Hemicelluloses at Interfaces: Some Aspects of the Interactions - The Nanoscience and Technology of Renewable Biomaterials - page 168

to the surface (Klein 1988). On the other hand, as discussed above, most probably more
xylan adsorbed from solution on the interacting surfaces during the measurements. It
would be expected that this should result in more dangling chains on the surfaces. Due
to the reasons described above, at higher electrolyte concentrations the adsorbed xylan
most probably has a rather compact conformation, possesses less dangling chains to
interpenetrate and to cause adhesion, but is still a source for steric interaction.

6.7 Conclusions

Dissolved spruce hemicelluloses isolated from the waters of TMP strongly adsorbed on
cellulose forming a thin, nanometer scale film the structure and thickness of which was
dependent on the ionic strength and on the pulp treatment, e.g., pulp peroxide bleach-
ing. Although the dependence of adsorption behavior on ionic strength can largely be
explained by electrostatics, the main driving force for adsorption seems to be nonelectro-
static in nature. Other factors such as polymer solubility and preferable polymer contacts
need to be considered when explaining the adsorption behavior. The affinity of birch
xylan towards cellulose was mainly explained by the low solubility of xylan molecules.
Xylan probably forms soluble clusters which adsorbs on cellulose and the electrosteric
rather than double-layer repulsion is dominating between xylan-coated cellulose surfaces.
The combined results from our QCM experiments and AFM force measurements bring
out information that deepens the understanding of adsorption behavior of the different
hemicelluloses and the properties of hemicellulose films on cellulose surfaces.

Acknowledgements

Laboratory of Wood and Paper Chemistry, Abo Akademi University is acknowledged for
donating the galactoglucomannan and pectin samples and Prof Mark Rutland, from the
Royal Institute of Technology for donating the cellulose spheres. Mrs Marja Karkkainen,
Mrs Ritva Kivela and Mr Timo Paakk onen are warmly thanked for their skilful laboratory
assistance.

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