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The composition and structure of the surface material of kraft fibres can affect properties of the pulp such as the reactivity in, for example, bleaching processes. In order to study the nature of the surface material, conditions for a gentle removal of fibre surface material from unbleached kraft fibres have been evaluated. An unbleached softwood kraft pulp with a lignin content of 6.2% (kappa number 32) was treated mechanically using three different types of laboratory equipment: a PFI-mill, a high intensity mixer, and a disintegrator. The number of revolutions and the pulp concentration were varied and the removal of surface material was followed by chemical and microscopical analyses. These analyses revealed that there is lignin-rich material present on the fibre surface which can be removed by a mild mechanical treatment. The lignin content of the surface material abstracted was between 2.5 and 4.5 times higher than that of the fibres. The primary fines (obtained by fractionation of unbeaten pulp, 20 ), also originating from the fibre surface, had a lignin content almost 5 times higher than that recorded in the fibres. For analytical studies of the surface material, a mechanical treatment of the kraft fibres in a disintegrator at a pulp concentration of 4.5% and at 20.000-200.000 revolutions is an efficient and suitable treatment for gradual removal of material from the fibre surface.

Acetylated pine wood samples were tested in ground contact (stake test) at two test sites, one located in Simla Êngsdalen, Sweden, and one in Viikki, Finland, according to European standard EN 252. The test stakes were inspected annually and their condition was compared with that of untreated controls and of stakes treated with two reference CCA preservatives. The use of untreated controls and preservative treated wood gave a measure of the aggressiveness of the fungal decay at the individual test sites. The resistance to fungal decay of acetylated wood with an acetyl content of about 20% is of the same magnitude as for CCA treated wood at a high retention level (10.3 kg/m 3 ).Exposure of acetylated mini stakes to three different unsterile soils in the laboratory showed that decay was signi®cantly reduced at acetyl contents of 15.1%. An acetyl content of 18.5% prevented most attack by brown, white and soft rot fungi. Acetyl levels above 20.9% were required to eliminate attack by tunneling bacteria.Acetylated wood samples were also tested in seawater on the Swedish West Coast for their resistance to marine borers (EN 275). Results show that the acetylation of wood gives only minor protection against marine borers, although the degree of attack is lowered with increased acetyl content. Resistenz von acetyliertem Holz gegen biologischen Abbau Acetylierte Holzproben wurden an zwei verschiedenenStandorten einem Bodentest nach EN 252 unterworfen. Die Holzpfa Èhle wurden ja Èhrlich untersucht und mit unbehandelten Kontrollen verglichen. Zum weiteren Vergleich dienten Proben, die mit zwei CCA-Schutzmitteln behandelt waren. Diese lieferten ein Maû fu Èr die Aggressivita Èt des Pilzabbaus an den zwei Standorten. Die Resistenz des acetylierten Holzes mit einem Acetylgehalt von 20% entspricht der einer CCA-Behandlung mit 10,3 kg/m 3 . Labortests an Kleinproben in unsteriler Erde ergaben, daû der Abbau schon bei einem Acetylgehalt von 15,1% deutlich verringert ist. Ein Gehalt von 18,5% verhindert weitgehend den Angriff von Braun, Weiû-und Rotfa Èulepilzen. Ein Acetylgehalt von 20,9% ist erforderlich, um das Eindringen von Tunnel-Bakterien auszuschlieûen. Acetyliertes Holz wurde auch in Meerwasser an der schwedischen Westku Èste gegen den Angriff von Bohrmuscheln nach EN 275 gepru Èft. Der Angriff ist zwar mit steigendem Acetylgehalt verringert; dennoch verleiht die Acetylierung nur einen geringen Schutz gegen Bohrmuscheln.

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