Spectroscopic Characterization of the Fluorescence of Paper at the Wet-Dry Interface
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_3_01_133_145.doc |
| Abstract: | Summaries. Changes in the fluorescence of an additive-free cotton cellulose paper in which a wet-dry interface has been created by capillary action using distilled water under static air have been characterised spectroscopically. Fluorescence was measured on the surface of the paper at the wet-dry interface, where a fluorescent tide line developed. Measurements were also carried out on the areas both above (original paper) and below (extracted paper) the wet-dry boundary. The fluorescence spectra recorded on the three different areas showed the same spectral distribution with excitation maxima at 260, 340, and 385 nm (Em = 500 run), and a single emission maximum at 440 nm (Ex = 254 and 340 nm). The intensities of the spectra recorded at the wet-dry boundary were approximately three times higher than those recorded on the original paper. Furthermore, a decrease in fluorescence intensity was observed for the extracted paper in comparison to the original paper. These results show that the migration and concentration of a fluorescent compound already present within the paper contributed to the enhanced fluorescence observed at the wet-dry interface. Spectroscopic analysis of the aqueous extract of the fluorescent tide line confirmed the presence of a water-soluble fluorescent compound. The results of this study are discussed in relation to the more general phenomenon of fluorescence accompanying the discoloration of paper. Conclusions. The spectroscopic characterisation of fluorescence at the wet-dry interface in Whatman No.l filter paper showed excitation maxima at 260, 340, and 385 nm (Em = 500 nm), and a single emission maximum at 440 nm (Ex = 254 and 340 nm). Transport and concentration of a water-soluble, fluorescent compound contributed to the formation of a fluorescent tide line at the wet-dry interface. Because Whatman No.l is an additive-free paper, made of purified cotton linters, the fluorescent species is likely to be a cellulose degradation product formed in the course of manufacturing and/or during natural ageing of the paper. The results also indicated that if oxidative degradation of cellulose at the wet-dry interface, yielding fluorescent species, did occur within the time-scale of the experiment, the chromophoric structure of the reaction products should be equivalent to that of the already existing fluorescent compound. The spectral similarity between the degradation-related fluorescence of paper observed in relation to the wet-dry interface, foxing stains and artificial ageing, suggests a common degradation mechanism at some level. It is possible that the fluorescent species is a product of hydrolytic and/or oxidative reactions of cellulose, which invariably take place in the course of degradation promoted by different factors. Subsequent oxidation and condensation reactions undergone by that fluorescent species may contribute to the discoloration of paper. |
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| ISSN: | ISSN 0034-5806 |
