Some Thoughts on the Monitoring of Pristine and Aged Plastics by FT-IR Spectroscopy

Plastics can be identified by infrared-(IR)-spectroscopy. Often, the materials possess additives that confer special properties to them, such as elasticity, hardness, UV stability and color, but make it inherently more difficult to identify the polymer material associated. The inorganic salt calcium carbonate (CaCO3) is one such additive that is used as filler, often in polythene-type plastics. Frequently, the IR absorption bands of CaCO3 obscure the underlying bands of polythene. This may lead to misidentification of the material, especially in the case of microplastics (MPs), particles of less than 5 mm in size, where only small amounts of material are at hand. Over time, plastic material ages, where an automated identification of aged plastics can also lead to misidentification of the plastic, especially in the case of MPs. Here, the authors show that photo-oxidative aging does not only happen with polythene and polypropylene, but also with polystyrene and acrylonitrile-butadiene-styrene (ABS) co-polymer. Finally, the identification of the extent of photo-oxidation in the material can help monitor the integrity of plastics. Typical examples of monitoring the soundness of plastic chemical containers in a laboratory setting are given.