DETAILED DESCRIPTION It is the object of the present invention to provide a process which avoids the above-described disadvantages.
The present invention relates to a process for the manufacture of discontinuous fibrils by the abrupt pressure release of a two-phase liquid mixture of molten polymer and solvent, which is at elevated temperature and pressure, so as to bring about the instantaneous vaporization of the solvent and to tend to form a continuous fibrillated structure.
According to the invention, the continuous fibrillated structure produced by the above-described process is shredded at the moment of its formation by a transverse stream of fluid.
By the designation "discontinuous fibrils" is meant elongated fibrillated structures consisting of very slender filaments, of a thickness of the order of a micron, connected with one another so as to form a three-dimensional network.
These fibrils which are of a fluffy appearance generally have an elongated shape.
Their length varies from 1 mm to about 5 cm and their diameter from about 0.
01 to 5 mm.
The specific surface area of these products is greater than 1 m.
sup.
2 /g.
These fibrils are particularly suitable for production, by the usual methods, of non-woven textiles and synthetic papers.
The process according to the invention may be carried out by using any polymer which is suitable for spinning.
Among the polymers which can be used one may mention the polyolefins such as polyethylene, polypropylene, ethylene/propylene copolymers, polyisobutylene, etc.
, polyamides, polyesters, polyurethanes, polycarbonates, vinyl polymers such as polyvinyl chloride, which may also be postchlorinated, polyvinyl fluoride, acrylic polymers such as the homopolymers and copolymers of acrylonitrile, etc.
This list is by way of example and is not restrictive.
Nevertheless, the applicants prefer to use crystallizable polymers whose rate of crystallinity measured by X-ray diffraction is at least 10% and preferably at least 20%, because the stretch to which these polymers are subjected, as a result of the action of vapors released during the abrupt pressure release, imparts to them an oriented structure which results in good mechanical properties
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