AbstractThe current state of the art in respiratory protection uses cartridges of packed adsorbent beads to provide protection from chemical respiratory hazards. These cartridges impose a significant pressure drop, which has a physiological impact on the user. This work seeks to reduce this impact by developing a new material to contain the adsorbent in the cartridge instead of packed beads. This material was a polymeric foam, using polymer to contain and support a chosen adsorbent powder within a foam matrix. Foams can offer lower pressure drop and the ability to mould the material into any desired shape.
Polyimide and polyurethane foam formulations were developed, which proved capable for the first time of containing significant amounts of 13X adsorbent powder. Polyimide formulations proved capable of containing 67 wt% 13X but were superseded by polyurethane formulations containing 75 wt% 13X. These polyurethane formulations were further modified with additional surfactant to give control over the density and pressure drop of the resulting foams, improving their adsorption density. A novel heat treatment technique was developed to improve the accessibility of the adsorbent in the foams and to
increase the mass of adsorbent in the foam after production.
Polyurethane 13X foams were investigated by use of adsorption breakthrough testing with 1000ppm n-butane and isotherm measurements with cyclohexane using the Thomas model to extract mass transfer data from the breakthrough curves. True adsorbent mass loadings of the materials were measured via a thermogravimetric analysis technique developed during the research to dry the samples and burn off the polymer fraction. Pressure drop behaviour was investigated by use of flowing air through dry cylindrical foam samples. Scanning electron microscopy was used to measure bubble and window sizes of the foams
produced and helium pycnometry to measure the void fraction of the foams.
Heat treated foams showed isotherm uptake of up to 11.5 wt% cyclohexane based on total composite weight, compared to 17.0 wt% for 13X powder and 20.6 wt% for commercial 13X beads. Kinetic accessibility of the foams was found to be up to -4.236x10-7 ppm-1s-1 compared to -5.11x10-7 ppm-1s-1 for the commercial beads, showing inferior adsorption performance. However this was balanced out with superior pressure drop characteristics with the PU-13X foams, with activated foams showing pressure drops as low at 7.59% of the adsorbent beads. A literature model for pressure drop through the foams by Dietrich
(2012) was modified to create a new model which was used to successfully predict pressure drop through the PU-13X foams. Void fraction of the foams was found to be the critical physical parameter governing pressure drop.
Combining pressure drop and adsorption data found that the superior pressure drop could compensate for the lower adsorption uptake offered by the foams compared to the commercial beads, as long as the foams had a high mass density. One PU-13X foam offered this required density, a sample which had used additional surfactant in the formulation in order to suppress foam formation to make a significantly more dense material. This work developed the techniques for creating a successful PU-13X adsorbent foam, including both
their formulation and heat treatment. This work also identified the control variables for these processes, outlining the path for further adsorbent foam development.
|Date of Award||28 Apr 2021|
|Sponsors||Defence Science and Technology Laboratory|
|Supervisor||Barry Crittenden (Supervisor), John Chew (Supervisor) & Semali Perera (Supervisor)|