60 Years of NETZSCH-Gerätebau: The Thermobalance in Use at the Department of Polymer Materials at the University of Bayreuth

Learn, how the Department of Polymer Materials at the University of Bayreuth uses the thermobalance TG 209 F1 Libra® in conjunction with Kinetics Neo for the prediction of the aging behavior of plastics. 

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Our long-standing customer, the University of Bayreuth, Germany, also uses a TG 209 F1 Libra®. Find out in the following field report how the Department of Polymer Materials at the University of Bayreuth uses the TG 209 F1 Libra® in conjunction with the NETZSCH Kinetics Neo software for prediction of the aging behavior of plastics. 

User report from the University of Bayreuth:

Source: uni-bayreuth.de (© University of Bayreuth)

Resist the Ravages of Time or Predict Them?

How the Department of Polymer Materials at the University of Bayreuth uses the NETZSCH TG 209 F1 Libra® in conjunction with the NETZSCH Kinetics Neo software for prediction of the aging behavior of plastics. 

Everyone knows things that get better with time. Red wine might be the first thing that comes to mind; or a beautiful, well-maintained classic car. However, no one would generally have red wine aged for 60 years since – unlike the products by NETZSCH-Gerätebau – there is no continuous striving for perfection in winemaking to ensure that such a high level of quality is achieved.

Polymer Degradation – A Challenge in Construction

In contrast with both NETZSCH and the aforementioned red wine, the properties of polymers unfortunately do not always improve over time. As plastics age, their properties often change until the material fails. On the molecular level, the atomic bonds in the polymer chains break, whereby the side groups can dissolve or failure of the main chain occurs. Post-crystallization, plasticizer migration and formation of stress cracks, however, can also be mentioned here as aging effects.

They all have in common that they take place as a function of temperature and time, each with different kinetic reaction models. One advantage of the reactions that take place, however, is that they are often accompanied by a change in mass. Plasticizers exiting from the volume, such as gaseous products of polymer degradation, cause a decrease in weight. Following this principle, dynamic TGA measurements are used to elucidate the relationship between temperature and degradation and – based on the data obtained – a kinetic model is created which can be used for simulations under isothermal conditions.

Figure 1. Epoxy resin under different aging conditions

In the current case, novel epoxy resin systems are being investigated for use in aircraft components and thus being exposed to high temperatures. These materials must withstand the given conditions, without failure, for at least the duration of the service life of the assembly, or even better, of the entire aircraft. Real exposure tests under the operating conditions, however, cannot be carried out over a period of 15 years. Thus, an alternative from the bag of tricks will be sought to predict material behavior.

Thermogravimetry as a Basis for Simulations

Photo: Building view of the Faculty of Engineering at the University of Bayreuth (© University of Bayreuth; © Polymer Engineering)

At the Department of Polymer Materials at the University of Bayreuth, a NETZSCH TG 209 F1 Libra® is used for such measurements. The direct temperature measurements carried out by the instrument allow for the most accurate setting of the actual temperature, even for endo- and exothermal reactions. To establish simulations, a high degree of accuracy is required for inputted data sets since error propagation would otherwise multiply deviations. Thanks to the ceramic interior of the TG, even polymers with highly corrosive decomposition products can be characterized.

Figure 2. Measurement curves for dynamic TGA measurements at different heating rates

Modelling and Prediction by Means of Kinetics Neo

Most chemical reactions do not occur in a single step; the same applies to decomposition reactions of polymers. Depending on the polymer, a combination of parallel and serial steps may occur. By means of Kinetics Neo, models of the overall reactions can be established by combining these individual reactions. Specific parameters can be assigned to each step. The program offers both automatic optimization and manual adjustment of each value. This way, the user enjoys a maximum of possibilities. The model is established by fitting it to the actual measurement data. The evaluation is performed by outputting the R² value or the F-test.

Figure 3. Measurement curves from the TGA along with fitted curves of the model

For cases in which the model reveals a small error when compared to the measured data, predictions can be calculated based on the mathematical function of the model. Here, it becomes clear why good measurement equipment, like the TG 209 F1 Libra®, is necessary. Only through the application of accurate measurement data can a precise simulation be established that correctly represents reality.

Figure 4. Isothermal predictions of the polymer degradation based on the model established

Further applications of the TG 209 F1 Libra® at the department Polymer Engineering

In addition to the application described the TG 209 F1 Libra® is used for many other material characterizations. Industrially relevant properties are examined, such as the filler content of thermoplastics or the fiber volume content of composite materials. Also scientific questions such as the thermal stability under different atmospheres of newly developed duromers can also be answered. This versatility makes the TG 209 F1 Libra® a device that is constantly in use at the department.

We congratulate NETZSCH-Gerätebau on its 60th anniversary. If NETZSCH continues to move forward with innovation and strive for perfection, as it has in the past, we look forward to many more years of successful collaboration.

Photo: Research assistant Lukas Endner (left) together with TG 209 F1 Libra® and Prof. Ruckdäschel in the thermos-analytic laboratory of the Department of Polymer Materials. (© University of Bayreuth; © Polymer Engineering)

Many thanks go to the Department of Polymer Materials at the University of Bayreuth for this interesting report and the warm wishes. We, too, look forward to many more years of collaboration!

Take Part in our Raffle!

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Win a voucher** in the amount of €1,500, redeemable for such transactions as the purchase of a spare part or accessory, the booking of a customer training session (on-site, online, NOA) or contract testing, the commissioning of a repair, or the purchase of one of our analyzers. Entry deadline is May 9.

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