Low field NMR for analysis of rubbery polymers
The goal of this work is to investigate the molecular dynamics as well as the composition and the structures of different types of industrial polymers such as thermoplastic polyurethanes (TPU) and filled raw EPDM samples. The NMR measurements were restricted to transverse relaxation of the magnetization and DQ NMR experiments, done on a low field spectrometer (0.5 T) at a proton Larmor frequency of 20 MHz. The measurement temperatures were varied, depending on the glass transition temperature of the investigated materials. A measurement temperature 100° C above the glass transition temperature provides a high molecular mobility and an enhanced contrast in the NMR signal. Moreover, thermal (DSC) and mechanical (rebound resilience, hardness and tensile testing) tests have been done on the TPU materials, and their macroscopic properties have been determined.The purpose of investigating the TPU samples is a better characterization of these materials by combining a set of measurements, in particular differential scanning calorimetery, rebound resilience, hardness, tensile testing, and NMR techniques. The mechanical and the thermal properties of thermoplastic polyurethanes, as well as their chain dynamics determined by NMR are influenced by the number average molecular weight of the segments, the type and the amount of the hard and soft segments, the interaction between these two phases and by the capacity of soft segments to crystallize. The good correlation between the macroscopic properties as determined by classical methods and the microscopic properties determined by NMR recommends low-field NMR as a potential method for quality control, with the particular of being fast, inexpensive and partially non-destructive.The influence of the filler amount and activity on the unvulcanized EPDM polymer matrices was investigated via transverse relaxation NMR experiments. The results were interpreted using both the Sotta, Fülber, Demco, Blümich, Spiess and the Gotlieb-Fedotov-Schneider models. The sensitivity of the determined effective relaxation times in both models is discussed, for varying the composition of the fillers. Moreover, the values of the average dipolar coupling results from the relaxation and double-quantum build up experiments are compared and discussed.These studies have led to a phenomenological description of the changes in the chain mobility and order under the influence of the composition. The interpretation of the results has been given based on the available theory for polymers and on the cumulative information obtained from all measurements done on these materials. The NMR methods employed are relatively easy and highly sensitive to the changes in the chain mobility and segmental order of matter, factors which recommend them as applicable to all kinds of polymeric materials, for which microscopic parameters and phase compositions shall be determined. The investigation of these materials as a function of time and temperature can provide additional information regarding the chain mobility, segmental order and phase composition before and after thermal transitions, thus helping to improve the processing parameters. The quality of the phase separation which results from different processing steps and types can thus be evaluated.
info:eu-repo/classification/ddc/660, Technische Chemie, Mehrquanten-NMR-Spektroskopie, Kernspinrelaxation, thermoplastischer Urethane, gefüllter EPDM-Werkstoffe, DSC, Rückprallelastizität, Zugversuche, thermoplastic polyurethane, filled EPDM rubber, rebound resilience, tensile tests
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