The overall goal of my thesis work was to incorporate sustainable materials into polymer matrices to create nanocomposites with enhanced transport properties. Primarily, I focused on the study of ion structure to improve the fundamental understanding of cellulose-based sorbets, on the development of enhanced water transport materials for applications in membrane filtration and in new types of wicking materials, and on the improvement of heat transfer through thermally active materials. In chapter 1, I introduce cellulose nanocrystals (CNCs) as a sustainable material and the qualities that make them promising nanofillers for polymer nanocomposites. I then discuss the potential applications of CNCs as sorbents and membranes for water purification, as the wicking component of rubbery wicking materials, and as the active component in thermally active materials. In chapter 2, we used Anomalous Small Angle X-ray Scattering (ASAXS) to determine quantitatively the three-dimensional distribution of metal ions of different valencies surrounding negatively charged carboxylate functionalized CNCs. These distributions can affect water and ionic permeability in these materials. The data show that increasing the carboxylate density on the surface of the CNCs changed the nature of the structure of the adsorbed ions from a monolayer into a multilayer structure. Additionally, the data show that the CNCs can leverage multiple mechanisms, such as electrostatic attraction and the chaotropic effect, to adsorb ions of different valencies. By understanding the spatial organization of the adsorbed metal ions, the design of cellulose-based sorbents can be further optimized to improve uptake capacity and selectivity in separation applications. In chapter 3, I present our work on the use of polymer grafted CNCs in membrane applications. The impact of the polymer grafting density and polymer conformation was investigated and showed that by increasing the grafting density of PEG such that it adopted a semi-dilute polymer brush conformation, the water flux through the membranes could be increased by up to three orders of magnitude while maintaining their rejection performances. In chapter 4, I report our studies aimed at accessing moisture wicking rubbery films by the incorporation of CNCs into a hydrophobic latex matrix. This design is inspired by treated-wool fibers, which exhibit excellent wicking properties aided by a hydrophobic cuticle coated by a hydrophilic exterior layer. The hydrophobic cuticle mitigates water absorption while the hydrophilic protein sheath provides a wetting surface for the water to wick. Using a latex templating approach, CNC:polydimethylsiloxane (PDMS) composites were prepared with the ability to wick water through the composite film. I then used this rubbery wicking composite to develop a prototype for a sweat wicking prosthesis liner. In chapter 5, I present our work on a thermal switching composite that changes its thermal conductivity based on applied strain. The composite is composed of CNCs incorporated into a shape-memory polymer matrix. Measurements show up to a two-fold increase in the thermal conductivity upon application of strain.