This is likely due to iron rust promoted polymerisation. A range of deactivants were tested for their ability to decrease the oxygen absorption capacity, increase the thermal stability and increase ignition temperature of the samples by destroying peroxidic or other groups on the polymer. Of the deactivants tested, sodium hydroxide was found to be the most effective. The solution is circulated through the column for several hours to deactivate the polymer. The excess sodium hydroxide is neutralized with hydrochloric acid to pH 7 and the column drained.
Air is drawn into the column and the trays removed.
The trays and column surfaces are cleaned using brushes and sand-blasted to remove all polymer and rust. During cleaning the polymer is kept wet to prevent possible auto-ignition of any deposit which may have been in contact with the sodium hydroxide solution. The trays are replaced and all surfaces pacified by circulating an agent such as sodium nitrite for several hours. This is necessary because the fresh metallic surfaces formed by mechanical cleaning have increased surface area and catalytic activity. The pacifying solution is drained off.