Polyimide surface degradation under

Where the filter medium is in the form of a needle felt (as found in pulse-jet collectors), some manufacturers have offset the deficiencies found in some of the above fibres by producing composite structures, e.g. polyar-amid, polyimide or PPS fibres on the surface of the felt with a PTFE scrim or base-cloth providing a framework of support. Although under certain physicochemical conditions the surface fibres become degraded, it has been found that the skeleton of support provided by the PTFE base-cloth is often sufficient to enable satisfactory performance to continue. 

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