The Influence of Secondary Chromophores on the Light Induced Oxidation of Paper The Influence of Light on Cellulose and Secondary Chromophores
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_1_03_18_35.doc |
| Abstract: | SUMMARIES. The light induced oxidation of cellulose in pure cellulose is caused mainly by UV radiation and, to a lesser extent probably also by visible light (VIS). If some oxidation degradation products as formed in groundwood paper are present, the oxidation of cellulose caused by irradiation with daylight with a partly reduced UV component is sharply increased. This process occurs in a neutral or acidic environment; it is the result of mainly visible light action. It is possible that it refers to an activation of cellulose oxidation in the course of the light induced oxidation degradation of chromophores in a bleaching process. The chromophores lose this activation effect by shifting to an alkaline pH, i.e. by deacidification, in this study done by the methanolic MMC method. Chromophores themselves are submitted to significant light induced oxidation degradation under the influence of visible light, which results in the bleaching of the paper. A UV filter considerably limits the light induced oxidation of cellulose, but does not stop the degradation of the chromophores. CONCLUSION. Light induced oxidation of cellulose, manifested in carbonyl creation, is not accompanied by a significant change in pH or of reflectance, and the increase of degradation products during the process is very small. UV radiation provokes this oxidation more than visible light. UV filtering significantly reduces light induced degradation of cellulose; it limits carbonyl creation and stops the creation of coloured degradation products. Further creation of carbonyls in cellulose is activated by chromophores and depends on their concentration. Visible light in particular provokes the creation of carbonyls. The process is not accompanied by significant changes of pH, of bleaching or of the amount of extractable agents. UV filtering has little influence. Degradation of chromophores occurs under the influence of visible light; UV filtering has no influence. The chromophores are bleached and pH decreases; that means the chromophores are changed to colourless acidic compounds. It seems that this process can initialize the light induced oxidative degradation of cellulose. The composition of the chromophores can make a significant difference: ch2 showed more bleaching, less acidic degradation, a smaller influence of the light induced oxidation of cellulose, and a higher share of UV in the light induced oxidation of cellulose. Providing an alkaline environment promotes the oxidation of cellulose. Further oxidation induced by light, however, is reduced, and it is provoked only by UV. Splitting of the cellulose molecule does not occur and no chromophoric extract-able degradation products are formed. Chromophores in an alkaline environment have no influence on the light induced oxidation of cellulose. This is the most important difference between an alkaline and an acidic or neutral environment. In alkaline paper, bleaching of Chromophores takes place under the influence of visible light, and the use of a filter has no significant advantage. The extent of bleaching and, consequently, the formation of acidic compounds is great, but the alkaline reserve is able to eliminate them. The extent of bleaching of chromo-phores (light induced oxidation degradation) in an alkaline environment is much more significant than in the neutral one. |
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| ISSN: | ISSN 0034-5806 |
