Patent ID: 8177938

Claim:
A method of making microfibers of regenerated cellulose comprising: a) preparing a first cellulosic dope having a first composition; b) preparing a second cellulosic dope having a second composition which differs from the first composition of the first cellulosic dope; c) spinning the first and second cellulosic dopes into composite nascent fibers each having a length and a segmented cross-section comprising a plurality of segments across the cross-section of the nascent fiber, the segments also extending along the length of the fiber and the nascent fibers including at least one longitudinally-extending segment formed from the first cellulosic dope juxtaposed with at least one longitudinally-extending segment formed from the second cellulosic dope; d) regenerating the nascent fibers to splittable composite regenerated cellulose fibers each having a plurality of regenerated cellulose segments across the cross section of the regenerated fiber, the segments also extending along the length of the fiber and including at least a first longitudinally-extending regenerated cellulose segment formed from the first cellulosic dope juxtaposed with at least a second longitudinally-extending regenerated cellulose segment formed from the second cellulosic dope, wherein the first longitudinally-extending regenerated cellulose segment is joined to the second longitudinally-extending regenerated cellulose segment along a splittable interface; and e) splitting the composite regenerated cellulose fibers into microfibers of smaller cross-section along the splittable interface between segments, wherein the geometry of the nascent fibers is regulated, the first and second cellulosic dope compositions are cellulosic dopes without other fiber-forming components, and are selected, and the steps of regenerating and splitting the fibers are controlled, such that the composite regenerated cellulose fibers are split into micro fibers with a coarseness between 0.05 mg/100 m and 10 mg/100 m with a microfiber yield of more than 50% based on larger splittable regenerated cellulose composite fibers subjected to step (e) and said microfibers have a length weighted average length of from about 20% to about 50% of said larger splittable regenerated cellulose composite fibers.