Browsing by Author "Nyakombi, Priscilla"
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- ItemSilk-cellulose nanofiber membranes for application in water treatment(Stellenbosch : Stellenbosch University, 2019-12) Nyakombi, Priscilla; Gule, Nonjabulo Prudence; Vollrath, Fritz; Klumperman, Bert; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Electrospinning (ES) of biopolymers down to nanoscale size has received considerable interest in efforts to address specific millennia problems, which include materials for application in medical and water treatment spheres. The main aim of this study was to fabricate silk fibroin (SF) and cellulose (CE) nanofiber membranes via the ES method, then characterized for morphology using scanning electron microscopy and transmission electron microscopy, structurally using X-ray diffraction, Fourier Transform Infra-red spectrometry, Raman spectroscopy and Solid-State NMR. To establish thermal stability of the fabricated nanofibers when compared to the pure polymers, differential scanning calorimetry and thermal gravimetric studies were conducted. Several properties such as biodegradability, biocompatibility and nontoxic were considered with applications in filter media and tissue engineering in mind. Both cellulose and silk are natural fibers that degrade naturally, and they have remarkable mechanical properties, which, from an environmental friendliness point of view, a blended material from these biopolymers can be a good candidate, and secondly utilize the blended nanofibers as candidates in filtration media. Furthermore, both materials are mechanically strong and therefore can withstand the pressures associated with water treatment. A further advantage is that both silk and cellulose fibers have been reported to exhibit antimicrobial properties. Hence, it was envisaged that fiber combinations from these two biopolymers may have some degree of antimicrobial activity, which would open a wide range of applications. Randomly oriented SF/CMC nanofibrous mats were fabricated with average diameters of about 153 ± 20 nm. The electrospun mats were also crosslinked with N-(3-dimethylaminopropyl)-N’- ethylcarbodiimide hydrochloride (a nontoxic crosslinking agent) and N-hydroxysuccinimide to enhance water stability for water treatment applications. The antimicrobial activity of the fibers was examined against different bacteria including Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). Various methods were used to assess the antibacterial activity, including zone inhibition and fluorescence imaging. Enzymatic biodegradation of the materials was studied using cellulase (Aspergillus niger) and protease type XIV (Streptomyces griseus). The degradation of the electrospun mats was confirmed using SEM and FTIR. From the results, SF/CMC fibers displayed diameter increases when compared to fibers obtained from pure silk solutions. Structural characterization using ATR-FTIR, XRD, Raman, and SolSt-13C NMR showed the transfiguration of SF from a random coil to a -sheet in the electrospun blends with CMC. The TGA results of the SF/CMC blended nanofibers exhibited thermal behavior very similar or better than that of SF nanofibers. The SF and SF/CMC blends nanofibers were all successfully crosslinked by EDC/NHS crosslinking agent. After crosslinking, it was observed that the nanofiber mats became more pliable and their average diameter increased compared to the non-crosslinked nanofiber mats and achieved more water stability as the crosslinking agent was increased. The results from zone inhibition tests showed that SF is slightly active against E. coli and CMC indicated positive result towards E. coli and moderate results towards S. aureus. The degradation of all electrospun nanofibers was investigated through the action of enzymes. Results show that SF/CMC nanocomposites can be classified as enzymatically degradable. The increase in weight loss as the degradation period increased was observed. From the findings, it was concluded that protease XIV degrades SF by breaking down the peptide bonds of the SF into amino acids and cellulase degrades CMC.