Crack analysis of unfilled natural rubber using infrared microspectroscopy

Several spectroscopic methods are available for characterizing the crack tip region of natural rubber on the molecular scale to develop a material with fatigue resistant properties. Attenuated total reflectance or ATR-IR has been used to characterize the structure of many different polymers, including rubbers. Transmission has also been well established as a viable technique for the molecular characterization of transparent materials including thin films of unfilled natural rubber.Unfilled natural rubber was stretched to 629% elongation until cracks appeared in the surface. A cross section of the sample containing a crack was then microtomed at -85°C into slices approximately 0.5 µm thick. Similarly, samples were cut with a razor and microtomed under the same conditions. The crack tip region was mapped using the IRμs™/SIRM Molecular Microanalysis System. The map consisted often spectra taken in the x and y directions as shown in Figure 1. The same region was analyzed for orientation of molecular structures. Points were selected along the crack tip, crack edges, and the bulk. Dichroic ratios of all prominent peaks were calculated. ATR was used to verify the results of the mapping experiments for both stressed and unstressed material.