Determination of Limonene in Recycled HDPE Pellets

Significance of the Topic

Recycling of high density polyethylene pellets is vital for reducing plastic waste and producing food grade materials. Limonene, a citrus oil contaminant, can impart undesirable odors and must be removed to ensure compliance with safety standards.

Objectives and Study Overview

This study aims to develop and validate a rapid and sensitive method for determining limonene levels in recycled HDPE pellets. The method must reliably detect concentrations below the 20 parts per million limit required for food contact applications.

Methodology and Instrumentation

Pellet samples were extracted by incubating 0.1 grams of HDPE in one milliliter of carbon disulfide at ambient temperature for sixty minutes. Extracts were injected into a gas chromatograph coupled to a single quadrupole mass spectrometer. A full scan over m/z 42 to 350 was used to identify limonene based on quantifier ion m/z 93 and qualifier ion m/z 68.

• Injector type and temperature split splitless at 250°C
• Column 30 meter by 0.25 millimeter by 1.4 micrometer Scion624-MS
• Oven program 55°C hold one minute then ramp to 220°C at 20°C per minute
• Carrier gas helium at 1 milliliter per minute
• Transfer line temperature 250°C; ion source 200°C

Instrumentation Used

The analysis employed a SCION 436 gas chromatograph with single quadrupole mass spectrometer and an 8400 autosampler. Library matching and quantitation were performed using MSWS software with the NIST database.

Main Results and Discussion

The retention time for limonene was 7.265 minutes. Calibration standards from 0 to 40 parts per million showed excellent linearity with an R2 value of 0.9996. Triplicate pellet samples yielded an average concentration of 0.01 micrograms per gram (0.01 parts per million), well below the 20 parts per million threshold. Precision was high, with 0.20 percent relative standard deviation for peak area and zero percent for calculated concentration.

Benefits and Practical Applications

The method offers rapid sample preparation and high sensitivity, enabling quality control laboratories to verify that recycled HDPE meets regulatory limits for odor and safety. It supports production of food grade plastics and other sensitive applications by ensuring contaminant removal.

Future Trends and Potential Applications

Advances may include automated headspace sampling, solid phase microextraction techniques, and coupling with high resolution mass spectrometry for even lower detection limits. Expanding the method to other terpenes and contaminants can further improve recycling quality control.

Conclusion

The SCION 436 GC-MS method provides a robust, reproducible approach for determining trace limonene in recycled HDPE pellets. Results confirm effective deodorisation during recycling and compliance with food contact requirements.

References

• Viridor co uk Plastic Recycling 2018
• Welle F Develop A Food Grade HDPE Recycling Process The Waste and Resources Action Programme 2005