|
(11) | EP 0 472 834 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | Anisotropic spin dopes of reduced viscosity |
| (57) Poly-p-phenylenebenzobisthiazole and similar polymers as prepared in polyphosphoric
acid can be used as spin dopes upon addition of methanesulfonic or chlorosulfonic
acids. |
Background of the Invention
[0001] Poly-p-phenylenebenzobisthiazole, poly-p-phenylenebenzobisoxazole and poly-2,5-benzoxazole are commonly prepared in polyphosphoric acid (PPA). (See U.S. Patent Nos. 4,225,700 and 4,533,693). Liquid crystalline solutions of poly-p-phenylenebisthiazole in solvents such as polyphosphoric acid, methanesulfonic acid and chlorosulfonic acid are taught in U.S. 4,225,700 to be useful in the preparation of high modulus, high strength materials having excellent thermal stability. There are substantial problems involved, however, in spinning the highly viscous solution that is available directly from the polymerization. See Macromolecules 1981, V. 14, pp. 1135-1139 which describes attempts to spin polybenzobisthiazole directly from the polymerization medium (polyphosphoric acid) containing 5-6% polymer. Attempts to spin the highly viscous solution taxes the material strength limits of the equipment and causes excessive wear. A solution to this problem is a worthwhile objective.
Figure
[0002] The Figure is a curve of dope viscosity as a function of concentration at 170°C at a shear rate of 0.1 reciprocal second for a solution of poly-p-phenylenebenzobisthiazole in polyphosphoric acid.
Summary of the Invention
[0003] This invention provides an improved process for spinning a polymer selected from poly-p-phenylenebenzobisthiazole, poly-p-phenylenebenzobisoxazole or poly-2,5-benzoxazole directly from the polyphosphoric acid solution in which it was prepared, comprising adding to the polymer solution an amount of a solvent selected from methanesulfonic or chlorosulfonic acids sufficient to reduce the viscosity to less than about 50,000 poises at 170°C and 0.1 reciprocal second shear rate, spinning the solution through a spinneret and coagulating the extrudate to form fiber.
Detailed Description of the Invention
[0004] In accordance with the present invention, the viscosity of solutions of poly-p-phenylenebenzobisthiazole, poly-p-phenylenebenzobisoxazole or poly-2,5-benzoxazole in their polyphosphoric acid (PPA) polymerization medium is reduced by addition of methanesulfonic acid (MSA) or chlorosulfonic acid to yield spin dopes that can be readily extruded to form fiber. This simple technique substantially eliminates the difficulties mentioned in the art and experienced previously by the present applicant.
[0005] As-produced solutions of the aforementioned polymers in the PPA polymerization medium are highly viscous materials and in general can be spun only with great difficulty if at all. To help with this problem, spinning speeds can be reduced, stronger equipment can be used to withstand the greater pressures which are needed to transfer the solution and clearances can be increased among other stop-gap measures. The problem is avoided if the polymer is separated from the polymerization medium and redissolved in methanesulfonic acid, for example and then spun (See Japanese Patent Application Disclosure Tokukai 61-28015, 1986). Attempts to reduce viscosity by forming more dilute solutions by addition of PPA to the as-produced polymer solution in PPA does not accomplish the desired objective and, in fact, may increase the viscosity as seen in the Figure. The addition of MSA brings the viscosity down to readily spinnable levels.
[0006] The polymers under consideration and their preparation are well-known in the art. The polymer intrinsic viscosities (I.V.)range from about 10 to 25 with poly-p-2,5-benzoxazole generally exhibiting viscosity levels at the upper end of this range. The polymer concentrations in PPA as produced, can vary from 5 to 15 wt.% but is generally at least 10%.
[0007] It is anticipated that commercial spinning of the dopes will be at a temperature below 130°C and it is important that the spin dope viscosity be sufficiently low so that it can be handled, i.e. transferred and extruded, with commercially available equipment. The viscosity of the as-produced solution of the polymer in the polymerization medium at any particular temperature and shear rate will depend on the polymer, its molecular weight and its concentration in the polymerization medium. For this reason, the amount of MSA to be added will necessarily vary. As an acceptable standard, a spin-dope viscosity of less than 50,000 poises and preferably less than 30,000 poises at 170°C and 0.1 reciprocal second shear rate is used. Since the viscosity of the as-produced solutions of polymer in the polymerization medium often exceed 100,000 poises at 170°C and 0.1 reciprocal second shear rate, the MSA or chlorosulfonic acid is added to reduce the viscosity to a readily spinnable level. It is expected that the final mixed solvent of the spin dope will contain from 20 to 60 wt. % MSA. Amounts of MSA in excess of 60 wt. % are not preferred because the polymer content will be too low for economic operation. One should also avoid the possibility of converting from an optically anisotropic to an isotropic spin-dope.
[0008] The figure is a plot of viscosity versus concentration of a solution of poly-p-phenylenebenzobisthiazole in polyphosphoric acid at 170°C and at a shear rate of 0.1 reciprocal second. As can be seen in the plot, the viscosity of the solution rises as the concentration is increased to about 4% (the isotropic range) and then drops precipitously beyond that point as the concentration increases further. The addition of MSA or chlorosulfonic acid in essence reduces the viscosity by lowering the curve.
[0009] After the spinnable dope containing the mixture of solvents has been prepared, it may be spun by procedures well known in the art as shown by Japanese Patent Application Disclosure Tokukai 61-28015 (1986) and U.S. Patent No. 4,533,693. The spin dope is extruded through a spinneret into a coagulating bath from which the fibers are withdrawn. Preferably the extruded dope is first passed through an air gap prior to entry into the coagulating bath which may be an aqueous solution or water itself.
Example 1
[0011] To 321.7 grams of a dope containing 15% by wt. poly-p-phenylenebenzobisthiazole (I.V. - 22.1) in PPA and having a 100,000-poise viscosity (measured at 170°C and 0.1 reciprocal second shear rate) was added 117.2 grams of MSA. The mixture was mixed in a glass vessel continuously purged with nitrogen, using a double helical mixer for 6 hours at 95°C. An additional 65.1 grams of MSA was added with mixing overnight at 102°C. The resulting dope had a concentration of 10.6% and viscosity of 61,000 poises measured at 110°C. The calculated dope viscosity at 170°C and 0.1 reciprocal second shear rate is 24,000 poises.
Example 2
[0012] 49 lbs. of the same 15% 100,000-poise dope as in Example 1 was mixed with 27.8 lbs of MSA in a 10-gallon Atlantic Mixer. The mixture was mixed under vacuum at 40 rpm for 3 hours. The resulting dope of 10.6% concentration was extruded at 110°C through a 290-hole spinneret through an air-gap and into a water quench bath. The resulting yarns were washed with fresh water until most of the acid solvents were extracted. The as-spun wet yarns were then heat-treated on the run (30 meters/min.) under 1.0 gpd tension at 670°C for 9 seconds. The as-spun yarns had filament strengths ranging from 13.6 to 15.0 gpd and moduli of from 380 to 449 gpd. The heat-treated yarns had filament strengths of about 20 gpd and moduli between about 1,800 and 2,000 gpd.
Example 3
[0013] 46 lbs. of a 15% dope as in Example 1 was mixed with 26.0 lbs of MSA in a 10-gallon Atlantic Mixer. The mixing and processing conditions of Example 2 were used. The as-spun yarns had filament strengths of from 13.1 to 14.8 gpd and moduli of from 286 to 411 gpd. The heat-treated yarns had filament strengths of from 19.3 to 21.9 gpd and moduli between about 1,800 and 2,000 gpd.
1. An improved process for spinning a polymer selected from poly-p-phenylenebenzobisthiazole,
poly-p-phenylenebenzobisoxazole or poly-2,5-benzoxazole directly from the polyphosphoric
acid solution in which it was prepared, comprising adding to the polymer solution
an amount of a solvent selected from methanesulfonic or chlorosulfonic acids sufficient
to reduce the viscosity to less than about 50,000 poises at 170°C and 0.1 reciprocal
second shear rate, spinning the solution through a spinneret and coagulating the extrudate
to form fiber.
2. The process of claim 1 wherein the polymer solution in the polymerization medium has
a viscosity of at least 100,000 poises at 170°C and 0.1 reciprocal second shear rate.
3. The process of claim 2 wherein sufficient methanesulfonic acid is added to reduce
the viscosity to less than about 30,000 poises at 170°C and 0.1 reciprocal second
shear rate.
4. The process of claim 3 wherein the methanesulfonic acid ranges from 20 to 60 wt.%
of the final mixed solvent.
5. The process of claim 1 wherein the spinning solution contains at least 10% of the
polymer.
6. The process of claim 1 wherein the polymer has an intrinsic viscosity of from 10 to
25.