Cellulose nanofibrils and nanocrystals are excellent materials for hydrogels and as reinforcers in polymer composites due to their high aspect ratio, mechanical strength and colloidal stability. Nonetheless, the production of these outstanding materials is expensive, energy demanding and, in most cases, it requires the use of chemicals that put into question their sustainability. This work explores a mild, straight forward chemical modification using maleic anhydride to simultaneously decorate the fibers with carboxylate and alkene groups. The surface charge of the modified fibers can be tuned from 150 μmol/g to 1000 μmol/g by controlling the reaction temperature. As a proof of concept, we developed rubber-like, water-stable hydrogel composites by using in situ polymerization of telechelic-PEG followed by free-radical crosslinking. The degree of modification of the fibers, the polymerization strategy and the molecular weight of the telechelic-PEGs enable control over the network formation within and around the fibers. The hydrogels were designed for a circular economy; therefore, it is possible to recover fibers and polymers precursors through alkaline hydrolysis. The recycled fibers may then be reused in other processes for the pulp and paper industry or returned to nature to continue its natural degradation path. Fiber-reinforced hydrogels are just an example of what it is possible to do with these fibers, far more applications are possible.