| Summary: | This project deals with solvent purification, a new
approach for the preparation of high-yield dissolving pulp
with characteristics similar to those recommended by the
standards. At the same time, the solvent purification
technique aims at removing and recovering chemically
unmodified, low molecular weight sugars that could further
be processed as by-products. In addition, the process offers
a reduction in waste water amounts associated with
dissolving pulp purification and economical reuse of the
solvent. Thus, environmental abatement is also taken into
account. The current technology is unable to achieve these
goals.
The major objective of this work is the elucidation and
characterization of the mechanism of the solvent
purification process, i.e., the acetonation mechanism. In
this thesis a detailed study on the mechanism of
purification of cellulose in acidified aqueous aceton has
been carried out. The mechanism has been proved to be of a
physico-chemical character. The physical phenomenon has been
found to be based on the H-bond disruption/destruction in
crystalline cellulose by acetone as a solvent. On the other
hand, the chemical hypothesis of the mechanism is verified
to be the formation of isopropylidene groups on carbohydrate
chains that leads to disproportionation of the polymer and
protection of the sugar ring. The validity of these
hypotheses has been investigated as follows; cotton has been
used throughout this study as a model compound and different
techniques such as DRIFT, Ge, HPLC, C-13 CP/MAS solid state
NMR, X-ray diffraction, GPC, and viscosity measurements have
been employed.
Factors affecting solvent purification treatment such
as acidity, residence time, temperature, type of acid, and
acetone concentration have also been investigated. The
investigation of those factors was conducted in a manner
that has helped elucidation of the acetonation mechanism
rather than optimization of the solvent purification
technique. Their impact on hydrogen bonding (1st hypothesis)
and isopropylidenation (2nd hypothesis) has been observed to
vary considerably.
Results obtained on hydrogen bonding, sugar
derivatives, crystallinity, molecular weight distribution,
and viscosity of cotton residues are in accord with the
above assumptions.
Based on the experimental findings of this work, a
mechanism of purification of cellulose in acidified aqueous
acetone is described.
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