Green Manufacturing of High-Performance Multilayered Boron Nitride Composites via Modulus-Contrast-Assisted Stack Pressing

Controlling the in-plane orientation of two-dimensional nanosheets during repeated forming remains challenging because deformation can become nonuniform through the film thickness. Here, alternating 60 and 80 wt % boron nitride nanosheet/thermoplastic polyurethane (BNNS/TPU) layers were used to introduce a moderate modulus contrast during water-based stack pressing and were compared with homogeneous 70 wt % films having the same nominal average filler content. Repeated pressing increased BNNS alignment in both architectures, while the binary film exhibited a slightly narrower SEM-derived angular distribution after six total pressing operations. The binary film reached an in-plane thermal conductivity of 17.85 W m-1·K-1, a through-plane thermal conductivity of 0.22 W m-1 K-1, a tensile strength of 17.48 MPa, and a thermal anisotropy ratio of approximately 81. Under the present point-heating configuration, its hotspot temperature was 5.7 °C lower than that of the unitary film at 60 s. Idealized linear-elastic finite-element analysis qualitatively illustrates modulus-dependent stress and strain partitioning but does not model interfacial damage or nanosheet rotation. Fabrication of 400 × 400 mm films further demonstrates large-area batch-processing feasibility.