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This study shows that oxalic acid is a very effective additive for the ozone treatments compared with other additives. The required concentration is very small and even lower than the concentration formed during the stage itself. Several different mechanisms for the action of oxalic acid as an additive during the ozone bleaching are examined. He is advisable to have a pH acid during Z stage, but it has been proved that pH value is not the only factor that positively influences. Oxalic acid has an additional effect due to different factors that increase the selectivity of the Z stage. This acid has a minor o OH scavenging capacity than others acids, however, it prevents the cellulose degradation to a greater extent. Moreover, less o OH are formed when oxalic acid is added. Oxalic acid decreases swelling of cellulose and stabilises ozone avoiding its decomposition, then ozone is not consumed by oxalic acid. Metal ions, which are detrimental during ozone stage, can be chelating by oxalic acid. The most interesting outcome is that oxalic acid could act as hydrogen donor inhibiting the formation of o OH radicals. Thus, in studying the effects of oxalic acid, we have determined the requisites for an additive to be optimally effective to protect cellulose during ozone treatments. |
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