The Role of Fiber Architecture in Interfacial Adhesion and Fracture Toughness of Polylactic Acid/Lignocellulosic Fiber Biocomposites

ABSTRACT This work investigates the influence of fiber architecture on the fracture toughness and interfacial adhesion of polylactic acid (PLA) biocomposites reinforced with coir, fique, and sisal fibers. Composites containing 1, 3, and 5 wt.% fiber were prepared under identical processing conditions using untreated and alkali‐conditioned fibers, enabling a comparative assessment of the structure–interphase–property relationship. Thermal behavior was evaluated by differential scanning calorimetry and thermogravimetric analysis, tensile properties were determined under uniaxial loading, and fracture response was analyzed using double‐deeply edge‐notched tensile specimens to determine the critical J ‐integral under quasi‐static conditions. Results indicate that fiber architecture is the primary factor governing energy dissipation; coir and fique systems demonstrated a superior capacity for increasing fracture resistance and ductility compared to neat PLA. Coir‐ and fique‐reinforced systems showed the most significant increase in fracture toughness, accompanied by higher ductility and improved interfacial features in scanning electron microscope observations, whereas sisal composites exhibited a more limited response. Thermal analysis revealed only moderate changes in glass transition, crystallization, and degradation behavior, indicating that the main effects of conditioning are associated with interfacial efficiency rather than bulk thermal transitions. The results support a structure–interphase–property framework in which fiber architecture governs the effectiveness of alkali treatment and the activation of toughening mechanisms in PLA‐based biocomposites.