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        Last update : December 12, 2005
                  First session - Ozone treatment of chemical pulps              
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            5 - Effect of ozone on fiber morphology and papermaking properties            
Christine Chirat, RaphaŽl Passas, Bertine Khelifi, Flora Ludovina (EFPG)

Site Web de l'EFPGOzone is now being used in about 28 bleaching lines mainly for softwood and hardwood kraft pulps. In some cases there has been some informal reporting on the fact that the ozone bleached pulps would behave differently in the paper mill: the refining ability would be different as well as the runnability on a paper machine. The literature does not contain any precise information on these aspects. Furthermore there is also a lack of information on the effect of ozone, if any, on fibre characteristics.

EFPG has launched a study on the effect of ozone on fibre characteristics and papermaking properties including the refining and behaviour in the wet end part of the paper machine.
The first part of this study is presented in this paper. A Nordic softwood kraft pulp with a starting kappa number of 26.4 was used. It was bleached with a control DEDED sequence and an ozone based sequence ZDEDD. The objective being to study the effect of ozone on fibre characteristics, a significant amount of ozone was applied on the unbleached kraft pulp (0,8%). These two pulps were refined in a PFI mill. The ozone bleached pulp had higher įSR and WRV values before refining than the control sequence.

During refining the ozone treated pulp presented slightly lower bulk and air permeability values than the DEDED bleached pulp. The strength properties (tear index, breaking length, zero-span) were similar for the two pulps.
The Morfi equipment was used to analyse some morphological characteristics of the unrefined pulps: the ozone bleached pulp fibres had a slightly higher curl and macro-fibrils content and a slightly lower width than the control bleached pulp fibres. The ESM observation of the fibres concluded that the ozone bleached fibres seemed more flexible and collapsed than the DEDED bleached fibres. Furthermore the ozone treated fibres presented a more pronounced detachment of macrofibrils. These results were in accordance with the properties measured on the paper: more flexible and collapsed fibres can indeed lead to lower bulk and air permeability.

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