Chestnut Burr as a Multifunctional Filler for PLA-Based Bio-Composites: Processing, Characterization, and Antioxidant Functionality

This study explores the valorization of chestnut burrs (Castanea sativa), an abundant agro-industrial residue, as a natural filler for polylactic acid (PLA)-based biocomposites with potential applications in additive manufacturing. PLA/chestnut burr composite filaments were prepared by melt extrusion with filler contents of 2.5%, 5%, 10%, and 15% w/w, and their chemical, thermal, morphological, and mechanical properties were systematically characterized. ATR-FTIR confirmed the absence of major chemical modifications of the PLA matrix. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), the latter performed on both the extruded filaments and the material after fused deposition modeling (FDM) 3D printing, revealed a slight decrease in thermal stability with increasing filler content, coupled with enhanced crystallinity. Mechanical properties analysis showed that the addition of chestnut burrs did not negatively impact the viscoelastic behavior of the filaments. Scanning electron microscopy (SEM) highlighted good filler dispersion up to 5% loading, while higher percentages led to increased surface roughness and microvoids. Importantly, antioxidant activity assays (DPPH, ABTS, FRAP, and Folin–Ciocâlteu) demonstrated that the incorporation of chestnut burr significantly enhanced the radical-scavenging capacity, reducing power, and total phenolic content (TPC) of PLA. These functionalities were preserved, and in some cases amplified, after FDM 3D printing, indicating that the processing conditions did not degrade the bioactive constituents. Overall, chestnut burrs are confirmed as an effective multifunctional filler for PLA, improving its antioxidant activity while maintaining structural and thermal performance, supporting the development of sustainable biocomposites for emerging applications.