Preparation and electrospinning of chitosan from waste Black Soldier Fly biomass
Zimri, Monushia Natasha
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Black soldier flies are important in sustainability because of their ability to voraciously degrade organic waste without constituting a nuisance to the environment. In South Africa, Agriprotein Ltd, a company producing high-protein animal feed is rearing black soldier fly (Hermetia illucens, BSF) larvae on organic waste that would otherwise go into landfills. During the process of mass rearing large quantities of dead adult BSF flies and pupae shells are being generated. This motivated the extraction of chitin from the waste materials generated by Agriprotein. This waste can be utilised as an economic source of chitin and its derivative chitosan. Hence, this is the first study to be focused on the chemical extraction of chitin from the pupae shells and adult BSF biomass waste, the conversion of the extracted chitin to chitosan and to fabricate nanofibers from the commercial chitosan by electrospinning technique. Chitin was optimally extracted from both the pupae shells and adult BSF through demineralisation, deproteinisation and decolouration processes. The extracted chitins were optimally converted to chitosan by deacetylation process. The commercial chitosan were electrospun into nanofibers by optimising the concentration, voltage, flow rate and tip-to-collector distance. The synthesised and fabricated products were characterised using different analytical techniques such as FTIR to examine the spectral patterns and peaks corresponding the stretching and vibrations of various functional groups, XRD to examine the crystalline structure, SEM to examine the morphology and TGA to investigate the thermal stability. Elemental analysis was carried out to determine the degree of acetylation and degree of deacetylation. The commercial shrimp chitin and chitosan were compared to determine the purity of the extracted products. The electrospun chitosan nanofibers were compared to the bulk chitosan to determine how the structure, crystallinity and thermal stability had been altered after the electrospinning process. The best optimum conditions obtained at 1 M HCl, 100 min and 50 ºC for demineralisation and 1 M NaOH, 10 h and 85 ºC for deproteinisation yielded the highest final dry weight yield of 13% and 5% for pupae shells and adult BSF chitin respectively. The best optimum conditions obtained at 70% NaOH, 5 h and 100 ºC for deacetylation yielded the highest final dry weight http://etd.uwc.ac.za ii yield of 11% and 2% for pupae shells and adult BSF chitosan respectively. The elemental analysis results revealed that both chitins with a degree of acetylation of 115.1% for pupae shells and 91.5% for adult BSF are of acceptable purity. In addition, both chitosans with a degree of deacetylation of 67% for pupae shells and 69% for adult BSF are of acceptable purity. FTIR, TGA and XRD analysis results demonstrated that the chitins from both pupae shells and adult BSF were in the α-form. Both chitins extracted proved to be fibrous in nature with no porosity, whereas the pupae shells and adult BSF chitosan were characterised without any nanofibers and/or nanopores. The MW of chitosan samples was 217 kDa for pupae shells and 216 kDa for adult BSF. The optimum conditions of the electrospun commercial chitosan nanofibers were obtained at 6 wt% commercial chitosan in TFA, an applied voltage of 25 kV, a tip to collector distance of 10 cm and a flow rate of 0.1 mL/h. The morphology of the optimised commercial chitosan nanofibers had a regular smooth morphology with some small variations in fiber diameter in a bead free network with an average diameter of 130 nm in a range of 60 nm to 200 nm. FTIR analysis revealed that the chemical nature of the polymer during the electrospinning process was not altered. The XRD analysis revealed that the electrospun nanofibers are amorphous and TGA showed that the bulk chitosan (310 °C) was more thermally stable than the electrospun commercial chitosan nanofibers (272 °C).