Influence of Layer Thickness on the Detection of Plastic Films Using Optical Photothermal Infrared Spectroscopy...

Area of Science:

• Materials Science
• Spectroscopy
• Polymer Chemistry

Background:

• Accurate identification of plastic materials is crucial for recycling and quality control.
• Optical photothermal infrared spectroscopy (O-PTIR) offers a non-destructive method for chemical analysis.
• Understanding the detection limits of O-PTIR based on film thickness is essential for its practical application.

Purpose of the Study:

• To investigate the effect of varying film thickness on the qualitative identifiability of common plastics using O-PTIR.
• To determine the minimum detectable film thickness for polyamide 6 (PA6) and polyethylene terephthalate (PET) using O-PTIR.
• To assess the feasibility of O-PTIR for analyzing thin plastic films.

Main Methods:

• Thin films of PA6 and PET were prepared on different polymer substrates (polyethylene and polypropylene).
• Film thicknesses were progressively reduced using a drop deposition process.
• O-PTIR spectroscopy was employed to monitor the characteristic signals of the plastic films as thickness decreased.

Main Results:

• The characteristic O-PTIR signals for PA6 and PET decreased with decreasing film thickness, as anticipated.
• The O-PTIR detection limit was not reached; signals remained detectable at the minimum achievable stable film thicknesses (approx. 0.18 μm for PET, 0.29 μm for PA6).
• Characteristic peaks of the substrate plastics were still clearly visible even with the thinnest applied plastic films.

Conclusions:

• O-PTIR is highly sensitive for qualitative identification of plastic films, even at sub-micron thicknesses.
• The drop deposition method limited the study to minimum film thicknesses of approximately 0.18-0.29 μm.
• Further research is needed to explore other factors influencing O-PTIR measurements of plastic films and to potentially achieve even lower detection limits.