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COUPLED DYNAMICS OF HEAT TRANSFER AND FLUID FLOW IN SHEAR RHEOMETRYSridharan, Harini 26 August 2020 (has links)
No description available.
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Evaluation of the critical parameters and polymeric coat performance in compressed multiparticulate systemsBenhadia, Abrehem M.A. January 2019 (has links)
Compression of coated pellets is a practical alternative to capsule filling. The
current practice is to add cushioning agents to minimize the stress on the
coated pellets. Cushioning agents however add bulkiness and reduce the
overall drug loading capacity. In this study, we investigated the performance
of compressed coated pellets with no cushioning agent to evaluate the
feasibility of predicting the coat behaviour using thermo-mechanical and
rheological analysis techniques. Different coating formulations were made of
ethyl cellulose (EC) as a coating polymer and two different kinds of additives
were incorporated into the polymeric coating solution. Triethyl Citrate (TEC)
and Polyethylene glycol 400(PEG400) were used as plasticizers at different
levels to the coating formulations (10%, 20%, 30%). Thermal, mechanical
and rheological measurements of the coating film formulations were
achieved to investigate the effect of plasticizers. Thermal gravimetric
analysis results (TGA) showed higher residual moisture content in films
plasticised with PEG 400 compared to their TEC counterparts. Differential
Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and
Parallel Plate Shear Rheometer (PPSR) were used to study the influence of
the level and type of plasticisers incorporated in coating film formulation on
the performance of the coating film. In this study, both DSC and DMA were used to investigate the Tg for each film coating formulation in order to
evaluate the effect of the additives. In general DMA results for the Tg value
of the films were always higher by 10-20% than those measured by the DSC.
Furthermore, clamp size and the frequency of the oscillation have an
influence on the evaluation of Tg. Complex viscosity for different coating film
formulations revealed that the shear hinning gradient changes with
temperature and plasticiser type and concentration. The value of complex
viscosity from DMA and PPSR exhibits power law behaviour. The rheological
moduli were indirectly affected by the level of plasticiser. There was a
discrepancy between the complex viscosity results obtained from both DMA
and PPSR at similar temperature but they follow the same trend. The non
plasticized polymer showed a 10 time higher complex viscosity values when
measured by DMA over that measured by PPSR. The difference was smaller
in plasticized films but it was not consistent. Therefore a consistent
coefficient to correlate the DMA and PPSR couldn’t be accurately determined
Coated pellets were compressed and key process parameters were
evaluated. The obtained results revealed that the coating thickness has a
significant effect on the release profile of the final products. It was found that
by increasing the coating film thickness, the percentage released decreased.
Also the compression force has lower influence on the drug release profile,
while the dwell time has very low effect on the percentage release from the
final products. Optimum release profile was obtained at a coating level of 5.5%
w/w and a compression force of 4700N
In conclusion, the elasticity of the plasticised EC films in this study meant
that the internal stress is not dissipated during compression and the dwell time range that was used in this experiment. Increasing the thickness
therefore was necessary to enhance the strength of the film and avoid
cracking. The mechanical and rheological profiling was helpful therefore to
understand the behaviour of the coated pellets and predict the film properties
at various steps of the process of coating and compression (i.e., various
shear rate regimes). Experimental design approach to studying the key
process and formulation parameters helped identify the optimum values for
the process.
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Thermal and rheological approaches for the systematic enhancement of pharmaceutical polymeric coating formulations : effects of additives on glass transition temperature, dynamic mechanical properties and coating performance in aqueous and solvent-free coating process using DSC, shear rheometry, dissolution, light profilometry and dynamic mechanical analysisIsreb, Mohammad January 2011 (has links)
Additives, incorporated in film coating formulations, and their process parameters are generally selected using a trial-and-error approach. However, coating problems and defects, especially those associated with aqueous coating systems, indicate the necessity of embracing a quality-by-design approach to identify the optimum coating parameters. In this study, the feasibility of using thermal and rheological measurements to help evaluate and design novel coating formulations has been investigated. Hydroxypropyl methylcellulose acetate succinate (HPMCAS), an enteric coating polymer, was used as the film forming polymer. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and Parallel Plate Shear Rheometery (PPSR) were used to evaluate the effect of different plasticisers on the performance of HPMCAS. The results illustrate that, for identical formulations, the DSC and DMA methods yielded up to 40% differences in glass transition temperature (Tg) values. Moreover, Tg measured using loss modulus signals were always 20-30 oC less than those measured using tan delta results in DMA testing. Absolute and relative Tg values can significantly vary depending on the geometry of the samples, clamp size, temperature ramping rate and the frequency of the oscillations. Complex viscosity data for different formulations demonstrated a variable shear thinning behaviour and a Tg independent ranking. It is, therefore, insufficient to rely purely on Tg values to determine the relative performance of additives. In addition, complex viscosity results, obtained using both the DMA and PPSR techniques at similar temperatures, are shown to be comparable. The results from both techniques were therefore used to produce continuous master curves for the HPMCAS formulations. Additionally, step strain tests showed that HPMCAS chains do not fully III disentangle after 105 seconds as predicted by the Maxwell model. Finally, in situ aqueous-based coating experiments proved that mixtures of triethyl acetyl citrate and acetylated monoglyceride (TEAC/AMG), even without cooling of the suspension, do not cause blocking of the spray nozzle whereas triethyl citrate (TEC) based formulae did. TEAC (alone or in a combination with AMG) exhibits superior wettability to HPMCAS than TEC/AMG formulations and can be used to enhance the efficiency and film quality of the dry coating process.
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Thermal and rheological approaches for the systematic enhancement of pharmaceutical polymeric coating formulations. Effects of additives on glass transition temperature, dynamic mechanical properties and coating performance in aqueous and solvent-free coating process using DSC, shear rheometry, dissolution, light profilometry and dynamic mechanical analysis.Isreb, Mohammad January 2011 (has links)
Additives, incorporated in film coating formulations, and their process
parameters are generally selected using a trial-and-error approach. However,
coating problems and defects, especially those associated with aqueous
coating systems, indicate the necessity of embracing a quality-by-design
approach to identify the optimum coating parameters. In this study, the
feasibility of using thermal and rheological measurements to help evaluate and
design novel coating formulations has been investigated. Hydroxypropyl
methylcellulose acetate succinate (HPMCAS), an enteric coating polymer, was
used as the film forming polymer. Differential Scanning Calorimetry (DSC),
Dynamic Mechanical Analysis (DMA), and Parallel Plate Shear Rheometery
(PPSR) were used to evaluate the effect of different plasticisers on the
performance of HPMCAS. The results illustrate that, for identical formulations,
the DSC and DMA methods yielded up to 40% differences in glass transition
temperature (Tg) values. Moreover, Tg measured using loss modulus signals
were always 20-30 oC less than those measured using tan delta results in DMA
testing. Absolute and relative Tg values can significantly vary depending on the
geometry of the samples, clamp size, temperature ramping rate and the
frequency of the oscillations. Complex viscosity data for different formulations
demonstrated a variable shear thinning behaviour and a Tg independent
ranking. It is, therefore, insufficient to rely purely on Tg values to determine the
relative performance of additives. In addition, complex viscosity results,
obtained using both the DMA and PPSR techniques at similar temperatures, are
shown to be comparable. The results from both techniques were therefore used
to produce continuous master curves for the HPMCAS formulations.
Additionally, step strain tests showed that HPMCAS chains do not fully
III
disentangle after 105 seconds as predicted by the Maxwell model. Finally, in situ aqueous-based coating experiments proved that mixtures of triethyl acetyl citrate and acetylated monoglyceride (TEAC/AMG), even without cooling of the suspension, do not cause blocking of the spray nozzle whereas triethyl citrate (TEC) based formulae did. TEAC (alone or in a combination with AMG) exhibits superior wettability to HPMCAS than TEC/AMG formulations and can be used to enhance the efficiency and film quality of the dry coating process.
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SHEAR RHEOMETRY PROTOCOLS TO ADVANCE THE DEVELOPMENT OF MICROSTRUCTURED FLUIDSEduard Andres Caicedo Casso (6620462) 15 May 2019 (has links)
<p></p><p>This doctoral dissertation takes the reader through a
journey where applied shear rheology and flow-velocimetry are used to
understand the mesoscopic factors that control the flow behavior of three
microstructured fluids. Three individual protocols that measure relative
physical and mechanical properties of the flow are developed. Each protocol
aims to advance the particular transformation of novel soft materials into a
commercial product converging in the demonstration of the real the chemical,
physical and thermodynamical factors that could potentially drive their
successful transformation. </p>
<p> </p>
<p>First, this dissertation introduces the use of rotational
and oscillatory shear rheometry to quantify the solvent evaporation effect on
the flow behavior of polymer solutions used to fabricate isoporous asymmetric
membranes. Three different A-B-C triblock copolymer were evaluated:
polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(4-vinylpyridine) (ISV);
polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>N</i>,<i>N</i>-dimethylacrylamide)
(ISD); and polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>tert</i>-butyl methacrylate) (ISB). The resulting evaporation-induced
microstructure showed a solution viscosity and film viscoelasticity strongly
dependent on the chemical structure of the triblock copolymer molecules. </p>
<p> </p>
<p>Furthermore, basic shear rheometry, flow birefringence, and
advanced flow-velocimetry are used to deconvolute the flow-microstructure relationships
of concentrated surfactant solutions. Sodium laureth sulfate in water (SLE<sub>1</sub>S)
was used to replicate spherical, worm-like, and hexagonally packed micelles and
lamellar structures. Interesting findings demonstrated that regular features of
flow curves, such as power-law shear thinning behavior, resulted from a wide
variety of experimental artifacts that appeared when measuring microstructured
fluids with shear rheometry.</p>
<p> </p>
<p>Finally, the successful integration of shear rheometry to
calculate essential parameters to be used in a cost-effective visualization
technique (still in development) used to calculate the dissolution time of
polymers is addressed. The use of oscillatory rheometry successfully quantify
the viscoelastic response of polyvinyl alcohol (PVA) solutions and identify
formulations changes such as additive addition. The flow behavior of PVA
solutions was correlated to dissolution behavior proving that the developed
protocol has a high potential as a first screening tool.</p><br><p></p>
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