Low viscosity kraft fiber having an enhanced carboxyl content and methods of making and using the same

A method of making an oxidized acid-treated kraft fiber comprising:

• subjecting cellulose fiber to a kraft pulping step;
• oxygen delignifying the cellulose fiber following the kraft pulping step;
• and
• bleaching the cellulose fiber following oxygen delignification using a multi-stage bleaching process;
• oxidizing the cellulose fiber with a peroxide and a catalyst under acidic conditions in at least one stage of the multi-stage bleaching process;
• treating the fiber with a carboxylating acid comprising the addition of a combination of either sodium chlorite and hydrogen peroxide or chlorine dioxide and hydrogen peroxide in at least one stage of the multi-stage bleaching process prior to the at least one oxidation stage;
• and
• treating the fiber with a carboxylating acid comprising the addition of a combination of either sodium chlorite and hydrogen peroxide or chlorine dioxide and hydrogen peroxide in at least one stage of the multi-stage bleaching process following the at least one oxidation stage
• wherein the multi-stage bleaching process is a five-stage bleaching process comprising a sequence chosen from one of (C/A)(OX)(C/A)E2D2, (C/A)(OX)D1E2(C/A), (C/A)(OX)(C/A)E2(C/A), (C/A)E1D1(OX)(C/A), D0E1(C/A)(OX)(C/A), (C/A)E1(C/A)(OX)(C/A), (C/A)(OX)(C/A)(OX)D2, or (C/A)(OX)D1(OX)(C/A),
• where C/A refers to a carboxylating acid stage, OX refers to an oxidation stage, D refers to a chlorine dioxide stage without the addition of hydrogen peroxide, and E refers to an E, EO, Ep, or EoP bleaching stage.