Thermo-mechanical Analysis of SPLA- Based Biocomposites Reinforced with Rice Husk and Titanium Nanoparticles for Sustainable Orthopedic Insoles

The mechanical performance of soft polylactic acid (SPLA) biocomposites, reinforced with rice husk (RH), TiO₂ nanoparticles, and their hybrids, was evaluated for orthopedic insole applications. Samples included virgin SPLA, RH-reinforced (R-series: R1–R3), TiO₂-reinforced (T-series: T1–T3), and hybrid RH/TiO₂ (H-series: H1–H3) variants. Assessments covered tensile strength, elastic modulus, elongation at break, and dynamic mechanical analysis (DMA) for viscoelastic properties. TiO₂ nanoparticles significantly improved tensile strength in the T-series, peaking at 25.20 MPa (T3) due to efficient stress transfer from well-dispersed fillers, surpassing the R-series maximum of 21.62 MPa (R2). The hybrid H2 achieved the highest overall at 28.62 MPa, elastic modulus was maximal in T3 (293.71 MPa) and minimal in R3 (197.53 MPa). Elongation at break ranged from 16.05% (H1, highest) to 9.14% (R2, lowest). DMA revealed H1's superior storage modulus (900 MPa) and loss modulus (142 MPa), with onset temperature of 104.0°C, indicating excellent toughness and energy absorption. Glass transition temperature (Tg) peaked at 123.8°C in H3, attributed to RH/TiO₂ synergy enhancing intermolecular forces; T1 showed the lowest (88.5°C) due to plasticizer-induced matrix weakening. The highest tan δ (0.272) occurred in T2 at Tg, reflecting enhanced damping for insoles, while HI reduced it to 0.093, increasing stiffness and lowering energy dissipation. Superior filler-matrix adhesion in hybrids minimized voids and stress concentrations, optimizing rigidity and ductility for load-bearing applications. This study develops cost-effective, ecofriendly, biodegradable orthopedic materials with optimized mechanical and viscoelastic properties through strategic natural and nanoscale filler incorporation, contributing sustainable solutions to biomedical and industrial fields.