Cellulose nanofibrils (CNF) can form impressive barrier layers but difficult rheological properties, brittleness, and sensitivity to moisture limit their use. To overcome these challenges, esterification reactions were performed in water without volatile organic solvents to create carbic-functionalized CNFs (cCNFs) that enabled versatile, thiol-norbornene secondary modifications. Chemical analysis determined that on average 5% anhydroglucose repeat units were functionalized with norbornene groups. Thiol-norbornene reactions added molecules with varying polar surface areas to the CNFs. Modifications did not change the film properties to a large extent. All CNF films were excellent grease barriers. The modifications significantly changed the rheology of CNF suspensions as the complex viscosity of the modified CNF was 27 times lower than unmodified CNFs. Modification also reduced the filtration rate by a factor of four. Surface modifications appeared to alter the colloidal forces between fibers in suspension that influence the flow and drainage properties.