Enhancing Schizostachyum brachycladum bamboo fiber reinforced PLA composites via plant ash alkali treatment: Interfacial and mechanical performance for lightweight and protective engineering components

Plant ash derived alkali treatment has been previously explored for bamboo fiber modification in cement-based composites. However, its effectiveness in polymer matrices, particularly hydrophobic polylactic acid (PLA), remains largely unexplored. In this study, the novelty and environmentally friendly plant ash alkali treatment was applied to bamboo fibers to enhance interfacial adhesion in PLA-based biocomposites. Plant ash alkali treatment roughened fiber surfaces, improving wettability that enhanced the fiber matrix bonding. Untreated bamboo fiber reinforced PLA composites containing 5 wt%, 10 wt%, and 20 wt% fiber (BFPLA-5, BFPLA-10, BFPLA-20) and equivalent to plant ash–treated bamboo fiber composites reinforced PLA composites with same fiber loading with untreated fiber (APBFPLA-5, APBFPLA-10, APBFPLA-20) were fabricated via internal mixing followed by compression moulding to evaluate structure–property relationships. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed partial removal of amorphous constituents and enhanced cellulose crystallinity after treatment, with APBFPLA-20 exhibiting the highest diffraction intensity at 22.2°. Scanning electron microscopy (SEM) revealed improved fiber–matrix interfacial contact and reduced void formation in treated composites. These interfacial improvements resulted in significant mechanical enhancement, where the tensile strength increased by approximately 170% compared with untreated BFPLA-20 (15.46 MPa), reaching about 73% of neat PLA strength, while the flexural strength achieved 96.07 MPa with increased hardness. Thermogravimetric analysis (TGA) showed improved thermal stability, with the degradation onset temperature increasing to 328.59 °C for APBFPLA-10, and dynamic mechanical analysis (DMA) confirmed enhanced viscoelastic performance. Overall, APBFPLA-10 demonstrated the most balanced mechanical and thermal performance, indicating that plant ash alkali treatment is an effective and sustainable interfacial engineering strategy for bamboo fiber reinforced PLA composites intended for lightweight structural and protective engineering applications.