Copolymer fibers and yarns and processes for making same
View Patent ↗The present invention concerns methods for obtaining high-tenacity aramid yarn, wherein the yarn is made of a copolymer obtained from a mixture of monomers comprising 5-(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic para-diamine, and an aromatic para-diacid. The method comprises: a) spinning said copolymer from an inorganic acid solvent to produce the aramid yarn; b) washing the yarn with a basic aqueous solution for at least 5 seconds; and c) heating the yarn; wherein the yarn is heated in at least two process steps, comprising (i) in a first step the yarn is heated at a temperature of 200 to 360° C. at a tension of at least 0.2 cN/dtex, followed by (ii) a second step wherein the yarn is heated at a temperature of 370 to 500° C. at a tension of less than 1 cN/dtex.
1. A method for obtaining aramid yarn having a hydrolytic strength retention of greater than 60%, wherein the yarn is made of a copolymer obtained from a mixture of monomers comprising 5-(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic para-diamine, and an aromatic para-diacid;
said method comprising:
a) spinning a dope solution comprising said copolymer and sulfuric acid to produce the aramid yarn;
b) washing said yarn with a basic aqueous solution for a time period of greater than 20 seconds; and
c) heating said yarn; wherein the yarn is heated in at least two process steps, characterized in that
in a first step the yarn is heated at a temperature of 200 to 360° C. at a tension of at least 0.2 cN/dtex, followed by
a second step wherein the yarn is heated at a temperature of 370 to 500° C. at a tension of less than 1 cN/dtex,
wherein said yarn having an Effective Polymer Cation To Sulfur Content Molar Ratio of at least 0.3; said
Effective
Polymer
Cation
to
Sulfur
Content
Molar
Ratio
=
(
[
Na
]
+
2
[
Ca
]
+
[
K
]
-
[
Cl
]
)
[
S
]
,
where the symbols [Na], [Ca], [K], [Cl], and [S] are the concentration of these ions in moles/kilogram of polymer; and
wherein the hydrolytic strength retention is computed by dividing the strength of a skein of yarn treated with saturated steam at 150° C. for 24 hours by the strength of an untreated skein of yarn and multiplying by 100.
2. The method of claim 1 , wherein the Effective Polymer Cation To Sulfur Content Molar Ratio is at least 1.0.
3. The method of claim 1 , wherein the effective Effective Polymer Cation To Sulfur Content Molar Ratio is at least 1.5.
4. The method of claim 1 , further comprising washing said yarn with water before and after contacting said yarn with said basic aqueous solution.
5. The method of claim 1 , wherein the yarn after the first heating step is directly led to a heating device for performing the second heating step without winding and unwinding the yarn between the two heating steps.
6. The method of claim 1 , wherein the first heating step is performed at 240 to 330° C. at a tension of at least 3 cN/dtex.
7. The method of claim 1 , wherein the second heating step is performed at 400 to 470° C. at a tension less than 0.5 cN/dtex.
8. The method of claim 1 , wherein the copolymer is obtained from a mixture of monomers at least comprising a) 5-(6)-amino-2-(p-aminophenyl)-benzimidazole, b) terephthaloyl dichloride and/or 2-chloroterephthaloyl dichloride, and c) p-phenylene diamine and/or 2-chloro-p-phenylenediamine.