Meaning
Vibrational overtone absorption bands in the seven hundred to twenty-five hundred nanometer spectral range differentiate organic polymer structures. Applying near infrared spectroscopy allows rapid non-destructive identification of resin types and moisture levels in plastic pellets and recycled flakes. The technique measures molecular absorption from carbon-hydrogen, oxygen-hydrogen and nitrogen-hydrogen bonds to identify polymer chemistries instantly.
It marks the boundary between laboratory wet chemistry testing and real-time online material identification in recycling streams.
Spectral Analysis
Molecular absorption patterns generate unique spectral fingerprints for distinct polymer families. Utilizing near infrared spectroscopy enables quantitative measurement of hydroxyl numbers in polyols and moisture content in polyamides without solvent extraction.
Sorting Utility
Automated sorting facilities deploy optical sensors above conveyor belts to separate post-consumer polymer streams. Near infrared spectroscopy identifies polyethylene terephthalate and polypropylene containers in milliseconds, directing air jets to sort flakes accurately. Dark pigments containing carbon black absorb infrared energy across all wavelengths, preventing spectral reflection and causing identification failure.
Recycling operators combine optical sorting with density separation to process dark resin fractions.
Process Monitoring
Optical probes fitted to extrusion barrels measure melt composition continuously during compounding. Shifts in near infrared spectroscopy data alert operators to feed throat segregation or copolymer ratio drift before off-spec pellet batches fill storage silos. In-line monitoring reduces sampling labor and eliminates laboratory testing delays during continuous compounding.
Chemometric calibration models translate raw absorbance spectra into direct concentration readings for active additives.
