Biomedical Engineering Reference
In-Depth Information
6
Hemicelluloses at Interfaces:
Some Aspects of the Interactions
Tekla Tammelin, Arja Paananen and Monika Osterberg
6.1
Overview
Hemicelluloses play an important role in papermaking. They can enhance paper strength
properties but on the other hand, as liberated in the white waters, they may bring harmful
side effects, e.g. interact with other papermaking chemicals and additives increasing
the consumption of these. At present there is also growing interest for the use of by
products of forest industry, for example, as a source for value added chemicals. Thus
hemicelluloses, as being an abundant plant material, can be considered as a large source
of renewable raw material for such purposes.
The goal of this study was to investigate the interfacial behavior of the hemicelluloses
in order to enhance the understanding of the formation of hemicellulose films on cellulose
and how the film formation is affected by parameters such as ionic strength and hemi-
cellulose charge density. The adsorption of dissolved hemicellulose fractions isolated
from unbleached and peroxide bleached spruce thermomechanical pulp (TMP) as well as
pure galactoglucomannan (GGM), pure pectin and pure xylan on a Langmuir-Schaefer
cellulose film was studied using the quartz crystal microbalance with dissipation moni-
toring (QCM-D). The QCM-D data was further modeled using the Voigt-based model for
viscoelastic solids to estimate layer thicknesses and shear viscosity and shear elastic mod-
ulus of the adsorbed hemicellulose layers. These results were combined with colloidal
probe microscopy. Spruce hemicelluloses significantly adsorbed on cellulose forming
a uniform film whereas birch xylan seemed to form cluster like assemblies. Based on
the results the driving force for adsorption of different hemicelluloses on cellulose was
discussed.
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