Shaped articles of polypyrrolidone and method of preparation thereof

DETAILED DESCRIPTION OF THE INVENTION It is essential to the practice of the invention that a substantially hydrous formic acid solution be employed for forming the polypyrrolidone articles.
More specifically, it is critical to the practice of the invention that formic acid solutions containing from about 3 to about 20% by weight of water to be utilized to form the polypyrrolidone solutions.
Preferably, formic acid solutions containing from 3 to 9% by weight of water have been found to be particularly valuable in forming articles of the highest tensile strength from polypyrrolidone.
When employing formic acid solutions containing more than about 20% by weight of water, there is a tendency for the solutions to gel.
When employing formic acid solutions containing less than about 3% by weight of water, weaker fibers and more opaque films are produced.
In order to achieve satisfactory production of strong fibers, filaments, and films, the ratio of polypyrrolidone to hydrous formic acid solutions must be at least about 20% by weight.
Obviously, the higher the polymer concentration in the solution, the more optimum the conditions for the formation of filaments and fibers.
As the molecular weight of the polypyrrolidone employed increases, however, the less polymer is usually required for the formation of suitable fibers and filaments.
It is preferred to employ solutions comprising from about 1.
5 to about 4 parts by weight of hydrous formic acid per part of polypyrrolidone.
This range has been found suitable for the formation of strong shaped articles of polypyrrolidone from all molecular weight ranges of polypyrrolidone employing 80-97% hydrous formic acid.
It is generally preferred to employ polypyrrolidone having a molecular weight corresponding to a relative viscosity within the range of about 2 to about 10, as determined by the relative viscosity of a 1% solution thereof in metacresol.
It is more specifically preferred to employ polypyrrolidone having a relative viscosity of from about 3 to about 6