Engineering the Pore Architecture in Nanocellulose/Polymer Composites for Optimized Thermal and Mechanical Properties

Porous polymer composites have significant potential for applications demanding lightweight structures, mechanical resilience, and thermal insulation. Here, we report a systematic approach to engineering the pore architecture of cellulose nanofiber (CNF)/polymer composites via water-in-oil (w/o) emulsion templating, in which CNFs serve as both Pickering emulsifiers and reinforcement agents. By applying different mechanical treatments during emulsion formation, we tuned the pore size of the composite while maintaining a consistent porosity. The continuous phase consisted of a styrene/ethylene glycol dimethacrylate (EGDMA) copolymer, with EGDMA acting as a cross-linker. Mechanical testing demonstrated that a reduced pore size led to notable enhancements in the bending modulus, strength, and strain at failure. These improvements were attributed to mitigation of stress concentration at the pore/solid matrix interface and better load transfer through the matrix. In contrast, the thermal conductivity was largely independent of the pore size but exhibited a linear inverse relationship with the porosity, in accordance with theoretical predictions. We fabricated composites with porosities of up to 76% and achieved a thermal conductivity of 58 mW m–1 K–1, approaching values suitable for thermal insulation applications. These findings highlight the critical importance of pore architecture engineering in tailoring the structural and thermal performance of porous CNF/polymer composites. This work provides a versatile platform for the development of lightweight multifunctional materials.