Analysis of Plastic Waste for Sorting in Recycling Plants: An Inquiry-Based FTIR Spectroscopy Experiment for the Organic Chemistry Laboratory

This experiment introduces undergraduate organic chemistry students to analysis and interpretation of Fourier transform infrared (FTIR) spectra through characterization of postconsumer plastics. Students use FTIR spectra to identify and differentiate the common recyclable polymer resins #1-6: polyethylene terephthalate (PETE), polyethylene (HDPE or LDPE), polyvinyl chloride (PVC), polypropylene (PP), or polystyrene (PS). They then use an FTIR spectrometer with an attenuated total reflectance (ATR) accessory to investigate a self-sourced plastic container, including closures and labels, to identify the resins that compose its various components. Through these activities, students familiarize themselves with the collection and interpretation of IR spectra, a skill they subsequently use throughout the semester in the organic chemistry laboratory. Students' findings often show that a single-use container can be made up of three or more different polymer resins. This experiment has important practical applications for the sorting of plastic resins using IR-based technology in modern recycling facilities. For example, IR sensors used for automatic sorting cannot penetrate shrink-wrapped full-body sleeve labels to identify the container below, which confounds the automatic sorting processes that make plastic recycling economically viable. This experiment could also be implemented in an environmental chemistry course, ideally in conjunction with a field trip to a local recycling facility.