Optical, Opto-Mechanical, and Antimicrobial Characterization of TiO₂ and ZnO-Enhanced Polypropylene Fibers Using Interferometric Techniques and Fourier Transform Analysis

This study investigates the optical, mechanical, and antimicrobial properties of polypropylene (PP) fibers enhanced with titanium dioxide (TiO₂) and zinc oxide (ZnO) nanoparticles. Using a Mach–Zehnder interferometric system, we examined the refractive indices, birefringence, and opto-mechanical behavior of blank PP, PP/TiO₂, and PP/ZnO nanocomposite fibers under various conditions, including different polarization orientations and during cold drawing processes. The 2D Fourier transform algorithm is employed to analyze interferometric data, enabling precise measurements of refractive index profiles and birefringence. Results show that both TiO₂ and ZnO nanoparticles significantly enhance the optical and mechanical properties of PP fibers. PP/TiO₂ fibers exhibited the highest refractive index (1.530) and birefringence (0.0459), followed by PP/ZnO (1.522 and 0.040) and blank PP (1.520 and 0.031). The maximum draw ratios achieved were 4.2, 3.9, and 3.5 for PP/TiO₂, PP/ZnO, and blank PP fibers, respectively, indicating improved mechanical properties in the nanocomposites. Antimicrobial efficacy was evaluated using the shaking flask method and optical density measurements against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. PP/ZnO fibers demonstrated the highest antimicrobial activity, with growth reductions ranging from 64.8% to 80.4%, followed by PP/TiO2 fibers (56.0% to 70.3%).