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Rheological characteristics of aqueous wax emulsions used for the controlled release of pheromones as an alternative to the use of pesticides for insect pest management

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Stephen Daniel Ballew (Creator)
Institution
Western Carolina University (WCU )
Web Site: http://www.wcu.edu/404.asp
Advisor
Cynthia Atterholt

Abstract: Most pesticides produce some risk of harm to the environment because pesticides are designed to kill or adversely affect living organisms (US EPA, 2010). It is desirable that alternate, safer forms of pest control be developed. One alternative is the controlled release of pest insect sex pheromones to produce a mating disruption effect (Ahmed et al., 1993; Atterholt, 1996). Aqueous paraffin wax emulsions have shown much promise as formulations for this controlled release when applied to tree bark or foliage (Atterholt et al., 1996; Rice et al., 1997; Atterholt et al., 1998; Atterholt et al., 1999; Meissner et al., 2000; de Lame, 2003). Soy wax has recently become of interest in pheromone formulations because it is renewable, biodegradable, commercially available, and acceptable for organic farming (Behle, 2008). Emulsions exhibit complex flow behavior which can be studied using rheometry (Macosko, 1994; Mezger, 2006). Rheometry refers to experimental techniques to determine the fundamental relationships between force and deformation in materials (Macosko, 1994). The rheological properties of emulsions are very important for production, storage, and application of these formulations (Mezger, 2006). In this project the flow and viscoelastic properties of aqueous 30% paraffin wax and soy wax emulsions were investigated using three different emulsifiers: sorbitan monostearate (Span 60®), triethanolamine (TEA) stearate, and a 50%-50% mixture of both. Span 60® has already been used to make effective emulsions for the controlled release of pheromones, and it is food safe (Atterholt et al., 1996; Rice et al., 1997; Atterholt et al., 1998; Atterholt et al., 1999; Meissner et al., 2000; de Lame, 2003). TEA stearate is widely used to make nontoxic wax emulsions in the cosmetics industry (Wilkinson, 1940). The investigations were carried out in both the rotational and oscillatory modes of a parallel-plate rheometer. The flow curves at three different temperatures (15 °C, 25 °C and 35 °C) of each emulsion were fitted with the Herschel-Bulkley model with the yield points determined using the one tangent method. The resulting equations can predict flow behavior at different conditions (Mezger, 2006). The emulsions were also tested using a temperature sweep at low shear from 15 °C to 50 °C to investigate temperature dependent changes. The viscoelastic properties were investigated using oscillatory shear tests and expressed in terms of elastic modulus and loss modulus. This gives information about time-dependant behavior like storage and the elastic character of the formulations which were found to be weak gels (Mezger, 2006). The Span 60® emulsions displayed faux shear-thickening behavior due to droplet subdivision while the other emulsions generally displayed shear-thinning behavior. Each emulsion approaches an infinite shear viscosity. The yield points and other flow parameters for the emulsions varied with temperature, depending on the formulation in question. All soy wax emulsions showed an increase in viscosity between 45 °C and 50 °C while the paraffin wax emulsions did not. Every emulsion showed long-term and short-term stability (Mezger, 2006).

Additional Information

Publication
Thesis
Language: English
Date: 2011
Keywords
emulsion, paraffin wax, pesticide, rheology, rheometry, soy wax
Subjects
Pheromones
Emulsions
Rheology