Plastic Material Identification with Raman Spectroscopy

Raman spectroscopy is a polymer characterization technique that detects vibrations that modify the polarizability of a polymer molecule.

As such, it is a non-destructive tool and is suitable for the examination of both polymers and their additives. In general, Raman spectra can be utilized for identification purposes by producing a collection of fingerprint spectra. Those spectra can yield information about the identity and molecular characteristics of the polymer that is being studied.

Until recently, however, Raman spectroscopy has been primarily applied to the characterization of polymers in applications that are largely of a research nature. With the development of modern instrumentation, it has become more feasible to obtain Raman spectra rapidly. In addition, the equipment to generate Raman data is more affordable and easier to use than in the past.

So, let's take a look at which polymer related processes can be followed for analytical purposes in industrial applications using Raman spectroscopy as a characterization tool. Before that, let's understand briefly about Raman Spectroscopy and the equipment developments that allow for the easier utilization of the technique.

What is a Raman Spectrum?

First, double and triple bonds of polymers generally have Raman bands that tend to be much higher in intensity than when measured using other spectroscopy techniques, such as infrared analysis.

In fact, sometimes the presence of double or triple bonds may be totally absent in infrared spectra. This can make it difficult to follow certain polymerization processes in which the disappearance of the band that corresponds to the double bond is monitored. However, it is relatively easy to follow the degree of polymerization in the Raman spectrum of the material.

Advantages of Raman Spectroscopy

Other examples of molecular features that are more amenable to Raman spectroscopy than other spectroscopic techniques are sulfur bonds, such as -S-S - and -C-S-. For studies in which vulcanization is an important aspect of the chemical processes that are occurring, the detection of sulfur species can be significant. Thus, Raman spectroscopy can be used to follow the changes that occur in the vulcanizate materials as a function of different curing parameters, including time. This means that the optimum cure time can be obtained through the appropriate analysis of the data.

Finally, solutions that are based on water can be studied using Raman spectroscopy because the Raman spectrum of water is very weak in nature. On the other hand, such solutions are extremely hard to monitor using infrared spectroscopy due to the opaque feature of the solvent. Due to these overall features, emulsion polymerization reactions are more readily monitored by Raman spectroscopy than they are by infrared spectroscopy.

Applications of Raman Spectroscopy in Polymer Analysis

One application that has already been briefly discussed for Raman spectroscopy is its use to follow polymerization reactions. For certain reactions, the Raman spectrum is more sensitive than other spectroscopic techniques, such as IR.

Determining Polymer Chemical Structure, Property, Orientation...

As such, it can be effectively used to know the chemical structure of a polymer that guarantees that the desired structure and the associated properties are obtained in the final product. This is an example of the increasing use of Raman spectroscopy for the chemical identification in the production of polymer materials. In many cases, using equipment that will be described later, the analysis can be performed during the actual processing operation. That allows for the savings of time in the production process itself.

Another growing application for Raman spectroscopy is to monitor the development of both orientation and crystallization in finished parts. Those parameters can be particularly important in the manufacturing of fiber-based products. Raman spectroscopy is well suited for the study of property/structure/processing relationships in polymers. This is because it is very sensitive to small crystallinity differences as well as different conformational states in addition to the base chemical structure of polymers in general.



Raman spectroscopy can be used to deduce information on the orientation of a polymer in a part. This orientation level can have significant implications on the mechanical and other physical properties of the polymer. A primary example of a polymer for which such studies have been performed is polyethylene terephthalate or PET. In that polymer, the C=O bond tends to sharpen significantly in the crystalline form and that band can be used to monitor the orientation and crystallinity changes that are occurring due to both the thermal and stress history of a particular sample.

Advanced and Efficient Raman Analysis System

Many of the emerging applications for the use of Raman spectroscopy that have been discussed are due to equipment developments within the technology. One of the most important recent advances with Raman spectroscopy is the development of new, efficient and easy - to - use portable and handheld Raman analysis systems.



The majority of these types of handheld systems have the capability for performing the analysis of substances directly through packages thereby eliminating the need for any addition sample preparation and possible exposure to chemicals. These developments have made Raman spectroscopy directly applicable to a wide variety of field applications for which bringing samples to a laboratory for analysis is somewhat impractical.

The use of handheld Raman spectroscopy units can significantly improve cases for a significant number of practical field applications or also extend the applicability of handheld Raman units to new fields. Those new areas include both laboratory settings as well as polymer analysis directly on the process line.

Carrying out Polymer Analysis using Handheld Raman Unit

An example of a polymer analysis that can be performed in line using a handheld Raman unit is the extrusion of a polymer blend. Raman data can be collected during the actual extrusion process itself. The data that are obtained can provide important information about the proportion of the various components in the mixture.

As such, a verification of the desired blend composition can be obtained during its actual production rather than after it has been made. Necessary process adjustments can, thus be made during the blend manufacturing to guarantee that the appropriate ratio of materials is being produced. This leads to both a time savings as well as the utilization of a relatively small amount of component materials.

In summary, then, Raman spectroscopy provides a fast and non-destructive method for the analysis of different polymers. Through the development of advanced equipment, it has become possible to extend the application of Raman spectroscopy to new areas. It is anticipated that those new fields will continue to grow and expand as the overall utility of the characterization technique continues to be realized.