Review of CCI Research on Epoxy Resin Adhesives for Glass Conservation
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 1605-8410 |
| Online Access: | http://www.viks.sk/chk/revincon9.doc |
| Abstract: | SUMMARIES. This article reviews epoxy resin adhesive research for glass conservation undertaken at the Canadian Conservation Institute (CCI) since 1978. This includes information on various aspects of yellowing of commercial products, strength retention after ageing and removability. Relevant work by other researchers on Hxtal NYL-1, controlling refractive index, additives and use with cyanoacrylates is also included to give a comprehensive overview of the subject. CONCLUSION. Not all the questions have been answered, but there is a fair amount of knowledge available to the conservation community on ERAs for glass conservation because of the research done over the last 20 years. The research and limitations can be summarized in the following way. Although ERAs tend to yellow rather quickly, Hxtal NYL-1 and Epo-Tek 301-2 have been identified with better yellowing resistance than others tested. Nothing simple has been found to date, that will successfully inhibit yellowing of ERAs. Perhaps a stabilizer exists that will help yellowing resistance, but more work in this area would be needed to find the specific stabilizer for each specific ERA chemistry at the best concentration. This would be particularly useful to improve the yellowing resistance of Hxtal NYL-1 and Epo-Tek 301-2, which have been identified as the best formulations. It would be interesting to know if they could be improved. Storing ERA components longer than recommended by the manufacturer and diluting ERA components with certain solvents before curing can increase yellowing. It is thought that the mechanism of yellowing involves unsaturation in the bisphenol A portion of the resin and that it may be a surface phenomenon on films of some, but not all, formulations. Although the strength of ERAs increases to a maximum with thermal ageing and then starts to decrease, it is felt that loss of strength should not pose a major problem for the use of ERAs in glass conservation. However, the effect of humidity on strength retention should be assessed more thoroughly as it appears it may be a problem for some formulations. Also, investigation of adequate strength for fragile glass needs to be determined. No universal solvent for swelling and removing ERAs has been found. Generally, solvents such as DMF, THF, chloroform and methylene chloride were more effective than alcohols and ketones. Enzymes were found to be ineffective but some acids were better than others with propionic being the best. Marginal control of RI was obtained by varying the ratio of the resin/hardener or using halogenated compounds, but these modifications changed the properties of the ERA and also increased their tendency to yellow. The lessons learned about adding any compounds to ERAs, be it for RI, dyeing or pigmentation, or temporary bonding (e.g., cyanoacrylates), is that they should first be tested well to ensure that no drastic or unexpected changes occur, such as to colour, opacity and curing. |
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| ISSN: | ISSN 1605-8410 |
