The fully-bleached pulp Fb was degraded with ZEo, H, and enzymatic C endo treatments using increasing chemical charges. When introduced on fully-bleached pulps, ozone is assumed to directly depolymerise carbohydrates and form some carbonyl groups leading to a further depolymerisation in the subsequent alkaline extraction stage via a β-elimination mechanism. In the acidic conditions of Z (pH 2.5) it is suspected that ozone mostly attacks accessible cellulose, probably the more amorphous regions as well as fibrils surface . For low ozone doses -up to 0.5% on o.d. pulp -ZEo did not cut in the long cellulose chains and so the cellulose fraction lost its true gaussian profile (Figure ). For an ozone dose as high as 1%, the long chains were also affected. This was confirmed by using a tri-pVoigt deconvolution model which exposed the presence of two cellulose fractions C High-Mr and C Low-Mr in those pulps (Figure ). This suggests that some cellulose chains are more difficult for ozone to access than others and that others are just purely unavailable. The intact cellulose fraction may represent more ordered regions with higher average crystallinity. Another interesting point is that the ozone-cleaved cellulose chains represented by the C Low-Mr peak seem to be preserved from further depolymerisation by ozone (Figure ), even for higher ozone doses (unshown results). This result points out the difficulty for ozone to degrade cellulose crystallites. Contrarily to ozone oxidation performed at very acidic pH thus strongly limiting ozone decomposition into radicals, hypochlorous acid affects cellulose via both ionic and radical pathways . We assume that it is the effect of radicals that allowed the H treatment to provoke such a contraction of the high-M r end of the MMD on Figure . The attack of crystalline cellulose domains would give access to hitherto untouched amorphous cellulose regions, further increasing the extent of the oxidation. Noticeably, the H treatment generated a lot of low M r material compared to ZEo. This is probably due to the absence of an alkaline stage that might wash off part of the cleaved polysaccharides.