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.
Infrared Spectroscopy
Meaning
Analytical technique that measures the absorption of electromagnetic radiation to identify chemical functional groups within a polymer matrix. Infrared spectroscopy generates a unique spectral fingerprint based on the vibrational frequencies of the covalent bonds in the polymer chain. This method differentiates between similar resins, evaluates copolymer ratios, and detects oxidation or degradation.
Vibrational Mechanism
Energy absorption occurs when the frequency of the incoming light matches the natural vibration of a molecular bond. In infrared spectroscopy, the molecule must undergo a change in dipole moment during vibration to absorb the radiation. This interaction creates distinct peaks in the spectrum that correspond to carbonyl, hydroxyl, or amide groups.
The intensity of these peaks relates directly to the concentration of the specific functional group in the sample, allowing for both qualitative polymer identification and quantitative measurement of additive packages.
Process Monitoring
In-line monitoring allows moulders to track chemical changes during the extrusion or reaction process. Infrared spectroscopy can be integrated into extrusion dies using high-pressure fiber-optic probes. This setup measures real-time polymer blend ratios and additive levels as the melt flows through the die.
Such direct monitoring avoids the delay of laboratory testing and prevents the production of off-specification batches.
Resin Identification
Quality control departments rely on quick identification of incoming raw materials. With infrared spectroscopy, a technician can verify whether a delivery consists of polypropylene, polyamide, or polyethylene within minutes. This rapid test prevents resin contamination in silos and ensures that only the correct grade is fed to the injection moulding machine.