The development and characterization of double layer hydrogel for agricultural and horticultural applications.

摘要

This research aimed to develop hydrogels for agricultural and horticultural application. The most remarkable characteristic of hydrogels is their ability to absorb large amounts of aqueous solutions, such as pure water and nutrient solution. They could make plants grow at optimal environments as the release of water and nutrients is controlled into soils. The advantages not only keeps continuous optimal environment but also reduces the use of freshwater and associates labor cost, being compared to directly sprinkling water to plants.;Currently, commercial hydrogels are being produced from these hydrogel advantages. However, there are a few drawbacks. Firstly, while these hydrogels can rapidly absorb large amounts of water, they also dehydrate very rapidly in a matter of hours. Secondly, they are fragile and break apart easily losing their water retention properties. In this study, we tried to overcome the weakness of commercial hydrogels.;We researched the dehydration and mechanical characteristics of various types of hydrogels, such as pure hydrogels and ionic hydrogels. Based on these studies, we designed a double layer PAAm-based hydrogel to overcome the inherent weakness of pure and ionic hydrogels which are kinds of commercial hydrogels. The inner layer gel consists of soft, low crosslinked PAAm which retains the high water absorbing property, ensuring its ability is to supply sufficient water, while the outer layer is made up of either highly crosslinked PAAm or polyurethane (PU), providing low aqueous permeability and high mechanical strength. The dehydration rates of PU-PAAm double layer hydrogels could be controlled by the pore sizes of PU coating layer determined by the molecular weight of polyethylene glycol and by the thickness of coating layer.;In addition, the cross-linking density of inner gel and the temperature of coating solution affected the dehydration rate of PU-PAAm double layer hydrogels. Such a double layer design resulted in mechanical stability for deployment in soils as well as continuous dehydration time over a week at a room atmosphere and nutrients release until one week in DI water.