Novel Slow-Release Nanocomposite Nitrogen Fertilizers: The Impact

Article pubs.acs.org/IECR

Novel Slow-Release Nanocomposite Nitrogen Fertilizers: The Impact of Polymers on Nanocomposite Properties and Function Elaine I. Pereira,†,‡ Camila C. T. da Cruz,†,‡ Aaron Solomon,§ Anh Le,∥ Michel A. Cavigelli,∥ and Caue Ribeiro*,† †

EMBRAPA Instrumentation, 1452 XV de Novembro Street, São Carlos, São Paulo 13560-970, Brazil Department of Chemistry, Federal University of São Carlos, Hwy. Washington Luiz, km 235, São Carlos, São Paulo 13565-905, Brazil § University of Maryland, College Park, Maryland 20742, United States ∥ USDA-ARS, Sustainable Agricultural Systems Laboratory, Henry A. Wallace Beltsville Agricultural Research Center, 10300 Baltimore Ave., Beltsville, Maryland 20705, United States ‡

ABSTRACT: Efficient use of fertilizers, especially nitrogen, is essential and strategic to agricultural production. Among the technologies that can contribute to efficient use of fertilizers are slow- or controlled-release products. This study describes the impact on structure, urea release rate, and function in the field of urea nanocomposites associated with an exfoliated clay mineral prepared using various concentrations of hydrophilic or hydrophobic polymers. The nanocomposites have a high nutrient load (75% by weight), which itself acts as a structural matrix. Our manufacturing processthe extrusion of a plastic mixtureis simple and can be scaled up, allowing granule production without high costs. Nanocomposites were prepared by adding varying amounts (less than 4% by weight) of polyacrylamide hydrogel or polycaprolactone, which influenced mechanical properties and urea release profiles. Nitrous oxide (N2O) emissions in the field were reduced substantially for nanocomposites, whether composed of polyacrylamide hydrogel or polycaprolactone.

■

INTRODUCTION The fertilizer industry faces ongoing challenges to improve the efficiency of their products because the efficient use of these materials is essential and strategic to obtain maximum economic productivity of crops and to minimize nutrient losses to the environment.1 This can be achieved by improving compounds already in use or by developing new types of fertilizers. Among the variety of fertilizers used, nitrogenous fertilizers are the most susceptible to losses by leaching of nitrate, runoff of various forms of nitrogen, or through gaseous emissions of ammonia, nitric oxide (NO), nitrous oxide (N2O) or dinitrogen (N2).2 In soil, NO and N2O gases are produced as reaction intermediates, mainly via nitrification and denitrification.3,4 The production of these gases, which is due primarily to N inputs in agriculture,5 is particularly important in view of the negative effect they have on the chemistry of the atmosphere, effectively contributing to the greenhouse effect and stratospheric ozone depletion.2,6 Thus, it is essential to control the amount of N2O produced in soil in order to ensure lower environmental impacts of nitrogenous fertilizers. Among the possible technologies that might contribute to more efficient use of N fertilizers are slow or controlled release compounds, especially those based on association of fertilizers with lamellar materials and polymers. New materials being developed involve coating urea granules with polymers,7 sulfur,8 or urease inhibitors.9 Several examples include starch−urea−borate adhesives for coating slow-release urea;10 encapsulated urea with a membrane prepared based starch matrix modified by vinyl acetate;11 nitrogen and phosphorus fertilizer coated using poly(acrylic acid-co-N© XXXX American Chemical Society

hydroxymethyl acrylamide)/wheat straw composite and wheat straw/sodium alginate blends.12 However, these products have limited use as well as the costs incurred in the manufacturing process increase final product prices. A previous study by our research group described the preparation and characterization of nanocomposites obtained by extrusion from a mixture of montmorillonite (MMT) and urea in different mass proportions, which was effective in the retention of urea.13 In this study it was possible to show that urea release is dependent on the relative MMT/urea composition, and properties such as the mechanical resistance of granules were significant increased, giving this method as a new alternative for the large-scale production of fertilizers. In this topic, further studies are necessary to show the influence of compatibilizersthat is, molecules or materials that improve the adhesion or interaction of different surfaces in a multiphase material, such as a compositeon improving specific properties. Two aspects are especially worthy of investigation: the impact of compatibilizers on granule mechanical properties, which impact handling during application, and on N2O emissions, because the environmental aspects of controlled release fertilizers are poorly investigated. Thus, the goal of the present experiment was to study the impact of preparation of urea nanocomposites associated with an exfoliated clay mineral on its structure in the presence of Received: January 13, 2015 Revised: February 23, 2015 Accepted: March 20, 2015

A

DOI: 10.1021/acs.iecr.5b00176 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

were heated from room temperature to 600 °C at 10 °C min−1 under air flow. Scanning Electron Microscopy. Morphology was analyzed by SEM (JEOL microscope model JSM 6510). The sample was dispersed over a carbon tape pasted on the surface of a metallic disc (stub). Then, the disc was coated with carbon in a Leica EM SCD050 chamber and analyzed. X-ray Microtomography. For XMT analysis, a pellet of each composite was placed in a rotating steel bracket and analyzed using a microtomograph (model 1172, SkyScan). In the image acquisition process, the following parameters were adopted: no filter, spatial resolution (voxel size) of 2 μm, rotation step of 0.3°, 180° rotation, and 6 frames to averaging process. The reconstruction process of the images of the tomographic sections was performed using the NRecon software of the SkyScan in which the following parameters were used: smoothing −5; ring artifact correction −5, and beam hardening correction −60%. Diametrical Compression Tests. Appropriate specimens were prepared for the diametrical compression tests. The same compounds used in the preparation of composites (MMT, urea, and polymer) were weighed and mixed in a rheometer (base unit Polylab Rheodrive and mixer RHEOMIX OS4 equipped with “roller” type rotors). After blending, the mass was divided into 5 g portions, and each one was molded into cylindrical dimensions of 20 mm by 10 mm with the aid of a hydraulic press (Oxi-Maq, 50t) and a mold. To perform the test, one diametrical compression testing machine (EMIC/DL 3000) was used to apply compression to the samples at a constant loading rate of 10 mm min−1 up to a maximum deformation of about 70% to the limit of the load cell (3000 kgf). The tests were performed at room temperature. The load values were digitally recorded at the control unit. The results were obtained from an average of 18 specimens of each composition. Representative curves of rupture stress to diametrical compression (σF in MPa) versus strain were obtained using eq 1 to calculate σF:

polymers that modify the interface between urea and clay. A set of composites with added hydrophilic or hydrophobic polymers were investigated. These nanocomposites have a high nutrient load (75% by weight), which itself acts as a structural matrix. Our manufacturing process, the extrusion of a plastic mixture, is simple and can be scaled up, allowing granule production without high costs. The materials were characterized by X-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), X-ray microtomography (XMT), and diametrical compression testing. The nanocomposites were also tested with respect to the release rate of urea in water and N2O emissions in a field experiment.

■

MATERIALS AND METHODS Materials. Urea ((NH2)2CO, Synth), montmorillonite clay without purification (Bentonita, Drescon S/A, Produtos de Perfuraçaõ ), and polycaprolactone (PCL) or polyacrylamide hydrogel (HG) were used as components of the nanocomposites. Clay material (average particle size of 230 nm) was used as received. Urea and PCL were previously ground in a hammer mill (Tecnal, TE-330) and in a cryogenic milling apparatus, respectively. The HG was synthesized in the lab, based on the methodology described in previous work.14 HG was obtained by chemical polymerization of the acrylamide monomer in aqueous solution of the MMT. For synthesis, we used a constant mass ratio of monomer (acrylamide) to clay of 1:1. After drying, the HG was ground in a ball mill (SERVITECH, CT 242) and sifted through a 45 mesh sieve (0.35 mm openings). MMT was introduced into the HG matrix to improve the mechanical properties and to increase the degree of mixing between the components during mixing with urea in final composite preparation. Preparation of Composites. The synthesis of the nanocomposites with polymer departed from the previously described methods.13 Preparation of the composites consisted of premixing, extrusion, and drying. MMT, urea, and polymer were separately weighed and premixed. Water at room temperature was added at 13% (relative to the total weight of dry materials) to complete the mixture. Mixtures were then extruded in a twin-screw extruder (Coperion ZSK 18) at 120 rpm and about 40 °C and converted into pellets of approximately 3 mm diameter and 5 mm length. The materials were dried at room temperature and stored. The mass ratio between MMT and urea (1:4) was the same for all materials. However, the mass of polymer added ranged between 1, 2, and 4%, based on the total mass. The materials were designated HG 1%, HG 2%, and HG 4% for those prepared with polyacrylamide hydrogel and PCL 1%, PCL 2%, and PCL 4% for those prepared with polycaprolactone. For comparison, a composite with only MMT and urea (1:4 ratio), designated MMT/Ur, was also tested.

σF =

2F 100πDH

(1)

where F is the tensile strength in Newton (N), D is the diameter, and H is the height of the specimen, both in centimeters. Values of the modulus of elasticity (E) were obtained by linear regression of the elastic region (linear) of the strain−stress curves. At the maximum limit of the linear phase, the value of maximum rupture stress to diametrical compression for each material was also determined. Release Rate of Urea in Water. A test in aqueous medium was performed, adapted from Tomaszewska and Jarosiewicz15 and previously reported in Pereira et al.,13 where the release rate of urea as a function of time at room temperature was compared for each of the composites. An apparatus was designed that allowed a known mass of the material to be placed in an aqueous medium in a beaker that was stirred externally to ensure that the urea measured in the liquid medium corresponded to the diffusion to the middle and not due to the mechanical action of the stirrer. Aliquots of 1 mL were collected and centrifuged (15 min, at 14 000 rpm; MiniSpin Plus) at various time intervals over 120 h. The amount of urea added in each experiment was the same, that is, different mass values for the composites were calculated so that each experiment included the same amount of urea. The urea concentration in solution was determined by UV−vis

■

CHARACTERIZATIONS X-ray Diffraction. A Shimadzu XRD 6000 diffractometer was used to conduct XRD analyses of the composites. The relative intensity was registered in a diffraction range (2θ) of 3−40°, using a Cu Kα incident beam (λ = 0.1546 nm). The scanning speed was 1° min−1, and the voltage and current of the X-ray tubes were 30 kV and 30 mA, respectively. Thermogravimetry. TG was carried out using a TGAQ500 analyzer (TA Instruments, New Castle, DE). The samples B


Article


interpolation between N2O emissions values on subsequent sampling days was used to calculate N2O emissions for dates when samples were not collected. Daily emissions (measured or interpolated) were summed for the 76 day sampling period. Cumulative N2O emissions during this period were analyzed using analysis of variance using the PROC MIXED procedure in SAS.18

spectrophotometry (Shimadzu-1601PC), according to With et al.16 Each measurement was replicated three times under identical laboratory conditions for each composite type. Determination of Nitrous Oxide Emission. Experimental Site. This experiment was conducted on a field seeded with wheat at the Beltsville Agricultural Research Center, a campus of the U.S. Department of Agriculture Agricultural Research Service, located on the western edge of the Atlantic Coastal Plain in Beltsville, Maryland (39° 2′ N, 76° 55′ E). The experimental procedure was based on the static chamber method as described by Parkin and Venterea17 and was conducted between the end of October 2012 and the beginning of January 2013. Experimental Design. In this experiment, only the pure urea, MMT/Ur (no polymers), and composites HG 1 and 4% and PCL 1 and 4% were used. The 2% composites were not used due to constraints on the number of plots that could be sampled in a timely fashion. An additional control treatment to which no N fertilizer was added resulted in seven fertilizer treatments. Wheat was planted on October 18, 2012. On October 26, 28 aluminum chamber anchors (internal dimension, 0.635 × 0.325 m; 0.206 m2 each) were installed in the ground to a depth of about 10 cm. Each chamber encompassed four rows of wheat 0.635 m in length. Seven frames were placed in each of four areas of the field to create four replicated plots. The fertilizer composites were applied between the crop rows inside each anchor at a rate of 100 kg N ha−1, based on total nitrogen content of each composite. A trench (2 cm deep × 10 cm wide) was dug between the two center rows of wheat. Fertilizer materials were scattered in the trench by hand, and covered with the excavated soil to minimize any potential volatilization of urea from the composites. Each anchor was fit with a gutter along its outer perimeter. At the time of sampling, gutters were filled with water, and a lid that fit inside the gutter17 was placed over each anchor. Gas samples were taken from the resulting chamber headspace through a sampling port using a syringe and needle. Headspace samples (10 mL) were injected into prelabeled 12 mL Exetainer vials that had previously been flushed with 99.9% nitrogen. Four samples were taken every 7 min for a deployment time of 21 min for each chamber. Lids were removed immediately after sampling. Gas samples were taken over 16 days between October 26, 2012, and January 9, 2013. Samples were taken on three consecutive days following rain events and approximately once per week during periods with no rain event. Gas was extracted from the chamber headspace. N2O concentration in each vial was determined using a Varian 450 gas chromatograph equipped with an electron capture detector (temperature 300 °C), a split/splitless type injector (temperature 120 °C) and a fused silica Porapak QS column. N2 was used as carrier gas and CH4/Ar as auxiliary gas, both set at 30 mL min−1. An auto sampler injected 5 mL samples from each vial into the GC. N2O concentrations in the vials were converted to N2O concentrations in the chamber headspace using standard curves and the ideal gas law, corrected for temperature in the chambers at sampling time and for the dilution effect of injecting headspace samples into a preflushed vial. Chamber volumes were calculated using measured values of the height above the soil surface for each frame. Linear regression of N2O concentration over time was used to calculate the rate of emission for each chamber for each sampling day. Linear

■

RESULTS AND DISCUSSION Results of XRD analyses, which were used to verify interlayer expansion and MMT exfoliation in composites, are shown in Figure 1. The XRD pattern of pristine MMT shows typical

Figure 1. X-ray diffractograms (approach to smaller angles) of the MMT pure and of the HG and PCL nanocomposites.

features of this material, with the value of d001 (2θ = 6.6°) equal to 1.34 nm, noting that this value is calculated based on the Bragg eq (2d sin θ = nλ). However, for MMT present in the composites, the peak position of the crystallographic plane d001 was shifted to smaller angles in all materials, and its intensity decreased significantly to almost nil. This suggests that the MMT became exfoliated after the extrusion process in the presence of urea and polymer (HG or PCL). It is important to note that the polymers did not alter the exfoliation, that is, the extrusion process was sufficient to guarantee homogeneous MMT dispersion. Furthermore, because the dispersed phase (MMT) has at least one dimension in the nanometer range, such materials may be classified as nanocomposites.19 TG was used to verify thermal stability of the nanocomposites compared to their precursors, which enabled us to observe some interactions between nanocomposite constituents. The profiles of the nanocomposites prepared with HG are shown in Figure 2. The pristine HG curve shows a degradation profile in three steps, corresponding to a first stage (100−230 °C) attributed to the elimination of water associated with the polymer; a second stage (300−430 °C) with maximum at 376 °C attributed to oxidation of the amide side groups of the polymer and of the cross-linking agent; and last, the final C


Article


Figure 2. (a) Thermogravimetric curve and (b) derivate thermogravimetric of the precursor materials (urea, MMT, and HG) and of the HG nanocomposites.

Figure 3. (a) Thermogravimetric curve and (b) derivate thermogravimetric curves of the precursor materials (urea, MMT, and PCL) and of the PCL nanocomposites.

degradation of polyacrylamide chains, between 430 and 560 °C, with maximum at 478 °C.20 It is worth noting that HG does not present the total mass loss up to 600 °C, as HG was prepared with 50 wt % MMT, which does not fully decompose in this temperature range. All nanocomposites, because they contain large quantities of urea, have similar degradation profiles, and HG materials 2 and 4% showed some temperature variation in urea decomposition peaks. The DTG curve of HG 2% shows a reduction of 10 °C in the first degradation peak

showing that the presence of intermediate quantities of this polymer affects the cohesion of the urea fraction, facilitating its volatilization. For HG 4% the same behavior is observed, but the weight loss range is broader, indicating a greater range of volatilization of urea. However, this material also shows an increase of approximately 20 °C in the second stage of degradation, which may be related to greater interaction between the degraded fractions of urea and HG hindering its thermal degradation. D


Article


Figure 4. SEM images of milled urea, pure MMT, and nanocomposites.

crystals present in the nanocomposites compared to the pure, milled, and not processed urea crystals. This change is related only to the solubilized portion of the material, because the amount of water initially added is not sufficient to solubilize all the urea used in preparing the materials (solubility of urea in water, 167 g/100 mL at 40 °C). To aid the characterization of the nanocomposites’ microstructure, we also characterized these materials by XMT (Figure 5) because this analysis provides a 3D reconstruction of bodies, without fracture. This is particularly important to characterize pore distribution, an important component that regulates properties such as hardness and resistance.24 The images obtained by XMT show that the materials prepared with HG showed better porosity distribution throughout the material, with smaller pores compared to the nanocomposite prepared with only MMT and urea. The value of the polymers is even more evident when comparing nanocomposites with PCL to those with no polymers added in that the PCL nanocomposites had the most segregated porosity and even larger pores. These results corroborate the SEM images, indicating that HG is a better compatibilizer than PCL, giving higher uniformity to nanocomposites. The compatibility of the constituent materials impacts mechanical properties by increasing the load transference between the components of the microstructure (urea crystals and nanocomposite regions), and by reducing the critical porosity, which decreases the internal flaws. Analysis of the mechanical strength of the blends produced, MMT, urea, and polymer (HG or PCL) was performed using a diametrical compression test. Figure 6 shows representative curves of stress versus strain for each material. From these curves, mean values of the rupture stress to diametrical compression (σR) and elasticity modulus were calculated, as shown in Table 1. The curves in Figure 6 show that all compositions proved to be deformable, not showing rupture until the maximum deformation supported by the equipment. With respect to resistance to deformation, it can be noted that the blends prepared with PCL showed similar behavior to the compound produced only with MMT and urea, with low deformation resistance behavior. The presence of PCL at 2 and 4% slightly

Figure 3 shows the thermal performance of the composites prepared with PCL as well as their precursors. The PCL showed only one stage of decomposition from approximately 250 to 490 °C, the same as described in Machado et al.21 As the PCL used in the preparation of the composite was previously mixed with MMT (1:1 by mass) in a rheometer, a high content waste appears up to 600 °C. Three PCL nanocomposites, as for HG nanocomposites, presented degradation profiles dominated by urea. All nanocomposites exhibited similar behavior, except those with higher polymer content, for which a slight reduction in the temperature of the first degradation peak was observed. In general, for all materials, it is observed that the residual mass equals the mass of MMT initially added. These results are important since HG and PCL are both water insoluble polymers but with very different hydrophilicities; PCL exhibits very weak water uptake (swelling degree low, the amount of water absorbed in relation to the composite dry mass),22 whereas HG may attain values over 7000.23 Results show that interactions between water and HG are stronger than those between water and PCL, probably due the hydrophilicity of HG. SEM characterizations were performed to observe the microstructure and morphology of pure MMT, milled urea, and surface fractures of the nanocomposites (Figure 4). Significant differences can be observed between the morphology of the nanocomposite MMT/Ur and nanocomposites prepared with HG and PCL. Nanocomposites with either polymer had more uniform surface fractures than the MMT/Ur nanocomposite, which has no voids. However, a comparative analysis among the nanocomposites containing polymers shows that HG leads to the formation of a material with a smoother fracture surface, while those prepared with PCL showed irregular surface morphology, characteristic of unstable fracture. This analysis indicates that HG acts as a better processing additive than PCL in that it improves uniformity of the material. This fact may be related to greater chemical interaction between HG and both MMT and urea because all are hydrophilic materials. The result is an improved interfacial adhesion between these materials compared to that in the PCL composites. It is also possible to observe changes in the urea E


Article


Table 1. Values of Mechanical Parameters Obtained from Diametral Compression Tests σR (MPa)a MMT/Ur HG 1% HG 2% HG 4% PCL 1% PCL 2% PCL 4%

0.066 0.187 0.248 0.234 0.048 0.057 0.065

± ± ± ± ± ± ±

0.004 0.013 0.020 0.018 0.008 0.008 0.008

σR = rupture stress to diametrical compression. modulus.

a

E (MPa)b 1.65 3.26 6.88 7.08 1.36 1.77 1.96 b

± ± ± ± ± ± ±

0.19 0.40 0.87 0.58 0.22 0.43 0.35

E = elasticity

This event increases the quality of the interfaces and, consequently, the resistance of the material. HG mixtures showed greater resistance to diametrical compression. The most significant results were for the 2 and 4% compositions. The 1% HG composition showed intermediate behavior. The improvement in mechanical strength attributed to the presence of HG in the 1:4 mixture of urea and MMT confirms the higher degree of interaction between the components. According to Ruiz-Hitzky and van Meerbeek,25 hydrogen bonds occur between the carbonyl oxygen of the polyacrylamide molecule (PAAm) and the surface of the mineral; and ion-dipole interactions occur between the polar group of the PAAm molecule and the interlayer cations. These interactions permit the formation of compounds more rigid and therefore more resistant mechanically. Another factor that must be considered is the introduction of MMT in the synthesis of hydrogel used in the preparation of nanocomposites. The presence of clay mineral in the polymer structure can also contribute to the increased compatibility of the components of the granule and contribute to increased mechanical strength. These results agree well with those obtained by SEM and XMT, whereby it was observed that the presence of HG favors the formation of a structurally compact and uniform nanocomposite. Calculated values of the modulus of elasticity (Table 1) show also that the stiffness of the mixtures with PCL is similar to that for the MMT/Ur mixtures and lower than that for mixtures with HG. These results indicate a significant increase in the stiffness of the mixture with the addition of HG, confirming the observations made above. The results of the total amount of urea released versus time for each material tested in water are shown in Figure 7. The instantaneous dissolution of pure urea was observed, and all nanocomposites, even without polymers, showed slower release behavior. However, a comparative analysis between them shows that the nanocomposites produced with HG showed a slower release kinetics than the others, especially in the first ∼50 h, during the period of granule swelling, as noted by the slope of the curves presented in Figure 7c. Thus, we note that the hydrophilic polymer (HG) may act by competing with water entering the pellet, preventing fast solubilization of urea and determining the highest retention time. After 74 h, urea release for all materials was similar, indicating no irreversible adsorption on polymers. However, we note that the rate of release of urea was slower for intermediate amounts of added HG (2%), indicating an optimum amount of interaction in the system. Materials prepared with PCL showed no significant differences in urea release rate, indicating that the polymer interacted little with the system (MMT and urea) and suggesting there was no effect of water entering the pellets. It

Figure 5. Cross-sectional images obtained by XMT of the nanocomposites.

Figure 6. Stress−strain curves obtained from diametral compression test of the nanocomposites compositions.

improved the mechanical performance of the MMT/Ur mixture. This indicates that, despite the presence of PCL, the materials have unstable fracture surfaces and pores are more segregated (in accordance with the SEM and XMT results). In larger quantities, PCL can occupy voids, closing critical failures. F


Article


approximately 70% of urea being released in 13 h. In the present work, 70% of urea is released by nanocomposite HG 2% over 72 h. Chen et al.27 found that 100% of urea encapsulated in a copolymer matrix of starch and poly(Llactide) solubilized in approximately 25 h. Costa et al.28 used polyhydroxybutyrate and ethyl cellulose for coating of urea granules, and they observed that complete release of urea in distilled water observed for products obtained between 3 and 5 min. The longer time achieved for urea dissolution was 1 h. A study by Niu and Li11 showed that maximum period for urea solubility in water was 28 h, when this compound was coated with membrane of starch-g-poly(vinyl acetate). Our results show that the nanocomposite strategy is superior, in terms of release performance, than the above-mentioned systems. To evaluate the impact of the nanocomposite materials on greenhouse gas emissions, we conducted a field experiment to measure N2O emissions from the compound fertilizers applied in soil seeded to winter wheat. Results are shown in Figure 8. The highest values of N2O flux were detected immediately after the application of fertilizer compounds during a substantial rain event and remained higher than those observed in the control treatment (no added N) for a maximum of 9

Figure 7. Urea release rate for MMT/Ur and its nanocomposites prepared with (a) HG and (b) PCL (neutral pH and room temperature). A comparison between the three types of nanocomposites is represented in (c). The release rate for pure urea was included for all cases.

was observed that the urea release is dependent on the structure, that is, there are physical barriers (MMT) probably affecting the diffusion profile. These physical barriers were probably improved by the competition by water from the polymers dispersed in structure. Xiaoyu et al.26 described the preparation of a slow release fertilizer compound based on urea, bentonite (predominant clay mineral, MMT) in small quantity, and an organic polymer. In an experiment studying dissolution of urea in an aqueous medium, similar to that described in this work but under controlled temperature (25 °C), the slowest release rate was

Figure 8. (a) N2O emissions in a wheat field following application of 100 kg N ha−1 as urea, montmorillonite plus urea (MMT/Ur), and the 1 and 4% HG and PCL nanocomposites. (b) Cumulative values of N2O emitted for each fertilizer treatment (minus emissions from the control to which no fertilizer had been added) over the 76 day duration of the experiment (Oct 26, 2012, to Jan 9, 2013). Bars with the same letter above them are not statistically different at the P < 0.05 level according to analysis of variance. Data were calculated from N2O measurements made in four replicated chambers of each treatment. G


Article


tion). However, the HG material showed better urea retention during the first ∼50 h after water was added, indicating that the polymer probably competes for water diffusing into the granule, thereby favoring urea retention during granule swelling. The presence of PCL did not significantly improve the MMT/Ur mixture mechanical resistance but affected the diffusion process. These compounds were also able to substantially reduce the emission of N2O when applied to soil planted with wheat, showing that reducing the diffusion of urea to the soil can have some substantial environmental benefits.

days (Figure 8a). Nitrous oxide emissions are commonly high soon after fertilizer application, especially when soils are wet, due to high amounts of available N in the soil and low oxygen levels, a combination that favors denitrification activity.29−31 Cumulative N2O fluxes for each fertilizer treatment during the 76 day sampling period were subtracted from cumulative fluxes for the control treatment, which received no fertilizer. The results (Figure 8b) show that N2O emitted following the application of conventional urea was greater than in any other treatment, reaching a value of approximately 1850 g ha−1. All nanocomposite materials had statistically lower N2O emissions than the conventional urea (P < 0.05), ranging from 99 to 560 g ha−1, and these values were not statistically different between different systems. The MMT/Ur mixture showed intermediate N2O emissions. The principle of action of the clay mineral in controlling the release of urea and decreasing N2O emission can be related to two factors: (1) The structural MMT lamellae in the composites can act as a physical barrier, preventing exposure of the urea molecule, thereby reducing the rate of hydrolysis of this molecule. (2) The retention by adsorption of NH4+; because MMT is electrically balanced by cations, NH4+ can be exchanged with Ca2+ or Na+ in its structure, providing a cation retention effect. This reduces NH4+ concentration in the soil solution and, consequently, its transformation into other nitrogenous compounds such as N2O.31 The presence of the polymers in the blend of MMT and urea resulted in a significant decrease in N2O emissions compared to urea. This result indicates that the presence of polymers can alter the kinetics of formation of N2O. It is possible that the presence of the PCL can reduce the emission of N2O by retaining part of the NH4+ hydrolyzed by the action of urease present in the soil, though the PCL did not influence release of urea into the environment. Regarding the incorporation of these materials into the soil after the release process, there are some important aspects about PCL, which is a biodegradable polymer and can be incorporated to the soil along the time, offering no risk in terms of soil contamination. On the other hand, polyacrylamide-based HGs are not biodegradable, but some factors must be considered: these polymers are extensively used as soil moisture conditioners, in large amounts, and generally assumed as nontoxic for soil microorganisms. Also, in our nanocomposite, this polymer is present in small amounts; after the release process, the preparation route may increase the soil incorporation process by the fine mixture with MMT, which may accelerate the polymer degradation process. In summary, the composites have been produced using MMT, urea and two different polymers: polyacrylamide hydrogel (hydrophilic) and polycaprolactone (hydrophobic). Diffraction studies show the MMT present in the composites becomes exfoliated after the extrusion process in the presence of urea and a polymer (HG or PCL), whereas thermogravimetric studies indicated stronger interaction of HG than PCL in the nanocomposites. The polymers, even inserted in small quantities during production of the granules by cold extrusion, were effective in increasing the mechanical strength (as measured by diametrical compression). The addition of HG in the 1:4 mixture of urea and MMT generated a new interface between these materials with strong interactions; consequently, it was effective in increasing the mechanical strength. Release of urea in water showed little variation when compared to the reference (MMT/Ur composite, without polymer modifica-

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +55 16 2107 2915. Fax: +55 16 2107 2903. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank CNPq, CAPES (Program Science with No Borders), FAPESP, FAPED, FINEP, and Rede AgronanoEmbrapa for their financial support. This publication is based upon work supported by the United States Department of Agriculture, Agricultural Research Service under the ARS GRACEnet Project.

■

REFERENCES

(1) Trenkel, M. E. Slow- and Controlled-Release and Stabilized Fertilizers: An Option for Enhancing Nutrient Use Efficiency in Agriculture. International Fertilizer Industry Association (IFA): Paris, 2010. (2) Snyder, C. S.; Bruulsema, T. W.; Jensen, T. L.; Fixen, P. E. Review of greenhouse gas emissions from crop production systems and fertilizer management effects. Agr. Ecosyst. & Environment 2009, 133, 247. (3) Bremner, J. M. Sources of nitrous oxide in soils. Nutr. Cycling Agroecosyst. 1997, 49, 7. (4) Kool, D. M.; Dolfing, J.; Wrage, N.; Van Groenigen, J. W. Nitrifier denitrification as a distinct and significant source of nitrous oxide from soil. Soil Biol. Biochem. 2011, 43, 174. (5) Intergovernmental Panel on Climate Change (IPCC). 2007. Climate change 2007: The physical science basis. 4th Assessment Report. http://www.ipcc.ch/publications_and_data/publications_ and_data_reports.shtml (accessed Jan 20, 2012). (6) Serrano-Silva, N.; Luna-Guido, M.; Fernández-Luqueno, F.; Marsch, R.; Dendooven, L. Emission of greenhouse gases from an agricultural soil amended with urea: A laboratory study. Appl. Soil Ecol. 2011, 47, 92. (7) Gagnon, B.; Ziadi, N.; Grant, C. Urea fertilizer forms affect grain corn yield and nitrogen use efficiency. Can. J. Soil Sci. 2012, 92, 341. (8) Costa do Nascimento, C. A.; Vitti, G. C.; Faria, L.; de, A.; Luz, P. H. C.; Mendes, F. L. Ammonia volatilization from coated urea forms. Rev. Bras. Cienc. Solo 2013, 37, 1057. (9) Singh, J.; Kunhikrishnan, A.; Bolan, N. S.; Saggar, S. Impact of urease inhibitor on ammonia and nitrous oxide emissions from temperate pasture soil cores receiving urea fertilizer and cattle urine. Sci. Total Environ. 2013, 465, 56. (10) Naz, M. Y.; Sulaiman, S. A. Testing of starch-based carbohydrate polymer coatings for enhanced urea performance. J. Coat. Technol. Res. 2014, 11, 747. (11) Niu, Y.; Li, H. Controlled Release of Urea Encapsulated by starch-g-poly(vinyl acetate). Ind. Eng. Chem. Res. 2012, 51, 12173. (12) Xie, L.; Liu, M.; Ni, B.; Wang, Y. New environment-friendly use of wheat straw in slow-release fertilizer formulations with the function of superabsorbent. Ind. Eng. Chem. Res. 2012, 51, 3855.

H


Article

Industrial & Engineering Chemistry Research (13) Pereira, E. I.; Minussi, F. B.; Cruz, C. C. T.; da Bernardi, A. C. C.; Ribeiro, C. Urea-montmorillonite-extruded nanocomposites: A novel slow-release material. J. Agr.Food Chem. 2012, 60, 5267. (14) Aouada, F. A.; Moura, M. R.; de Silva, W. T. L.; da Muniz, E. C.; Mattoso, L. H. C. Preparation and characterization of hydrophilic, spectroscopic, and kinetic properties of hydrogels based on polyacrylamide and methylcellulose polysaccharide. J. Appl. Polym. Sci. 2011, 120, 3004. (15) Tomaszewska, M.; Jarosiewicz, A. Use of polysulfone in controlled-release NPK fertilizer formulations. J. Agric. Food Chem. 2002, 50, 4634. (16) With, T. K.; Petersen, T. D.; Petersen, B. A simple spectrophotometric method for determination of urea in blood and urine. J. Clin. Pathol. 1961, 14, 202. (17) Parkin, T. B.; Venterea, R. T. Chamber-Based Trace Gas Flux Measurements. In USDA-ARS GRACEnet Project Protocols. Follett, R. F., Ed., 2010. p 3/1−3/39. URL (www.ars.usda.gov/research/ GRACEnet) (March 2012). (18) SAS Institute. 2002. SAS/Statistical User’s Guide, 6.03 ed., SAS Institute, Inc., Cary, North Carolina. (19) Wang, K. H.; Choi, M. H.; Koo, C. M.; Choi, Y. S.; Chung, I. J. Synthesis and characterization of maleated polyethylene/clay nanocomposites. Polymer 2001, 42, 9819. (20) Zhou, C.; Wu, Q. A novel polyacrylamide nanocomposite hydrogel reinforced with natural chitosan nanofibers. Colloids Surf., B 2011, 84, 155. (21) Machado, A. V.; Botelho, G.; Silva, M. M.; Neves, I. C.; Fonseca, A. M. Stability of nanocomposites of poly(ε-caprolactone) with tungsten trioxide. J. Polym. Res. 2011, 18, 1743. (22) Kehren, D.; Lopez, A. C. M.; Pich, A. Nanogel-modified polycaprolactone microfibres with controlled water uptake and degradability. Polymer 2014, 55, 2153. (23) Bortolin, A.; Aouada, F. A.; Mattoso, L. H. C.; Ribeiro, C. Nanocomposite PAAm/methyl cellulose/montmorillonite hydrogel: Evidence of synergistic effects for the slow release of fertilizers. J. Agric. Food Chem. 2013, 61, 7431. (24) Rattanasak, U.; Kendall, K. Pore structure of cement/pozzolan composites by X-ray microtomography. Cem. Concr. Res. 2005, 35, 637. (25) Ruiz-Hitzky, E.; van Meerbeek, A. Clay mineral and organoclay−polymer nanocomposite. In Handbook of Clay Science; Bergaya, F.; Theng, B. K. G., Lagaly, G., Eds.; Elsevier, Amsterdam, 2006. (26) Xiaoyu, N.; Yuejin, W.; Zhengyan, W.; Lin, W.; Guannan, Q.; Lixiang, Y. A novel slow-release urea fertiliser: Physical and chemical analysis of its structure and study of its release mechanism. Biosyst. Eng. 2013, 115, 274. (27) Chen, L.; Xie, Z.; Zhuang, X.; Chen, X.; Jing, X. Controlled release of urea encapsulated by starch-g-poly(L-lactide). Carbohyd. Polym. 2008, 72, 342. (28) Costa, M. M. E.; Cabral-Albuquerque, E. C. M.; Alves, T. L. M.; Pinto, J. C.; Fialho, R. L. Use of polyhydroxybutyrate and ethyl cellulose for coating of urea granules. J. Agric. Food Chem. 2013, 61, 9984. (29) Díaz-Rojas, M.; Aguilar-Chávez, A.; Cárdenas-Aquino, M.; Del, R.; Ruíz-Valdiviezo, V. M.; Hernández-Valdez, E.; Luna-Guido, M.; Olalde-Portugal, V.; Dendoovena, L. Effects of wastewater sludge, urea, and charcoal on greenhouse gas emissions in pots planted with wheat. Appl. Soil Ecol. 2014, 73, 19. (30) Hou, A.; Akiyama, H.; Nakajima, Y.; Sudo, S.; Tsuruta, H. Efects of urea form and soil moisture on N2O and NO emissions from Japanese Andosols. Chemosphere 2000, 2, 321. (31) Fernández-Luqueño, F.; Reyes-Varela, V.; Martínez-Suárez, C.; Reynoso-Keller, R. E.; Méndez-Bautista, J.; Ruiz-Romero, E.; LópezValdez, F.; Luna-Guido, M. L.; Dendooven, L. Emission of CO2 and N2O from soil cultivated with common bean (Phaseolus vulgaris L.) fertilized with different N sources. Sci. Total Environ. 2009, 407, 4289.

I


Novel Slow-Release Nanocomposite Nitrogen Fertilizers: The Impact

Recommend Documents