2022 Annual Meeting

Method Development of a Compression Test for Hydrogel Beads Using a Parallel-Plate Rheometer

Chlorinated Aliphatic Hydrocarbons have been reported as “the most frequently occurring type of contaminant in soil and groundwater at Superfund and other hazardous waste sites in the United States'' by the U.S. EPA. Long-term contamination of sites has led to the contamination of low-permeability zones, such as clay layers, where common remediation techniques become costly and unsustainable. Bioremediation can be employed to treat the contaminants in situ, and can be enhanced when applied as a permeable reactive barrier. Permeable reactive barriers consist of well reactors in the direction of the groundwater flow that treats the groundwater as it passes through the barrier. We propose implementing bioremediation in permeable reactive barriers with immobilized bacteria cultures, where cultures are entrapped into the matrix of hydrogel beads. For bioremediation applications, hydrogels must exhibit high mechanical strength and biocompatibility. Alginate is a biocompatible polymer, naturally occurring in brown algae. This polymer can be ionically crosslinked, forming a molecular network with high mechanical properties.

To ensure hydrogel beads can withstand the weight of packing and constant groundwater flow, the hydrogel beads must exhibit a high strength. The compressive modulus, or Young’s modulus, constitutes the bead strength. Many methods exist to characterize the Young’s modulus of a hydrogel bead; however the unconfined compression tests using a parallel plate geometry on a rheometer provided reproducible results comparable to literature values. Thus, our goal is to demonstrate the capability of our method to match other Young’s modulus data, determine Young's modulus as a function of the polymer concentration and time of crosslinking, and elucidate how modifying the geometry surfaces (slip vs. non-slip surfaces) effects the Young’s modulus.

In this study, we investigated the young’s moduli of alginate beads determined by compression tests on our AR-G2 TA Instruments rheometer. We evaluated the young’s modulus at 5 different crosslinking times and 5 different concentrations of alginate in the hydrogel beads. Further, we examined the implications of slip vs. non-slip geometries on the compression test using a smooth surface and sandpaper.