Determination of Irganox 1010 in polyethylene by infrared spectroscopy

Significance of the Topic

The accurate determination of antioxidant stabilizers such as Irganox 1010 in polyethylene is critical for ensuring polymer performance, longevity and safety. Process control of additive levels prevents under- or over-stabilization, which can lead to premature aging or unnecessary cost. Infrared spectroscopy offers a rapid, non-destructive approach well suited for routine quality assurance in industrial and research laboratories.

Objectives and Overview of the Study

This work presents a validated analytical method to quantify Irganox 1010 and chemically equivalent antioxidants in unfilled polyethylene. The method exploits the ester carbonyl absorbance at 1745 cm⁻¹, normalized against a built-in reference band of the resin at 2019 cm⁻¹. A linear calibration model relates the absorbance ratio to concentration, enabling simple, on-site monitoring of additive content, primarily for process control applications.

Methodology and Instrumentation

Sample Preparation

• Representative resin samples are hot-pressed into thin films (0.5–0.7 mm) using a hydraulic press at 200 °C, ensuring no exposure above 250 °C for more than 2–3 minutes.
  Multiple aluminum sheets and a chase mold control film uniformity, followed by inspection for defects and precise thickness measurement.

Measurement and Calibration

• Infrared spectra are recorded at ≥4 cm⁻¹ resolution, collecting a minimum of 70 scans (~30 s) per film.
• The additive peak area at 1745 cm⁻¹ is measured against a baseline from 1775 to 1706 cm⁻¹; the reference band at 2019 cm⁻¹ uses a baseline from 2108 to 1981 cm⁻¹.
• Standards are prepared by compounding known Irganox 1010 levels into polyethylene under nitrogen, molding films, and measuring triplicates.
• A linear least-squares regression of weight percent versus normalized absorbance (A1745/A2019) yields the calibration slope (M) and intercept (N) for concentration calculations (Wt% = M·ratio + N).

Instrumental Configuration

• Agilent Cary 630 FTIR spectrometer with DialPath or TumblIR transmission accessories (1000 µm path length).
• Alternative compatible platforms include the mobile/portable Agilent 5500/4500 series FTIR.
• Supporting equipment: film micrometer, hydraulic press (200 °C, 40 000 lb ram force), chase mold, aluminum sheets, scissors.

Main Results and Discussion

The calibration curve demonstrated strong linearity across the studied concentration range, confirming the reliable response of the ester carbonyl band. Triplicate measurements of both standards and unknowns exhibited high reproducibility, with minimal variation in the calculated weight percent of Irganox 1010. The use of an internal reference band effectively corrects for film thickness fluctuations, enhancing method robustness.

Benefits and Practical Applications of the Method

The described FTIR approach offers multiple advantages:

• Rapid, non-destructive analysis with minimal sample preparation.
• High throughput via easy mounting of polymer films in DialPath/TumblIR cells.
• Automated data processing through MicroLab PC FTIR software, which handles baseline setting, peak integration and concentration calculation.
• Suitability for routine quality control and process monitoring in polymer manufacturing.

Future Trends and Potential Applications

Emerging opportunities include integrating portable FTIR units for on-line or in-plant monitoring, expanding the method to other antioxidants and polymer matrices, and coupling spectroscopy with advanced chemometric models for multi-component analysis. Further developments may enable non-invasive thickness determination and automated feedback to production systems.

Conclusion

This method provides a straightforward, accurate and reproducible way to quantify Irganox 1010 in polyethylene films using FTIR spectroscopy. The combination of specialized transmission accessories and dedicated software simplifies routine implementation, making it well suited for both laboratory and industrial quality assurance environments.