Jenifer Santos

Optimization of a green emulsion stability by tuning homogenization rate

Green chemistry increases the design of new products and processes that consider the reduction or removal of the use or production of hazardous substances. This study is focused on the development of stable emulsions using ecofriendly ingredients, taking into account that energy requirements should be minimized. The physical stability of the emulsions studied was explored by means of a combination of different techniques, such as laser diffraction, multiple light scattering and rheology. The coalescence process was detected, not only by laser diffraction measurements, but also by the analysis of the plateau modulus with aging time. This rheological parameter was also useful to distinguish between grades of flocculation. In addition, the Turbiscan stability index showed that the stability was enhanced at higher homogenization rates for 30 wt% emulsions, and the opposite was true for 40 wt% emulsions. The results obtained from the combination of different techniques demonstrated that the most stable emulsion was achieved with the 40 wt% dispersed phase, using less energy input, which lies at the heart of a sustainable society.

Development of eco-friendly submicron emulsions stabilized by a bio-derived gum

Many traditional organic solvents are being gradually replaced by ecofriendly alternatives. D-Limonene is a terpenic (bio)-solvent that fulfils the requirements to be considered a green solvent. D-Limonene sub-micron emulsions suffer from Ostwald ripening destabilization. In this study, we examined the influence of the addition of a natural gum (rosin gum) to D-limonene in order to prevent Ostwald ripening. This contribution deals with the study of emulsions formulated with a mixture of D-limonene and rosin gum as dispersed phase and Pluronic PE9400 as emulsifier. The procedure followed for the development of these formulations was based on the application of product design principles. This led to the optimum ratio rosin gum/D-limonene and subsequently to the optimum surfactant concentration. The combination of different techniques (rheology, laser diffraction and multiple light scattering) was demonstrated to be a powerful tool to assist in the prediction of the emulsions destabilization process. Not only did the addition of rosin gum highly increase the stability of these emulsions by inhibiting the Ostwald ripening, but it also reduced the emulsions droplet size. Thus, we found that stable sub-micron D-limonene-in-water emulsions have been obtained in the range 3-6 wt% Pluronic PE-9400 by means of a single-step rotor/stator homogenizing process.

Assessing differences between Ostwald ripening and coalescence by rheology, laser diffraction and multiple light scattering

This contribution deals with the study of the influence of surfactant ratio, namely triblock copolymer (Pluronic PE9400) to polyoxyethylene glycerol fatty acid ester (Levenol C201), on the stability of emulsions formulated with a mixture of two biosolvents (N,N Dimethyl Decanamide and D-limonene), which find applications as carriers of agrochemicals. Emulsions containing Pluronic, regardless of the concentration studied, underwent Ostwald ripening while coalescence controlled the destabilization process of emulsions containing Levenol C201 as the only emulsifier. The physical stability of the emulsions was analysed not only by means of mean diameters determined by laser diffraction but also with respect to their rheological properties and the so-called TSI parameter derived from multiple light scattering measurements with aging time. We propose that the different structures of both surfactants at the oil/water interface may be responsible for the occurrence of different destabilization mechanisms. It is likely that Copolymer Pluronic PE9400 formed multilayers in the emulsions studied, which may promote flocculation during processing and, subsequently, Ostwald ripening. In contrast, Levenol C201 probably formed a compact adsorbed layer with the molecules perpendicularly oriented to the interface. This work illustrates to what extent the combination of information provided by Multiple Light Scattering, rheology and laser diffraction enables the detection and monitoring of destabilization mechanisms such as Ostwald ripening and coalescence. In addition, this research highlights the importance of surfactant selection for the physical stability of emulsions that exhibited similar droplet size distributions just after preparation.

Caracterización reológica de una suspoemulsión comercial para uso agroquímico

Se estudian las propiedades reologicas de una suspoemulsion comercial para uso agroquimico. Se comparan los resultados obtenidos mediante curvas de flujo y ensayos en cizalla oscilatoria de baja amplitud para cinco temperaturas distintas en el intervalo de 5 a 25oC. Las curvas de flujo, ponen de manifiesto que la suspoemulsion se caracteriza por presentar un comportamiento pseudoplastico, menos acusado a medida que aumenta la temperatura, que se ajusta al modelo de Sisko. Barridos de esfuerzo realizados a 0,1Hz permiten determinar el reducido rango viscoelastico lineal de la suspoemulsion, que depende de la temperatura. Los espectros mecanicos, entre 3Hzy 0,01 Hz, revelan que el sistema manifiesta propiedades viscoelasticas con un comportamiento tipico de gel debil. La aparicion de un minimo en el valor de G” respecto a la frecuencia ha permitido estimar el modulo plateau, el cual desciende con el aumento de temperatura segun una ecuacion tipo Arrhenius. Aun asi, la suspoemulsion presenta un caracter elastico que favorece su estabilidad fisica con el tiempo de almacenamiento. Se ha demostrado ademas que el sistema no sigue la regla de Cox-Merz.

Effect of temperature and shear on the microstructure of a microbial polysaccharide secreted by Sphingomonas species in aqueous solution

Diutan gum is a biological polymer produced by Sphingomonas sp. In aqueous solution it shows gel-like structure under quiescent conditions. However, the flow-induced evolution of its viscoelastic properties and its microstructure are not known. In this work, the viscoelastic moduli were obtained under a flow field, applied in parallel, as a function of the temperature for 0.5 wt% diutan gum aqueous solutions. As both stress and temperature increase a decrease in the viscoelastic properties occurred, due to the fact that the molecular interactions decreased. Nevertheless, at stresses within the zero-shear viscosity region of the flow curves, no changes were observed. In addition, high stress values dampened the effect of the temperature. The results obtained are very interesting from an industrial application perspective.

Development of food emulsions containing an advanced performance xanthan gum by microfluidization technique

Gums are often used to increase the viscosity of the continuous phase of oil-in-water emulsions in order to reduce or inhibit some destabilization processes such as creaming. A new type of xanthan gum, advanced performance xanthan gum, which possesses improved rheological properties, has been used as a stabilizer. The addition of advanced performance xanthan gum to egg protein-based emulsions prepared at different homogenization pressures in Microfluidizer was studied. These emulsions showed different droplet size distributions and flocculation degrees. However, all the emulsions studied exhibited the same viscoelastic properties, characterized by a crossover point in the mechanical spectra. This work demonstrates the essential role of this novel gum in the rheology of emulsions. In addition, there is a direct relation between homogenization pressure and flocculation degree. This flocculation led to destabilization by coalescence in these emulsions, being the emulsion processed at the smallest homogenization pressure the most stable.

Time-dependent behavior in analyte-, temperature-, and shear-sensitive Pluronic PE9400/water systems

AbstractPluronic PE9400/water binary systems at different concentrations were characterized by means of rheological and microstructural techniques. Temperature ramps revealed a structural transition defined by three zones, which determine time-dependent behaviors. Thus, non-time-dependent, antithixotropic, and thixotropic behaviors were observed depending on Pluronic’s concentration and temperature. These phenomena were analyzed resorting to rheological tools, namely hysteresis loops and transient tests, and supported by Cryo-SEM. The results obtained demonstrated the shear-sensitive character of these systems. All properties presented by these systems make them adequate and interesting for many applications such as injectable systems for tissue repair. Graphical abstractInfluence of temperature on viscoelastic functions and microstructure for 25 wt% Pluronic PE9400/water system