AbstractThe removal of mercury-based catalysts from polyurethane (PU) could potentially affect the properties, processability and durability of the material when used as a protective overmould in a cable-connector-assembly for the sub-marine industry. Teledyne-Impulse-PDM were required to firstly comply with the registration, evaluation, authorisation or restriction of chemicals (REACH) regulation, by selecting a non-Hg catalysed PU system and secondly to meet customer demands by providing confidence that the replacement is as effective and durable in the end-use environment. A series of analysis techniques was used to fully characterise the commercial PUs considered; these included the starting materials and cured product. It was possible to identify the polyol type, NCO:OH ratio, catalyst type and quantity as well as degradation temperatures. Most importantly, how these values affect the cured product’s properties (resistance to absorbing moisture, strength, curing profile and electrical properties) which are crucial to the functioning of a cable-connector-assembly, was investigated. Applying an accelerated life testing (ALT) regime allowed a direct comparison of the degradation of the PU to prove durability.
The most noteworthy techniques used in this research were 19F NMR spectroscopy, AFM, bond testing, electrical testing, mass change and an ALT regime. The result was the selection of a suitable PU, proven to behave in a predictable way as the NCO:OH increases, with good resistance to degradation. The removal of Hg+ ions in the catalyst had no obvious effect on the as-manufactured mechanical properties but did have a large effect on the bond strengths achieved. Hence, some adjustments were required to ensure consistent processing and a reaction rate similar to that achieved using a Hg-based catalyst. It was also noted that there was no relationship with the electrical properties, deducing that electrical resistivity could be influenced by the curing process.
The result was a final selection of a PTMEG polyol-based PU with excellent mechanical properties, a tensile strength of 44.67 ± 0.64 MPa and good bond strength to 316L SS of 19.53 ± 0.34 N mm-2 , which is greater than values given in the literature. A controlled reaction rate to gel time and comparable electrical resistivity to the obsolete PU in the TΩ range were also achieved, as were a superior resistance to degradation immersed in a saltwater environment and an exceptional compression set for a PU of 35 %.
|Date of Award||Oct 2019|
|Supervisor||James Smith (Supervisor) & Zhong Yi Zhang (Supervisor)|