Browsing by Author "Bester, Lia Mari"

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    Development and optimisation of a process for cellulose nanoparticle production from waste paper sludge with enzymatic hydrolysis as an integral part
    (Stellenbosch : Stellenbosch University, 2018-12) Bester, Lia Mari; Chimphango, Annie F. A.; Görgens, J. F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The identification of low-cost and renewable resources is critical to meet environmental concerns associated with fossil-based materials. Waste pulp and paper fibres is a renewable, low-cost, cellulose-rich resource with potential for the production of cellulose nanoparticles. Cellulose nanoparticles are light materials that have desired properties such as biodegradability, non-toxicity, electrical conductivity and high tensile strength. Current production methods involve enzymatic, mechanical pressure and/or chemical treatments. This project developed and optimised a process of enzymatic hydrolysis of waste paper sludge for cellulose nanoparticle production. Based on content of inorganics, two types of paper sludge (PS) from South-African paper and pulp mills, namely printed recycle PS and virgin pulping PS were selected as feedstocks. Commercial enzymes were screened for lab scale enzymatic hydrolysis of PS to cellulose nanoparticles. A cellulase cocktail, Cellic® CTec2, and a monocomponent endoglucanase, FiberCare® R, were preferred commercial enzymes for nanoparticle formation and minimisation of by-product formation for both PS feedstocks. Multi-response statistical optimisation of enzymatic hydrolysis of both feedstocks were conducted, investigating solids loading, hydrolysis times and different ratios of the Cellic® CTec2 and FiberCare® R. Optimised enzymatic hydrolysis conditions based on the mean cellulose particle size and the glucose concentration models indicated that FiberCare® R dosage, Cellic® CTec2 dosage, hydrolysis time and solids loading of 75 ECU/gdPS, 10 FPU/gdPS, 9 hrs and 3% (w/w), respectively were optimum for virgin pulp PS. These optimised conditions resulted in mean cellulose particle size and glucose concentrations of 232 nm and 5.44 g/L, respectively. Selected conditions for printed recycle PS required higher FiberCare® R and Cellic® CTec2 dosages of 100 ECU/gdPS and 20 FPU/gdPS, respectively, at longer hydrolysis times of 12 hrs and a higher solids loading of 6% (w/w). At these selected conditions a mean cellulose particle size and glucose concentrations of 226 nm and 6.38 g/L, respectively were achieved for printed recycle PS. Spherical cellulose nanoparticles (SCN) were produced by these mentioned conditions of both enzymatically-hydrolysed PS feedstocks. Microfiltration of hydrolysed supernatant through a 0.45 μm membrane increased the cellulose nanoparticle quality with decreased mean particle sizes and improved particle size distributions for both PS feedstock. Addition of a high-shear homogenization step subsequent to enzymatic hydrolysis marginally decreased the mean size of microsized particles, with no effect on samples with particles smaller than 1000 nm. Dialysis of the hydrolysed suspensions with a membrane with cut-off molecular weight of 12400 Da improved the purity of produced cellulose nanoparticles. Washing and centrifugation of isolated cellulose nanoparticles from residual hydrolysed solids further increased purity and quality. After purification, final cellulose nanoparticle yields of 7.5% for virgin pulp PS and 6.9% for printed recycle PS were achieved. Microfiltration of hydrolysed supernatant through a 0.45 μm membrane increased the cellulose nanoparticle quality with decreased mean particle sizes and improved particle size distributions for both PS feedstock. Addition of a high-shear homogenization step subsequent to enzymatic hydrolysis marginally decreased the mean size of microsized particles, with no effect on samples with particles smaller than 1000 nm. Dialysis of the hydrolysed suspensions with a membrane with cut-off molecular weight of 12400 Da improved the purity of produced cellulose nanoparticles. Washing and centrifugation of isolated cellulose nanoparticles from residual hydrolysed solids further increased purity and quality. After purification, final cellulose nanoparticle yields of 7.5% for virgin pulp PS and 6.9% for printed recycle PS were achieved.