ATR FTIR Spectroscopy Calibration for Slip Additive Surface Concentration Measurement
ATR FTIR spectroscopy quantifies polyolefin slip bloom within the evanescent zone, linking surface migration to friction without solvent extraction delays.
Diamond Crystal
Meaning
Solid-state internal reflection elements manufactured from single-crystal carbon provide the chemical inertness and extreme hardness required for pressure-contact infrared spectroscopy of rigid polymeric materials. Within attenuated total reflectance sampling accessories, a diamond crystal transmits infrared energy across the mid-infrared region while withstanding clamping pressures exceeding 400 MPa. The high refractive index of 2.4 allows adequate penetration of the evanescent wave into stiff thermoplastic matrices.
Intrinsic multiphonon absorption bands suppress signal throughput between 1800 cm-1 and 2600 cm-1, marking the physical boundary where this material cannot gather quantitative spectral data.
Mechanical Durability
Contact with hard, highly filled polymer systems causes rapid abrasive wear on softer internal reflection elements. Mineral-filled nylon, glass-reinforced polypropylene, and metal-filled compounds can be forced against the diamond crystal without scratching or fracturing the substrate. Clamping pressures must deform tough thermoplastic pellets to establish the intimate optical contact necessary for reproducible peak intensities.
Lower-cost crystal alternatives shear under identical clamping torques. The mechanical rigidity ensures consistent path lengths over thousands of sample loadings.
Optical Path
Total internal reflection at the interface creates an evanescent field whose penetration depth depends directly on the refractive index of diamond. When testing polyolefins with an index of 1.5, the diamond crystal yields an effective penetration depth of approximately two micrometers at 1000 cm-1. This optical property restricts the sampling volume to the immediate surface boundary layer of the polymer coupon.
Consequently, bulk structural properties cannot be confirmed if surface segregation has occurred.
Inspection Procedure
Quality assurance desks use these optics to identify unknown regrind compositions and assess filler loadings directly on finished moulded components. Surface bloom of slip agents or internal antistats produces disproportionately strong signals against a diamond crystal due to shallow penetration depths. Testing bulk properties requires carving away the outer skin before clamping the specimen.
Virgin pellets require maximum clamp load to generate stable quantitative spectra.