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Plastics can be divisive since they are convenient and inexpensive, yet have a harmful impact on the environment. These materials are found everywhere – from museums to modern medicine, and even in the ocean waves. Plastic is ubiquitous, and Raman spectroscopy can be used anywhere it is located for identification, classification, and quality testing purposes.

Raman spectroscopy for polymer analysis

Raman spectroscopy is increasingly chosen for polymer analysis because it is non-destructive, requires no sample preparation, and gives results in just seconds. It is easy on the user; even non-technical operators can collect data on-site. Raman is also environmentally friendly – requiring no chemicals, solvents, or materials for sample prep – and it does not generate any waste.
 

Learn more about the fundamentals of Raman spectroscopy in our blog article. 

FAQ about Raman spectroscopy: Theory and usage

Figure 1. Metrohm offers benchtop, handheld, and process (not pictured) Raman spectrometers.

Raman spectroscopy has many fundamental qualities that surpass other techniques for polymer analysis. These include: high material specificity, large libraries of known substances and mixtures, and the ability to sample plastics in myriad forms including clear and colored composites, coatings, and adhesives. Such accuracy and flexibility is key for the precise characterization of plastic materials and mixtures; any deviation from a standard polymer mixture can change its physical properties and color. 

What makes Raman spectroscopy unique?

Few spectroscopic techniques meet the need for fast, easy, accurate, non-destructive, and flexible testing: near-infrared (NIR) and Raman spectroscopy top this list. These techniques qualify and quantify different polymers for research, analysis, and quality control purposes.

Measuring through containers with Raman spectroscopy keeps operators safer from unknown substances.
Figure 2. Measuring through containers with Raman spectroscopy keeps operators safer from unknown substances.

The major advantages of using Raman spectroscopy for polymer and plastic analysis include:

  • In-situ sampling, made possible with high-resolution handheld Raman devices.
  • Improved safety by testing through thin barriers to avoid both human contact and material contamination (Figure 2).
  • High specificity – Raman spectroscopy is ideal for discriminating between very similar substances.
  • Elimination of interfering fluorescence. Raman can analyze more modern materials than ever before, including colored plastics.
    Find out more in our related White Paper.
  • Raman spectroscopy shows promise as a quantitative analytical technique.

How Raman spectroscopy can impact the polymer industry

The global movement toward 100% testing of incoming goods and quality checks down the production line requires efficient and low-resource methods. Raman’s capabilities make it an ideal quality control (QC) technique. With Raman, manufacturers can quickly check raw materials at the point of receipt before they enter production and avoid costs associated with long laboratory wait times, production interruptions, and training of technical personnel. Among the highest recommendations for Raman are its simplicity and ease of use for the operator. One does not have to be a trained spectroscopist to use Raman!

Knowing the exact composition of raw materials and resin blends allows manufacturers to control and optimize polymerization processes and make more consistent products that best meet customer specifications. 

For example, raw polymer materials often appear as white or black pellets, but it can be difficult to identify their composition just by looking at them. Precursors to Metrohm’s current Raman devices were used to build a Raman library of spectra based on a set of polymer references from the ResinKit Company, located in Woonsocket, RI (USA). This library was used by a global maker of artificial joints at every step of the production process. While it is impossible to discriminate between polyamide and polycarbonate visually, it is essential to distinguish each of them because different resin mixtures influence the performance and longevity of the finished product.
 

For more information about using Raman spectroscopy to identify and characterize polymers, read our Application Note.

The Benefits of Raman Spectroscopy for the Identification and Characterization of Polymers

Raman polymer analysis applications

Polymer identification can be done in less than two minutes with Raman spectroscopy. 

Hauff-Technik GmbH & Co. KG in Hermaringen, Germany, is one of the world's leading manufacturers of plastic cables, pipes, and building supplies. These products are made from polymer pellets supplied by the chemical industry. When Hauff-Technik was ready to develop a QC process for incoming materials, they opted for Raman spectroscopy instead of investing in a costly lab. Now they verify incoming polymer pellets from various suppliers with a MIRA XTR handheld Raman device in a fast, easy, and convenient receiving process.

MIRA XTR is uniquely suited to the Hauff-Technik QC process. Many polymer pellets are colored and can pose a challenge to Raman spectroscopy.  For example, black polymer pellets are known to cause fluorescence, which leads to a poor Raman signal. MIRA XTR can deal with these challenges and verify the identity of colored pellets and fluorescent samples accurately and reliably. 
 

Read on to learn more about Hauff-Technik’s experience with MIRA for polymer identification.

MIRA XTR for ID verification of incoming polymer pellets

The earliest commercial plastics, developed as viable alternatives to natural ivory, are found in celluloid billiard balls and dentures. The chemical characterization of early plastics in museum collections informs us about early celluloid composition and degradation risks. These are perfect applications for Raman spectroscopy, as it can collect important data without damaging historical artifacts. 

A 155-year-old billiard ball invented by John Wesley Hyatt is a pioneering example of reinforced polymer composites. MIRA was used to help reveal the complex composition of the Smithsonian Institution’s «original» 1868 Hyatt celluloid billiard ball [1].

MIRA was also used to study formulations and degradation states of 21 different early celluloid dentures from the National Museum of American History and Dr. Samuel D. Harris's National Museum of Dentistry [2]. A quote from the article [2] states: «Handheld Raman was demonstrated as an excellent in-situ tool for studying polymeric materials.»

 

Microplastics, defined as plastic litter less than 5 mm in size, are the most abundant form of marine debris, and are a growing concern worldwide. Research teams are reaching for Raman as an effective tool for identifying microplastics, as robust characterization of microplastics elucidates their origin and helps predict biological impacts. 

Microscopic samples are poor candidates for traditional Raman analysis, but Raman microscopy can be used to sample tiny, individual plastic particles. In an exciting application, water samples collected from the Delaware Bay (USA) surface estuary waters were sieved, and the collected microplastic particles were identified using the i-Raman EX Portable Raman Spectrometer. 
 

More information can be found in our Application Note.

Identification of microplastics with Raman microscopy


In another scenario, MIRA does precisely what it was designed for: to provide lab-quality results in non-traditional test scenarios. The handheld MIRA spectrometer is being used to analyze and trace the sources of plastic particles collected by Expedition MED campaigns in the Mediterranean Sea [3]. With this information, decision-makers can better institute environmental protection.

The Raman spectra of major commercial plastics are easily distinguished, even with additives like dyes and after years of environmental exposure.
Figure 3. The Raman spectra of major commercial plastics are easily distinguished, even with additives like dyes and after years of environmental exposure.

Research groups worldwide use Raman spectroscopy to characterize, sort, and determine the effects of long-term environmental exposure on plastic litter to solve what has been named «The Recycling Conundrum» [4]. Before plastic recycling can become more efficient and significantly impact global plastic waste, sorting complications and identification of mixed and degraded materials must be overcome. Raman is an effective solution to all of these issues (Figure 3). 

Summary

Not only is Raman spectroscopy a fast analytical technique, it is also non-destructive, environmentally friendly, and easy to use. Handheld and portable Raman instruments help this technology to become widely adopted even in nontraditional locations. The use of Raman for the analysis of various polymers is a great example of how technology can help us read the world—from the sea to QC!

References

[1] Neves, A.; Friedel, R.; Melo, M. J.; et al. Best Billiard Ball in the 19th Century: Composite Materials Made of Celluloid and Bone as Substitutes for Ivory. PNAS Nexus 2023, 2 (11), pgad360. DOI:10.1093/pnasnexus/pgad360

[2] Neves, A.; Friedel, R.; Callapez, M. E.; et al. Safeguarding Our Dentistry Heritage: A Study of the History and Conservation of Nineteenth–Twentieth Century Dentures. Heritage Science 2023, 11 (1), 142. DOI:10.1186/s40494-023-00989-2

[3] Bruno. A device used by the scientific police to study the nature of plastics collected at sea. Expédition MED. https://www.expedition-med.org/actualites/un-appareil-utilise-par-la-police-scientifique-pour-etudier-la-nature-des-plastiques-preleves-en-mer/ (accessed 2024-08-08).

[4] emmao. The Recycling Conundrum. Plastic Free Communities, 2024.

Your knowledge take-aways

Interview: Polymer ID verification in under two minutes

Application Note: Identification of microplastics with Raman microscopy

Application Note: The Benefits of Raman Spectroscopy for the Identification and Characterization of Polymers

Fluorescence-free 785 nm material ID with MIRA XTR DS

Click here to download

This free White Paper presents a survey of fluorescence suppression methods, the benefits of MIRA XTR DS, and application examples (e.g., hazardous chemicals, illicit drugs, ingredients and products used in the food and beverage industry, and manufactured materials).

Author
Gelwicks

Dr. Melissa Gelwicks

Marketing Specialist
Metrohm Raman (a division of Metrohm Spectro), Laramie, Wyoming (USA)

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