Sustainable Fatty Acid Modification of Cellulose in a CO2-Based Switchable Solvent and Subsequent Thiol-Ene Modification

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.

Automated summary

The study introduced a sustainable synthesis method for fatty acid cellulose esters, showcasing how varying reaction parameters led to the generation of different substitution degrees. The modification process through thiol-ene reaction further allowed for the tuning of structure and properties of the cellulose derivatives. Mechanical testing of films produced from the samples revealed that the DS and thiol type used for modification impacted the materials' performance. Additionally, contact angle measurements indicated an increase in surface hydrophobicity for the thiol-ene-modified samples.