Production of Biodegradable Microbeads for Controlled Release of Micronutrients

: (Alternative Format Thesis)

Abstract

The burden that plastics put on natural environments is in part due to the persistence of petroleum-derived hydrocarbons. This is an unfortunate by-product of their tough and unreactive nature which has both increased their economic utility due to their elongated lifetimes. As such,there has been an increased focus on producing biodegradable alternatives, from renewable sources and with minimal environmental footprint. Cellulose positions itself well as a suitable alternative: it is both globally available and economically[1] feasible to obtain. There exist multiple vegetal and bacterial sources of cellulose, many of which are obtain from within currently valorised waste-streams. This work sought to increase the use of cellulose within the production of spherical microbeads, to reduce the use of plastics in this field which would reduce the quantity of such microplastics entering into riverine and marine waterways. The contribution of plastic microbeads to environmental pollution is somewhat unique in that their route of disposal is a de facto release of these beads into the environment.

To counter this issue, this work sought to improve the production of cellulose microbeads by investigating droplet production methods that have been overlooked previously. In assessing methods such as rotary jet atomization, it was found that processing issues that have previously hindered droplet production for cellulose solutions - mainly viscosity - could be harnessed to enhance the ability to produce droplets in the microscale range. The physio[1] chemical parameters of cellulose solutions such as cellulose dissolved in solutions of ionic liquid and dimethyl sulfoxide were found to create ideal situations for droplet production by rotary jet atomization, where the use of centrifugal forces on liquid jets caused thinning of the jets to a thin liquid filament. This thinning reduced the size of the subsequent droplets that detached from the liquid filament, in a uniform manner. This stability of this process was further reinforced by the resistance of these droplets to secondary fragmentation. This resilience was due to the high viscosity of solution, which is further elaborated on in this work.

Working towards the applications of such cellulose beads,the use of cellulose microbeads as nutrient delivery mechanisms within the field of agronomy was investigated using cellulose and cellulose derivatives within the macroscale, as preliminary case studies on the nutrient impregnation and release steps. These studies found that cellulose and cellulose acetate beads can achieve uptake and release, with these controlled by their impregnation methods and judicious selection of metal salts with preferable counteranions.

This thesis brings together the innovation in the field of droplet production for the purposes of creating biodegradable microbeads, and widening the potential for these biodegradable micro and macrobeads to replace plastics which are currently used across numerous industrial sectors.