Donald Trimnell

Controlled release formulations of atrazine in starch for potential reduction of groundwater pollution.

Abstract The availability of the herbicide atrazine [2-chloro-4-ethylamino-6-isopropylamino- s -triazine to a soil-water system was greatly diminished by entrapping the herbicide in starch granules. Factors influencing the preparation of and release from these granules were determined. The delivery of atrazine from the granules to a soil-water system was compared with delivery to water. Availability of atrazine from unentrapped commercially available atrazine was also determined. In 15 minute soil-water tests, the rate of delivery of atrazine at a constant level of active ingredient increased as the surface area available in the formulations increased, which was made possible by decreasing the loading, by making the granules smaller, and by improving the degree of atrazine dispersion during granule formulation. Aging of the starch formulations from one to nine days diminished atrazine release. When the soil-water tests were conducted over 20 days, the larger granules (14–20 mesh), as a result of the smaller sample size, released atrazine slower than smaller granules (20–40 mesh). The larger granules induced 35% of saturation in 6 days and the smaller induced 45% of saturation in 3 days. Controlled release over these intervals was proportional to the square root of time according to the theory for controlled matrix diffusion. The larger granules kept in water under these conditions showed release to cause over 70% of saturation in 4 days and indicated that over 60% of the available atrazine was adsorbed by the soil. Atrazine present in saturated aqueous solutions was about 80% recoverable under the conditions of filtration and extraction. No controlled release was observed in soil-water mixtures.

The effect of α-amylases upon the release of trifluralin encapsulated in starch

Abstract Release of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] encapsulated in starch was induced by water and starch-degrading α-amylases. Factors investigated that influenced the rate of release are: encapsulation procedure, particle size of the encapsulated material, and pH of the medium. Variations within a procedure such as additional covalent crosslinking, starch retrogradation, and inclusion of enzyme inhibitors can affect the rate of release. For the three basic encapsulation methods used (xanthide, calcium, or borate), the rate of release was borate > calcium > xanthide when the particles were placed in pH 6.0 buffer. Coarse fractions (4–8 mesh) released trifluralin at less than one-fifth the rate of fine fractions (20–40 mesh). Release rates varied little upon varying the source of the α-amylase or the level of active ingredient (4–20%) within the particles. Trifluralin release from particles prepared by the borate procedure was slowed by crosslinking of the starch matrix with epichlorohydrin and by addition of heavy metal ions. The ability to detect variations in the rate of release as a function of these variables can serve as a basis for producing starch-encapsulated herbicides for particular end uses.

Autoencapsulation: A new method for entrapping pesticides within starch

Abstract A simple method to entrap pesticides under mild conditions is described. Pesticide is mixed with pregelatinized starch or ungelatinized starch containing a gelatinizing agent and enough water is added to allow agglomeration into 12- to 40-mesh granules. At this stage, much of the pesticide is not entrapped but is held firmly enough by the granules for handling. When the granules become wet, they also become gelatinous and then on drying form a solid matrix encapsulating the pesticide. Several pesticides were encapsulated by this method, and the encapsulation efficiencies for encapsulated products were determined.

BIOACTIVITY OF CONTROLLED RELEASE FORMULATIONS OF STARCH­ ENCAPSULATED EPTC*

Abstract Using a bioassay technique, the biological activities of starch-encapsulated formulations of EPTC (S-ethyl dipropylthiocarbamate) were determined in relationship to their controlled release characteristics. The bioactivity of the highly volatile herbicide EPTC was retained on a wet soil surface for 6 to 8 days by starch encapsulation utilizing several crosslinking processes (both chemical and non-chemical) and starches with different ratios of amylopectin to amylose. The rate of release, a measure of the integrity of the granule, depended on the nature of the starch and the crosslinking process. With the herbicide EPTC, encapsulation with a pearl or high amylose starch utilizing the jet-cooking process produced the best controlled release formulation even under the most adverse conditions.

Thio sugars by isomerization of carbohydrate thionocarbonates

Abstract Certain thionocarbonate derivatives of sugars isomerize to the corresponding monothiolcarbonates in the presence of potassium iodide. Structural requirements for isomerization are that the thionocarbonate must include a primary carbon atom of the sugar in a ring and that there be no unprotected hydroxyl groups in the derivative. The 3-O-acetyl (1) and the 3-O-p-tolylsulfonyl (2) derivatives of 1,2-O-isopropylidene-α- D -glucofuranose 5,6-thionocarbonate gave the corresponding monothiolcarbonates (3) and (4) in excellent yields. In contrast, the parent compound unprotected at C-3 gave no monothiolcarbonate. Methyl 2,3-di-O-methyl-α- D -glucopyranoside 4,6-thionocarbonate (5) afforded the 4,6-monothiolcarbonate (7). With each isomerized product, thiolation occurred at the C-6 position. When treated under similar conditions, two carbohydrate cyclic thionocarbonates involving only secondary carbon atoms, and two acyclic thionocarbonates of fully protected sugars, underwent negligible isomerization.

Behavioral responses of Diabrotica adults to plant-derived semiochemicals encapsulated in a starch borate matrix

The concept of encapsulating semiochemicals into a starch matrix is being studied for potential use in corn rootworm (CRW) management programs. During 1987, experiments were conducted to determine: 1) If volatile plant‐derived Diabrotica spp. attractants could be encapsulated in a starch borate matrix (SBM), and 2) If various SBM‐semiochemical formulations would attract Diabrotica species over time in field corn. Chemical analyses of fresh SBM formulations indicated that indole, estragole, veratrole, phenylacetaldehyde, and trans‐anethole were not retained during formulation but trans‐cinnamaldehyde, Beta‐ionone, 1,2,4,‐trimethoxybenzene, eugenol and isœugenol were successfully encapsulated. Encapsulated semiochemical formulations were made into 20 mesh granules, placed in Pherocon ® 1C traps that were tied to corn plants, and sampled for CRW adults every 4 days from 11 July to 8 September. Field data indicated that encapsulated semiochemicals were retained in the SBM for varying lengths of time and were released at rates attractive to CRW adults. A two‐component mixture of trans‐cinnamaldehyde and 1,2,4‐trimethoxybenzene was the most effective formulation tested; however, no formulation was effective during corn silking and pollination. Although seasonal variation in CRW response could limit the usefulness of some plant‐derived semiochemicals, the starch matrix concept may be useful as a delivery system for semiochemicals and may have potential as a tool that could be used in the development of new more biorational CRW management programs.

Migration of thiolthiocarbonyl groups in selectively protected methyl α-d-glucopyranoside xanthates

Abstract A series of benzylxanthate esters of methyl α- d -glucopyranoside selectively methylated at various hydroxyl groups was synthesized. The esters were converted into the corresponding xanthate salts, and their behavior was investigated under alkaline conditions typical of xanthation media. Results reveal that migration of thiolthiocarbonyl groups from the 2- or 3-position to the 6-position proceeds via the hydroxyl group at C-4. Direct migration across the pyranose ring from the 2- or 3-position to the 6-position was negligible. The (benzylthio)thiocarbonyl position for each ester was identified by n.m.r. spectroscopy. Primary substitution caused the signals for the two protons at C-6 to be displaced downfield by about 1.0 p.p.m., and secondary substitution caused a 2.4-p.p.m. downfield shift of the signals for protons at C-2, C-3, and C-4.

Migration of thiolthiocarbonyl groups of methyl α-d-glucopyranoside xanthates☆

Abstract If similar reactant ratios are used, the xanthation of methyl α- d -glucopyranoside parallels the xanthation of starch. Degrees of substitution in the range of 0.3–0.4 were achieved, and changes in distribution from secondary to primary positions were observed. Synthesis of the individual, isomeric, xanthate salts of methyl α- d -glucopyranoside, and treatment of each with 18% sodium hydroxide, showed that the 2-, 3-, and 6-xanthate salts rearranged to mixtures in each of which the 6-isomer preponderated. Evidence is presented suggesting that the 2-isomer migrates intramolecularly to the 6-isomer by way of the 3-isomer. However, observation of the presence of minor proportions of polyxanthates in these mixtures suggests that intermolecular migration of thiolthiocarbonyl groups also occurs.

Entrapment of herbicides in starch for spray applications

Abstract Sprayable controlled-release formulations were made with the herbicides trifluralin, 2,4-D ester, alachlor and butylate. Aqueous dispersions of gelatinized cornstarches or flours containing herbicides were sprayed and dried to water-resistant films that entrapped the herbicide. Formulations containing 3% Miragel®, 3% cooked pearl, or 7% pregelatinized corn flour and one tenth these levels of active ingredient (a.i.) provided as emulsifiable concentrates had stable viscosities in the 75–260 cP range over 24 hours. The best entrapment was obtained by cooking 3% starches or flours at least 30 min at 100° C and dispersing the emulsifiable concentrates into the cooled whole pastes. Dried formulations based upon 3% Miragel® entrapped 88% trifluralin, 96% 2,4-D ester, 75% alachlor, and 9% butylate. Butylate retention increased to 42% with 6% Miragel® that had been pyrolyzed 1 h at 200° C. Release of trifluralin from Miragel® in the presence of αamylase solution increased with decreasing particle size and increasing level of active ingredient.

Comparison of steam injection cooking versus twin-screw extrusion of pearl cornstarch for encapsulation of chloroacetanilide herbicides

Abstract Liquid chloroacetanilide herbicides were encapsulated more effectively in a 30 mm twin-screw extruder at 35% starch solids than in a steam injection cooking/Sigma blade mixing process. Excellent mixing in the twin-screw extruder allowed the use of a starch level of 65% and provided for more efficient encapsulation. Extruder prepared products had smaller cells of active agent (via SEM), decreased swellability and slower release of active agent into water than steam injection cooked samples. Using liquid metolachlor, swellability of extruded products increased and encapsulation decreased as starch solids were increased from 35% to 65%. After alachlor had been melted at 50°C, injected, and the product extruded, it solidified in the starch matrix and was more effectively encapsulated than metolachlor. Increasing the concentration of active ingredient in the encapsulated product from 10 to 20% decreased swellability, rate of release into water and encapsulation efficiency. When a 57 mm twinscrew extruder was used to scale up the process for continuous production, encapsulation improved if the water content of the extrudates was reduced to below 10% before grinding.