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United States department of Agriculture
Agricultural Research Administration
Bureau of Entomology s-nd Plant uwiraw tine
STORAGE TESTS ON 'C'TfDITICNOED ATD WETTABLE '-.'nc
cONTATIrirG 90 PERCENT OF DDT
By E. L. Gooden and R. L. Updike, Jr.,
Division of Insecticide Investigations
There is a demand for free-flowing fine-powder formulations contain-
ing DDT in high enough concentration to be regarded as essentially undi-
luted. For some purposes these powders must be easily water-wettable,
whereas for others they are not necessarily so.
Such high-concentration preparations are especially advantageous
where shipping of bulky or heavy materials presents a problem, because a
concentrate processed at a central point may be combined easily at remote
stations with locally available diluents for dusting preparations and for
dilute powders to be used in spray suspensions. In extreme cases most .
the transportation on more than 90 percent of the weight going into the
finished powder could be eliminated. In spray powders for uses requiring
a minimum of solid residue, as on ornamental plants, the practical elim-
ination of solid diluents offers an obvious advantage. For the Fprayi:f
of aqueous suspensions from airplaneF, it is essential to economic opera-
tion that the DDT concentration in the suspension be rather hirl-, 12 per-
cent being common. This high concentration makes such thick suspe7c-Ions
that the inclusion of any appreciable amno-;:t of inert solids Impos,-s a
decided handicap for use in spraying nachiri,?-y that does not provi':
forceful agitation. Where even higher DDT concentrations are used (around
30 percent in some soil treatments), the omission of usel.:s solids is
At the Beltsvllle, Md., laboratory experiments directed toward the
development of concentrated D1DT powders possessing the desired physical
characteristics have demonstrated that concentrations up to 90 percent
(technical TrDT) are feasible. Two representative preparations in this
concentration, one water-dlspersible and one not, were subjected to stor-
age tests for a 3-year period, and the results of the tests are presented
in this paper.
The nonwettable, noncaking powder, resirnated as "conditioned DDT,"
was made from 90 parts by weight of technical TrT and 10 parts of a finely
divided silica aerogel. The ingredients were given a preliminary miring
by tumbling in a closed roomy container, the mixture was ground in an
g-inch hammer mill, and the complete batch of ground material was given
a final blending by tumbling as before.
The water-dispersible, or wettable,1'powder was prepared in the same
manner as the conditioned DIT, amnd from the same ingredients, with the excep-
tion that 2 parts of a wetting agent, described as a sodium salt of sulfonated
ethyl oleate, was substituted for 2 of the 10 parts of conditioner. The
final product contained 8 percent of conditioner, 2 percent of wetting agent,
and 90 percent of DDT.
The grincing of either type of preparation is greatly facilitated by
chilling the ingredients with dry ice, crushed to pass a quarter-inch sieve.
The ingredients are mixed with the dry ice and allowed to stand for an hour
or less before they are ground. The two batches used for these tests, how-
ever, were prepared without the a!'- of this chilling.
Samples of each preparation 'were stored under four different conditions:
(1) In a screw-caD jar, closed tightly with a rubber gasket; (2) in an
unclosed jar prcder' with an open paper hood to keep out excessive dust and
at the same time -rmit air circulation; (3) in a closed paper bag; and (4)
in an open beaker in an oven kept at 55 C. In the first three conditions
ordirary room temperatures prevailed.
The two preparations here discussed were made early in the development
of 9C-percent DDT powders, and do not necessarily represent in physical
characteristics the best that may be expected of present or future products.
This report is considered of current value, however, because it gives a
durability record such as is obviously not available for the newer prepara-
The surface-mean particle diameters of the two freshly prepared powders
were 5 and 6 microns by air permeation (1), and the weight percentages of the
pc.vders passing through a U. S. No. 120 sieve by dry sifting were93 and 94.
Yo deterioration was detectable by the sieve test in 36 months of storage
except in one case, that of the wettable powder at the elevated temperature,
and in this case the percentage passing through the sieve was always around
90, generally above. None of the powders stored at room temperature showed
any great change in ourface-pean diameter, whereas under the elevated temper-
ature the surface-mean particle diameters of both preparations were approxi-
mately doubled within the first few days after grinding and remained almost
constant from then on. Details of the results obtained in the sieve and air-
permeation tests are shown in table 1.
(1) Gooden, Ernest L.
1944. Particle size of commercial calcium areenates by air-permea-
tion tests. Jour. Econ. Ent. 37: 104-105.
l/The formula used in compounding the wettable powder was developed by
J. Weisser, formerly of this Bureau.
Table 1.-Results of tests with cor.Jitioned and wettable LDT powers stored under
different conditions J/
f Open jar
I Tied paper bag ,
I mean 'No. 120
Percent Miirrons Perc nt Micrr
I/ All tests except those with the open beaker
tures. The open beaker was held at 55 0C.
were conducted at room termioera-
UNIVERSITY OF FLORIDA
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