The Development of Chitosan Microspheres for Use as Agrochemical Delivery or Agropollutant Adsorption Systems

The aim of this thesis was the development of a hydrogel bead agrochemical delivery system for the nitrification inhibitor, dicyandiamide (DCD) and the development of a hydrogel bead adsorption system for the herbicide, paraquat. The hydrogel bead was based on the biopolymer chitosan which was protonated in order for it to be soluble in water. The aqueous chitosan solution was then used to form hydrogel beads, either by precipitation with NaOH solution or by crosslinking. The resulting chitosan hydrogel beads were loaded with DCD and their release properties investigated using UV/vis spectroscopy. It was found that chitosan hydrogel beads formed by precipitation or ionic crosslinking only exhibited uncontrolled DCD release while chitosan hydrogel beads covalently crosslinked exhibited controlled DCD release. The factors influencing the rate of DCD release from the beads such as, pH, release medium temperature and crosslinking agent, were investigated. N-acylated chitosan hydrogel beads were synthesised and then characterised using a range of techniques including scanning electron microscopy, Fourier-transform infrared spectroscopy, elemental analysis and differential scanning calorimetry. The N-acylated chitosan hydrogel beads were loaded with DCD and their release properties investigated using UV/vis spectroscopy. It was found that these beads exhibited controlled DCD release. The factors influencing the rate of DCD release from the beads such as, pH, release medium temperature and degree of substitution, were investigated. Chitosan hydrogel beads crosslinked with p-sulfonatocalix[4]arene sodium salt were synthesised. These beads were formed in order to investigate their potential use as a pollution remediation technology, as p-sulfonatocalix[4]arene sodium salt is known to form a stable inclusion complex with a herbicide called paraquat. The hydrogel beads were characterised using scanning electron microscopy and energy dispersive X-ray analysis. Adsorption experiments were performed using UV/vis spectroscopy and it was found that they were capable of removing paraquat from aqueous solution