In the late 80’s AT&T annually produced millions of polycarbonate (PC) connectors forconnecting copper conductors in telephone circuits. In 1992 three years after a number of theseconnectors had been installed as part of large chemical plant’s communication system, several telephonecircuit failures occurred at this customer’s site. The failures were tracked to cracked connectors in thecustomer’s storage cabinets. Laboratory tests including DSC and GC/MS studies showed that the flameresistantpolycarbonate connector was not chemically degraded during manufacture or aging for threeyears at the customer’s plant. The cause of failure was found to be stress cracking in the field due tochemical contamination.The chemical that caused the stress cracking was a terpene (limonene), a common component ofmany “environmentally-safe” cleaning solvents. Limonene, found in cable-gel-removers, was introducedinto the connectors during their installation. The gel cleaning solvent was initially sorbed into the cablefilling compound and eventually absorbed into the PC connector. Limonene is soluble in PC and enablesthe polymer to undergo partial crystallization, leading to stress cracking. All limonene-containingcleaners in our tests were found to readily stress crack polycarbonate under the conditions of a Bellcorechemical resistance test.
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