Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO<sub>2</sub>, 2. Influence of Coating Solution Viscosity, Stickiness, pH, and Droplet Diameter on Agglomeration

Hede, Peter Dybdahl; Bach, Poul; Jensen, Anker Degn

doi:10.1021/ie800941x

Cited by 11 publications

(12 citation statements)

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“…These results indicate that the colloidal silica particles were being stabilized as agglomerates and could not adequately be dispersed through the polymer layer, which resulted in a coating layer more comparable to when S1 was used (when no colloidal silica was present) than S2 or S5 where the colloidal silica particles were dispersed effectively. These results are comparable to the findings of Hede et al who observed that improved TiO 2 dispersion in a PVA solution decreased the "stickiness" of the suspension, and in turn reduced agglomeration of 400 -500 m sodium sulfate beads [52].…”

Section: The Effect Of the Presence Of Colloidal Silica And Colloid supporting

confidence: 90%

“…The colloidal silica particles encased in the film coating will introduce asperities to the polymer coated ibuprofen to reduce cohesion, create separation between the core particles, and ultimately prevent agglomeration during spray coating. Several other authors have shown that agglomeration can be minimized when colloidal dispersions are sprayed instead of polymeric solutions [51,52]. Figure shows that the presence of the 180 nm colloidal silica particles allowed for higher coating weight gains without significant agglomeration.…”

Section: The Effect Of the Presence Of Colloidal Silica And Colloid mentioning

confidence: 89%

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Fluid bed film coating of fine ibuprofen particles

Davé

2016

Powder Technology

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Fine pharmaceutical powders pose significant challenge in fluid bed (FB) film coating due to their high cohesion. Ibuprofen powders, considered as model Geldart group C powders with Sauter mean diameters of 41 m (coarse) and 22 m (micronized), could not be fluidized due to severe agglomeration, solid-bridging, and poor flowability. Dry coating, applied as a pre-processing method that coats nano-silica on the surface of ibuprofen, enabled sufficiently improved flow, hence fluidization via reduced cohesion. Resulting coarse and micronized ibuprofen powders were successfully polymer film coated in a top spray fluidized bed. As a major novelty, apart from pre-processing through 20 nm silica surface coating that enabled fluidization, agglomeration during FB processing was minimized by introducing 180 nm colloidal silica particles that were pH stabilized in polymer spraying suspension using NaOH. In contrast, lack of or poorly stabilized colloidal particles led to significant agglomeration. Spray rate and fluidization velocity were both investigated to understand their effect on agglomeration of the coarse ibuprofen powders. Increased spray rate led to increased agglomeration due to the overly wet conditions, while increased fluidization velocities unexpectedly led to increased agglomeration resulting from electrostatic charging. To simplify the experimental design, a simple scaling relationship was introduced to estimate the coating conditions for the micronized ibuprofen powders based on the processing conditions of the coarse ibuprofen powders. This relationship, based on the minimum fluidization velocity, led to comparable agglomeration levels for powders with Sauter mean diameters of 21 and 42 m. To the author's knowledge these are the first successful results where micronized pharmaceutical powders were polymer coated in a traditional top spray fluidized bed.

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Section: The Effect Of the Presence Of Colloidal Silica And Colloid supporting

confidence: 90%

Section: The Effect Of the Presence Of Colloidal Silica And Colloid mentioning

confidence: 89%

Fluid bed film coating of fine ibuprofen particles

Davé

2016

Powder Technology

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“…The conclusions from the experiments in the first part of this study and the second part of this study, especially regarding the viscosity and stickiness, may be used to suggest a modification to the original viscous Stokes number. Instead of defining St v based on the viscous energy dissipated in the liquid bridge, the suggestion is to define a tack Stokes number ( St tack ) based on the tack work measured in the probe tack test.…”

Section: Testing Possible Causes For Differences In Processingmentioning

confidence: 97%

“…Analogously, an increased liquid layer (increasing h liq values) result in larger St v * values meaning that more particles will agglomerate. More information on the viscous Stokes theory may be found in the work of Ennis et al, Tardos and co-workers, , and Salman et al…”

Section: Viscous Stokes Theory: Agglomeration Of Nondeformable Granulesmentioning

confidence: 99%

Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO₂, 3. The Role of Tackiness and the Tack Stokes Number

Hede

Bach

Jensen

2009

Ind. Eng. Chem. Res.

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In the first and second parts of this study [Hede, P. D.; Bach, P.; Jensen, A. D. Ind. Eng. Chem. Res. 2009, 48, 1893 and 1905], agglomeration tendencies were studied for two types of coatings: sodium sulfate and PVA−TiO2. Results showed that the agglomeration tendency is always lower for the salt coating process than for the polymer coating process, under similar process conditions, because of differences in stickiness, not because of differences in bulk viscosities. It was further shown that it is possible to optimize the PVA−TiO2 coating formulation and process to achieve a low tendency of agglomeration, similar to the salt coating process. With the PVA−TiO2 coating liquid layer thicknesses encountered during these fluid-bed coating processes, agglomeration seems to be governed primarily by liquid surface phenomena. A modification to the original viscous Stokes number is suggested in the present paper, which defines the Stokes number in terms of the work needed to reach maximum tack instead of the viscous dissipation energy. The new tack Stokes number correlates well with the observed levels of agglomeration and, as a promising feature, proportionality is observed between the agglomeration weight percentage and the difference between the new tack Stokes number and the critical tack Stokes number.

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“…The surface waves were taking time to grow and destabilize the liquid sheet. 34 In response, the sheet surface was not thin enough to initiate the breakup at near nozzle points.…”

Section: Axial Smd Distributionmentioning

confidence: 99%

Effect of the borax mass and pre-spray medium temperature on droplet size and velocity vector distributions of intermittently sprayed starchy solutions

Naz

Sulaiman

Ariwahjoedi

2015

Phys. Chem. Chem. Phys.

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Spray coating technology has demonstrated great potential in the slow release fertilizers industry. The better understanding of the key spray parameters benefits both the environment and low cost coating processes. The use of starch based materials to coat the slow release fertilizers is a new development. However, the hydraulic spray jet breakup of the non-Newtonian starchy solutions is a complex phenomenon and very little known. The aim of this research was to study the axial and radial distributions of the Sauter Mean Diameter (SMD) and velocity vectors in pulsing spray patterns of native and modified tapioca starch solutions. To meet the objective, high speed imaging and Phase Doppler Anemometry (PDA) techniques were employed to characterize the four compositions of the starch-urea-borax complex namely S0, S1, S2 and S3. The unheated solutions exhibited very high viscosities ranging from 2035 to 3030 cP. No jet breakup was seen at any stage of the nozzle operation at an injection pressure of 1-5 bar. However, at 80 °C temperature and 5 bar pressure, the viscosity was reduced to 455 to 638 cP and dense spray patterns emerged from the nozzle obscuring the PDA signals. The axial size distribution revealed a significant decrease in SMD along the spray centreline. The smallest axial SMD (51 to 79 μm) was noticed in S0 spray followed by S1, S2 and S3. Unlikely, the radial SMD in S0 spray did not vary significantly at any stage of the spray injection. This trend was attributed to the continuous growth of the surface wave instabilities on the native starch sheet. However, SMD obtained with S1, S2 and S3 varied appreciably along the radial direction. The mean velocity vector profiles followed the non-Gaussian distribution. The constant vector distributions were seen in the near nozzle regions, where the spray was in the phase of development. In far regions, the velocity vectors were poly-dispersed and a series of ups and downs were seen in the respective radial distributions.

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Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO₂, 2. Influence of Coating Solution Viscosity, Stickiness, pH, and Droplet Diameter on Agglomeration

Cited by 11 publications

References 10 publications

Fluid bed film coating of fine ibuprofen particles

Fluid bed film coating of fine ibuprofen particles

Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO₂, 3. The Role of Tackiness and the Tack Stokes Number

Effect of the borax mass and pre-spray medium temperature on droplet size and velocity vector distributions of intermittently sprayed starchy solutions

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Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO2, 2. Influence of Coating Solution Viscosity, Stickiness, pH, and Droplet Diameter on Agglomeration

Cited by 11 publications

References 10 publications

Fluid bed film coating of fine ibuprofen particles

Fluid bed film coating of fine ibuprofen particles

Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO2, 3. The Role of Tackiness and the Tack Stokes Number

Effect of the borax mass and pre-spray medium temperature on droplet size and velocity vector distributions of intermittently sprayed starchy solutions

Contact Info

Product

Resources

About

Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO₂, 2. Influence of Coating Solution Viscosity, Stickiness, pH, and Droplet Diameter on Agglomeration

Fluidized-Bed Coating with Sodium Sulfate and PVA−TiO₂, 3. The Role of Tackiness and the Tack Stokes Number