Advances in Pesticide Formulation Technology - American Chemical

14 Steps of Water Dispersible Granule Development J. F. WRIGHT and Ν. I. IBRAHIM

Downloaded by UNIV OF MINNESOTA on October 19, 2013 | http://pubs.acs.org Publication Date: June 5, 1984 | doi: 10.1021/bk-1984-0254.ch014

FMC Corporation, Agricultural Chemical Group, Princeton, NJ 08540

The development and marketing of water dispersible granule (WDG) or dry flowable (DF) formulations is on the increase. Unique physical parameters are required in a delicate balance of formulation ex cipients. Development activities need to stress physical stability under a variety of storage conditions and packaging con siderations. An experienced formulation chemist prepares viable prototype formu lations on a laboratory scale basis. The pilot plant processing requires extensive trial runs to pinpoint a potential com mercial formulation and manufacturing procedure. After this, the strengths and weaknesses of the formulation need to be highlighted to the consumer in how to properly use this formulation type. The purpose of this paper is to discuss the other side of water dispersible granules or WDG's, also known as dry flowables usually not presented in discussions with respect to preparing WDG's. I am referring to the side that deals with the develop ment of these easy to make, readily dispersible products. As you can t e l l by my comments, there are some factors to consider in making WDG's. This form of product is relatively new to the agricultural market, the major impact being registered in the last 5 years. An examination of the literature during this

0097-6156/ 84/ 0254-0185S06.00/ 0 © 1984 American Chemical Society

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

ADVANCES IN PESTICIDE FORMULATION TECHNOLOGY


186

time yields mostly empirical recipes indicating how a few key pesticides can be formulated into acceptable WDG's. Such d i s cussions often avoid any mention of the problems or the d i f f i culty of getting from the lab where anything seems to work to the production step where everything must work. Therefore the purpose of this paper is to discuss what happens from the time a lab t r i a l is initiated to a plant t r i a l is made. What must the formulator, product manager and production supervisor consider in examining or testing this product? Needless to say, the work will be general in nature and descriptive at best. I will attempt to use photographs to graphically illustrate what can go wrong and what can go right in making WDG's. Before I set out in our discussions one needs f i r s t to define the characteristics of the WDG so that we will be operating with the same definition. A water dispersible granule formulation consists of hard, uniform in size, free flowing, low dust granules which readily disintegrate in water and under minimal agitation forms a homogeneous sprayable suspension. If one analyzes each characteristic, a dependent relationship develops among the characteristics. The quality of each charact e r i s t i c is directly related to processing parameters. The most noticeable attribute of a WDG is i t s bloom or rapid d i s i n tegration in water. The aesthetic value of this property is highly visible in the advertising literature. At times, too much emphasis is placed here, and the consumer looks for i t under a l l types of use patterns. Before examining the preparation of WDG's, let's try to understand why they have grown in user acceptance and what problems can be associated with their use. The importance of each advantage or disadvantage of the WDG's varies for each toxicant but are generally listed as: Advantages: Free flowing, empties completely from container Easy to measure Low dust More concentrated Greater density Reduced transportation and warehousing costs Eliminates physical problems of flowables, i . e . , settling, thickening, etc. Easier to handle than wettable powder, less chance to s p i l l and easier to clean up Novel, generates consumer interest. With every set of advantages there is a corresponding set of disadvantages. These are key to point out and have impact on the overall development cost.


14.

WRIGHT AND IBRAHIM

Water Dispersible Granules

187

Disadvantages: Formulation is sensitive to process variables arrd raw materials Requires capital expenditures Employs s k i l l e d operators Need to educate the consumer on how to use properly.


Development of the Water Dispersible Granules Several general references on WDG formulations are available in the literature (1-3). In developing a good foundation, i t is also recommended that one v i s i t the various surfactant suppliers and get a hands on view of their product in action · This forms an excellent starting point. But i t is just that, a starting point. Unless you plan to merely scale up what you saw, the task becomes much more involved. As a starting point, let's review a general, a l l purpose finished formulation in Table I.

Table I.

Typical WDG Formulation

Components

% w/w

Toxicant Dispersant Binder Diluent Wetting agent

50-95 1-7 0-2 0-45 0-2

The dry components are uniformly blended and ground to appropriate particle size required for b i o l i g i c a l efficacy and suspension characteristics. The material is conditioned, agglomerated, dried, and sieved to desired mesh range. Wettable powder formulations are not generally suited for granulation due to presence of diluents such as amorphous s i l i c a t e s , which significantly increase the amount of water required for granulation. In addition, i t s presence effects the integrity of the granules. In reality, i t is better to start from the technical, than any formulated goods when designing WDG formulations. Proper wettability of the formulation is crucial i f one is to achieve good agglomeration and subsequent performance under f i e l d conditions. The type and level of wetting agent used in


ADVANCES IN PESTICIDE FORMULATION TECHNOLOGY

188

the system is determined by matching the solid surface tension Xs of the toxicant with the liquid surface tension >1 of the wetting agent at the f i e l d dilution rate. The solid surface tension frs of the toxicant can be determined by: 1)

transfer behavior of particles in two immiscible liquids having two different known surface tensions, i . e . ,


* U

Advances in Pesticide Formulation Technology - American Chemical

Recommend Documents