semi-solid and solid formulations – crystallization …...beta-prime: 37 c / 111 kj/mol beta: 44 c...
TRANSCRIPT
Lipid knowledge for the personal care industry
Semi-solid and Solid Formulations
– Crystallization Topics
Benjamin Schwartz
Ontario SCC Education Day
September 18, 2018
Crystallisation and film forming– efficacy and sensory properties
Commercial formulations2 mg/cm2Dried at 40 CPolarised microscopy
2
3
Molecules in the liquid state do not have any organised structure
4
The behaviour of oleic acid in crystals
Size and shape matters
5
Tripalmitin
A simple, saturated triglyceride
Alpha: 45 °C / 96 kJ/molBeta-prime: 56 °C / 127 kJ/molBeta: 66 °C / 171 kJ/mol
6
StOSt
a not so simple triglyceride found in shea butter and in chocolate
Alpha: 23 °C / 73 kJ/molBeta-prime: 37 °C / 111 kJ/molBeta: 44 °C / 154 kJ/mol
Size comparison
double and triple chain packing in triglycerides
60-70 Å
40-50 Å
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8
Triglycerides with oleic acid in mid position (sn-2) favour triple chain packing in the beta form
Saturated triglycerides normally go to the doublechain packing in beta form if the difference in chainlength is less than 4 carbons
Alpha and beta-prime forms are normally onlydouble chain tending
Triple chain packing requires more time to stabilise: need for tempering!
Triglyceride polymorphism revisited
Double and triple chain packing
9
Melting points of fatty acids are dependenton both size and degree of unsaturation
Melting point as function of chain length
-10
0
10
20
30
40
50
60
70
80
90
4 6 8 10 12 14 16 18 20 22 24
Meltin
g p
oin
t(°
C)
Saturated Monounsaturated (cis)
Melting point as function of unsaturation for C18 fatty acids
-20
-10
0
10
20
30
40
50
60
70
80
0 1 2 3 4
Meltin
g p
oin
t(°
C)
Number of double bonds
10
Melting profile is more important than melting point
Determined by low-resolution pulsed H-NMR
11
Look at the shape of the curve– A flat curve indicates a less temperature sensitive ingredient and
better stability against bloom
– A sharp melting ingredient can give a contrast in skin feel: solid-to-liquid transformation at body temperature
Look at the solids content at ”room temperature”– High solids (>60%) at 20C indicate a waxy product, <50% a
pasty product
Look at the solids at 35 C (body temperature)– Less than 5%: liquid,oily skinfeel
– More than 10%: drier but heavier skinfeel
Look at the solids at 40-45C– >5 % solids can help to stabilise emulsions at high temperature
Practical application ofthe solid phase content
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This is bloom…
How to avoid it?
Bloom occurs in chocolate, cookies, lipsticks, balms, shampoos, body butters and concentrated creams
Bloom is the results of crystal growth
How can we control crystal growth behaviour?
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Bloom has many possible causes:
Composition
Polymorphism
Incompatibility
Processing and storage
Shea butter bloom examples
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Complex molecules show polymorphism: triglyceride behaviour
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Consequences ofpolymorphic behaviour
Optimal cooling(22-25°C)
Creation ofsmall beta-
prime crystals
Beta-primecrystals
transform to beta
Slight growth ofcrystals
Stableproduct
Excessivecooling
(<20°C)
Creation ofalpha crystals
Alpha crystalsmelt and
transform to beta-prime
Beta-primecrystals growand dissolve
Beta crystalsare graduallyformed and
grow to largesize
Unstableproduct with
bloom
No cooling(>25°C)
Very few beta-prime crystals
form
Beta-primecrystals grow to
large size
Beta-primecrystals
transform to beta
Beta crystalsgradually
grow to largesize
Stable butinhomogeneous
product
Temperatures given are valid for Lipex shea butters
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Small crystals are invisible and do not cause grainy skinfeel ifsize is <20 micrometer
Polymorphic transformations cause the crystals to grow– Alpha -> liquid -> beta-prime -> beta
Mixed crystals cause the crystals to grow– ABABABAB -> AAAA + BBBB
– Low melting component goes into solution and recrystallises in purer crystals which can grow to larger sizes
Very small crystals dissolve and recrystallise on larger ones(Ostwald ripening)– Small crystals have higher energy because of curvature and are
more easily dissolved. The material is instead deposited on largercrystal surfaces -> crystal growth
Bloom is caused by crystal growth!
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Molecules that are too different do not mix well in the solid state
– Shea butter and coconut oil
– Commonly used in lip balms and lip butters
– If you ”must” use the combination, let one of the components dominate
• 1 part coconut oil to 5-6 parts of shea butter
• 1 part of shea butter to 5-6 parts coconut oil
– Other ingredients to watch out for
• Cocoa butter, shorea butter, illipe butter, cupuacu butter (stearic acid basedbutters)
• Hydrogenated coconut glycerides, palm kernel oil, babassu oil (”laurics)
• Hydrogenated castor oil and derivatives (hydroxyl group)
• Silicone waxes (limited solubility in solid state)
Incompatibility in the solid state
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Molecular modelling: StStSt & LaLaP
Layer distances for some fats:Lipex Shea (beta): 47-50 ÅLipex 102 (beta): 69-72 Å Lipex BC (beta-prime): 47-51 ÅKristal (beta-prime): 37-38 Å
Layer distance
Determined by X-ray diffraction
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Crystallisation dynamics
Solidification of complex molecules is not instantaneous!
Understanding crystallisation dynamics helps to avoidscale-up problems
Melting consumes heat / crystallisation releases heat
Fats are thermal insulators -> if the heat of crystallisationis not removed, the solidification process slows down
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Short movie showing a molecularmodel of a triglyceride going from liquid to solid state.
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The solidification process starts withnucleation followed by growth and cluster formation
Liquid Nucleation
Low -Isolated particles
Medium –Clusters
High –NetworksConsistency:
Growth
Influenced by:CompositionTimeTemperatureStirring (shear)
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Cooling profile
0
10
20
30
40
50
60
70
0 0,2 0,4 0,6 0,8 1 1,2
Time (hours)
Tem
pera
ture
(C
elc
ius)
Temperature
5min 30min 24h
20 C
15 C
10 C
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The consistency is strongly influencedby cooling conditions: rate, startingpoint and end temperature
Cooling process: Lipex Shea cooled in glass jars Results of texture analysis afterstabilisation at 20 °C for 24 hours
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An anhydrous balm based on shea butter (Lipex Shea) wascooled in different packaging types at two different coolingtemperatures
The temperature was measured in the center as function of time
Internal target temperature was 25 C
The consistency was measured in three places in the jars afterstabilization for 24 hours at 20C
How long does it take to cool a balm?– a practical illustration
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Cooling at low temperature (8C): effect of packaging material
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The texture, consistency and stability are influenced by composition and cooling conditions
Important processing parameters: shear, cooling profile
Inherent physical properties (composition & interactions)
Understanding crystallization and ingredient interactions will help youto create stable formulations