Polyolefin Resin Grade Verification via Attenuated Total Reflectance Spectroscopy
ATR-FTIR verifies polyolefin grades by measuring specific infrared absorbance ratios to quantify comonomer content, branching density, and copolymer structure.
Germanium Optic
Meaning
Crystalline high refractive index element used in infrared spectroscopy to analyze polymers with very high absorption coefficients. A germanium optic has a refractive index of approximately four point zero, which reduces the penetration depth of the probing light beam to a fraction of a micrometre. This extreme surface sensitivity makes it ideal for highly filled rubbers and carbon-loaded black plastics.
Surface Profiling
Depth-resolved analysis requires precise control over the optical interaction volume. Utilizing a germanium optic limits the penetration of the evanescent wave to about zero point six micrometres. This shallow reach is less than half that achieved with zinc selenide or diamond.
It allows the analyst to characterize thin surface degradation layers, skin-core effects, and oxidized structures without signal contribution from the unaffected underlying polymer matrix. This capability is especially important when evaluating weathered automotive parts where oxidation is confined to the outer ten micrometres of the plastic component.
Optical Transmission
Wavelength boundaries restrict the use of this heavy metal crystal. The germanium optic is transparent only from two to fourteen micrometres, which corresponds to the mid-infrared region. It cuts off completely below seven hundred wavenumbers, obscuring several diagnostic bending modes of chlorinated polymers.
This makes it unsuitable for analyzing polyvinyl chloride formulations that rely on low-frequency band evaluations.
Refractive Index
High index contrast is necessary to maintain total internal reflection at the sample interface. When the refractive index of the crystal is close to that of the polymer, the light beam refracts into the sample instead of reflecting. The germanium optic possesses a high index that prevents this light leakage even when analyzing high-index polymers like polycarbonates and filled polyamides.