The term totally chlorine free bleaching (TCF) was established during the 1990s after the
mill trials carried out by Eka Chemicals at the Swedish Aspa mill in 1989–90. In the mill trials
it was shown that it was possible to bleach oxygen delignified softwood kraft pulp to high
brightness with only hydrogen peroxide (H2O2) if correct conditions were used. This had earlier
been impossible to achieve due to the presence of transition metal ions in the unbleached pulp,
especially manganese, which resulted in severe decomposition of the added hydrogen peroxide.
However, by first treating the pulp with a chelating agent like DTPA or EDTA and then wash
the pulp before the hydrogen peroxide was added it was shown to be possible to more or less
eliminate the manganese ions prior to the peroxide stage. Earlier hydrogen peroxide had been
used but only to a small extent earlier in pulp bleaching but this new discovery made it possible
to successfully use even high charges (20–40 kg/t) of hydrogen peroxide in the bleaching sequence.
Modern pressurized peroxide bleaching stages uses this finding together with higher
temperature to be able to reach high brightness levels with hydrogen peroxide.