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Polyadipamide yarn is made by a melt-spinning process in which sufficient succinic acid is added to the polymer prior to melt spinning so that the polymer and thus the resulting yarn contain by weight about 50 ppm to about 3000 ppm succinic acid.
The present invention relates to fiber of a polyadipamide polymer such as a yarn of nylon 66 or nylon 46 polymer and processes for making such fiber.
Polyadipamides such as nylon 66 and nylon 46 are desirable for use in the manufacture of high strength yarns for industrial use. Increasing the relative viscosity (RV) of polyadipamides enables tenacity to be increased to higher levels than are customarily obtainable with lower RV polymer. However, the high viscosity polymer has been found to limit production rates due to the high pressure drops which occur as the molten polymer is pumped to the spinneret. In addition, the use of high RV polymer 66 sometimes results in high yarn break levels and low yarn strength which limit yield of the resulting yarn.
Succinic acid(cas:110-15-6) is typically present at low levels in polyadipamides since it is present as an impurity in the adipic acid used to make the polymer. Typical levels of succinic acid(cas:110-15-6) in the polymer are in the range of 10 to about 25 parts-per-million (ppm) by weight.
SUMMARY OF THE INVENTION
In the manufacture of polyadipamide fiber, it has been discovered that increasing the succinic acid(cas:110-15-6) to a level above that typically present as an impurity provides significant advantages in the spinning of fiber of polyadipamides. In accordance with the invention, polyadipamide yarn is made by a melt-spinning process in which sufficient succinic acid(cas:110-15-6) is added to the polymer prior to melt spinning so that the polymer and thus the resulting yarn contains by weight about 50 ppm to about 3000 ppm succinic acid(cas:110-15-6). Preferably, the polymer contains about 100 ppm to about 3000 ppm succinic acid(cas:110-15-6).
The invention is advantageously used when the polymer has a relative viscosity of at least about 55, preferably, at least about 90.
In a preferred form of the invention, the process comprises at least one drawing step and the yarn is drawn at least about 5.5× and the tenacity of the yarn is preferably at least about 9.0 g/d.
The polyadipamide preferably is comprised of at least 85% of polymer units selected from the class consisting of hexamethylene adipamide and tetramethylene adipamide. Most preferably, the polyadipamide is poly(hexamethylene adipamide).
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