Doctoral Degrees (Chemical Engineering)

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Browsing Doctoral Degrees (Chemical Engineering) by Author "Bello, Fatimatu"

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    Development of multi-step biorefinery schemes for the production of nanocellulose and high value-added bioproducts from mango seed
    (2022-04) Bello, Fatimatu; Chimphango, Annie Fabian Abel; Görgens, Johann Ferdinand; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Due to environmental and health concerns associated with non-renewable and synthetic-based packaging materials, there is an upward demand for bioproducts from renewable sources, particularly for food packaging. Nanocellulose is one such bioproduct and is generally produced from woody biomass due to its fibrous nature, however, woody biomass is in high demand. Mango (Mangifera Indica L.) seed is a major lignocellulosic waste from mango fruit processing, whose management is limited to disposal by incineration, burning, or landfilling with no current commercial use, resulting in environmental and economic burdens such as green-house gas emissions and land use concerns. However, mango seed has potentials for various bioproduct exploits including nanocellulose, due to the high cellulose content comparable to woody biomass and valuable co-products (hemicellulose, starch, polyphenols, and lignin). Thus, compared to the woody biomass, biorefinery exploits for the mango seed focused on the comprehensive fractionation and conversion into bioproducts and the nanocellulose offers additional advantages of enhancing the economic exploits through the additional product recoveries. However, the conventional nanocellulose production processes involving controlled sulphuric acid treatment of bleached cellulose-rich Kraft pulp, degrades the valuable components of polyphenols, lignin, and hemicellulose, and the sulphuric acid applied lowers the thermal stability of the nanocellulose thereby limiting its application in thermo-processing. In addition, due to the different biomass components responding differently to process conditions and the specificity of optimal extraction conditions for each product, challenges of low product yields and qualities could be envisaged for non-optimized extraction processes. Thus, establishing appropriate and optimal multi-step fractionation/conversion processes for the multi-product biorefinery schemes is essential for the sustainable recovery of the bioproducts. Therefore, this study aimed at developing multi-step biorefinery schemes for fractionating mango seed into high-value products such as hemicellulose, lignin, starch, cellulose, and polyphenols. Furthermore, produce nanocellulose from the cellulose fibers using organic acids and compare with the classical sulphuric acid-based process. Additionally, evaluate the potential of the hemicellulose extract as a material for biocomposite film development for food packaging without external additives. A multi-step biorefinery process consisting of sequential organosolv extraction (OE) [ethanol concentration (50–80% v/v), temperatures (20–60°C)], enzymatic hydrolysis (EH) [Termamyl®SC; (300 mL of Termamyl SC per ton starch in MSK) and Saczyme®Plus; (800 ml Saczyme Plus/ ton starch in MSK)] and alkaline pretreatment (AP) [(40–90 °C), NaOH concentrations (1–2 M), time (2–4 h)] for the recovery of polyphenols, starch, and bioactive hemicellulose from mango seed kernel (MSK) while minimizing the degradation of cellulose and lignin in the residual solids was developed. In addition, a multi-step sequential AP and rotor-stator high shear homogenization-assisted organosolv (HSHO) [ethanol concentration (50–70%), temperature (130–150 °C), homogenizing time (10–20 min)] process to recover hemicellulose (xylan/xyloglucan), lignin and cellulose-rich fibers from mango seed husk (MSH) was developed. The feasibility of the MSH hemicellulose extract to form self-supporting biocomposite film without external additives as applicable with xylan-based films was assessed. In addition, the feasibility of producing nanocellulose from the cellulose-rich fibers obtained from the multi-step process via optimized non-catalyzed formic acid-based treatment was investigated. Effect of an alternative CNC production process involving acetic acid treatment [pulp-to-acid ratio (1:20–1:40), reaction time (6–12 h)] on the preparation and acetylation of CNCs from the cellulose-rich fibers was also evaluated versus the combined acetic acid plus high shear homogenization and the classical sulphuric acid-based process. Results from the optimized multi-step sequential OE, EH, and AP process route for the fractionation of MSK led to the recovery of polyphenols, starch, bioactive hemicellulose, and solid residue enriched in cellulose and lignin. The optimized OE process (64.99%w/w ethanol, 54.18 ºC) resulted in an extract with total polyphenol content (TPC) and antioxidant activity (AA) of 95.21 mg GAE/g and 84.69% respectively with >90% cellulose, lignin, starch, and hemicellulose retention in the residual solids. The EH of the OE process resulted in >90% starch removal (as simple sugars). The optimized conditions for the subsequent AP of the destarched OE solids resulted in >50% hemicellulose recovery with 34.96 mg GAE/g TPC and 55.05% AA, and solids having 88.3% and 91.12% cellulose and lignin retention respectively that could be further valorized to increase the product range from the MSK. At the optimized AP process conditions (1.92 M NaOH, 86.0 °C, and 3.84 h), the recovered MSH hemicellulose extract possess suitable properties for thermally stable biocomposite film for food packaging. Subsequently, at the optimized HSHO pretreatment conditions (60% ethanol, 148.41 ºC, 15 min homogenization), over 70% lignin dissolution with high purity (>95%), 3247 g/mol molecular weight (Mw), and 298 ºC maximum thermal degradation temperature (Tmax) were obtained based on the AP MSH. The recovered solids post-HSHO process had >77% cellulose with fibers separated into individual strands of diameters <1 to 10 μm, and >55% crystallinity suitable for CNC production. Thus, the multi-step sequential AP and HSHO biorefinery route is promising for multi-products recovery in addition to the cellulose-rich material for CNC production.