By Dr. Carolin Fischer, Application Specialist and Dr. Natalie Rudolph, Manager Business Field Polymer
Sporting goods and toys for kids or pets are often made of flexible plastics. Some examples are sensory chewing toys, action figurines as well as balls of various kinds. A common polymer used for these applications is PVC (polyvinylchloride), because it can be made softer and more flexible by adding plasticizers. These compounds are not covalently bonded to the polymer chain. Therefore, they can evaporate or be rinsed out by saliva or sweat. This outgassing or diffusion of plasticizers can be harmful.
One such example is the family of phthalates, which is known to cause a number of health risks. They act like hormones, and have been shown to cause liver damage, infertility, diabetes, cancer and more. Therefore, the European Union has banned a number of phthalates in products, which are in contact with food, in toys, in baby articles and medical supplies in its REACH regulation that is in effect since 2007.
Harmful components can be detected by thermal analysis
Thermal analysis can be used to detect plasticizers in polymers. By means of TGA-FT-IR analysis, it is possible to not only identify the kind of plasticizer used, but also analyze products regarding their plasticizer content.
In the following use case, the surface layer of different toy balls was cut in small pieces and measured with the PERSEUS® TG 209 F1 Libra . The following table gives an overview of the measurement conditions:
Detect plasticizer content with the TG 209 F1 Libra
Figure 1 shows that the inspected ball exhibits several mass-loss steps during pyrolysis. These mass-loss steps result from the evaporation of plasticizer or other organic additives and at last the pyrolysis of the polymer in the temperature range between 200°C and 500°C.
The Gram Schmidt curve (in red) displays the overall IR intensities and behaves as a mirror image of the DTG curve. It shows also maximum intensities during the mass-loss steps. This proves the interaction of the evolved compounds with the IR beam.
More detailed composition results with a FT-IR spectrum
For detailed analysis of the plasticizer contained, a 2D FT-IR spectrum was extracted and compared to gas phase libraries to identify the evolved compounds. High similarity was found for the spectrum at 266°C to the library spectra of di-n-octylphthalate (DOP, blue) und bis(2-ethylhexyl)phthalate (DEHP, green). It can be assumed that a single compound or a mixture of different phthalates was released. However, this comparison clearly indicates that the ball contains harmful phthalates. Further analysis is required to identify the plasticizers.
A second ball was investigated under the same measurement conditions. A clear difference can be observed in the pyrolysis behavior. The comparison of the extracted FT-IR spectra for the two ball samples, both extracted at 266°C, show completely different vibration patterns (see figure 3).
The comparison of the spectra at 266°C of ball no 2 (blue) to the gas phase library gives clear accordance with the spectrum of tributyl citrate (green). For ball no. 2, the toxic phthalate plasticizers were replaced by nontoxic citric ester, which also acts as a plasticizer.
Make sporting goods and toys safer!
Outgassing and decomposition processes of polymers can be investigated by thermal analysis. Thermogravimetry indicates the release of gases already below 300°C. Only evolved gas analysis like FT-IR can identify the gases released.
The above example explains how to identify the different plasticizers used and therefore, to distinguish between toxic and non-toxic additives. The PERSEUS® TG 209 F1 Libra® is perfectly suited to help make sporting goods and toys safer for us and our children.