How to analyse odours in post-consumer recycled plastics

Recycled plastic bottlesWhat are post-consumer recycled plastics?

Post-consumer recycled (PCR) plastics are plastic materials that are recycled from plastic waste after it has been used by a consumer.

With a global push to move towards a circular economy, which is resulting in an increase in the use of recycled materials to reduce waste, manufacturers are being urged to produce or use more PCR plastics, especially for food and beverage packaging.

Rigorous quality control (QC) is needed to ensure the recycled plastics do not produce volatile emissions that could be harmful or have a negative impact on the packaged product (e.g., malodours).

To do this, an efficient way to detect and identify the volatile organic compounds (VOCs) responsible for the malodours, or bad smells, must be found.

 

Challenges with detecting malodours in recycled plastics

However, analysts are faced with the following challenges:  

  • Some approaches to detecting bad smells, such as the eNose or human sensory panels, cannot identify the precise compounds responsible for the odours, meaning the recycling process cannot be improved and QC failures continue to occur.

  • Gas chromatography–mass spectrometry (GC–MS) is a widely-used analytical method for analysing VOCs, but conventional one-dimensional GC–MS chromatograms are dominated by highly-abundant aliphatic compounds, while odorants are often trace components, making them difficult to spot.

  • Traditional sample extraction techniques that are used with GC–MS, such as headspace or solid-phase microextraction (SPME), often struggle to reach the sensitivity required to detect trace odorants.

  • Analysis must be simple, automated and compatible with high-throughput QC laboratories.

 

Overcoming low sensitivity, poor detection of compounds and slow processes when analysing recycled plastics for bad smells

 

Applying the appropriate instrumentation and techniques can help to overcome these challenges:

  • Identifying precise compounds: Enhanced separation using two-dimensional gas chromatography (GC×GC) with time-of-flight mass spectrometry enables confident identification of odorants that cannot be identified using 1D GC–MS, allowing recycling processes to be improved.

  • Detecting trace odorants: Improved detection of trace odorants can be achieved by combining preconcentration using thermal desorption (TD) at the sample preparation stage, followed by enhanced separation and high-sensitivity mass spectrometry using a time-of-flight mass spectrometer.

  • Simple, automated workflow: Direct desorption of volatiles from plastic pellets is simple and the whole workflow can be automated and streamlined by software designed to control all the analytical instruments and conduct data processing. Further, differences between batches of plastics can be automated using an alignment and chemometrics platform within the software.

  • Compatible with QC laboratories: It is simple to translate from TD–GC×GC–TOF MS to TD–GC×GC–FID in QC laboratories.  

 

 

Improved characterisation of odours from recycled plastics

 

 

 

Further information:
 

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