Clariant's MEVOPUR materials resist moisture-related property loss
Combining formulation skills allow laser absorbing/transmitting in a range of polymers/colors. (Photo: Clariant)
Clariant’s new polymer compounds, offered under the MEVOPUR brand name, are specially formulated to limit or even eliminate hydrolytic degradation, which is known to affect certain materials commonly used in catheters.
In polyether block amides (PEBA and certain thermoplastic polyurethanes (TPU), adsorbed moisture can cause a breakdown of the polymer chains and reduce the mechanical properties, rendering ductile, tough materials brittle. This effect may be especially pronounced in resins with radiopaque fillers that make them visible to physicians and surgeons when exposed to X-rays. Even with careful pre-drying of the ingredients prior to compounding and tube extrusion, hydrolysis remains a risk. Moisture also can condense from the atmosphere, even inside foil-lined packaging, due to changes in temperature during transportation or storage.
One of the first indications of chain scission is an increased melt-flow index (MFI). So, researchers compared the MFI of a standard, unmodified tungsten-filled PEBA 35 Shore A compound against a sample of the new MEVOPUR.
After 10 weeks storage under humid conditions, the unmodified compound showed more than double the original MFI values, and a wider spread, indicating chain scission and reduction in molecular weight. In comparison, the MEVOPUR compound maintained its MFI values in the same range as before the test began. These results indicate that the polymer chains had not been broken to same extent.
Similar results were noted in testing of tungsten-filled aliphatic thermoplastic polyurethane (TPU) Shore 90A compound. Again, the MFI of the MEVOPUR compound was hardly affected by the humid conditions.
Tensile strength and elongation properties in standard test bars molded from the test materials were similarly unaffected in MEVOPUR compounds, while the standard material shows significant degradation in these critical properties.