Characterization of local deformation in filled-silicone elastomers subject to high strain – NMR MOUSE and Magnetic Resonance Imaging as a diagnostic tool for detection of inhomogeneities

Abstract

Magnetic Resonance Imaging (MRI) and unilateral Nuclear Magnetic Resonance (NMR) relaxometry with the NMR MOUSE (MObile Universal Surface Explorer) have been used to characterize local permanent deformation in silicone parts subject to high compressive strain. Samples returned from field service have been characterized by areas of high compression set. Materials excised from these damaged sections have been shown to be clearly distinguishable from undeformed material from the same part and from pristine material by NMR spin-echo, NMR MOUSE and MRI protocols. The results of these studies have been interpreted in the context of studies of model materials of varying crosslink density. The areas of local deformation have been characterized by a reduction in the residual dipolar coupling, which is proportional to the crosslink density and in the non-network sol fraction. These differences were likely to be present in these polymers at the time of production due to inefficient mixing. Additionally, both T 2 weighted Single Point Imaging (SPI) and T 2 weighted MRI experiments have been used to map out the location of different crosslink densities, ultimately determining the quality or homogeneity in silicone components.