October 1%8 E-758 l; y STATE PLANT BOARD United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine STORAGE TESTS ON CONDITIONED AND WETTABLE POVDEHS CONTAINING 90 PERCENT OP DDT By E. L. Gooden and R. L. Updike, Jr., Division of Insecticide Investigations There is a demand for free-flowing fine-povder formulations contain- ing DDT in high enough concentration to he regarded as essentially undi- luted. Por some purposes these powders must he easily water-wet table, \fhereas 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 of 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. Por the spraying of aqueous suspensions from airplanes, it is essential to economic opera- tion that the DDT concentration in the suspension be rather high, 12 per- cent being common. This high concentration makes such thick suspensions that the inclusion of any appreciable amount of inert solids imposes a decided handicap for use in spraying machinery that does not provide forceful agitation. Where even higher DDT concentrations are used (around 30 percent in some soil treatments), the omission of useless solids is imperative. At the Beltsville, Md. , laboratory experiments directed toward the development of concentrated DDT powders possessing the desired physical characteristics have demonstrated that concentrations up to 90 percent (technical DDT) are feasible. Two representative preparations in this concentration, one water-dispersible 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, designated as "conditioned DDT," was made from 90 parts by weight of technical DDT and 10 parts of a finely divided silica aerogel. The ingredients were given a preliminary mixing by tumbling in a closed roomy container, the mixture was ground in an 8-inch hammer mill, and the complete batch of ground material was given a final blending by tumbling as before. -2- The water-dispersible, or wet table,— powder was prepared in the same manner as the conditioned DDT, and from the same ingredients, with the excep- tion that 2 part? 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 grinding 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 aid of this chilling. Samples of each preparation were stored under four different conditions: (l) In a screw-cap jar, closed tightly with a rubber gasket; (2) in an unclosed jar provided with an open paper hood to keep out excessive dust and at the same time permit air circulation; (3) in a closed paper bag; and (k) in an open beaker in an oven kept at 55° C. In the first three conditions ordinary room temperatures prevailed. The two preparations here discussed were made early in the development of 90-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- tions. Results The surface-mean particle diameters of the two freshly prepared powders were 5 and 6 microns by air permeation (l_), and the weight percentages of the powders passing through a U. S. No. 120 sieve by dry sifting were 93 and $k. No 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 surface-mean diameter, whereas \inder 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. Literature Cited (l) Goo den, Ernest L. I9UU. Particle size of commercial calcium arsenates by air-permea- tion tests. Jour. Econ. Ent. 37: 10U-105. i'The formula used in compounding the wettable powder was developed by J. Weisser, fomerly of this Bureau. - 3 - Table 1. — Results of tests with conditioned and wettable DDT powders stored under different conditions l/ , ' - ■ ' r ( Closed jar , Open — ■ i jar , Tied paper bag , Open beaker Time after 1 Passing' Surface Passing 'Surface ' Passing ' Surface 'Passing 1 Surface grinding 1 No. 120' mean No. 120 mean No. 120 mean 'No. 120 mean sieve ' diameter' sieve 'diameter* sieve 1 diameter sieve 'diameter ■ t i » i r ? Days Percent Microns Percent Microns Percent Microns Percent Microns Conditionea powaer 0 93 _ _ .. _ _ _ _ 1 94 5 — - - — — - 4 96 6 - — — • - - 9 95 - 95 — 95 - 95 - 10 - 5 — 5 ~ 6 - 9 21 96 6 96 6 96 6 96 9 Months 1 96 6 97 6 97 6 96 9 2 97 6 97 6 97 6 96 9 A - - — — — - 97 10 10 93 6 98 6 97 6 97 10 12 98 5 98 6 98 6 97 10 24 97 6 97 7 97 6 97 11 36 97 6 97 6 97 6 97 10 Wettable powder Days 0 94 1 94 6 — _ _ _ _ _ 4 96 6 — - — — _ - 8 95 - 95 — 96 • — — 9 - 6 - 6 — 6 89 11 21 96 7 97 7 96 7 92 12 Months 1 96 7 97 7 96 7 97 9 2 97 6 97 7 97 7 87 11 4 — - — _ _ _ 92 12 10 97 7 97 7 97 7 92 11 12 98 7 97 7 97 7 91 12 24 97 7 97 8 97 8 93 12 36 97 8 97 8 97 8 89 12 1/ All tests except those with the open beaker were conducted at room tempera- tures. The open beaker was held at 55°C. ■Ilililllill 3 1262 09239 Wgm