Saponins: a renewable and biodegradable surfactant from its microwave-assisted extraction to the synthesis of monodisperse lattices

Synthetic surfactants are widely used in emulsion polymerization, but it is increasingly desirable to replace them with naturally derived molecules with a reduced environmental burden. This study demonstrates the use of saponins as biodegradable and renewable surfactants for emulsion polymerization. This chemical has been extracted from soapnuts by microwave assisted extraction and characterized in terms of surfactant properties prior to emulsion polymerization. The results in terms of particle size distribution and morphology control have been compared to those obtained with classical nonionic (NP40) or anionic (SDS) industrial surfactants. Microwave-extracted saponins were able to lead to latexes as stable as standard PS latex, as shown by the CMC and CCC measurements. The saponin-stabilized PS particles have been characterized in terms of particle size and distribution by Dynamic Light Scattering and Asymmetrical Flow Field Flow Fractionation. Monomodal and monodispersed particles ranging from 250 to 480 nm in terms of diameter with a particle size distribution below 1.03 have been synthesized.

Solid state NMR for determination of degree of acetylation of chitin and chitosan

The degree of acetylation (DA) of various samples has been evaluated by 1H liquid-state NMR and 13C and 15N CP-MAS solid-state NMR over the whole range of DA. A good agreement has been found for all the experiments. The 13C and 15N CP-MAS experiments have permitted the evaluation of the chitin DA and content in the structural polysaccharides in a fungus named Aspergillus niger. The fungus structural carbohydrates mainly consist in pure chitin associated with glucans. Comparison of the 13C CP-MAS spectra with standard (1-->3)-beta-D-glucans strongly suggests that chitin and glucans are linked via covalent bonds.

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.

Characterisation of sorbed water molecules on neutral and ionic polysaccharides

Ionic and neutral polysaccharides with well-defined structures were chosen to investigate the mechanism of water sorption at different relative humidities. From an experimental point of view, the freezing water was determined by DSC when the total sorbed water was obtained from thermogravimetry. The isotherms of sorption and enthalpies of interaction were determined using the combination of a microbalance and a microcalorimeter. It is shown that freezing water appears for P/P(zero) > 0.85 especially with the neutral polymers. The differential molar enthalpy of interaction is higher for P/P(zero) < 0.85 corresponding to the fixation of two water molecules forming double H-bonds; this result is confirmed by molecular modelling; saturation is obtained experimentally for 4 water molecules interacting per glucose unit. On ionic polymers, the water retention increases especially over P/P(zero) approximately 0.8 and the enthalpy of interaction is higher for the first water molecules sorbed. For P/P(zero) approximately equal to 0.8, the numbers of bound water molecules found are 2 per glucopyranosyl unit for neutral polysaccharides, 5 for glucuronan and 9-10 for carboxymethylcellulose (CMC) of DS = 2 and hyaluronan (HA).