As a general rule, we begin a plastic material identification with
an FT-IR Analysis,
with the term 'FT-IR' standing for Fourier Transform Infrared Spectroscopy. Basically
speaking that means we direct a beam of infrared light at the unknown plastic material,
vary the frequecy in a linear manner, and record 'energy' given off by the substance at each
Every family of plastic materials has its own unique 'FT-IR Fingerprint' with different
types and sizes of peaks representing different types of bond energies given off by organic chemical bonds
holding the elements together within the material.
By comparing the FT-IR scan of an unknown material to the scans of literally 10's of thousands of scans of reference materials
we can usually narrow down the field of possibilities to one family of plastic materials, though sometimes we may need additional
pieces of the puzzle such as degradation tempertaure, melting temperature, and/or glass transition temperature before we can confidently
tell a client what base plastic material a finished part or resin contains.
The above graphic contains the FT-IR scans of two very similar, yet subtly different plastic materials. Most likely a difference in the grade of plastic, pigments/colorants, and/or filler content account for the differences observed in the two materials' scans.
If after the FT-IR Analysis (see above) we still have questions or doubts about a
platic material's base family, we turn to a handy analytical technique called Thermogravimetric Analysis, usually abbreviated as TGA, for help.
In a nutshell, TGA involves taking a carefully measured mass of a material and recording mass loss as the material undergoes thermal heating at a controlled rate. Each marked period of mass change (loss) represents a material thermally degrading. The temperature at which a material thermally degrades is called the material's Degradation Temperature.
We use an unknown plastic material's degradation temperature to rule out possibilities suggested by the results of FT-IR Analysis and to
help us set up for the next test called Differential Scanning Calorimetry, usually abbreviated as DSC.
Below you will see an example of a data plot from a typical Thermogravimetric Analysis of a plastic material.
With data from the FT-IR Analysis and Thermogravimetric Analysis as our starting point,
we then use Differential Scanning Calorimetry, typically abbreviated as DSC, to determine
the material's Melting Temperature, usually abbreviated as Tm, and Glass Transition Temperature, usually abbreviated as Tg.
At this point we compare the Tm, Tg, and degradation temperature values to those of the plastic materials indicated as possibilities by the FT-IR Analysis and decide on the best possible matches.