Optimization of Mechanical, Thermal, and Rheological Properties of Carbon Nanotube-Reinforced Polylactic Acid/Thermoplastic Polyurethane Nanocomposites via Melt Mixing

Polylactic acid (PLA), a bio-renewable, biodegradable, and biocompatible polymer, offers high strength, transparency, and acceptable processability with lower energy requirements compared to petroleum-based polymers. Its combination with thermoplastic polyurethane (TPU), a highly elastic material impervious to impact, tearing, and abrasion, presents a promising approach for property enhancement. Furthermore, the incorporation of carbon nanotubes (CNTs) was investigated to further improve mechanical characteristics. In this study, PLA/TPU blends containing carbon nanotubes were prepared using melt mixing in an internal mixer. Initially, CNT/polymer masterbatches were fabricated to improve the dispersion and distribution of CNTs, followed by the production of PLA/TPU/CNT nanocomposites. After determining the optimal mixing method, the effect of CNT content on the mixture’s properties was systematically investigated. The morphology, physical, mechanical, and rheological properties of the samples were analyzed using Scanning Electron Microscopy (SEM) images, tensile testing, Differential Scanning Calorimetry (DSC), and Frequency Sweep Analysis. The melt mixing method yielded more favorable mechanical, thermal, and rheological properties. SEM micrographs revealed a droplet morphology of TPU within a continuous PLA phase. Upon the introduction of 0.2 wt% CNT, the size of the TPU domains diminished and stabilized. The highest tensile strength and toughness were achieved with the addition of 0.5 wt% CNT. DSC analysis indicated that blending PLA with TPU significantly increased the degree of PLA crystallization and reduced the cold crystallization temperature. The degree of crystallization was further enhanced by CNT addition, while the cold crystallization temperature remained unaffected. Frequency sweep tests demonstrated that CNT addition up to 0.5 wt% had a negligible effect on the storage modulus of PLA. However, higher CNT loadings (1 and 2 wt%) led to an increase in storage modulus and a plateau at low frequencies, attributed to the formation of a network structure.