The Influence of Deacidification on Groundwood Paper
| Main Author: | |
|---|---|
| Format: | Article |
| Language: | English Slovak |
| ISBN: | ISBN 80-227-1942-0 |
| Online Access: | http://www.viks.sk/chk/wpp3_2003.doc |
| Abstract: | SUMMARIES. The newsprints of low quality form a special group of groundwood papers were tested. Such papers have not been made for long-term storage in archives and libraries. Several factors influence the degradation of groundwood paper. There are two main degradation processes: acid hydrolysis of cellulose and oxidation/ photooxidalion of cellulose and lignin. The rescue of groundwood paper is nowadays a first-rate problem. The most endangered is the lifetime of papers from the last century, but very short live time of modern papers (1) makes the solving of this problem very urgent. In our libraries almost 75 % of book items are of such type of paper (2). Since acidity of these papers is a main reason for their disintegration, deacidification is a crucial step lo be done for their rescue. Other important factors of cellulose and lignin degradation are reactions in alkaline medium after deacidification of paper (3). On the other hand light induced oxidation reactions have significant degradation influence on the molecule of lignin (4). Under the influence of UV radiation the groundwood papers yellows and under the light with longer wavelenghts the main fotooxidation reaction is bleaching. In real situation these processes are in dynamic equilibrium (5). Complicated structure of lignin is changing and various low-molecular weight degradation products with chromophoric properties split off consequently. These degradation products stay in paper and significantly influence the lifetime of groundwood papers. The presence of free phenolic hydroxyl groups and C-carbonyl groups in lignin are needed for the course of light induced radicals reactions (6). Other important factors of cellulose and lignin degradation are hydrolytic and light induced photo-reactions in alkaline medium after deacidification of paper (7). In these work we tried to describe the influence of acid medium on mechanical properties of groundwood papers in the conditions of dry accelerated ageing (AA) before and after deacidification with methyl methoxymagnesium carbonate (MMMC) in metha-nol (8.9). In this experiment we modelled the course of natural ageing corresponding to 100 years (10). On the same paper samples we studed influence of sunlight on mechanical properties of paper in conditions, which reflect the most resemble the reality of presentation of documents in libraries and archives. Comparing the results we tried to evaluate both main degradation factors of groundwood paper-acid hydrolysis and light induced oxidation before and alkaline hydrolysis and photooxidation of lignin after deacidification (11). CONCLUSION. Deacidification ˙ deacidification with MMMC leads to significant shift of medium to the alkaline area and to significant yellowing. ˙ substantial part of yellowing is extractable and includes even non-oxidative degradation products of lignin. ˙ neutralization inhibits oxidation reactions. ˙ deacidification of paper hinders the acid hydrolysis of cellulose, but it facilitates lignin degradation. ˙ neutralization agent MMMC binds to lignin and causes the increase of yellowing. ˙ deacidification considerably slows down thermo-oxidation reactions. Accelerated ageing (AA) ˙ certain deterioration of the mechanical qualities of paper in the first stage of AA can be a reaction of oxidative degradation of paper. ˙ considering the presence of sulfuric acid in the paper during AA, the hydrolysis and oxidation go on simultaneously, with bigger share of hydrolysis. ˙ during AA the papers being under the influence of acid hydrolysis loose their mechanical strength very quickly. ˙ on the other hand, it is necessary to note that deacidification of modern newsprints, respectively their production on neutral or alkaline papers, has considerably positive influence on their lifetime in a process of long-term storage, despite the presence of lignin. Photooxidation ˙ we presume that the schare od cellulose in degradation reactions of groundwood papers is low and obtained knowledge is mainly a picture of lignin degradation ˙ acid degradation products can be extracted from paper ˙ paper significantly yellows ˙ in some types of paper the long-term irradiating by daylight can have bleaching effect ˙ light induced oxidation is manifested by big creation of carbonyls ˙ intense deterioration of the mechanical qualities takes place already shortly after irradia- tion and this deterioration is crucial for the strenght of paper. Mainly light induced oxidation reactions of lignin. less the hydrolytic reaction of cellulose and lignin share in the deterioration ˙ alkaline medium inhibits the cration of carbonyls in the process of light induced oxidation of lignin, but increase the share of hydrolysis reaction in the degradation of paper ˙ inhibition effect on the course of light induced oxidation of lignin is probably caused by the presence of Mg ions in paper. The ions bond to phenolic hydroxyl groups which hinders their change into the reactive phenolic radicals ˙ deacidifiction increases the yellowing of paper ˙ deacidification has significantly unfavourable influence on the mechanical qualities of modern and historic groundwood papers ˙ unfavourable influence of light on the lifetime of groundwood papers is considerably bigger then we expected. ˙ deacidification groundwood papers results in good conditions for their storage in dark rooms, but limits their utility for presentations in museums, galeries, libraries and archives. W 1 ˙ very low UV radiation content in the light used for irradiation induced oxidation reactions take place to small extent even on cellulose ˙ pH is not changing during irradiation ˙ amount of color extracable agents is very low and witnesses the low reactivity of cellulose ˙ brightness of paper is not significantly changing during irradiation ˙ paper has low carbonyl content ˙ after deacidification with MMMC there is an inhibition of creating of carbonyls. This inhibition is probably considerably caused by the anti-oxidant effect of Mg ˙ deacidification with MMMC has very positive influence on the strenght of paper made from pure cellulose, but even on handmade papers |
|---|---|
| ISBN: | ISBN 80-227-1942-0 |
