CPC D01F 6/74 (2013.01) [C08G 73/18 (2013.01); D06M 11/70 (2013.01); D01F 1/07 (2013.01); D06M 11/84 (2013.01); D06M 2200/30 (2013.01)] | 5 Claims |
1. A method of making a phosphonated polybenzimidazole (PBI) fiber comprising the steps of:
spinning an untreated PBI resin into a PBI fiber;
immersing the PBI fiber in a phosphoric acid bath, wherein the bath is maintained at 35° C.;
squeezing the phosphoric acid-treated PBI fiber to dry the fiber;
washing the squeezed-dry PBI fiber with water at room temperature;
drying the washed PBI fiber in an air non-contact oven at 350° C.; and
heat-treating the air-dried PBI fiber in a nitrogen-blanketed oven at 565° C. to fix the acid within the polymer structure;
thereby obtaining a phosphonated PBI fiber with a phosphoric acid pick-up (APU) in the range of 1-25 wt % and having a Limiting Oxygen Index (LOI) per ASTM 2863 of about ≥47%.
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