ABSTRACT

This paper describes an investigation into 1:1 Paraloid® B-72/B-48N as a conservation adhesive for use in hot climates. The study was driven by archaeological conservation work at El-Kurru, Sudan, a Saharan Desert site where daytime high temperatures can reach 45°C. Paraloid® B-72 is a favorite adhesive for use with archaeological materials for many reasons – notably its stability and long-term reversibility – but its product literature reports a glass transition temperature (Tg) of 40°C. Pottery reconstructed with Paraloid® B-72 slumps within one year at El-Kurru, and joins fail completely after another year. For this reason, we investigated blending Paraloid® B-72 with another thermoplastic acrylic resin, Paraloid® B-48N, which has a reported Tg of 50°C. Research included a literature search to investigate Paraloid® B-48N’s long-term stability, reversibility, and the temperature at which it fails. Dynamic mechanical analysis (DMA) was conducted to determine the Tg behavior of Paraloid® B-72, Paraloid® B-48N, and a 1:1 blend of the two resins. Pottery joined with the 1:1 mixture was observed over a four-year period at El-Kurru to evaluate the mixture’s performance in a hot archaeological field setting. Although the 1:1 blend performed better than Paraloid® B-72, it was less heat tolerant than expected based on our DMA results as well as literature reports of the performance of similar adhesives. Tg can be defined in multiple ways, and we suggest that the most useful Tg measurement for conservators is the onset temperature at which the glass transition begins. Further, we suggest that creep testing will provide a better indication of the long-term stability of adhesives under mechanical stress, surpassing Tg as a reliable predictor of performance.

摘要

本文介绍了对 1:1 Paraloid® B-72/B-48N 作为在炎热气候下使用的保护粘合剂的研究。这项研究是由苏丹 El-Kurru 的考古保护工作推动的，这是一个撒哈拉沙漠遗址，白天的高温可以达到 45°C。Paraloid® B-72 是考古材料最受青睐的粘合剂，原因有很多——特别是其稳定性和长期可逆性——但其产品文献报道的玻璃化转变温度 (Tg) 为 40°C。在 El-Kurru，用 Paraloid® B-72 重建的陶器在一年内坍塌，一年后连接完全失败。出于这个原因，我们研究了将 Paraloid® B-72 与另一种热塑性丙烯酸树脂 Paraloid® B-48N 混合，据报道其 Tg 为 50°C。研究包括文献检索以调查 Paraloid® B-48N 的长期稳定性，可逆性，以及它失败的温度。进行动态机械分析 (DMA) 以确定 Paraloid® B-72、Paraloid® B-48N 和两种树脂的 1:1 混合物的 Tg 行为。在 El-Kurru 观察了 4 年期间加入 1:1 混合物的陶器，以评估混合物在炎热的考古现场环境中的性能。尽管 1:1 混合物的性能优于 Paraloid® B-72，但根据我们的 DMA 结果以及类似粘合剂性能的文献报告，它的耐热性低于预期。Tg 可以通过多种方式定义，我们建议对保存器最有用的 Tg 测量值是玻璃化转变开始的起始温度。更远，