Liliana Olaru

Carboxymethylcellulose synthesis in organic media containing ethanol and/or acetone

A study of the carboxymethylation of wood pulp cellulose and cotton linters cellulose in different organic media, namely, ethanol, acetone, and ethanol-acetone mixtures, is performed. Previously, the ethanol-acetone 1 : 1 (w/w) mixture used as reaction medium was found to give a higher degree of substitution (DS) than the pure solvents separately. In the present work, the kinetic investigation of cellulose carboxymethylation was carried out in ethanol-acetone 3 : 7 (w/w) mixture, as well as in acetone as reaction media, and the same synergistic effect of the solvents mixture was observed. The data suggested a pseudo-first-order kinetic behavior satisfactorily described by the following equation: ln(1.11 − DS) = −kt. The two reaction steps observed are related to the transformations of less ordered regions with higher reaction rate and more ordered regions with smaller reaction rates, respectively. A possible explanation for this behaviour is given, taking into account the different structural changes of cellulose crystallinity and accessibility produced by ethanol-acetone 3 : 7 (w/w) mixture, ethanol, and acetone, as revealed by X-ray diffraction and calorimetry determinations.

On the hydrolysis of cellulose acetate in toluene/acetic acid/ water system

Abstract This paper deals with the influence of the toluene presence in the reaction medium on the distribution of substituents and the degradation of macromolecular chains during the partial hydrolysis of cellulose acetate in toluene/acetic acid/water media, using sulfuric acid as a catalyst. Products with a low degree of substitution were obtained in shorter times than in the conventional procedure (acetic acid/water system). The presence of toluene in the hydrolysis bath leads to products with a higher amount of primary hydroxyls than in those obtained in the conventional process. The degradation of the polymeric chain during hydrolysis is lower in the first period of reaction and higher in the last one in comparison with that produced in a toluene-free system.

Morphological Properties and Antibacterial Activity of Nano-Silver-Containing Cellulose Acetate Phthalate Films

Modification of the rheological properties of cellulose acetate phthalate in 2-methoxyethanol/acetone/water, at different compositions of solvent mixtures, allowed the identification of optimal composition of solvent mixtures for obtaining fibers with controlled diameters. Changing the solvent content in the casting solutions favors modification of the morphological aspects of cellulose acetate phthalate (CAP) films, as observed from atomic force microscopy images. Silver nitrate was incorporated into CAP, as a dispersion medium, and the silver-containing polymer (Ag-CAP) films thus obtained were studied for obtaining information on antimicrobial activity, using Escherichia coli ATCC 10536 and Staphylococcus aureus ATCCC 6538 microorganisms. The results were compared with the antibacterial activity of nano-silver-containing cellulose acetate (Ag-CA) films. The different inhibiting effects of CA or Ag-CA and of CAP or Ag-CAP on the tested Escherichia coli and Staphylococcus aureus bacteria are due to a different antimicrobial activity of the polymers and to the antiseptic character of nano-silver.

Influence of the Substitution Degree on the Dilute Solution Properties of Cellulose Acetate

Modification of intrinsic viscosity, coil size, and preferential adsorption coefficients of cellulose acetate with various substitution degrees in single and mixed solvents was investigated at different temperatures. Miscibility is attained by specific competitive interactions between the solvent-solvent and solvent-polymer systems, which induce modification in the composition of solvent mixtures both inside and outside the polymer coil. The conformational properties in solutions were correlated with the preferential adsorption coefficients, known as depending on the interaction parameters of the polymer/solvent/solvent systems. The intermolecular interactions observed in the cellulose acetate solutions assure the main properties necessary for obtaining membranes with different applications.

Influence of Casting Solution Characteristics on Cellulose Acetate Membranes: Rheology and Atomic Force Microscopy

Cellulose acetates with different substitution degrees were investigated as to their rheological properties and morphology. Atomic force microscopy (AFM) studies on membranes showed ordered domains, in which pores and nodules with different sizes and intensities are distributed. The substitution degree, as well as the history of the membranes formed from the solutions in acetone and water nonsolvent mixtures, influenced the aspect of surface images.

Surface Properties of Cellulose Acetate

Cellulose acetates with different substitution degrees were investigated as to their surface tension properties and morphology. Atomic force microscopy (AFM) studies on membranes, obtained from solution in acetone/water nonsolvent mixtures, evidenced pores and nodules of different size and intensity, depending on the substitution degrees of cellulose acetate and on the water contents in nonsolvent mixtures. Modification of hydrophilicity, put into evidence by the apolar components and by the electron acceptor and electron donor parameters of the polar components, was correlated with the pores volumes — influenced both by their diameter and depths, and by surface roughness as illustrated by AFM images. Surface wettability trends were also studied by means of the free energy of hydration between compounds and water.

Influence of Benzene-Containing Reaction Media on Cellulose Reactivity in the Carboxymethylation Process

The evolution of the degree of substitution during the transformation of both amorphous and crystalline domains of cellulose during carboxymethylation in systems consisting of ethanol/ benzene mixtures is properly described by a pseudo-first-order kinetic equation with a higher reaction rate for less ordered regions. In the amorphous domains, the rate constants depend on the composition of the solvent mixture just for the higher molar ratio NaOH/AGU, which is the main factor influencing the reaction rate in the studied conditions. For the predominant transformation of crystalline regions, the reaction rate depends both on NaOH content and on the proportion of the two inert solvents. The increase of the reaction rate with the increase of the ratio ethanol/benzene is more pronounced than is its decrease with the increase of the molar ratio NaOH/AGU. This behavior is explained by the changes of polymorphism produced in the alkalization step.