Tuning Sustainable Nanocomposite Interphase Behavior through Surface-Modification of Cellulose Nanocrystals

Sustainable alternatives to petroleum-based plastics are needed urgently, but biodegradable materials from renewable sources often suffer from inadequate mechanical properties. Here, we demonstrate a bio-inspired strategy to enhance soy protein isolate (SPI) nanocomposites through surface modification of cellulose nanocrystal (CNC) reinforcing particles with polydopamine (polyDOPA). This modification creates multifunctional interfaces that simultaneously improve CNC dispersion and strengthen filler-matrix interactions. PolyDOPA-modified CNCs increases the tensile strength and elastic modulus of SPI films (plasticized with 50% glycerol) by more than threefold compared to unreinforced controls. Transmission electron microscopy, spectroscopic techniques, and thermal analysis reveal that polyDOPA coatings influenced nanocomposite structure across multiple length scales, tripling the effective diameter of the CNC inclusions, reducing the tendency of CNC nanocrystals to aggregate, and increasing the glass transition temperature. The increase in glass transition temperature suggests reduced molecular mobility due to enhanced interfacial interactions at the CNC surface. Micromechanical modeling suggests that property improvements arose from both enhanced interfacial interactions and reduced filler aggregation. Results reveal how polyDOPA-modified CNCs influence the interphase effectiveness and filler dispersion of SPI-glycerol nanocomposites, providing a pathway to further improve their performance.