Hydrophilic-lipophilic Balances Research Articles

Incorporation of Nonionic Emulsifiers Inside Particles in Emulsion Polymerization: Mechanism and Methods of Suppression

Emulsion polymerizations of styrene were carried out using two kinds of polyoxyethylene lauryl ether nonionic emulsifiers having different hydrophilic-lipophilic balances (HLB): Emulgen 109P (HLB 13.6); and Emulgen 150 (HLB 18.3). In both cases, incorporation of emulsifier inside polystyrene (PS) particles was clearly observed, as previously reported for the emulsion polymerization of styrene and methacrylic acid using polyoxyethylene nonyl phenyl ether (Emulgen 911, HLB 13.7) nonionic emulsifier. The generality of the incorporation phenomenon of nonionic emulsifier inside polymer particles in emulsion polymerization was clarified. In the case of Emulgen 109P, which is more hydrophobic than Emulgen 150, about 30% of the total amount was incorporated inside the PS particles, higher than for Emulgen 150 (15%). The difference seemed to be ascribed to the difference in the affinities between the nonionic emulsifiers and styrene, which cause the incorporation of emulsifier. On the basis of this idea, suppression of the incorporation was achieved by decreasing the polymerization temperature and the monomer-feed rate. This strongly supports the proposed incorporation mechanism.

Aggregation of sodium 1-(n-alkyl)naphthalene-4-sulfonates in aqueous solution: micellization and microenvironment characteristics.

In aqueous solution, the micellization and microenvironment characteristics of the micelle assemblies of three anionic surfactants, sodium 1-(n-alkyl)naphthalene-4-sulfonates (SANS), have been investigated by steady-state fluorescence and time-resolved fluorescence decay techniques using pyrene, Ru(bpy)3(2+), and 1,6-diphenyl-1,3,5-hexatriene as fluorescence probes. The critical micelle concentrations (cmc's), effective carbon atom numbers (neff's), hydrophilic-lipophilic balances (HLBs), mean micelle aggregation numbers, micropolarities, and microviscosities of these surfactant micelles have been determined. The logarithmic cmc of the alkylnaphthalene sulfonates decreases linearly with an increase in the neff. The logarithmic aggregation number of the alkylnaphthalene sulfonates increases linearly with an increase in the neff. However, in contrast to the alkylsufonates and the alkylbenzene sulfonates, the aggregation for these alkylnaphthalene sulfonate molecules is less sensitive to the increase in the neff. The micropolarity of these alkylnaphthalene sulfonate micelles is less sensitive to the increase in the alkyl chain length and is lower than that of sodium dodecyl sulfate (SDS). The microviscosity of these alkylnaphthalene sulfonate micelles increases with an increase in the alkyl chain length and is lower than those of nonionic surfactants and zwitterionic surfactants. These results suggest that naphthyl rings have a notable effect on the micellization of SANS.

Rheological behavior of drug suspensions in Gelucire ® mixtures and proxyphylline release from matrix hard gelatin capsules

Mixtures of Gelucires ® 50/02 and 50/13 showing different hydrophilic-lipophilic balances (HLB) and of proxyphylline were used to prepare suspensions at a concentration of 25% and to manufacture extended release hard gelatin capsules by cooling. The rheological behaviors of Gelucire ® mixtures with and without drug were determined by adjustment of the rheograms to the Ostwald power-law and by statistical assessment of the flow index. Pure Gelucire ® mixtures were very slightly shear thickening whereas proxyphylline suspensions had a thixotropic shear thinning behavior. These rheological behaviors can be explained by the chemical composition and by the ratio of the two Gelucires ® used. Extended release of proxyphylline was obtained with all these mixtures. Drug release increased with Gelucire ® mixture HLB owing to higher erosion. A viscosity-release relationship was found and allowed, with these two Gelucires ® of extreme HLB and viscosities, to define the formulations which will give an optimal drug release, by the determination of their suspension viscosity. Modeling of dissolution kinetics has generally shown the predominance of surface erosion of the plugs relative to drug diffusion inside the matrix. This was confirmed by the better linearization of percentage released, according to Hixson–Crowell as compared with Higuchi.

Rheology of polyol behenates and drug release from matrix monolithic capsules

Three polyol behenates with similar melting points (MP) and different hydrophilic–lipophilic balances (HLB) were studied (MP/HLB: 70/02, 63/05 and 57/13). After melting at MP+30°C, the rheological behaviour of behenates was determined by adjustment of the rheograms to the Ostwald power-law and by statistical assessment of the flow index. Behenates showed slight shear thickening. This shear thickening increased when HLB of behenates decreased. This behaviour accounted for a reorganization of the particles under the shear, which became easier when the proportion of the polyethylene glycol chains in the wax decreased. Proxyphylline was used to prepare suspensions at a concentration of 25% in the melted behenates, and to manufacture monolithic capsules by cooling. The suspensions had a shear-thinning behaviour with or without thixotropy. Colloidal particles and aggregates formed in these suspensions directly influenced the rheological properties, as observation of solidified suspensions by scanning electron microscopy confirmed. Extended release of proxyphylline was obtained with the three waxes. Behenates 63/05 and 70/02 gave inert matrices and released drug very slowly. Hydrodispersible behenate 57/13 swelled and made up a kind of hydrophilic matrix that released proxyphylline more quickly, due to slight erosion. In the three cases, the release mechanism was basically diffusional in nature.

Synthesis of alkyl β-glycosides of 6-(N-acetylmuramoyl-L-alanyl-D-isoglutaminylamino)hexanoic acid and its 4-aminobutyl ester

The synthesis has been effected of alkyl β-glycosides containing spacers with amino and carboxy groups at the end. As “prespacers” we used benzyl and 4-azidobutyl esters of 6-(L-alanyl-D-isoglutaminylamino)hexanoic acid. The use of the butyl and hexadecyl β-glycosides of N-acetylmuramic acid has enabled us to obtain glycopeptides with different hydrophilic—lipophilic balances.

Effect of Sugar Esters on the Textural Properties of Nonfat Low Calorie Yogurt

The influence of sugar esters (.05%) of various hydrophilic-lipophilic balances on the textural properties of nonfat low calorie yogurts was assessed over 14-d storage at 4°C. Aspartame was used (200ppm) to sweeten a skim milk-based yogurt that was stabilized with starch (.5%). The total solids content was 12.68% by weight. Sugar esters improved the overall quality of the yogurt. Yogurts with sugar esters, mainly the stearates with a hydrophilic-lipophilic balance range of 5 to 9, had better body, texture, and mouthfeel compared with yogurts without sugar esters, which were rated as coarse and grainy. The nonfat low calorie yogurts sweetened with aspartame had 101.4 (i.e., 50%) fewer calories per 226.8-g (8-oz) serving than regular yogurt containing 3.25% fat and 4% sucrose.