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Investigation and Removal of Foxed Spots on Paper-based Culyural Relics
|關鍵字:||Foxing;褐斑現象;Biodegradation of papers;Conservation;Fungi;Maillard Reaction;Paper washing;紙張生物劣化;維護;真菌類;莫納反應;紙張漂洗||出版社:||森林學系||摘要:||
紙張褐斑在顏色上多呈黃色系，外觀常可分為：靶心狀、雪花狀、陰影狀及複合型等形狀。紙樣褐斑區域以掃描式電子顯微鏡觀察，發現有真菌類之菌絲及孢子。由於微生物在生長期間之代謝產物，造成褐斑著生部位之pH值下降。經培養及鑑定紙張著生褐斑之真菌類，以 Aspergillus 及 Penicillium 兩屬真菌所佔比例最高。分別為：Aspergillus niger, Aspergillus flavus, Aspergillus ochraceus, Aspergillus ustus, Aspergillus spp.,Penicillium citrinum, Penicillium chrysogenum, Penicillium spp.,Chaetomium globosum, Trichoderma viride,Fusarium solani, Cladosporium sp., Rhizopus sp., Phoma sp.,Umbelopsis sp., Metarrhizium sp., Eurotium sp.等。在室溫下，隨相對濕度增高，70﹪相對濕度以上，真菌類於紙面上生長越發茂盛，60﹪以下相對濕度，可抑制真菌類微生物於紙張上繁衍。在褐斑紙樣及誘發褐斑真菌類萃取液中，皆可發現含草酸、蘋果酸、乳酸等有機酸及γ-胺基丁酸等17種胺基酸成分，可證實紙張褐斑之成因與上述成分有關。由HPLC分析發現，褐斑萃取液含木糖及葡萄糖成分，可推斷紙質受微生物作用而導致降解。以ESCA配合顯微FTIR分析，顯示褐斑紙樣及真菌著生紙樣上含有空白紙樣闕如的氮元素。接菌處理之濾紙以顯微FTIR分析發現，代表 C=O 官能基之1654 cm-1及代表 N-H 官能基之1550 cm-1吸收峰之相對強度顯著高於對照組，顯示紙質纖維因微生物劣化及菌類之新陳代謝作用，而生成酸性劣解產物；此一結果與褐斑紙樣於1654 cm-1具顯著吸收結果一致。
本論文以胺基與羰基作用引起之莫納反應（Maillard reaction）來解釋紙質文物褐斑之成因。葡萄糖、木糖或有機酸等單一成分不會在紙面形成褐斑。糖液配合有機酸及胺基酸時，紙面因褐變反應呈黃褐色。自然褐斑與人為褐斑均可在365 nm UV燈照射下發現螢光現象，故紫外光可為紙張褐斑之簡易偵測方法。
本論文探討γ-射線照射對紙張性質傷害最低之滅菌組合方法，以為文物維護開拓另一可行方向。對選用菌株之有效滅菌劑量為 3∼5 KGy，照射劑量在 3 KGy時，對於黴斑之紙張具有良好之滅菌效果。γ-射線照射前施以加熱處理，有助於降低照射時之有效滅菌劑量。文物、藝品先施以50 ℃加熱24 hr，再採用輕微劑量（1∼2 KGy）進行照射，除可有效達到滅菌目的，且可使紙質文物之損傷控制在最低程度。紙張褐斑可藉漂洗處理移除之，以肉眼評估漂洗效果，次氯酸鈉、高錳酸鉀及氫硼化鈉等漂劑，可有效移除手工紙樣及書頁上之褐斑，然而在色斑相同位置上，以365 nm之紫外燈觀察時，仍存在著螢光現象，此部位是否再度復發褐斑，仍有待觀察。以漂洗處理對紙張性質影響為基礎，區分出適用漂洗處理之優先排序：（1）2 ﹪氫硼化鈉→（2）2 ﹪過氧化氫→（3）2 ﹪次氯酸鈉→（4）熱水洗滌→（5）0.5 ﹪高錳酸鉀＋3 ﹪草酸→（6）2 ﹪氯胺-T → （7）0.5 ﹪氫氧化鈉→（8）0.5 ﹪皂液。
" Foxing " could be caused by the biodegradations of paper. Brown stains not only apparently decrease the life of rare books, paintings and art crafts, but also affect the preservation of cultural relics. The aim of this study is to explore the contributing factors of foxed spots showed on paper-based materials, and remove the foxed paper there after. The experimental results are summarized as follows:
Bull''s-eye shaped, snowflake shaped, shadows shaped or complex foxed spots of foxing type can be observed on paper specimens. Foxed spots usually showed yellowish color and can be interpreted as +b* in CIE LAB system. Hyphae and conidia of microorganisms were observed on the foxed area in SEM observation. A lower surface pH value of foxed area was present compared with that of unfoxed area. Among 17 species of fungi isolated from paper-based materials of which the main species, were identified as the genera of Aspergillus and Penicillium. The foxing-causing fungi of Pineapple xuan paper were inhibited by less than 60﹪R.H. at room temperature, and over 70﹪R.H.,the fungal growth was very vigorous.We identified the foxing-caused fungi organic acids, such as oxalic acid, malic acid, lactic acid and 17 kinds of amino acids, especially the γ-aminobutyric acid, from foxed papers and fungi extractives. These results indicated that paper foxing spots were related to those components. The monosaccharides in the extractives of paper foxed area were identified as glucose and xylose by HPLC analysis. The metabolic products, such as organic acids and amino acids induced from microorganisms, can be elucidated by ESCA spectra for further verification the degree of paper biodegradation. Moreover, nitrogen spectra in ESCA were observed in both of the foxed and fungi inoculated papers. Relative peak intensity of C=O at 1654 cm-1 and N-H at 1550 cm-1 in foxed and fungi inoculated papers were apparently higher than those of unfoxed papers in FTIR spectra. The formed foxing spots on paper surface may be attributed to the Maillard browning reaction. Brown spot can''t be formed on the surface of paper by single component of sugar, amino acids or organic acids. The combination of glucose(or xylose), amino acids and organic acids induced the formation of brown spots after dropping on the surface of paper. Distinct fluorescence around the brown spots of paper was observed after the paper exposing to UV light at the wavelength of 365 nm, and the treatment is an effective method to detect the foxing induced either by natural or artificial origin. The feasibility of γ- radiation for the disinfection of paper-based artifacts was also investigated in this study. The load at 3∼5 KGy of γ- radiation gave the sufficient biocidal dosage to the fungi strains, and the load at 3 KGy was the biocidal dosage for the moldy papers. The load of gamma irradiation could be reduced to 1∼2 KGy if papers were preheated at 50℃ for 24 hours. The foxed spots on the surface of papers can be removed by washing treatments. Bleaching agents, such as sodium hypochlorite, potassium permanganate and sodium borohydride, were effective chemicals to remove the foxed stain from paper-based materials, and the results could be obviously observed after washing treatments. However, fluorescence in foxed area of washing treated paper was still observed as the control specimens. The reappearing of brown stains on the washing treated paper needs further investigation. The suggested sequences of bleaching agents for paper conservation purpose are as follows: (1)2 ﹪NaBH4→(2)2 ﹪H2O2→(3)2﹪NaOCl→(4)Hot water →(5)0.5 ﹪KMnO4＋3 ﹪Oxalic acid→(6)2 ﹪Chioramine-T→ (7)0.5 ﹪NaOH→(8)0.5 ﹪Soap solution.
|Appears in Collections:||森林學系|
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