Niculae 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.

Polycinnamates and Block Co-polymers Prepared by Atom Transfer Radical Polymerization and Microwave Irradiation

Homo-polymers of 2-cinnamoyloxyethyl methacrylate (PCEMA) and block co-polymers with methyl-methacrylate (MMA) synthesized via copper(I)bromide/pentamethyldiethylentriamine-mediated atom transfer polymerization (ATRP) and microwave irradiation, under homo(co)polymerization conditions, are reported. Method 1 led to homo-polymers with relatively low molecular weight (PCEMA-1: 5100; PCEMA-2: 25 000), while the second method offered polymer of 100 000 average molecular weight (PCEMA-3), the polymerization being completed within 60 min. Two di-block co-polymers, poly(2-cinnamoyloxyethyl methacrylate-block-poly(methyl methacrylate)) ((PCEMA-b-PMMA)-1, (PCEMA-b-PMMA)-2) with 0.33 and, respectively, 0.5 molar fraction of photo-cross-linkable PCEMA were also prepared and utilized for this study. Subsequent gel-permeation chromatography (GPC) measurements on block co-polymers have indicated molecular weights of 24 000 and 45 700, respectively. In addition, structural characteristics for all photo-polymers were determined by FT-IR, 1H-NMR, UV-Vis spectroscopy, AFM and SEM/ESEM measurements. Photochemistry in thin polymeric films suggested that UV irradiation is accompanied by an insolubilization of the film caused by the transformation of cinnamate moieties and the formation of intermolecular cross-links, with important effects on the morphology. As expected, it was found that by electrospinning the above photo-polymers produced electrospun fibers of small diameter.

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.

Silver Nanoparticles in Cellulose Acetate Polymers: Rheological and Morphological Properties

Silver nitrate was incorporated in cellulose acetate with different substitution degrees as a dispersion medium. Silver-containing polymer solutions in 2-methoxyethanol were rheologically investigated, both before and after boiling, which permitted a better understanding of the morphological aspects of the corresponding cast films. The different distribution of the obtained silver nanoparticles in the polymer matrix, as well as the influence of the hydrophobic character of cellulose acetate, induced by the substitution degree, were established by atomic force microscopy and environmental scanning electron microscopy. Increasing of cellulose acetate hydrophobicity resulted in a more uniform distribution of the silver nanoparticles, with dimensions higher, in the matrix of cellulose acetate second to smaller surface roughness.

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.

Synthesis and characterization of new optically active monomers based on 4-maleimidobenzoic acid

Optically active bismaleimide and N-(p-substituted phenyl)maleimide-type monomers were synthesized from 4-maleimidobenzoic acid (MBA) or its acid chloride (MBAC). The new synthesized compounds were characterized by IR spectroscopy, 1H-NMR spectrometry, and elemental analysis. The solubility, optical activity of all the monomers, and the thermal properties of the bismaleimides are reported. New optically active polymers derived from some of the synthesized monomers were obtained by Michael-type polyaddition or by addition polymerization.

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.

Preparing and structuring of block copolymers with cinnamate and adamantane moieties

Two new block copolymers containing photocrosslinkable moieties, poly(2-cinnamoyloxyethyl methacrylate)-block-poly(N-methacryloyloxyethyl N′-adamantyl urea) (PCEMA-b-PMAdU) and poly(2-cinnamoyloxyethyl methacrylate)-block-poly(methyl methacrylate)-block-poly(N-methacryloyloxyethyl N′-adamantyl urea) (PCEMA-b-PMMA-b-PMAdU) were synthesized by atom transfer radical polymerization. The structure, thermal properties, and morphology of the synthesized copolymers were investigated by 1H NMR and Fourier transform infrared/UV/vis spectroscopy, thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, atomic force microscopy(AFM), and scanning electron microscopy/environmental scanning electron microscopy. 1H NMR analysis of the copolymer structure confirmed a molar fraction of adamantane units of 0.39 and of 0.66 for diblock and triblock copolymer ,respectively. Special attention was given to the effect of UV/laser irradiation and operating conditions on the block copolymers properties, which could be exploited in the development of micro(nano)structures. The degree of phototransformation of cinnamate groups was between 57 (thin film) and 84% (solution). Modifications of the polymer morphology and surface roughness were induced after laser irradiation (308 and 248 nm) with different fluences (83–203 mJ cm−2). Also, copolymers solutions of different concentrations (c: 25% for PCEMA-b-PMAdU and c: 10, 15 and 20% for PCEMA-b-PMMA-b-PMAdU) were used in electrospinning/electrospraying processes for the preparing of micro/nano particles (0.5–2 μm) and micro/nanofibers (0.6–2.6 μm), the Gaussian distribution curves confirming that the resulting products are dimensionally homogeneous.