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Disintegration of agglomerates in liquid

Gabrie M.H. MeestersErik M. Bosma, Merel OostveenJ. Ruud van OmmenSheila Khodadadi

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Introduction

Instant powders

Wetting behaviour

Dispersing behaviour

AIM: • Good instant properties• Rapid and complete reconstitution• No lump formation

Reducing the reconstitution time• Understanding the rehydration behaviour• What is the rate limiting step

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Powder rehydration

(Forny, Marabi et al. 2011)

(Fang, Selomulya et al. 2007)

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Wetting of powders

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Experimental

• Prepare powder beds by sieving & pressing

• Determine the bulk density

• Place droplet on powder bed

• Record time required to sink in

Drop penetration time method

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Results

• Current model assumes Drawing Area (DA) = Penetration Area (PA)

• Experiments show widening by factor 1.5

Model adaption – penetration area

DA

PA

DA

PA

Original model Adapted model I

Adaption I decreases difference theory / experiments by factor 2.3 (Kozeny Carman)

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Micro Computed Tomography

Potato starch ɛ=075

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Results

• Current model estimates pore size ~ 10-7 m

• Experimental pore size (micro CT) ~ 10-6 m

Model adaption – pore size

Original model Adapted model II

Adaption II decreases difference theory / experiments by factor 4.2 (Washburn)

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Results

• Corresponds well to model predictions

• Instant starch behaviour dominated by maltodextrin

(Maltodextrine & Instant starch)

Drop penetration time [s]

Weights [#] Corn starch Maltodextrin Instant starch

1 2.0 0.14 0.14

3 1.5 0.11 0.13

12 2.3 0.09 0.10

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Disintegration of powders

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Disintegration

Rehydration of formulated potato starch

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Disintegration

Rehydration of formulated potato starch

Static version

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Disintegration

Disintegration

“The dissolution of the solid bridges between the primary particles followed by dispersion of the primary particles within the

liquid volume”(Richard, Toubal et al. 2012)

A B C D

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Modelling the data

Various researchers have modelled dispersion as a first order process existing of either a single or multiple exponential terms 1

𝑦 = 𝐴 1 − exp −𝑘𝐴 ∗ 𝑡 + 𝐵 1 − exp −𝑘𝐵 ∗ 𝑡

These researchers measured a property which is linked to disintegration, like the change in:• Viscosity• Conductivity• Light back scattering

1 To, Mitchell, Hill, Bardon and Matthews - 1994

Kravtchenko, Renoir, Parker, Brigand – 1999

Larsen, Gåserød and Smidsrød – 2003

Galet, Vu, Oulahna and Fages - 2004

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Questions to answer

• How can we quantify the disintegration time?

• Can the existing models be used for consumer product?

• What dependency exist for the rate constant?

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Experimental setup

Two measurements methods are used during this project to describe disintegration

• Laser light diffraction• Measure the particle size distribution and follow this over time• Changes in the D90 reflect how the particles get smaller• Applicable to powders with good wetting properties

• Spectrophotometer• Measure the change in optical density over time• Other reconstitution effects are also measured

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Laser diffraction Introduction

• Reservoir is filled with water

• Powder is added to the top

• Powder is pumped around to the laser

• The laser light is scattered by the particles

• A particle size distribution (PSD) is sought that best fits the scatter pattern

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Laser diffractionPSD

A PSD is obtained over time, giving insight how the distribution is affected

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Laser diffractionPSD

A PSD is obtained over time, giving insight how the distribution is affected

Static version

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Laser diffractionD90

Following the D90 over time gives us insight into how fast a particle disintegrates

0

100

200

300

400

500

600

700

800

0 50 100 150 200 250 300

D9

0 [

µm

]

Time [sec]

Formulated Potato Starch

D90

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Laser diffractionResults

A higher temperature will lead to a higher rate constant and thereby also a faster disintegration time

0.00

0.04

0.08

0.12

0.16

0.20

0 5 10 15 20 25 30 35

Init

ial r

ate

co

nst

ant

[1/s

]

Temperature [°C]

Formulated potato starch

0.00

10.00

20.00

30.00

40.00

50.00

0 5 10 15 20 25 30 35

Dis

inte

grat

ion

tim

e [

1/s

]

Temperature [°C]

Formulated potato starch

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Photo-spectrometryObscuration

• Powder and a magnetic stirrer are added to a cuvet

• Water is added from the top

• Light is passed through the sample

• As the particles disintegrate they block more light

• If soluble components are present they disappear over time, letting more light pass

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Spectrophotometry

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SpectrophotometryIntroduction

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 20 40 60

Ab

sorb

ance

un

it [

-]

Time [sec]

Milk powder

• Peaks at the beginning are caused by the initial addition of the powder

• Disintegration follows a exponential function

• Variations in the final value are caused by different concentrations

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SpectrophotometryChanging temperature

0

25

50

75

100

125

150

0 20 40 60 80

Tim

e [

sec]

Temperature [°C]

Disintegration time

Cocoa powder - Nesquik

Cocoa powder - Benco

Coffee creamer

0.01

0.10

1.00

0 20 40 60 80

Tim

e [

sec]

Temperature [°C]

Rate constant

Cocoa powder - Nesquik

Cocoa powder - Benco

Milk powder

Same behaviour is observed as for laser diffraction

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The questions

• How can we quantify the disintegration time? Laser diffraction and photo-spectrometry seem to work

• Can the existing models be used for consumer product? Literature models that described dispersion/dissolution rate

can also be applied to describe the disintegration of different powders. TO BE PROVEN YET

• What dependency exist for the rate constant? Temperature effect on both measurement methods are in

agreement with each other and with literature 1

1 Larsen, Gåserød and Smidsrød – 2003

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Issues

• Difficult to study disintegration on its own, e.g. when wetting is already critical

• Determination of time constants for the four stages will tell us where to opimise our formulations

• Model description of disintegration still to be proven

• Sinkability also difficult to determine. Will be dealt with in next research