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Projeto de investigação
Center for Natural Resources and Environment
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Iron(III) based Metal-Organic Frameworks in cellulose acetate film preservation
Publication . Mohtar, Abeer Al; Severino, Maria Inês; Tignol, Pierre; Ranza, Luigi; Neves, Artur; Nouar, Farid; Pimenta, Vanessa; Lopes, João; Ramos, Ana Maria; Rodrigo, Juan Ignacio Lahoz; Melo, Maria João; Wallaszkovits, Nadja; Pinto, Moisés L.; Dupont, Anne Laurence; Serre, Christian; Lavédrine, Bertrand; LAQV@REQUIMTE; DCR - Departamento de Conservação e Restauro; DQ - Departamento de Química; Elsevier
Low-temperature storage to slow down degradation is accepted by the film conservation community. Still, this solution prohibits public access, is price-sensitive, has high energy costs, and there are concerns about their effects on the physical stability and material lifetime. In this research, a smart solution is developed based on the selective capture of acetic acid produced by the cellulose acetate polymer. This innovative approach is based on Metal-Organic Frameworks (MOFs) for acetic acid adsorption, specifically a highly selective porous iron(III) based MOF, MIL-100(Fe), which was synthesized using a green approach. The stability of MIL-100(Fe), under acetic acid exposure, was demonstrated by accelerated aging experiments, with no noticeable changes in crystallinity and/or porosity as deduced from powder X-ray diffraction analysis, infrared spectroscopy, thermogravimetric analysis, nitrogen porosimetry, and electron microscopy. Compatibility tests with the artefacts were performed to prove the safety of the MIL-100(Fe) to the artefacts. A field application in a demonstration prototype (smart box) was performed at Institut Valencià de Cultura. A recently developed hybrid model provided recommendations on the quantity of adsorbents to use in the smart box. Good agreement was observed between the model predictions and the in-field experimental results, which validated the model application. The model predicted that the new adsorbent (5% of the film's weight, replaced every 10 years, at 16°C or 22°C) extends the film's lifetime equivalently to cold storage (5°C). Finally, environmental impact assessment and life cycle analysis were performed to compare the two preservation approaches. The new approach based on this Fe-MOF yielded an average reduction of carbon footprint related to movie film preservation of about 50% considering the current European Union (EU) energy mix and about 40% considering the 2030 EU energy mix (where a transition towards renewable energy is expected). The proposed innovative technology represents a robust solution towards efficient and more sustainable film preservation while significantly contributing to moving toward climate transition objectives in the culture heritage sector.
Decision making based on hybrid modeling approach applied to cellulose acetate based historical films conservation
Publication . Al Mohtar, Abeer; Pinto, Moisés L.; Neves, Artur; Nunes, Sofia; Zappi, Daniele; Varani, Gabriele; Ramos, Ana Maria; Melo, Maria João; Wallaszkovits, Nadja; Lahoz Rodrigo, Juan Ignacio; Herlt, Kerstin; Lopes, João; LAQV@REQUIMTE; DCR - Departamento de Conservação e Restauro; Nature Publishing Group
Preserving culture heritage cellulose acetate-based historical films is a challenge due to the long-term instability of these complex materials and a lack of prediction models that can guide conservation strategies for each particular film. In this work, a cellulose acetate degradation model is proposed as the basis for the selection of appropriate strategies for storage and conservation for each specimen, considering its specific information. Due to the formulation complexity and diversity of cellulose acetate-based films produced over the decades, we hereby propose a hybrid modeling approach to describe the films degradation process. The problem is addressed by a hybrid model that uses as a backbone a first-principles based model to describe the degradation kinetics of the pure cellulose diacetate polymer. The mechanistic model was successfully adapted to fit experimental data from accelerated aging of plasticized films. The hybrid model considers then the specificity of each historical film via the development of two chemometric models. These models resource on gas release data, namely acetic acid, and descriptors of the films (manufacturing date, AD-strip value and film type) to assess the current polymer degradation state and estimate the increase in the degradation rate. These estimations are then conjugated with storage conditions (e.g., temperature and relative humidity, presence of adsorbent in the film’s box) and used to feed the mechanistic model to provide the required time degradation simulations. The developed chemometric models provided predictions with accuracy more than 87%. We have found that the storage archive as well as the manufacturing company are not determining factors for conservation but rather the manufacturing date, off gas data as well as the film type. In summary, this hybrid modeling was able to develop a practical tool for conservators to assess films conservation state and to design storage and conservation policies that are best suited for each cultural heritage film.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UIDP/04028/2020