PH-responsive microparticles for controlled release of pesticides

Abstract

The present invention relates to pH-responsive microparticles, comprising a modified cellulose-based core and coated with an alginate layer, capable of encapsulating and releasing a pesticide in a controlled manner. The present invention further relates to a process for obtaining such microparticles, a solid composition and a liquid composition comprising such microparticles, and the use of such microparticles and compositions as an agrochemical.

Description

[0001] TITLE

[0002] PH-RESPONSIVE MICROPARTICLES FOR CONTROLLED RELEASE OF PESTICIDES

[0003] FIELD OF THE INVENTION

[0004] The present invention relates in general to the field of agrochemicals. In particular, the present invention relates to pH-responsive microparticles, i.e., which are sensitive to pH variation, showing a response when placed under variable pH conditions, comprising a modified cellulose-based core coated with an alginate layer, capable of encapsulating and releasing a pesticide in a controlled manner.

[0005] The present invention further relates to a process for obtaining such microparticles, a solid composition and a liquid composition comprising such microparticles, and the use of such microparticles and compositions as an agrochemical.

[0006] BACKGROUND ART

[0007] Effective management of pests, and more generally of any organism harmful to plants for better agricultural production, is one of the main objectives to meet the growing demand for food.

[0008] In this context, agrochemicals, and the pesticides contained therein, play a key role in ensuring crop productivity and promoting the sustainable growth of agricultural production; however, the harmful effects thereof on the environment and health require careful handling.

[0009] One of the substances most used as a pesticide for the protection of plants from fungi and bacteria is copper: in fact, in the presence of Cu2+ions, fungal spores or bacterial cells cannot mature or reproduce, therefore the fungus or bacterium is effectively killed. However, the cupric ion is easily subject to leaching due to the strong ability to coordinate many water molecules with very fast dynamics. Furthermore, by virtue of the ability thereof to create stable bonds with organic matter, copper is considered a "persistent" substance and for this reason the research over the last 15 years has focused on the possibility of replacing the copper compounds or minimizing the amounts used in crop protection.

[0010] In conventional agrochemicals, the active component is typically combined with inert materials so as to ensure effectiveness, stability and functionality thereof in field use, and finally for safe and easy handling. In particular, the biggest problem to be addressed is what is called "burst effect", that is, the immediate release of the active components due to degradation processes such as photolytic, hydrolytic and microbial degradation processes as well as phenomena such as volatilization, evaporation, and washing. Therefore, the concentration of the active component rapidly falls below the desired values, resulting in a reduced efficacy.

[0011] Traditional pesticide formulations are typically used in the form of liquids, for example concentrated suspensions (SC), soluble liquids (SL), emulsifiable concentrates (EC), or as solids, for example as wettable powders (WP), dispersible granules (WG), soluble powders (SP), and are sprayed onto the soil or directly onto plants with a considerable loss of the active components caused by various phenomena including poor dispersion, resulting in the formation of heaps of solid material, and leaching of the active ingredients.

[0012] In order to obviate the problems described above and increase effectiveness and coverage throughout the crop cycle, agrochemicals are typically applied repeatedly to plants, with heavy environmental repercussions and a significant increase in costs, also increasing the risk of toxic effects for the plants themselves.

[0013] This is why more recently studies have focused on slow-release and / or controlled-release formulations, which allow for the release of the active components in a gradual and prolonged manner, controlled according to the needs of the plant and / or soil (see for example Singh, Amrita, et al. "Advances in controlled release pesticide formulations: Prospects to safer integrated pest management and sustainable agriculture." Journal of hazardous materials 385 (2020): 121525).

[0014] Many of these formulations use polymer systems for the encapsulation of the active component, the pesticide, and can have different release profiles based on the physical characteristics thereof and the mechanism controlling the release. Encapsulation also protects the active components from external agents such as water and light, and prevents the oxidation and evaporation thereof, as well as obtaining products with better storage and transport properties.

[0015] One of the strategies for controlling and regulating the release of active components is to use materials for encapsulation which are responsive to external stimuli, in particular light, pH, temperature and humidity, as well as to the presence of biological stimuli, such as specific metabolites, bacteria, or enzymes.

[0016] In this sense, pH-sensitive polymers show great potential, as they are easily soluble and have good permeability. They are characterized by the presence of weakly acidic or weakly alkaline groups, for example carboxyl groups or amino groups, which are easily protonated or deprotonated in response to a change in the external pH value. Therefore, the variation in the degree of ionization of these pH-sensitive polymers has been used to encapsulate pesticides and direct the release mechanisms thereof.

[0017] In this respect, application WO2023 / 072943 describes the preparation of microencapsulated compositions based on the ionic interaction between cationic groups (e.g., amines of chitosan or other natural polymers, or copper ions) and anionic groups, e.g., carboxylates or sulfonates, present on chemically modified cellulose or alginates.

[0018] Song et al. (J. Applied Polymer Sci) describes the encapsulation and spraydrying of Tea Tree Oil in a system consisting of methylcellulose and chitosan or alginate, utilizing the amphiphilic features of alkyl cellulose acting as emulsifiers for the oily active ingredient.

[0019] For example, nanometric encapsulation systems have also been developed which utilize such a principle, see for example the system described by Zhang, Yilin and collaborators in the publication "Temperature-and pH-responsive star polymers as nanocamers with potential for in vivo agrochemical delivery." (ACS nano 14.9 (2020): 10954-10965). However, these systems typically make use of very complex and expensive polymers, thus making the application thereof on an industrial scale difficult. SUMMARY OF THE INVENTION

[0020] The Applicant has thus set the objective of developing a pesticide formulation capable of minimizing phytotoxicity and making the administration thereof to the plant more efficient, reducing material waste.

[0021] The Applicant has also set the objective of developing a pesticide formulation capable of increasing the effectiveness thereof, so as to make the necessary administration thereof less frequent and in smaller doses.

[0022] At the end of extensive experimentation, the Applicant has found that it is possible to obtain a formulation which at least partially solves the problems of the prior art, and which fulfills the aforementioned objectives, encapsulating the desired pesticide agent in pH-responsive microparticles, comprising a modified cellulose-based core coated with an alginate layer. The system according to the present invention uses readily available and inexpensive polymers, so as to make the application thereof on an industrial scale highly convenient.

[0023] Therefore, a first aspect of the present invention relates to microparticles comprising a core comprising at least one modified cellulose and a coating comprising at least one alginate, where said microparticles are loaded with at least one pesticide.

[0024] In a second aspect, the present invention relates to a process for obtaining the microparticles according to the present invention, said process comprising the following steps: a) Preparing an aqueous mixture comprising at least two chemically modified celluloses having different polarity features, at least one pesticide and at least one alginate, in this order; and b) Subjecting the mixture obtained in step a) to a spray-drying process.

[0025] According to the latter aspect, preferably the mixing in a) is advantageously carried out in the same container (one-pot).

[0026] In a third and a fourth aspect, the present invention relates to a solid composition, preferably in powder form, and a liquid composition comprising the microparticles according to the present invention, and optionally one or more additives. In a fifth aspect, the present invention relates to the use of the microparticles or compositions according to the present invention as agrochemicals.

[0027] In a further aspect, the invention relates to microparticles obtainable with the process as defined above; these particles prove to have peculiar features as compared to those described in the prior art.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The description is illustrated herein with reference to the accompanying drawings, provided merely by way of non-limiting example of the invention.

[0030] Figure 1 shows the FTIR-ATR spectrum of: tribasic copper sulfate (panel A), a sample of microparticles obtained from a solution of carboxymethyl cellulose and hydroxyethyl cellulose (panel B), and a sample of microparticles according to the present invention (panel C).

[0031] Figure 2 shows Scanning Electron Microscopy (SEM) images of a microparticle sample according to the present invention at the resolution of 100 pm (panel A) and 40 pm (panel B).

[0032] Figures 3-5 show, for three samples of microparticles according to the present invention (Fig. 3 formulation F1 , Fig. 4 formulation F2 and Fig. 5 formulation F3), the trend of the average size of the microparticles as a function of the time and pH of the solution in which they are suspended, recorded by laser diffraction experiments.

[0033] Figures 6-8 show, for three microparticle samples according to the present invention (Fig. 6 formulation F1 , Fig. 7 formulation F2 and Fig. 8 formulation F3), the percentages of Cu2+ion release as a function of time (after 1 , 4, 8, and 24 hours) at different pHs (from pH 3 to pH 8).

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] Definitions

[0036] For the purposes of the present invention, the term "pesticide(s)" is intended to refer to any substance or mixture of substances intended to prevent, destroy or control harmful organisms (including microorganisms and weeds), or inhibit or prevent the damage thereof, in the stages of production, processing, storage, transport and sale of crops, foods, timber. The term comprises for example substances intended for use as plant growth regulators, defoliants, desiccants or agents for thinning fruits or preventing the premature fall thereof, and substances applied to crops before or after harvest to protect goods from spoilage during storage and transport.

[0037] For the purposes of the present invention, the term "agrochemical(s)" is intended to refer to a product comprising the pesticide substance(s), i.e. , the active component(s), and any other ingredient adapted to obtain a product for use on plants.

[0038] For the purposes of the present invention, the term "microparticle(s)" is intended to refer to particles of sizes in the micrometer range, in particular between 0.1 microns (pm) and 100 microns (pm).

[0039] For the purposes of the present invention, it is possible to define the polarity of a molecule by means of the dipole moment generated, depending on the presence of more or less polar groups in the substituents even of high molecular weight polymers, such as cellulose, and as described in: Minkin, Vladimir Isaakovich. Dipole moments in organic chemistry. Springer Science & Business Media, 2012.

[0040] Specifically, considering the presence of carboxyl groups in CMC (COOH) and hydroxyl groups in HEC (OH), it is possible to define: HEC polarity lower than CMC polarity, since the polarity values for the OHs are equal to 1.7-1.8 and are instead equal to 4.5-4.6 Debey for the COOH groups. Therefore, for the purposes of the present invention, chemically modified celluloses containing carboxyl groups, e.g., carboxyalkyl celluloses are defined as polar, while alkyl celluloses and hydroxyalkyl celluloses are defined as neutral.

[0041] Detailed description

[0042] In a first aspect, the present invention relates to microparticles comprising a core comprising at least two chemically modified celluloses, at least one pesticide and a coating comprising at least one alginate, where said chemically modified celluloses have a different degree of polarity.

[0043] Preferably, the chemically modified celluloses are of two types: one cellulose is more polar and the other cellulose is less polar, or neutral.

[0044] In embodiments of the present invention, the weight ratio in the microparticles between said at least one alginate and said at least one modified cellulose is from 0.15 to 2.5, preferably from 0.20 to 2, even more preferably from 0.25 to 1 .5.

[0045] Preferably, said at least one modified cellulose is selected from hydroxyalkyl cellulose, preferably with linear or branched C1 -C10 alkyl, for example hydroxyethyl cellulose, or ethyl cellulose; carboxyalkyl cellulose, preferably with linear or branched C1 -C10 alkyl, for example carboxymethyl cellulose; and mixtures thereof. In preferred embodiments in which the modified cellulose is a mixture of at least two types of cellulose, the weight ratio of alginate to cellulose reported above is to be understood as the weight ratio of alginate to the sum of the celluloses present.

[0046] In embodiments of the present invention, the core comprises, or essentially consists of, a mixture of a polar carboxyalkyl cellulose and a hydroxyalkyl cellulose with polarity lower than the previous one (or neutral); preferably it is a mixture of carboxymethyl cellulose and hydroxyethyl cellulose.

[0047] In such embodiments, the weight ratio in the microparticles between the carboxyalkyl cellulose, preferably carboxymethyl cellulose, and the hydroxyalkyl cellulose, preferably hydroxyethyl cellulose, is between 1 :1 and 3:1 , preferably between 2:1 and 3:1 , even more preferably it is 3:1. In such embodiments, the weight ratio in the microparticles between said at least one alginate, carboxyalkyl cellulose, and hydroxyalkyl cellulose (alginate : carboxyalkyl cellulose: hydroxyalkyl cellulose), and preferably between alginate, carboxymethyl cellulose, and hydroxyethyl cellulose (alginate : carboxymethyl cellulose: hydroxyethyl cellulose), is preferably between 1 :3:1 and 6:3:1 , for example 1 :3:1 , 2:3:1 , 3:3:1 , 4:3:1 , 5:3:1 , 6:3.1.

[0048] In the present description and in the following claims, the term "alginate" is intended as any salt of alginic acid, polymer of anionic nature, for example sodium alginate or potassium alginate.

[0049] In embodiments of the present invention, said coating comprises, or essentially consists of, sodium alginate.

[0050] In a particularly preferred form of the present invention, said microparticles comprise a core comprising, or essentially consisting of, carboxymethyl cellulose and hydroxyethyl cellulose, and a coating comprising, or essentially consisting of, sodium alginate.

[0051] Pesticides useful for the purposes of the present invention are selected from the group comprising copper salts, preferably copper (II) salts, zinc salts, aluminum salts, silver salts, palladium salts, gold salts, platinum salts, and nickel salts.

[0052] In particularly preferred embodiments of the present invention, said pesticide is a copper salt, preferably a copper (II) salt, even more preferably copper sulfate, e.g., tribasic copper sulfate.

[0053] In a particularly preferred form of the present invention, said microparticles comprise a core comprising, or essentially consisting of, carboxymethyl cellulose and hydroxyethyl cellulose, a coating comprising, or essentially consisting of, sodium alginate, and are loaded with a copper salt, preferably a copper (II) salt, even more preferably copper sulfate.

[0054] Carboxymethyl cellulose and hydroxyethyl cellulose represent only a preferred example of modified celluloses having different polarity.

[0055] In particular, carboxymethyl cellulose is a modified cellulose which has polar features by virtue of the carboxyl group, while hydroxyethyl cellulose is an amphipathic cellulose with lower polarity or neutral.

[0056] In embodiments of the present invention, said pesticide is present in the microparticles in an amount equal to or less than 50% by weight, preferably equal to or less than 30% by weight, even more preferably equal to or less than 10% by weight, for example from 1 % to 10% by weight.

[0057] Preferably, said microparticles have an average size of 1 -100 microns in diameter, preferably 10-80 microns in diameter, more preferably 10-50 microns in diameter, as measured by scanning electron microscope (SEM) (Figure 2).

[0058] In a second aspect, the present invention relates to a process for obtaining the microparticles according to the present invention, said process comprising the following steps: a) Preparing an aqueous mixture comprising at least two chemically modified celluloses having different polarity features, at least one pesticide and at least one alginate; and b) Subjecting the mixture obtained in step a) to a spray-drying process.

[0059] Advantageously, step a) of the process according to the present invention includes the following steps, in the order shown below: a’) dissolving the chemically modified cellulose in water; a”) adding the pesticide to the solution obtained in step a’); and a’”) adding the at least one alginate to the mixture obtained in step a”), stirring until a homogeneous mixture is obtained.

[0060] Alternatively, in process step a) according to the invention, steps a’ and a” can be carried out simultaneously, leaving step a’”) as the last step.

[0061] According to a preferred aspect, the chemically modified celluloses are represented by at least one polar cellulose and a neutral cellulose.

[0062] Furthermore, step a) of the process is preferably carried out at pH between 5 and 7, even more preferably between 5.5 and 6.5.

[0063] In embodiments of the present invention, the water used in steps a) and a’) of the process according to the present invention is low calcium ion water.

[0064] Advantageously, the spray-drying process of step b) of the process according to the present invention can be carried out using any spray-dryer known to those skilled in the art, for example using the following operating conditions:

[0065] - Inlet temperature: 190-220°C

[0066] - Feed: 5-10 mL / min

[0067] - Airflow: 7-13 L / min

[0068] - Aspirator power: 80-100%

[0069] By means of the process according to the present invention, it is possible to obtain the microparticles according to the present invention typically in powder form.

[0070] In a third aspect, the present invention relates to a solid composition, preferably a composition in powder form, comprising the microparticles according to the present invention, and optionally one or more additives.

[0071] In embodiments, the water content of the solid compositions according to the present invention is equal to or less than 20% by weight, preferably 0-15% by weight, even more preferably 0-5% by weight.

[0072] Additives useful in the solid compositions according to the present invention are for example dispersing agents, emulsifiers, anticaking agents, and mixtures thereof.

[0073] In a fourth aspect, the present invention relates to a liquid composition comprising the microparticles according to the present invention, and optionally one or more additives.

[0074] Additives useful in the liquid compositions according to the present invention are for example dispersing agents, emulsifiers, wetting agents, antifoaming agents, stabilizers, adhesives, humectants, and mixtures thereof.

[0075] Preferably, the liquid compositions according to the present invention comprise an aqueous solvent, preferably water, or an organic solvent, for example aliphatic hydrocarbons, esters, alcohols and ketones, or mixtures thereof.

[0076] Finally, in a fifth aspect, the present invention relates to the use of the microparticles or compositions according to the present invention as agrochemicals. In particular, said use occurs by foliar application.

[0077] EXPERIMENTAL SECTION

[0078] The present description will be better illustrated in the following examples which are merely for the purpose of non-limiting example.

[0079] 250 mL of low calcium ion water was placed in a magnetic stirrer, operated at a speed of 300-750 rpm, and carboxymethyl cellulose and hydroxyethyl cellulose were slowly added in the desired amounts. Tribasic copper sulfate was then added, in the desired amount, and the mixture was stirred until completely dissolved. Sodium alginate was then added slowly in the desired amount, taking care to avoid the formation of lumps. The mixture was then stirred until a homogeneous solution was obtained.

[0080] The solution thus obtained was then injected into a spray-dryer and, once the process parameters had been set, drying was carried out.

[0081] The powder thus obtained was then collected and placed in a well-closed container, preferably provided with desiccant material.

[0082] Example 2 - weight ratio optimization

[0083] In order to identify the optimal weight ratios between the components of the formulation, several microparticle samples were prepared following the method described in Example 1 and varying the amounts of sodium alginate (ALG), carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC).

[0084] The formulations prepared are shown in Table 1 below. The amounts refer to the content in 500 mL of distilled water, volume selected to obtain final solutions with optimal viscosity. The solutions obtained were subjected to a spray-drying process using the following operating conditions:

[0085] - Inlet temperature: 190-220°C

[0086] - Feed: 5-10 mL / min

[0087] - Airflow: 7-13 L / min - Aspirator power: 80-100%

[0088] Table 1

[0089] The microparticles thus obtained were subjected to FTIR-ATR spectroscopy and light microscope and SEM analysis for the preliminary characterization of the sample in terms of chemical structure, component content, morphology and size, and solid-state size distribution.

[0090] Figure 1 shows, by way of example, the FTIR-ATR spectrum of: a) tribasic copper sulfate; b) microparticles obtained only with CMC and HEC in a weight ratio of 3:1 (sample 1 , table 1 ); c) microparticles obtained from formulation F3.

[0091] The figure clearly demonstrates that there is no formation of any binding or complexation of the Cu2+ions by the carboxyl groups of the alginate. In particular, there are typical polysaccharide peaks in the following regions:

[0092] • Region I (4000-2500 cm’1) related to -OH, -CH and -CH2

[0093] • Region II (1800-1500 cm’1) related to -COO’

[0094] • Region III (1500-1200 cm’1) related to the deformation of -CH2 and C-OH

[0095] • Region IV (1200-800 cm’1) related to glycosidic bonds.

[0096] Light microscope analysis revealed that the microparticles have a size of the order of 30 pm with narrow distribution and spherical shape. Both features represent a great advantage for obtaining uniform pesticide release.

[0097] Figure 2 shows, by way of example, SEM images at the resolution of 100 pm (A) and 40 pm (B) of the microparticles obtained from formulation F3. These analyses confirmed the spherical shape of the microparticles, with homogeneous morphology and a narrow size distribution.

[0098] Following the morphological analysis of the particles obtained according to the formulations shown in Table 1 , together with the optimal yield results, it was decided to continue the laser diffraction and release studies on samples 13 and 17-18, hereinafter referred to as F1 , F2 and F3, respectively.

[0099] Example 3 - Laser diffraction studies

[0100] The change over time of the mean diameter of the microparticles in different buffer solutions was monitored by laser diffraction. The study was carried out on the microparticles obtained according to what is reported in examples 1 -2, and specifically on those obtained from the three formulations considered optimal: F1 , F2, F3.

[0101] The measurements were carried out using a 200 mL sample of a suspension of each microparticle sample at a concentration of 25 mg / mL in each buffer solution at the following pHs: 3; 4; 5; 6.5; 7; 8. The measurements were carried out at time intervals from 0 to 480 minutes, at a temperature of 27°C ± 0.1 °C.

[0102] The data are shown in Figure 3 for formulation F1 , Figure 4 for F2 and Figure 5 for F3.

[0103] As can be seen from the comparison of the three graphs, the three samples show a similar behavior with a marked increase in particle size in the first minutes after suspension in the buffer solution (phase I), due to a swelling phenomenon. After the rapid increase in diameter, a second phase (phase II) is observed, in which the size tends to increase slowly or to fluctuate, until reaching the swelling equilibrium in phase III.

[0104] In all three cases it can be seen how the pH affects the intensity of the swelling: as the pH increases, in the same period of time, the average diameter of the microparticles increases.

[0105] Small variations in behavior can be noted between the three samples, both as for the duration of each phase and as for the increase in particle size.

[0106] The increase in the average diameter of the microparticles in suspension is due to swelling, i.e. , the ability to absorb and retain a fluid: all the components of the formulation show such an ability, therefore it is inevitable that the size of the microparticles increases. The sudden increase in particle size in the first minutes after contact with the solution is due to the presence of polysaccharides, which have a high capacity for hydration and therefore swelling. The effect of pH on swelling is attributable to the carboxyl groups: for pHs lower than pKa, the carboxyl groups of alginic acid are protonated, resulting in a reduction in the absorption of liquids; on the contrary, at pHs higher than pKa, the carboxyl groups are in ionized form, causing repulsion between the chains favoring the absorption of liquids; at equilibrium, the maximum swelling is therefore achieved.

[0107] From the aforementioned Figures 3-5 it is possible to clearly observe the presence of the three phases as described above: the swelling is functional to the release process, in fact by expanding, the structure allows for the exit of the copper salt encapsulated within the alginic coating. Such a swelling is a function of the ratios between the polysaccharides that, depending on the amount thereof, have a modulable release dynamic.

[0108] Example 4 - Release studies

[0109] Cumulative release studies were carried out in buffer solutions at the same pH as used for the laser diffraction studies (pH 3; 4; 5; 6.5; 7; and 8) under light magnetic stirring and controlled temperature at 27 ± 0.5 °C.

[0110] The amount in mg of released cupric ion was monitored by UV-Vis, sampling a 3 ml aliquot of the release solution at set intervals up to 8 hours. Prior to UV- Vis analysis, the sample was treated with the chelating agent PEI to form the Cuprammonium complex. The absorbance was measured at 275 nm and 630 nm. For each sample, the release was carried out in triplicate and simultaneously.

[0111] For this study, microparticles obtained from the same formulations used in Example 3, and described in Example 2, namely F1 , F2, F3, were used. 5 g of sample (containing 30 mg / g, then 150 mg, of tribasic CuSCU, measured by colorimetric method for copper quantification) were suspended in 500 mL of each buffer solution.

[0112] The results are shown in Figures 6-8, which show the release rates as a function of time, in particular after 1 , 4, 8, and 24 hours, of each formulation at different pHs.

[0113] In each case, the release occurs in three phases:

[0114] 1 . Rapid release phase (burst effect), in which the copper ion content located near the surface of the microparticles is immediately released after contact with the medium. The release percentage depends on the pH of the medium which, as demonstrated in example 3, affects the swelling capacity of the alginate, and on the size of the microparticles;

[0115] 2. Slow and continuous release phase, in which the copper ions located in the innermost part of the microparticles begin to be released. The duration of this phase is closely related to the alginate content: in fact, it takes longer for the water to diffuse through the alginate layer, dissolve the copper sulfate and allow the copper ions to diffuse outwards. Depending on the pH of the medium, complexation phenomena of the copper ions can also occur, attributed to the ionized carboxyl groups of the alginate;

[0116] 3. Stationary phase, in which only a small percentage of copper ions, generally about 15%, remain to be released. 100% release is observed only upon complete dissolution of the microparticles in the aqueous medium.

[0117] Furthermore, at pH 3 a latency phase was observed, i.e., a time interval between the suspension of the particles in solution and the start of the release of cupric ions. This is due to the protonation of the carboxyl groups of the alginate, resulting in reduced water flow within the microparticles and consequent slowing of the dissolution of the copper sulfate and diffusion of the copper ions.

[0118] Similar to what was observed for the variation in size, the quantification of copper also follows a three-phase trend. In fact , copper slowly finds the way through the alginic coating, which expands as time increases. Furthermore, changing the pH as a function of the greater or lesser protonation capacity of the solution accelerates or decelerates the diffusion process of the active ingredient.

[0119] Example 5 - Measurement of moisture absorption

[0120] Moisture absorption was assessed by recording the change in weight of the dried microparticles at defined time intervals, up to 7 days. The microparticles were stored under uncontrolled temperature and humidity conditions, therefore at room temperature (21 -28°C) and humidity, and exposure to natural light. Microparticles obtained from the formulations used in the previous examples were used for this study: F1 , F2, F3.

[0121] The results are shown in Table 2 Table 2

[0122] * with respect to the weight on day 0

[0123] The data reported in the table demonstrate the excellent stability of the microparticles according to the present invention up to 7 days, even under uncontrolled temperature and humidity conditions. In fact, in all cases there is a moisture absorption of less than 25%, evaluated based on the increase in weight of the particles, and even less than 11 % at 5 days of aging.

Claims

CLAIMS1. Microparticles comprising a core comprising at least one chemically modified polar cellulose and at least one chemically modified neutral cellulose, at least one pesticide and a coating comprising at least one alginate.

2. Microparticles according to claim 1 , wherein the weight ratio between said alginate and said chemically modified cellulose is comprised from 0.15 and 2.5.

3. Microparticles according to claims 1 -2, wherein the modified neutral cellulose is selected from a hydroxyalkyl cellulose and an alkyl cellulose, and wherein said chemically modified polar cellulose is a carboxyalkyl cellulose.

4. Microparticles according to any one of claims 1 -3, wherein said at least one alginate is selected from sodium alginate and potassium alginate.

5. Microparticles according to any one of claims 1 -4, wherein said at least one pesticide is selected from the group comprising copper salts, zinc salts, aluminum salts, silver salts, palladium salts, gold salts, platinum salts, and nickel salts.

6. Microparticles according to claim 5, wherein said pesticide is a copper (II) salt, preferably copper sulfate.

7. Microparticles according to any one of claims 1 -6, wherein said at least one pesticide is present in the microparticles in an amount from 1 % to 10% by weight.

8. Microparticles according to any one of claims 1 -7, wherein said core comprises carboxymethyl cellulose and hydroxyethyl cellulose.

9. Microparticles according to claim 8, wherein the weight ratio between carboxymethyl cellulose and hydroxyethyl cellulose is from 1 :1 to 3:1.

10. Microparticles according to claims 8-9, wherein the weight ratio between alginate, carboxymethyl cellulose, and hydroxyethyl cellulose is comprised of from 1 :3:1 to 6:3:1.

11. A process for obtaining the microparticles according to claims 1 -10 comprising the following steps:a) Preparing an aqueous mixture comprising at least one chemically modified polar cellulose and at least one chemically modified neutral cellulose, such a process comprising the following steps: a’) dissolving the chemically modified cellulose in water; a”) adding at least one pesticide to the solution obtained in step a’); and a’”) adding at least one alginate to the mixture obtained in step a”), stirring until a homogeneous mixture is obtained; and b) subjecting the mixture obtained in step a) to a spray-drying process.

12. The process according to claim 11 , wherein in step a) steps a’ and a" are carried out simultaneously.

13. A microparticle comprising at least one pesticide obtainable according to the process according to each of claims 11 or 12.

14. A solid composition comprising the microparticles according to each of claims 1-10, or 13, and optionally one or more additives.

15. The solid composition according to claim 14, wherein said composition is in powder form.

16. A liquid composition comprising the microparticles according to each of claims 1-10 or 13, or the solid composition according to claims 14 or 15 and optionally one or more additives.

17. Use of the microparticles according to each of claims 1 -10, 13, or of the compositions according to claims 14-16, as an agrochemical.

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