Abstract
In the laundry industry, colorimetry is a common way to evaluate the stain removal efficiency of detergents and cleaning products. For ease of visualization, the soiling agent is treated with a dye before measurement. However, it effectively measures the dye removal rather than stain removal, and it cannot provide depth-resolved information of the sample. In this study, we show that full-field (FF) optical coherence tomography (OCT) technique is capable of measuring the cleaning effect on cotton fabric by imaging the sub-surface features of fabric samples. We used a broadband light-emitting diode (LED) source to power the FF-OCT system that achieves the resolution of 1 µm axially and 1.6 µm laterally. This allows the micron-sized cotton fibres/fibrils at different depth positions to be resolved. The clean, the soiled, and the washed samples can be differentiated from their cross-sectional images using OCT, where the cleaning effect can be correlated with the sub-surface fibre volume. The experimental results of the proposed method were found to be in good agreement with those of the standard colorimetry method. The proposed technique therefore offers an alternative way for measuring the stain removal from fabric substrate to assess the effectiveness of laundry detergent products.
Highlights
The ability to measure and monitor the removal of semi-solid fats or oils from substrates is important for the assessment of the effectiveness of the current surfactant systems for stain removal
We demonstrate for the first time that FF-optical coherence tomography (OCT) is able to resolve the removal of oily and fatty stains in fabrics, which have been subjected to cleaning processes
We investigate the feasibility of using OCT cross-sectional images (B-scans) to discriminate between the cleaning effect of the washed and unwashed fabrics
Summary
The ability to measure and monitor the removal of semi-solid fats or oils from substrates is important for the assessment of the effectiveness of the current surfactant systems for stain removal. Colorimetry, the science of color measurement, has been widely employed for wash studies to quantify color and to derive color differences from the soiled samples before and after washing [1,2,3]. The colors of tested fabric can be measured by using a spectrophotometer and recorded numerically in terms of color formulae such as the CIE L*a*b* (known as CIELAB) color space. This colorimetric method is easy to use, but it requires the stains or soils to be colored for the level of removal to be measured. The colorimetry method does not provide depth-resolved information of the sample either
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