Melt-Compounded Thermoplastic Polyurethane/Single-Walled Carbon Nanotube Nanocomposites: Pellet-Based 4D Printing, Joule-Heating Capability, and Thermally Activated Shape Recovery

Thermally activated four-dimensional printing allows additively manufactured structures to change shape with temperature, providing potential for adaptive polymeric systems. In soft thermoplastic polyurethane (TPU) composites, this is hindered by inadequate thermal transitions, reliance in conductive fillers, solvent-based processing, and the poor printability of very soft TPUs. Here, a thermally reversible switching transition, Joule-heating capability, and pellet-extrusion printability were incorporated into a soft TPU through scalable, solvent-free melt compounding with a commercial masterbatch (MB) of single-walled carbon nanotubes (SWCNTs) in a polyol-ester blend. MB dilution produced composites containing approximately [range-units=single]13wt.% SWCNTs and [range-units=single]927wt.% polyol-ester blend. All composites were thermally stable with a polyol-ester-related melting transition near 54∘C identified by differential scanning calorimetry.ncreasing the MB content enhanced the complex viscosity and viscoelastic moduli while preserving shear-thinning behavior. Conductive atomic force microscopy showed heterogeneous surface-connected current pathways. And mean bulk electrical conductivity increased from 1.09S/m to 18.15S/m as MB content increased from the lowest to the highest loading. The most conductive formulation exhibited voltage-dependent Joule heating, reaching an initial heating rate of 61.8∘C/min at 22V. The cycle-averaged shape-fixity ratios for vacuum-molded samples were 87.290.7 over three cycles, whereas cycle-averaged shape-recovery ratios were 82.685.2 over the two reported recovery cycles. A deformable lattice was produced by fused granulate fabrication (FGF) and exhibited temporary-shape retention and recovery toward its original geometry during external reheating. Collectively, the results demonstrate a melt-processable route to conductive TPU composites, combining electrothermal heating capability with thermally activated shape-memory functionality for future 4D-printing applications.