Abstract
Despite the similarity of their structural basic units,
cellulose- and starch-based materials behave differently
in many industrial applications. In this thesis, the
structure and properties of these polysaccharides and
their selected derivatives were studied by means of five
comprehensive examples.
In the first investigation, highly crystalline cellulose
was identified from Valonia macrophysa vesicles by atomic
force microscopy. The role of water as a possible
modifier on the surface of cellulose was found to be very
important. The monoclinic phases were found on the
cellulose surfaces with a lateral resolution of about 4
Å, indicating that water molecules cannot penetrate and
thus disturb the surface structure of monoclinic
cellulose. On the other hand, the absence of triclinic
phases was explained by the used measuring geometry
without liquid cell.
The ageing of metastable oat and barley thermoplastic
starch films was followed by frictional imaging. As a
consequence of the ageing, the films lose some of their
mechanical properties. In the oat films, glycerol used as
a plasticiser diffused from the starch-glycerol-water
matrix to the surface of thermoplastic starch, resulting
in areas with low friction. In the case of barley starch
films, the ageing first resulted in short range
reorientation of polymers and finally slow
crystallization of amylopectin branches.
Solution precipitation techniques were applied to produce
ideally spherical starch ester particles (with a diameter
about half the wavelength of visible light), suitable for
fillers in paper coatings in the third study. Particles
assume their shape and size spontaneously when solvated
starch polymer is mixed with non-solvent, due to the free
mobility of the modified starch chains. Starch pigment
has improved affinity to paper surface and it can be used
as such or mixed with other pigments to enhance the
optical or printing properties of paper.
Starch-based pigmenting materials with improved optical
performance were prepared in the laboratory by the
complexation approach. Analytical results indicated that
the complexation of carboxymethyl starch and inorganics
strongly depends on the carboxymethyl group in the
starch-based hybrid pigmented materials. The formed
insoluble hybrids were mostly amorphous and the
crystalline contribution of the inorganic component was
not evident. The resulting precipitates exhibited
composite structures.
Finally, three starch-based and two cellulose-based
polymers were selected for flocculation and filtration
tests. In shearless dewatering conditions, the retention
and dewatering properties of the starch-based polymers
were similar to those of commercial polyacrylamide-based
polymers. The flow studies in higher shear conditions
showed that with the studied dosages the starch-based
polymers could not reach the flocculation levels needed
to maintain sufficient retention properties. The
performance of the cellulose-based polymers as
flocculating agents was less efficient. The reasons for
the more limited performance of the polysaccharide-based
flocculants were too low molecular weight and the charge
density distribution. Better understanding of how to
improve the hydrodynamic properties of bio-based polymers
will be essential when planning new bio-based
flocculants.
The deeper understanding of the relationships between the
desired structures and properties of polysaccharides
helps to utilize them more effectively. In this way it is
possible to obtain better bio-based and environmentally
sustainable products in the competition with the current
products based on conventional petrochemistry.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 24 May 2013 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 978-951-38-7997-6 |
Electronic ISBNs | 978-951-38-7998-3 |
Publication status | Published - 2013 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- cellulose
- starch
- derivative
- industrial
- application
- structure
- property