Cellulose nanofibrils (CNF) have attractive properties such as high strength and high aspect ratio. Maximal mechanical performance of CNFs in the macroscale materials can be achieved by controlled assembly of them into the ordered structures via hydrodynamic assembly process. Furthermore, the chemical pre-treatment enhances colloidal stability, facilitates disintegration of these fibrils, introduces several chemical anchoring sites (carboxylic acids) on their surface, and enables them to form 3D structures (gels). However, due to the broad size distribution of CNFs and the complexity of their colloidal behavior, optimizing the processing parameters (viscosity, flow rates, pH, etc.) are essential for fabricating strong filaments. Ultra-strong filaments can be spun using double flow-focusing channels, but the lack of bioactive sites hinders them from being used in biomedical applications. A possible remedy is to use dendritic polymers, which can be designed with controllable charge and structure. These properties make them highly attractive as a complementary component in CNF nanocomposites. Hence, to spin a functionalized filament and improve the interaction between individual CNFs, we have used hydrodynamic assembly to obtain composite filaments from Helux, a polyampholyte hyperbranched polymer, and CNF. Due to an excess of amine groups on the filaments, they can be further functionalized for biological purposes like biomedical sutures or cell scaffolding thread. Also, composite filaments show higher toughness than pure CNF filaments. Moreover, elastic modulus and ultimate strength of composite filaments increased after crosslinking at high temperature. Analysis of fibril dynamics reveals a trade-off between alignment during assembly and enhancement of mechanical properties: the addition of Helux gives crosslinking and functionalization. Still, it can also make the CNF less prone to stay aligned during assembly.

Functional cellulose/dendritic polyampholyte composite filaments

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.