Determination of Irganox 1010 in polypropylene by infrared spectroscopy

Significance of the topic

This method addresses the quantitative determination of the common phenolic antioxidant Irganox 1010 in polypropylene. Antioxidants are critical for preventing polymer degradation during processing and in-service life. Reliable, rapid quantification of such additives is essential for process control, quality assurance and compliance with material specifications in plastics manufacturing.

Objectives and overview

The primary goal is to develop a robust FTIR spectroscopy protocol for measuring Irganox 1010 levels in unfilled, unpigmented polypropylene where the additive package is predefined. The approach employs a characteristic ester carbonyl absorption at 1745 cm⁻¹ normalized to a polypropylene reference band at 4062 cm⁻¹. Calibration is established by linear regression of normalized absorbance ratios versus known additive concentrations.

Methodology

Sample films of 0.5–0.7 mm thickness are prepared by hot pressing polypropylene powder blended with known amounts of Irganox 1010. Minimal thermal exposure (≤250 °C for ≤3 min) preserves sample integrity. FTIR spectra are acquired at 4 cm⁻¹ resolution over 70 scans per film. Peak areas are measured under the additive carbonyl band (1745 cm⁻¹) and the polypropylene reference band (4062 cm⁻¹) using dual-baseline integration. The ratio A1745/A4062 is substituted into a linear calibration equation (Wt% = M×ratio + N) to compute additive content. Triplicate measurements ensure statistical reliability.

Instrumentation

• Agilent Cary 630 FTIR spectrometer with DialPath or TumblIR transmission accessory (1 000 µm path length)
• Alternative portable FTIR units (Agilent 5500/4500 Series)
• Hydraulic press with 200 °C heated platens and ≥40 000 lb force
• Chase mold and aluminum sheets (0.051–0.178 mm)
• Film micrometer (accuracy ±0.01 mm)

Main results and discussion

The calibration curve exhibited excellent linearity across the tested concentration range, with minimal scatter among triplicate films. The method reliably detected Irganox 1010 down to approximately 0.05 wt% with relative standard deviations below 2%. The DialPath and TumblIR accessories allowed rapid, reproducible sample mounting and real-time positioning, reducing measurement variability.

Benefits and practical applications

• Fast, non-destructive analysis of polymer films without extensive sample preparation
• High reproducibility and accuracy for process control of antioxidant addition
• Applicability to on-line or at-line quality assurance in polymer manufacturing
• Adaptable to other carbonyl-bearing additives given known additive packages

Future trends and possibilities

Advances in portable FTIR instrumentation, coupled with automated sampling accessories, will enable field or production-floor measurements. Integration of multivariate calibration and chemometric models can extend the method to complex additive blends and filled or pigmented resins. Emerging mid-IR imaging and mapping techniques may offer spatially resolved additive distribution analysis in molded parts.

Conclusion

An FTIR-based approach using the Agilent Cary 630 and associated transmission cells provides a streamlined, accurate method for quantifying Irganox 1010 in polypropylene films. Its speed, reproducibility and minimal sample preparation make it well suited for routine process control and QA/QC in polymer production.

References

• Collins W, Seelenbinder J, Higgins F. Determination of Irganox 1010 in polypropylene by infrared spectroscopy. Agilent Technologies Application Note 5991-0505EN, 2012.