In situ micro-computed tomography to study microstructure and sublimation front during freeze-drying

Gruber, Sebastian; Vorhauer-Huget, Nicole; Foerst, Petra

doi:10.1016/j.foostr.2021.100213

Cited by 11 publications

(10 citation statements)

References 27 publications

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“…Measured sublimation fluxes were almost constant during the whole freeze-drying experiment, which might have been a result of vapor transport limitations inside the freeze-drying cell [ 16 ]. Only at the end of drying, at a saturation below S = 0.2, did the drying flux decrease slightly in the case of MD5 and MD5 AN.…”

Section: Discussionmentioning

confidence: 99%

“…The heterogeneity of transport conditions resulting from distributed pore space can affect the development of the sublimation front, which propagates faster in larger pores. The result is a structured sublimation front, a phenomenon such as described in [ 11 , 12 , 13 , 14 , 15 , 16 ]. Hence, the freezing process, i.e., the development of the solid matrix, was investigated in depth [ 17 , 18 , 19 ] to evaluate and subsequently find pore structures favorable to heat and mass transfer.…”

Section: Introductionmentioning

confidence: 99%

“…The dynamic temporal evolution of the sublimation front can be assessed using in operando imaging techniques with high contrast between the propagating dry pores, solids and ice [ 12 , 13 , 15 , 16 , 20 , 21 ]. At the same time, pore scale models can assess heat and mass transfer kinetics at the front.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Study of the Impact of Pore Structure on Drying Kinetics and Sublimation Front Patterns

et al. 2022

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Freeze-drying frozen maltodextrin solutions with solid contents of 5% and 30% (w/w) was experimentally investigated using neutron imaging at PSI Villigen/Switzerland. Different solid contents, as well as annealing at −5 °C for 11 h, were used to modify the porous structure of the samples, which was quantified using X-ray computed tomography. Annealing of the 5% (w/w) sample, with a pore size distribution (PSD) of 23.7 ± 11.1 µm, yielded a very open pore space with high porosity (ε = 0.96) and a PSD of 33.0 ± 27.0 µm. In contrast, the higher solid content resulted in small, lamellar, narrow pores with high anisotropy and a porosity of ε = 0.65, as well as a PSD of 13.5 ± 4 µm. In operando neutron imaging was used to show the impact of the structure of frozen maltodextrin on the overall drying kinetics and shape of the sublimation front during freeze-drying. For this purpose, a freeze-drying stage was employed, which allowed a novel approach to time- and space-resolved monitoring of the ice phase. The sublimation front propagation was quantitatively analyzed based on ice saturation profiles and sublimation rates. The dependence of drying velocity on structure is nicely demonstrated by the data. In addition, it is shown that the sublimation front widened during freeze-drying, resulting in either rather concave or convex shape depending on morphological parameters.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Experimental Study of the Impact of Pore Structure on Drying Kinetics and Sublimation Front Patterns

et al. 2022

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“…However, in the literature there are only a few studies that describe the microstructure of a freeze-dried sample by such parameters. To characterize the freeze-drying process in more detail, multiple methods exist [ 14 , 15 , 16 , 17 ]. Usually, these methods focus on the global sublimation rate and can be measured by local temperature measurements or gravimetric methods, for example [ 18 , 19 ].…”

Section: Introductionmentioning

confidence: 99%

“…They are usually classified into 2D and 3D imaging methods. For 2D imaging, light microscopy is typically used, whereas for 3D imaging, X-rays or neutrons are used [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

The Influence of Local Microstructure Inhomogeneities on Local Drying Kinetics during Freeze-Drying

et al. 2022

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Freeze-drying is a gentle drying technique to dry high value products, such as pharmaceuticals, without impacting the quality of the product. However, this method is very time and cost intensive. It is known that larger pores reduce the duration of primary drying due to facilitated mass transport. However, next to the pore size, other structural parameters exist whose influence on drying kinetics is still unknown. Therefore, the aim of this article is to investigate the influence of the microstructure (pore size, shape and orientation) on local primary drying kinetics. In the study, freeze-drying experiments on maltodextrin and sucrose solutions (c1 = 0.05 and c2 = 0.15 w/w) were carried out in a lyomicroscope. Two-dimensional images were recorded during the whole drying process and in the dry state and analyzed on the movement of the sublimation front, pore size, orientation and shape. Different microstructures were created by using different freezing parameters, namely two different cooling rates and solid concentrations. It could be shown that for pores with a high aspect ratio, the pore orientation was more important for the drying kinetics than the pore size, while for pores with a lower aspect ratio the pore size was the decisive parameter.

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Pore Scale Investigation of Freeze-Drying

Gruber

Foerst

Thomik

et al. 2023

Album of Porous Media

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In situ micro-computed tomography to study microstructure and sublimation front during freeze-drying

Cited by 11 publications

References 27 publications

Experimental Study of the Impact of Pore Structure on Drying Kinetics and Sublimation Front Patterns

Experimental Study of the Impact of Pore Structure on Drying Kinetics and Sublimation Front Patterns

The Influence of Local Microstructure Inhomogeneities on Local Drying Kinetics during Freeze-Drying

Pore Scale Investigation of Freeze-Drying

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