Paper Number
GG24 

Session
Arrested Systems: Gels and Glasses

Title
Cellulose nanocrystals for gelation and percolation-induced reinforcement of a photocurable poly(vinyl alcohol) derivative

Presentation Date and Time
October 13, 2021 (Wednesday) 1:30

Track / Room
Track 6 / Ballroom 1

Authors (Click on name to view author profile)

  1. Corder, Ria D. (North Carolina State University, Chemical and Biomolecular Engineering)
  2. Adhikari, Prajesh (North Carolina State University, Chemical and Biomolecular Engineering)
  3. Burroughs, Michael C. (North Carolina State University, Chemical and Biomolecular Engineering)
  4. Rojas, Orlando J. (University of British Columbia, Chemical and Biological Engineering)
  5. Khan, Saad A. (North Carolina State University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Ria D. Corder1, Prajesh Adhikari1, Michael C. Burroughs1, Orlando J. Rojas2 and Saad A. Khan1
1Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC; 2Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia, Canada

Speaker / Presenter 
Khan, Saad A.

Keywords
experimental methods; composites; gels; polymer solutions; suspensions

Text of Abstract
Nanomaterials are regularly added to crosslinkable polymers to enhance mechanical properties; however, important effects related to gelation behavior and crosslinking kinetics are often overlooked. In this study, we combine cellulose nanocrystals (CNCs) with a photoactive poly(vinyl alcohol) derivative, PVA-SbQ, to form photocrosslinked nanocomposite hydrogels. We investigate the rheology of PVA-SbQ with and without CNCs to decipher the role of each component in final property development and identify a critical CNC concentration (1.5 wt%) above which several changes in rheological behavior are observed. Neat PVA-SbQ solutions exhibit Newtonian flow behavior across all concentrations, while CNC dispersions are shear-thinning <6 wt% and gel at high concentrations. Combining semi-dilute entangled PVA-SbQ (6 wt%) with >1.5 wt% CNCs forms a percolated microstructure. In situ photocrosslinking experiments reveal how CNCs affect both the gelation kinetics and storage modulus (G') of the resulting hydrogels. The modulus crossover time increases after addition of up to 1.5 wt% CNCs, while no modulus crossover is observed >1.5 wt% CNCs. A sharp increase in G' is observed >1.5 wt% CNCs for fully-crosslinked networks due to favorable PVA-SbQ/CNC interactions. A percolation model is fitted to the G' data to confirm that mechanical percolation is maintained after photocrosslinking. A ~120% increase in G' for 2.5 wt% CNCs (relative to neat PVA-SbQ) confirms that CNCs provide a reinforcing effect through the percolated microstructure formed from PVA-SbQ/CNC interactions. The results are testament to the ability of CNCs to significantly alter the storage moduli of crosslinked polymer gels at low loading fractions through percolation-induced reinforcement.