Hydrogels have been the subject of much research recently due to their absorption of high amounts of water. Due to their hydrophilicity, biodegradability, and compatibility with human tissue, the nanocellulose hydrogels are of particular interest for possible application in medicine. In the thesis I studied the influence of zirconium ion crosslinker on properties of TEMPO-modified nanocellulose hydrogels.
TEMPO-modified nanocellulose (and other anionic polymers) can crosslink in the presence of cations. This is due to electrostatic interactions between cation and anionic functional group on the polymer, which results in crosslinking of the polymer into three-dimensional structure. The crosslinking results in an increase in values of storage and loss modulus and viscosity. It also makes hydrogel more durable and easier to handle.
In my master's thesis, I studied the rheological properties of TEMPO-modified nanocellulose hydrogels crosslinked with zirconium ions. For crosslinking, I used Bacote crosslinker, which is a basic solution of zirconium ions. I also observed the effect of pH value on the rheological properties of the hydrogel and the effect of crosslinking with a dropper or spray on the TEMPO-NFC suspension. I found that increasing the proportion of crosslinker in the hydrogel increases its viscosity and elastic response. I also found that hydrogels in an acidic environment reduce the viscosity and value of the elastic and viscous modulus, most likely due to the protonation of carboxylate functional groups on the polymer. The results also show that drip crosslinking was more effective than spray crosslinking due to the better distribution of the crosslinker over the surface of the TEMPO-NFC suspension.
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