Experts from the German Plastics Center (SKZ) and the Magnetic Resonance and X-ray Imaging (MRB) department of Fraunhofer IIS are investigating the use of high-temperature NMR up to 300 °C in a joint project. This should enable accelerated testing of engineering thermoplastics and thermosets.
Schematic of the measurement principle (Photo: SKZ)
The current project aims to demonstrate the feasibility of NMR measurements up to 300 °C and thus enable industry, especially SMEs, to improve quality control and thus gain a competitive advantage. In addition to engineering thermoplastics, thermosets will also be investigated in detail over the next two years and a material database will be compiled. By increasing the sample temperature to 300 °C, measurements on engineering thermoplastics such as PA, PC, PBT and PET will be possible. These have better thermal and mechanical properties than polyolefins and allow a significantly higher profit margin due to their higher price. Accordingly, the need for testing is also higher and the amortization of new measurement technology is possible more quickly.
In the future, the novel measurement and evaluation methods of high-temperature NMR will achieve results comparable to those of established thermal analysis methods. The decisive advantages of the new high-temperature NMR compared to previous methods include significantly shorter measurement times, the elimination of time-consuming sample preparation, and the possibility of investigating larger sample quantities in each individual measurement. Industry is expressly invited to participate in the project committee free of charge. Interested companies are welcome to contact the research institutions.
NMR offers advantages over conventional laboratory analysis
Laboratory analysis plays an important role in the production, processing and damage investigation of plastics. Due to their temperature-dependent material properties, differential scanning calorimetry (DSC) as well as rheological and (dynamic) mechanical tests at specific temperatures have become established as standard methods. These test methods have the disadvantage that the samples must be elaborately prepared for the respective tests or only very small sample quantities (a few mg) can be investigated.
Nuclear magnetic resonance (NMR) offers an alternative for characterizing plastics. It is sensitive to the mobility of polymer chains and is good at detecting temperature-induced changes. Low-cost compact benchtop NMR instruments have become increasingly popular in recent years. They allow the investigation of plastic pellets (a few g) or thermoset molding compounds. However, due to the current use of temperature-sensitive permanent magnets, measurement is only possible at room temperature or just above.
First commercially available approaches for measurement at higher temperatures allow sample temperatures up to 200 °C for measurements on polyolefins. However, since these material types allow only low profit margins, they are often not tested.
Project 22869 N of the research association "Fördergemeinschaft für das Kunststoff-Zentrum e. V." is funded by the German Federal Ministry of Economics and Climate Protection through the German Federation of Industrial Research Associations (AiF) as part of the program for the promotion of joint industrial research (IGF) based on a resolution of the German Bundestag. We are grateful for the financial support.
Further information on the research unit non-destructive testing