Effects of Halloysite Nanotubes on Binary Blends of Thermoplastic Starch With Polyhydroxybutyrate and Polylactic Acid: Investigation of Morphological, Rheological, Mechanical, and Thermal Properties

Abstract

This study explores the influence of halloysite nanotubes (HNTs) on the morphological, rheological, and thermal properties of biodegradable thermoplastic starch (TPS) blends with polyhydroxybutyrate (PHB) and polylactic acid (PLA). Binary and ternary TPS/PHB/HNT and TPS/PLA/HNT nanocomposites were fabricated via melt mixing followed by twin-screw extrusion with varying HNT loadings (0–5 wt.%) and different polymer blend ratios (85/15, 70/30, 50/50). Scanning electron microscopy (SEM) revealed a matrix–droplet morphology, with HNTs reducing the dispersed phase domain size and narrowing the size distribution at moderate loadings, and compatibilization effects. Rheological analysis showed enhanced complex viscosity and more pronounced shear-thinning behavior with increased HNT content, reflecting improved nanoparticle dispersion and network formation. Mechanical testing indicated marginal changes in tensile properties at lower HNT loadings, with ductility increasing notably at higher PLA or PHB contents, especially in TLH-50 and TBH-50 blends. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed that HNT addition improved the thermal stability and crystallization behavior of the blends. Overall, HNTs act as multifunctional additives enhancing phase compatibility, viscosity, and thermal behavior, supporting their potential for developing high-performance biodegradable packaging materials.