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.
Carbonyl Oxidation Band
Meaning
Infrared absorption intensity within the 1700 to 1750 inverse centimetre region quantifies the concentration of carbonyl groups produced by photo-oxidative degradation in polymeric materials. A carbonyl oxidation band appears when ultraviolet radiation or thermal stress breaks polymer chains, resulting in the formation of ketones, aldehydes, or carboxylic acids. Spectroscopic analysis of this spectral feature allows laboratory technicians to track the chemical aging of thermoplastic resins.
Processing Baseline
Baseline measurements for this peak often rely on the virgin resin feedstock before any thermal history occurs in the extruder. Injection moulding machines can induce shear heating that promotes early chemical modification even when the material remains within recommended temperature ranges. Production runs involving high ratios of regrind show elevated absorbance levels in this region because recycled material contains a higher concentration of chain scission products.
Degradation Mechanism
Chain scission represents the fundamental event that alters the polymer backbone and introduces oxygenated functionalities. Radical reactions propagate through the matrix once the first carbonyl groups form, which accelerates the loss of mechanical strength and flexibility. Thin wall sections of a moulded part show higher levels of oxidative damage because the surface area to volume ratio allows for faster penetration of oxygen into the internal structure.
Cost Impact
Excessive accumulation of these oxidative products during moulding leads to brittle failure modes under impact loading or cyclic stress. Quality departments reject batches displaying absorbance values above established failure thresholds to avoid field failures in parts intended for long term outdoor exposure. Precise control of melt temperature and residence time limits the growth of this peak and preserves the physical properties required for final application.