The Identity Card of a polymeric material: some of the main identification analysis.

For those who produce or transform polymeric materials (and/or compounds based on polymeric materials), to verify or to understand, for various reasons, the type of material they are dealing with is a very common need.

Whether it concerns issues relating, for example, to the quality of the product (constancy of the used material, quality control of the produced material, conformity check of the material in case of disputes, etc.) or whether it is a matter of understanding which material a piece or article of unknown composition is made of, the determination of the nature of the polymeric material is of fundamental importance.

The "world" of identification analysis is really vast and includes a huge variety of techniques, and combinations of techniques.

Even just introducing the principles of the methods would imply a very extensive treatment to say the least and therefore we will describe, through specific examples, only some specific identification analysis.

Among the most common and complementary identification analysis, it’s possible for sure to consider infrared spectroscopy (FT-IR) (https://rdlab137.it/en/laboratory-tests/spectroscopy.html) and differential scanning calorimetry (DSC) (https://rdlab137.it/en/laboratory-tests/composition-thermal-analysis.html).

Without going into the details of the aforementioned analysis, in general terms it can be said that the first one (FT-IR) is a chemical analysis, particularly useful in determining the family to which the polymer belongs, while the second one (DSC) is a physical analysis (thermal) suitable for evaluating thermal transitions, such as the melting temperature, of a material.

The complementarity of these analysis is linked to the specific information provided by them: for example, the FT-IR analysis is able to identify well if the polymeric matrix is ​​polyethylene (PE) but not to discriminate between the various types of PE which, however, having different melting points, are identifiable by DSC.

The same thing (FT-IR spectrum practically identical but different DSC thermogram) also applies to a series of PA6T / 66 copolymers which differ only in the percentage of one of the monomers (terephthalic acid, TA) (Fig.1a and Fig.1b).

Fig.1a: FT-IR spectra of two different PA6T/66; PA6T/66T with 55%TA (green) and PA6T/66 with 65%TA (red)

Fig.1b: DSC thermograms of two different PA6T/66; PA6T/66T with 55%TA (green) and PA6T/66 with 65%TA (red). Tests carried out in N2 with heating rate of 20K/min

Conversely, in front of polymers with a similar melting temperature (for example PBT and PA6), the FT-IR analysis helps to distinguish the family they belong to (Fig.2a and Fig.2b).

Fig.2a: FT-IR spectra of PA6 (green) and PBT (red)

Fig.2a: DSC thermograms of PA6 (green) and PBT (red). Tests carried out in N2 with heating rate of 20K/min

When we consider filled materials (for example with glass fiber, mineral fillers, carbon fiber, etc.) or containing specific additives (for example flame retardant additives), another analysis can also be considered, i.e., thermogravimetric analysis (TGA). (https://rdlab137.it/en/laboratory-tests/composition-thermal-analysis.html).

This analysis makes possible to evaluate weight losses during the heating (in an inert atmosphere or not) of the material, which can be associated, in specific cases, to certain components.

The combined use of these three analyses is able to provide a good starting point not only for the identification of the polymer matrix but also for obtaining information on the composition of the compound based on the identified polymer matrix.

As an example, of combined use of the various analysis, we can consider what can be deduced from the spectra and thermograms shown in Figures 3, 4 and 5, relating to a compound whose general composition we desire to know.

From the FT-IR analysis (fig. 3) it is shown that the polymer matrix is ​​polyamide (peaks in the area 3300-2850 cm^-1), this information is confirmed and completed by the DSC thermogram (fig. 4) since the melting peak is typical of PA66. From the FT-IR analysis (fig. 3) the presence of PTFE and silicone is also highlighted (specific peaks in the area 800-500 cm^-1).

Fig.3: FT-IR spectra of PA66 (blue), specific silicon (red), PTFE (green) and of the compound to identify (violet). On the right a magnification of the 1200-500 cm^-1 zone

Fig.4: DSC thermograms of PA66 (green) and of the compound to identify(red). Tests carried out in N2 with heating rate of 20K/min

From the TGA analysis in nitrogen (fig. 5) the presence of PTFE is confirmed (and also quantified with a good approximation) as well as the absence of fillers or reinforcements (no residue, not attributable to the carbonaceous ones of the matrix, remain at the end of the test).

Fig.5: TGA thermograms of PA66+20%PTFE (green) and of the compound to identify (red). Tests carried out in N2 with heating rate of 20K/min up to 800°C

For completeness, an evaluation of the density and possible incineration of the material can give further confirmation on the presence or absence of some inorganic fillers or reinforcements and on the quantity of PTFE.

In summary, through these three analyses (FT-IR-DSC-TGA) it is possible to have an indication not only of the nature of the polymeric matrix but also a good indication of the composition (formulation) of the compound under analysis: it is in fact of a PA66 with PTFE (about 20%) and silicone, not filled.

Clearly, for a correct interpretation (comparison) of the thermograms and spectra it is necessary to have available the thermograms and spectra relating to polymeric matrices and additives of various types and kinds (i.e., it is necessary to have suitable databases available).

Further investigation, if necessary, can be done using other specific analysis (such as density measurement and incineration, as well as extractions, chromatographic analysis, SEM-EDX, etc.) (https://rdlab137.it/it/laboratorio.html).

Indeed, as ID ("identity card") of a compound, a certification body such as UL94, considers the spectra and thermograms obtained from the three mentioned analysis (FT-IR, DSC, TGA), comparing them with those acquired on the material supplied as a reference, considering specific tolerances for the spectra and thermograms obtained from the various analysis.

In RDLab137 we can support in the identification and check of the composition of a material through FT-IR analysis (also on residual after incineration of the material), DSC (also modulated) and TGA (also at high resolution).

A series of further specific analysis are also available, such as SEM-EDX (on the material or on the residue after incineration (https://rdlab137.it/en/laboratory-tests/electron-microscopy-sem-edx.html) and various chromatographic analysis (https://rdlab137.it/it/laboratorio/cromatografia.html).

RDLab137 can also provide support and advice relating not only to compositional analysis, but also on functional tests and analysis aimed at evaluating the specific behaviour of a material for the possible development of new compositions, optimization of existing ones and counter-typing.

Ing. Luca Ciceri - RDLAB137 srl

Last revision: 01/04/2021