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

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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

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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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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

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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

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-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

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Melting profile is more important than melting point

Determined by low-resolution pulsed H-NMR

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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