Jacques Desbrières

Hydrophobic derivatives of chitosan: Characterization and rheological behaviour

Chitosans which are substituted with alkyl chains having a minimum of six carbon atoms demonstrate hydrophobic interactions in solution. The chemical structure of synthetized polymers is determined from NMR spectroscopy and microanalysis and the distribution between the different types of substituted units is obtained. In relation to the rheological behaviour different parameters are studied such as the nature of the hydrophobic chain and the substitution degree, the polymer concentration, the temperature and the ionic content of the polymeric solution. All the observations tend to prove the hydrophobic nature of the interaction mechanism.

Water soluble derivatives obtained by controlled chemical modifications of chitosan

Abstract Chemical modifications of polysaccharides are increasingly studied as they have the potential of providing new applications for such abundant polymers. Water soluble chitosan derivatives (quaternized and N-carboxylated chitosans) are prepared, using techniques which allow homogeneous modifications without any sharp decrease in molecular weight, and characterized using NMR spectroscopy and viscometry. In addition a new method for nearly complete deacetylation of chitin is proposed and the role of the acid used for solubilizing chitosan derivatives is mentioned.

Physical properties of acetylated starch- based materials: relation with their molecular characteristics

Abstract In order to obtain thermoplastic starch-based materials with a reinforced hydrophobicity, amylose and amylopectin were acetylated following the pyridine-acetic anhydride procedure. An amylose-rich starch triacetate was saponified under controlled conditions to obtain products with different acetyl contents. The adsorption of water by these polymers equilibrated in a 98% r.h. atmosphere was studied using thermogravimetric analysis and differential scanning calorimetry. A slight increase of non-freezing water content is observed when the acetyl content increases up to DS ≈ 1.3–1.4. For higher acetyl contents, the hydrophobicity of the material is efficiently enhanced and no more freezing water is adsorbed. Tensile strength measurements were performed on films with different amylose acetate-amylopectin acetate ratios: no variation of the tensile modulus (2.5 ± 0.5 GPa) was observed when composition changed, but the elongation at break was strongly decreased when the amylopectin acetate content increased. The influence of acetyl content on thermal properties was also studied. The position of glass transition (∼150°C in the dried state) was unchanged when DS ranged from 1.7 to 3, and moved towards higher temperatures when the acetyl content decreased. This thermal characteristic when DS > 1.7 will allow easy processing of these materials.

Novel transparent nanocomposite films based on chitosan and bacterial cellulose

New nanocomposite films based on different chitosan matrices (two chitosans with different DPs and one water soluble derivative) and bacterial cellulose were prepared by a fully green procedure by casting a water based suspension of chitosan and bacterial cellulose nanofibrils. The films were characterized by several techniques, namely SEM, AFM, X-ray diffraction, TGA, tensile assays and visible spectroscopy. They were highly transparent, flexible and displayed better mechanical properties than the corresponding unfilled chitosan films. These new renewable nanocomposite materials also presented reasonable thermal stability and low O2 permeability.

Synthesis and Biological Activity of Some New 1,3,4-Thiadiazole and 1,2,4-Triazole Compounds Containing a Phenylalanine Moiety

New 1,3,4-thiadiazole, 6, 7 and 1,2,4-triazole derivatives, 8, 9 containing a phenylalanine moiety have been synthesized by intramolecular cyclization of 1,4-disubstituted thiosemicarbazides, 4, 5, in acid and alkaline media, respectively; the thiosemicarbazides were obtained by reaction of hydrazide 3 with appropriate aromatic isothiocyanates. The toxicity of the synthesized compounds was evaluated and the anti-inflammatory study of the triazole compound 9 established an appreciable anti-inflammatory activity that is comparable with that of other nonsteroidal anti-inflammatory agents.

Hydration of α-maltose and amylose: molecular modelling and thermodynamics study

Abstract Hydration of α-maltose and amylose were investigated using molecular modelling and thermodynamics methods. The structure and energy of hydration of three low-energy conformers of α-maltose were determined by the MM3 molecular mechanics method. The hydration structure was found to be sensitive to the conformation of α-maltose and hydration numbers 10 or 11 were estimated for the different conformers. Differential scanning calorimetry and thermogravimetric analysis were used to determine the number of water molecules specifically bonded (non-freezing water) to amylose and different samples of α-maltose. Due to high crystallinity of α-maltose samples, the observed non-freezing water content was lower than predicted by molecular modelling. In contrast, the experimental number of non-freezing molecules of water per d -glucopyranose residue for amorphous amylose (nh = 3.8) is in good accordance with the value of 3.8 extracted from our calculations.

Effect of the synthetic methodology on molecular architecture: from statistical to gradient copolymers

Styrene-butyl acrylate (S-BuA) copolymers were synthesized by nitroxide-mediated controlled radical polymerization using an alkoxyamine as an initiator. Using different synthetic methodologies, statistical copolymers were be obtained by batch nitroxide mediated polymerization while the gradient composition was a forced gradient by continuous addition of S during BuA polymerization (semi-batch process). These gradient copolymers have been studied by H NMR and size exclusion chromatography to characterize the gradient composition molecular structure. The evolution of the composition was correlated with the glass transition temperature () of the copolymers. The gradient copolymers exhibit one with a value in between the of polystyrene and poly(butyl acrylate), indicating that the materials did not present well defined microphase separation. Specific organization at the air-polymer interface of such copolymers has also been demonstrated by comparison between classical and attenuated total reflection (ATR) Fourier transform infra-red spectra. This bulk soft matter assembly was confirmed by AFM analysis, which showed a different morphology at the surface and in the bulk following removal of the top layer. Moreover, for the most well defined gradient composition, a specific nano-structuring was demonstrated by small angle neutron scattering. The preliminary rheological properties of these gradient copolymers were studied and are discussed in relation with their molecular structure.

Rapid and quantitative determination of critical micelle concentration by automatic continuous mixing and static light scattering.

We present the rapid and quantitative characterization of ionic, non-ionic and zwitterionic surfactants based upon the combination of an automatic continuous mixing technique and static light scattering. Collection and subsequent analysis of data are both rapid and semiautomatic, which increases precision, sensitivity, and range of applicability while substantially decreasing the amount of manual intervention required by the investigator. By treating the continuous data, the entire data set may be rapidly analyzed in the context of the closed association model to determine the critical micelle concentration cmc and aggregation number Nag of a detergent; these technique are comparable in the scope and resolution currently obtainable from other conductimetric, fluorescence and surface tension techniques.

Biosorption of chromium by alginate extraction products from Sargassum filipendula: investigation of adsorption mechanisms using X-ray photoelectron spectroscopy analysis.

The alginate extraction products from Brazilian brown seaweed Sargassum filipendula were studied for chromium biosorption. Batch experiments were conducted at pH 2 and 3 and 20°C to determine the sorption capacity of this biosorbents for chromium (VI) and (III). The biomass was characterized before and after metal binding by X-ray photoelectron spectroscopy (XPS) in order to determine the mechanisms of chromium biosorption. The residue has a high adsorption capacity, close the value obtained with seaweed and higher than that of alginate for both Cr(III) and Cr(VI). XPS analysis of the biosorbents revealed that carboxyl, amino and sulfonate groups are responsible for the binding of the metal ions. The analysis also indicated that the Cr(VI) bound to the biomass was reduced to Cr(III).

Interfacial properties of chitin and chitosan based systems

Chitin and chitosan can be modified to obtain amphiphilic systems with controlled structures and architectures. The hydrophile–lipophile balance (HLB, also called hydrophilic–hydrophobic balance) may be modified with respect to different parameters (pH, degrees of substitution of ionic and alkyl groups), and therefore their properties (especially rheological and interfacial) can be adapted to a specific application. The surface activity of ionic derivatives can be improved either by the addition of an oppositely-charged surfactant, which plays the role of counterion by electrostatic interaction (forming a surfactant–polyelectrolyte complex, SPEC), or by N-alkylation. SPECs are found to be more efficient than alkyl derivatives, and the necessary surfactant concentration to reach tensioactive properties is much lower than its critical micellar concentration in the pure solution. The diversity and the control over such structures and architectures make possible their use in numerous domains, strengthening the current interest in these materials.