Hemicelluloses at Interfaces: Some Aspects of the Interactions - The Nanoscience and Technology of Renewable Biomaterials - page 158

handled in Excel. The cantilever sensitivity value was determined separately for each
measurement from the force curve with high loading force. The sensitivity value was
used for calculating the deflection of the cantilever from the raw data. Forces were
calculated by the Hooke's law and normalised by the radii of the interacting beads (R 1
and R 2 ). The normalized force is related to the interaction free energy W f between flat

surfaces by the Derjaguin approximation (Derjaguin 1934):

R 1 R 2
R 1 + R 2 · W f

F(D) = 2 π · (6.5)

where F(D) is the force as a function of distance D. The distance between the sample
and the cantilever was calculated as the sum of the deflection and the sample position.

AFM imaging. AFM was also used to verify the xylan deposition on the cellulose
surface. The images of the cellulose coated QCM-D crystals after the xylan adsorption
experiments were scanned in tapping mode in air using silicon cantilevers (Pointprobes,
type NCH) delivered by Nanosensors, Neuchald, Switzerland with a resonance frequency
around 300 kHz. No image processing except flattening was made and several areas on
each sample were measured.

6.5 Results

6.5.1 Adsorption of Hemicelluloses on Cellulose

Figures 6.1a and 6.1b compare the adsorption of dissolved hemicelluloses isolated from
unbleached and peroxide bleached TMP as well as the adsorption of pure GGM, pectin
and xylan on cellulose at low ionic strength. QCM-D data are presented as change
in dissipation as a function of change in frequency (change in mass detected by the
quartz crystal). This procedure enables concomitant comparison of several adsorption

experiments.
Figure 6.2 compares the adsorption data of dissolved hemicelluloses isolated from
unbleached TMP and xylan at high ionic strength.
From these figures and on the basis of the detailed investigations reported in Tammelin
et al . (2007) and Paananen et al . (2003), the following preliminary interpretations can
be made about the adsorption of hemicelluloses from different sources on cellulose
surface, that are essential to the interpretation of the viscoelastic properties of the formed
hemicellulose layers.

1. Dissolved hemicelluloses isolated from unbleached TMP significantly adsorbed on a
weakly anionic cellulose surface and the adsorption increased with increasing ionic
strength since the repulsion between anionic charges within the hemicellulose chain
and cellulose surface was screened (Figures 6.1 and 6.2), see also Tammelin et al .
(2007).
2. Dissolved hemicelluloses isolated from peroxide bleached TMP adsorbed much less
on cellulose since higher anionic charge of the hemicellulose molecules leads to stiffer
and more rodlike conformation of the polyelectrolyte chains due to higher repulsion
between anionic segments. Thus, these hemicelluloses tend to form a flatter and