Advances in Pesticide Formulation Technology: An Overview

1 Advances in Pesticide Formulation Technology An Overview HERBERT B. SCHER

Downloaded by 5.189.205.204 on October 7, 2016 | http://pubs.acs.org Publication Date: June 5, 1984 | doi: 10.1021/bk-1984-0254.ch001

Stauffer Chemical Company, Richmond, CA 94804

Pesticide formulation science is a very broad field because i t must deal with formulation development, production and storage (1-4) as well as the interaction of the pesticide with plants, insects, mammals, soil, air and water (5). Pesticide formulations can be classified into the following types: ˙

Aqueous Solutions

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Emulsifiable Concentrates

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Dispersion Concentrates (Aqueous and Nonaqueous Flowables)

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Wettable Powders

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Dry Flowables (Water Dispersible Granules)

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Granules

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Controlled Release

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Others (Dusts, Aerosols, etc.)

The factors which influence the choice of formulation are pesticide physical properties (melting point, solubility, volatility), pesticide chemical properties (hydrolytic stability, thermal stability), soil application vs. foliar application, crop and cultural practice, pesticide biological properties (crop selectivity, transport), and economics. This book is a collection of papers concentrating on pesticide formulation topics which are currently receiving the greatest attention and where the greatest advances are being made. These topics are listed below and make up the four sections of the book. The number of papers in each section is given in parenthesis. 0097-6156/ 84/0254-0001 $06.00/ 0 © 1984 American Chemical Society

Scher; Advances in Pesticide Formulation Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

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ADVANCES IN PESTICIDE FORMULATION TECHNOLOGY

Flowable P r e p a r a t i o n and S t a b i l i z a t i o n [4] Use of Computers f o r E v a l u a t i o n and Optimization of Formulations [4] C o n t r o l l e d Release Formulations

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Selected General Formulation Topics Jo] Introductory remarks f o r each of these s e c t i o n s w i l l f o l l o w . I have a l s o added a f i f t h s e c t i o n to t h i s overview i n order to l i s t and b r i e f l y d i s c u s s t i m e l y p e s t i c i d e formulation t o p i c s which because of time l i m i t a t i o n s could not be included i n the symposium program. Important references are l i s t e d f o r each of these f i v e s e c t i o n s . Flowable P r e p a r a t i o n and S t a b i l i z a t i o n (6) If the t e c h n i c a l p e s t i c i d e has inherent p h y s i c a l p r o p e r t i e s (high melting p o i n t , f r i a b l e c r y s t a l , low s o l u b i l i t y and high chemical s t a b i l i t y i n continuous phase) that allow the development of a flowable formulation, many use advantages can be gained. Flowable formulations are easy to measure and a r e not dusty. In a d d i t i o n s i n c e the flowable formulation i s a predispersed system, good d i s p e r s i b i l i t y upon d i l u t i o n can be r e a d i l y achieved. Aqueous based flowables c o n t a i n no organic solvents and hence have high f l a s h p o i n t s and reduced t o x i c i t y and p h y t o t o x i c i t y . Water s o l u b l e or water d i s p e r s i b l e adjuvants such as f i l m forming agents can be added d i r e c t l y to aqueous based flowables. These f i l m forming agents are used to improve adhesion on f o l i a g e and to provide c o n t r o l l e d r e l e a s e . O i l based flowables where a l i q u i d p e s t i c i d e or i n e r t o i l comprises the continuous phase and an i n s o l u b l e s o l i d p e s t i c i d e comprises the dispersed phase a r e a l s o r e c e i v i n g a t t e n t i o n these days. Flowable formulations a l s o a f f o r d the opportunity to optimize b i o l o g i c a l a c t i v i t y and p h y s i c a l s t a b i l i t y by v a r y i n g p e s t i c i d e p a r t i c l e s i z e and shape. As described i n the previous paragraph, flowable formulations o f f e r many advantages. However i t i s i n the area of flowable p r e p a r a t i o n and s t a b i l i z a t i o n where problems can a r i s e and where extensive t e s t i n g must take p l a c e to assure high f o r m u l a t i o n quality. The type of d i s p e r s i n g and m i l l i n g equipment and type and c o n c e n t r a t i o n of wetting agents, d i s p e r s i n g agents, suspending agents, f i l m forming agents and f r e e z i n g point depressants must be chosen c a r e f u l l y to optimize b i o l o g i c a l and p h y s i c a l s t a b i l i t y . As w i l l be seen i n the second s e c t i o n , computer techniques are very u s e f u l i n t h i s o p t i m i z a t i o n process. R h e o l o g i c a l measurements are used to p r e d i c t p h y s i c a l s t a b i l i t y , and a c c e l e r a t e d and long term storage t e s t s a r e used to confirm p h y s i c a l s t a b i l i t y . There are four papers i n t h i s s e c t i o n which d e a l with these t o p i c s . The papers by Knowles e t a l . and Warrington e t a l . d e a l with novel



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An Overview

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suspension systems and the p r e d i c t i o n of s t a b i l i t y u s i n g rheol o g i c a l measurements. The papers by F r a l e y and Dombrowski d e a l with d i s p e r s i n g and m i l l i n g equipment. The paper by G l a t z h o f e r forms a bridge between t h i s s e c t i o n (Flowables) and the second s e c t i o n (Computer A p p l i c a t i o n s ) . G l a t z h o f e r d e s c r i b e s a system where a computer i s coupled to a viscometer. He uses t h i s system to evaluate flowable formulations a f t e r a c c e l e r a t e d and long term storage. One t o p i c which i s not covered i n t h i s s e c t i o n i s the p r e p a r a t i o n and s t a b i l i z a t i o n of emulsion type flowables ( o i l i n water flowables ) (7). T h i s type o f f l c w a b l e i s j u s t beginning to r e c e i v e widespread a t t e n t i o n and i s s t i l l very much i n the experimental stage. In a d d i t i o n to the other f a c t o r s considered above, f a c t o r s which i n f l u e n c e o i l d r o p l e t coalesence, such as i n t e r f a c i a l f r e e energy, e l e c t r o s t a t i c s t a b i l i z a t i o n and s t e r i c s t a b i l i z a t i o n , must be taken i n t o c o n s i d e r a t i o n f o r t h i s s p e c i a l type flowable. Use of Computers f o r E v a l u a t i o n and O p t i m i z a t i o n of Formulations Computers a r e being used v e r y e f f e c t i v e l y f o r e v a l u a t i o n and o p t i m i z a t i o n o f p e s t i c i d e f o r m u l a t i o n s . Computer a s s i s t e d o p t i m i z a t i o n o f f o r m u l a t i o n p h y s i c a l and b i o l o g i c a l p r o p e r t i e s and cost (responses) v s . type and c o n c e n t r a t i o n of i n g r e d i e n t s ( i n dependent v a r i a b l e s ) can be d i v i d e d i n t o three p a r t s . 1. Experimental Design and C o l l e c t i o n of Data (8) S t a t i s t i c s are u t i l i z e d to e f f i c i e n t l y sample e x p e r i mental space. 2. C o r r e l a t e Experimental Data by Regression A n a l y s i s ( 9 ) S t a t i s t i c s a r e u t i l i z e d to measure the degree of c o r r e l a t i o n between responses and independent v a r i a b l e s . Important independent v a r i a b l e s are i d e n t i f i e d . 3. Optimize P h y s i c a l and B i o l o g i c a l P r o p e r t i e s and Cost (10) - Construct response s u r f a c e s and choose a s e t of independent v a r i a b l e s to optimize responses. Since each response may not be optimized by the same s e t of i n dependent v a r i a b l e s , compromises may have to be made which r e f l e c t the r e l a t i v e importance of the responses. In a d d i t i o n to u t i l i z i n g computers to optimize p e s t i c i d e f o r mulations, computer programs can be designed to operate equipment used to evaluate p e s t i c i d e f o r m u l a t i o n s and to perform complex t h e o r e t i c a l c a l c u l a t i o n s used to guide choice of i n g r e d i e n t s . Of course, computers can a l s o be used f o r f o r m u l a t i o n data storage and a c q u i s i t i o n . There a r e four papers i n t h i s s e c t i o n which d e a l with these t o p i c s . Papers by Botts and Mookerjee d e s c r i b e the theory and programs a s s o c i a t e d with experimental design, c o r r e l a t i o n and o p t i m i z a t i o n . Both authors work through a c t u a l problems.


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The paper by G l a t z h o f e r describes how a computer can be used to operate a viscometer and the paper by Meusberger describes how computer c a l c u l a t i o n s based on s o l u b i l i t y parameter theory can be used to optimize the choice of e m u l s i f i e r s f o r p e s t i c i d e emulsif i a b l e concentrates. C o n t r o l l e d Release Formulations (.11-15) C o n t r o l l e d r e l e a s e p e s t i c i d e formulations can be used to reduce mammalian t o x i c i t y and extend a c t i v i t y , to c o n t r o l evaporation, to reduce p h y t o t o x i c i t y , to p r o t e c t p e s t i c i d e s from environmental degradation, to reduce l e a c h i n g and to reduce p e s t i c i d e l e v e l s i n the environment. C o n t r o l l e d r e l e a s e p e s t i c i d e formulations can be d i v i d e d i n t o four main systems: 1) polymer membrane - p e s t i c i d e r e s e r v o i r systems; 2) matrix systems c o n t a i n i n g p h y s i c a l l y trapped p e s t i c i d e s ; 3) polymer systems c o n t a i n i n g c o v a l e n t l y bound p e s t i c i d e s ; and 4) coated p e s t i c i d e granule systems. The polymer membrane - p e s t i c i d e r e s e r v o i r systems are d i f f u s i o n c o n t r o l l e d and i n c l u d e microcapsules and m a c r o s t r i p s . The matrix systems can be subdivided i n t o i n e r t and e r o d i b l e c a t e g o r i e s . The r e l e a s e of p e s t i c i d e from an i n e r t matrix system i s d i f f u s i o n c o n t r o l l e d while the r e l e a s e of p e s t i c i d e from an e r o d i b l e matrix system i s c o n t r o l l e d by the r a t e of degradation of the matrix. The r a t e of r e l e a s e of a p e s t i c i d e c o v a l e n t l y bound to a polymer depends on the r a t e of cleavage of the s p e c i f i c chemical l i n k a g e which attaches the p e s t i c i d e to the s u b s t r a t e . The r a t e of r e l e a s e of p e s t i c i d e from a polymer coated p e s t i c i d e granule depends on f a c t o r s such as the r a t e of degradation of the c o a t i n g and the r a t e of water entry through the c o a t i n g . There are three papers i n t h i s s e c t i o n which d e a l with these t o p i c s . The paper by Dahl and Lowell deals with the e f f e c t of Methylparathion microcapsules on bees and d e s c r i b e s f o r m u l a t i o n e f f o r t s underway to reduce bee toxicity. The paper by Evans d e s c r i b e s the use of microencapsulat i o n to combine the e f f e c t s of i n s e c t pheromones ( a t t r a c t i n s e c t s ) and s y n t h e t i c p y r e t h r o i d s ( k i l l i n s e c t s ) . The paper by Peterson d e s c r i b e s spray d r y i n g of a polymer l a t e x on a a c a r i c i d e powder formulation to reduce p h y t o t o x i c i t y . Selected General Formulation Topics There are s i x papers i n t h i s s e c t i o n . They d e a l with b i o l o g i c a l i n s e c t i c i d e formulations (Ward), water d i s p e r s i b l e granules (Wright and Ibrahim), a n a l y s i s of formulations f o r q u a l i t y c o n t r o l and i d e n t i f i c a t i o n of t o x i c contaminants (Plimmer), i d e n t i f i c a t i o n of s u r f a c t a n t metabolites (Stolzenberg et a l . ) , e l e c t r o s t a t i c spraying (Law) and c o m p a t i b i l i t y and tank-mix t e s t i n g (Tarwater). Timely P e s t i c i d e Formulation Topics Not Included i n Symposium E f f e c t of S u r f a c t a n t s on Wetting, P e n e t r a t i o n and Transport of P e s t i c i d e s i n P l a n t s and Insects (16-17). Some of the f a c t o r s which a f f e c t the wetting, p e n e t r a t i o n and t r a n s p o r t processes are



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droplet s i z e , surface tension, contact angle, and concentration and nature of s u r f a c t a n t . The nature of the s u r f a c t a n t includes p r o p e r t i e s such as h y d r o p h i l e - l i p o p h i l e balance, s o l u b i l i t y p a r a meter, molar volume and e l e c t r o n i c charge. T h i s i s a t o p i c where i t i s very d i f f i c u l t to separate e f f e c t s and understand mechanism of a c t i o n . Hence i t i s d i f f i c u l t to t r a n s f e r information from one p e s t i c i d e or biosystem to another and a great deal of t r i a l and e r r o r work must s t i l l go on. Vegetable O i l D i l u e n t s f o r P e s t i c i d e A p p l i c a t i o n (18-19), Veget a b l e o i l s such as soybean o i l and cottonseed o i l are being t e s t e d as p e s t i c i d e d i l u e n t s to replace water i n u l t r a l o w volume (ULV) f o l i a r a p p l i c a t i o n s . Most of the t e s t s are being conducted using f o l i a r i n s e c t i c i d e s and f u n g i c i d e s , however some t e s t s using post-' emergent h e r b i c i d e s are a l s o i n progress. For ULV a p p l i c a t i o n s , the p e s t i c i d e i s blended w i t h vegetable o i l to produce a formulat i o n of known p e s t i c i d e l o a d i n g and t h i s formulation i s d i l u t e d with more vegetable o i l i f necessary i n order to achieve an o i l coverage ranging from 1/4 to 1/2 g a l l o n per acre. Some ULV a p p l i cators using vegetable o i l have claimed l e s s p e s t i c i d e h y d r o l y s i s problems, fewer adjuvants r e q u i r e d , p r o t e c t i o n of p e s t i c i d e from s u n l i g h t , l e s s r a i n washoff, b e t t e r spreading and p e n e t r a t i o n on i n s e c t s and weeds, reduction i n v o l a t i l i t y , l e s s d r i f t , and the r e d u c t i o n of r a t e s . However, a l o t more f i e l d work (with the appropriate c o n t r o l s ) w i l l be required to f u l l y s u b s t a n t i a t e these claims. In a d d i t i o n , formulators using vegetable o i l w i l l have to guard against the o x i d a t i o n of the p e s t i c i d e during manufacture, storage and a p p l i c a t i o n , the v a r i a b i l i t y i n o i l composition and the impact on mammalian t o x i c i t y . Vegetable o i l s with an e m u l s i f i e r are a l s o being tank mixed with p e s t i c i d e formulations i n water i n an attempt to achieve some of the advantages l i s t e d above f o r ULV a p p l i c a t i o n s . Results are i n c o n c l u s i v e at t h i s time. P e s t i c i d e Formulations f o r Seed Treatment (20) and Dry F e r t i l i z e r Treatment (21). P e s t i c i d e handling, a p p l i c a t i o n and i n c o r p o r a t i o n can be s i m p l i f i e d and made l e s s expensive by using seeds and f e r t i l i z e r granules as p e s t i c i d e c a r r i e r s . These techniques r e duce the number of passes a farmer needs to make over a f i e l d , although c u l t i v a t i o n i s o f t e n required i f h e r b i c i d e coated seeds are placed too f a r apart. One problem i n using these techniques i s g e t t i n g s u f f i c i e n t quantity of p e s t i c i d e adhered to the seed or f e r t i l i z e r granule. Solutions to t h i s problem i n c l u d e using a powdered c l a y or s i l i c a to help absorb l i q u i d p e s t i c i d e s , using microencapsulated l i q u i d p e s t i c i d e s , and using a polymer coating to increase adhesion of pesticide particles. In a d d i t i o n to g e t t i n g s u f f i c i e n t p e s t i c i d e loading on the seeds or f e r t i l i z e r granules, there are two other p o t e n t i a l problem areas which r e q u i r e extensive i n v e s t i g a t i o n : phytot o x i c i t y of p e s t i c i d e on seeds and chemical degradation of p e s t i c i d e on f e r t i l i z e r granules.


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P e s t i c i d e Formulations f o r Use with Conservation T i l l a g e (22). R i s i n g f u e l costs and the need to prevent s o i l e r o s i o n and to save s o i l water has spurred i n t e r e s t i n conservation t i l l a g e techniques. These techniques o f t e n r e q u i r e s p e c i a l granular formulations capable of p e n e t r a t i n g p l a n t r e s i d u e and preventing p e s t i c i d e evaporation and UV a t t a c k while the granules remain on the s o i l surface. In c o n c l u s i o n I t h i n k i t can be s a f e l y s a i d that the advances i n p e s t i c i d e f o r m u l a t i o n technology which are described i n t h i s book are p l a y i n g a v i t a l r o l e i n the development of s a f e , e f f i c a c i o u s and economically a t t r a c t i v e p e s t i c i d e products.


Literature Cited 1. 2. 3. 4. 5. 6. 7.

8. 9. 10. 11. 12. 13. 14. 15.

Geissbuhler, H. (Editor) "Advances in Pesticide Science Part 3"; Pergamon Press: Oxford, U.K., 1979; pp. 717-826. Miyamoto, J. and Kearney, P.C. (Editors) "Pesticide Chemistry - Human Welfare and the Environment - Volume 4"; Pergamon Press: Oxford, U.K., 1983; pp. 241-400. Valkenburg, W. van (Editor) "Pesticide Formulations"; Marcel Dekker, Inc: New York, USA, 1973. Seymour, K.C. (Editor) "Pesticide Formulations and Applica tion Systems: Second Conference"; ASTM: Philadelphia, PA, 1983. Hartley, G.S. and Graham-Bryce, I.J. "Physical Principles of Pesticide Behavior"; Academic Press: London, U.K., 1980. Tadros, Th. F. Advances in Colloid and Interface Science 1980, 12, 141-261. Tsuji, K. and Fuyama, Η., in "Pesticide Chemistry - Human Welfare and the Environment - Volume 4"; Miyamoto, J. and Kearny, P.C., Ed.; Pergamon Press: Oxford, U.K., 1983; p. 361. Hendrix, C.D., Chem Tech 1979, 9, pp. 167-174. Daniel, C. and Wood, F.S. "Fitting Equations to Data"; Wiley Interscience: New York, N.Y., 1971. Hare, L.B. and Brown, P.L., J. Quality Technology 1977, 9, 193-197. Cardarelli, N.F. "Controlled Release Pesticide Formulations"; CRC Press: Clevland, Ohio, 1976. Paul, D.R. and Harris, F.W. (Editors) "Controlled Release Polymeric Formulations" ACS SYMPOSIUM SERIES No. 33; American Chemical Society: Washington, D.C., 1976. Scher, H.B. (Editor) "Controlled Release Pesticides" ACS SYMPOSIUM SERIES, No. 53; American Chemical Society: Washington, D.C., 1977. Kydonieus, A.F. "Controlled Release Technologies: Methods, Theory and Applications"; CRC Press: Clevland, Ohio, 1980, Langer, R., Chemical Engineering Communications 1980, 6, pp. 1-48.


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16. Hodgson, R.H. (Editor) "Adjuvants for Herbicides"; Weed Science Society of America: Champaign, Illinois, 1982. 17. Mittal, K.L. and Fendler, E.J. (Editors) "Solution Behavior of Surfactants"; Plenum: New York, N.Y., 1982; Seaman, D. (Author), pp. 1365-1380. 18. Kyle, J., Agrichemical Age, June 1982, p. 24. 19. Sckerl, Μ., Agrichemical Age, April 1983, p. 25. 20. Porter, F., Agrichemical Age, March 1982, pp. 21-22. 21. Gubrud, R., Agrichemical Age, October-November 1982, pp. 34-36. 22. Richardson, L., Agrichemical Age, October-November 1982, pp. 10-11. February 9,

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Advances in Pesticide Formulation Technology: An Overview

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