Periodic Reporting for period 4 - COMPLEX (The Degradation of Complex Modern Polymeric Objects in Heritage Collections: A System Dynamics Approach)
Okres sprawozdawczy: 2021-10-01 do 2022-09-30
Plastic has transformed society. From the invention of early materials such as celluloid or cellulose acetate in the late 19th and early 20th centuries, to our contemporary mass production and consumption of plastics, plastic has influenced the way we dress, consume food, make art, conduct warfare and communicate with one another. In addition to its impact on society, plastic waste has had a catastrophic effect on our natural environment, with millions of tonnes entering our oceans every year.
Such a consequential part of modern history and our impact on the planet needs to be documented and understood. Collecting and caring for plastic artefacts in helps to ensure that the complicated legacy of plastics can be understood and evaluated both now and by future generations. Unfortunately, the conservation of plastics in museums presents a difficult challenge. Many plastics are very unstable under museum conditions. Plastic artefacts in museums have been found to deteriorate dramatically over much shorter periods than more traditional materials such as stone or glass.
The challenges of conserving plastics in museums have been understood for approximately 30 years and key degradation mechanisms have been identified. However, translating this into an understanding of how plastic objects actually behave is challenging, as different degradation mechanisms have complex relationships both with each other and with the environmental conditions surrounding a plastic object such as the temperature or relative humidity. This was expressed shortly before COMPLEX by researchers at the Getty Conservation Institute in Los Angeles:
“our understanding of plastics stability remains rudimentary. We have a menu of mechanisms that potentially explain degradation, but there is a tendency to default to them and recite them, rather than investigate sceptically what is actually going on.”
Tom Learner and Odile Madden (2014)
The COMPLEX project aimed to address this gap. Inspired by the field of system dynamics, COMPLEX mathematically modelled the degradation of plastic museum objects as complex systems. With a focus on the polymer cellulose acetate, COMPLEX developed a mathematical model that captured the key chemical and physical degradation processes of a plastic artefact and the relationships between these processes and the surrounding environment. This allowed us to identify processes or compositional factors which have the most significant impact on the degradation of plastic museum artefacts, supporting improved conservation decision-making. In addition, COMPLEX introduced a novel way of approaching the study of polymer degradation, as this systems-based approach can be applied to other problems such as plastic waste in the environment.
The key objectives of COMPLEX can be summarised as follows:
- to introduce to the fields of both plastics conservation and polymer degradation a new way of understanding and modelling the degradation of plastic objects: using a system dynamics approach.
- to provide evidence-based guidance on the storage and display of plastic objects in museum collections
The project was done in collaboration with expert partners Tate, the Museum of London, Lacerta Technologies and Process Systems Enterprise.
Such a consequential part of modern history and our impact on the planet needs to be documented and understood. Collecting and caring for plastic artefacts in helps to ensure that the complicated legacy of plastics can be understood and evaluated both now and by future generations. Unfortunately, the conservation of plastics in museums presents a difficult challenge. Many plastics are very unstable under museum conditions. Plastic artefacts in museums have been found to deteriorate dramatically over much shorter periods than more traditional materials such as stone or glass.
The challenges of conserving plastics in museums have been understood for approximately 30 years and key degradation mechanisms have been identified. However, translating this into an understanding of how plastic objects actually behave is challenging, as different degradation mechanisms have complex relationships both with each other and with the environmental conditions surrounding a plastic object such as the temperature or relative humidity. This was expressed shortly before COMPLEX by researchers at the Getty Conservation Institute in Los Angeles:
“our understanding of plastics stability remains rudimentary. We have a menu of mechanisms that potentially explain degradation, but there is a tendency to default to them and recite them, rather than investigate sceptically what is actually going on.”
Tom Learner and Odile Madden (2014)
The COMPLEX project aimed to address this gap. Inspired by the field of system dynamics, COMPLEX mathematically modelled the degradation of plastic museum objects as complex systems. With a focus on the polymer cellulose acetate, COMPLEX developed a mathematical model that captured the key chemical and physical degradation processes of a plastic artefact and the relationships between these processes and the surrounding environment. This allowed us to identify processes or compositional factors which have the most significant impact on the degradation of plastic museum artefacts, supporting improved conservation decision-making. In addition, COMPLEX introduced a novel way of approaching the study of polymer degradation, as this systems-based approach can be applied to other problems such as plastic waste in the environment.
The key objectives of COMPLEX can be summarised as follows:
- to introduce to the fields of both plastics conservation and polymer degradation a new way of understanding and modelling the degradation of plastic objects: using a system dynamics approach.
- to provide evidence-based guidance on the storage and display of plastic objects in museum collections
The project was done in collaboration with expert partners Tate, the Museum of London, Lacerta Technologies and Process Systems Enterprise.
The COMPLEX project combined both experimental and mathematical modelling work, including the analysis of material properties, artificial and natural ageing experiments, the analysis of real plastic heritage objects in museum collections and the mathematical modelling of plastic degradation.
The key achievement of COMPLEX is the development of a mathematical model that describes the degradation of the polymer cellulose acetate (CA). CA is an early plastic, known to be both common and problematic in museum collections. The COMPLEX model describes the chemical degradation of CA and physical processes such as the diffusion of plasticiser, a process that can lead to embrittlement or the presence of sticky deposits on a museum object. The model was validated using artificial ageing experiments.
The model can be used to predict the rate of degradation of a CA-based object under different environmental conditions relevant to museums. This enables comparisons to be made between e.g. open and closed storage conditions or dry and damp environments, making the model very relevant to the practice of museum professionals. It can also address sustainability questions, such as the impact of refrigerated storage on degradation rates of CA, which can then be weighed against the environmental and financial costs of such storage.
Key material parameters were also measured as part of the project, including diffusion coefficients and partition coefficients, as these were needed for the development of the model. The dependencies of these parameters on both material and environmental properties were explored and the work published in peer-reviewed papers.
The work of COMPLEX was widely disseminated at conferences in the UK, in Europe and in the USA. COMPLEX led to the publication of 10 peer-reviewed journal articles and 1 peer-reviewed conference paper and was actively disseminated on social media through our website and our Twitter account.
Given the importance of making the results relevant to museum practice, towards the end of COMPLEX an event called the Festival of Plastics aimed at museum professionals was held, in collaboration with project partners the Museum of London and Tate.
The key achievement of COMPLEX is the development of a mathematical model that describes the degradation of the polymer cellulose acetate (CA). CA is an early plastic, known to be both common and problematic in museum collections. The COMPLEX model describes the chemical degradation of CA and physical processes such as the diffusion of plasticiser, a process that can lead to embrittlement or the presence of sticky deposits on a museum object. The model was validated using artificial ageing experiments.
The model can be used to predict the rate of degradation of a CA-based object under different environmental conditions relevant to museums. This enables comparisons to be made between e.g. open and closed storage conditions or dry and damp environments, making the model very relevant to the practice of museum professionals. It can also address sustainability questions, such as the impact of refrigerated storage on degradation rates of CA, which can then be weighed against the environmental and financial costs of such storage.
Key material parameters were also measured as part of the project, including diffusion coefficients and partition coefficients, as these were needed for the development of the model. The dependencies of these parameters on both material and environmental properties were explored and the work published in peer-reviewed papers.
The work of COMPLEX was widely disseminated at conferences in the UK, in Europe and in the USA. COMPLEX led to the publication of 10 peer-reviewed journal articles and 1 peer-reviewed conference paper and was actively disseminated on social media through our website and our Twitter account.
Given the importance of making the results relevant to museum practice, towards the end of COMPLEX an event called the Festival of Plastics aimed at museum professionals was held, in collaboration with project partners the Museum of London and Tate.
COMPLEX has moved the field of plastics conservation forward. It has taken it from the “menu of mechanisms” described in 2014 to an approach that models multiple, interacting degradation processes within a plastic museum object. This is a new approach within plastic heritage and is also a contribution to the wider field of polymer degradation. This system dynamics approach has broader applications beyond plastic heritage such as plastic waste.
In addition, novel methodologies for studying the properties of heritage plastics were developed. For example, Nuclear Magnetic Resonance (NMR) spectroscopy is widely used in chemistry but has been under-used to date in the field of heritage science. A method was developed for the quantification of plasticiser content and the extent of degradation in historic CA using NMR spectroscopy.
COMPLEX explored the use of Dynamic Vapour Sorption (DVS) to study moisture transport in CA and interactions between water, plasticiser and environmental conditions. DVS is another technique that is under-used within the field of heritage science and has great potential for application to a wide range of heritage materials. The diffusion coefficients that were measured as part of this work and their dependencies on other parameters were used as inputs for the mathematical model produced in COMPLEX.
A key interdisciplinary achievement of COMPLEX is the output from a system dynamics workshop held at the start of COMPLEX in 2017. This was led by system dynamics expert Nici Zimmermann and involved the COMPLEX project team, our museum partners and UCL colleagues and students. The degradation of plastic heritage objects was mapped as a complex system. The workshop involved a fascinating inter-disciplinary conversation which illuminated the way in which an interdisciplinary field like heritage science operates in practice. The conversations were recorded, transcribed, and analysed, leading to two publications.
In addition, novel methodologies for studying the properties of heritage plastics were developed. For example, Nuclear Magnetic Resonance (NMR) spectroscopy is widely used in chemistry but has been under-used to date in the field of heritage science. A method was developed for the quantification of plasticiser content and the extent of degradation in historic CA using NMR spectroscopy.
COMPLEX explored the use of Dynamic Vapour Sorption (DVS) to study moisture transport in CA and interactions between water, plasticiser and environmental conditions. DVS is another technique that is under-used within the field of heritage science and has great potential for application to a wide range of heritage materials. The diffusion coefficients that were measured as part of this work and their dependencies on other parameters were used as inputs for the mathematical model produced in COMPLEX.
A key interdisciplinary achievement of COMPLEX is the output from a system dynamics workshop held at the start of COMPLEX in 2017. This was led by system dynamics expert Nici Zimmermann and involved the COMPLEX project team, our museum partners and UCL colleagues and students. The degradation of plastic heritage objects was mapped as a complex system. The workshop involved a fascinating inter-disciplinary conversation which illuminated the way in which an interdisciplinary field like heritage science operates in practice. The conversations were recorded, transcribed, and analysed, leading to two publications.