Polybenzazole fibers and processes for their preparation
View Patent ↗The present invention relates to polybenzazaole (PBZ) fibers and processes for the preparation of such fibers. The invention further relates to yarns, fabrics, and articles incorporating fibers of this invention, and processes for making such yarns, fabrics, and articles.
1. A process for removing polyphosphoric acid from a polybenzazole dope filament, comprising:
(a) during or immediately after the dope filament is coagulated, contacting the coagulated dope filament with a washing solution containing water, or a mixture of water and polyphosphoric acid, under conditions sufficient to hydrolyze the polyphosphoric acid; and then
(b) contacting the coagulated dope filament with a neutralizing solution containing water and an effective amount of a base under conditions sufficient to neutralize polyphosphoric acid in the filament to a salt of the base and the acid,
such that the resulting filament has an average degree of polymerization of the polyphosphoric acid content in the filament less than or equal to 1.5, wherein in step (a) a catalyst is present during said contacting for increasing the rate of hydrolysis of the polyphosphoric acid.
2. The process of claim 1 , wherein the neutralization of the polyphosphoric acid in the dope filament is evidenced by a reduction in the pH of the neutralization solution.
3. The process of claim 1 , wherein the molar equivalent ratio (M/P) of the base cation (M) and phosphorous (P) present in the neutralized filament is 2.5 to 3.4.
4. The process of claim 1 , wherein in step (a) the first solution contains an effective amount of a catalyst for increasing the rate of hydrolysis of the polyphosporic acid, the catalyst selected from the group consisting of cerous nitrate, cupric sulfate, phosphorylase, and mixtures thereof.
5. The process of claim 1 , wherein the polyphosphoric acid comprises polymer and/or monomer species of the formula HO—[—HPO 3 —] n —H where n is 1 to 12.
6. The process of claim 1 , wherein the polybenzazole dope filament comprises a homopolymer or copolymer selected from the group consisting of polybenzoxazole (PBO), polybenzothiazole (PBT), and polybenzimidazole (PBI).
7. The process of claim 1 , further comprising:
(c) after step (b), contacting the filament with a washing solution containing water to remove all or substantially all excess base.
8. The process of claim 1 , wherein in step (a) the washing solution is 50° to 120° C. and the time that the coagulated dope filament is contacted by the washing solution is 10 seconds to 10 days.
9. The process of claim 1 , wherein in step (b) the base is selected from the group consisting of NaOH, KOH, Ca(OH) 2 , Mg(OH) 2 , Sr(OH) 2 , Na 2 CO 3 , NaHCO 3 , K 2 CO 3 , KHCO 3 , CaCO 3 , Ca(HCO) 2 , CaO, trimethylamine, triethylamine, triethylenediamine, tributylamine, pyridine, and mixtures thereof.