Surfactant additive for the controlled-release of agrochemicals

Abstract

A controlled-release fertilizer composition comprises a nutrient core containing macro and micronutrients (1), enclosed within a coating layer formed of mesoporous nanosilica particles (2) bound by a mixture natural metabolites (3). The coating is uniformly applied over the nutrient core to form a continuous shell. When exposed to moisture and soil conditions, the nanosilica coating gradually dissociates, enabling a time-controlled release of nutrients into the soil. The nanosilica aggregates provide plant-available silicon and enhance retention in the soil matrix. The invention addresses the technical challenge of nutrient leaching common in conventional fertilizers while offering sustained nutrient delivery during the plant growth cycle.

Description

[0001] SURFACTANT ADDITIVE FOR THE CONTROLLED-RELEASE OF AGROCHEMICALS

[0002] The present invention relates to a surfactant additive adapted for the controlled-release of agrochemicals.

[0003] BACKGROUND OF THE INVENTION

[0004] Agrochemicals or chemical nutrients applied into soil for plant growth and development are defined by composition and content. The key elements that form the nutrient core consist of nitrogen (N), phosphorus (P) and potassium (K). Others, such as the secondary nutrients and micronutrients are incorporated in a much lower concentration. In general, the densely concentrated synthetic agrochemicals come in a designated nutrient ratio. However, synthetic agrochemicals are subjected to fast leaching (hygroscopic) and the dissolved nutrients are rapidly washed out from the soil profile by percolating water. When water moves downward through the soil, the dissolved nutrients are carried along beyond the root zone, causing poor nutrient availability to the plants. Leaching is aggravated by soil texture and structure, rainfall and irrigation, the type of agrochemical and the rate of application.

[0005] Controlled-release agrochemicals are designed specifically for gradual nutrient release over an extended period. The rate of nutrient release aligns closely to the nutrient uptake pattern by plants and thereby improves the nutrient uptake efficiency through reduced nutrient losses to the environment. Controlled-release fertilizers (CRFs) were first commercialized in the mid-20th century (e.g. sulfur-coated urea or urea-formaldehyde) to mitigate rapid nutrient loss via volatilization or leaching during crop growth. Conventional controlled-release agrochemicals typically use sulfur, inorganic mineral films, synthetic polymers such as polyethylene, polyurethane and polyvinylidene chloride as the primary building material to regulate nutrient diffusion according to crop demand. However, early coating materials were primarily non- biodegradable, leading to microplastic accumulation in soils over time, a recognized environmental concern. Most of the polymers used in the coatings of controlled-release formulation are non- biodegradable polymers, leaving residues in soils. In tropical and humid conditions, CRFs face high displacement from rainfall, reducing field retention and nutrient efficacy. Traditional coatings alone inadequately prevent runoff and poor surface adhesion, especially for granular or aqueous fertilizer forms.

[0006] Surfactant additives have been used extensively in agricultural formulations, particularly pesticides and foliar fertilizers to improve adhesion, spreading, wetting and retention on plant or soil surfaces. A surfactant additive is an activator that improves the performance of the agrochemical by enhancing surface contact and thereby decreasing runoff. Surfactants are categorized by the charge on their hydrophilic “head”: i) anionic, ii) non-ionic, iii) cationic, and iv) amphoteric (zwitterionic). Anionic surfactants provide strong wetting and dispersion control. Non-ionic surfactants offer compatibility, biodegradability and spray stability. Cationic surfactants enhance the antistatic and anticaking properties. However, they require careful dosage due to their phytotoxic potential. Amphoteric surfactants exhibit pH-responsive behaviour suited for narrow applications.

[0007] Surfactant additives used in agrochemical formulations may originate from two main substrate types: bio-based (renewable) or petrochemical-derived (synthetic). Bio-based surfactants, such as alkyl polyglycosides (APGs) or sucrose esters, are obtained from plant sugars, vegetable oils or microbial fermentation, and are well- recognized for their high biodegradability, low toxicity and reduced carbon footprint compared to synthetic equivalents. They may qualify as wholly or majority bio-based (>50% biogenic carbon) under industry standards. In contrast, petrochemical-derived surfactants such as ethoxylated fatty alcohols, linear alkylbenzene sulfonates (LAS) and polyethoxylated tallow amines are synthesized from non-renewable feedstocks, typically lower cost and high-performing, but often less biodegradable, more toxic and associated with higher environmental persistence. When formulating controlled-release fertilizers for tropical agricultural use, selecting between bio-based and petrochemical surfactants involves trade-offs in cost, efficacy, sustainability and environmental impact, with bio-based options increasingly favored under green chemistry and regulatory trends.

[0008] Current CRF formulations lack integrated surfactants designed to improve retention and reduce nutrient runoff. This is despite emerging innovation demonstrating surfactant coatings can enhance adhesion and nutrient uptake, especially under high- rainfall conditions. There is a gap between conventional CRF technology, which focuses solely on controlled nutrient release via polymer coatings and the proven benefits of surfactant-driven retention enhancement. The present invention incorporates a surfactant additive that functions as an activator, improving surface contact of agrochemical formulations and thereby decreasing nutrient runoff, while maintaining biodegradability and slow-release nutrient kinetics.

[0009] Surfactant for agrochemicals

[0010] Figure 1 illustrates a typical prior art of the surfactant additive system composed of nanosilica particles. More particularly, with reference to Figure 1 , a plurality of nanosilica aggregates mesoporous silicon dioxide particles averaging <100 nm in diameter are dispersed within. The surfactant matrix containing a binding agent (metabolites and bio-based resin) is in combination with a dispersant. The composite coating thus formed is applied over a agrochemical granule (1 ), creating a hydrophilic shell that significantly lowers the water contact angle and enhances adhesion to soil or leaf surfaces.

[0011] The contact angle reduction (typically <10° as nanosilica loading exceeds ~50 vol%) improves surface wettability and hydrophilicity of treated films yielding super hydrophilic behaviour stable over time.

[0012] The surfactant matrix (2) functions as an “activator”, enhancing surface contact between the agrochemical granule (1 ) and the target surfaces by reducing interfacial tension and resisting displacement during rainfall. The inclusion of nanosilica aggregates (3) provides skeletal particle architecture that adsorbs at the air-water-solid interface, boosting permanence of the coating professionalomic distribution. All surfactants in the matrix (3) are amphiphilic compounds composed of a hydrophobic tail and a hydrophilic head. Typical surfactant concentrations range from 0.1-10 wt% of the additive, is a bio-based compound. The nanosilica component (2) anchors the surfactant at interfaces and shapes the wetting layer, while the matrix (3) enables dispersion, stability and controlled-release.

[0013] The surfactant additive of the present invention addresses the limitations of traditional coating such as poor adhesion and loss through runoff. Nanoscale silica aggregates and amphiphilic surfactant chemistry is leveraged to actively reduce runoff, improve droplet retention and enhance fertilizer or pesticide efficacy under high rainfall conditions.

[0014] SUMMARY OF THE INVENTION

[0015] According to the present invention, a bio-based surfactant acts as a nanoparticle coating for encapsulating fertilizer, also known as the nutrient core. The surfactant is composed of nanosilica particles smaller than 100 nm and a binding agent, providing controlled-release nutrient profile through gradual dissociation of nanosilica aggregates, influenced by soil texture, pH and moisture. The nanoparticle coating forms a uniform layer that adheres strongly to the nutrient core.

[0016] In an embodiment of the invention, the nanoparticle coating thickness tailors gradual and controlled-delivery of nutrients, matching the plant nutrient uptake pattern.

[0017] In an embodiment of the invention, the nutrient release activity is determined by a mathematical model comprising of soil pH, soil type, soil moisture and soil temperature parameters.

[0018] In an embodiment of the invention, the mesoporous silica nanoparticles enhance the efficacy of plant nutrient uptake through an enhanced plant transport mechanism.

[0019] In an embodiment of the invention, the silica nanoparticles enhance the interaction with the soil particle, aiding long retention in the soil system.

[0020] In an embodiment of the invention, the nanosilica particles provide additional benefits to plants by acting as a source of silicon, also a beneficial element vital in plant defense response against biotic and abiotic factors

[0021] In an embodiment of the invention, the use of nanosilica particles in place of conventional polymer coatings reduces the environmental impact of fertilizer application, promoting sustainable agricultural practices

[0022] In an embodiment of the invention, the utility of nanosilica-coated agrochemicals in replacement of coating-free traditional agrochemicals, reduce the number of multiple split applications of fertilizers significantly, saving input and labour costs for farmers.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 shows an outer view of the nanosilica-coated controlled-release agrochemical, depicting a central nutrient core (1 ) uniformly surrounded by a continuous nanosilica (2) coating layer (3).

[0025] Figure 2 presents a detailed cross-sectional view of the coated agrochemical, illustrating the arrangement: the nutrient core (1) encased in a thin, uniform nanosilica layer (3) bound firmly by a binding agent (4).

[0026] Figure 3 depicts the release mechanism upon soil application: the mesoporous nanosilica aggregates (3) gradually dissociate under moisture, soil pH, and texture triggers, enabling sustained nutrient release (5) from the nutrient core. Remaining nanosilica particles integrate into the soil as plant-available silicon (6), thereby providing agronomic benefit without leaving microplastic residues.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] Referring to Figure 1 , the invention comprises a nutrient core (1 ) enclosed within mesoporous nanosilica particles (2) formed a coating layer (3). The coating layer adheres uniformly to the nutrient core, producing a continuous, adhesive shell around the agrochemical nucleus.

[0029] The coating layer (3) is constructed from aggregates of silicon dioxide nanoparticles, each with embedded pores and a size distribution of less than 100 nm. Upon exposure to soil moisture, these nanosilica aggregates gradually dissociate under the influence of soil pH, texture, and temperature, resulting in controlled nutrient release over time.

[0030] The nutrient core of agrochemicals (1 ) is the primary source of essential nutrients for plant growth. This core typically may contain a mixture of macronutrients, which among others includes nitrogen (N), phosphorus (P) and potassium (K) on specific ratios or urea, ammonium nitrate, ammonium sulfate, calcium ammonium nitrate, ammonium sulfate nitrate and calcium cyanamide. The concentrated nutrient core provides crop-specific nutrients in support of optimal plant growth and development.

[0031] Referring to Figure 2, the coating layer (3) is affixed to the nutrient core (1 ) using a binding agent (4) comprising natural metabolites. The binding ensures strong adhesion, preventing premature nutrient release and preserve coating integrity until environmental triggers initiate dissociation.

[0032] Referring to Figure 3, once applied to the soil, the nanosilica coating layer (3) gradually dissociates, allowing steady migration of nutrients (5) from the nutrient core (1 ). This controlled dissociation reduces nutrient leaching and promotes continuous nutrient availability. The remaining nanosilica particles (6) act as a source of plant-available silicon, offering additional agronomic benefits without polymer residue.

[0033] Unlike polymer-coated fertilizers, the nanosilica coating dissolves (6) cleanly in the soil, leaving no persistent microplastic residue, while contributing to soil health through silicon delivery.

Claims

CLAIMS1 . A controlled-release fertilizer composition comprises: a) a nutrient core of one or more agrochemicals (1 ) selected from nitrogen (including urea), phosphorus, potassium; b) coating layer (3) surrounding the nutrient core, said coating layer comprising aggregates of nanosilica (silicon dioxide) particles (2) and a binding agent (4); wherein the coating layer adheres directly to the nutrient core to form a uniform shell; dissociates gradually under environmental conditions to release nutrients (5) in a time-controlled manner during plant growth; and provide a source of plant-available silicon (6) and wherein the nanosilica particles (3) interact significantly with soil matter to retain the fertilizer in the soil zone and thereby reduce nutrient leaching and support sustained release over a crop cycle.

2. The additive surfactant for controlled-release agrochemical (3) as claimed in claim 1 , wherein the nanosilica coating layer is formed by aggregates of mesoporous silicon dioxide (2) nanoparticles at a distribution size of <100nm. The coating layers adheres to the nutrient core (1) by a binding agent (4) comprised of natural metabolites. The binding agent is applied thoroughly to the nutrient core before the application of mesoporous silica nanoparticles to form nanosilica- coated controlled release fertilizer.

3. The additive surfactant for controlled-release agrochemical (3) as claimed in claim 1 , wherein the continuum nutrient supply of nutrients (5) otherwise measured as the rate of nutrient release and retention are predicted through a mathematical model parameterized with soil pH, soil type, soil moisture and soil temperature.

4. The additive surfactant for controlled-release agrochemical as claimedin claim 1, wherein the nano dimension silica particles (2) otherwise define as particles existing at one billionth per metre size carries high surface area and interactions with the soil components such as organic matter and soil minerals. The structural feature provides long retention of nanosilica-coated fertilizer in the soil system.

5. The additive surfactant for controlled-release agrochemical as claimed in claim 1, wherein the nanosilica particles serve as a source of silicon nutrition (6), upon the dissociation event forms freely available beneficial element to plants, providing plant defense response against biotic and abiotic factors, which includes resistance against pest, microorganisms and lodging, tolerance against drought and salinity, and plant cell wall strengthening.

6. The additive surfactant for controlled-release agrochemical as claimed in claim 1 , wherein the use of nanosilica particles (2) in substitute of polymer coatings available in conventional controlled release fertilizers reduce the ecological footprint of fertilizer usage. Silica is naturally occurring material that is non-toxic and in its bulk form is not fitted for plant uptake. However, nanosilica offers a new dimension which matches perfectly with the plant silicon uptake efficiency. Further, mesoporous nanosilica structure is rendered for effective engineering with nutrient core (1) as compared to the conventional polymer-coated fertilizers.

7. The nanosilica coating for controlled-release agrochemical (1) as claimed in claim 1 , wherein the utility of nanosilica-coated fertilizers in replacement of polymer-coated and coating-free traditional fertilizers, reduce the number of multiple split applications significantly, saving input and labour costs for farmers. Silica is environmentally benign compared to synthetic polymers used in the formulation of coating layers of controlled-release fertilizers. It reduces the risk of soil and water pollution due to degradation of polymers into microplastics.

8. The nanosilica coating for controlled-release agrochemical (1) as claimed in claim 1 , wherein the total nanosilica content constitutes from 1 wt% to 15 wt% of the total composition weight.

9. The nanosilica coating for controlled-release agrochemical (1) as claimed in claim 1 , further comprising micronutrient chelates selected from peptides, amino acids, metabolites, iron, magnesium, zinc, copper or boron at 0.5-2 wt% of the nutrient core.

10. The nanosilica coating for controlled-release agrochemical (1) as claimed in claim 1 , use the nutrient composition dedicated in tropical agriculture including oil palm, rice, or horticultural crops, to improve nitrogen use efficiency by at least by 10% and reduce soil leaching by at least 20% compared to conventional uncoated fertilizers.

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