Relation Between the Conditions of Modification and the Properties of Cellulose Derivatives: Thermogelation of Methylcellulose

Homogeneous deacetylation and degradation of chitin in NaOH/urea dissolution system

Since being discovered, alkali/urea has been widely used in the dissolution of natural polysaccharides and the preparation of functional materials such as hydrogels, fibers, films and nanoparticles. This work will focus on verifying the structural stability, homogeneous degradation and deacetylation of chitin in alkali-soluble systems. The chitin was dissolved in NaOH/urea solution and stored at different temperature. At the specific time, the structure, viscosity, acetylation degree (DA) and biocompatibility of chitin and prepared chitosan were determined. The results indicated that dissolution process did not affect the structure and bioactivity of chitin. However, with the increase of storage time and temperature, chitin undergone significant homogeneous deacetylation (DA from 99.5% to 33.2%) and degradation (viscosity from 9284 cP to 1538 cP), accompanying by changes in crystalline structure and thermal stability. Moreover, the processed chitins were no-toxic for the biomedicine applications. This work will provide new ideas for the application of alkali-soluble systems.

Non-Covalent Interactions in Polysaccharide Systems

[Chemical structure: see text] This paper describes the behavior of some polysaccharides with well-known chemical structures and in which the influence of cooperative secondary interactions play an important role. The roles played by hydrophobic and ionic interactions (including ionic selectivity) on polysaccharide conformation and gelation are discussed. Electrostatic attractions are also important in the complexes formed between surfactants and polyelectrolytes of opposite charge. Finally, van der Waals dipolar interactions and particularly hydrogen-bond formation are examined. The role of hydrogen bonds in solubility, conformation, and especially the local stiffness of polysaccharides, but also in polymer-polymer complexes frequently obtained with polysaccharides, is developed. Repeat unit for a number polysaccharides.

Synthesis, control of substitution pattern and phase transitions of 2,3-di-O-methylcellulose

An improved heterogeneous procedure has been found for the regioselective introduction of trityl and 4-methoxytrityl groups at the primary positions of cellulose. The 6-O-tritylcelluloses produced were completely methylated by MeI-NaOH in Me2SO solution. The trityl groups were then completely removed to afford 2,3-di-O-methylcellulose without significant degradation of the polymer. 1H and 13C NMR spectroscopy and degradation analysis showed less than 5% deviation from the regular substitution pattern. Under optimum reaction conditions, almost perfectly regular cellulose derivatives could be obtained. Small changes in the substitution pattern had a strong effect on the phase transitions of the O-methylcelluloses in water. It was shown by DSC for the first time that perfect 2,3-di-O-methylcellulose does not undergo phase separation at elevated temperatures.