Nanotech 2010

Study of Environmental Stress Cracking of Polyurethane using Nanoscale Thermal Analysis

A. Hung, K. Sahagian, M. Colvin, R. Shetty
Boston Scientific, US

Keywords: thermal analysis, polyurethane, environmental stress cracking

Abstract:

Polyurethane has been widely used as the structural material in catheter and pacemaker leads. However, if polyurethane is improperly fixated in the patient’s body, it can fail due to environmental stress cracking. To test the degradation process, polyurethane samples were soaked in the concentrated CoCl2 and H2O2, with a constant pull force applied. After 1 month, the polyurethane samples were analyzed with Anasys Nano-Thermal Analysis system. The system uses Atomic Force Microscopy tips with an integrated heating element near the end of the cantilever. From deflection of the probe tip, the system measures the melting point of the test material. Samples that were submerged in peroxide show a clear decrease in the melting point from an intrinsic value of 128.4C to 96.2C. If multiple temperature ramps are performed on a spot without moving the tip, it was found that the aged sample shows clear phase separation by the 3rd ramp. The melting point of the degraded product can be measured to be about 68C. In contrast, the unaged polyurethane displays an increase in the local transition temperature.
 
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