Electrical tracking resistance of polymers II. RESULTS WITH LINEARIZED AND ACCELERATED TEST PROCEDURES

At this Conference last year, one of us summarized the results of standard surface-tracking resistance tests, both wet and dry, on a large number of polymers, and showed how some of these results depended on polymer chemical structure and filler content¹. It was further indicated that the wet tracking resistance of many materials (measured by a "standard" dust-fog test procedure) was often a simple power function of the dry tracking resistance (computed from ASTM D495 arc-resistance test results), thus L_DFS = K(L₄₉₅)^1.5 (1). A graphical display of the results for various polymer types was included in a formal paper² as a plot of log L_DEF, vs. log L₄₉₅. It was found that the short-time D₄₉₅ tests could usually be used to predict the long-time dust-fog lives if L₄₉₅ was low, but not if L4₉₄₅ was high, except for certain known classes of polymers. Polymers rich in amine or amide groups and filled polymers rich in phenyl groups were among the notable exceptions to Eq. (1), i.e., they might be called “weak-wet, strong-D495” materials in regard to track resistance. This difficulty in predicting the wet tracking resistance of materials, coupled with the fact that dust-fog tests have become more expensive and time-consuming as better materials are developed has created greater interest in devising wet tracking test procedures that will provide reliable results more quickly and cheaply. One approach to this problem is to make the dust-fog test more linear and of greater average severity (accelerated dust-fog methods) and another approach is to explore the possibilities of electrolyte-drop and film testing techniques.