Revalorisation of recycled PLA through Halloysite nanotube integration for mechanical and thermal property improvement

This study investigates the effect of Halloysite nanotube (HNT) reinforcement on the mechanical, thermal, and structural properties of recycled polylactic acid (rPLA) composites. Composites were prepared with 1–5 wt.% HNTs and characterised using tensile, flexural, compressive testing, thermogravimetric analysis (TGA), and X-ray diffraction (XRD). Tensile strength increased from 42.98 MPa for neat rPLA to a maximum of 49.39 MPa at 2 wt.% HNT, while tensile modulus improved steadily from 2423.13 MPa to 2971.26 MPa at 5 wt.%. Flexural strength peaked at 78.54 MPa (22% improvement compared to neat rPLA) at 3 wt.%, and the highest flexural modulus of 2292.30 MPa was achieved at 4 wt.% HNT. Under compressive loading, strength and modulus increased from 100.94 MPa and 2361.52 MPa for neat rPLA to 108.69 MPa and 2479.87 MPa, respectively, at 5 wt.% HNT, showing improved resistance to deformation. Thermal degradation temperatures rose from 452.12 °C for rPLA to 465.58 °C at 5 wt.% HNT, with char residue at 600 °C increasing from 4.23% to 9.96%, confirming the thermal barrier effect of Halloysite. XRD analysis showed enhanced crystallinity, increasing from 57.49% (neat rPLA) to 59.22% at 5 wt.% HNT, indicating effective nucleation and structural ordering induced by the nanotubes. Overall, the incorporation of 2–4 wt.% Halloysite offered the most balanced improvement in strength, stiffness, and thermal stability. These results demonstrate that rPLA–Halloysite composites can be suitable for sustainable, high-performance applications in packaging, automotive interiors, and structural bioplastics.