Absorbent Protein Meal Based Hydrogels
Non-purified soymeal is used as an inexpensive and biobased reactive filler in preparing high capacity hydrogels. Preparation of these hydrogels involves partial neutralization of acrylic acid, which is subjected to free-radical initiated polymerization in the presence of crosslinkers such as trimethylolpropane triacrylate. A key approach in obtaining high performance hydrogels involves the removal of low molecular weight acrylic acid oligomers by a simple extraction procedure.Description
Absorbent hydrogels are formed by grafting a monomer such as acrylic acid or acrylamide with a protein meal base, such as soybean meal. More specifically, a mixture of protein meal base, a radical initiator, a cross-linking agent and a polymerizable monomer is degassed and heated at a temperature of approximately 80° C. for about 2 hours to form an absorbent hydrogel. Optionally, a radical accelerant of tetramethylethylenediamine (TMEDA) or sodium bisulfite (NaHSO3) is also added to the mixture. Preferably, the radical initiator is ammonium persulfate (APS) or potassium persulfate (KPS); and the cross-linking agent is trifunctional trimethylolpropane trimethacrylate (TMPTMA) or methylene bis acrylamide (MBA). The polymerizable monomer is preferably acrylic acid, or a combination of acrylic acid and acrylamide. Useful hydrogel compositions include ratios of acrylic acid to protein meal base between 5:1 and 1:1. Broadly, typical particle sizes for soy meal or bone meal and the like include 100-1500 mesh, preferably between 300-1000 mesh. The as-formed hydrogel is then subjected to a washing process utilizing either water or an organic solvent, an initial water wash followed by washing with organic solvent, or using a mixture of water and organic solvent in order to extract non-reactant components from the gel, before subjecting the gel to a final drying process. The resultant dried absorbent and superabsorbent hydrogels have high water uptake ratios, and can be utilized for a variety of applications.Benefits
• Incorporation of soymeal concentrations approaching 40 percent significantly decreases the cost of acrylic acid-based hydrogels.
• Water uptake values as high as 600-800g water per gram dry hydrogel have been obtained.
• Comparative testing against commercial hydrogels indicates that Battelle hydrogels absorb 2-3 times more water than commercial hydrogels.
• Whereas the water uptake of “anionic” type hydrogels is typically decreased by exposure to salt-containing water, the water uptake values of Battelle “anionic” hydrogels were found to be less susceptible to salt in water than well-known commercial hydrogels.
• Agricultural remediation in which hydrogels are applied to the soil or used to coat seeds prior to planting
• Forest fire-fighting wherein the fully loaded hydrogel can be dropped in the path of the fire and the contained water will not soak into the ground
• Remediation of toxic metal- contaminated areas (feasible but not yet demonstrated)
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Absorbent protein meal base hydrogels
Absorbent hydrogels are formed by reacting a protein meal base, a radical initiator and a polymerizable monomer. Optionally, a cross-linking agent and/or a radical accelerant, such as tetramethylethylenediamine (TMEDA) or sodium bisulfite (NaHSO.sub.3), is also added to the mixture. Preferably, the radical initiator is ammonium persulfate (APS) or potassium persulfate (KPS), and the cross-linking agent is preferably trifunctional trimethylolpropane trimethacrylate (TMPTMA) or methylene bis acrylamide (MBA). The polymerizable monomer is preferably acrylic acid, or a combination of acrylic acid and acrylamide. The as-formed hydrogel is washed in order to extract non-reactant components from the gel and then dried. The resultant absorbent and superabsorbent hydrogels have high water uptake ratios, and can be utilized for a variety of applications.
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