Nacre-Inspired Layered Cu2P2O7/Bacterial Cellulose Composites with Low Thermal Expansion and High Strength

Abstract Advanced electronic packaging requires lightweight substrate materials with thermal expansion coefficients compatible with semiconductor components, high mechanical reliability, and low relative permittivity and dielectric loss. However, conventional negative thermal expansion (NTE) filler/polymer composites often suffer from compromised mechanical strength, increased density, or deteriorated dielectric performance. We report a nacre-inspired layered Cu2P2O7/bacterial cellulose (CPO/BC) composite fabricated through directional ice templating, compression densification, layer-by-layer assembly, and chitosan/Ca2+-assisted interfacial bonding. The optimized composite exhibits an in-plane coefficient of thermal expansion of 3.82 × 10−6 K−1, which is close to that of silicon-based electronic components, while retaining a high flexural strength of 193.54 MPa. In addition, it delivers a low relative permittivity of 1.65 and a dielectric loss below 0.07. The results demonstrate that the nacre-like layered architecture and strengthened interfacial interactions facilitate efficient stress transfer and effectively suppress thermal deformation. This bioinspired design provides a promising strategy for developing dimensionally stable, mechanically robust, and low-dielectric polymer composites for advanced electronic-packaging substrates.