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drying at 105 °C is unfavorable over drying at room temperature with respect to
The homogeneity of the cellulose triacetate solution, as expressed by the increased
Turbidity value (Tab. 11.15).
Tab. 11.15 Chemical and physical characterization of a neverdried
Beech acid sulfite pulp in the course of different drying
conditions [86].
Sample treatment Triacetate solution quality
Yellowness coefficient Turbidity
Air-dried
C 0.59 296
C 0.59 367
C 0.89 1030
The loss in pore volume by drying at 160 °C is clearly reflected in a significant
Increase in the yellowness coefficient, haze, and the amount of undissolved particles.
The severe decrease in reactivity has also been described by Gruber et al.,
using comparable conditions [87].
To summarize, water uptake is largely controlled by morphological features of
The cellulose fiber, consisting of a hierarchy of domains of gradually different
Accessibility. By drying swollen fibers, some of these domains become inaccessible
(hornification). In agreement with many previous reports, chemical reactivity in
Particular has been found to be sensitive to drying conditions.
Degradation of Dissolving Pulps
The behaviour of dissolving pulps within heterogeneous degradation reactions
Provides insight into their supramolecular structures, functionalities, and changes
In MWD. A comprehensive description of all relevant cellulose degradation processes
is reviewed in Ref. [4]. The different modes of cellulose degradation comprise
Chemical, mechanical, thermal, and radiation degradation. In many conversion
Processes of cellulose, the molecular weight must be adjusted by controlled
Degradation procedures.
The degradation of cellulose plays an important role in the chemical processing
Of dissolving pulps. The aim of controlled cellulose degradation is to adjust polymer
Properties related to the molecular weight such as solution viscosity (ethers)
Or strength properties of the final product (regenerated fibers). The most important
Conversion processes of dissolving pulps, viscose and cellulose ethers, operate
Dissolving Grade Pulp
Under alkaline conditions. There, molar mass is adjusted by oxidative alkaline degradation,
Also known as ageing of alkali cellulose. In recent years, a new route of
Controlled degradation of the dissolving pulp prior alkalization by high-energy radiation
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Thermal treatment has a negligible effect on the amount of nonfreezing bound | | | Has been extensively investigated and technologically developed by Fischer |