(332f) Surface-Modified Microfibrillated Cellulose: Enabling Reversible Dehydration

Microfibrillated cellulose (MFC) has potential applications as a rheological modifier to change flow characteristics of a product, including changing the viscosity or enabling phase transitions in response to external stimuli. Our work focuses on characterizing MFC derived from wood to determine whether it can be used as a rheological modifier. The ultimate goal this work is to use these results to enable design MFC rheological modifiers from paper waste. MFC can be added to formulations to adjust rheology including those for personal, cosmetics, fabric and home care products. MFC fibers have high fiber aspect ratio, which changes rheology with minimal added material. However, the high aspect ratio increases their tendency to associate even at low concentrations. To maintain a stable structure and preserve their dimensions, MFCs are typically produced and stored as aqueous dispersions. While effective for stability and keeping their dimensions, the high-water content presents challenges for large-scale applications, including increased transportation costs and environmental impact. Designing formulations that allow water removal during shipping and easy rehydration at the point of use would offer a more efficient and sustainable solution. Drying MFC generally leads to irreversible aggregation due to strong hydrogen bonding, causing loss of nanoscale structure and mechanical properties, such as material elasticity. The mechanical properties of MFC are largely due to their individual nanoscale structure and their ability to form strong, interconnected networks. When MFC aggregates, this network structure is disrupted. The aggregated material no longer has the same level of elasticity that the well-dispersed MFC fibers. To overcome this limitation, we modify MFC surface chemistry to enable dehydration and rehydration while maintaining material properties. Here, we synthesize surface-oxidized MFC (OMFC), a negatively charged colloidal rod suspension, and graft a thermoresponsive polymer, Jeffamine polyetheramine M2005, onto its surface. Both types of MFC, OMFC and thermoresponsive MFC, are subjected to dehydration using different methods, including freeze-drying, vacuum drying and oven drying. We then measure equilibrated material properties of OMFC and thermoresponsive MFC, using amplitude and frequency sweeps before and after a dehydration-redispersion cycle. We also measure the dynamic rheology of thermoresponsive MFC fibers as a function of temperature. By modifying the surface chemistry and partially blocking hydroxyl groups, we successfully redisperse MFC while maintaining most of its rheological properties. We measure similar equilibrated material properties in both MFCs and thermoresponsive functionality in thermoresponsive MFC. Overall, this work provides a strategy for designing MFC effectively while enabling cost-efficient shipping for large-scale applications. By maintaining the nanoscale structure and dynamic material properties we are able to potentially use MFC in products that undergo cycles of dehydration, shipping and rehydration.