Distinguishing liquid ammonia from sodium hydroxide mercerization in cotton textiles

Abstract

The question addressed in this paper is whether cotton textiles mercerized with liquid ammonia (L-NH3) can be distinguished from NaOH mercerized cotton textiles with FTIR-ATR spectroscopy. In collaboration with a process-house, cotton textiles were treated with L-NH3, NaOH, neither or both. The treatment conditions were set to mimic commercial-scale operations. The samples were then analyzed with FTIR-ATR spectroscopy, and for comparison, also with powder X-ray diffraction. The analyses were aimed at detecting changes in the cellulose crystal lattice structure that result from the two mercerization processes. The measured spectra and diffractograms were evaluated both visually and with Principal Component Analysis (PCA), and the results show that with FTIR-ATR spectroscopy it was possible to differentiate between the untreated, L-NH3 mercerized and NaOH mercerized textiles, whereas with X-ray diffraction it was difficult to detect differences between the untreated and treated samples. The better performance of FTIR-ATR spectroscopy is attributed to the method being more sensitive to changes on sample surfaces, whereas X-ray diffraction results are more representative of the sample bulk. The samples were treated under conditions mimicking commercial-scale operations, which are optimized to maximize treatment speed. Hence, the mercerization induced changes are likely to be limited to sample surfaces and hence detectable with FTIR-ATR spectroscopy but not with X-ray diffraction. It is reported that Sum Frequency Generation Vibrational Spectroscopy, another surface-limited analytical method, may also be employed for detection of mercerization type, but FTIR-ATR spectroscopy has the advantages of ease of operation and the devices are less expensive.