Polymer- Profiler: mobile magnetic resonance profiling in laboratories and production areas

Plastics, adhesives, and sealants as well as other MR-visible materials can be analyzed and characterized nondestructively by the Fraunhofer EZRT Polymer-Profiler program. The software, developed for the mobile MRI systems of Pure Devices GmbH, uses dedicated hardware for this application, which ensures outstanding sensitivity. The signals are measured with magnetic fields and high-frequency radio waves. They are then processed and displayed. Changes to the material, such as those caused by chemical, thermal, or aging processes, affect the MR measurement signal so that actions with regard to quality assurance or process regulation can be taken in a timely manner.

Relaxometry measurement principle

Relaxometry is the measurement of MR relaxation times T1, T2, and T2*. These material-characteristic parameters are measured quantitatively with special measurement sequences. These parameters can be used to generate maps, also called fingerprints, which show patterns characteristic of the examined materials (similar to a human fingerprint). The acquisition of relaxation times T1, T2, and T2* starts about 5 µs after the first excitation and has a respective time resolution of 8 ns (T2*) and 20 µs (T2). These short scanning times, which have never been achieved before, not only increase the scan quality of the quickly decaying signals, but they also directly affect the differentiation of the fundamental and complex decaying processes.

 

Characteristic response curves for different materials

In this way, the characteristic measuring points of short relaxations, e.g., in plastics, are also recorded, which makes it possible to analyze individual processes in these materials. Relaxometry is able to monitor, nondestructively, both quick and very small changes in T2* relaxation times, such as those that occur during hardening or drying processes. Changes to the relaxation curve are registered almost in real time, so the measurement system can be used not only for quality assurance, but also to control in-line processes such as extrusion.  

Monitoring of a hardening process with continuous measurement of the characteristic relaxation curve ( blue - liquid, red - hardened)

For material characterization, the Polymer-Profiler software also offers a 2-D fingerprint measurement method that correlates two of the relaxation times characteristic of the material and generates a detailed map of its corresponding properties as a result. The analysis of this map shows the characteristic relaxation profiles of the correlated times T1 and T2. The maps generated by this method can be used for the unambiguous identification of materials or to monitor material changes over time.

The 2-D fingerprint measurement method depicts the correlation of two relaxation times. This improves the significance of the characteristic material information. In contrast, uncorrelated, single measurements only contain information regarding the projections (see the time axis profiles).

Application areas

The new system can be used in numerous areas for which monitoring the properties of plastics, adhesives, and sealants is relevant. In the area of material research, the correlation of 2-D fingerprints and material properties is interesting. For example, expected durability can be observed or the effects of the aging process of polymers on their properties. Adhesives and sealants can be characterized and optimized by monitoring their hardening processes under various ambient conditions such as temperature and humidity. In this way, companies in the manufacturing industry can test the quality of purchased adhesive and sealant components and monitor changes between batches directly upon delivery. Another application is in the recycling industry. The Polymer-Profiler can differentiate plastics that cannot be categorized with conventional, established measurement techniques. This makes it possible to separate these plastics for recycling in a fully automated process.