High-performance PLA/CNT– Delonix regia bio ash composites developed through the FDM process: a sustainable approach to enhanced functionality

Polylactic acid (PLA) is a promising biodegradable polymer for green engineering applications but suffers from inherent brittleness, moisture sensitivity, and flammability. Mechanical strength, water absorption, and flammability were evaluated in this study for neat PLA, 1 wt.% carbon nanotube-reinforced PLA (PLA/CNT), and PLA/CNT composites with 3, 6, and 9 wt.% Delonix regia ash (DRA), all produced using fused deposition modeling (FDM). Compared to neat PLA (40 ± 4 MPa), PLA/CNT recorded a 17.5 % enhancement in tensile strength (47 ± 3 MPa), whereas the DRA-filled composite with 6 wt.% DRA attained a 40 % enhancement (56 ± 2 MPa). Flexural strength also improved from 70 ± 2 MPa for PLA to 80 ± 3 MPa (+14.3 %) with CNT and 94 ± 1 MPa (+34.3 %) with 6 wt.% DRA. Water uptake reduced from 33 ± 1.3 % (PLA) to 22 ± 0.9 % (PLA/CNT) and 17 ± 0.5 % at 6 wt.% DRA. Flammability analysis yielded ignition delay times of 6.41 ± 0.31 s (PLA), 8.42 ± 0.22 s (PLA/CNT), and 10.27 ± 0.28 s (6 wt.% DRA), with corresponding flame spread rates of 59, 48, and 39 mm min −1 . Thermogravimetric analysis also verified improved thermal stability, with degradation onset shifting from ∼325 °C (PLA) to ∼335 °C (6 wt.% DRA) and char yields ranging from 1.8 % to 7.5 %. Scanning electron microscopy fracture surfaces of the 6 wt.% DRA composite showed significant crack deflection and particle pull-out, which is characteristic of strong interfacial bonding. In general, the hybrid PLA/CNT–DRA system with 6 wt.% DRA provides the best balance of mechanical, moisture resistance, flame retardancy, and thermal performance for high-performance green structural applications.