The Influence of Mg on the Light Induced Oxidation of Newsprint
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| Online Access: | http://www.viks.sk/chk/res_4_01_208_227.doc |
| Abstract: | Summaries. The aim of deacidification is to provide an alkaline environment in the paper as a means to guard against acid catalysed hydrolysis. A drawback is that paper in an alkaline environment is sensitive to oxidation. An important effect of deacidifying groundwood paper with methoxy methyl-magnesium carbonate is that some of the Mg is bound directly to lignin, thus significantly inhibiting the light induced oxidation degradation of the paper and increasing its resistance towards irradiation. The amount of this inhibition is about 50%. In choosing the most apt concentration of MMMC solution it should be taken into account that it must be enough not only to neutralize the acid present in the paper and to provide a buffer against acid that will be formed in or picked up by the paper in the future, but enough also to limit the light induced oxidation degradation of groundwood papers to the highest possible degree. Conclusions. Deacidification with various MMMC concentrations results in ˙ considerable increase of alkaline reserve and magnesium content; ˙ remarkable increase of pH; ˙ brightness of groundwood paper is decreased and yellowing increased; ˙ amount of extractable degradation products is increased; ˙ folding endurance is decreased; ˙ pure cellulose paper shows a significant tendency to improved mechanical strength. Deacidification followed by 35-day irradiation: ˙ low concentration deacidification results in lower pH after irradiation than after dark storage. After high concentration deacidification there is no or only little difference between the pH of irradiated and non-irradiated samples; ˙ some groundwood papers show a significant increase of extractable degradation products with increased deacidification concentration; ˙ significant decrease of brightness and increase of yellowing, together with an increase of alkaline reserve; ˙ the brightness of the non-irradiated side decreased as well as the irradiated side, which is related to the diffusion of degradation products through the paper; ˙ folding endurance after irradiation considerably decreases only in modern papers; mechanical properties in historic papers are not further reduced by irradiation; ˙ significant light induced oxidation related to the increase of the amount of carbonyls takes place; ˙ in groundwood paper deacidification with Mg compounds reduces the light induced formation of carbonyls in an amount of 46-57%, if 33-42 mmol Mg/100 g paper are provided; ˙ 5.1-7.6 mol of Mg are necessary to inhibit 1 mol of carbonyls to be formed in the photo-oxidation process. It is important to chose the right concentration of MMMC solution: that which provides the amount of Mg necessary for maximum inhibition of photo-oxidation in groundwood papers; ˙ the Mg-caused inhibition of photo-oxidation in very old groundwood paper is probably very intensive but much more Mg is necessary; ˙ even in pure cellulose paper a positive effect of deacidification with Mg on the light induced oxidation can be seen, but its amount and its chemical character is difficult to describe. There is only a small decrease of brightness, but a positive influence in mechanical strength. |
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| ISSN: | ISSN 0034-5806 |
