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Controlled Release Fertilizers And Nanotechnology Traces

One of the very most significant problems of crop fertilization by typical fertilizers is nutritional damage to environment which causes plenty of environmental and real human health issues besides decreasing the efficiency of crop nitrification. As a remedy, controlled or gradual release fertilizers have been developed to defeat drawbacks of traditional fertilizers. On this review common types of CRFs and some related ideas. Also, focusing on polymer covered CRFs, different prep and different covering application methods will be examined. Furthermore, some features of nanotechnology and nano-materials in prep of managed release fertilizers in earlier works will be evaluated.

Introduction

In general, crops must be given nutrients during the entire vegetation period. In horticulture this is attained by applying quickly soluble fertilizer once to double weekly, for example. This kind of fertilizer software is very labour-intensive and requires significant specialist knowledge, to be able to select the accurate rate of program, appropriate time of application and correct structure for the particular plants to ensure maximum plant production. With the use of slow or controlled release fertilizers the entire amount of nutrients necessary for the whole vegetation period can be applied at the time of planting or at the initial stages of flower growth, by means of a nutrient pool Also, about half of the applied fertilizers, depending on method of request and earth condition, is lost to the surroundings, which results in the contamination of water [1]. This sort of environmental concerns of feeding vegetation with traditional fertilizers has led to expanding Slow Release Fertilizers (SRFs) or Controlled Release Fertilizers (CRFs). SRFs or CRFs are easy and safe to use. They reduce threat of incorrect fertilizer software. Also, they are labour keeping and minimize nutrient losses by leaching or fixation.

The idea of producing SRFs originated since 1963 by encapsulation of fertilizers by waxes. From then on, these products have been commercialized. There are lots of SRF and CRF brands. Some of these products are Scotts Professional with key brands such as Osmocote, Sierrablen and Osmoform. Aglukon and SunGro Company are also producing handled release fertilizers.

Like tons of scientific areas, agriculture industry has been over shadowed by nanotechnology. Applications of nanotechnology in agriculture includes agriculture crop improvement, nano-biotechnology evaluation of gene manifestation and regulation land management, plant disease diagnostics, useful pesticides and fertilizers, normal water management, bioprocessing, post harvest technology, monitoring the identification and quality of agricultural produce and detail agriculture. Efficient pesticides and fertilizers are just lately being developed in conditions of nano-composite structured slow or managed release fertilizers. Using nanoparticles as reinforcing or cementing agent of polymer coatings and also as tank of fertilizers are top features of nanoparticles which were used in preparing poor release fertilizers [2-4].

Fertilizers

Fertilizers are put on soil to promote plant expansion. They contain some beneficial nutrients including macronutrients and micronutrients. Macronutrients are nitrogen, phosphorus, and potassium which can be added to dirt in amounts from 0. 2% to 4. 0% (over a dry matter weight basis) and are usually more essential than micronutrients. Micronutrients are elements which are applied to garden soil in much small amounts, which range from 5 to 200 ppm, or significantly less than 0. 02% dry out weigh. These elements could be boron (B), copper (Cu), flat iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn)[5].

2. 2. Types of fertilizers

Fertilizers would be categorized from source of creation and also from release properties items of view. All fertilizers could be organic and natural or man-made from creation source viewpoint. Organic and natural fertilizers are in a natural way produced including seaweed, worm casting, manure, slurry, peat, humic acid, guano and brassin. They offer sluggish release of nutrient as they want soil's bacteria to be broken down to needed elements. Also, they may increase the biodiversity of garden soil by supplying organic and natural concerns and micronutrients for organisms. Organic and natural fertilizers are cheaper and safer than fabricated fertilizers.

The main synthetic or mineral fertilizers which are the sources of nitrogen (N), potassium(K), phosphate (P) are urea, ammonium sulfate, ammonium phosphate, phosphate rock, potassium chloride, excellent phosphates, calcium ammonium nitrate, potassium sulfate. Fertilizers could be in compound form (NP, PK, NPK). The main drawback of man-made fertilizer is their long term sustainability. Also, they are simply more expensive in contrast to organic and natural fertilizers [5].

In addition, fertilizers can be grouped into regular and controlled release fertilizers from release properties points of view.

Drawbacks of non-controlled release fertilizers

Ordinary fertilizers leach to ground rapidly and most of them are not employed by the plants. Relating to characters about 40-70% of nitrogen, 80-90% of phosphorous, and 50-70% of the applied normal fertilizer is lost to environment and can't be used by vegetation [6]. This swift leaching may cause burning of vegetation and growing in spurts. Also, the lost elements may cause some serious problems for environment. Eutrophication, blue baby symptoms, soil acidification, prolonged organic pollutants, heavy metal accumulation, atmospheric results are environmental concerns of common fertilizers. Another consequence of quick leaching of fertilizer is repeating the application of fertilizers that may increase the cost [5].

Slow or handled release fertilizers

Slow release fertilizers or managed release fertilizers are granules covered in a substance that decrease the launching time of nutrients and eliminates need for continuous fertilization and higher efficiency rate than soluble fertilizers [7].

Some of benefits of controlled release fertilizers are long option of nutrients during growing-season, reduced loss of nutrition through leaching, reduced cost and labor outlay, better safe-keeping and handling of fertilizer, reduced immobilization reactions in garden soil, reduced amount of nitrification effect and nitrogen loss through ammonia volatilization and denitrification, elimination of seed harm because of high attentiveness of salts, eradication of leaf burning from high rates of applied fertilizers, better seasonal progress circulation and better acclimatization in home or display environment [8].

Differences between poor and manipulated release fertilizers

Although there is not special difference between basic function of CRF and the main one for SRF, but it should be mentioned they are made by different materials and techniques with different properties. In sluggish release fertilizers elements are present in fertilizers in a chemical substance form, which is unavailable to plants and they'll be turned by physiochemical results or microorganisms activities into nutrient varieties in the dirt. But in manipulated release fertilizers elements are loaded in covered granules and are released through the layer over the certain time frame. Also, in SRFs nutrition available period is afflicted by a lot of factors such as water content of dirt, pH, temperature, microorganism's activity and aeration. However, the durability of CRF relies mostly on covering thickness and temperature of earth. Only layer method is effective in changing pattern of nutrients release and a set coating thickness control nutrition release. In CRFs announced release time identifies soil temperature of 20-21oC. Higher temperature accelerate the factor release and lower temperature make it much longer [9].

SRFs are fertilizers with a substance structure that happen to be inherently slow released. Some kinds of SRFs are Urea Aldehydes (UA) and Chelated Micronutrients (CM). Common type of UAs is urea formaldehyde which is high nitrogen fertilizer. Starting release rate of UAs is high but it dies off slowly for 3 years. This kind of fertilizer depends upon microorganisms to break it down for flower use. CMs are substances that hold securely together iron, manganese, zinc, and copper. They gradually releases over an extended period of time [8].

2. 4. 2. Types of CRFs

2. 4. 2. 1. Sulfur Coated (SC)

When elemental sulfur is oxidized to its sulfate form, the merchandise would be one of the nutrients which is essential for some vegetation and is normally combined with other fertilizers. Using sulfur coating is also another way to provide sulfur while making slow release properties for a central granular fertilizer. As the sulfur made up of materials like polysulfides or lingosulfonate are brittle and also give a low wetting of problems, they are usually mixed with waxes or plasticizers. Many formulas are for sale to SCs. Their release time is normally 3-4 calendar months and the nutrient is released from SCs by microorganism's activity [10-14].

2. 4. 2. 2. Wax coated (WC)

One of the methods of lowering fertilizer release rate is dispersing granular fertilizers with molten wax and then chilling the mixture below the melting point of the wax [15]. Paraffin is one of the most used waxes as a covering for fertilizers. Paraffin wax is a white, tasteless, odorless sound, with a typical melting point between about 47 C and 64 [16]. Other types of waxes are fabricated oil structured, petroleum or mineral waxes. Waxes are usually used by an additive or a tackifier to make good sealing properties [17, 18]

2. 4. 2. 3. Polymer Coated (PC)

Polymer-coated fertilizers (PCF) stand for the most technically advanced controlled released fertilizers. They include a water-soluble fertilizer center and a number of than one levels of polymer. A couple of large types of polymers to coating the key fertilizer also the coatings level could be the same one or different. In Laptop or computer fertilizers release of nutrients may happen by diffusion by having a semi permeable polymer membrane. Water penetrates the finish and dissolves the primary. Release rate can be handled by differing the composition and thickness of the coating. In addition, pressure builds up can cause breaks to form, from which fertilizer passes in to the land [8].

2. 5. Overview of different kinds of polymer covered CRFs

2. 5. 1. Singular Polymer covered CRFs

One type of polymer coated CRFs is the one that the fertilizer central which could be N, P, K or compound fertilizer, is just coated with a number of than one coating of polymer layer. In cases like this the polymer could be solvent centered or water-based. The application form process starts with dissolving the polymer within an organic and natural solvent or water. After dissolving, the covering will be sprayed onto the fertilizer in a coating drum or substance bed [19]. Polymer coated fertilizers involve some. One of them is that uniform and defect free coating will surround fertilize. The other would be that the layer will be very hard and durable which is protected against mechanical break down. Also, polymer coatings are biologically inactive so they'll not breakdown by earth microbes.

In most conditions except for degradable polymers release of fertilizers will occur by diffusion through the polymer coating rather than through defects. In a few other coated fertilizers like sulfur coatings there should be a flaw in coating to cause releasing of fertilizer.

There are lots of illustrations for polymers which have been used in the literatures as coating for fertilizers. A few of them include dicyclopentadien [20], urea and urethane founded [21-26], epoxy based [27-29], polyvinylidene chloride-based latex [19] carboxyl-carrying ethylene polymers [30], biodegradable starch based mostly [31], urea formaldehyde [32].

However, polymer coated fertilizers involve some week items. About solvent-based coatings using massive amount organic and natural solvents like toluene or xylene will lead to environmental concerns. These solvents are volatile and releasing those to environment makes some dangers for real human health. Also, polymer coatings are more costly than sulfur coatings because not only polymer materials are more costly but also process and gadgets which are being used for development of polymer layered fertilizers are also more complex than equipments used for other coatings.

2. 5. 2. Sulfur-polymer coated CRFs

One of most common layered fertilizers will be the ones where core fertilizer is covered by a level of sulfur layer and a layer of polymer. Polymer part can be the primer or outside layer. It means that sulfur covering in some studies has been the first part and in a few others the outside layer.

Using polymers as covering is suggested method to remove disadvantages of sulfur layered CRFs. Among these drawbacks is extremely fast release of sulfur coated fertilizer in first couple of days after software. The other the first is brittleness of sulfur coatings which may lead for some fractures during handling or storage space and shedding the fertilizer. Another problem is that sulfur coatings have a higher surface anxiety with normal water and cannot provide enough wetting for a good diffusion [11, 13, 19, 28].

The most common method for applying the sulfur finish is by spraying. Molten sulfur chemical substance will be sprayed over a pre-polymer covered fertilizer granule [28, 33].

2. 5. 3. Wax-polymer coated CRFs

There are a lot of researches focusing on making manipulated release fertilizers using wax-polymer coatings. A polish level has three major benefits. Some may be that they are applied in the polymer coating for reducing the fracture possibility of layer and the other one is for decreasing the amount of polymer and keeping away from consuming tons of polymers to help make the process affordable. Also, they can eliminate imperfection of granules surface to make a good surface finish.

Most common waxes which have been used in advanced are C30 alpha-olefin and paraffin. Other petroleum products like lubricants and bitumen or natural basic products like canola engine oil, soybean essential oil, coconut essential oil and palm engine oil, likewise have been used.

After melting the polish it will be applied by simply mechanical mixing up with polymer coated granules. Normally the polymer is thermoset to avoid any problems of polymer by the wax's temperature in its melting point. The wax normally should have drop melting point from 50 to 120C. Polish is generally about 0. 2% to 10 % by weight of fertilizer [17, 28, 34, 35].

2. 5. 4. Filler-polymer covered CRFs

As discussed earlier, despite a lot of advantages of polymer layer to make slow release properties when such polymers are used as a singular coating material the best product would be costly as you have to consume large amounts of polymer. Using nutrient or organic fillers is one way to avoid using massive amount polymer. Also, in some researches fillers play the role of detackifier, to prevent adherence of coated granules to each other. In addition they are building up agent of coatings [36].

Fillers can be utilized either as a combination with polymer to make a nano-composite polymer [37] or as a separate layer. The most frequent method is the second option in which the filler will be added by combining with polymer layered granules before drying the granules. Most popular used fillers are some very fine(less than 20 microns) inert inorganic materials like clay, diatomaceous globe, bentonite, kaolin, gypsum powdered limestone, talc, barium sulfate. Some other fillers like throw away cellulosic materials also have used as filler in combo with polymer [37-41].

2. 6. Techniques of making use of polymer coating

According to earlier studies have been done, encapsulation methods of fertilizers can be split into three methods including in-situ, spraying and mixing.

2. 6. 1. In situ

This method includes formation of liquid dispersion of the soluble fertilizer in a solvent and blending the well prepared solution with monomers of any polymer finish. Polymerization may happen and with regards to the method, granules or debris of fertilizers will form.

Ni et al [42] have developed a double-coated urea fertilizer. For preparation of poly (N-vinyl-pyrrolidone) hydrogels filled with urea (PCU), the monomer and a remedy of urea in N-vinyl-pyrrolidone were merged mutually. The polymerization was carried out at 65-C for 3 h. The resulting samples were vacuum-dried, milled, screened and stored. From then on first coating was dried, sample and some levels of urea were blended with sodium alginate (SA) solution. Mixed solution was then added drop wise into 5% (w/w) CaCl2 aqueous solution and stirred constantly. The drops immediately turned into granules (about 4mm in diameter) because the SA in the drop was crosslinked by Ca2+ simultaneously. The granules were filtered and dried out in oven at 70- C. Then your granules were added to ethylcellulose - ethanol solution. Multiple ethylcellulose (EC) coatings were made by immersion of the recently coated granules in to the ethylcellulose solution regularly. Thus, EC-coated urea granules with different coating width were obtained.

Hanafi et al [43], have layered a chemical substance fertilizer by polyvinyl chloride (PVC), polyacrylamide (PA), natural plastic (NR), and polylactic acid solution (PLA) using in situ method. For encapsulation of compound fertilizer with polyacrylamide the granules were put into the solution combination of monomers. Then the polymerization reaction will start in existence of fertilizers. The thickness of the coating layer on the compound fertilizer granules, dependant on SEM(Fig. 2), offered PVC compound covered fertilizer the best value of 3. 04 lm, and the cheapest was obtained by PA (2. 04 m). Variant in the characteristics of the polymers would be utilized in producing CR compound fertilizer that fit the requirements of growing crops.

Hudson et al [28] used epoxy to coat the fertilizer. In this research the urea granules were incurred to a pan and warmed to 95C. Then your hydrogenated tallaw amine, 2-amino ethyl peperazine and bisphenol A diglycidyl ether were blended and were added to the granules. In the meantime polymerization took place and prepared concoction was agitated till the fertilizer granules dried.

2. 6. 2. Spraying method

This method is most frequent method for layer program on fertilizer granules in state-of-the-art. Usually, the answer of polymer in the right solvent is sprayed on the granule of fertilizer and then your granules are dried out to eliminate the solvent through evaporation. The treatment is repeated as often as necessary until the desired coating ratio is come to.

Tomaszewska et al [44] have used spray technique for encapsulation of fertilizers. To be able to increase the properties of coatings, the granules of previously covered fertilizer (wet method) were sprayed with a polymer solution or pure solvent (N, N dimethylformamide). Attentiveness of the polymer in solutions used for spraying was in the range of 13-17 wt%. Measurements of thickness, porosity of prepared coatings and microphotographic observation of the coatings were used. Fig. 3 shows the cross section of two times coated fertilizer.

Ma et al [45] are suffering from a way for encapsulation of fertilizer with a self applied assembled layer. The fertilizer granules were heated in a rotary drum to 75C for 10 minutes. Then the do it yourself assembling amphiphilic substances (N, N-bisaminoethyl eleostearate) were sprayed on the fertilizer. After 20 minutes aliphatic isocyanates were sprayed over fertilizer. This technique was repeated once again. The fertilizer kept for drying in the 75C for 20 minutes.

Dai et al [46] also, are suffering from a handled release fertilizer using a water soluble resin as a covering. The granular chemical substance fertilizer was coated in fluidized bed.

Lan et al [47], prepared a double-coated slow-release NPK fertilizer with superabsorbent and water-retention properties (DSFSW), whose internal layer was chitosan (CTS), and the exterior finish was crosslinked poly (acrylic acid solution)/diatomite-containing urea (PAADU). This well prepared product not only has slow-release property but also could absorb a huge amount of drinking water and preserve the soil moisture at the same time. In addition, the outer finish (PAADU) could protect the internal layer (CTS) from mechanised damage. We were holding significant advantages over the normal poor release or controlled-release fertilizers, which generally have only a slow-release property. The results indicated that the DSFSW could be found a credit card applicatoin in agriculture and horticulture, especially in drought-prone parts where the option of water is insufficient. At first, the outer layer made up of urea diatomite (PAADU) was ready. The NPK chemical substance fertilizer granule was placed into a rotary drum, and the chitosan powder was stuck on the granules by means of epoxy dissolved in acetone. The adhesive was applied by spraying at regular time intervals. The procedure was completed until compact and homogeneous coating produced on fertilizer granule. The layered granules were dried to a regular mass at room temps for 6 h. Then your CTS-coated NPK compound fertilizer granules were obtained. CTS-coated fertilizer granules were dipped in water and then were immediately placed on PAADU powder and shaken. This way, PAADU could abide by the surface of CTS-coated NPK chemical substance fertilizer and form the outside coating. The top of product was crosslinked by spraying methanol solution of epoxy chloropropane and then dried out in a 70 C range to get the final product which really is a double-coated slow-release fertilizer with superabsorbent and water-retention properties.

Hansen et al [26], encapsulate the granular fertilizer with the epoxy resin using squirt method. With this research not layered fertilizer was placed in a spinning drum and pre heated up to 250 F. An instant drying solution of copolymers dicyclopentadiene and a customized vegetable essential oil were applied over fertilizer using squirt in a skinny blast of resin. Simultaneously hot air was handed down through drum. Next monomers of second resin including a mixture of epoxidized soybean petrol and polyester healing agent were applied over well prepared granules. The solvent was a mixture of xylene and Cellosolve acetate.

Hansen et al [29] likewise have used the above mentioned way for encapsulation of fertilizer with polyurethane. To begin with the preheated fertilizer was coated by a fabricated drying oil. After drying the coating for a few momemts fertilizer were dusted by clay. Then urethane solution in xylene and Cellosolve acetate was applied using spray.

2. 6. 3. Mixing

In this method granules are simply blended with the covering at its melting point or with a remedy of polymer in a suitable solvent.

Tomaszewska et al [48] used this technique for covering the granular NPK fertilizer with polysulfone (PSF), cellulose acetate (CA) and polyacrylonitrile (Skillet). The covering solutions were prepared by the dissolution of the solid polymer in adequate solvent. The NPK fertilizer was successively put into adequate polymer solution, and was covered by a thin covering of the answer. Eventually, granules were fell into water, where in fact the gelation process occurs. The coated granules were removed from the precipitation shower and then dried to a constant mass. The multiple coatings were made by immersion of the solitary covered fertilizer into satisfactory polymer solution, then into drinking water and drying.

Hon [37] has ready the covered granules by combining method. After melting the thermoplastic polymer by warming, the cellulosic additive has been put into melt resin. Then after allowing the temp to drop, for preventing the fertilizer damage, the granules or natural powder fertilizer has been blended with the prepared blend by using a Brabender Mixer.

Markusch et al [49] just has combined the fertilizer pellets with at first, a diluted polyol and then with a diluted isocyantae to make a polyurethane coating. Then your feretilizer were positioned in oven for drying.

2. 7. Polymers used as covering for CRFs

A broad range of polymers has been found in fertilizer covering. These polymers could be thermoset, thermoplastic or biodegradable.

Some of common thermoset polymers are urethane resin, epoxy resin, alkyd resin, unsaturated polyester resin, phenol resin, urea resin, melamine resin, phenol resin, silicon resin. Included in this, urethane resin urethane is quite typical used [26, 50].

Thermoplastic resins aren't very common found in fine art because of some problems. As stated before a very preferable method of making use of polymers is spraying the dissolved polymer over granules. Either some of thermoplastic resins are not soluble in a solvent or make an extremely viscose solution which is not suited to spraying. Polyolefine is employed in artwork for layer the fertilizer granules [37, 51].

Biopolymers, dispose in bioactive conditions, degrade by the enzymatic action of microorganisms such as bacteria, fungi, and algae and their polymer chains can also be divided by non enzymatic processes such as chemical hydrolysis. Non-biodegradable polymers aren't environmental friendly. Due to environmental concerns there are a few trends of swapping non-bio with bio degradable polymers as finish materials from 1970s. Nonetheless it should be pointed out that they are expensive yet and not very affordable. Also, in creation process toughness of polymer should be changed with release time of fertilizer.

Among natural and fabricated biopolymers starch and cellulose established polymers, chitosan (a linear polysaccharide), poly lactic acid and poly(-caprolactone) credited to low cost and abundance are a few of used biopolymers in fertilizer industry[31, 42, 47, 52-58]

Generally, polymer coatings are applied in a thickness which would work to make a desired controlled release property. Width could be related to characteristic of polymer and also it will depend on existed porosity of polymer surface. If water vapor transmission rate of finish materials is 0. 01 to 20, covering width would be 1 to 100 microns. Preferred layer thickness is 1 to 50 microns. Covering process could be repeated more than one layer to get desired nutritional release [39].

Typical physical way for encapsulating fertilizers are squirt coating, squirt drying, pan finish, rotary disk atomization. Special tools for these procedures are rotary drum, pan or ribbon or paddle mixing machine and fluidized bed [59, 60]

2. 8. Exploration of release behavior of CRFs

Release device of nutrition for different coatings differs. Heavy encapsulated granules like sulfur finish allows the nutrient to release whenever a flaw or rupture appears on the covering surface. In cases like this, rupture may happen because of permeation of water into finish and inside osmotic pressure. Also, biodegradable polymers will release nutrients while destroying by earth microbe's activity. In polymer coatings or blend of different coatings release will happen by diffusion of drinking water through wall's porosities. In cases like this release rate can be controlled by the particle size of coated granules, thickness of finish and permeability of layer surface.

Also, changing the substance composition of fertilizer key as well as the coating will change permeability of covering. This means that even basic or acidic environment changes the permeability. In a few studies when the coating has been starch-vinyl, increasing size of encapsulated granules has led to slowing the nutrient release [61, 62].

There are some standard test methods for measurement of handled release properties. According To Western standard the standard release time of N during 24 h should be 15%

of total core nutrient. Also, release rate for 15 day should be 75% of total nutrients. Also American and Japanese expectations say that the original release must not be more than 40% of total nutrient.

According to Western standards for calculating the release rate encapsulated fertilizer should be immersed in pure water at 25 C (room heat range) in incubated talk about [63, 64]. For instance Detrick et all [33] have looked into the release action of their product by immersion of 20 g of encapsulated granules for 8 h in water. After purification of sturdy they dried the sound. Evaporation of water was done at 100 C for 8 hours. Also, Ma et all [21] located 14 g of granules in line mesh holder and then located it into a jar with 300 ml normal water at 23 C and agitated it by an orbital shaker. Then, sufficient water was considered for elemental research. Locquenghien et al [30] for analysis the gradual release aftereffect of fertilizer extracted some amounts of fertilizer continually with water. For this purpose the granules were set up in level in a cylindrical vessel field with drinking water. Water was passed through this coating and its nitrogen content was examined.

2. 9. Tracing nano-technology features in fertilizer industry

Reviewing literature demonstrates researches which have used nano-technology features in fertilizer industry are incredibly uncommon. Nano-Clay is the most common nano-particle which have been used to produce CRFs. The main great things about nano-clay contaminants in these studies are using them as tank of urea or as filler for polymer covering.

2. 9. 1. Nano-clay as carrier of urea

The split clays like montmorillonite and kaolinite are constructed of high aspect proportion nano levels. Large surface areas and reactivity of nanolayers is a lot greater than that of micrometer size materials. Also, their areas and interfaces provide an energetic substrate for physical, chemical substance, and biological reactions [65]. Because of these features nanolayers could be a ideal carrier or tank of fertilizers.

Mechanisms which get excited about interaction between clay and organic materials is determined by some factors like clay type, useful groups of organic and natural material and physical or chemical substance properties of organic material. For example basic molecules relationship firmly to montmorillonite but anionic molecules show much weaker connection bands. Also, for occasion benzoic acid solution or anionic varieties are adsorbed on the edge face of clay or cationic( crystal violet) are adsorbed on the basal aircraft.

According to desk 1 which ultimately shows different relationship of organic compound with clay, discussion between clay and urea could be through cation exchange, cation bridging and hydrogen bonding [66].

Table 1

Interactions between clay vitamins and organic substances [66]

Mechanism

Mineral examples

Organic functional teams involved

Hydrophobic relationships (vehicle der Waals)

Any clay with natural sites (e. g. , kaolinite, smectites)

Uncharged, non polar (e. g. , aromatic, alkyl C)

Hydrogen bonding

Any clay with air areas (e. g. , kaolinite)

Amines, carbonyl, carboxyl, phenylhydroxyl, heterocycle N

Protonation

Alumino silicate advantage sites, Fe and Al oxides, allophane, imogolite

Amines, heterocycle N, carbonyl, carboxylate,

Ligand exchange

Aluminosilicate advantage sites, Fe and Al oxides, allophane, imogolite

Carboxylate, Phenolate

Cation exchange (permanent charge sites)

Smectite, vermiculite, illite

Amines, band NH, heterocyclic N

pH-dependent fee sites (anion exchange usually, cation exchange almost never)

Aluminosilicate border sites, Fe and Al oxides, allophane, imogolite

Carboxylate for anion exchange, amines, wedding ring NH, heterocyclic N for cation exchange

Cation bridging

Smectite, vermiculite, illite

Carboxylate, amines, carbonyl, alcoholic OH

Water bridging

Reviewing the literatures demonstrates intercalation of urea into clay d-spacing has been done by three methods including solution method, mechano-chemical blending and melt mixing method. The sole shared work about intercalation of urea into clay d-spacing to provide manipulated release fertilizer has used melt combining method. In such a research, intercalation of metal-urea complexes has been done providing handled release N containing fertilizer. The primary known reasons for using Mg (Urea) x instead of natural urea are two barriers. One is decomposing urea at its melting temperature (132. 7) and another is neutral structure of urea which is not accommodated easily by anionic Na+ montmorillonite. Fig. 4 is a schematic illustration of intercalated montmorillonite and release process in this work.

The intercalation process was done through blending Urea-MgCl2. 6H2O with montmorillonite clay with percentage of 1 1:1. The combining was done under warming to 105C. The merchandise has 34. 8 wt. % urea. The XRD patterns demonstrated increasing d-spacing of clay.

Release of urea from clay was looked into learning IR and XRD patterns. Releasing of urea will be done by ligand exchange response with water. Two times cleaning of product was done to investigate the urea release. As the Fig. 4 shows shrinkage of clay d-spacing occurred because of urea release [67].

2. 9. 2. Using clay as fillers for finish of CRF

In another aspect, nano-clay has been used as ideal fillers for polymer coating of managed release fertilizers. Among advantages of this type of nano-composite polymer finish is that they are more amount of resistance against defect as well as are more economical because of minimizing the polymer usage.

Mixing clay and liquid or semi-liquid materials can make three kinds of nanocomposites depending on new composition of clay. For example incorporating clay in a polymer matrix will produce three clay configuration depending on process condition (Fig. 4) When polymer diffuse between unchanged linens intercalated nano-composite is formed(b) Also, mixing may produce exfoliated nano-composite if nano tiers exfoliate or delaminate in the matrix(c). If no intercalation or exfoliation happens, product will be traditional composite (a) [68]

Intercalation of clays has been done by some methods including in situ, solution mixing, mechanical blending and melt combining. Within the first method which is common in setting up polymer-clay nano-composite, monomers will be pushed into clay levels while polymerization going on. Second method identifies dissolving intercalating materials in the right solvent and then intercalating solution into d-spacing of clay using ultrasound or mechanised mixers. In mechanised mixing method the intercalating material will be pushed into tiers using ultrasound or other mechanical tools like ball-mill or three move mill. In last method materials would be in melt or sturdy talk about and intercalation will be done using mechanical forces under shear stress [68, 69].

Making polymer-clay nanocomposites is something common in establishments. Lots of researches have been done in this area, but a few researches have been done for providing nano-composite coatings as fertilizer pills.

In one work, urea granules were covered by two layers of different polymers including humus-polyester, plastic-starch, clay-polyester. The leaching properties of nano-composite covering CRFs were compared with some cemented fertilizer with nano-caly. Results of leaching test demonstrated that the nitrogen release rate of covered fertilizer was least expensive than the main one for cemented fertilizers [3].

Liu et al [70] also well prepared two sorts of nano-coating for providing controlled release fertilizer including kaolinite-polystyrene nano-composite and a nano-structured polystyrene-starch layer. To get ready kaolinite nano-composite, polystyrene monomer was mixed with kaolinite using ultrasonic technique. Nano- structured finish was prepared by semi-emulsification approach.

Barati [71] has found in situ method to prepare nano-composite structured CRFs. Within this work monomers including acrylonitrile and carbohydrate in occurrence of initiator are blended. Then inorganic nano powder will be dispersed in blend and fertilizer nutrient will be added. Nano natural powder could be bentonite, kaolinite, natural zeolite, talc, titanium dioxide. After adding crosslinking agent (methylene bis-acrylamide) polymerization will happen and granules will form.

3. Conclusion

Among prep methods used by scientist for developing polymer layered CRFs, spray method and mechanised mixing methods seem to be more convenient especially because of tools that could be accessible. Also, the review of studies about the polymers, drinking water absorbent coatings seems good choices for drought-prone areas because of fluid retention; not very suitable for rainy areas like Malaysia. Alternatively, biodegradable coatings like ethylcellulose or starch containing polymers are suitable selections because of environmental concerns and automatic degrading.

From current books review, we will get out that posted articles and patents using nano-technology features in setting up manipulated release fertilizers are very rare. Although there are several ideas and potential suggestion about using nano-particles characteristics in CRF industry and you can find just a few published articles in this field. But using nanoparticles in other areas like medication delivery [86-88], smart inhibitor release [89] would be a good idea to develop in CRF industry. High surface area of nanoparticles is one of the useful properties of nanoparticles which can be used for carrying and reserving the fertilizers. Using Urea as an intercalating agent for Clay allergens is one of the more interesting areas have been completed by researchers, although, there are rare published any application of these altered nano-clays in CRFs.

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