NMR IMAGING OF MORPHOLOGY, DEFECTS, AND COMPOSITION OF TIRE COMPOSITES AND MODEL ELASTOMER BLENDS

Multiple-slice, three-dimensional (3D) H-1 NMR imaging at medium resolution (100-200-mu-m) and short echo times (0.5-2 ms) has been used to visualize the elastomeric components of several tire sections. The various rubber layers and cords were readily distinguished for a non-steel-belted tire section at 200-mu-m resolution, presumably based on T2 differences among the different components. Carbon-13 magic angle spinning NMR of samples from each layer provided elastomer composition, which supported the origin of the intensity differences seen by NMR imaging. The ability to detect small differences of composition in actual tires was confirmed by imaging well-characterized diblends of cis-polybutadiene (BR) and styrene-butadiene rubbers (SBR). From T2-weighted images or from the total intensity profiles, a 20% difference in blend composition was distinguished. Experimental tire tread sections with good and poor carbon black dispersions produced substantially different images at 150-mu-m in-plane resolution. Artifactual intensity patterns from bulk magnetic susceptibility differences between certain defects and the elastomer matrix were observed in some of the samples and may be useful for defect identification.