Polymeric Rheology Modifier for Oil Dispersions

Abstract

A typical oil dispersion (OD) contains an oil, a powder (agrochemical) suspended in the oil as a carrier, an emulsifier capable of emulsifying the oil when diluted in water before spraying, a rheology modifier that can thicken and suspend the powder in the oil during storage, and optionally a suspension aid that can suspend the powder during spraying after the OD is diluted in water. Current commercially available rheology modifiers (thickeners) used or suggested for OD formulations have drawbacks. They are either difficult to handle (very dusty powder) or require heating or the use of a protonic solvent to activate thickening. In addition, their thickening property is sensitive to ionic surfactants such as Ca-DDBS and temperature change. In this paper, a new type of oil thickener, a polymer, without the drawbacks of current oil thickeners, is introduced. It is believed that the new type of oil thickener uses a chain entanglement or excluded volume-thickening mechanism rather than the associative- or solidification-thickening mechanism employed by the current thickeners. A few stable OD prototypes containing powder pesticides (5 %–48 %), emulsifiers (6 % or less), and this unique polymeric rheology modifier (3 % or less) in oils (soy methyl ester or Aromatic 200) are presented. A correlation between OD stability and the loss-factor frequency dependence (G″/G′, the ratio of loss modulus to storage modulus) is established. In particular, when G″/G′ is less than 1, the OD is stable. When G″/G′ is greater than 1, the OD is unstable and the solid particles tend to settle to the bottom.