Polylactic acid (PLA) is widely used in fused filament fabrication (FFF), but its engineering applications are constrained by brittleness and limited thermal resistance. Here, micronized banyan tree aerial-root (BTAR) powder was incorporated into PLA at 5–25 wt.% and processed into composite filaments by single-screw extrusion for FFF printing. The composites showed a composition-dependent response. At 15 wt.% BTAR, tensile and flexural strengths increased by approximately 47% and 43%, respectively, compared
with neat PLA. The highest impact energy absorption was obtained at 25 wt.% BTAR, reaching 2.93 J versus 1.07 J for neat PLA. XRD and FTIR results indicated a predominantly amorphous PLA matrix with superimposed cellulose-I features and spectral changes suggesting possible interfacial interactions. SEM revealed relatively uniform filler dispersion at intermediate loading, whereas higher BTAR contents promoted agglomeration. Thermal analysis showed a slight reduction in degradation onset temperature but increased char residue from 0.1% for neat PLA to 5.4% at 25 wt.% BTAR.
These results indicate that untreated BTAR is a promising regional particulate filler for FFF-grade PLA, with 15 wt.% favoring strength and 25 wt.% enhancing impact resistance
and char formation.