Fiber-reinforced polymer composites (FRPs) are indispensable in modern structural engineering owing to their exceptional specific strength and ultralow density. However, their advancement remains constrained by an intrinsic trade-off between strength and toughness. Herein, an orientation-induced crystallization strategy is proposed to construct lightweight FRPs that simultaneously achieve high strength and toughness. This approach couples bidirectional freezing with hot-press processing to create a cellulose nanofiber (CNF) oriented polyvinyl alcohol (PVA) composite architecture. During bidirectional freezing, CNFs align along the ice crystal growth direction, guiding the ordered arrangement of PVA chains. Subsequent hot pressing enables the oriented CNFs to act as crystallization templates, promoting controlled recrystallization of the PVA matrix and significantly enhancing its molecular alignment and crystallinity. Moreover, robust interfacial hydrogen bonding between CNFs and PVA ensures efficient stress transfer, mitigates local stress concentrations, and facilitates superior energy dissipation during deformation. As a result, the resulting PC-orientation composite exhibits a remarkable combination of high tensile strength (44.42 MPa) and impressive toughness (34.74 MJ·m^-3) while maintaining a ultralow density (0.75 g·cm^-3), representing the state-of-the-art in reported FRPs. This work provides a universal pathway to break the long-standing strength-toughness trade-off in FRPs and highlights a promising design paradigm for lightweight structural components.

Three-dimensional (3D) graphene is a promising active component for various engineering fields, but its performance is limited by the hidebound electrical conductivity levels and hindered electrical transport. Here we present a novel approach based on interlayer engineering, in which graphene oxide (GO) nanosheets are covalently functionalized with varied molecular lengths of diamine molecules. This has led to the creation of an unprecedented class of 3D graphene with highly adjustable electronic properties. Theoretical calculations and experimental results demonstrate that ethylenediamine, with its small diameter acting as a molecular bridge for facilitating electron transport, has the potential to significantly improve the electrical conductivity of 3D graphene. In contrast, butylene diamine, with its larger diameter, has a reverse effect due to the enlarged spacing of the graphene interlayers, resulting in conductive degradation. More importantly, the moderate conductive level of 3D graphene can be achieved by combining the interlayer spacing expansion effect and the π-electronic donor ability of aromatic amines. The resulting 3D graphene exhibits highly tunable electronic properties, which can be easily adjusted in a wide range of 2.56–6.61 S·cm⁻¹ compared to pristine GO foam (4.20 S·cm⁻¹). This opens up new possibilities for its use as an active material in a piezoresistive sensor, as it offers remarkable monitoring abilities.