CORROSIVITY TEST METHODS FOR POLYMERIC MATERIALS .5. A COMPARISON OF 4 TEST METHODS

This is the fifth in a series of papers published by the Polyolefins F ire Performance Council, a unit of The Society of the Plastics Industr y, Inc. In this paper, four test methods are compared for their abilit y to evaluate smoke corrosivity of polymeric materials: 1) the propose d ASTM E05.21.70 radiant combustion/exposure standard test method, 2) the CNET corrosivity test standard being reviewed by ISO (DIS 11907-2) , 3) the DIN 57 472 acid gas test standard, and 4) the proposed ASTM D 09.21.04 cone corrosimeter standard test method. The ASTM E05.21.70, C NET, and ASTM D09.21.04 test methods directly determine the corrosive effects of combustion gases, as they measure the resistance changes in copper circuit targets exposed to the gases. The ASTM tests report th e resistance change in terms of metal loss and the CNET test reports t he resistance change in terms of % corrosivity factor. The DIN test st andard determines the conductivity and pH changes of aqueous solutions through which combustion gases are passed. Twenty-four polymeric mate rials were evaluated for smoke corrosivity by these four test methods, so that the test methods could be reliably compared based on results from many types of polymeric materials. The polymeric materials evalua ted are commercially available and they cover a broad range of composi tions used for wire and cable insulation and jacketing. The ASTM E05.2 1.70, CNET, DIN and ASTM D09.21.04 tests are evaluated based on severa l criteria. Each test is evaluated on the basis of precision, or wheth er the test is repeatable, and accuracy, or whether the test different iates corrosive potentials consistent with the expectations based on t he known chemistry of the material compositions. To also determine acc uracy, the ASTM E05.21.70, CNET, and D09.21.04 test methods are compar ed to the DIN 57 472 test method, as this test and similar acid gas te sts are accepted standards that have been historically used to measure corrosive potential. Recommendations are made for improving the propo sed test methods.