Abstract
Recent advances in high resolution X-ray tomography (μCT) technology have enabled in-situ dynamic μCT imaging (4D-μCT) of time-dependent processes inside 3D structures, non-destructively and non-invasively. This paper illustrates the application of 4D-μCT for visualizing the removal of fatty liquids from kitchen sponges made of polyurethane after rinsing (absorption), squeezing (desorption) and cleaning (adding detergents). For the first time, time-dependent imaging of this type of system was established with sufficiently large contrast gradient between water (with/without detergent) and olive oil (model fat) by the application of suitable fat-sensitive X-ray contrast agents. Thus, contrasted olive oil filled sponges were rinsed and squeezed in a unique laboratory loading device with a fluid flow channel designed to fit inside a rotating gantry-based X-ray μCT system. Results suggest the use of brominated vegetable oil as a preferred contrast agent over magnetite powder for enhancing the attenuation coefficient of olive oil in a multi fluid filled kitchen sponge. The contrast agent (brominated vegetable oil) and olive oil were mixed and subsequently added on to the sponge. There was no disintegration seen in the mixture of contrast agent and olive oil during the cleaning process by detergents. The application of contrast agents also helped in accurately tracking the movement and volume changes of soils in compressed open cell structures. With the in house-built cleaning device, it was quantified that almost 99% of cleaning was possible for contrasted olive oil (brominated vegetable oil with olive oil) dispersed in the sponge. This novel approach allowed for realistic mimicking of the cleaning process and provided closer evaluation of the effectiveness of cleaning by detergents to minimize bacterial growth.
Highlights
Sponges are ubiquitous implements used in household and industrial cleaning tasks thanks to their flexibility and absorption ability
Due to the inert chemical behaviour of magnetite powder with olive oil and their difference in bulk densities, sedimentation of magnetite powder occurred at concentrations higher than 50%
A sample holder with a flow channel and the capability to squeeze and flush the sample was designed to follow the dynamic processes inside the sponge during oil removal
Summary
Sponges are ubiquitous implements used in household and industrial cleaning tasks thanks to their flexibility and absorption ability. For liquid soil (vegetable oil, dissolved proteins, dissolved starch) they can be wicked inside the porous structure due to capillary action. These residues whether on the surface or inside the pores may be used by micro-organisms (bacteria, fungi) as a source of food for their growth, giving rise to biofilm formation over time, and potential hygiene risks. Formulations that are effective in preventing bacterial growth is preferred by ensuring food soils are completely removed inside the sponge. Key to this is the mixture of ingredients in the formulation and the fluid dynamics required for removal. Outcomes from this paper can be used as modeling inputs for the evaluation of how sponge absorbs food soil from dishes into the sponge and how these are subsequently removed and released into the wash solution upon squeezing
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