Modified cellulosic fibers and fibrous webs containing these fibers

Modified cellulosic fibers, having a dry zero span tensile index that is at least about 35% less than the dry zero span tensile index of the corresponding unmodified cellulosic fibers and a wet zero span tensile index that is at least about 70% less than the wet zero span tensile index of the corresponding unmodified cellulosic fibers, that exhibit a ratio of dry zero span tensile index to wet zero span tensile index of from about 1.5 to about 3, and wherein the fibers are at least partially bleached.

A fibrous structure having a density of not more than about 0.4 g/cc, wherein the fibrous structure comprises modified cellulosic fibers having a dry zero span tensile index that is at least about 35% less than the dry zero span tensile index of the corresponding unmodified cellulosic fibers and a wet zero span tensile index that is at least about 70% less than the wet zero span tensile index of the corresponding unmodified cellulosic fibers, wherein the fibers are at least partially bleached;

• and wherein the fibrous structure has a bending modulus per unit dry tensile that is at least about 30% less than the bending modulus per unit dry tensile of a fibrous structure prepared from corresponding unmodified fibers.

A method for preparing modified cellulosic fibers, the method comprising combining one or more cellulase enzymes and cellulosic fibers, and allowing the combination to react for a period sufficient to reduce the dry zero span tensile index of the fibers by at least about 35% compared with the dry zero span tensile index of the corresponding unmodified cellulosic fibers and to reduce the wet zero span tensile index by at least about 70% compared with the wet zero span tensile index of the corresponding unmodified cellulosic fibers, wherein the fibers are at least partially bleached.

A method for preparing modified cellulosic fibers, the method comprising combining one or more cellulase enzymes, cellulosic fibers, and one or more debonding agents, wherein the cellulosic fibers are allowed to react with the one or more cellulase enzymes and the one or more debonding agents for a period sufficient to reduce the dry zero span tensile index of the fibers by at least about 35% compared with the dry zero span tensile index of the corresponding unmodified cellulosic fibers and to reduce the wet zero span tensile index by at least about 70% compared with the wet zero span tensile index of the corresponding unmodified cellulosic fibers, wherein the fibers are at least partially bleached.

A method for preparing a fibrous structure having a density of not more than about 0.4 g/cc, wherein the fibrous structure comprises modified cellulosic fibers and wherein the fibrous structure has a bending modulus per unit dry tensile that is at least about 30% less than the bending modulus per unit dry tensile of a fibrous structure prepared from corresponding unmodified fibers, the method comprising the steps of:

• i. creating the modified fibers by combining one or more cellulase enzymes, cellulosic fibers, and one or more debonding agents, wherein the cellulosic fibers are allowed to react with the one or more cellulase enzymes and the one or more debonding agents for a period sufficient to reduce the dry zero span tensile index of the fibers by at least about 35% index compared with the dry zero span tensile index of the corresponding unmodified cellulosic fibers and to reduce the wet zero span tensile index by at least about 70% compared with the wet zero span tensile index of the corresponding unmodified cellulosic fibers, wherein the fibers are at least partially bleached;
• and
• ii. forming the fibrous structure from the modified fibers.