Particle de-agglomeration with an in-line rotor-stator mixer at different solids loadings and viscosities

Particle de-agglomeration with an in-line rotor-stator mixer at different solids loadings and viscositie

Particle de-agglomeration with an in-line rotor-stator mixer at different solids loadings and viscosities

In-line rotor-stators are used in a range of energy intensive processes but there is relatively little published work with these devices on which to base process design. This study was performed to investigate the performance of an in-line rotor-stator for the de-agglomeration of nanoparticle clusters in a liquid with the objective of determining the effects of solids loading (up to 15%wt) and continuous phase viscosity (up to 100 mPa·s) on the mechanisms and kinetics of breakup and dispersion fineness. A Silverson 150/250MS rotor-stator equipped with the EMSC (Emulsor) screen was used in the recirculation loop of a stirred tank charged with 100 litres of pre-dispersion. It was shown that the power number values previously obtained at Reynolds numbers greater than 200,000 are constant at Reynolds numbers as low as 2,400. It was found that the breakup kinetics were not significantly affected by the solids loading, within the range covered in this study. Whilst 10 and 15%wt. pre-dispersions in water were non-Newtonian, during the course of deagglomeration, the dispersion rheology changes resulting in a Newtonian final dispersion of a low viscosity- only slightly higher than that of water. On the other hand, when the viscosity of the continuous phase was increased, the de-agglomeration became slower even though the solids concentration was low (1%wt.) and the flow through the rotor-stator was still turbulent. This indicates that it is the flow conditions around the particle and not the bulk rheology of the dispersion that determines the kinetics of the de-agglomeration process. Breakup mechanism was found to be erosion and the dispersion fineness was determined by the size of aggregates

Break up of silica nanoparticle clusters using ultrasonication

This study is concerned with the deagglomeration of hydrophilic silica nanoparticle clusters (Aerosil® 200V) in water using an ultrasonicator operated in batch mode. An impeller was also present in the tank to ensure homogeneity. The effect of power input was studied in the range of 18 to 77 W (9 to 39 kW m-3) on the kinetics and mechanisms of deagglomeration and the dispersion fineness. The effect of particle concentration was also studied in the range of 1 to 15% wt. The process was monitored through the evolution of particle size distribution (PSD), which indicated erosion as the dominant mechanism of breakup. The smallest attainable particle size was found to be independent of power input and solid concentration. Faster break up kinetics were noted as the power input was increased whereas increasing the solids concentration to 15% wt. slowed the process. It could also be shown that processing concentrated dispersions can be beneficial as the break up rate assessed on the basis of energy per unit mass of solids was faster for increased particle concentration

Break-up of nano-particle agglomerates by hydrodynamically limited processes

When dry nano-particulate powders are first added into a liquid, clusters as large as hundreds of microns can be formed. In this study, high shear impellers, such as the sawtooth Ekatomizer and rotor-stator impellers were used to suspend and break-up these agglomerates in a stirred vessel. The high local energy dissipation rates generated by these impeller could slowly break up clusters to sub-micron sizes by an erosional mechanism. In comparison, single and multiple passes through a valve homogeniser could quickly break the nano-particle clusters to sub-micron sizes; single pass operation had the highest breakage efficiency for a given specific energy input. For both equipment types, the rate of fines generation was found to be controlled by the maximum energy dissipation rate. However, the size of the fine aggregates produced was a constant and was not a function of the energy dissipation rate

Comparative performance of in-line rotor-stators for deagglomeration processes

Comparative performance of in-line rotor-stators for deagglomeration processe

Dispersion of clusters of nanoscale silica particles using batch rotor-stators

Nanoparticle powders added into a liquid medium form structures which are much larger than the primary particle size (aggregates and agglomerates)-typically of the order of 10’s of microns. An important process step is therefore the deagglomeration of these clusters to achieve as fine a dispersion as possible. This paper reports the findings of a study on the dispersion of hydrophilic fumed silica nanoparticle clusters, Aerosil 200 V, in water using two batch rotor-stators: MICCRA D-9 and VMI. The MICCRA D-9 head consists of a set of teeth for the stator and another for the rotor, whereas the VMI has a stator with slots and a rotor which consists of a 4-bladed impeller attached to an outer set of teeth. The dispersion process, studied at different power input values and over a range of concentrations (1, 5, 10 wt.%), was monitored through the evolution of PSD. Erosion was found to be the dominant breakage mechanism irrespective of operating conditions or rotor-stator type. The smallest attainable size was also found to be independent of the power input or the design of the rotor-stator. Break up kinetics increased upon the increase of power input, and this also depended on the rotor-stator design. With MICCRA D-9 which has smaller openings on both the stator and rotor, the break up rate was faster. Increasing the particle concentration decreased break up kinetics. It could also be shown that operating at high concentrations can still be beneficial as the break up rate is higher when assessed on the basis of specific power input per mass of solids

Breakup of nanoparticle clusters using microfluidizerM110-P

A commercial design, bench scale microfluidic processor, Microfluidics M110-P, was used to study the deagglomeration of clusters of nanosized silica particles. Breakup kinetics, mechanisms and the smallest attainable size were determined over a range of particle concentrations of up to 17% wt. in water and liquid viscosities of up to 0.09 Pa s at 1% wt. particle concentration. The device was found to be effective in achieving complete breakup of agglomerates into submicron size aggregates of around 150 nm over the range covered. A single pass was sufficient to achieve this at a low particle concentration and liquid viscosity. As the particle concentration or continuous phase viscosity was increased, either a higher number of passes or a higher power input (for the same number of passes) was required to obtain a dispersion with a size distribution in the submicron range. Breakup took place through erosion resulting in a dispersion of a given mean diameter range regardless of the operating condition. This is in line with results obtained using rotor-stators. Breakup kinetics compared on the basis of energy density indicated that whilst Microfluidizer M110-P and an in-line rotor-stator equipped with the emulsor screen are of similar performance at a viscosity of 0.01 Pa s, fines volume fraction achieved with the Microfluidizer was much higher at a viscosity of 0.09 Pa s

Casein fibres for wound healing

The name casein is given to a family of phosphoproteins which is commonly found in milk. Until recently, this was a constituent of milk that was commonly discarded; however today, it is widely used in health supplements all over the world. In this work, a high loading (50 wt%) of casein is mixed with a solution of polycaprolactone (PCL) to produce bandage-like fibres with an average fibre diameter of 1.4 ± 0.5 µm, which would be used to cover wounds in a series of tests with diabetic rats. Mouse fibroblast cell viability tests show that the casein-loaded fibres had little cytotoxicity with over 90% observed viability. A 14-day in vivo trial involving three groups of rats, used as control (no treatment), pure PCL fibres and casein-loaded fibres, showed that the casein within the fibres contributed to a significantly more extensive healing process. Histological analysis showed increased development of granulation tissue and follicle regrowth for the casein-loaded fibres. Further analysis showed that casein-loaded fibres have significantly lower levels of TNF-α, TGF-β IL-1β, NF-κB and IL-6, contributing to superior healing. The results presented here show an economical and simple approach to advanced wound healing

Assessment of Thiol/Disulphide Homeostasis in Patients with Knee Osteoarthritis

Our aim was to explore the thiol/disulphide homeostasis and the link with functional status in patients who have knee OA. Sixty knee OA patients and 50 healthy individuals were enrolled in this study. We measured serum levels of native thiol, total thiol and disulphide. In order to measure the alterations in functional status such tests as the Western Ontario, MacMaster steoarthitis index (WOMAC), walking test and Visual Analogue Scale (VAS) were utilized. The total thiol levels were higher in the control group than the knee OA patients (P< 0.05). Disulphide and disulphide/total thiol levels were significantly lower when control group were compared to knee OA patients (P< 0.05).Activity pain was negatively associated with native thiol levels (P< 0.05), walking test scores were negatively correlated with the native thiol levels (P< 0.05) and positively correlated with disulphide levels (P< 0.05) in knee OA patients. In knee OA patients, no correlation was observed between thiol/disulphide parameters and WOMAC scores. Conclusion, thiol/disulphide homeostasis is impaired in patients with knee osteoarthritis. Disulphide level increased and thiol level decreased due to oxidative stress. Thiol/ disulphide homeostasis had not noticeable impact on the on functional status. Thiol/disulphide homeostasis may help to explain the pathogenesis of osteoarthritis