Identifying the most critical parameters for an optimized design through electrical conductivity in TPU/CNT nanocomposites obtained by extrusion: Theoretical modeling and experimental findings

Abstract

This work presents a comprehensive experimental–theoretical study on the electrical behavior of thermoplastic polyurethane (TPU) nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs), highlighting the novelty of integrating scalable processing with a physics-based analytical model. The study introduces a model that combines percolation theory, shear mechanics, and nanotube aspect ratio degradation, highlighting the critical processing parameters that govern conductivity and enabling direct correlation between extrusion conditions and the resulting conductivity. TPU/CNT filaments with 2.5–6 wt% filler and 3.30 ± 0.70 mm of diameter were produced via twin-screw extrusion under controlled dispersion times (1–5 min) and subsequently hot-pressed into flexible films (293.63 ± 44.72 μm of thickness). Electrical conductivity was systematically analyzed and linked to morphological characterization (FEG-SEM/TEM) and extrusion parameters (torque, viscosity, shear strain). Results revealed an optimum extrusion time of 3 min, yielding 0.071 ± 0.055 S/m in filaments with 6 wt% CNT, attributed to a balance between dispersion and structural preservation. Hot pressing further enhanced conductivity up to 9.60 ± 1.36 S/m, lowering the percolation threshold from 3.60 to 1.00 vol% by promoting filler redistribution and reducing agglomeration. The model successfully explained these conductivity trends through aggregation parameters (ξ and ε), offering a new route to justify dynamic percolation behavior. Beyond DC conductivity, the study also evaluated AC impedance response, mechanical properties, strain sensitivity, cyclic electromechanical behavior, and proof-of-concept wearable tests (all detailed in the Supporting Information). Altogether, this dual experimental–theoretical framework not only advances the fundamental understanding of dispersion–conductivity relationships but also demonstrates the scalability and multifunctionality of TPU/CNT composites for next-generation wearable electronics, soft robotics, and biomedical sensing applications.