Effect of mixing sequence and carbon nanotube loading on the mechanical, thermal, and rheological properties of PLA/TPU nanocomposites

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 resistant to impact, tearing, and abrasion, presents a promising approach for property enhancement. Carbon nanotubes (CNTs) were incorporated to further improve mechanical characteristics. PLA/TPU blends containing CNTs were prepared via melt mixing, using CNT/polymer masterbatches to enhance dispersion. After optimizing the mixing method, the effect of CNT content on the morphology, mechanical, thermal, and rheological properties was systematically investigated. SEM micrographs revealed TPU droplet morphology within a continuous PLA phase, with TPU domain size decreasing upon 0.2 wt% CNT addition. The highest tensile strength and toughness were achieved at 0.5 wt% CNT. DSC analysis showed increased PLA crystallinity with TPU blending and further enhancement with CNT addition, while cold crystallization temperature remained unchanged. Frequency sweep tests indicated the formation of a CNT network at higher loadings, suppressing terminal relaxation behavior. Surface properties, including hydrophobicity and printability, were also evaluated, highlighting potential packaging applications.