Susceptibility of Printed Paper to Attack of Chewing Insects after Gamma Irradiation and Ageing
| Main Authors: | , |
|---|---|
| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0034-5806 |
| Online Access: | http://www.viks.sk/chk/res_2_03_95_105.doc |
| Abstract: | SUMARRIES. In the context of a larger research project on the recovery of books and documents stored in libraries and archives and further of an analogous work related to cellulose just published, three different types of printed paper (newspaper, magazine paper, "permanent durable" paper) were submitted to two different experimental trials. In the first the papers were irradiated by gamma rays, while in the second they were also subjected to thermal accelerated ageing. The assessment was made by observing the extent of the damage that the Periplaneta americana (American cockroach) was able to do to the different and differently treated papers, in the form of erosion during the following storage period. The results indicate that the papers irradiated with doses up to 10 kGy do not show greater erosion damage compared to the untreated papers. The same is true for pa-pers subjected to the combined treatment of irradiation + ageing. In the case of very high irradiation dose (100 and 200 kGy) a relationship between the quantity of radiation absorbed by the paper and the "desirability" for the chewing insects was observed. This effect is significandy higher after the combined treatment, at least for two of the papers. Finally considerations on the practical importance of these phenomena are presented. CONCLUSION. Our experiment confirmed that P. americana, like other cockroach species, causes varying degrees of erosion to paper since, especially when other food sources are lacking, they feed on it. It also showed that, regardless of the state of deterioration of the paper components, if left undisturbed, the insects' action is always destructive, if left for longer periods, this would lead to the total erosion of the paper. It is interesting to note that, although it is empirical and apparently primitive, the type of analysis we chose for testing the degree of degradation of a paper subjected to radiation treatment, using a living organism (in particular a common cockroach), proved to be extraordinarily sensitive in assessing even minimum changes occurring in the material. A comparison of the responses of the diree different types of paper, among them but also with those obtained previously from Whatman paper11, would seem to indicate that the changes caused by radiation and ageing do not produce the same effects on a pure cellulose paper as they do on a more complicated sheet of printed paper. Therefore, while Whatman paper is the best material for studying the behavior of cellulose (which makes up paper), we cannot automatically attribute to paper the same behavior that we observed for cellulose. The different degree of corrosion which, after the treatments, also varied with the type of the material treated, may be attributed to the toxicity of the inks used for printing. But we would not be at all surprised if someone would want to attribute the responsibility for negative effects to the components of the "loading" which, in the manufacture of coated (and durable) papers, is added to the cellulose mixture to improve its quality in the final product (calcium carbonate, sodium chloride, optical whiteners, bluing agents, cationic starch, comstarch, acrylic components, alkyldiketenes, etc.) and which might have been transformed by accelerated ageing into a nutritional source for insects. Just a few more comments on the accelerated ageing treatment. Comparing the data of the 0 kGy columns of the aged and unaged samples we can state that simple ageing does not cause greater susceptibility to insect attack in any of the three types of paper. However, when accelerated ageing is combined with gamma ray irradiation at dosages of 100 and 200 kGy, a synergic relationship between the two treatments becomes clear: at very high radiation doses, the well-known phenomenon of depolymerization of cellulose - caused by the radiation and proportional to the dose absorbed - causes negative effects that are increased by the ageing and which the ageing treatment alone would not be able to cause. Thus our observations for pure cellulose11 are confirmed for paper. It is interesting to remember that others have used gamma ray13,14 and UV ray8 irradiation for accelerated ageing. Based on our results we should like to emphasize that the action mechanism of ageing by irradiation does not act in the same ways as thermal ageing according to ISO 5630/3. We observed effects which were different from those recorded by these authors, with the irradiated papers compared to aged papers as well as with those which have been both irradiated and aged. In other words, we would like to recommend that the reader keep in mind that the effects of a treatment depend on the particular mechanism of the chosen treatment and, may even themselves differ. From these experiences, aiming to identify in irradiation a cause of greater susceptibility of paper to the attacks of biodeteriogens, and from the other studies4,5,10,11 it becomes clear that the changes induced by the treatment with ionizing radiation on the chemical-physical properties of paper are strongly connected to the gamma ray dose absorbed by the material. With regard to this, it should be remembered that all the analyses we have carried out lead us to conclude that treating paper with ionizing radiation using doses of up to 10 kGy does not cause evident alterations15. Alterations become evident when the quantity of radiation absorbed exceeds the quantity necessary for the recovery treatment by one or two levels. In fact, the dose range between 3 and 10 kGy is sufficient to clean the material of microscopic fungi and is well beyond the 0.2-0.5 kGy necessary to eradicate every insect population12,16. Therefore, any contraindications of the treatment and their practical importance are negligible or nil. From this standpoint it may be useful to remember that, even though it is an entirely different application field and entirely different material - even if also of organic and of natural origin - human food irradiated at doses of 4.5 kGy-7 kGy maintains unaltered its protein level and nutritional quality as well as consistency, odor, and colour16. The latter characteristics are associated with molecules that are generally much more sensitive to chemical-physical attacks than cellulose. In meat, only the level of vitamins is compromised, but that would be affected by cooking in any case. |
|---|---|
| ISSN: | ISSN 0034-5806 |
