Cellulose nitrate and acetate are materials at risk in heritage collections because it is not possible to predict the evolution of their conservation state over time. Knowing that the degree of substitution (DS) of these materials correlates with their state of conservation because the fundamental degradation mechanism is hydrolysis, in this work, DS was measured in historical objects and artworks. Infrared spectra were used to develop and optimize calibration curves for cellulose nitrate and acetate references that were next applied to calculate DS values of heritage objects. The extent of hydrolysis measured, with this tool, correlated well with the physical deterioration assessed through the sample hardness (Shore A) which was measured with a Durometer. Calibration curves were optimized in reference materials by Attenuated Total Reflectance (ATR-FTIR) and Micro Fourier Transform Infrared Spectroscopy (μFTIR). The DS values of the AC reference materials was previously calculated by nuclear magnetic resonance spectroscopy. The calibration curves were obtained plotting DS as a function of the ratio between a reference peak (which does not suffer relevant changes during degradation) and selected peaks that monitor the degradation for cellulose acetate and nitrate polymers (avoiding the interference of plasticizers). The reference peak for both was the COC stretching mode (νCOC). The probe peak was, for cellulose nitrate, the NO₂ asymmetric stretching (ν_aNO₂) and, for cellulose acetate, the OH stretching mode (νOH). This ratio was then applied to calculate DS values of historical materials, in good and poor conservation condition; in situ by ATR, and in micro-samples collected from artworks by μFTIR. This selection comprises cinematographic and photographic films dated from the 1890s to the 1960s, and contemporary works of art made with cellulose acetate sheets by Portuguese artist José Escada dated from the 1960s. Finally, by comparison with the original estimated DS values, we show how this tool permits to define the state of degradation of these complex polymer matrixes. Thus, establishing the quantification of the DS as a novel tool to monitor the degradation of cellulose ester plastics, contributing in this way for a sustainable preservation of an irreplaceable heritage.

Plastics recycling remains a challenge due to the relatively low quality of the recycled material, since most of the developed recycling processes cannot deal with the additives present in the plastic matrix, so the recycled products end up in lower-grade applications. The application of volatile organic solvents for additives removal is the preferred choice. In this study, pretreatment of plastic packaging waste to remove additives using biosolvents was investigated. The plastic waste used was high-density polyethylene (HDPE) with blue and orange colorants (pigment and/or dye). The first step was to identify the type of colorants present in the HDPE, and we found that both plastics presented only one colorant that was actually a pigment. Then, limonene, a renewable solvent, was used to solubilize HDPE. After HDPE dissolution, a wide range of alcohols (mono-, di-, and tri-alcohols) was evaluated as antisolvents in order to selectively precipitate the polymer and maximize its purity. The use of limonene as solvent for plastic dissolution, in combination with poly-alcohols with an intermediate alkyl chain length and a large number of hydroxyl (OH) groups, was found to work best as an antisolvent (1,2,3-propanetriol and 1,2,4-butanetriol), leading to a removal of up to 94% and 100% of the blue and orange pigments, respectively. Finally, three cycles of extraction were carried out, proving the capability of the solvent and antisolvent to be recovered and reused, ensuring the economic viability and sustainability of the process. This pretreatment provides a secondary source of raw materials and revenue for the recycling process, which may lead to an increase in the quality of recycled polymers, contributing to the development of an economical and sustainable recycling process.

Plastics have been increasingly used to create modern and contemporary art and design, and nowadays, museum collections hold numerous objects completely or partially made of plastics. However, the preservation of these materials is still a challenging task in heritage conservation, especially because some plastics show signs of degradation shortly after their production. In addition, different degradation mechanisms can often take place depending on the plastic composition and appropriate environmental and packaging conditions should be adopted. Therefore, methods for in situ and rapid characterization of plastic artifacts’ composition are greatly needed to outline proper conservation strategies. Infrared (IR) spectroscopy, such as attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR), is a well-established method for polymeric material analysis. However, ATR FT-IR requires an intimate contact with the object, which makes its application less appropriate for the in situ investigation of fragile or brittle degraded plastic objects. Mid-FT-IR reflectance spectroscopy may represent a valid alternative as it allows in situ measurements with minimum or even no contact, and IR data can be acquired rapidly. On the other hand, spectral interpretation of reflectance spectra is usually difficult as IR bands may appear distorted with significant changes in band maximum, shape, and relative intensity, depending on the optical properties and surface texture of the material analyzed. Presently, mid-FT-IR reflection devices working in external reflection (ER FT-IR) and diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) modes have been used in cultural heritage research studies. As the collected vibrational information depends on the optical layout of the measuring system, differences between ER FT-IR and DRIFT spectra are thus expected when the same polymer is analyzed. So far, ER FT-IR and DRIFT spectroscopy have been individually explored for the identification of plastic objects, but comparative studies between the application of two reflectance FT-IR modes have not been presented yet. In this work, the use of two portable FT-IR spectrometers equipped with ER FT-IR and DRIFTS modes were compared for plastics identification purposes for the first time. Both references of polymeric materials and historical plastic objects (from a Portuguese private collection) were studied and the differences between ER FT-IR and DRIFT spectra were discussed. The spectra features were examined considering the two different optical geometries and analytes’ properties. This new insight can support a better understanding of both vibrational information acquired and practical aspects in the application of the ER FT-IR and DRIFTS in plastic analysis.