Semi-solid and Solid Formulations Crystallization Topics

Transcription

1 Semi-solid and Solid Formulations Crystallization Topics Benjamin Schwartz Ontario SCC Education Day September 18, 2018 Lipid knowledge for the personal care industry

2 Crystallisation and film forming efficacy and sensory properties Commercial formulations 2 mg/cm2 Dried at 40 C Polarised microscopy 2

3 Molecules in the liquid state do not have any organised structure 3

4 The behaviour of oleic acid in crystals Size and shape matters 4

5 Tripalmitin A simple, saturated triglyceride Alpha: Beta-prime: Beta: 45 C / 96 kj/mol 56 C / 127 kj/mol 66 C / 171 kj/mol 5

6 StOSt a not so simple triglyceride found in shea butter and in chocolate Alpha: Beta-prime: Beta: 23 C / 73 kj/mol 37 C / 111 kj/mol 44 C / 154 kj/mol 6

7 Size comparison double and triple chain packing in triglycerides Å Å 7

8 Triglyceride polymorphism revisited Double and triple chain packing Triglycerides with oleic acid in mid position (sn-2) favour triple chain packing in the beta form Saturated triglycerides normally go to the double chain packing in beta form if the difference in chain length is less than 4 carbons Alpha and beta-prime forms are normally only double chain tending Triple chain packing requires more time to stabilise: need for tempering! 8

9 Melting point ( C) Melting point ( C) Melting points of fatty acids are dependent on both size and degree of unsaturation Melting point as function of chain length Melting point as function of unsaturation for C18 fatty acids Saturated Monounsaturated (cis) Number of double bonds 9

10 Melting profile is more important than melting point Determined by low-resolution pulsed H-NMR 10

11 Practical application of the solid phase content 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: solidto-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 11

12 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? 12

13 Shea butter bloom examples Bloom has many possible causes: Composition Polymorphism Incompatibility Processing and storage 13

14 Complex molecules show polymorphism: triglyceride behaviour 14

15 Consequences of polymorphic behaviour Optimal cooling (22-25 C) Creation of small betaprime crystals Beta-prime crystals transform to beta Slight growth of crystals Stable product Excessive cooling (<20 C) Creation of alpha crystals Alpha crystals melt and transform to beta-prime Beta-prime crystals grow and dissolve Beta crystals are gradually formed and grow to large size Unstable product with bloom No cooling (>25 C) Very few betaprime crystals form Beta-prime crystals grow to large size Beta-prime crystals transform to beta Beta crystals gradually grow to large size Stable but inhomogeneous product Temperatures given are valid for Lipex shea butters 15

16 Bloom is caused by crystal growth! Small crystals are invisible and do not cause grainy skinfeel if size 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 larger crystal surfaces -> crystal growth 16

17 Incompatibility in the solid state 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 based butters) Hydrogenated coconut glycerides, palm kernel oil, babassu oil ( laurics) Hydrogenated castor oil and derivatives (hydroxyl group) Silicone waxes (limited solubility in solid state) 17

18 Molecular modelling: StStSt & LaLaP Layer distance Layer distances for some fats: Lipex Shea (beta): Å Lipex 102 (beta): Å Lipex BC (beta-prime): Å Kristal (beta-prime): Å Determined by X-ray diffraction 18

19 Crystallisation dynamics Solidification of complex molecules is not instantaneous! Understanding crystallisation dynamics helps to avoid scale-up problems Melting consumes heat / crystallisation releases heat Fats are thermal insulators -> if the heat of crystallisation is not removed, the solidification process slows down 19

20 Short movie showing a molecular model of a triglyceride going from liquid to solid state. 20

21 The solidification process starts with nucleation followed by growth and cluster formation Growth Liquid Nucleation Consistency: Low - Isolated particles Medium Clusters High Networks Influenced by: Composition Time Temperature Stirring (shear) 21

22 Temperature (Celcius) Cooling profile C Temperature ,2 0,4 0,6 0,8 1 1,2 Time (hours) 15 C 10 C 5min 30min 24h 22

23 The consistency is strongly influenced by cooling conditions: rate, starting point and end temperature Cooling process: Lipex Shea cooled in glass jars Results of texture analysis after stabilisation at 20 C for 24 hours 23

24 How long does it take to cool a balm? a practical illustration An anhydrous balm based on shea butter (Lipex Shea) was cooled in different packaging types at two different cooling temperatures 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 after stabilization for 24 hours at 20C 24

25 Cooling at low temperature (8C): effect of packaging material 25

26 Understanding crystallization and ingredient interactions will help you to create stable formulations The texture, consistency and stability are influenced by composition and cooling conditions Important processing parameters: shear, cooling profile Inherent physical properties (composition & interactions) 26