Interfacial engineering, processing, and microstructure relationships in PLA/Diss fiber biocomposites for improved mechanical performance

This study reports the development of fully bio-based polylactic acid (PLA) biocomposites reinforced with short Ampelodesmos mauritanicus (Diss) fibers using a powder-based processing route. To improve fiber-matrix compatibility, the fibers were subjected to sequential HCl/NaOH treatment to modify their surface morphology. A fixed concentration of 10 wt.% was selected to isolate the effect of surface treatment on fiber-matrix interaction rather than to optimize the reinforcement level. Multiscale characterization using SEM, AFM, FTIR, Raman spectroscopy, and DSC showed that the treatment improved interfacial adhesion by promoting mechanical interlocking and molecular interactions between PLA and the exposed cellulose-rich fiber surface. AFM observations confirmed a marked increase in surface roughness, while DSC analysis revealed that treated fibers influenced PLA crystallization through the combined effects of heterogeneous nucleation and restricted chain mobility at the interface. These microstructural changes enhanced load transfer, with the treated-fiber composite reaching a Young’s modulus of 4.24 GPa and a tensile strength of 46.8 MPa. The powder-processing route also promoted homogeneous fiber dispersion and may help reduce thermal and shear-induced degradation compared with conventional melt processing. Overall, the results demonstrate that combining interfacial engineering with powder processing provides an effective strategy for designing lightweight, high-performance, and sustainable PLA/Diss biocomposites.