9 Correlation of Carrier Properties with Malathion Stability GARTH COOMBS
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Johns-Manville Research & Engineering Center, Manville, N. J. The stability of toxicant-carrier combinations used in pesticide wettable powder formulations
cannot be easily pre-
dicted by evaluating various properties of the carrier. Several types of synthetic calcium silicates and their modifications were evaluated for
malathion
stability and
other
properties. The carriers were evaluated for pH (slurry), pK
a
(surface acidity),
moisture
content, absorptive
and/or ion exchange capacity.
capacity,
These properties were corre-
lated with actual malathion stabilities as measured at storage for 1, 2, 3, and 7 months.
40°C.
The carrier properties
evaluated did not offer a simple means of predicting
com-
patibility in the variety of carriers tested.
One
aspect of the development of pesticide formulations is the selection of suitable carriers for wettable powders and for similar dry formulations. With some sensitive toxicants, it is often difficult to find a carrier that can be used for high percent formulations without some loss in activity. To select a suitable carrier, the pesticide formulator would like to utilize his knowledge of carrier properties rather than proceed by trial and error modified by prior experience. During a program to develop an improved, inert, absorptive carrier for malathion, we had an opportunity to attempt to correlate actual stability results with various carrier property measurements. We worked with a variety of synthetic silicates and their modifications by various physical or chemical treatments or by various chemical additives. We particularly evaluated many synthetic hydrated calcium silicates, with and without additional treatments. These treatments included various organic and inorganic acid compounds, organic surfaceactive agents, and inorganic salts. We also studied samples dried to remove free moisture and/or some water of hydration. The modifications were selected to effect favorably the properties of the carriers. 91 Van Valkenburg; Pesticidal Formulations Research Advances in Chemistry; American Chemical Society: Washington, DC, 1969.
92
PESnCIDAL FORMULATIONS RESEARCH
Table I. Data Obtained
Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0086.ch009
pH 8.80 8.50 8.50 8.45 6.25 8.10 7.80 7.75 11.60 8.45 10.25
8.15 9.20 9.05 9.55 8.30 8.55 8.95 8.15 7.50 7.05 8.35 9.05 8.40 8.25 8.25 8.35 8.35 9.20 8.35 8.25 8.20 9.30 9.25 9.40 7.90 9.05 8.90
Ion Exchange meq./gram Moisture, %
Water Absorption, % 588 590 590 400 200
+3.3/1.5 +3.3/1.5 +3.3/1.5 +1.5/-3.0 -3.0
185 300 394
-3.0 +4.0
