Biological Investigation on Sizing for Permanent Papers
| Main Authors: | , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_2_98_61_84.doc |
| Abstract: | Summaries. We have conducted a research on the biodegradability of papers conforming to UNI 10332 "Carta per documenti - requisiti per la massima permanenza e durabilita" (Paper for documents - requirements for maximum permanence and durability) caused by the cellulolytic fungi. A particular importance was given to the effect of three sizings most widely used in the manufacture of papers intended for printing of documents, books and any printed matter that for its historical, legal importance has to be preserved for a long time. We prepared samples of paper in accordance with the Standard different only for the sizings. Successively we tested the biodegradability both of the sizings on an inert backing and of the samples of paper left in incubation at ranging temperatures (20°C and 30°C) and relative humidity (100%, 92%, 85%, 75%, 63%, 53%) for twenty weeks. We used for the tests fungus strains of the types most frequently isolated from paper materials. We then studied the effect of the sizings on paper hygroscopicity and the existing relationships between the thermo-hygrometric values of paper incubation and the incidence of the spore's survival. The results obtained were summarized as follows: The paper conforming to UNI 10332 supported the fungus attack only under particularly critical thermo-hygrometric conditions. Its neutral alkaline pH value has inhibited the growth of most cellulolytic fungi; The accelerated ageing helped cellulolytic fungi attack because of the degrading action on the cellulose fibres and on the sizings, despite the reduction of the moisture content available to micro-organisms; The thermo-hygrometric conditions of incubation and the accelerated ageing deeply affected the spore's life: in particular, it was pointed out that the spores survived for a longer time under the thermo-hygrometric conditions suggested for paper conservation; The choice of the sizings has sometimes strongly affected the paper biodegradability and its hygroscopicity: one sizing, in particular, was suited for the manufacture of the "permanent paper": paper sized with it has supported the fungus development at only 100% relative humidity, both before and after the accelerated ageing. We hope this work is a practical contribution to the choice of the sizings that from biological view point, are best suited for the manufacture of paper to be preserved as long as possible. Conclusions. In the light of these results, we pointed out that paper samples conforming the characteristics for maximum permanence and durability do not promote the cel-lulolytic fungi growth under the thermo-hygrometric conditions suggested for paper conservation. Anyway, in most cases, the microclimates of the librarian and archival storehouses do not correspond to the ideal microclimates because of the absence of air conditioning systems. The results reported in 4.3.1 concerning the biodegradability test of paper samples at different microclimates, are somehow promising because the fungal growth occurred only at high hygrometric levels. In particular paper sized with AKD has never supported the microfungi growth below 100% relative humidity. Remarks on the influence of the sizings The results reported in Section 4.3.1 stress the importance of the choice of the best suited sizings. Indeed they can help or prevent the biodeterioration processes of paper, depending on the fact they constitute or do not constitute a trophic resource for the micro-organisms or they increase or decrease the hygroscopicity. The AKD, among others, is the best suited to meet these requirements. The AKD sized paper samples have never supported the growth of fungi at hygrometric values below 100% RH and when it occurred, the growth was in general slower and less heavy if compared to other samples. Data in Section 4.4 point out that the AKD sized samples with a few exceptions, have a lower moisture percent content than the unsized samples, at the same hygrometric values. The table of results shows that these samples are the only ones that at a relative humidity below 100%, never reach a moisture percent content over 10%. The samples sized with the other synthetic size the alkenilsuccinic anhydride ASA, indicated on the one hand a moisture percent content lower than the unsized samples, on the other hand the microfungi test found the trophic resources necessary to support a faster and heavier growth than that on the reference samples. In the light of these results, the ASA can be considered less suited than AKD for the sizing of paper to be preserved as long as possible. Finally, papers sized with starch have better supported the fungal growth than synthetic materials, and it was also pointed out that starch has two negative characteristics: it is a source of organic carbon more quickly available than cellulose as proved by a fast and heavy growth of microfungi (Table 7 and 8); it distinctly increases the moisture percent content of aged and unaged papers (Table 11 and 12) that was higher than that of other samples under every thermo-hygrometric condition. We thus give a negative opinion as regards the use of starch for the sizing of papers conforming the requirements for "maximum permanence and durability" that according to UNI standard 10332 must not contain substances capable of degrading it. It is a widespread opinion that the results concerning the sizings on an inert medium are similar to those obtained on a paper medium; in both cases AKD prevented growth of fungi more than ASA with emulsifier and vice versa, starch supported it better. Tests conducted on an inert medium and not those on paper medium, gave a new indication: the biodegradability of ASA size was deeply influenced when adding an emulsifier compound, the acrylamide polymer. In fact ASA without emulsifier recorded low values of growth, lower than those of other materials. It is evident that nitrogen present in the emulsifier polymer helped the micro-fungi growth. It is thus suggested for the carrying out of future tests the possibility of replacing the above polymer with an alternative compound. Remarks on the effects of neutral alkaline pH Some remarks can be made on the effects of neutral alkaline pH of permanent paper samples ranging between 8.0 and 8.2, on biodegradability. The results in Section 4.3.1 show a difference among the microfungi tests as regards the growth rate. In particular the Chaetomium globosum had the fastest growth on nearly every paper sample. This is particularly interesting if we consider that Chaetomium globosum, being a Ascomycete fungus has a life cycle longer than the Deuteromycetes, Asper-gillus terreus, Aspergillus niger and Penicillium pinophilum (asexual reproduction). In this case alkaline neutral pH of paper probably reduced the growth of the three deuteromycetes whose optimum growth is in acid environment but did not prevent the growth of Chaetomium whose optimum range is between 7.1 and 10.417. This remark is confirmed by the result of a previous experiment19 according to which alkalinity partially or totally inhibited the enzymes of the cellulasi complex of some microfungi. The Aspergillus terreus, for example, showed a progressively reduced cellulolytic activity passing from a culture medium (with cotton cellulose as only source of carbon) buffered at 4.5 pH to culture medium at 6.0 and 7.0 pH. The presence of the alkali reserve of calcium carbonate renders the substrate less available to the microfungi attack because it causes a reduction of the acid hydrolysis process as well as the swelling of cellulose. Remarks on the effects of thermo-hygrometric conditions Paper samples never supported microfungi growth at a relative humidity below 100% and at 20°C temperature. On the basis of the results obtained we reported the following: the rise in temperature hasten the microfungi growth (Table 7 and 8); the rise in temperature shorten the life span of the spores (Table 9 and 10). As to the first point, the results in Section 4.3.1 show that in some cases the rise in temperature helped the biodegradation due to the microfungi growth at relative humidity below 100%, because the optimum temperature for the microfungi growth is at 30°C more than at 20°C. [A. terreus 35-40°C, A. niger 17-42°C, P. pinophilum 25-28°C and C. globosum 24-28°C). As to the second point, the results in Section 4.3.2 pointed out that the lifespan of the spores is longer at 20°C than at 30°C. It is thus possible that higher values hasten the latent metabolism of the spores thus rapidly exhausting their resources. The experiments indicated that the hygrometric values affect the vitality of spores as well as the temperature. At 85 %, 75 % RH and sometime at 63 % RH a reduced capacity to germinate was observed. In most cases spore's life was preserved at 53 % RH On the basis of the above results, it can be affirmed that the life of the spores is longer under the microclimatic conditions suggested for paper conservation. This is confirmed by the results of a recent research conducted by the Istituto Centrale per la Patologia del libro9. Remarks on the effects of accelerated ageing From the comparison between the growth values of accelerated aged and unaged paper it results that the growth on an aged material is faster at 100% RH and that it more easily occurs at 92 % relative humidity. The above data can be explained considering that the accelerated ageing process adopted to simulate the effect of natural ageing causes significant changes in the structure of paper; cellulose tends to hydrolize and to swell while the main additives, like the sizings, may degrade. The changes in the structure of cellulose cause a drop of the polymerization degree and a transition from crystalline form to amorphous form. A few researchers have stressed that these effects, regardless the causes, bring about an increase of the hydrolysis rate produced by the enzymes of the fungal cellulase. In fact, the depolymerization exposes a greater number of cellulose molecules to the action of the esoglucanasic component of the cellulase complex and the increased percent content of amorphous cellulose makes the substrate easily accessible to the action of hydrolytic enzymes3. The results given in Section 4.4 indicate that the accelerated ageing causes a reduction of the moisture percent content. The above data, confirmed by previous experiments 20 21 22, clearly do not promote the metabolic activity of the biological substances causing the degradation of paper. It is reduced, but this is not sufficient to compensate the effects due to the reduction of the polymerization degree and the cristallinity degree of the cellulose. Finally the experiments indicate that paper ageing has a negative effect on the preservation of spore's vitality. It can be assumed that this remark is to be correlated to the moisture percent content of aged paper which could cause the spores to exhaust more rapidly their reserves. |
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| ISSN: | ISSN 0034-5806 |
