Controlled Release Modeling of Urea from Chitosan Microspheres: Effect of Stirring Speed and Volume Ratio of Continuous to Dispersed Phase

The purpose of this study was to determine the release kinetics and diffusion coefficient of chitosan microspheres containing urea based on changes in the stirring speed and the volume ratio of the continuous to dispersed phase (CP/DP). Chitosan microspheres filled with urea were prepared using the emulsion cross-linking method. The initial stage of this method has formed an emulsion then slowly dripped with glutaraldehyde saturated toluene as a crosslinker. Urea-loaded chitosan microspheres were washed and dried and then tested for release in an aqueous medium. The calculated cumulative release was used to determine the release kinetics and diffusion coefficient of chitosan microspheres. The appropriate release kinetics model was Simple Power Law with the Burst Effect because it produces an R2 value of 0.99. The mechanism of urea release from chitosan microspheres is Case II the transport mechanism represents pure relaxation behavior. Determination of the diffusion coefficient values from 1,180 x 10-14 up to 1,433 x 10-14 cm2/sec.

Kinetics of slow release of nitrogen fertiliser from multi-layered nanofibrous structures

Fertilisers are essential in modern agriculture to enhance plant growth, crop production and product quality. Recent research has focused on the development of delivery systems designed to prolong fertiliser release. This study introduces a new technology to encapsulate and release molecules of fertilisers by using multi-layered electrospun nanofibre as a carrier. Single-layer poly L-lactic acid (PLLA) nanofibres loaded with urea were fabricated using electrospinning. Triple-layer nanofibrous structures were produced by electrospinning polyhydroxybutyrate (PHB) nanofibres as external layers with PLLA nanofibres impregnated with urea fertiliser as the middle layer. Scanning electron microscopy (SEM) and Fourier transform infrared spectrophotometry (FTIR) were employed to characterize the morphology of electrospun nanofibres. Urea release dynamic was analysed using a total nitrogen instrument (TNM-1). The results indicated that triple-layered urea-impregnated nanofibrous structures led to lower initial rate of nitrogen release and slower release rate of cumulative nitrogen which extended for more than three months. It is concluded that triple-layer nanofibrous structures have the potential for slow release delivery of fertilisers.

Urea-functionalized amorphous calcium phosphate nanofertilizers: optimizing the synthetic strategy towards environmental sustainability and manufacturing costs

Nanosized fertilizers are the new frontier of nanotechnology towards a sustainable agriculture. Here, an efficient N-nanofertilizer is obtained by post-synthetic modification (PSM) of nitrate-doped amorphous calcium phosphate (ACP) nanoparticles (NPs) with urea. The unwasteful PSM protocol leads to N-payloads as large as 8.1 w/w%, is well replicated by using inexpensive technical-grade reagents for cost-effective up-scaling and moderately favours urea release slowdown. Using the PSM approach, the N amount is ca. 3 times larger than that obtained in an equivalent one-pot synthesis where urea and nitrate are jointly added during the NPs preparation. In vivo tests on cucumber plants in hydroponic conditions show that N-doped ACP NPs, with half absolute N-content than in conventional urea treatment, promote the formation of an equivalent amount of root and shoot biomass, without nitrogen depletion. The high nitrogen use efficiency (up to 69%) and a cost-effective preparation method support the sustainable real usage of N-doped ACP as a nanofertilizer.

Effect of Temperature on the Behavior of Slow Release Fertilizer from ENR-50/RH/Urea Composites

Generally, chemical fertilizer is considered as a one of the most significant materials for increasing food production. However, the fast release of the conventional fertilizer could effect negatively on the plants. Thus, the idea of using controlled release method in the agriculture application has emerged recently due to the efficiency of fertilizers can be improved by the controlled-release method. The objective of this work is to synthesize a new Slow Release Fertilizer from three different materials; the first one is urea, which is the conventional fertilizer, the second one is the rice husk (RH), which represents the carrier material, and the third one is epoxidized natural rubber (ENR-50), which represents the coating material. This work was divided into three series. The first series is the production of RH/Urea beads. RH was treated with alkaline NaOH at 1wt.% according to the weight of RH. The treated RH was then mixed with urea that produced treated RH/urea beads. In the second series, 200 mg of ENR-50 was applied to produce thicknes of coating material for treated RH/urea beads. In the third series, treated RH/urea beads coated with 200 mg of ENR-50 were subjected to the released behavior at different temperature in the water. After that, the prepared samples were characterized using Scanning Electron Microscopy (SEM) and UV-visible spectroscopy. Results suggested that the increasing of temperature has increased the rate of urea release of SRF samples in the water. Furthermore, the SRF sample at 35, 45, and 55 °C showed shorter time of release at 40, 34, and 17 day as compared to 47 day of SRF at room temperature.

Investigation of slow release of urea from biodegradable single- and double-layered hollow nanofibre yarns

Urea is the most common form of nitrogenous fertiliser. Recently, research has focused on the development of delivery systems to prolong fertiliser release and prevent fertiliser loss through leaching and volatilization. This study investigates and compares single- and double-layered hollow nanofibrous yarns as novel delivery systems to encapsulate and release urea. Single-layered hollow poly l-lactic acid (PLLA) nanofibre yarns loaded with urea fertiliser were fabricated using a customized electrospinning. Double-layered hollow nanofibre yarns were produced by electrospinning polyhydroxybutyrate (PHB) nanofibres as an outer layer, with urea-impregnated PLLA nanofibres as the inner layer. Scanning electron microscopy (SEM) with an energy-dispersive spectroscopy (EDS) was used to characterize the morphology of hollow electrospun nanofibre yarns. A total nitrogen instrument (TNM-1) was used to study the urea release from single- and double-layered hollow nanofibres yarn in water. A Carbon:Nitrogen (CN) elemental analyser determined encapsulated nitrogen in PLLA nanofibres samples. Results indicated that urea-impregnated double-layered hollow nanofibre yarns significantly started nitrogen releasing at much lower amount during first 12 h compared to single-layered hollow nanofibre yarns (P value = 0.000). In conclusion, double-layered hollow nanofibre yarn has potential as an effective alternative to current methods for the slow release of fertilisers and other plant-required chemicals.

A Theoretical Multifractal Model for Assessing Urea Release from Chitosan Based Formulations

This paper reports the calibration of a theoretical multifractal model based on empirical data on the urea release from a series of soil conditioner systems. To do this, a series of formulations was prepared by in situ hydrogelation of chitosan with salicylaldehyde in the presence of different urea amounts. The formulations were morphologically characterized by scanning electron microscopy and polarized light microscopy. The in vitro urea release was investigated in an environmentally simulated medium. The release data were fitted on five different mathematical models, Korsmeyer–Peppas, Zero order, First order, Higuchi and Hixson–Crowell, which allowed the establishment of a mechanism of urea release. Furthermore, a multifractal model, used for the fertilizer release for the first time, was calibrated using these empirical data. The resulting fit was in good agreement with the experimental data, validating the multifractal theoretical model.

Synthesis and Characterization of Controlled-Release Urea Fertilizer from Superabsorbent Hydrogels

It is very important to develop controlled-release fertilizers to ensure efficiency and environmental protection. This study aims to make a superabsorbent hydrogel-based controlled-release urea fertilizer. Superabsorbent hydrogels were prepared from the cellulose of corn cobs cross-linking with epichlorohydrin, and then an amount of urea as a fertilizer was stored inside the hydrogels (GEL-A). The GEL-A functionalization with carboxy-methyl was also carried out in this study to improve the hydrophilicity of hydrogels (GEL-B). GEL-A and GEL-B were immersed in water at a certain pH and temperature range and the urea concentration released from the hydrogels was monitored by a spectrophotometer. The results showed that the urea released by GEL-A and GEL-B was not much different. Respectively, the urea efficiency of GEL-A and GEL-Bwas around 5.29% and 5.56% for 180 min. The urea released from both hydrogels was not significantly affected by changes in the temperature of the solution. Urea release was influenced by pH, and the rate of urea release of GEL-B was faster than GEL-A, so pH control was needed in the application of this slow-release fertilizer.

Matriks Pengontrol Pelepasan Urea Berbasis Karagenan: Pengaruh Konsentrasi Glutaraldehid

Abstrak. Pada penelitian ini, matrik hidrogel berbasis karagenan dibuat dan diaplikasikan untuk mengontrol pelepasan urea. Tujuan penelitian ini adalah mempelajari pengaruh konsentrasi glutaraldehid terhadap kecepatan pelepasan urea dan menyusun model kecepatan pelepasan urea. Film karagenan dimodifikasi secara kimiawi menggunakan ikatan silang atau crosslinking dengan glutaraldehid. Larutan karagenan 7 g/100 mL dicetak menjadi lembaran dan kemudian dikeringkan sehingga diperoleh lapisan film. Film direndam dalam larutan glutaraldehid dengan konsentrasi tertentu selama 2 menit dan dilanjutkan dipanaskan pada suhu 110oC selama 20 menit. Film yang dihasilkan dicuci dengan etanol dan dikeringkan. Pengisian urea ke dalam matrik film menggunakan metode difusi. Film kering direndam dalam larutan urea 0,074 g/mL selama satu jam dan selanjutnya dikeringkan. Kecepatan pelepasan urea dari film ke dalam media air dievaluasi berdasarkan data konsentrasi urea dalam cairan sebagai fungsi waktu. Berdasarkan hasil penelitian didapatkan bahwa semakin besar konsentrasi glutaraldehid (1-5%) menyebabkan urea yang tersimpan di dalam film semakin rendah. Model matematika yang diusulkan dapat mewakili peristiwa pelepasan urea dari film. Film berbasis karagenan yang dihasilkan berpotensi sebagai matrik pengontrol pelepasan urea. Kata kunci: crosslinking, glutaraldehid, hidrogel, karagenan, urea. Abstract. Controlled Release Matrices of Urea from Carrageenan: Effect of Glutaraldehyde Concentration. In this study, carrageenan-based hydrogel matrices were prepared and applied for urea controlled release. The aim of this work was to study the effect of glutaraldehyde concentration on the rate of urea release in water. Carrageenan films were chemically modified by crosslinking with glutaraldehyde. The films were prepared by casting the aqueous carrageenan 7 g/100 mL and then followed by drying. The films obtained were immersed in certain glutaraldehyde concentration for 2 min and then heated in the oven at 110oC for 20 min. The crosslinked films were washed using ethanol and then air-dried until the weight is constant. The dried films were immersed in a urea solution (0.074g/ml) for 1 hr and then dried. The rate of urea release was determined by measuring the urea concentration in water as a function of time of release. Results showed that higher glutaraldehyde concentration (1–5%) produced films with less urea content. The proposed mathematic model of urea release from the film can represent the rate of urea release. The prepared carrageenan-based film has the potential for controlling of urea release. Keywords: carrageenan, crosslinking, glutaraldehyde, hydrogel, urea. Graphical Abstract