1. Field of the Invention
The present invention relates to processes for oxidative (using hydrogen peroxide) and reductive bleaching of fibers, and fibers bleached by the aforementioned processes.
2. Description of the Prior Art
German Offenlegungsschrift 3,433,926 (3/27/86) to Streit et al, discloses a single bath reductive and oxidative bleaching process, in which the reductive bleaching with thiourea dioxide precedes an oxidative hydrogen peroxide bleaching, whereas in the processes of the present invention the reductive bleaching is subsequent to the oxidative bleaching. Japanese Pat. No. 51-64082 (6/3/76) is drawn to a process in which hydrogen peroxide and thiourea are mixed at the start of the bleaching processes (i.e., bleaching with a single mixture which contains both hydrogen peroxide and thiourea), while by contrast the instant invention utilizes separate steps of oxidative bleaching followed by reductive bleaching. It has unexpectedly and surprisingly been discovered that the process of the present invention provides greatly improved results (including, a higher Whiteness Index, lower Yellowness Index, and lower degree of damage) as compared to the results achieved by either of the aforementioned prior art processes.