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Title:

Outdoors! Transparent acrylics in cultural heritage exposed to weather - case studies: degradation phenomena and their possible causes

Document type:
Nicht veröffentlichter Vortrag
Author(s):
Brunner, Susanne
Abstract:
How to preserve outdoors historic transparent acrylics is a complex but current question. Knowing the material, its physical properties, its state of degradation and the possible causes of degradation is a prior condition for the conservation of acrylics, as there can be wide varieties. For this purpose, various construction elements were examined that contain naturally aged acrylics, namely windows and roofs of buildings and airplanes. In the proposed paper, three case studies of cultural heritage and several historic fragments are presented with focus on the characterization of the naturally aged acrylics and how to investigate their production, composition and degradation phenomena. The buildings and technical objects include the Felix-Wankel-Institute in Lindau (1961), the Olympic Sports Facilities in Munich (1972) and the airplane Transall C-160 (Deutsches Museum, 1971), where transparent acrylics can be found as windows, barrel-shaped roofs and cupolae. All investigated elements were weathered and exposed and need immediate conservation treatments to prevent further damage of the acrylics. To understand the production techniques of the transparent acrylics from the 1960s and 1970s, archival research (Deutsches Museum / Evonik archives Röhm & Haas) and interviews with company Röhm have been conducted. The acrylics from the case studies were cast, could be biaxially stretched and either thermoformed over molds or cold formed into their metal frames. The composition of the acrylics was analysed by means of FTIR and py-GCMS. Next to the main polymer poly (methyl methacrylate), copolymers and various additives were detected that are beneficial especially in buildings, eg. UV-absorbants and flame retardants. Different to indoor acrylics, outdoor acrylics are exposed to weather and natural light. By means of microscopy, polariscope and colorimetry, the degradation phenomena were detected, examined and classified. Degradation phenomena include the loss of transparency, matte and rough surface, flaking, whitening, deformation, micro crazing, cracks and breaks. The degradation phenomena of historic acrylics are typical for the material and gathered on a macroscopic and microscopic level for the first time. UV-light, oxygen and water have a huge effect on acrylics and lead to a matte, white, rough surface. Physical stress can lead to cracks, crazes or deformation. Temperature changes can lead to deformations. Further, the production technique, the material’s composition and physical forces in the construction element can lead to degradation phenomena. Biaxially stretched material will degrade by flaking of off the surface, as the weakest molecular strength is in the direction of the z-axis, such can be seen at the Olympic roof. Cold formed acrylic sheet tends to break at the highest point of physical tension, which can be seen at the barrel-shaped roof of the cash points at the Olympic sports facilities. The acrylic’s surface at the Felix-Wankel-Institute is glossy and even, but cloudy structures in the shape of drops, lines and waves can be seen on the weathered surface to different extents. Can crystallisation be the cause of the cloudiness and does the rain wash out low-molecular degradation products which leads to the structures of drops and waves? The paper presents and discusses several methods that may help to characterize naturally aged transparent acrylics and their degradation phenomena. The research is part of the ongoing project Strategies for the conservation of outdoors transparent poly (methyl methacrylate) (PMMA) in architecture and museum objects funded by the Deutsche Bundesstiftung Umwelt (DBU), which aims to develop suitable methods for the maintenance of transparent acrylics in outdoor objects.
Event:
Future Talks Conference 2021
Organization:
Die Neue Sammlung
Publisher address:
München
Date of publication:
08.11.2021
Year:
2021
Month:
Nov
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