Spectral IR reflectance analysis of black polymer samples with different electrical conductivities. Important results concerning plastics recycling

The infrared spectroscopic analysis of black polypropylene (PP) polymers with varying electrical conductivities shows that increasing conductivity leads to a pronounced attenuation or complete masking of characteristic infrared absorption bands. This behavior arises from interactions between the incident electromagnetic radiation and free charge carriers, thereby limiting the applicability of Fourier-transform infrared (FTIR) spectroscopy for reliable material identification. Comparable limitations may also occur in non-black polymers that exhibit sufficiently high electrical conductivity. Theoretical modeling and experimental measurements of the samples are presented.