9 Computerized Optimization of Emulsifiers for Pesticide Emulsifiable Concentrates KEN MEUSBURGER
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Thompson-Hayward Chemical Company, Kansas City, KS 66106
The art of developing emulsifiers and emulsifier blends for pesticide emulsifiable concentrates has been practiced f o r many years. In a large number of cases, due to the complexity of emulsion systems and the time pressure placed on the p r a c t i t i o n e r , emulsif i e r s are designed by empirical test data coupled with i n t u i t i o n and experience. This t a l k will discuss a logical, numeric method of a) defining an emulsification problem i n terms of averaging e a s i l y understood parameters foroilmixtures, defining the water types, and emulsifier types desired; b) mathematically determining a near neighborhood "best" emulsifier combination to solve the emulsification problem; and c) a subsequent, computerization of the mathematical methods described above. The a g r i c u l t u r a l formulation chemist i s faced with myriad v a r i ables to evaluate i n the development of a new product. This i s an ideal type of problem environment for the employment of a s u i t able conçuter program. The computer program, based on a mathematical model, should be of such character to allow: 1) 2)
Ease of input data c o l l e c t i o n Logical evaluation of a l l pertinent variables and data within a clear, understandable, mathematical model 3) Generation of output data i n a sorted c o l l e c t i o n of "near-neighborhood" best results
For the development of agricultural emulsifiable concentrates the application of the principles of Cohesive Energy Density yields a mathematical model. This model, when written into a computer program, s a t i s f i e s the c r i t e r i a above. To demonstrate the effectiveness of t h i s approach, a review of the C.E.D. p r i n c i p l e s , with an example application, i s given 0097-6156/ 84/ 0254-0121 $06.00/ 0 © 1984 American Chemical Society
Scher; Advances in Pesticide Formulation Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
122
ADVANCES IN PESTICIDE FORMULATION TECHNOLOGY
below. The concept of Cohesive Energy Density was f i r s t develop ed by Hildebrand and Scott (1,2) i n t h e i r research to define a physical parameter which would predict the m i s c i b i l i t y of solvents. They found that the square root of the heat of vaporization divided by the molar volume of a solvent gave a useful s o l u b i l i t y parameter. Thus AHy - R T ^ 6 =
=
ΝπΓ» Hfc—>
where AHy i s the heat of vaporization, V i s the molar volume, and RT (3) i s a correction factor involving the universal gas constant and temperature. This parameter squared has the physical dimensions of calories per cubic centimeter. The theory implies, when considering two solvents, that i f t h e i r parameters d i f f e r by a value of less than 2, they are miscible, and i f t h e i r parameters d i f f e r by more than 3.5, they are immiscible. Using these paramemeters, Hildebrand was able to formulate an expression to de termine the energy of mixing and an approximate heat of mixing for the combination of two solvents (2)
Downloaded by CORNELL UNIV on October 7, 2016 | http://pubs.acs.org Publication Date: June 5, 1984 | doi: 10.1021/bk-1984-0254.ch009
m
Μ
Μ
ΔΗ ,ΔΕ =φ Φ Α
Β
(X V * X V ) ( 6 - δ / A
A
B
B
A
This equation uses the volume fractions of the two solvents, nominally A and B; the molar fractions of the two solvents φ Λ and φ ; the molar volumes of the two solvents and V ; and the difference between t h e i r respective C.E.D. parameters squared. This approach makes very reasonable predictions concerning the interactions of solvents. Charles M. Hansen (4) was working i n the area of paint tech nology. He was aware οΓ the Hildebrand/Scott s o l u b i l i t y param eter, and explored the use of the s o l u b i l i t y parameter i n poly mer-solvent interactions. He began his research with the con sideration of the thermodynamic equation f o r the energy of mixing Β
B
^MIX
=
TAS
^ I X " MIX
SOLUBILITY * AS Η^χ Ψ He noted that the s o l u b i l i t y increased f o r the interaction of two materials as the heat of mixing decreased. He, therefore, took note of the Hildebrand expression f o r the approximation of the heat of mixing
He found that the C.E.D. parameter d i f f e r e n t i a l was not accurate enough for his purposes. Further research showed that added precision could be given to the bulk parameter by considering that parameter as being composed of three d i s t i n c t types of
Scher; Advances in Pesticide Formulation Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
MEUSBURGER
9.
Computerized Optimization of Emulsifiers
123
interactive energies. He postulated that these three s p e c i f i c cohesive energies were attributed to the London cohesive energy, the Keesom cohesive energy, and the hydrogen bonding cohesive energy. He further postulated that these three energy contri butions to the bulk cohesive energy density parameter could be described i n a straightforward vector summation expression
Downloaded by CORNELL UNIV on October 7, 2016 | http://pubs.acs.org Publication Date: June 5, 1984 | doi: 10.1021/bk-1984-0254.ch009
6 2
= έ δ
+
6
P
+
δ
Α
He then proceeded to break up the solvent bulk parameter into respective dispersion forces: Keesom, or p o l a r i t y forces; hydrogen bonding forces; and London forces. He did the same for the polymers which were under his consideration. He compared these parameters for solvents and polymers term-wise, and ana lyzed their d i f f e r e n t i a l s i n order to make predictions concern ing t h e i r s o l u b i l i t y interactions. In conducting 10,000 inter action experiments involving solvents and polymers, he found that he could make accurate predictions i n 97% of the cases using his C.E.D. refinements. A. Beerbower and J.R. Dickey (5) were also concerned with the interactions of solvents and polymers as they were working i n an area concerning the effects of hydraulic f l u i d s on hoses and l i n i n g s . In applying the Hansen approach to their particu l a r set of polymers and solvents, they found that accurate pre dictions required the addition of a correction factor:
^
6
= ( DA "
+
δ
< ΡΑ - W
2
+
δ
< ΗΑ " W
2
2
"
