Delignifying kraft pulps

Moreira MT, Feijoo G, Sierra-Alvarez R, Lema J, Field JA (1997) Biobleaching of oxygen delignified kraft pulp by several white rot fungal strains. J Biotechnol 53 237-251... 

Figure 9.2 shows that, during recycling of chemically delignified (Kraft) pulp fibres, irreversible pore closure within the cell wall takes place which leads to a reduction in their cell wall water content as measured by the fibre saturation point (see Chapter 5). The net effect of this is a loss in fibre flexibility which, in turn, leads to less effective inter-fibre bonding. 

Because of its simplicity, the concept of Donnan equilibrium is an attractive approach for the modelling of fibre-ion interactions. However, despite its general success in many cases, the Donnan theory alone is not sufficient to describe the experimentally observed distributions. In those cases, it is necessary to use ion-specific complexation equilibria with the acidic groups as a part of the model to describe the observed phenomena satisfactorily. Such behaviour has been shown to exist, for example, with chemically modified highly charged fibres. An apparent systematic deviation in the ionic distribution from the predictions of the Donnan theory has also been noted with common oxygen-delignified kraft pulps, partly, but... 

MG Paice, ID Reid, R Bourboimais, PS Archibald, L Jurasek. Manganese peroxidase, produced by Trametes versicolor during pulp bleaching, demethylates and delignifies kraft pulp. App/ Environ Microbiol 59(l) 260-265, 1993. 

MT Moreira, G Feijoo, R Sierra-Alvarez, J Lema, JA Field. Manganese is not required for biobleaching of oxygen-delignified kraft pulp by the white rot fungus Bjerkandera sp. Strain BOS55. Appl Environ Microbiol 63 1749-1755, 1997. 

Softwood oxygen delignified kraft pulp, kappa no = 15. Mediator applied at 1% on pulp followed by a peroxide reinforced alkaline extraction (Ep). 

In kraft pulping it is possible to delignify to a lower kappa number without undue carbohydrate loss by a process known as extended delignification. This involves adding alkali in two or more stages so as to maintain a fairly constant alkali concentration during the cook. The process is important as it reduces the extent of bleaching required subsequently and reduces the environmental impact of the bleach plant. 

The H faetor was derived from the kinetics of kraft pulping by Vroom (1957) as follows. Under eonditions of eonstant alkali concentration (high liquor-to-wood ratio) kraft delignifieation obeys first order kinetics ... 

RM Berry, BI Fleming. Why do chlorination and extraction fail to delignify unbleached kraft pulp completely Holzforschung 41 177-183, 1987. 

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