Searching for more sustainable materials as an alternative to petroleum-based products is of increasing interest due to different environmental issues. Cellulose and fatty acids are two very promising candidates for biobased material design. Herein, we report a sustainable synthesis of fatty acid cellulose esters (FACEs) via transesterification of cellulose with methyl-10-undecenoate in a CO2-based switchable solvent system. FACEs with a degree of substitution between 0.70 and 1.97 were synthesized by simple variation of reaction parameters and characterized in detail. Subsequently, a FACE with a degree of substitution (DS) of 0.70 was modified via thiol-ene reaction, demonstrating an efficient and versatile method to tune the structure and properties of the new cellulose derivatives. Films were produced from each sample via solvent casting, and their mechanical properties were examined using tensile tests. Elastic moduli (E) ranging from 90 to 635 MPa and elongations at break between 2 and 23% were observed, depending on the DS of the FACE and the type of thiol employed for the modification. Finally, contact angle measurements confirmed an increase in the surface hydrophobicity (75-91 degrees) for the thiol-ene-modified samples.