Plastics can be polarizing because, while convenient and inexpensive, they negatively influence the environment. These materials can be found in various settings, including museums, modern medicine, and even ocean waves. Raman spectroscopy can identify, classify, and assess plastic quality wherever it is found.
Raman Spectroscopy for Polymer Analysis
Raman spectroscopy is increasingly used for polymer characterization because it is non-destructive, requires no sample preparation, and produces data in seconds. It is also simple for the user; even nontechnical personnel can collect data on-site.
Raman is also environmentally benign, using no chemicals, solvents, or sample preparation equipment and producing no waste.
Figure 1. Metrohm offers benchtop, handheld, and process (not pictured) Raman spectrometers. Image Credit: Metrohm Middle East FZC
Raman spectroscopy provides numerous inherent advantages over other techniques for polymer investigation. These include excellent material specificity, extensive libraries of known chemicals and mixes, and the capacity to test plastics in various forms, such as clear and colored composites, coatings, and adhesives.
Such accuracy and flexibility are essential for precisely characterizing plastic materials and combinations; any divergence from a conventional polymer mixture might alter its physical properties and color.
What Makes Raman Spectroscopy Unique?
Few spectroscopic techniques match the need for rapid, easy, accurate, non-destructive, and flexible testing, with near-infrared (NIR) and Raman spectroscopy at the top of the list. These methods qualify and quantify various polymers for research, analysis, and quality control applications.
The primary benefits of employing Raman spectroscopy for polymer and plastic investigation are:
- High-resolution handheld Raman instruments enable in-situ sampling capabilities.
- Improved safety by testing through thin barriers, preventing human touch and substance contamination (Figure 2).
- Raman spectroscopy has high specificity, making it useful for distinguishing between identical compounds.
- Eliminates interfering fluorescence and can analyze contemporary materials such as colored plastics.
- Raman spectroscopy is a promising quantitative analytical tool.
Figure 2. Measuring through containers with Raman spectroscopy keeps operators safer from unknown substances. Image Credit: Metrohm Middle East FZC
How Raman Spectroscopy Can Impact the Polymer Industry
The global push for 100 % testing of incoming items and quality inspections along the production line necessitates efficient and low-resource approaches. Raman's characteristics make it an excellent quality control (QC) method.
Raman allows manufacturers to inspect raw materials immediately upon receipt before they enter production, saving money on long laboratory wait times, production disruptions, and technical personnel training.
Raman is highly recommended for operators because of its simplicity and convenience. You do not need to be a trained spectroscopist to use Raman.
Knowing the exact composition of raw materials and resin blends enables producers to better regulate and optimize polymerization operations, resulting in more consistent products that satisfy client demands.
Raw polymer materials, for example, frequently appear as white or black pellets, but it is challenging to identify their composition based solely on appearance.
Precursors to Metrohm's current Raman devices were used to create a Raman spectra library based on polymer references from the ResinKit Company in Woonsocket, Rhode Island (USA).
A multinational manufacturer of artificial joints used this library at every stage of the manufacturing process. While it is impossible to tell the difference between polyamide and polycarbonate visually, it is critical to do so because differing resin compositions affect the completed product's performance and durability.
Raman Polymer Analysis Applications
Quality Control
Raman spectroscopy allows you to identify polymers in less than two minutes.
Hauff-Technik GmbH & Co. KG of Hermaringen, Germany, is a renowned manufacturer of plastic cables, pipes, and building supplies. These products are created with polymer pellets provided by the chemical industry.
When Hauff-Technik decided to build a quality control method for incoming materials, they chose Raman spectroscopy over a pricey lab. They now verify arriving polymer pellets from numerous sources using a MIRA XTR handheld Raman device in a quick, simple, and convenient receiving procedure.
MIRA XTR is perfectly adapted to the Hauff-Technik QC procedure. Raman spectroscopy can be difficult to perform on many colored polymer pellets.
For example, black polymer pellets are known to induce fluorescence, which results in a weak Raman signal. MIRA XTR can handle these obstacles while precisely and reliably verifying the identity of colored pellets and fluorescent samples.
Research and Education
Celluloid billiard balls and dentures contain the earliest commercial polymers created as viable substitutes for genuine ivory. The chemical analysis of early plastics in museum collections provides information regarding early celluloid composition and degradation risks.
These are ideal applications for Raman spectroscopy because they may collect critical data while preserving historical objects.
A 155-year-old billiard ball invented by John Wesley Hyatt is an early example of reinforced polymer composites. MIRA was used to expose the intricate structure of the Smithsonian Institution's "original" 1868 Hyatt celluloid billiard ball.1
MIRA was used to analyze the compositions and degradation of 21 early celluloid dentures from the National Museum of American History and Dr. Samuel D. Harris' National Museum of Dentistry.2 According to the article, “Handheld Raman was demonstrated as an excellent in-situ tool for studying polymeric materials.”2
Environmental Monitoring of Microplastics
Microplastics, defined as plastic litter less than 5 mm in size, are the most common marine debris and an increasing global concern. Researchers are using Raman to discover microplastics since its robust characterization elucidates their origin and aids in predicting biological repercussions.
Microscopic materials are unsuitable for typical Raman analysis, although Raman microscopy can collect tiny, individual plastic particles.
In an intriguing application, water samples from the Delaware Bay (USA) surface estuary waters were sieved, and microplastic particles were identified with the i-Raman EX Portable Raman Spectrometer.
In another case, MIRA performs exactly as intended: it produces lab-quality results in non-traditional test circumstances.
The handheld MIRA spectrometer is being used to identify and trace the sources of plastic particles collected during Expedition MED activities in the Mediterranean Sea.3 With this information, policymakers can better implement environmental protection.
Recycling
Raman spectroscopy is used by researchers worldwide to define, classify, and identify the impacts of long-term environmental exposure on plastic litter to solve what is known as "The Recycling Conundrum".4
Before plastic recycling becomes more efficient and substantially impacts global plastic waste, sorting issues and the identification of mixed and degraded materials must be addressed. Raman provides an excellent answer to these problems (Figure 3).
Figure 3. The Raman spectra of major commercial plastics are easily distinguished, even with additives like dyes and after years of environmental exposure. Image Credit: Metrohm Middle East FZC
Summary
Raman spectroscopy is rapid, non-destructive, ecologically safe, and simple. Handheld and portable Raman equipment enable this technology to be extensively implemented, even in unconventional settings.
The application of Raman to the examination of diverse polymers is an excellent illustration of how technology can help us interpret the world—from the sea to QC.
References
- 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
- 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
- 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).
- emmao. The Recycling Conundrum. Plastic Free Communities, 2024.
This information has been sourced, reviewed and adapted from materials provided by Metrohm Middle East FZC.
For more information on this source, please visit Metrohm Middle East FZC.