(722a) Development of Double-Layer Hydrogels for Agricultural Applications

Hydrogels offer the ability to slowly release moisture and nutrients to plants which can considerably reduce the amount of freshwater and fertilizer needed and the associated labor costs in agriculture. Polyacrylamide (PAAm) hydrogels are being produced commercially for such applications, but they are quite fragile and break apart easily losing their water retention properties. Additionally, while these hydrogels can rapidly absorb large amounts of water, they also dehydrate very rapidly in a matter of hours. In this study, we are developing a two layer PAAm-based hydrogel to overcome these disadvantages. The outer layer is made up of either highly crosslinked PAAm or polyurethane (PU), providing low aqueous permeability and high mechanical strength. Dehydration measurements showed that the double layer hydrogel with a PU outer took longer to dehydrate than the hydrogel with a PAAm outer layer. The hydration/dehydration rates of these PU-PAAm hydrogels are a function of the pore sizes of the PU outer layer hydrogel, which in turn was determined by the molecular weight of the polyethylene glycol used to synthesize PU. The inner layer of these gels consists of soft, low crosslinked PAAm which retains the high water absorbing property, ensuring its ability is to supply sufficient water to plants. The combined system results in a gel with adequate mechanical strength for deployment in soils as well as extending the gel dehydration time to nearly a week.