Design and production of functional hydrogels for microbial and pest control

Abstract

A Malodour Control (MOC) hydrogel has been designed to reduce and inhibit sulfate-reducing bacteria, and a separate controlled-release hydrogel has been designed to kill mosquito larvae. This study focuses on designing and optimising these two hydrogels to control the two species mentioned above. A comprehensive study on MOC hydrogel production has been carried out first to analyse the temperature profile along with the production and calculate the heat of reaction of hydrolysis. It has been observed that when nitric acid concentration is increased, the amount of heat generated from the reaction gradually reduces and when the TEOS percentage is raised, the amount of heat generated from the reaction has risen. Effects of temperature, thickness, and NaClO₂ concentration on the MOC hydrogel's gelation time also have been analysed. Simultaneously, experiments have been implemented in order to optimise the formulation of MOC hydrogel. The effect of AS40 on current hydrogel has been analysed and determined that producing the gel without AS40 does not change the gel's texture. In addition to that, to reduce thymol separation from the gel, the effect of tween 20 has been examined. It has been discovered that thymol is not separated from gel when 0.003 vol.% of tween 20 has been added. ASPEN Plus simulations have been performed for the continuous reactor for MOC hydrogel production. Using Aspen Plus V9 software, the continuous flow reactor has been simulated. The amount of heat dissipated during the hydrolysis reaction has been calculated as 0.1245 kJ/g TEOS, a similar value obtained from experiments (0.1018 kJ/g TEOS). A lab-scale continuous production set up was assembled, which produce about 5 litres of the hydrolysed solution in one hour. Separate controlled-release hydrogel beads have been designed to kill mosquito larvae using chlorine dioxide. Chlorine dioxide aqueous solution has been proved safe to humans and the environment and can effectively kill mosquito larvae. This study demonstrates a hydrogel which kills larvae by releasing encapsulated chlorine dioxide. The larval mortality was checked at different time intervals with different weighted gel beads. According to the results obtained, when 10% (v/v), i.e. 100g/L gel beads are used, 100% larval mortality is achieved in 3 days.

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	King Lun YEUNG (Supervisor) & Wei HAN (Supervisor)