Effect of the Molecular Structure of Polymer Dispersants on Limestone Suspension Properties in Fine Grinding

Polymer dispersants are widely used as grinding aids to reduce the viscosity of mineral particle suspensions and to improve energy efficiency during fine grinding. The authors studied here the effects of polymer dispersants of different molecular structure on limestone suspension properties in wet stirred media milling. The polymers differed in their molecular weight and PDI （polydispersity index）. Two traditionally fractionated polymer dispersants having a high PDI （over 2） and one made by controlled radical polymerization having a low PDI （1.2） were tested. It was noticed that these dispersants worked as electrosteric stabilizers and prevented the agglomeration of ground limestone particles. Their addition allowed increased solids concentrations to be used in the grinding experiments and at the same time lowered the particle size and specific energy consumption. The particle sizes obtained were about 1 μm regardless of the dispersant or its dose. The dispersant with a low PDI reduced the viscosity more than did the high PDI dispersants. The results indicate that higher solids concentrations can be used at the same dispersant dose when a low PDI dispersant is used, leading to energy savings via increased throughput. Alternatively, a lower dose of low PDI polymer dispersant than of a high PDI polymer dispersant can be used at the same solids concentration.

Enhancing pharmaceutical potential and oral bioavailability of Allium cepa nanosuspension in male albino rats using response surface methodology

Objective:To enhance the pharmaceutical potential and oral bioavailability of quercetin contents of Allium cepa peel extract by novel nanosuspension technology.Methods:Nanoprecipitation approach was successfully used for the formulation of nanosuspension.To obtain pharmaceutical-grade nanosuspension with minimum particle size and polydispersity index,sodium lauryl sulphate was selected as a stabilizer.Important formulation parameters were statistically optimized by the response surface methodology approach.The optimized nanosuspension was subjected to stability and in vitro dissolution testing and characterized by scanning electron microscopy,atomic force microscopy,Fourier transform infrared spectroscopy,and zeta sizer.To evaluate the preeminence of nanosuspension over coarse suspension,comparative bioavailability studies were carried out in male albino rats.The pharmaceutical potential of developed nanosuspension was evaluated by antioxidant,antimicrobial,and toxicity studies.Results:The optimized nanosuspension showed an average particle size of 275.5 nm with a polydispersity index and zeta potential value of 0.415 and−48.8 mV,respectively.Atomic force microscopy revealed that the average particle size of nanosuspension was below 100 nm.The formulated nanosuspension showed better stability under refrigerated conditions.Nanosuspension showed an improved dissolution rate and a 2.14-fold greater plasma concentration of quercetin than coarse suspension.Moreover,the formulated nanosuspension exhibited enhanced antioxidant and antimicrobial potential and was non-toxic.Conclusions:Optimization of nanosuspension effectively improves the pharmaceutical potential and oral bioavailability of Allium cepa extract.

Determination of Hydrodynamic Parameters of Chitosan Stabilized Bimetallic Nanoparticles

The hydrodynamic characteristics of bimetallic Ag/Cu and Co/Ag nanopar­ticles stabilized by chitosan were determined.The polydispersity index and the diameter of nanoparticles were observed to decrease in contrast to the original polymer during the creation of chitosan stabilized bimetallic nanoparticles,decreasing from 0.342 to 0.12±0.04 and 2.5 micron to 180 nm,respectively.However,the diffusion coefficient of chitosan was in­creased from 0.2 cm^(2)/s to 2.71 cm2/s during the production of stable bime­tallic nanoparticles.The lack of absorption bands at 500 nm and 700 nm-900 nm in the UV spectra of the samples suggests that in the presence of a reducing agent,copper(II)and cobalt(II)ions undergo full reduction.The relationship between the synthesis conditions and the kind of structure of bimetallic nanoparticles“core-shell”has been discovered.Silver atoms have been shown to be both a core and a shell,depending on the synthesis conditions and chemical nature of metal ions.

Statistical thermodynamic properties of a new self-condensing vinyl polymerization system

A new self-condensing vinyl polymerization system consisting of *ABf-type inimers is studied by the principle of statistical mechanics. To obtain the relevant average properties of the system, a differential equation satisfied by the polymeric moment of interest is given, and as a result the zeroth, first, second, and third polymeric moments together with the size distribution function of hyperbranched polymers(HBPs) are explicitly presented. As an application of the method of statistical mechanics, several thermodynamic quantities such as the equilibrium free energy, law of mass action, isothermal compressibility, internal energy, and the specific heat associated with the polymerization are all derived. Furthermore, the scaling behavior of asymptotic size distribution function is discussed, by which a reasonable interpretation of the polydispersity index near the end of polymerization can be made. Also, the expressions of some structural parameters such as the numbers of inimers, terminal units, chain units, branched units, and the degree of branching(DB) are calculated. It is found that a high functionality is helpful to improve the DB of the resultant HBPs. These results show that the functionality f has a significant effect on the thermodynamic quantities and structural properties of HBPs.

Using the discrete element method to assess the mixing of polydisperse solid particles in a rotary drum

Despite the wide applications of powder and solid mixing in industry, knowledge on the mixing of polydisperse solid particles in rotary drum blenders is lacking. This study investigates the mixing of monodisperse, bidisperse, tridisperse, and polydisperse solid particles in a rotary drum using the dis- crete element method. To validate the model developed in this study, experimental and simulation results were compared. The validated model was then employed to investigate the effects of the drum rotational speed, particle size, and initial loading method on the mixing quality. The degree of mixing of polydis- perse particles was smaller than that for monodisperse particles owing to the segregation phenomenon. The mixing index increased from an initial value to a maximum and decreased slightly before reaching a plateau for bidisperse, tridisperse, and polydisperse particles as a direct result of the segregation of par- ticles of different sizes. Final mixing indices were higher for polydisperse particles than for tridisperse and bidisperse particles. Additionally, segregation was weakened by introducing additional particles of intermediate size. The best mixing of bidisperse and tridisperse particles was achieved for top-bottom smaller-to-larger initial loading, while that of polydisperse systems was achieved using top-bottom smaller-to-larger and top-bottom larger-to-smaller initial loading methods.