Surface Characterization
Spectroscopic analysis identifies the molecular composition of a material surface by measuring how it absorbs infrared light. This method is commonly known as attenuated total reflectance ftir and works by pressing a sample against a high refractive index crystal. It allows for the direct examination of solid paper or plastic films without the need for complex sample preparation like pelletizing.
The resulting spectrum shows the functional groups present in coatings or additives.
Chemical Identification
Infrared radiation enters the crystal at an angle that causes internal reflection but creates an evanescent wave that penetrates into the sample surface. Chemical bonds absorb specific frequencies from this wave and the detector records the reduction in intensity. In the paper industry, attenuated total reflectance ftir helps verify the presence of moisture barriers or synthetic sizing agents.
If the pressure is insufficient, the signal strength drops and the baseline of the spectrum becomes noisy. For porous papers, the penetration depth might even cover a mix of coating and top-layer fibres.
Sample Depth
Effective depth of the analysis is limited to a few microns depending on the wavelength and the crystal material. This shallow reach ensures that only the surface chemistry is captured rather than the bulk fibre properties. Contact pressure between the crystal and the substrate must be uniform to produce a repeatable signal.
High-density coatings require more pressure to achieve the necessary optical contact for a clear reading.
