ABSTRACT
Polyurethanes prepared from vegetable oils display a number of desirable properties useful for many commercial and industrial applications. One unique application is that of an agricultural seed treatment. Seed treatments are used to incorporate pesticides onto the seed coat and to decrease the disease susceptibility of the seed during its germination in the soil. In addition, by altering the movement of water across the seed coat and by incorporating protective pesticides in the coating, seed coating polymers can enhance the germination and survival of the seed under adverse environmental conditions. Soy polyols alone, and in combination with glycerin, polymerized with 4,4'-diphenylmethane diisocyanate (MDI) were studied for their seed treating properties and impact on soybean seed germination. The cross-linking density and properties of these polyurethane compounds were varied by changing the isocyanate/hydroxyl molar ratios. In order to optimize the coating qualities and to increase the efficiency of the coating, acetone was also studied as a diluting solvent to reduce the viscosity of the polyurethane mixture prior to polymerization on the seed coat. Optimal polymerization and resulting germination (95%) were obtained using a 1:1 isocyanate/hydroxyl molar ratio consisting of a mixture of soy polyol 180 and glycerin, and the use of an equal volume of acetone as a dilution solvent. This optimal polyurethane seed treatment had several desirable qualities including: reduced viscosity, decreased seed coating thickness, increased seed coating uniformity and permitted larger volumes of seed to be treated with the same volume of polymer. This optimal seed treatment increased the soybean seed germination by 15%, as compared with untreated seed. In addition, preliminary studies of the compatibility of these unique formulations with commercial and experimental fungicides also support the use of these polymers as seed treatments due to their enhanced stability, longevity and slow active ingredient water teaching characteristics. Compatibility of these seed coating polymers as formulations with captan, metalaxyl, thiabendazole and novel antimicrobial lipids and triterpenoid compounds display that the active ingredients can readily provide a zone of fungal inhibition around the seed as it germinates in the presence of Macrophomina phaseolino, causal agent of charcoal rot of soybeans. However, the release of the active ingredient from the polyol seed treatments is less affected by water leaching as compared to commercially available water-soluble seed treating polymer formulations. This is most likely due to the polyols unique polymer cross-linking characteristics. These results support the continued exploration of soy polyol derived polymers as seed coating compounds.
