Jaroslav Katona

Influence of polymer-surfactant interactions on o/w emulsion properties and microcapsule formation.

The aim of this work was to investigate the influence of interactions between 1.00%w/w hydroxypropylmethyl cellulose (HPMC) and the anionic surfactant sodium dodecylsulfate (SDS) on the properties of 20%w/w sunflower oil/water emulsion and the corresponding microcapsules obtained by spray drying technique. On the basis of the viscosity and rheological measurements, particle size and particle size distribution, and stability assessment, it was concluded that the emulsion characteristics depend strongly on the interaction mechanism. Significant increase in viscosity and non-Newtonian thixotropic behavior was observed in the SDS concentration range from 0.15 to 1.00%w/v, corresponding to HPMC-SDS interactions in the continuous phase. In the interaction region, a three-dimensional network is formed in the continuous phase by intermolecular binding of SDS molecules to the adjacent HPMC chains, which contributes to increase in the viscosity and thixotropic properties. The mean diameter of emulsion particles, d(vs), decreases with increase in SDS concentration, but emulsion stability depends on the adsorption layer structure, i.e. HPMC-SDS interactions. The HPMC/SDS complex adsorbed at the o/w interface makes the layer more compact, enhancing thus emulsion stability. Microcapsules, obtained in the form of powder by spray drying of emulsions, have good redispersibility in water, but their stability changes depending on the HPMC-SDS interaction mechanism, i.e., the HPMC/SDS complex forms a more compact layer that is resistant to breaking during the drying process. The highest encapsulation efficiency was found in the interaction region.

Preparation and Characterization of Oil Containing Microcapsules Obtained by an Interaction Induced Coacervation

A novel method for microencapsulation of oil by coacervation is presented. The method employs segregative phase separation between sodium carboxymethyl cellulose (NaCMC) and a complex of hydroxypropylmethyl cellulose (HPMC) and sodium dodecylsulfate (SDS), which results in coacervate formation. Microstructural properties of the coacervate can be varied by tuning NaCMC-HPMC/SDS interaction, which is achieved by changing SDS concentration. Microcapsules preparation route is presented. Encapsulation efficiency and dispersion properties of microcapsules with coacervate shell of different properties and different oil content were tested. Microcapsules with smallest droplet size, the narrowest droplet size distribution, and with lowest extractability of encapsulated oil were obtained when NaCMC-HPMC/SDS interaction results in formation of the most compact coacervate shell, no matter of the encapsulated oil.

An investigation of chitosan and sodium dodecyl sulfate interactions in acetic media

Polymer/surfactant association is a cooperative phenomenon where surfactant binds to the polymer in the form of aggregates, usually through electrostatic or hydrophobic forces. As already known, polyelectrolytes may interact with oppositely charged surfactants through electrostatic attraction that results in polymer/surfactant complex formation. This behavior could be desirable in wide range of application of polymer/surfactant mixtures, such as improving colloid stability, gelling, emulsification and microencapsulation. In the present study surface tension, turbidity, viscosity and electrophoretic mobility measurements were used to investigate interactions of cationic polyelectrolyte chitosan (Ch) and oppositely charged anionic surfactant, sodium dodecyl sulfate (SDS), in buffered water. Obtained results show the presence of interactions that lead to Ch/SDS complexes formation at all investigated pH and for all investigated polymer concentrations. Mechanisms of interaction, as well as characteristics of formed Ch/SDS complexes, are highly dependent on their mass ratio in the mixtures, while pH has no significant influence.

Study of interaction between chitosan and sodium lauryl ether sulfate

Chitosan is a biopolymer that has many potential applications in the industry because of its unique physicochemical properties. Many of these properties depend on its ability to interact with surfactants. The purpose of this study was to investigate interactions between chitosan (Ch), a cationic polysaccharide, and sodium lauryl ether sulfate (SLES), an anionic surfactant with ethylene oxide groups in the polar part of the molecule, in aqueous solution. Changes in the Ch/SLES mixtures were monitored by turbidity, surface tension, electrophoretic mobility, and viscosity measurements. Obtained results show that electrostatic interactions that occur at low SLES concentrations were less pronounced than hydrophobic. The region of hydrophobic interactions was linearly dependent on the concentration of the polymer, so that it ends at Ch/SLES mass ratio 1:3 by forming neutral complexes, which were completely precipitated as a coacervate phase. The research also demonstrates that small variations in structure of anionic surfactant (SDS and SLES) can lead to significant differences in interactions with cationic polymer-chitosan.

Functional properties of pumpkin (Cucurbita pepo) seed protein isolate and hydrolysate

Pumpkin seed protein isolate (PSPI) was enzymatically hydrolysed by pepsin to obtain pumpkin seed protein hydrolysate, PSPH. Investigation on solubility, interfacial and emulsifying properties of both PSPI and PSPH was conducted under different conditions of pH (3–8) and ionic strength (0–1 mol/dm 3 NaCl). PSPI had the lowest solubility, i.e. isoelectric point (pI), at pH 5. PSPH had higher solubility than PSPI over whole range of pH and ionic strengths tested. Decrease in surface and interfacial tension evidenced that both proteins adsorb at air/protein solution and oil/protein solution interface. 20 % oil in water emulsions stabilized by 1 g/100cm 3 PSPI or PSPH solution were prepared at pH 3, 5 and 8 and ionic strength of 0 and 0.5 mol/dm 3 NaCl. PSPH stabilized emulsions from coalescence at all pH and ionic strengths tested. PSPI was able to stabilize emulsions at pH 3 and 0 mol/dm 3 NaCl and at pH 8, regardless of ionic strength while emulsions at pH 5 and both 0 and 0.5 mol/dm 3 NaCl and at pH 3 when ionic strength was increased separated to oil and serum layer immediately after preparation. All emulsions were susceptible to creaming instability.

Investigation on Drop Formation Process by CaBER ‘Hanging Drop’ Experiments

We use a commercial apparatus, the Capillary Breakup Extensional Rheometer (CaBER from ThermoFisher Scientific), in an unconventional way, and present the CaBER “hanging drop” experiment as a possible tool for studying drop formation process. In the CaBER ‘hanging drop’ experiments a microsyringe is used to place a drop of liquid onto the upper plate to create a drop hanging in the air. The volume of the drop is sufficiently small (up to a couple of tenths of microliters), so that surface tension of the liquid successfully overpowers the gravity and the formed hanging drop has a more or less, hemispherical shape. Then, the upper plate is suddenly moved in vertical direction, at a given speed, to reach the maximum distance the instrument allows. Inertial and gravity forces resist the sudden movement of the drop, caused by its adhesion to the moving plate. Thus, the continuous extension, deformation and movement of the drop take place. The drop movement and the shape evolution are monitored by a high speed ...