A process for producing cellulosic fiber with a high curl index is disclosed. The process can include mechanically treating and chemically crosslinking kraft pulp. The mechanical treatment of the pulp can include convolving and mechanically treating a pulp at in a plug screw and steam tube at temperatures above 100 °C and pressures above 3 bar. The mechanically treated pulp can be crosslinked with a crosslinking agent. The product fiber can exhibit a curl index of greater than 0.35, and can be at least 50% higher than the initial curl of the starting pulp material.
