One of the most enduring areas of surface technology is fabric modification, which is performed to add or enhance the properties or performance of a fabric. For several years garments have been coated with different coatings to increase their waterproofing capabilities, and for fiber conditioning to make them very soft. Recently fabric surfaces have been treated with nanomaterials to optimize UV protection factor, stain resistance, or anti-bacterial properties.
Surface treated samples can be suitably analyzed using X-ray photoelectron spectroscopy (XPS). XPS, also called as electron spectroscopy for chemical analysis (ESCA), is capable of finding the chemical composition from the outer 10 nm of the surface of a material. Both fabrics and fibers can be analyzed using this technology, as it can analyze both the conducting and insulating samples without special sample preparation. This article discusses the application of the Thermo Scientific K-Alpha surface analysis system (Figure1) in the study of the surface treatment of polyester fabric.
Figure 1. The Thermo Scientific K-Alpha
The sample used for the analysis was a 25 × 50 mm piece of polyester lint-free cloth. A soft furnishings protector was sprayed on half of the cloth, which was then allowed to dry in air. This cloth was then placed on the standard 60 × 60 mm K-Alpha sample holder using four clips (Figure 2). The fabric protector is optically invisible on a dry cloth and its position can only be found analytically. The sample was designed to simulate a production failure, caused by an inconsistent application of the transparent coating onto the sample fabric.
Figure 2. Mosaic view of polyester sample mounted on the K-Alpha sample holder
Analysis of a point in each half of the sample was completed, using a 400 µm X-ray spot to obtain quantified elemental data of untreated and treated areas on the sample in order to compare their chemical compositions. The involvement of the insulating samples required the use of the K-Alpha turnkey charge compensation system. The electrons lost from the surface due to the photoelectric effect are replaced by this system. Surface charge buildup that could affect the acquired data can be avoided.
The K-alpha spectrometer is extremely useful in the analysis of insulators, but is not needed for conducting samples. The user-friendly system can retain uniform analysis conditions across even the most difficult sample set. The 400 µm X-ray spot, with a 400 µm step size was used to map a 16 × 12 mm sample area, which is depicted in green in Figure 2. The C1s, O1s, Cl2p, F1s, N1s, Si2p and S2p regions were recorded in all analysis positions using the 128-channel detector, operated in snapshot acquisition mode. This reduces the total acquisition time, without compromising chemical information.
The elemental quantification of untreated and treated parts of the polyester sample, given by the survey scans is shown in Figure 3. The elemental composition of the untreated sample is in good agreement with cleaned polyester. However the composition of the treated sample shows the presence of elements from compounds on the treated surface, such as fluorine and sulfur from perfluorobutane sulfonic acid and silicon from silicone and nitrogen.
Figure 3. Overlay of survey scans on untreated and treated areas of the polyester sample
Figure 4 displays the atomic percent maps of the different chemical states of each of the elements identified in the survey scan. The untreated part of polyester in the top 3 mm, and the treated part in the lower section are clearly distinguished in the atomic percent chemical maps.
Figure 4. Atomic percent chemical maps of each chemical state over an interface area between treated and untreated parts of the sample
Figure 5 shows the averaged C1s spectra from the treated and untreated side of the sample. The anticipated components for polyester are shown by the untreated C1s spectrum. A decrease in the amount of C-O and C=O is evident in the treated spectrum, representing the presence of the ester groups in the untreated region. An increase in C-F bonding is also observed in the treated spectrum, representing the contribution of the perfluorobutane sulfonic acid in the fabric protector.
Figure 5. Averaged C1s spectra from the treated and untreated side of the sample
The chemical map overlay can then be created by overlaying these chemical maps on the optical view of the sample as illustrated in Figure 6.
Figure 6. Atomic percent chemical maps overlaid on the optical image of the sample.
XPS is suitable to analyze areas applied with undetectable surface modification, like a fabric protection coating, and to find the amount of coating applied as it is a quantifiable, surface sensitive, analytical method. The application of invisible coatings on fabrics and other materials can also be quality controlled using XPS to evaluate whether the coatings have been applied homogeneously.
This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Materials & Structural Analysis.
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