ICAPS 2024
Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/28744
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Item Synthesis and characterization of carboxymethyl cellulose-based hydrogels to be used as a slow-release fertilizer(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Abeysinghe, A. M. N. A.; Jayasuriya, C. K.; Permachandra, J. K.Chemical fertilizers are heavily used in the agricultural sector in Sri Lanka. Since SriLanka does not have high quality raw materials to produce chemical fertilizers, Sri Lanka has to import chemical fertilizers regardless of the rising prices of chemical fertilizers in the global market. On the other hand, the traditional fertilizing methods used in the country result in the overuse of chemical fertilizers and the loss of such fertilizers to the environment through surface runoff and leaching. These hazardous fertilizing methods, pollute soil, and water and contaminate the human food chain leading to critical diseases such as chronic kidney disease (CKD). To overcome this problem, slow-release fertilizers (SRFs) can be used. SRFs are made using materials such as hydrogels, polyolefin resin and other polymeric materials. Such hydrogels can be synthesized in a cost-effective and environmentally friendly processes using natural sources. In this research a series of hydrogel samples were synthesized using carboxymethyl cellulose (CMC) and epichlorohydrin (ECH) as crosslinker, with varying crosslinking densities. The degree of substitution (DS) of the CMC powder was determined by a titrimetric method, whereas crosslinking density (CD) and average molar mass between successive crosslinks (Mc) were determined using the Flory-Rehner theory. The chemical structure of the resulting CMC- hydrogels was analyzed using FTIR-ATR spectroscopy. The swelling ratio of CMC-hydrogels with different CDs in deionized water was also examined. The slow release behaviour of CMC-hydrogel samples was assessed by loading ammonium nitrate (AN) into the samples followed by monitoring the releasing behaviour of AN for two hours at 15 minute intervals using Nessler’s reagent and UV-visible spectrophotometry. Korsmeyer- Peppas model was applied to find the release mechanism of AN from hydrogel samples. Further, the effect of temperature on slow-releasing properties of hydrogel samples was investigated from 10 ºC-50 ºC, and the influence of pH of the medium on the slow- releasing properties of hydrogels was also investigated. As expected, the results indicate that CD and Mc of hydrogels significantly affect the swelling ratio and the release rate of AN. The swelling ratio decreases with the increase of CD and the rate of release of AN at a given time, pH and temperature, decrease as CD is increased. The slow-release mechanism of all the hydrogel samples can be fitted to Fickian diffusion model. Prepared CMC-based SRF hydrogels can be classified as a lower critical solution temperature (LCST) type hydrogel since those showed a decrease in the rate of release of AN with an increase in temperature. Hydrogels showed that the releasing rate of AN increases with increasing pH of the medium. The results of the study proved the suitability of the prepared CMC-based hydrogels in the agriculture sector as SRF.