When recycling plastics, it is important to classify the types of plastic recovered. This process demands the following conditions: (1) instantaneous identification, (2) measurements unaffected by shape, and (3) online measurement. The Fourier Transform Infrared spectroscopy (FTIR) analysis of waste plastics using a horizontal ATR with a diamond prism is shown below. This method is relatively unaffected by the shape of the plastic and can analyze hard plastics.

Spectrum of polyethylene and polystyrene

Fourier Transform Infrared Spectrophotometer (FTIR)

Fourier Transform Infrared Spectrophotometer (FTIR)

This instrument shines infrared light onto the molecules, which absorb infrared radiation equivalent to the interatomic vibrational energy of the atoms that comprise the molecules. It then estimates the structure and quantifies the compound by investigating this IR absorbance.