When it comes to moisture and powders, flowability (caking and clumping) dominates the conversation. But there is much more to explore. In this webinar, scientists Mary Galloway and Dr. Zachary Cartwright address the top five moisture-related issues in powders, including: - Flowability—how to determine RHc and use it in shelf life, packaging, and formulation decisions - Moisture migration—how to predict and control it - Hygroscopicity—strategies for quantifying - Structure changes—how to determine boundaries between amorphous vs. crystalline, anhydrous vs. hydrate - Temperature effects: measuring effects on RHc and smoothing transitions Presenters: Mary Galloway is a lead scientist in the METER Food Research & Development lab. She specializes in using and testing instruments that measure water activity and its influence on physical properties. She has worked with many customers to solve their moisture-related product issues. Zachary Cartwright is a lead food scientist at METER Group. He helps customers achieve complete moisture analysis of their products and is an expert in the use of the Vapor Sorption Analyzer (VSA). He has a Ph.D. in food science from Washington State University and a bachelor’s degree in biochemistry from New Mexico State University.

2. MASTERING MOISTURE IN POWDERS
FLOWABILITY & BEYOND
Mary Galloway
Application Scientist
METER Group, Inc. USA
Zachary Cartwright, PhD
Food Scientist

3. TOP 5 ISSUES WITH POWDERS
• Caking and clumping
• Moisture migration
• Hygroscopicity
• Temperature
• Assessing structure

4. CAKING & CLUMPING

5. CAKING & CLUMPING
• Food and pharma
» Adsorption of water
• 5 stages of caking
• Affected by many factors
» Particle shape & size
» Applied pressure
» Chemical composition
Wet
Sticky
Agglomerate
Compact
Liquefaction

6. PREDICTING & AVOIDING
• Depends on:
» Water activity, time and
temperature
• Critical water activity
» RHc
• Determined using a
high-resolution
isotherm
Milk Powder
aw
%MC

7. SHELF LIFE PREDICTION
• Calculated using a model
derived from Fick’s Law
• Takes into account:
» Packaging
» Storage conditions
» Sorption properties
» RHC
Packaging

8. KEEP IN MIND
• Adding moisture increases water activity
» Adsorbed from high humidity air
» Or other ingredients at a higher water activity (more later!)
• Measure to avoid problems
• A high-resolution isotherm is required
» Dynamic Dew Point Isotherms to pinpoint RHC
» Dynamic Vapor Sorption isotherms to determine time

9. CAKING & CLUMPING
CRYSTALLINE POWDERS

10. CAKING AND CLUMPING
CRYSTALLINE POWDERS
Examples of Crystalline Powders:
Certain salts, sugars, acids, vitamins, APIs
 Doesn’t adsorb moisture – water molecules will sit
on the surface only, until the energy (aw) is high
enough to break apart the crystal lattice
 Unique in that they go immediately from a solid to a
liquid form (deliquescence)

11. CAKING AND CLUMPING
CRYSTALLINE POWDERS
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
35.00%
40.00%
0.0000 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000 1.0000
%
Moisture
Content
(wb)
Water Activity
NaCl Sucrose

12. MECHANISMS FOR CRYSTAL CAKING
Particle size
Mingyang Chen, Songgu Wu, Shijie Xu, Bo Yu Mohannad Shilbayeh , Ya Liu, Xiaowen Zhu, Jingkang Wang, Junbo Gong
Caking of crystals: Characterization, mechanisms and prevention, Powder Technology, Volume 337, September 2018,
Pages 51-67

13. Particle size
• Smaller particles induce agglomeration
Particle Shape
• More surface area increases caking
Temperature Effecting RH
• Internal: increase temp = increase aw
• External: decrease temp = increased RH
Time
CAKING AND CLUMPING
CRYSTALLINE POWDERS

14.  Deliquescence point (RH0) of mix is lower than individual’s
 RH fluctuations → cycles of deliquescence and crystallization →
caking
 RH0 mix independent of ingredient ratios
 Temperature increases can reduce the RH0
 RH0 lowering can affect both chemical and physical stability
CAKING AND CLUMPING
CRYSTALLINE POWDERS

15. MOISTURE MIGRATION

16. MOISTURE MIGRATION
FOOD
• Adding ingredients
changes the water
activity
» In a predictable way
• Requires an
isotherm for each
ingredient
» And mixing modeling
Whey Protein Powder
aw
%MC
Maltodextrin
Whey Protein Blend
Sunflower Lecithin
7
6
5
4
3
2
1
0

17. MOISTURE MIGRATION
PHARMA
• Fill and capsule
» Microcrystalline cellulose
(MCC)
» HPMC cap
• How does this compare
to actual data?
aw
%MC

18. HYGROSCOPICITY

19. HYGROSCOPICITY
Hygroscopicity – tendency of a substance to adsorb moisture
from the surrounding atmosphere
 Amount of water will be a function of temperature and
humidity
 Can be determined by a sorption isotherm
 Important for excipient selection
ex. solubility, moisture scavenging, sorption kinetics, deliquescence

20. HYGROSCOPICITY
EXCIPIENTS
 Larger increase in %MC indicates a
more hygroscopic material
 Calculate increase in %MC or %wt
change to compare hygroscopicity
 Croscarmellose Na – most
hygroscopic
 Sorbitol and Sucrose at aw > 0.70, had
a transition and became very
hygroscopic
 Mannitol – non-hygroscopic

21. TEMPERATURE

22. TEMPERATURE
• As temperature
increases
» Water activity increases
» RHC decreases
• Predict aw at any
temperature
» Requires 3 isotherms at
different temps
15°C
40°C
Milk Powder
aw
%MC

23. ASSESSING STRUCTURE

24. ASSESSING STRUCTURE
Crystalline vs. Amorphous
 Degree of Transition?
Anhydrous vs. Hydrate
 Hydrate Formation
Isotherms show
the relationship
between aw and
%MC
Relationship is
based on the
structure of the
product
Possible to
assess different
structures with
isotherms

25. CRYSTALLINE VS. AMORPHOUS
0%
5%
10%
15%
20%
25%
30%
0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
%
Moisture
Content
(wb)
Water Activity
Structures of Sucrose
Crystalline Amorphous

26. CRYSTALLINE VS. AMORPHOUS
0%
5%
10%
15%
20%
25%
30%
0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
%
Moisture
Content
(wb)
Water Activity
Structures of Sucrose
Crystalline Amorphous 50:50 Mix

27. ANHYDROUS VS. HYDRATE
0%
5%
10%
15%
20%
25%
30%
35%
40%
0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140 0.160 0.180 0.200
%
Moisture
Content
(wb)
Water Activity
CaCl2 Forms
Anhydrous - Ads Dihydrate - Ads

28. ANHYDROUS VS. HYDRATE
10%
20%
30%
40%
50%
60%
0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400
Moisture
Content
(wb)
Water Activity
CaCl2 Anhydrous
Adsorption Desorption
0%
10%
20%
30%
40%
50%
60%
0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400
Moisture
Content
(wb)
Water Activity
CaCl2 Dihydrate
Adsorption Desorption

29. SNEAK PEAK
MOISTURE ANALYSIS TOOLKIT

30. MOISTURE ANALYSIS TOOLKIT

31. CONTACT INFORMATION
Mary Galloway
509-332-5534
mary@metergroup.com
Zachary Cartwright, PhD
509-402-1240
zachary.cartwright@metergroup.com