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Two wheat straw pulps (Kraft pulp and Chemimechanical pulp (CMP)) were treated with a crude enzymatic extract containing mainly manganese dependent peroxidase. The extract was prepared from the culture supernatant of a hypersecretory strain of Phanerochaete chrysosporium. Enzymatic treatment was applied to an unbleached pulp suspension (2% w/v). Lactate buffer (pH4.5) was used to regulate the pH at the MnP optimum activity and to stabilize the diffusing oxidative agent (Mn 3+ ). The enzymatic treatment was applied for 4 hours only. so as to ensure compatibility with industrial processes. After this treatment, the kappa number of unbleached Kraft pulp was reduced by about 50% and the consumption of bleaching reagent was subsequently reduced to the same extent. As with unbleached CMP, the enzymatic treatment substantially enhanced the physical properties of the pulps. In all the cases studied. transmission electron microscopy showed that structural changes had occurred in the treated fibres as compared with untreated samples. The main modification appeared to be a superficial defibrillation, which was sometimes accompanied by extensive delamination depending upon the extent to which the straw had been destructured by previous chemical and mechanical treatments.

On etudie la redeposition de xylanes sur la matrice cellulosique d'une pâte kraft de bouleau raffinee et on determine la nature des forces qui controlent la reassociation. L'etude est basee sur les interactions entre des microfibrilles de cellulose preparees a partir du roseau Arundo donax et le xylane correspondant pris comme modeles experimentaux simplifies