Pore architecture control in cellulose nanocrystal aerogels using electrosprayed lignin nanospheres for absorption-dominant electromagnetic interference shielding

The rapid expansion of high-frequency electronic systems has intensified electromagnetic interference (EMI), creating an urgent need for lightweight, sustainable shielding materials that attenuate electromagnetic waves (EMWs) through absorption rather than reflection. Conventional metal-based shields, although effective, are dense, corrosion-prone, and generate secondary electromagnetic pollution by reflecting incident waves. These limitations have driven increasing interest in absorption-dominant EMI (a-EMI) shielding architectures that dissipate electromagnetic energy within porous conductive structures. Engineering porosity levels in hierarchical lightweight aerogels has become a dynamic research frontier, because pore architecture directly governs mass transport, internal interfacial area, and wave-matter interactions. In absorption-dominant EMI shielding, this makes pore modulation a practical lever to enhance internal multiple scattering and energy dissipation without relying on higher filler loadings. In this work, a fully bio-based a-EMI shielding platform is developed using cellulose nanocrystals (CNCs) as a porous biocarbon scaffold and lignin nanospheres (LNS) as a multifunctional microstructural modifier. CNC hydrogels were transformed into highly porous aerogels via ice-templating and subsequently carbonized to produce lightweight conductive frameworks suitable for electromagnetic energy dissipation. LNS were fabricated by electrospraying lignin solutions modified with poly(ethylene oxide) (PEO), yielding particle populations of various diameters. Incorporation of size-engineered LNS into CNC matrices enabled systematic modulation of aerogel pore morphology and internal interfaces. The resulting carbonized LNS/CNC aerogels exhibited a-EMI shielding performance in the X-band (8.2-12.4 GHz). The optimal formulation, LNS-3L3P at 2.5 wt.%, achieved a total shielding effectiveness of 32 dB, an absorption coefficient of 0.66, and a specific shielding effectiveness (SSE/t) of 152 dB·cm2·kg-1. While the addition of LNS did not substantially increase overall shielding, it significantly enhanced electromagnetic absorption by modifying internal scattering pathways and energy dissipation mechanisms. In brief, this thesis demonstrates that size-engineered LNS can serve as an effective pore-modulation strategy within CNC-derived biocarbon aerogels, establishing a scalable and sustainable pathway toward next-generation a-EMI shielding materials.