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–FTIR), is a well-established method for polymeric material analysis. However, ATR-FTIR 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-FTIR 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-FTIR reflection devices working in external reflection (ER-FTIR) and diffuse reflection (DRIFT) 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-FTIR and DRIFT spectra are thus expected when the same polymer is analyzed. So far, ER-FTIR and DRIFT spectroscopy have been individually explored for the identification of plastic objects, but comparative studies between the application of two reflectance FTIR modes have not been presented yet. In this work, the use of two portable FTIR spectrometers equipped with ER-FTIR and DRIFT 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-FTIR 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-FTIR and DRIFT in plastic analysis.

塑料已经越来越多地用于创造现代和当代艺术和设计，如今，博物馆收藏品中保存着许多完全或部分由塑料制成的物品。但是，这些材料的保存仍然是遗产保护中的一项艰巨任务，特别是因为某些塑料在生产后不久就显示出降解的迹象。此外，取决于塑料成分，通常会发生不同的降解机理，应采用适当的环境和包装条件。因此，用于塑料工件的原位和快速表征的方法 非常需要构图来概述适当的保护策略。红外（IR）光谱，如衰减全反射傅立叶变换红外光谱（ATR？FTIR），是成熟的聚合物材料分析方法。但是，ATR-FTIR需要与物体紧密接触，这使得其应用不太适合对脆性或脆性降解塑料物体进行原位研究。中红外光谱反射光谱法可能是一种有效的替代方法，因为它允许以最小或什至没有接触的方式进行原位测量，并且可以快速获取红外数据。另一方面，反射光谱的光谱解释通常很困难，因为红外波段可能会出现扭曲，并且波段最大值，形状和相对强度发生明显变化，具体取决于所分析材料的光学特性和表面纹理。目前，在文化遗产研究中已经使用了以外部反射（ER-FTIR）和漫反射（DRIFT）模式工作的中速FTIR反射设备。由于收集的振动信息取决于测量系统的光学布局，因此在分析同一聚合物时，可以预期ER-FTIR和DRIFT光谱之间的差异。到目前为止，已经单独探索了ER-FTIR和DRIFT光谱用于识别塑料物体，但是还没有提出两种反射FTIR模式的应用之间的比较研究。在这项工作中，首次比较了两个配有ER-FTIR和DRIFT模式的便携式FTIR光谱仪用于塑料识别的目的。研究了聚合物材料和历史塑料物品（来自葡萄牙的私人收藏）的参考资料，并讨论了ER-FTIR和DRIFT光谱之间的差异。考虑到两种不同的光学几何形状和分析物来检查光谱特征。特性。这种新的见解可以支持对ER-FTIR和DRIFT在塑性分析中的应用，更好地理解所获得的振动信息和实际情况。