IE921425A1 - Microencapsulated agriculturally active agents and method of¹producing same - Google Patents

Abstract

A microencapsulated active agent, such as an insecticide, a hormone, or a fertilizer for application to vegetation and a method for its preparation is disclosed. An active agent is encapsulated in lignin, a naturally occurring polymer which is a structural component of the plant cell wall. Lignin serves not only as the capsulate material, but also as a sunscreen which protects the agent from ultraviolet radiation. There is also disclosed a process for the preparation of the microcapsules of the invention which does not use toxic materials requiring subsequent removal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to agriculturally active preparations and, aore particularly, to microencapsulated biological and chemical agriculturally active preparations, such ae pesticides and fertilizers having improved stability upon application in a given environment.

Microencapsulation of pesticides has been used as a means for providing controlled-release preparations, for reducing the toxicity to persons handling the pesticides, and for protecting the active ingredient from deactivation by exposure to environmental conditions. Exposure of non-encapsulated insecticides to these conditions can lead to leaching and run-off by rainfall, loss by volatilization, degradation by bacterial inactive metabolites, and sunlight, especially ultraviolet inactivation. Selection of an appropriate carrier material for use in an interactive delivery system can not only reduce this deactivation, but also produce specific desired effects when combined with the active insecticidal material. 2. Prior Art In an effort to provide a delivery system for an active ingredient meeting the criteria set forth above, the art has proposed a number of encapsulation materials.

Methods for preparing microencapsulated insecticidal pathogens have been described in which a capsule material itself shields the pathogen from sunlight-induced inactivation. US Patent No. 4,328,203 describes a microbial insecticide composition which comprises a microbead of a nucleic acid and a fl proteinaceous material which partially protects the insect pathogen froa UV inactivation. However, because these substances are not environmentally stable, the encapsulating material is easily broken down, and thus cannot efficiently protect the insecticide.

The use of sunscreens in controlled release preparations has also been described. Diisophorone derivatives are utilized in US Patent No. 3,839,561 to protect insecticidally active cyclopropane carboxylic acid compounds from UV-induced degradation. In US Patent No. 4,094,969, there is described the use of a sulfonated copolymer of catechin and leucocyanidin which stabilizes a pesticide by retarding degradation upon exposure to sunlight. However, these formulations do not maintain the sunscreen and insecticidal preparation in close enough contact to be effective against UV irradiation. Ignoffo and Batzer, in Microencapsulation and Ultraviolet Protectants to Increase Sunlight Stability of an Insect Virus, Journal of Economic Entomology. Vol 64, pp. 850-853 (1966), attempt to solve this problem through th· use of Buffalo Black, Carbo-Jet Black, carbon and aluminum oxide and powder with microencapsulated Heliothis nucleopolvhedrosls virus to protect preparations from UV irradiation. However, the microencapsulating materials used by Ignoffo, namely gelatin and ethylcellulose, are not environmentally stable and are thus readily broken down by the environment. Similarly, US Patent No. 2,090,109 discloses the use of chlorophyll green as a protectant of various insecticides in a gelatinous vehicle from UV light.

Fogle, et al. describe the use of UV absorbing materials such as carbon black in a polymer matrix composition containing - 2 IE 921425 an insect virus in US Patent No. 3,541,203. The microencapsulating process as well as the microcapsules obtained by Fogle et al. suffer from a number of disadvantages. The polymers forming ths walls of the capsules are not always capable of retaining the sunscreening agent within the interior of the capsule. This diminishes the stability of the insecticidal preparation because the loss of eunscreening agent makes the pathogen more susceptible to the damaging effects of ultraviolet light. In addition, the microcapsules of Fogle, et al. are prepared using highly toxic materials, and cumbersome washing steps are required for their removal. λ particularly preferred group of encapsulating polymers is disclosed in US Patents No. 4,844,896 and 4,948,586 by Bohm and Friend, of common assignee. These polymers are synthesized from acrylic and methacrylic acid esters with a low content of quaternary ammonium groups, and are known as Eudragit L, S, RL and RS. They are useful because they can yield capsules with strong walls which can be made soluble at a pH of 6 or 7.5, depending on the particular formulation used. The Eudragit capsules can be used effectively to retain sunscreening agents within the walls of the capsule until ingested by an insect.

The use of lignin in certain types of controlled release formulations is also known in ths art. US Patent No. 3,929,453 relates to controlled release preparations of lignin and biological materials which are produced via coprecipitationinclusion from an aqueous alkaline lignin solution, or via the elimination of a common solvent from a lignin-biologically active organic agent mixture. US Patent No. 4,244,729 describes a reversibly ewellable carrier gel for the incorporation of pesticides. These gels are foraed by crosslinking lignin with epichlorohydrin, leading to the formation of gels with differing surface chenical characteristics,: which are able to sustain controlled release of water-soluble and water-insoluble pesticides. The use of other cross-linking reagents such as formaldehyde, paraformaldehyde, glyoxal and glutaric dialdehyde is described in related US Patent No. 4,244,728. Methods for microencapsulation and protection from UV irradiation are not disclosed in any of these references.

One of the disadvantages of prior art lignin-based pesticidal preparations and to microencapsulated preparations using other known polymers, is that the insecticidal agent is subject to autocatalytic breakdown because of its partial exposure on the exterior of both the lignin gel matrices and the polymeric microcapsules. Thus, even.in the presence of sunscreens added to certain polymeric microcapsules, insecticide which is present near the surface of the microcapsule which is not protected by sunscreen can undergo UV degradation. As a result, this degradation produces an autocatalytic degradation of neighboring molecules of insecticide toward the interior of the microcapsuls. These interior molecules might have otherwise been protected by sunscreen which was present within the microcapsule. Therefore, prior art preparations, even those which seemed to effectively retain sunscreening agents within the microcapsuls, were still not capable of protecting the insecticidal preparation from autocatalytic degradation.which began at the surface of the microcapsule. In addition, microencapsulated insecticidal formulations characterizing the prior art typically required use of toxic materials in their preparation.

Another problem confronting the prior art was the inability to load sufficiently large amounts of active agent into a capsule. Difficulties were also encountered in tailoring the microcapsule sizes to the particular application.

SUMMARY AND OBJECTS OF THE I Wild, ΓΙΟΝ In view of the aforementioned disadvantages attendant with prior art formulations and processes as well as other disadvantages not specifically mentioned above, it should be apparent that there still exists a need in the art for microencapsulated active agents which (1) include no toxic components in either the final product or in the materials used to form such microcapsules, (2) provide protection for an active agent against environmental effects, such as sunlight, which could degrade an active agent and (3) break down to release the active agent once it has reached its desired target.

It is therefore a primary objective of the present invention to fulfill that need by providing an active agent, such as a biological or chemical insecticide, which is microencapsulated in lignin.

Another object of the present invention is to provide an active agent, such as a microencapsulated insecticide, which provides controlled release of the active agent when contacted with the desired target.

Yet another object of the present invention is to load sufficiently large< amounts of an active agent into a microcapsule.

Still another object of the present invention is to provide a process for preparing microcapsules which enables the size of the microcapsule to be tailored to the particular end use contemplated.

In particular, these and other objects of the present invention are achieved by providing a controlled-release preparation of an active agent which uses lignin not only as the capsule material, but also ae a sunscreening agent which protects the agent froa the harmful effects of light.

In a first aspect, the present invention relates to a microencapsulated active agent coaprising: (i) an active agent such as an insecticidal agent, and (ii) a polymeric encapsulating agent comprising lignin or a lignin compound.

In a second aspect, the present invention relates to a process for preparing a microencapsulated active agent comprising the steps of: (i) mixing (1) an encapsulating agent comprising lignin or a lignin compound, (2) an active agent in a form compatible with microcapsule formation and (3) an agueous solvent or cosolvent system which ie miscible with water and which dissolves lignin or the lignin compound to form a first mixture; (ii) preparing an emulsifying solution coaprising a surfactant and a liquid which is immiscible with said aqueous solvent or cosolvent system; (iii) preparing a solution to harden the capsules; (iv) mixing the first mixture and the emulsifying solution to form an emulsion; (v) mixing the resultant emulsion with the hardening solution to harden emulsion droplets to fora capsules; and (vi) concentrating and separating the capsules froa the water insoluble liquid.

With the foregoing and other objects, advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the preferred embodiments of the invention and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph depicting tbs percent mortality of cabbage looper larvae as a function of hours of exposure to ultraviolet radiation of encapsulated and free Bacillus thurinoiensls at different dosages; and Figure 2 is a graph depicting the percent mortality of cabbage looper larvae as a function of hours of exposure to ultraviolet radiation of an encapsulated and free viral biopesticide.

DETAILED. ΡΕ8£ΒΙΡΤΙ9&9Γ FRETEBBEE 1. Starting Materials The basic starting-materials for preparing the microencapsulated active agents of the present invention are the active agents themselves. In this regard, while the preferred embodiment of the present invention which is described relates to microencapsulation of insecticidal agents, it will be appreciated that other agriculturally effective agents may be utilized. Such agents include, but are not limited to, fertilizers and plant regulators, s.g.,plant hormones. Suitable insecticidal agents include insecticidal viruses, bacteria, fungi or chemical toxins. In addition, other starting materials include the lignin polymer used to encapsulate the insecticide, and optionally, the Eudragit - 7 IE 921425 polymer which can be used in combination with th· lignin to form the microcapsule. By Eudragit is meant a group of modified acrylic acid polymers which can be made soluble at various pH levels, depending on the modifying groups employed. Such polymers, as well as the techniques for modification thereof to obtain a desired pH solubility, are known in the art.

Any of the pathogens currently known to infect insects, including viral, bacterial and fungal pathogens or any chemical toxins known to act on insects, can be encapsulated by and protected from UV light by lignin. Such viruses include, but are not limited to the nuclear polyhedrosis virus (NPV) of the bullworm, Hellothis zea. of the gypsy moth Lvmantrla dlspar. of the Douglas fir tossock moth, Praia pssudotsuoata. of the European pine saw fly Neodiprion sertlfer or of Autoarapha californica. Bacteria known to be pathogenic to target insects, including hut not limited to Bacillus thurlnqlensle. Baciiiua Sohaericus. Bacillus Poplllias may also be encapsulated. Insecticidal chemical toxins including, but not limited to amidino hydrazones such as hydramethylnon (Amdro*) may also be used. Finally, it will be appreciated that a number of recombinant active agents which are now available may also be encapsulated in accordance with the present invention.

The insecticidal agents are employed in combination with a lignin. The lignin component is discussed first. By lignin is meant any lignin or modified lignin derived from the alkaline digestion of lignocellulosic material, including sulfated lignins, hydrolysis lignins, and lignin amines. Thus, any of the lignins may he employed to make ths carrier used in this invention. Most commonly, they are obtained as byproducts from the alkaline process of papermaking where sodiua hydroxide alone or in combination with sodiua sulfide is employed. These lignins are generally referred to as soda or sulfate lignins after the pulping process used. In ths preferred practice of this invention, the lignin employed is a kraft pins lignin. Likewise, lignins known as hydrolysis lignins obtained by snzyaatic or acidic reactions with lignocsllulosic materials may be used.

Also, sulfite waste liquor lignins and sulfonated alkali lignins may be used if the degree of sulfonation is controlled. Thus, mixtures of alkali lignin and sulfite or sulfonated lignin may be used if an immediate release of pesticide is desired. Lignin amines may also be used to form capsules. Lignin amines are soluble at a pH <3.5 or >8.5, and are generally supplied at about pH 10. Lignin amine at pH 6 is not soluble in water, but will dissolve in solutions of polyethylene glycol and water, for example, a solution of 70% PEG/30% water.

Ths present inventors have discovered that lignin is effective for use as a microencapsulating material as well as a sunscreening agent for agriculturally active agents such as pesticides. In some instances, the lignin and active agent can be formed into a microcapsule which concentrates ths active agent towards ths center of the capsule. Depending on ths nature of the interaction between the lignin carrier and the pesticide, the effects demonstrated by ths composite can vary from simple dilution of ths active ingredients to sustained release. The use of these types of microcapsules, whether interactive or not, also allows for ths reduction or elimination of some of the environmentally undesirable side effects of pesticide use such as contamination of non-target areas caused by toxicant run-off, leaching or evaporation. In addition, incorporation of the pesticide into the delivery system of the invention offers potential for decreasing chemical breakdown into biologically inactive compounds following exposure to light and extremes of pH. Thus, the active ingredient is shielded, its initial activity is reduced, and its release is sustained.

Lignin can be easily modified due to its phenolic hydroxyl, carboxylate and aliphatic hydroxyl groups, as well as its high aromatic content. Matrices of varying pore structure, polarity and solubility can be created by blocking certain groups on the lignin unit, and by crosslinking with reagents such as epichlorohydrin, formaldehyde, ammonia and formaldehyde, and hexamethylenetetramine, among others. It will be appreciated that the ability to modify lignin enables the use thereof against different targets. Thus, for example, when it is an insecticide which is encapsulated in the lignin, the lignin is designed to be insoluble at approximately neutral or acidic pH levels as encountered outdoors and soluble at alkaline pH levels as encountered within the gut of an insect.

The high aromatic content of lignin also gives it the property of excellent ultraviolet radiation absorption. This characteristic, along with its inert properties; makes lignin highly suitable for use with pesticides which are sensitive to UV-initiated or -catalyzed degradation. Finally, the good dispersant qualities, the low cost and the environmentally benign nature of lignin compared to other carriers such as high surface area, porous plastics, makes lignin highly desirable for use in virtually all pesticide formulations. The aicroencapsulated preparations of the present invention, through the process of emulsification, maintain their activity due to the physicalchemical protection and intrinsic sunscreening activity of the microencapsulating polymer, lignin. The capsules formed are spherical and can be made to have a large range of diameters depending on the final application. Thus/ for example, when insects are the target, they can be formed with average diameters of 10-50μ which allows the capsules to form free flowing suspensions which can be sprayed and are small enough that they are easily ingested by the target insect.

Thus, lignin provides an ideal encapsulating agent for an insecticide because it is insoluble in water at normal environmental pH values and thus protects the pesticidal agent while present on vegetation, but will dissolve in the alkaline pH of the insect's gut, releasing the pesticidal agent.

In a preferred embodiment, microcapsules are formulated with a mixture of lignin and the polymer Budragit which, depending on the active agent, can prevent autocatalysis and degradation until the time of ingestion. In this regard, it will be appreciated that Eudragits can be manufactured so as to have either a positive or a negative charge. Accordingly, depending on what charge the active agent has, an Budragit having the opposite charge can be selected. One particularly preferred combination is the chemical insecticide Amdro·, which has e positive charge, and a negatively charged Budragit. In fact, without being limited to theory, it is believed that such combination has been found to result, during microcapsule formation with the lignin encapsulating agent, in a partial phase separation as the droplet forms and a pulling of the active agent into the core of the microcapsule where it is better protected in the final product.

This, in turn, increases the resistance of the microcapsule to autocatalysis. λ water-immiscible liquid such as vegetable oil, kerosene or liquid hydrocarbon containing a surfactant can bs used to form an emulsion with the encapsulating polymer and insecticide.

Solutions such as soybean oil and other vegetable oils, non-polar liquids such as kerosene and other liquid hydrocarbons such as hexane, in combination with a surfactant can be used as the continuous phase for making the emulsion of the capsule material. The emulsifying agent can consist of a SPAN-80/Tween-80 mixture. For soybean oil, 20% of a mixture of 30% Tween-80/70% SPAN-80 has been found to be effective. For other continuous phase liquids, the ratio of SPAN to Tween is adjusted to optimize the formation of the emulsion. Surfactants other than SPAN and Tween may also be used. Volume ratios between 1.5 and 2.0 of oil to capsule material have been successfully used. Lower ratios are possible but viscosity increases at the lower ratios and the capsules which result are not as uniform in size and shape. In addition, lower ratios may revere» the phase of the emulsion, resulting in oil droplets in the capsule material and fonation of distorted capsules or lack of capsules.

Tween-20 can be used as a surfactant in the hardening solution for hardening lignin capsules. Concentrations between 2 and 10% have been used, but too little Tween results in poor separation of the capsules from the oil. 2.5% Tween ie sufficient, in most cases. Capsules made from alkaline solutions of lignin can be hardened using a water solution of an acid such as acetic acid or an acid buffer. Capsules mads with lignin dissolved in organic solvent/vater can be hardened in water alone. 2. Preparation of Microcapsules A number of schemes for preparing microencapsulated active chemical toxins are now described. It will be appreciated that such techniques are also applicable to the encapsulation of insecticidal viruses, bacteria and fungi as well as other active agents.

The first step of the process involves mixing ths encapsulating agent comprising lignin, an active agent in a form compatible with microcapsuls formation and a solvent or cosolvent system which is miscible with water and which dissolves lignin. The lignin component, and ths modifications which can be made thereto, were discussed previously. Ths active agent in a form which is compatible with microcapsuls formation is ons which does not interfere with the solvents eaployed to prepare the microcapsules. In general, such active agent is in the form of either a solid in an aqueous suspension or it is dissolved in an organic solvent which is- not miscible with the aicrocapsule forming solvents. Ths solvent or cosolvent system includes water and is ons which is miscible with water and which dissolves lignin and includes a solvent comprising ethylene glycol, polyethylene glycol, isopropyl alcohol, acetone or mixtures thereof. Other solvents known in ths art and meeting the above criteria can be used.

An emulsifying solution is also prepared including a surfactant and a liquid which is immiscible with ths solvent system described above used to dissolve lignin. Suitable cosolvent immiscible liquids include vegetable oils such as soybean oil, kerosene or a liquid hydrocarbon such as hexane.

The surfactant is selected from those known in the art such as Tween-80, Span-80 or mixtures thereof. The ratio of these surfactants can be adjusted to optimize the formation of the emulsion, depending on the particular materials selected.

A solution for hardening the capsule is also prepared. Such solution comprises water and a surfactant when lignin is the encapsulating agent. For lignin capsules, water with 2 to 10% by weight of Tween-20 has been found to be suitable. Capsules made from alkaline solutions of lignin may be hardened with 0.1 M acetate buffer, pH 4.5. Acetic acid will also work. For lignin amine capsules, the final pH should be*near neutral, such as by using a 0.1M phosphate buffer of pH 6.8.

The emulsion prepared above is than combined with the hardening solution to harden the emulsion droplets to form capsules. Such capsules are then concentrated and separated from the from the oil and hardening solution either by allowing the capsules to settle or by centrifugation.

The present method enables the preparation of microcapeules having a lignin content above 10% by weight, preferably between about 10 and 30% and most preferably between about 20 and 30%. Typically, below about 10%, it is possible to form microcapsules. However, at such low level·, an effective eunscreening effect is not obtained. At levels above about 30%, lignin solutions can become quits viscous and difficult to handle. The present invention, by employing a solvent or cosolvent system which is miscible with water and which dissolves lignin, enables handling of lignin solutions with such high percentages of lignin therein.

The apparatus for preparing microcapsules is one used conventionally in the art.

To prepare the microcapsulss including Eudragit*, Eudragit* is dissolved in a solution containing PEG, the pH is adjusted with NaOH, and the solution mixed until dissolved. Separately, lignin is dispersed in water to form a thick paste. Because lignin is insoluble in water, PEG is added to the solution, and the lignin is allowed to dissolve. Alternatively, ammonium or sodium salts of lignin can be used which are soluble in water. Lignin has only limited solubility in acetone and isopropanol, but it is soluble in mixtures of such with water. Lignin is soluble in PEG-400 solutions of greater than 50% PEG, but if adjusted to pH 7.3, can become soluble in 35% PEG. Therefore, capsules have been successfully made from lignin dissolved in 50% PEG/water or 70% isopropanol/water, the ammonium salt of lignin dissolved in water, and from lignin adjusted to pH 7.3 dissolved in 35% PEG/water.

The Eudragit-PEG solution is added and mixed until the lignin is completely dissolved. To this mixture is added the suspension of the insecticide. If it ia desired to add an additional sunscreening agent, it can he added to the EudragitPEG solution. After adding the suspended biopesticide to the lignin-Eudragit solution, SPAN-85/Hssson oil (1:1) is added and stirred at maximum speed for about one minute to fora the emulsion of capsule material in oil. This ie poured rapidly into a hardening solution of Tween-20 in acetic acid and stirred for an additional minute to form capsules. The mixture is centrifuged in a 50ml centrifuge tube to separate the oil and the capsules. The capsules are washed several times to rsmovs as much oil as possible, and stored in water. The average diameter of the capsules is 25μα. For lignin amine capsules, the final pH should be near neutral. 0.1M phosphate buffer pH 6.8 has been used to maintain the pH in this range. 3* Application of Microcapsule» to Vegetation The microcapaules prepared by any of the above-described methods can generally be applied anywhere a conventional insecticide or other active ingredient such as a fertilizer could be applied. Generally, the concentration of the microcapsules and the rate of application depend on the nature of the pathogen and on the nature of the vegetation being treated. Such are readily ascertainable by persons skilled in the art.

The following examples are presented in order to more fully illustrate the preferred embodiments of the invention. They should in no way be construed, however, as limiting the broad scope of the invention.

EXAMPLE 1 Microencapsulated Amdro* in Lignin-Budragit was prepared by dissolving 14.4g Budragit S-100 in 120g 40% PEG-400, adding lg NaOH and mixing until dissolved. In a separate beaker, 20g lignin was added to 15g water and 15g of PEG and mixed to form a thick paste. The mixture was stirred for 15 minutes on magnetic stirrer to improve mixing. 50g of the Eudragit-PEG solution was added and stirred 20-30 minutes until all of the lignin was dissolved. 333μ1 micronized Amdro* was added to lOg of the resulting mixture and stirred for about a minute12.5g 50% SPAN-85/50% soybean oil was added and stirred one minute to form the emulsion of capsule material in oil. 32ml of 7% Tween-20 in acetate buffer was poured rapidly into the emulsion, and stirred for on· minute to form capsulds. The capsules were separated by centrifugation at lOOOrpm. The capsules were then washed to remove the remaining oil.

Cotton leaves wars treated with capsules with and without sunscreen, and with Amdro* in a solution of acetone/water.

Leaves were excised and bioassayed as above. Amdro* formulations were used at 100 ppm at (1 ml per leaf.) Treated leaves were excised at various intervals and bioassayed for control of firstinstar larvae of Hellothis vlrescens. Plante received seven hours of direct sunlight in ths first 24 hours post-treatment, followed by a 14 hour photo period exposure to metal halide lamps in the greenhouse.

The above-described encapsulated product was compared with nonencapsulated Amdro*. After days of exposure to ths sun, the micrencapsulated active agent of the invention retained most of its activity whereas the activity of the unprotected agent was mostly lost.

EXAMPLE 2 Bacillus thurinqlsnsls was encapsulated in lignin. First, the capsule material was prepared by mixing 13 5g of lignin and 135g of PEG-400 and 8.1g of 25% NaOH in a 5 quart bowl thereby forming a thick paste. There were then added 240g of Bacillus thurinqlsnsls slurry in 4 aliquots, mixing thoroughly after each addition. After the last addition, nixing was carried out for an additional 5 minutes to assure complete mixing and dissolution of the lignin.

An emulsifying solution was prepared by mixing together 84Og soy bean oil, 47g of SPAN-80 and 63g of TWEEN-80. λ hardening solution vas prepared hy mixing together 1388g water, 75g TWEEN-20 and 4.5ml acetic acid.

The emulsifying solution was then added to the capsule material in the mixing bowl and emulsified by mixing with a mixer. The mixing vas continued for 15 minutes. The hardening solution vas then poured in followed by mixing for another minute to harden and separate the capsules from the oil. The capsules were then separated form the oil and concentrated followed by pouring off the oil and excess water.

Bioassays wars dons by first exposing' a dilute water suspension of capsules or free Bacillus thurinciensls to ultraviolet light for a given period of time followed by spreading aliquots of the saaple on the surface of food in small cups. Next several cabbage looper larvae were placed in each cup and allowed to feed for three days. The living and dead larvae were then counted and the results expressed as percent mortality, (dead larvae)/(total). The capsules prepared above at doses of 2ug, 1/jg, and 0.5gg were compared to the free Bacillus at doses of 2 Mg and 4 Mg. As' is shown in Figure 1, after only a few hours of exposure to ultraviolet radiation, the encapsulated products of the invention provided a much higher mortality against cabbage loopers as compared to the nonencapsulatsd products.

EXAMPLE 3 Microencapsulated viruses were prepared. The lignin component wee Lignin AT from Westvaco. Polyethylene glycol having a molecular weight of 400 was employed. As the emulsifying solution, there vas used 10% of (60% Span-80/40% Tween-80) by weight in soybean oil. A stock Eudragit S-100 vas employed including 14.4g Eudragit S-100 and 120g PEG and lg NaOH.

A working Eudragit S-100 solution was prepared by adding 2Sg of the stock Eudragit S-100 solution and 15.Og PEG and 10.Og water, to make a 5% Eudragit in 50% PEG/water. A 25% NaOH w/w solution was prepared by adding 25g NaOH to 75g water. The virus used was A. cal from American Cyanamid of approximately 1010 ΡΙΒβ/g. A hardening solution was prepared from 20g acetate buffer, 20g Tween-20, 160g water and lOOmg CaCl2 dihydrate.

To prepare the microcapsulee, 2g of Lignin-AT were added to a 50ml beaker with 1.5g of PEG, 2g of 5% Eudragit S-100 in 50% PEG, and ΙβΟμΙ of 25% NaOH. The liquids were next mixed into the lignin to form a paste. Then, there was added lg of water followed by mixing. The mixture was warmed slightly in order to speed the dissolution of the Lignin.

After all of the lignin was dissolved, the capsule solution was allowed to cool. Then, there were added lOOmg of virus dispersed in 0.3g water followed by mixing. There were then added lOg of emulsifying solution. An emulsion was formed by stirring with a stir bar at maximum speed on a magnetic stir plate for about 1 minute. Next, 30ml of the hardening solution was poured in and stirring continued for another minute. The mixture was then poured into a 50cc centrifuge tube, shaken, and centrifuged for 3 minutes at 1000 rpm. Ths oil and supernatant were removed and the capsules were retained and resuspended in water.

The encapsulated and nonencapsulated virus was again applied against ths cabbage looper larvae as described in Example 2. The results, shown in Figure 2, demonstrate the dramatic difference between ths encapsulated and nonencapsulated product in terms of the percent mortality after only a few hours of exposure to ultraviolet radiation. . -,-.

While the invention has- been described and illustrated herein by references to various specific materials, procedures and examples it is understood that ths invention is not restricted to the particular materiel combinations of material, and procedures selected for that purpose. Numerous variations of such details can be implied am will be appreciated by those skilled in the art.

Claims (24)

WHAT IS CLAIMED IS:

1. A microencapsulated active agent comprising: (i) an active agent, and (ii) a polymeric encapsulating agent comprising lignin or a lignin compound.

2. The microencapsulated active agent of Claim 1 wherein said active agent is an insecticidal agent.

3. The microencapsulated active agent of Claim 2 wherein said insecticidal agent is an insecticidal pathogen including a virus, bacterium or fungi which infects insects.

4. The microencapsulated active agent of Claim 3 wherein said insecticidal pathogen is a nuclear polyhedrosis virus.

5. The microencapsulated active agent of Claim 3 wherein said insecticidal agent is Bacillus thurinolsnsls., Bacillus Sphaerlcua, Bacilli» EPPilliaa or a recombinantly produced pathogenic microorganism.

6. The microencapsulated active agent of Claim 4 wherein said nuclear polyhedrosis virus is a nuclear polyhedrosis virus of Hellothis na, IL_ yicfiSSSfift, ly«ntrla dilEftr, Qxflia pggudQtgggataz Wtcdlprion iirtlter, or Autographa califocnlca

7. The microencapsulated active agent of Claim 2 wherein said insecticidal agent is a chemical toxin.

8. The microencapsulated active agent of Claim 1 wherein said encapsulating agent further comprises a modified acrylic acid polymer.

9. The microencapsulated active agent of Claim 8 wherein said modified acrylic acid polymer ham a positive or negative charge and said active agent has a charge opposite to that of said polymer.

10. The microencapsulated active agent of Claim 9 wherein said active agent is hydramethylnon and wherein said polymer has a negative charge.

11. The microencapsulated active agent of Claim 1, wherein said polymeric encapsulating agent further comprises a polymer synthesized from acrylic and methacrylic acid esters with a low content of quaternary ammonium groups.

12. The microencapsulated active agent of Claim 1 comprising about 10-30* by weight of said lignin or lignin compound.

13. Ths microencapsulated active agent of Claim 12 comprising about 20-30* by weight of said lignin or lignin compound.

14. A process for preparing a microencapsulated active agent comprising the steps of: (i) mixing (1) an encapsulating agsnt comprising lignin or a lignin compound, (2) an active agent in a form compatible with microcapsule formation and (3) an aqueous solvent or cosolvent system which is miscible with water and which dissolves lignin or the lignin compound to form a first mixture; (ii) preparing an emulsifying solution comprising a surfactant and a liquid which is immiscible with said agueous solvent or cosolvent system; (iii) preparing a solution to harden the capsules; (iv) mixing the first mixture and the emulsifying solution to form an emulsion; (v) mixing the resultant emulsion with the hardening solution to harden emulsion droplets to form capsules; and (vi) concentrating and separating the capsules from the water insoluble liquid.

15. The process of Claim 14 wherein said aqueous solvent or cosolvent system which is miscible with water comprises ethylene glycol, polyethylene glycol, isopropyl alcohol, acetone or mixtures thereof.

16. The process of Claim 14 wherein eaid active agent is an insecticide.

17. The process of claim 14 wherein said encapsulating polymer is lignin amine or lignin amine sulfonate.

18. The process of claim 14 wherein said solvent is polyethylene glycol, isopropyl alcohol, or acetone.

19. The process of claim 14 wherein said emulsifying agent is a liquid hydrocarbon.

20. The process of claim 19 wherein said liquid hydrocarbon is vegetable oil or kerosene.

21. The process of Claim 14 wherein said encapsulating agent is lignin and said hardening solution comprises water and a surfactant.

22. A microencapsulated active agent according to claim 1, substantially as hereinbefore described and exemplified.

23. A process for preparing a microencapsulated active agent according to claim 1, substantially as hereinbefore described and exemplified.

24. A microencapsulated active agent according to claim 1, whenever prepared by a process claimed in a preceding claim.