Line–Plane Thermally Conductive Networks in MWCNTs/Ti3C2Tx-Modified PVA Films: Construction and Effects on Film Properties

Thermal interface materials used in high-power electronic devices must combine efficient heat transfer with mechanical flexibility and suitable thermal stability. However, constructing continuous in-plane and through-plane heat-conduction pathways at low filler loadings while preserving mechanical properties remains challenging. A heterostructured hybrid filler (mMT), composed of one-dimensional multi-walled carbon nanotubes (MWCNTs) and two-dimensional Ti3C2Tx MXene, was prepared through electrostatic self-assembly. The mMT filler was then incorporated into a poly(vinyl alcohol) (PVA) matrix to produce composite films (mMTP) with enhanced thermal conductivity, improved mechanical properties, and reduced heat release. At an mMT loading of 7.5 wt.%, the in-plane and through-plane thermal conductivities reached 3.38 and 0.67 W·m−1·K−1, respectively. These values represent increases of 1370% and 191% compared with pristine PVA. The addition of mMT also enhanced the thermal stability, tensile strength, and elongation at break of the composite films. These results provide a strategy for designing water-processable PVA composites that combine enhanced thermal transport and mechanical performance with reduced heat release.