MAGNETIC RESONANCE TECHNIQUES (SPECTROSCOPY AND IMAGING) FOR THE NONDESTRUCTIVE CHARACTERIZATION OF POLYMERIC MATERIALS AND COMPOSITES

Abstract The contribution presents the state of the art in Nuclear Magnetic Resonance (NMR) — applications developed in our institute in the last two years. We have started our investigations using spectral information for the determination of aging states of different commercial prepreg materials Our NMR-system is a Broker MSL 400 solid state spectrometer with magic angle spinning device (MAS) and with micro imaging facilities which allow in a first step only the imaging of biological tissues. The system (superconducting coil) works with 9.4 T magnetic field corresponding to a resonance frequency of 400 MHz for 'H nucleus spins. The magnetic field gradient for imaging has a maximum strength of 70 G/cm In order to optimize the system for solid state imaging applications different techniques were implimented. Beside the well known Fourier-Transform-Imaging-algorithm with frequency and phase information, a back-projection-algorithm and a Fourier-Transform-Imaging-algorithm using only phase information now are available which are more reliable for solid state imaging. All of these algorithms can be combined with special designed pulse sequences for the determination of the relaxation times and to reduce and decouple the dipole-dipole-interactions. By using these parameters the distribution of the spin density and the molecular mobility in a polymer can be determined For elastomeric materials the inhomogeneity of the crosslink density and aging processes (e.g. oxidation) result in a change of molecular mobility. These effects can be determined in a quantitative manner and spatially resolved by using NMR-imaging techniques Also the resistivity of polymers (elastomers, thermoplastics, biopolymers) against water or organic solvents (fuels, engine oil, etc.) can be characterized nondestructively by measuring the content and the diffusion velocity of the swelling liquid. The nondestructive characterization of changes in the molecular mobility of the polymer is also possible during swelling, which result in a decrease of the impact strength of the polymer. Measuring the Relaxation time T2 in fibre reinforced composites the aging state of duroplastic prepregs can be characterized.