How to Increase in Crosslink Density

Increasing a liquid's crosslink density results in an increase of the viscosity.

Crosslink density determines the viscosity of a polymer. Viscosity refers to the ability of a liquid to flow and a polymer is a naturally occurring or synthetic compound consisting of large molecules. A polymer is composed of a repeating sequence of simple monomers. Low-density crosslinking results in a high rate of flow, whereas a large density of crosslinks results in a more viscous or even a rigid or glassy texture. It is possible to increase the crosslink density in polymers, thus changing the mechanical structure of the polymer as well as its uses.

Things You'll Need

• 1500 milliliter beaker
• Double-distilled water, 1500 milliliters or more
• 1 gram super absorbent resin
• 100 mesh wire gauze
• Soft open-cell polyurethane foam
• Glass stirring rod

Instructions

Increasing Crosslink Density in a Polymer

1. Prepare a clean 1500 milliliter beaker by cleaning it with hot water and drying. Fill the beaker three-quarters of the way with double-distilled water. Distilled water is water that has been purified by boiling the water and then condensing the steam. Double-distilled water has been processed twice. It is more cost-effective to purchase double distilled-water for this process than to create your own.

2. Obtain or create a super absorbent resin. A super absorbent is synthesized through solution polymerization. One example is that of cotton flock fibers used as a raw material, which are modified with chloroacetic acid to obtain carboxymethyl cellulose, or CMC. Through further chemical processing, the prepared resin absorbs 2500 times more water. The goal of this process is to increase the crosslink density of this resin.

3. Disperse one gram of the super absorbent resin into the 1500 milliliter beaker of double-distilled water. Agitate the mixture moderately with the stirring rod and allow 30 minutes for the resin to absorb the distilled water. This will result in the swelling of the resin as it absorbs the water. The resulting effect, in addition to the swelling of the resin, is an increase in the crosslink density of this polymer.

4. Strain the mixture through a 100 mesh wire gauze. Dry with a soft open-cell polyurethane foam. The resulting gel will contain a significant higher density of crosslinks and a more viscous, thicker resin. If the crosslink density increases significantly, this can change the potential uses of the polymer in industrial applications.

References

• Research Center of Iran; Swelling and Crosslink Density Measurements for Hydrogels; Omidian Hussein, et al.
• CAB Direct: Preparation of Super Absorbent Resin
• Nature.com: Glossary