Knowing what kind of plastic you’re working with is a great place to start when trying to create a new product or identifying a competitor’s product. If you know the composition of a product you can identify problem areas or improve on specific properties. Verification of products and their compositions is also important when conformance to regulations and directives are necessary.
Apart from reading the recycling code on the label, there are various ways to identify a polymer or even the composition of a polymer blend. Measuring polymer densities would be a classic high school experiment, but it has its limitations though as polymer products rarely consist of pure polymers and are usually loaded with additives such as colorants, fillers etc. These additives will compromise a polymers density measurement and result in an incorrect identification.
Using more efficient analytical instrumentation such as Fourier transform infrared (FTIR) and ultraviolet (UV) spectrometers delivers a high quality analysis of the polymer as well as the constituents at hand.
FTIR spectroscopy can easily identify the chemical nature of a material. It is a very powerful tool for investigating the composition of copolymers and polymer blends. Gauging the degree of degradation or identifying unknown contaminants can also be done using this technique. Antioxidants and UV stabilizers which consist of characteristic absorption peaks in the UV range can easily be identified using UV spectroscopy.
There are many other ways to determine the polymer composition, but these methods are without a doubt the cheapest. Other methods such as thermogravimetric analysis (TGA) or differential scanning calorimetry are also very useful tools in these applications, but should be kept in the arsenal until they're truly needed.
FTIR spectrum of a PET sample with an 82.53 % PET composition.
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