Development and optimisation of a process for cellulose nanoparticle production from waste paper sludge with enzymatic hydrolysis as an integral part

Bester, Lia Mari (2018-12)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

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.

AFRIKAANSE OPSOMMING: Die identifisering van laekoste en hernieubare hulpbronne is van kritieke belang om te voldoen aan die groeiende omgewingsbekommernisse wat verband hou met fossielgebaseerde materiale. Afvalpulp en papiervesels is 'n hernubare, laekoste, sellulose-ryke hulpbron met potensiaal vir die vervaardiging van sellulose-nanopartikels. Sellulose nanopartikels is ligte materiale wat verlangde eienskappe soos biologiese afbreekbaarheid, nie-giftigheid, elektriese geleidingsvermoë en hoë treksterkte het. Huidige produksiemetodes behels ensimatiese, meganiese–druk en/of chemiese behandelings. Hierdie projek ontwikkel en optimaliseer 'n proses van ensimatiese hidrolise vir sellulose-nanopartikels wat vervaardig word uit papierafval. Gebaseer op die persentasie van anorganiese materiaal, was twee soorte papierslyk (PS) van Suid-Afrikaanse papier- en pulp meule, naamlik gedrukte hersirkuleerde PS en reinpulp PS gekies as roumateriaal. ‘n Siftingsproses op grond van die gebruik van kommersiële ensieme vir laboratoriumskaal-ensimatiese hidrolise van PS na sellulose-nanopartikels was uitgevoer. Sellulase ensiem, Cellic® CTec2, en monokomponent endoglukanase, FiberCare® R, was betergeskikte, beskikbare, kommersiële ensieme gebaseer op nanopartikels en minimale byprodukvorming vir beide PS-roumateriale. Multi-respons statistiese optimalisering van ensiematiese hidrolise op beide roumateriale was uitgevoer, waartydens soliedemateriaalladings, hidrolise tye en verskillende verhoudings van die Cellic® CTec2 en FiberCare® R ondersoek was. Geoptimaliseerde ensiematiese hidrolise-toestande gebaseer op modelle vir gemiddelde sellulose-partikelgrootte en die glukosekonsentrasie het aangedui dat 'n monokomponent-endoglukanase dosis, sellulase ensiem dosis, hidrolise tyd en soliedemateriaalladings van 75 ECU/gdPS, 10 FPU/gdPS, 9 uur en 3% (w/w) onderskeidelik optimum was vir reinpulp PS, wat tot gevolg gehad het ‘n onderskeidelike gemiddelde sellulose partikelgrootte en glukosekonsentrasie van 232 nm en 5.44 g/L. Die gekose toestande vir gedrukte hersirkuleerde PS benodig hoër dosisse vir monokomponent-endoglukanase en sellulase ensieme van 100 ECU/gdPS en 20 FPU/gdPS, onderskeidelik met langer hidrolise tye van 12 uur en 'n hoër soliedemateriaallading van 6% (w/w). By hierdie gekose toestande was 'n onderskeidelike gemiddelde partikelgrootte en glukosekonsentrasie van 226 nm en 6.38 g/L vir gedrukte hersirkuleerde PS behaal. Sferiese sellulose nanopartikels (SSN) was geproduseer deur bogenoemde toestande van beide ensiem-gehidroliseerde PS-roumateriale. Mikrofiltrasie van gehidroliseerde supernatant deur 'n 0.45 μm membraan het die gehalte van sellulose nanopartikels verhoog met verminderde gemiddelde partikelgroottes en verbeterde partikelgrootteverdelings vir beide PS-roumateriale. Toevoeging van 'n hoë-skuif homogenisasie stap verminder die gemiddelde grootte van mikro-grootte partikels, maar het geen effek op die monsters met partikels kleiner as 1000 nm nie. Dialise van die hidroliseerde suspensies met 'n membraan met 'n afsny molekulêre gewig van 12400 Da, het die suiwerheid van geproduseerde sellulose-nanopartikels verbeter. Was en sentrifugasie van geïsoleerde sellulose-nanopartikels uit residuele hidroliseerde vastestowwe het verder die suiwerheid en kwaliteit verhoog. Na suiwering was’n uiteindelike sellulose nanopartikels opbrengs van 7.5% vir reinpulp PS en 6.9% vir gedrukte hersirkuleerde PS behaal. Deur gekontroleerde alleenstaande ensimatiese hidrolise toestande, kan 'n geselekteerde sellulose nanopartikeltipe, insluitende sellulose nanokristalle (SNK) en SSN vervaardig word wat voordelig is oor die alleenstaande suurhidrolise-proses, wat slegs 'n mengsel van SNK en SNF produseer. Verder is 'n voorgestelde meganisme vir die vorming van sferiese sellulose-nanopartikels uit sellulase-hidrolise van hoër sellulose-kristallisiteits-materiale geformuleer vir spesifiek korttermyn-hidrolise met 'n hoër endoglukanase tot eksoglukanase-verhouding.

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