The Degrading Action of Iron and Copper on Paper A FTIR-Deconvolution Analysis
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_4_02_205_221.doc |
| Abstract: | CONCLUSIONS. The FTIR-deconvolution analysis shown in this paper highlights the different pathway of iron and copper degradation. Iron(III) treatment in an acidic medium caused, after artificial ageing, the following reactions (Fig. 7): ˙ Strong hydrolysis of the cellulose chains induced by acidity, with a random attack (decrease of the DPv and absence of low-molecular-weight compounds); ˙ dehydration of the C4-C5 bond, with formation of a C=C group (small peak at 800 cm1); ˙ oxidation of the C6 hydroxyl to CHO and then to COOH (Fig. 7a,b). Together with the second step, this mechanism resulted in the formation of b- The Degrading Action of Iron and Copper on Paper Fig.7. Accelerated ageing (sealed tube technique).of iron-treated paper. Oxycellulose a accounts for the relatively high direct hydrolysis and, together with oxycellulose b, for the formation of the 1660 cm-1 signal; oxycellulose c causes the b-alcoxy fragmentation in CUEN found in Ref.1 unsaturated aldehydes C=C-CHO or acids C=C-COOH, inferred by the presence of the 1662 cm' band. As indicated by the FTIR-deconvolution analysis of the pH 10 washed sample and by the ki and ka values of Table 6, both unsaturated aldehydes and acids should have been present at the same time, and only the latter were ionised by alkalinity, with a low-frequency shift to 1594 cm-1; ˙ oxidation of the C6 hydroxyl without hydrolysis (Fig. 7,11). Copper(II) treatment in an acidic medium caused, after accelerated ageing, the following reactions, where oxidation prevails over hydrolysis, as illustrated in Fig.8: ˙ oxidation to aldehyde of the pyranose ring, with breaking of the C2-C3 bond (although this was the rate-determining step, the ki value was higher than that of the iron-treated sample, indicating a stronger oxidising power of copper), quickly followed by the formation of COOH groups (Fig. 8,1); ˙ random hydrolysis of the cellulose chains (induced by acidity), with an immediate oxidation of the new OH group in the C4 position; ˙ oxidation to COOH in the C6 position. Together with the previous step, this mechanism accounted for the 1622 cm ˙ band by the formation of a b-keto-acid, enol form C(OH)=C-COOH (Fig.8,11), the internal resonance of which disappeared with alkaline washing, when the carboxyl group became a car-boxylate. The relative importance of mechanisms I and II illustrated in Figs. 7 and 8 cannot be inferred from FTIR analysis alone, since the relationship between the actual concentration and the infrared absorbance of CO, CHO and COOH is unknown. Moreover, the absence of a well defined signal of unconjugated aldehydes11' I6 makes it difficult to detect such an important group, therefore, further studies are in progress to better determine the characteristics of oxidized groups. SUMMARY. The Degrading Action of Iron and Copper on Paper: a FTIR-deconvolution Analysis Samples of FeCb and CuCla treated cellulose paper were analysed by FTIR before and after accelerated ageing at 90+-10°C (sealed tube technique). The main mechanism of Fe(III) degradation appeared to be a strong hydrolysis and dehydration of cellulose chains, with formation of a C4-C5 double bond, and C6 oxidation. Cu(II) oxidized the C2- and C3-OH groups to aldehydes and carboxyls, thus opening the pyranose ring, and hydrolyses and oxidized the C4-OR group with the formation of a C4-C6 (5-ketoaldehyde or (3-ketoacid. Among the FTIR-deconvolution bands in the 1250-1850 cnv1 region, the -1660 cm ' signal is attributed to the unsaturated C=C-CO, and the 1612-1622 cnv1 signal to CO-C-CO group (chelate form of the enol tautomer). These bands, which can only be detected by the deconvolution technique, appear more significant than those of unconjugated CO groups above 1700 cnr1. |
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| ISSN: | ISSN 0034-5806 |
