suitable for structural and fire‐resistant industrial applications.