Carbon-Material-Modified Polyester Nonwoven Composites with Enhanced Mechanical, Electrical, and Thermal Properties

Carbon nanotube (CNT)- and graphene flake (GF)-modified polyester (PET) nonwoven composites were prepared using a one-sided impregnation process with waterborne polyurethane (PU) as the binder. The objective of this work was to clarify how the geometry and loading of one-dimensional CNTs and two-dimensional GFs regulate conductive network formation, anisotropic mechanical behavior, and thermal response in PU/PET nonwoven composites. The novelty of the study lies in the direct comparison of CNT and GF fillers in the same nonwoven/PU matrix and in correlating filler morphology with mechanical reinforcement, electrical conductivity, and textile-related thermal management performance. The sample codes C5 and C6 represent CNT contents of 5 and 6 wt.%, respectively, while G4 and G6 represent GF contents of 4 and 6 wt.%, respectively. Scanning electron microscopy (SEM) showed that GF tended to form sheet-like coatings on fiber surfaces and to fill inter-fiber pores, whereas CNTs showed more local aggregation because of their high surface energy. The composites exhibited anisotropic tensile behavior, with higher tensile strength in the longitudinal direction than in the transverse direction. In the longitudinal tensile test, G4 reached a tensile strength of 13.01 MPa, while C5 reached 11.35 MPa. With increasing carbon material content, both the electrical and thermal conductivities of the composites increased. The electrical conductivity reached 0.02100 S/cm for C6 and 0.05893 S/cm for G6. The thermal conductivity of the CNT/PU/PET composites increased from 0.1163 to 0.1923 W/(m·K), whereas that of the GF/PU/PET composites increased from 0.1793 to 0.2537 W/(m·K). Infrared thermal imaging further indicated that carbon material addition produced faster heating and slower heat dissipation than the unmodified PU/PET sample. These results provide a useful reference for developing multifunctional nonwoven composites for smart textiles, special protective clothing, wearable thermal management layers, and flexible electronic textile substrates.