The term "fibrils"* has been employed to define fiber-like materials that are prepared by dissolving a thermoplastic polymer such as an ethylene polymer in a solvent, subjecting the polymer solution to a shearing action, and simultaneously or immediately thereafter precipitating the polymer from the polymer solution by rapid cooling or by adding a nonsolvent to the polymer solution. The belief has been expressed in many literature and patent publications that the shearing action attenuates the solute polymer molecules to provide orientation therein. The orientation is retained as the polymer is rapidly precipitated from solution. The term fibrils suggests that the physical structure of the products is fiber-like, i.e., rod-like and having one principal dimension. In actual fact, when the fibrils are examined on a microscopic scale, they are observed to have a very complex structure that can not be meaningfully described in words. FNT *The term "fibrids" is sometimes used and has the identical meaning as "fibrils."
The principal applications of fibrils described in the literature are as full or partial replacements for cellulose fibers in the manufacture of water-laid sheets, i.e., synthetic paper. Prior to the rapid increases in petroleum prices beginning in the early 1970's, it was believed that the price of ethylene polymers ultimately would fall below the price of cellulosic fibers. On this basis, it was believed that ethylene polymer fibrils could partially displace cellulose fibers in the manufacture of paper on the basis of price alone. This view is no longer valid. It is now clear that ethylene polymer fibrils will remain more expensive than cellulose fibers and will be used in the manufacture of water-laid sheets only when their performance properties are sufficiently good to warrant a premium price vis-a-vis cellulose fibers. The majority of the ethylene polymer fibrils described in the art are actually somewhat inferior to cellulose fibers for use in the manufacture of water-laid sheets.
For the above reasons, there is a need in the art for ethylene polymer fibrils having significantly improved properties when used to manufacture water-laid sheets.
USPTO Backgrounds
USPTO Backgrounds