WO2018122682A1 - Controlled-release fertiliser and method for manufacturing same - Google Patents

Abstract

The present invention relates to a controlled-release hydrogel and the method for manufacturing same. Specifically, to a controlled-release hydrogel comprising a cross-linker, cellulose, a hydrogel-forming polymer and an active composition, whereby the composition may be nutritional or biocidal. The method for manufacturing same comprises (a) mixing a polymer in water with cellulose, (b) mixing a cross-linking solution and a composition, and finally mixing the solution from step (b) with the mixture from step (a), stirring constantly until a hydrogel is formed. Shaping and drying the hydrogel obtained.

Description

 CONTROLLED RELEASE FERTILIZER AND PROCESS OF

MANUFACTURING

 Technical Field of the Invention

The present invention can be used in agribusiness, particularly in the production of controlled release fertilizers and in the controlled release of organic pesticides.

Description of the state of the art

Losses due to absorption, leaching, volatilization and evaporation of fertilizers and pesticides in general applied to arable land, cause serious alterations such as eutrophication and contamination of water sources. In addition, they generate high costs in the agricultural production sector, coupled with an economic and environmental imbalance. This problem must be solved from the investigation, implemented innovative materials and systems that allow to solve the aforementioned difficulties. A possible solution that paves the way to this problem is the use of systems that allow controlled release of nutrients in the soil, so that their availability can be optimized, minimum losses are achieved and help alleviate ecosystems from a considerable burden of disturbing elements. Controlled release fertilizers are in the state of the art, as is the case of document CN102351608 which discloses a controlled release particle fertilizer consisting of a granular shaped double layer core. Particularly it comprises a first interface layer that covers a core, and a controlled release layer as a coating of the interface layer, controlling the dissolution of pesticides and fertilizers. There is also document CN 100457694 which discloses a biodegradable slow release fertilizer, which comprises a fertilizer within a surface composed of a coating of a water soluble polymer, which includes the formation of a polymer emulsion where they are mixed: cellulose, starch oxidized, polyvinyl alcohol, prepolymer polyurethane, epoxy resin, curing agents, crosslinking agent and emulsifier, which is subsequently applied to the fertilizer to control its release capacity.

In the state of the art there are also coatings of the current fertilizers, as is the case of CN 102167647, which discloses coating materials of biodegradable compounds, their manufacturing method and their application in slow-release fertilizers. The coating material is composed of starch, cellulose, polyvinyl alcohol, a crosslinking agent, a modifying compound and a powder filling. The preparation method comprises: adding starch, cellulose, polyvinyl alcohol, water and stirring; add crosslinkers and gradually heat the mixture; then add the modifying compound and stir the added powder filling. A spray-based emulsion is obtained, which is used as a coating material on the surface of controlled release granulated fertilizers.

Hydrogels have also been designed as systems capable of retaining substances that will then be released in a controlled manner in the environment in which they are available. Among these developments are: solid polymer matrices based on Chitosan and Xantane for controlled fertilizer release (Melaj, M., & Daraio, ME (2012). Solid polymer matrices based on Chitosan and Xantane for controlled fertilizer release (Advances in Science E Ingeniería, 3 (\), 1-9.) Other fertilizers are directed at the root of the plants with a carboxymethylcellulose matrix manufactured by ionic crosslinking (Davidson, DW, Verma, MS, & Gu, FX (2013). Controlled root targeted delivery of fertilizer using an ionically crosslinked carboxymethyl cellulose hydrogel matrix (SpringerPlus, 2 (1), 318), shows a wheat straw cellulose-based hydrogel with semi-penetrated polymer networks with retained water integration, for controlled release of fertilizers; this process requires a pretreatment to obtain cellulose, where wheat straw is milled and immersed in ammonia for 48 hours, Wash several times with distilled water and dry, then immerse in nitric acid at 100 ° C for 45 minutes, to finally wash with distilled water and dry (Li, X., Li, Q., Su, Y., Yue, Q., Gao, B., & Su, Y. (2015). A novel wheat straw cellulose-based semi-IPNs superabsorbent with integration of water-retaining and controlled-release fertilizers (Journal of the Taiwan Institute of Chemical Engineers, 0, 1-10.). A controlled fertilizer release system can also be found using straw graft copolymers in which requires that nutrients be loaded into the hydrogel by swelling from a solution with K2HPO4 + K2S2O8 + ((NH4) 2Ce (N03) 6), which is very different from the inclusion of the nutrient in the same conformation of the hydrogel (Li, Q. , Ma, Z., Yue, Q., Gao, B., Li, W., & Xu, X. (2012). Synthesis, characterization and swelling behavior of superabsorbent wheat straw graft copolymers. Bioresource Technology, 118, 204- 9.).

Considering the above, the present development proposes another alternative in the design of nutrient controlled release systems, particularly in hydrogels manufactured from cellulosic residues that can be disposed in soils, which is presented as an environmental solution against loss. of nutrients, as well as an innovation in the agricultural sector and in the development of new materials.

Brief Synthesis of the Invention

The present invention relates to a controlled release hydrogel, manufactured from cellulosic waste, and its manufacturing process. In particular, the controlled release hydrogel comprises a crosslinker, cellulose, a hydrogel-forming polymer and a composition, wherein the composition is nutritious or biocide. The manufacturing process comprises mixing a polymer in water with cellulose, mixing a crosslinking solution and an active composition, and finally mixing the solution of step (b) with the mixture step (a) under constant stirring until a hydrogel is formed. Form and dry the product obtained. Brief description of the figures

FIG. 1 Behavior of the degradation of the hydrogel over time, with different amounts of residual cellulose.

FIG. 2 Comparison between controlled release fertilizer and a commercial fertilizer, regarding the release of nitrogen in soil. Detailed description of the invention

The process for the manufacture of a controlled release hydrogel of the present invention comprises: a) mixing a polymer in water with cellulose; b) mixing a crosslinking solution and an active composition;

 c) mixing the solution of step (b) with the mixture step (a) under constant stirring, until a hydrogel is formed; d) form and dry the controlled release hydrogel. The controlled release hydrogel and its manufacturing process involve the following materials: polymer, water, cellulose, crosslinker and an active composition. Where "active composition" can refer to a composition that can be nutritious, biocide, pesticide or an organic pesticide (of botanical origin), depending on the production requirement. By active composition it can also refer to a nutritional element, nutritional compound, nutritional composition, biocide, etc. a) Mix a polymer in water with cellulose (Prepared 1)

The polymer mixture is formed from a hydrogel-forming polymer that dissolves in water in a proportion between 5 and 10%, under a temperature between 30 and 80 ° C and stirring 100 and 300 rpm or what is necessary until dilution. complete. The present invention comprises a hydrogel-forming polymer that is selected from the group of polyvinyl alcohol (PVA), cellulose, residual cellulose, lignin, chitosan, xanthan gum, carboxymethyl cellulose, polylactic acid, acrylic acid, acrylamide, sodium alginate, alginate calcium, hydroxymethyl cellulose, carrageenan and possible combinations of the above. The mixture of polymer in water with cellulose can be heterogeneous or homogeneous.

Once the hydrogel-forming polymer is homogenized and diluted, cellulose is added in a proportion of between 5 and 20%. Cellulose may or may not involve pretreatment; In one modality it is residual, so that it can be obtained from organic waste rich in this biopolymer, which can come from both the agribusiness sector (for example banana and banana, cotton, sugar cane, coconut and rice among others) , as of the industrial sector or others known by a moderately versed person. In one embodiment, a sludge containing more than 60% residual cellulose and the remaining percentage composed of carbonated and siliceous materials are used. The sludge is dried at room temperature until it reaches approximately 30% humidity, is ground and sieved. At this stage an active composition is optionally added which can be a nutrient (source of nitrogen, potassium, calcium, magnesium, iron or manganese) or a biocide (fungicide, herbicide, bactericide, insecticide, acaricide, among others) or possible combinations of the previous ones, in a proportion between 0.5 and 30%. It is mixed under stirring between 100 and 300 rpm at room temperature or until properly mixed with the polymer solution in water with cellulose. b) Mix a crosslinking solution and an active composition (Prepared 2)

The crosslinking solution is obtained from a crosslinking substance that dissolves in water. By "crosslinking" is meant a compound that forms bridges between polymeric molecules, converting thermoplastic polymers into thermosetting. The crosslinker of the present invention should be at least one, which is selected from the group of sodium tetraborate, carboxymethyl cellulose (CMC), phosphates, hydroxymethyl cellulose and possible combinations of the foregoing. It dissolves in a proportion between approximately 1 and 15%, between 30 and 50 ° C and constant agitation between 100 and 300 rpm or until its complete dilution. Once the crosslinker is homogenized, an active composition is added. The active composition can be nutritious, pesticide, herbicide, fungicide, among others. Among the pesticides are organic pesticides of botanical origin such as nicotine, terpenes, azaridactin, caffeine, eucalyptol, saponins and sapogenins. In one embodiment the active composition is nutritious and is composed of an anionic nutrient that is added in a proportion between 0.5 and 23% in constant agitation between 100 and 300 rpm or until a homogeneous paste is formed and even moisture loss between 30 - 60% c) Mix the solution of step (b) with the mixture step (a) under constant stirring until a hydrogel forms

In a preferred embodiment, the mixture obtained in step (b) is added on the mixture of the water-soluble hydrogel-forming polymer with residual cellulose obtained in step (a), under stirring between 100 and 200 rpm for about 2 and 10 minutes or until the crosslinkable moldable hydrogel forms. d) form and dry the controlled release hydrogel. To obtain a fertilizer or contracted release element, modules are prepared comprising combinations of the preparations (1 and 2), depending on the nutritional requirement. A module is understood as a single element consisting of several layers, each of which is a hydrogel formed with a specific composition or substance required (nutrient or biocide). Thus they can be formed: tablets, encapsulated, granulated, powders from a single preparation, or with combinations of both in multilayer tablets that meet the specific requirements. The step of step (b) can be carried out before that of step (a).

A controlled release hydrogel of a composition obtained by the above process is obtained, comprising at least one crosslinker, residual cellulose, hydrogel-forming polymer and a nutrient or biocide composition.

Examples

 Example 1. Preparation of a controlled release fertilizer with ammonium nitrate and potassium phosphate

Prepared 1: 2.1 g of PVA were mixed with 10 mL of water, taken to a heating plate until reaching a temperature of 80 ° C, with constant stirring of approximately 150 rpm until complete dilution (approximately 5 minutes). Once the PVA was homogenized, it was removed from the iron. 3.5 g of residual cellulose (dried, ground and sieved by # 30 mesh) were added and stirred until a homogeneous mixture was obtained, 6g of NH4NO3 was added and stirred for approximately 3 minutes at 150 rpm.

Prepared 2: 1.6 g of K2HPO4 was dissolved in 7 mL of water at room temperature and constantly stirred for approximately 3 minutes at 100 rpm until it reached full dilution; once homogenized, 1 g of CMC was added under constant stirring at 100 rpm to form a homogeneous paste. This paste was molded in a sheet of approximately 10 mm and taken to air dry for 24 hours, after this time tablets of 9.5 mm diameter and thickness of approximately 10 mm were punched.

Subsequently, 0.5 g of Borax was dissolved in 8 mL of water and brought to a temperature of 60 ° C for 3 minutes with stirring of 90 rpm. To prepare the hydrogel, the Borax solution is added to the homogeneous potassium phosphate paste and CMC, under stirring of 200 rpm for 2 minutes or until the crosslinkable moldable hydrogel is formed. The mixture is placed on a flat surface and a 5 mm thick sheet is formed, from which, before losing moisture, it is stamped to remove tablets of 9.5 mm in diameter and approximately 5 mm thick. Once both preparations were obtained and before preparation 2 dried, a tablet of preparation 1 was taken and placed in the middle of two tablets of preparation 2 to form a three-layer controlled release element.

Example 2. Degradation test of hydrogel formation material in water

The hydrogel formed under the preparation 2 of Example 1 was subjected to a water degradation test, for which square samples of lxl cm of the hydrogel were taken, dried at room temperature for 48 hours and its initial weight recorded, subsequently deposited in 15 mL containers of unsterilized water with pH 6.8 contained in containers with a lid. At 5, 10, 15, 20, 25 and 30 days the samples were removed, dried for 24 hours at room temperature and their degradation percentage was determined.

In FIG. 1 the degradation behavior of the material is presented with the minimum (0, lg) and the maximum (3.5 g) residual cellulose content (CR), for a total amount of hydrogel of 30 g, finding that the maximum amount of CR that the device can contain without losing its properties with a minimum of degradation in a period of 30 days is 3.5 g.

To verify the release of one of the nutrients, an N release kinetics test was performed from the preparation 2. The results are presented in FIG. 2 show the behavior of controlled release compared to a commercial fertilizer (positive control) and an organic soil sample without the addition of any fertilizer (negative control).

For this test, PVC columns 20 cm long and 1.5 inches in diameter covered at one end with a cloth and nylon filter were made, filled with 200 g of soil and 35 mg N / 200g Soil was added. The test was divided into three treatments, nomenclated as follows: treatment 1, negative control (without fertilizer); treatment 2, DAP - commercial fertilizer; treatment 3, slow release fertilizer (own).

70 mL of distilled H2O was added to each column until the soil was saturated, leachate was collected at the exit of each column after 1, 3, 5, 10, 15, 20, 25, 30, 45 days of assembly. All tests were repeated in triplicate. The nitrogen was quantified in 20 mL of the leachate by means of the Kjeldahl Total Nitrogen method.

Example 3. Encapsulation for controlled release of aqueous tobacco extracts with repellent and insecticidal activity

2.1 g of PVA were mixed with 10 g of 15% aqueous tobacco extract in nicotine, taken to a heating plate until reaching a temperature of 80 ° C, with constant stirring of approximately 200 rpm until complete dilution ( approximately 5 minutes). Once the PVA was homogenized, it was removed from the iron. The residual cellulose sludge was dried at room temperature to approximately 30% humidity, ground and sieved by # 30 mesh (average diameter 0.6 mm). 3.5 g of residual cellulose were added and stirred until a homogeneous mixture was obtained.

Subsequently, 0.5 g of Borax was dissolved in 8 mL of water and brought to a temperature of 60 ° C for 3 minutes with stirring of 90 rpm. To prepare the hydrogel, the Borax solution is added to the homogeneous paste of PVA and Residual Cellulose, under stirring of 200 rpm for 2 minutes or until the crosslinkable moldable hydrogel is formed; a 5 mm thick sheet is formed, from which, before losing moisture, it is punched out to remove tablets of 9.5 mm diameter and approximately 5 mm thick.

Example 4: Controlled release of Limonene emulsion

2 g of PVA are mixed with 5 mL of water, 10 g of 20% limonene oil emulsion are added, which consists of 20% limonene oil, 5% non-ionic ethoxylated emulsifier (tween 80) and 75% of water, were taken to a heating plate until reaching a temperature between 60 and 90 ° C, with constant stirring of approximately 200 rpm until complete dilution. Once the PVA was homogenized, it was removed from the iron. The residual cellulose sludge was dried at room temperature until reaching approximately 30% humidity, it was ground and sieved by mesh # 30 (average diameter of 0.6 mm). 3.5 g of residual cellulose were added and stirred until a homogeneous mixture was obtained.

Subsequently, 0.5 g of Borax was dissolved in 5.5 mL of water and brought to a temperature of 60 ° C for 3 minutes with stirring of 90 rpm. To prepare the hydrogel, the Borax solution is added to the homogeneous paste of PVA and Residual Cellulose, under agitation of 350 rpm for 2 minutes or until the crosslinkable moldable hydrogel is formed; a 5 mm thick sheet is formed, from which, before losing 100% moisture, it is cut to take out tablets of 9.5 mm diameter and approximately 5 mm thick.

Claims

1. A process for the manufacture of a controlled release hydrogel of a composition comprising: a) mixing a hydrogel-forming polymer in water with cellulose;  b) mixing a crosslinking solution and an active composition;  c) mixing the solution of step (b) with the mixture step (a) under constant stirring to form a hydrogel;  d) form and dry the controlled release hydrogel. 2. The process according to Claim 1 wherein the active composition is nutritious or biocide. 3. The process according to claim 1 wherein the polymer solution is obtained from a hydrogel-forming polymer that is selected from the group of polyvinyl alcohol, cellulose, residual cellulose, carboxymethyl cellulose, lignin, chitosan, xanthan gum, carboxymethyl Cellulose, polylactic acid, acrylic acid, acrylamide, sodium alginate, calcium alginate, hydroxymethyl cellulose, carrageenan and combinations of the above. 4. The process according to claim 1 wherein the crosslinker solution is obtained from a crosslinker that is selected from the group of sodium tetraborate, carboxymethyl cellulose, phosphates, hydroxymethyl cellulose and combinations of the foregoing. 5. A controlled release fertilizer obtained by the process of Claim 1 comprising at least one crosslinker, cellulose, hydrogel-forming polymer and an active composition.