PROCESSING | STANDARDS & TESTING
subjected to accelerated UV exposures, then evaluated using several instrumental methods of analysis – including optical microscopy and gel per- meation chromatography (GPC). Phase One of the project involved analysing a
Above: PSI determined that sunbath- ing – and UV exposure – was the main reason for the failure of the PU tube on a patient’s
medical device UV exposure
US-based testing laboratory Polymer Solutions Incorporated (PSI) has used multiple analytical methods to determine the reasons behind the failure of a sample of medical tubing. A medical device manufacturer had experienced an in-use failure of the polyurethane (PU) tube, which was used to enclose power supply cables for an implantable medical device. As well as back- ground data – related to the general characteristics of the PU tubing – the manufacturer supplied some general information related to the specific user characteristics from the patient who had received the implantable medical device. One important factor was the patient’s liking for sunbathing. As part of a three-phase failure analysis investi-
gation and product improvement project, the failed sample, control samples, and samples that were
control PU tube and the failed PU tube to under- stand the molecular characteristics of each. This led to a hypothesis for the cause of failure. Phase Two involved the intentional exposure of PU tubing samples to UV irradiation, in order to evaluate the proposed failure mechanism for the PU tubing. Phase Three involved modifying the composition of PU tube to stabilise it against UV degradation. After testing, PSI hypothesised that the failure was down to UV exposure – based partly on the patient’s extensive sunbathing. This was further tested by testing UV-exposed pipe. The team also prepared a new material formulation that incorpo- rated a UV inhibitor – and found it much more resistant to damage. “The product improvement project was success-
ful in prolonging the tolerance of the modified PU tubing to UV exposure,” said James Rancourt of PSI, who presented a paper on the project at Antec. “However, even greater UV stability would be achieved by using an inherently UV stable polymer – like silicone – in place of the aromatic PU polymer.”
CLICK ON THE LINKS FOR MORE INFORMATION: �
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www.drexel.edu �
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www.nicenergy.com �
www.polymersolutions.com
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