Mechanical and Morphological Properties of Alkali‐Treated Cotton Stalk Bark Fiber and Nano‐Silica Reinforced Polylactic Acid Composites: Fabrication and Characterization

ABSTRACT The overexploitation of natural resources and escalating environmental concerns have spurred significant interest in developing eco‐friendly materials. Significant quantities of agricultural byproducts produced annually represent sustainable fillers for biocomposite fabrication. Cotton stalk bark fiber (CSBF), an agricultural byproduct with ~41% cellulose content, exhibits high strength and modulus, rendering it an attractive reinforcement for polylactic acid (PLA) polymer matrices. To optimize interfacial adhesion in composites, we implemented a three‐step modification: alkaline treatment, silane coupling agent (KH550) functionalization, and hydrophobic nano‐silica deposition. Composites with 10–30 wt% CSBF were then prepared by injection molding. The interfacial modification mechanism and its influence on the mechanical performance of PLA were systematically examined using particle size distribution analysis, spectroscopy (FTIR), scanning electron microscopy (SEM), morphological characterization, and mechanical property evaluation. The experimental results demonstrate that CSBF reinforcement significantly improves the mechanical properties of PLA composites, particularly in terms of flexural strength and modulus. The composite with 20 wt% modified CSBF exhibited a tensile strength of 61.45 ± 2.43 MPa, a 14% increase over pure PLA. Flexural strength reached 136.78 ± 1.21 MPa (25.8% increase) with a modulus of 3.87 ± 0.02 GPa (36.3% improvement). These findings confirm that CSBF effectively enhances polymer mechanical properties, offering a sustainable alternative an eco‐friendly alternative to synthetic fibers in composite manufacturing.