Hydrogels are polymer chains comprising of repetitive units with the capability of absorbing water molecules. Certain hydrogels are capable of absorbing as much as 500 times their weight in water.
This superabsorbent property renders hydrogels useful in conserving water as well as solving other environmental issues.
There are two broad classifications of polyacrylamide (PAM) hydrogels, soluble (linear) and insoluble (cross-linked) hydrogels:
- Linear PAM is water-soluble and has been successful in minimizing irrigation-induced erosion in agricultural fields.
- Cross-linked PAM is not water-soluble but forms a gel when water is added and is used in landscaping, gardening and in typical nursery situations for retaining moisture.
Insoluble PAM products are commercially available as hydrating crystals or superabsorbent gels. These gels absorb water swelling to several times their original size. Water is slowly released to the soil as they dry.
When preparing hydrogels the physical structure features and ionic charge have to be taken into consideration into the classify them into:
- Homopolymer hydrogels
- Copolymer hydrogels
- Multipolymer hydrogels
- Interpenetrating polymeric hydrogels.
Use of Hydrogels in Preventing Soil Erosion
Soluble hydrogels have been used for more than a decade for reducing erosion and improving water infiltration of fine textured agricultural soils.
The soluble PAM hydrogels dissolve in water forming a thin slimy film, which coats the surface of the soil.
In irrigation furrows and other bare soils where irrigation may make erosion worse, this film helps in protecting the soil from washing away and hydrates the surface so that irrigation water can permeate easily.
Several studies have been done on a number of soils in varied environments showing that agricultural PAMs are a suitable solution to degradation and soil loss. Anionic soluble PAM hydrogels are more effective than cationic formulations in the reduction of soil erosion.
Hydrogels as a Replacement to Plastics
Plastic polymers can be made easily and, are both efficient and economical but not very eco-friendly. Hydrogels had not been considered previously as a suitable alternative since they are 'gels'. However, when they are attached to clay, they possess characteristics that make them a possible alternative to non-eco-friendly plastics.
They possess enhanced mechanical properties when compared to other hydrogels since they can be molded into free-standing shapes and are robust as well as undergo self-healing when cut. The most attractive aspect is that you just need a container of water and something to stir with.
Other Eco-Friendly Applications
Other Environmental applications for hydrogels are:
- They help conserve water and retain moisture by helping soil increase water holding capacity enabling the survival of plants during drought.
- They help the environment through soil management, erosion control and environmental cleanups
- The amount of available moisture is increased by the use of hydrogels and water stress of plants which is reduced, causing increased plant performance and growth.
- Hydrogels also claim to reduce leaching of fertilizers. This occurs when the fertilizer interacts with the polymer.
Other Applications for Hydrogels
Other applications for hydrogels include the following:
- Use as scaffolds in tissue engineering
- Hydrogel-coated wells for cell culture
- Environmentally sensitive hydrogels or intelligent gels or smart gels can sense changes in temperature, pH or concentration of metabolite and release their load due to this change
- Can be used as a sustained-release drug delivery systems.
- Can provide desloughing, absorption and debriding of fibrotic and necrotic tissue
- Hydrogels sensitive to specific molecules can be used as biosensors
- Can be used as contact lenses, ECG and EEG medical electrodes, water gel explosives
- Used for rectal drug delivery and diagnosis
- Breast implants, granules for retaining soil moisture, dressings for healing burns or hard-to-heal wounds
- Natural hydrogels are being studied for further tissue engineering
Common Applications: Hydrogels can be used in contact lenses
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Belgian scientist Willem Van Cotthem is aiming to grow tropical crops worldwide wherever it is warm. His technology uses agricultural hydrogels which, after trapping water, release them slowly into the roots of plants. Van Cotthem has devised a soil conditioner known as terracottem. Terracottem is an 8 – 12 inch dirt layer in which agricultural hydrogels are impregnated along with organic agents that nourish the natural bacteria present in soil.