TITLE OF THE INVENTION

COMPOSITION AND METHOD OF FORMULATION OF PHYSICALLY AND CHEMICALLY STABLE ENCAPSULATED PRODUCTS WITH DIUTAN GUM AND

ITS APPLICATIONS THEREOF

TECHNICAL FIELD

The present invention relate to the preparation of active loaded polyurea/polyurathane microcapsules (PU capsules) and stabilize/suspend the active loaded microcapsules in the aqueous media using diutan gum as a thixotropic agent/rheology modifier. Very high loadings of actives in the PU microcapsules formulations can be achieved by following the present inventive formulation methods. In addition, these capsules can also be separated from aqueous phase by suitable method and can be used as wet microcapsules or can be re-dispersed in a fresh optional fluid(s) with diutan gum, to impart the physico-chemically stability to the formulations. These products generally find applications in personal care and agricultural fields. The produced product showed excellent physical and chemical stabilities at various environmental conditions, thus, can be used across the globe in the personal care and agriculture applications at various seasons and environmental conditions, for example at temperatures between -20°C and 65°C.

BACKGROUND ART

For personal care and agricultural formulations, the chemical and physical stability of the formulations/products is a major issue as cited in reference Nature Nanotechnology (year 2012 Vol 7(2), P 87-90. The stability greatly affects the product performance. The performance of microencapsulated formulations used in these areas should be stable at various environmental and climatic conditions. The products should be compatible with various emulsions, suspensions and other active components when they are mixed together. However, arriving at a greater chemical and physical stability, without compromising the loading efficiency of actives, is a practical challenge. The newly formed active loaded microcapsules formulations is used in a variety of different application when and where there is a need of release/de livery of fragrance, flavor, herbicide fertilizer, pesticide, fungicides, nanoparticles etc. The new ways of stabilizing microcapsules by diutan gum can be extended to nano to even bigger size capsules. Microcapsules preparation methods are covered in the basic patents: US. Pat. No- 4,285,720 and 4,956, 129. Some improvements have been suggested in the later on patents (US. Pat. No- 4, 140,516 and 4,448,929). SUMMARY OF INVENTION

Problems in conventional microencapsulated products

The term microcapsules used in the art of work includes the encapsulation of actives in small capsules, typically having a diameter less than 300 microns, preferably less than 200 microns, more preferably less than 100 microns. Typically, these microcapsules comprise a spherical hollow shell of water insoluble, partially water soluble and/or homogeneous mixture of actives such as fragrance, perfumes, herbicides etc. Claims stated in most of these examples are contained to modification of microcapsules pertaining to specific end use applications such as control release, release of actives based on charge of surface, soil and environmental conditions etc. Nondimiting examples of microcapsules are available in the following references: US8216598B2; US6992047B2; US6133197A ; US6514439B2; WO2011154893A1

In the conventional procedures for microencapsulating active compounds (examples: fragrance, perfumes, herbicides etc.), the loading efficiency of active compounds are relatively low. This may be due to the presence of other additives being added to stabilize the emulsion system designed for specified application. In such cases, a compromise is required, such as drug loading, toxicity, release rate, control release etc, on product quality. Additionally, in the emulsion products (microcapsules), upto 10 wt% contributions goes to capsule wall, hence, the maximum active compounds concentration in the microcapsules could be around 90wt%. The other main concern, in the conventional procedures, is stabilizing the microencapsulated product emulsions. The physical stability becomes even more challenging when the capsule wall contribution goes beyond 5 wt% with respect to the active compounds in the microcapsule. This is mainly due to the presence of unreacted residual (example: crosslinker) that may cause the particles to bring closer together hence, over a period, leads the product coagulation/phase separation.

In the conventional system, even though a lot of work has been done to stabilize the product (both physically and chemically) by adding different agents like Guar Gum, Xanthan Gum, Hydroxy Propyl guar, low molecular weight glycols and amides, none of them are found to be very effective to eliminate the issues listed above.

Therefore, the existing formulations across the fields suffer from:

a. Product performance/stability vary with environmental/storage conditions b. Usage of unwanted chemicals in the products.

c. These existing formulation products have long time storage stability issues. And may not compatible as such when mixed with other actives.

d. The existing formulations have poor loading active compounds may be limited around 25-35 wt%. The active loaded microcapsules aggregate and get settle down or float in the aqueous media when stored longtime. Settling down or floating of microcapsules depends on the density of active components present in the microcapsules. For instance, when the density of active component that is loaded in PU microcapsules is more than "one” the loaded PU microcapsules aggregate and settle down at the bottom of the dispersing liquid medium, if the density of active component is less than“one” then the capsules afloat/cream and aggregates. In both cases either settles down or float of microcapsules are not suitable for any type of applications. Though many investigations have had beenattempted by many in pastin an endeavor to prepare the stable active loaded PU microcapsules formulations for personal care and agriculture applications, to achieve certain level of physical stability, these industries are compromised with the loading efficiency of actives in microcapsules. This indicates that the problem of microcapsule aggregation in aqueous media was not thoroughly addressed to compose a new method of formulation in deriving the physic- chemically stable encapsulated products.

Solutions to the current problems

In the present invention, we have developed physically and chemically stable and highly loaded active microcapsules formulations for personal care and agricultural applications. The present invention paved a path to investigate the challenges associated in the prior art when it comes to the problems with stability, loading efficiency of the active material in the microcapsules and aggregation of PU microcapsules in aqueous phase. A plausible mechanism involved in this method has been depicted as shown in Figure 1.

Also, the following factors have been identified to address the microcapsules stability issues.

a. Altering the microcapsule shell wall thickness

b. Selecting a suitable stabilizer/rheology modifier

c. The dosing of stabilizer

d. The dosing of aqueous phase

e. The density of the actives in microcapsules (IP)

By precise selection of wall thickness (2 to 5%, preferably 2.5 to 3% with respect to total formulation i.e. both IP and EP; or 1 to 2.5%, preferable 1.5 to 2% with respect to IP only), and by adding desired quantity of diutan gum stabilizer, the stabilization of the active loaded PU microcapsules in aqueous phase is effectively achieved. The density of active compounds which should be between 0.9 to 1.4% can be stabilized with this system without phase separation. Physical and chemical stability of stabilized capsules have been concluded based on accelerated aging tests or shelf life tests i.e. at 60°C for 3 weeks and found that no aggregation or loss of actives observed during the tests. The detailed formulation(s) is given as below. When the experiments were conducted for the comparison with varied thickness of the capsule wall, interesting effective results were deduced in support of the plausible mechanism and the factors identified for micro capsules stability and aggregation issues.

For example, two different experiments with PU microencapsulated products were conducted by using low capsule wall (2.5% with respect to both IP and EP) and high capsule wall (5.5 and 7% with respect to IP and EP). The emulsion products (after curing) obtained from low capsule wall (thinker wall) are more stable than the thicker wall containing emulsion products. These illustrations are shown in Figure 1. The low wall (thinner wall) containing emulsions are more stable than the high wall (thicker wall) containing emulation products.

Polyurea/Polyurathane (PU) microcapsules comprise core and shell morphologie. Core is the active compounds like fragrance or herbicide etc. and shell is PU wall. The microcapsules that were prepared contain 95-98% core (actives) and 2-5% shell (PU wall). In other words, when PU microcapsules are in water phase the core (actives) is around 50 to 65%, shell is around 1 to 2.5%, and aqueous phase is around 33 to 47 %. The PU shell wall is formed around the core by interfacial crosslinking between isocyanate (dimer or trimer or combined) and amine (di, tri or tetra amine) or various forms polyols in aqueous phase. A detailed description is tabulated in Table 1.

Preparations of active loaded PU microcapsules

The existing microencapsulation procedure mainly comprises two phases/steps:

The first step is called the internal phase or oil phase which has an active component such as a perfume or herbicide or fertilizer or pesticide that may be in solids, liquids or gas/vapor forms and isocyanate which may be diisocyanate or triisocyanate or polyisocyanate or low molecular weight aliphatic or aromatic or combination of both.

The second step is called the external phase or aqueous phase which comprises water, emulsifier (may be neutral, ionic), and crosslinker (may be low molecular weight or long chain amine).

Generally, the isocyanate and the crosslinker ratios are in the range of 1:0.8 to 1:1.1. The desired size product capsules can be obtained by combining these two phases followed by the emulsification. After emulsification, the microcapsules are cured by interfacial polymerization and/or crosslinking by adding amine crosslinker. These emulsions then further be cured at different temperatures to get loaded microcapsules (product capsules). In general, the curing temperature varies between 30 and 80°C. The time and curing temperature decide the crosslink density of the wall. In general, low temperature enables low cross-link density wall, and higher curing temperature gives high cross link density. Release of actives from capsules can be decided based on crosslink density. Low crosslink density capsules release the actives faster than that of high crosslink density capsules. The crosslink density and wall thickness can be adjusted based on curing time, temperature and amount of wall material (examples: isocyanate, and amine). Table 1 given below enlists some of example compounds being use in the various phases during the micro-encapsulation procedures

Upon completion of curing reaction, 0.01 to 0.5 wt% of the Diutan Gum was added and stirred for a while before storing the product. Stirring time varies between 15 and 60 min that mainly depends on the temperature at which point the diutangum was added to the product. In this unique and simplest way, the physically and chemically stable microcapsules are generated. A breakthrough in the current invention came by adding 0.01 to 0.5 wt % diutan gum as a reaction/rheology modifier after the polymerization process. The stabilizing of emulsion products with diutan gum works effectively when:

1) The capsule wall is relatively thin (generally less than <5wt% with respect to IP).

2) The density of active compounds is between 0.8 to 1.4

With the wall thickness goes beyond certain limit (example >5 wt%), capsules slowly get settled or cream, depending on densities of actives in the emulsion product. The concentration of diutan gum also plays an important role to increase the shelf life. Depending on the densities of actives, the concentration of diutan gum varies. If the density of emulsion product is around 1, then it required low concentration of diutan gum. If density of the emulsion products is much lower than 1 or much higher thanl, then it requires higher concentration of diutan gum to stabilize the system.

BRIEF DESCRIPTION OF DIAGRAMS

Fig.l illustrated the relation between the capsule wall thickness and stability with and without diutan gum formulations shown above. This Figure represents the stability of thinner (left side) and thicker (right side) wall capsules prepared without (top) and with (bottom) diutan modified formulations. No aggregation/settling of particles observed with thinner wall capsules with diutan in it. However, the thicker wall capsules with diutan do tend to aggregate, however, to a lesser magnitude. Above pictorial representation doesn’t represent the rheology changes in presence of diutan in the product. The products without diutan formulations (with other additives) aggregate/settle irrespective of wall thickness of the capsules, hence, are not at all stable.

BRIEF DESCRIPTION OF THE EMBODIMENTS

In this study, we developed physically and chemically stable formulation to encapsulate the model liquid actives like perfumes and herbicides for personal care and agricultural applications. The main breakthrough in the invention is identifying a reaction/rheology modifier, diutan gum, which works effective when the capsule wall thickness is below 5wt% with respect to IP (Figure 1). The diutan gum - a unique, anionic polymer produced by microbial fermentation. As a versatile rheology-modifying agent, diutan gum is useful in a wide range of industrial applications, providing excellent stabilization, high pseudoplasticity and high viscosity at low-use concentrations.

In this art work, we prepared active loaded PU microencapsulated emulsion products by taking model water immiscible liquid/solid active(s) as internal phase (IP) and adding aliphatic isocyanate as wall former. The active additive(s) are, sometimes, mixed with inert liquid(s) those are generally referred to as density modifiers or performance enhancing agents (PEA). The main purpose of these modifiers is to enhance the solubility of actives and control the release, when and where the product being used and these will also serve the purpose of adjusting the density of microcapsules. The IP was mixed with the second phase (external phase, EP) containing water and emulsifier (neutral or ionic, depending on requirement). The emulsifier concentration varies between 1-5 wt%. IP and EP were homogenized by mixing IP and EP together to get the emulsions with the desired size and wall thickness. The size of capsules may vary between 1 and 15 micrometers. Depending on the specific end use application, the product emulsions are cured by following the interfacial polymerization method in the presence of crosslinking agents and at different temperatures. Table.1 given enlists some of example compounds being use in the various phases during the micro encapsulation procedures.

Table 1: A brief description of various formulations used in the preparation of PU Microcapsules are tabulated below

Actives Materials or Compounds (Core): perfumes, detergents, insecticides, fertilizers, herbicides, fungicides etc.

Capsule Wall Materials: The capsule wall materials applied in this invention was hexamethylene diisocyanate (HDI), EXPN2291, HDI Biuret, OXAWM 33 (HDI based isocyanate, 65 % dimer and 35 % trimer), OXAWM 22, isophoronediisocynate (DPDI), tetramethyle xylene diisocyanate (TMXDI), EXPN2302 (modified methylene diphenyl diisocyanate (MDI) etc.

Crosslinkers: The amine crosslinkers used in this study were diethylene triamine (DETA), triethylene tetraamine (TETA), guanidine carbonate (GUCA), diethylene amine, polyethylene imine (PEI) etc.

The alcohol crossdinkers used were ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols, sorbitol, trimethylolpropane triol etc.

Emulsifiers/Surfactants : Polyvinyl alcohol ((PVA or PVOH), gum Arabic (GA), carboxymethylcellulose (CMC)/ tween and SPAN. Depending on the application, emulsifiers can be used as such or in combination with surfactants (example Tween and SPAN).

Rheology modifiers (RM)/Thickeners:Diutan gum.

For more additive examples, refer patent US 2008/0131695 A1

ADVANTAGES OF PRESENT MICROENCAPSULATION METHOD OVER CONVENTIONAL METHODS AND USES THEREOF

In the present microencapsulation procedure, the loading efficiency of the capsules for active compounds or materials have augmented up to 65 wt% which is more efficient than the loadings obtained by other conventional methods employed in both personal care and agricultural product applications in the present context. We have identified that the physical stability of product mainly depends on the combination of wall thickness (i.e amount of isocyanate and amine), and quantity of reaction/rheology modifier i.e. diutan gum. Amongst all stabilizers such as Xanthan Gum, Gellan Gum, Guar gum, Hydroxypropyl Guar and their combinations, the products obtained from Diutan gum exhibits greater physical and chemical stability. No other stabilizer effectively stabilizes the formulation as good as diutan gum. All of them, excluding diutan gum product, produced phase separating formulations at different temperatures and test conditions. In which, the diutan gum stabilizes the system at wide range of the temperatures ranging from -25 to 65° C with greater rheological properties. None of the other stabilizer available in market performed as good as diutan gum. Among all the rheology modifiers or viscosifying agents tested, Diutan gum works better plausibly, due to its thixotropic nature.

The current innovative formulation method can be used to encapsulate any water immiscible liquids or solids. However, the water immiscible liquids should not react with wall materials (isocyanates) and crosslinkers (amines).

The schematic representation of encapsulated products containing thinner and thicker wall capsules stabilized with other additives (examples Xanthan Gum, Gellan Gum etc) vis-a-vis with diutan gum (rheology modifier) is shown in Fig.l.

Cost Effectiveness and Quality Product with more advantages:

To the best of previous prior art and the knowledge concerned, as on date, no alternative or substitute formulations/methods available to stabilize the product. The diutan gum formulation in the present invention is a unique way of stabilizing the product.

When the product transported as wet capsules and re-dispersing them at the site with diutan gum saves huge transportation cost.

Very simplistic and easy to adopt formulation method with zero usage of adding excess quantities of chemicals as stabilizers/density modifiers to safeguard the environment and chemicals cost.

Much higher active compound load efficiency is observed in the capsules with the diutan gum formulations.

When estimated, the modified formulation method, i.e. the addition of diutan gum, can generate 20-50 % of cost benefits when compared with similar products produced in the market without diutan gum formulation herein disclosed in this invention.

Based on the necessity, this diutan gum formulated product emulsions can be washed (to remove trances or liquids), used as wet capsules or can be re-dispersed in a fresh optional fluid with diutan gum.

The present invention can be used in a wide range of reactions employed in the production of agriculture and personal care products.

The final encapsulated product is stored in water mixed with diutan solution to reduce or eliminate the aging effect.

Industrial Applicability and Advantages of the invention: The current invention of utilizing the diutan gum as a reaction/rheology modifier overcomes the majority of problems associated with currently existing methods. It also proved to have the following advantages:

a. The formulation can be used in multiple active systems.

b. It is can be mixed with existing formulations or at reduced concentrations of additives in the formulations.

c. Loading efficiency of active compound in the capsules gone beyond 97 wt% (rest is polymer capsule wall).

d. Stable product performance at various environmental/storage conditions.

e. The invention eliminates using several additives, hence the reaction is clean and eco-friendly and cost effective.

f. Lowering or elimination of aging effects associated with storage chemicals/methods.

g. Possible to separate the capsules from the product and use as wet capsules and re-disperse them when required. In this way, the loading efficiency of the overall product during the production goes beyond 75 wt %.

h. Formulations can be employed to multi-active compounds and encapsulated multi-active compound systems.

i. Formulations can be used to nano to several hundreds micron size capsules.

The diutan gum can also be mixed with storage liquids (water or water solutions) to prevent the coagulation, phase separation, and destabilization of product capsules. The current modified procedure of stabilizing the product with diutan gum is more suitable when the weight percent of polymer capsules wall falls in between 2.5 and 5.0 with respect to IP (rest is active compound). Diutan gum formulations showed higher stability with the products without walls and even thinner walls such as vesicles. Overall, with diutan gum formulations, the relative stability of products reduces with an increase in wall thickness as the stability of thicker wall < thinner wall< ultrathin or no wall capsules (vesicles).

Capsule wall thickness plays an important role in:

Control release applications

Where the stability of capsules is important especially when the products are stored/used at ambient temperatures

The integrity of capsules is important relative to the nature of active compound. When used as wet capsules

Washing of product (to remove the trances) and re-dispersion steps involved. Sizing of capsules is important

Diutan gum proved to give better results when mixed in the existing formulations with other additives such as Xanthan Gum, Gellan Gum, Guar gum, Hydroxypropyl Guar and their combinations.

Using diutan gum has the following additional features:

The EPA approved diutan gum as an inert ingredient.

It can be used in crop protection applications, including herbicides, insecticides, and fungicides.

It is used in pesticide products for animal production, such as topical insecticide sprays, gels, or pour-on liquids, as well as for use with companion animals, such as dogs and cats;

It is used in products for professional pest control, home lawn and garden, and turf management for golf courses and sports stadiums.

CITATION LIST

The term microcapsules used in the art of work includes the encapsulation of actives in small capsules, typically having a diameter less than 300 microns, preferably less than 200 microns, more preferably less than 100 microns. Typically, these microcapsules comprise a spherical hollow shell of water insoluble, partially water soluble and/or homogeneous mixture of actives such as fragrance, perfumes, herbicides etc. Claims stated in most of these examples are contained to modification of microcapsules pertaining to specific end use applications such as control release, release of actives based on charge of surface, soil and environmental conditions etc. Non-limiting examples of microcapsules are available in the following references: US8216598B2; US6992047B2 ; US6133197A ; US6514439B2; WO2011154893A1. The new ways of stabilizing microcapsules by diutan gum can be extended to nano to even bigger size capsules. Microcapsules preparation methods are covered in the basic patents: US. Pat. No- 4,285,720 and 4,956, 129. Some improvements have been suggested in the later on patents (US. Pat. No- 4, 140,516 and 4,448,929).