Solvent-free crosslinking of Hydroxypropyl cellulose via esterification: Towards green bioplastics

Resource depletion, waste management, and climate change drives innovation towards bioplastics. Among the renewable cellulose derivatives, hydroxypropyl cellulose (HPC) stands out for its biocompatibility, ease of processing, rheological tunability, and unique ability to form cholesteric mesophases at high concentrations. However, its water solubility has limited its use in advanced applications such as packaging, 3D printing, and smart labeling. To date, efforts to produce water-resistant HPC relied on solvent-based and catalyst-driven crosslinking approaches, which undermine its environmental benefits. Herein, we hypothesize that HPC can be effectively crosslinked under solvent-free conditions to produce biodegradable plastics. In the manuscript, we report a simple, one-step, solvent- and catalyst-free method to crosslink HPC using glutaric anhydride (GAn), combining high-shear mixing and heat-pressing. The resulting GAn@HPC material is water-insoluble, optically transparent, and mechanically tunable. Remarkably, upon rehydration and drying, the crosslinked polymer forms a cholesteric layered structure, demonstrating the potential to form structurally colored, crosslinked bioplastics with further tuning of cross-linking density. This scalable and sustainable method significantly enhances the functional potential of HPC while aligning with green chemistry principles. Our work contributes to advancing eco-friendly materials and positions crosslinked HPC as a promising alternative in sectors demanding both functionality and sustainability.