The aim of this study is to assess the performance of fluorinated material treatment methods, in terms of wash-resistance, by surface analysis methods.
Four different materials and two different fluorination methods were investigated in order to produce durable, high-performance clothing systems for outdoor use. For some time, fluorinated fabrics have been utilized in outdoor sportswear because of their breathability and liquid-repelling properties1.
Considerable research has been carried out into methods that can give low-cost textiles these properties. An important quality for these kinds of textiles should be the capability of the material to regain or retain its liquid-repellent nature after traditional washing cycles.
X-ray photoelectron spectroscopy (XPS) was used, in addition to other techniques, to investigate the surface properties of the treated materials. Identification of high amounts of fluorinated surface components indicated that the test material had the coating treatment.
First, samples of the test materials were subjected to the fluorinated surface treatments, and these were then analyzed by XPS to verify surface coverage of the fabrics. The samples were then boil-washed in traditional detergents, dried, and re-analyzed to ascertain the performance of the coating treatments.
The test materials consisted of four different fabrics: cotton (c), nylon (ny), nomex (no), and polyester (p). The fabrics were coated with either a fluorinated plasma polymer (named plasma), or a proprietary solution-based treatment (named fluorosolvent). The treatment processes are highlighted below:
- Solution-based treatment (fluorosolvent): The fluorinated coating, in solution form, was applied to the fabric surface. The fabric was methanol-rinsed and dried in air.
- Plasma Polymer (plasma): Using an electrically-pulsed, non-equilibrium, inductively-coupled glow discharge2, the fluorinated plasma polymer was applied to the fabric. The fabric was then kept in a clean glass reactor vessel, and a trapped rotary pump was used to evacuate the chamber.
When the base pressure was attained, the fluorinated monomer was transferred into the chamber at a fixed leak rate. A 13.56 MHz radio frequency source, inductively coupled to the plasma chamber, was employed to ignite a glow discharge in the chamber. Electrodes were positioned on the exterior of the reaction chamber to prevent unnecessary contamination issues.
The discharge was typically maintained for 10 minutes treatment time. The plasma was extinguished, but the monomer vapor was made to flow into the reactor system for 2 minutes more. Then, the vapor was isolated, and the chamber was pumped back to the base pressure.
After the surface treatment, the fabric samples were boil-washed in water consisting of a readily available detergent. The wash was carried out between one and five times. Later, the fabric samples were ironed or air-dried.
The AXIS Supra X-ray photoelectron spectrometer from Kratos Analytical was used to perform the surface analysis of the treated fabric samples. Efficient charge neutralization and high energy resolution were particularly important because of the complex surface chemistry of these samples. Kratos’ patented3 coaxial charge neutralization system was employed to reliably neutralize surface charge, and is described elsewhere.4
Figure 1 shows a typical survey spectra obtained from the plasma-treated nylon sample.
Figure 1. Survey spectrum of plasma-treated nylon, demonstrating a large amount of fluorine incorporation.
A high resolution C 1s spectrum was recorded at 10 eV pass energy from the same sample (Figure 2). The spectrum shows the exceptional spectral resolution obtained by the spectrometer on these irregular, highly insulating samples.
Figure 2. High resolution C 1s spectrum of plasma-treated nylon showing excellent resolution and charge neutralization.
The resolution helps detect the presence of many of the chemical functionalities: C-H; C-CF/C-CO2; C-CFn/C-O; C-F/C=O; CF-CFn/CO2; CF2; and CF3
Figure 3 presents a comparison of the percentage of fluorine detected on plasma-treated and fluorosolvent fabric. It is shown that, generally, plasma-treated fabrics had greater fluorine incorporation.
Figure 3. F content of treated fabrics, plasma treatment works best.
Polyester-treated material proved to be an exception, with comparable amounts of fluorine coverage on both samples. The relative amounts of the CF2 chemical functionality present on the fabric surfaces are shown in Figure 4.
The greatest amount of CF2 incorporation was obtained from plasma treatment. The plasma treatment was also apparently less substrate-dependent than the fluorosolvent treatment. Figure 5 shows that the C 1s spectra from all plasma-treated textiles looked similar for all the textiles: cotton, nomex, nylon, and polyester.
Figure 4. CF2 content of treated fabrics.
Figure 5. High resolution C 1s spectra of plasma-treated fabrics, demonstrating the substrate-independent nature of the plasma coating process.
It was found that after five washes, the fluorosolvent-treated fabrics lost much of their surface fluorine coverage (Figures 6 and 7). Approximately half of this fluorine loss was reversed in all cases by ironing. This showed that some of the reduction in surface fluorine was caused by the rearrangement of the water-repellent fabric fibers in aqueous solution, and not due to permanent loss of coating. This rearrangement was reversed to some extent by heat treatment.
Figure 6. F content of fabric after fluorosolvent treatment, 1 wash, 5 washes, and 5 washes and ironing.
Figure 7. High resolution C 1s spectrum of fluorosolvent-treated nylon (black) after 1 wash (blue) and 5 washes (red), demonstrating loss of surface coating.
Better fluorine group retention was seen from the XPS results for the plasma-coated textiles than for fluorosolvent-treated textiles after washing for all fabrics, except for cotton. This is shown in Figure 8. Moreover, nearly all the fluorine group losses observed following the washing cycle were reversed by ironing plasma-coated nylon, nomex, and polyester.
Figure 8. F content of fabric after plasma treatment, 1 wash, 5 washes, and 5 washes and ironing.
XPS surface analysis has been utilized to support the development of fabric surface treatments. It was found that plasma polymerization of a fluorinated monomer molecule was a viable method for producing a durable fluorine surface coating on various types of textiles.
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References and Further Reading
- Kissa, E. In Handbook of Fibre Science and Technology, Part B ed.; Lewin, M.; Sells, S. B., Eds.; Marcel Dekker Inc.: New York, 1984; Vol. II, pp. 143-209
- Yasuda, H. Plasma Polymerization; Academic Press, Inc.: London, 1985.
- Kratos Analytical Ltd. US Patent 5286974.
- Kratos Charge Neutraliser Technical Note MO222.
This information has been sourced, reviewed and adapted from materials provided by Kratos Analytical Ltd.
For more information on this source, please visit Kratos Analytical Ltd.