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Rop K, Mbui D, Karuku GN, Michira I, Njomo N. "Characterization of water hyacinth cellulose-g-poly (ammonium acrylate-co-acrylic acid)/nano-hydroxyapatite polymer hydrogel composite for potential agricultural application." Results in Chemistry. 2020;2:100020. AbstractResults in Chemistry

Polymer nano-composite was prepared by grafting partially neutralized acrylic acid onto swollen cellulose isolated from water hyacinth in the presence of nano-hydroxyapatite (nano-HA) using N,N-methylene-bis-acrylamide (MBA) as the cross-linker and ammonium persulphate (APS) as the free radical initiator. Water absorption tests showed an increase in swelling ratio of the copolymer with increased nano-HA content to value of 120 g/g at 2.5% w/v above which it declined. FTIR spectrum of nano-composite revealed grafting of the monomer (acrylic acid/ammonium acrylate) onto cellulose and nano-HA. Transmission electron microscopy (TEM) images of nano-HA synthesized in the presence of Triton X-100 (non-ionic surfactant) displayed rod-shaped agglomerates and nano-particle dispersion within the copolymer matrix. Energy dispersive X-ray (EDX) spectra revealed the constituents of nano-composite to be …

Rop K, Mbui D, Njomo N, Karuku GN, Michira I, Ajayi RF. "Biodegradable water hyacinth cellulose-graft-poly (ammonium acrylate-co-acrylic acid) polymer hydrogel for potential agricultural application." Heliyon. 2019;5(3):e01416. Abstract

Swollen cellulose fibres isolated from water hyacinth were utilized in the synthesis of water hyacinth cellulose-graft-poly(ammonium acrylate-co-acrylic acid) polymer hydrogel (PHG). Acrylic acid (AA) partially neutralized with NH3 was heterogeneously grafted onto swollen cellulose by radical polymerization reaction using N,N-methylene-bis-acrylamide (MBA) as the cross-linker and ammonium persulphate (APS) as the initiator. The reaction conditions were optimized through assessment of grafting parameters such as grafting cross-linking percentage (GCP), percentage grafting cross-linking efficiency (%GCE) and water absorption tests. Characterization of the copolymer by Fourier Transform Infra-red (FTIR) spectroscopy revealed successful grafting of the monomer onto cellulose. Transmission electron microscopy (TEM) image of acetone-extracted PHG displayed micro-porous structure. The optimized product …

Rop K, Karuku GN, Mbui D, Njomo N, Michira I. "Evaluating the effects of formulated nano-NPK slow release fertilizer composite on the performance and yield of maize, kale and capsicum." Annals of Agricultural Sciences. 2019;64(1):9-19. Abstract


Effect of formulated slow release NPK fertilizer [cellulose-graft-poly(acrylamide)/nanohydroxyapatite/soluble fertilizer] composite (SRF) on the performance and yield of maize, kale and capsicum was evaluated in a greenhouse experiment. No significant difference in growth parameters was observed between SRF and commercial fertilizer (CF) treatments. SRF recorded higher dry matter and yields relative to CF with similar application rates, though statistically insignificant. P deficiency was observed in maize at lowest SRF application rate of 45-57-17. N deficiency in CF was observed at the 8th week, but not in SRF with similar application rates during the same period. Kale showed both N and P deficiencies in the 7th week, while capsicum alone showed N deficiency in the 14th week in SRF at low application rates. NPK content in both maize and kale tissues, was significant between the amendments and control. Capsicum tissues had significantly (p ≤ 0.05) higher N content both in SRF and CF higher application rates of 125-159-45 & 100-100-100, respectively, compared to control. At final harvest, soil samples planted with maize and amended with the highest SRF rate showed significantly (p ≤ 0.05) higher P content, compared to lower rates and the control. The agronomic optimal rate of SRF determined by quadratic function were found to be higher than that of CF. SRF was found to enhance growth and yields of crops just like CF and could potentially have greater benefits such as improving soil health and resilience.

Rop K, Karuku GN, Mbui D, Michira I, Njomo N. "Formulation of slow release NPK fertilizer (cellulose-graft-poly (acrylamide)/nano-hydroxyapatite/soluble fertilizer) composite and evaluating its N mineralization potential." Annals of Agricultural Sciences. 2018;63(2):163-172. AbstractAnnals of Agricultural Sciences


Polymer nano-composite fertilizer formulation has the potential to enhance nutrient use efficiency. Slow release fertilizer (SRF) composite was formulated by incorporating nano-hydroxyapatite (nano-HA) and water soluble fertilizers (urea, (NH4)2HPO4 and K2SO4) into water hyacinth cellulose-graft-poly(acrylamide) polymer hydrogel. Fourier Transform Infra-red spectra revealed existence of chemical interaction between the monomer, cellulose, urea and nano-HA. The release of nutrients was assessed using laboratory incubation experiment. Significantly higher content of mineral nitrogen (MN) was observed in the first 4 weeks in conventional fertilizer (CF) compared to SRF treatments and the control. MN content in SRF treatments increased considerably between the 8th and 12th week, and declined in the 16th week. The values of potentially mineralizable N estimated using first order kinetics model related well to the observed cumulative MN at 16th week. No significant difference was observed between CF and SRF treatments for available P content in the 2nd week. Significantly higher P content was observed in CF compared to SRF treatment in the 4th week, whereas in the 8th week, some SRFs released significantly higher content than CF. Available P peaked in the 8th week in all the treatments and remained constant at 12th and 16th week. Availability of P in SRFs increased with increased content of soluble P and decreased content of nano-HA. Exchangeable K showed less variation during the incubation period, suggesting short release time. The data revealed reduced chances of leaching losses and toxic effect to the plant roots, as well as synchronized nutrient release and requirement by crops.

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