Unexpected and unusual failures of polymeric materials

Polymeric products are produced with the expectation that they will process satisfactorily and perform as intended without failure. Yet polymers do fail sometimes. The failures are often completely unexpected or unusual and the causes may not be easy to determine. This paper brings together such failures under five categories: 1. In production or processing of polymers. 2. Assembly of polymers into products. 3. Unauthorized or unexpected change in composition. 4. Service conditions. 5. Synergistic effect of two stresses acting simultaneously. Failures can occur for practically any polymeric material in various ways and at various stages of manufacture, assembly and service. They may be due to synergistic effects like environmental stress cracking and electric power cable water treeing in which failure is due to two service conditions operating simultaneously that are not particularly severe alone. In some cases possibility of failure was not adequately considered, such as replacing copper tubing with polypropylene tubing in hot water heaters. A risk/benefit assessment is desirable, considering even worst case scenarios. Not only is the reputation of certain polymers adversely affected by failures, but plastics in general receive a "black eye". Polymers are sufficiently different than metal that they require special care in handling, such as in plumbing. Unexpected and unusual failures will continue to surprise and plague us, such as the disintegration of a polyethylene liquid waste container. One person put toluene in and another nitric acid unbeknownst to each other. Over time nitrotoluenes that formed exploded. But we can learn from known failures to be alert to similar situations of composition, service conditions and all factors that together may make for success or failure with plastics and rubbers. (C) 2007 Elsevier Ltd. All rights reserved.