Coated agricultural products

Abstract: A controlled release agricultural composition comprises an active ingredient, for example a fertilizer,coated with a neutralized, sulfonated EPDM polymer having from about 2% to about 50% crystallinity. Preferably, the polymer is one having from 4 to 200 milliequivalents of neutralized sulfonate groups per 100 grams of polymer.

Description: The present invention relates to coated agricultural products, such as controlled release fertilizers. Elastomeric, sulfonated ionomers, such as sulfonated ethylene-propylene-diene (EPDM) terpolymers have been shown to be useful coating materials for fertilizers because of their water barrier properties, their elasticity and ability to be applied as thin continuous coatings free of pinholes. In this regard, see, for example, U.S. Patent 4,988,377 (to which WO-A-8706575 corresponds), which discloses the use of sulfonated elastomers as coating materials for agricultural substrates. Although elastomeric, sulfonated EPDM materials have been successfully used for preparing slow release fertilizers, there remains a need to provide slow release fertilizers that are capable of releasing their nutrients over even longer periods of time, for example, up to about six months at temperatures up to about 38°C. Surprisingly, it has now been discovered that sulfonated EPDM polymers that contain a measurable degree of crystallinity are especially useful coating materials for controlled release fertilizers. Thus, in one embodiment of the present invention, there is provided an improved controlled release fertilizer comprising a fertilizer coated with a neutralized, sulfonated EPDM polymer having from 2% to 50% crystallinity and an ethylene content of 55 to 80 wt%. Preferably, the coated fertilizer has a coating thickness of from 1 to 100 micrometers. US-A-3 887 530 discloses sulfonated ethylene-propylene-diene polymers having a crystallinity of 2 to 50 wt.% and states that such polymers have improved physical and rheological properties over their amorphous counterparts. The polymers used to form the improved composites of the present invention are neutralized, sulfonated EPDM polymers which contain a measurable degree of crystallinity and specifically from 2% to 50% crystallinity, as determined, for example, by x-ray diffraction at 25°C or by differential scanning colorimetry (DSC). Preferably, the EPDM polymer will have a crystallinity of between 3% to 20% more especially 3 to 15%. As will be readily appreciated, these crystalline, neutralized, sulfonated EPDM polymers contain from 55 wt% to 80 wt% ethylene. In contrast thereto, the non-crystalline elastomeric EPDM polymers generally contain 50 wt% or less of ethylene, although depending upon the type of catalyst used in making the polymer, higher levels of ethylene are possible with no observable crystallinity at room temperature. The preferred EPDM polymers employed in the invention contain 2 wt% to 10 wt% of a diene monomer and, preferably, between 3 wt% to 7 wt% of a diene monomer. The diene monomer typically is a nonconjugated diene such as hexadiene, dicyclopentadiene, ethylidene norbornene, methylenenorbornene, propylene norbornene and methyltetrahydroindene. The preferred sulfonated EPDM polymers employed in the present invention contain from 4 to 200 milliequivalents of pendant sulfonate groups per 100 grams of polymer and, more preferably, from 10 to 100 milliequivalents of pendant sulfonate groups. These pendant sulfonate groups are neutralized; preferably with metal ions from Groups IA, IIA and IIB of the Periodic Table of the Elements, for example zinc, sodium and potassium, or ammonium, counterions. The Periodic Table referred to is that shown on the inside cover of Lange's Handbook of Chemistry, 11th Edition, McGraw-Hill Book Company, 1973. Neutralization is achieved, for example, by contacting the acid form of the polymer with an appropriate metal hydroxide, metal acetate, metal oxide or ammonium hydroxide. The degree of neutralization of the sulfonate groups may vary widely, but will generally be greater than 2 mole percent up to 100 mole percent. It is particularly preferred, however, that the degree of neutralization be substantially complete; that is, with no free acid present. The elastomeric coatings are preferably formed by applying an organic solution of the neutralized, sulfonated polymer to the substrate at ambient temperature or at temperatures in the range of about 10°C to about 50°C by either dip-coating, spraying or with the use of other techniques for thin spreading, such as brushing. The organic solvent system is then permitted to evaporate with or without the aid of forced drying gas, such as air or nitrogen. The drying gas temperature can be from ambient temperature up to the boiling point of the organic solvent system. Preferably, the temperature of the drying gas is between 20°C to 100°C. The most preferred temperature of the drying gas should be about 70°C for fast evaporation of the organic solvent system. After drying, the thickness of the applied coating should be from 1 micrometer to 100 micrometers. Most preferred, the coating thickness should be 2 to 20 micrometers for both performance and economic reasons. On a weight basis, the coating preferably represents 0.6 to 6 wt% and, more preferably, 3 wt% of the composition. To control the thickness of the applied coating, the solution concentration of the sulfonated polymer applied is normally between 0.5 wt% to 6 wt%. Most preferably, the concentration should be 5 wt%. Normally, the solvent used to form the organic solution will be a solvent such as toluene, xylene, hexane, preferably in combination with a polar solvent such as aliphatic alcohols having from 1 to 10 carbon atoms. Basically, a fertilizer, such as urea or other micronutrient granules, can be coated to maximize the plant uptake of the applied fertilizer through minimization of losses, including evaporation, nitrogen fixation and leaching. The following examples will demonstrate the performance of a sulfonated polymer as a barrier coating. Comparative Example 1 Preparation of Sodium Neutralized Sulfonated EPDM Terpolymer A commercially available, non-crystalline, EPDM terpolymer (Royalene 521)®, sold by Uniroyal Corporation, Middlebury, Connecticut, which had about 50 wt% ethylene and about 5 wt% ethylidene norbornene, was sulfonated with acetyl sulfate according to the procedure of U.S. Patent 3,836,511 and then neutralized with sodium hydroxide, thereby providing a 10% solution of sodium sulfo-EPDM in toluene-methanol solution (97:3, wt.%:wt.%). The solution was diluted with additional toluene-methanol (97:3, wt.%:wt.%) to provide a 1.25 wt% solution of polymer. The solution of the neutralized, sulfonated EPDM polymer was then applied to urea to provide a 3 wt% coating on the urea. In order to measure the barrier properties of the coated urea, two series of test were conducted. In each series, fifteen grams of coated substrate were placed in a weighed 250 ml flask. Seventy-five grams of distilled water were added and the mixture incubated at a selected temperature (at 23°C in the first series and 38°C in the second). At hourly time intervals, the water was decanted from the sample into a weighed aluminum container and placed in a 98°C oven to dry. After drying and cooling, the aluminum container was weighed and the gain in weight represented the amount of substrate released. To the remaining coated material, 75 grams of distilled water were added and the incubation, decanting, etc. was repeated. Repetition of the procedure produces additional data points. The results of these tests are set forth in Figures 1 and 2. Example 1 Following the procedure outlined above, a commercially available, crystalline, EPDM terpolymer, namely, Vistalon 7000®, sold by Exxon Chemical Company, Houston, Texas, was sulfonated with acetyl sulfate, as in Comparative Example 1, and then neutralized with sodium hydroxide. The resultant 10% solution, which contained a sodium sulfo-EPDM having 25 milliequivalents of sulfonate groups per 100 grams of EPDM terpolymer in 95 wt% toluene, 3 wt% MeOH and 2 wt% heptane, was diluted with the same solvent to provide a 1.25 wt% solution, which was used to coat urea, as outlined above. The coated urea was then tested following the procedures also outlined in Comparative Example 1. The test results are plotted in Figures 1 and 2. A sample of the neutralized polymer employed in this Example 1 had a 10% crystallinity as determined by DSC. From the foregoing, it can be readily appreciated that materials having measurable crystallinity are particularly suitable because of the long-term release properties of these coatings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph comparing fertilizer releaae as a function of time at 23°C for a fertilizer coated with a non-crystalline, neutralized, sulfonated EPDM and a fertilizer coated with a crystalline, neutralized, sulfonated EPDM in accordance with this invention. Figure 2 is similar to Figure 1, except that the test conditions were conducted at 38°C.

Claims: A controlled release agricultural composition comprising: an agricultural substrate, preferably a fertilizer; and a polymer coating on the substrate, the polymer being a neutralized, sulfonated ethylene-propylene-diene polymer having a crystallinity in the range of 2% to 50% and an ethylene content of from 55 to 80 wt%. A composition as claimed in claim 1, wherein the polymer has a crystallinity of from 3% to 15%. A composition as claimed in claim 1 or claim 2, wherein the polymer has from 4 to 200 milliequivalents of neutralized sulfonate groups per 100 grams of polymer. A composition as claimed in any preceding claim, wherein the sulfonate groups are neutralized with ammonium counterions. A composition as claimed in any one of claims 1 to 3, wherein the sulfonate groups are neutralized with a metal ion selected from Groups IA, IIA and IIB of the Periodic Table of the Elements. A composition as claimed in any preceding claim, wherein the polymer coating is in the range of from 0.6 to 6 wt% of the composition. A composition as claimed in claim 6, wherein the polymer coating is 3 wt% of the composition. A composition as claimed in any preceding claim, wherein the polymer coating has a thickness of from 1 to 100 micrometers.

Inventors: SWARUP VIJAY, SWARUP, VIJAY
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1993
Main classification: C05C9
IPC codes: C05G3