Advanced Asphalt Emulsion Technology For Paving Applications 2009
Emulsion technology
description
Transcript of Emulsion technology
Emulsion technologyEmulsion technology
SCS Summer school July 13, 2013
Steve Boothroyd
Thinking about how you would develop any sort of product what are the key things you should consider during development?
My thoughts in no particular order of importance
Does your Consumer love it?Does it meet the Claims you want to make for it?Is it safe?Is it stable?Can you make it on a larger scale consistently?Can you afford it?
Does you consumer love it?
Why would you choose to use an emulsion instead of another technology?
Take a few minutes in your tables to come up with 5 possible answers
Does you consumer love it?
Possible answers…
•They feel good!•You can pack different actives in different phases•You have the option to change lots of things•They can take a range of formats•They are cost effective
What is an emulsion?
A dispersion of one or more immiscible liquid phases in another, the distribution being in the form of tiny droplets.
What is an emulsion?
A dispersion of one or more immiscible liquid phases in another, the distribution being in the form of tiny droplets.
Simple emulsion types
Water-in-oil
Water droplet(dispersed phase)
Oil(continuous phase)
Oil-in-water
Oil droplet(dispersed phase)
Water(continuous phase)
Emulsion orientation
• The phase that is added tends to become the internal phase
• The predominant solubility of the emulsifier tends to determine the external phase (Bancroft’s rule)
• Generally, the phase of the greatest volume tends to become the external phase
• The phase in which the stirrer is placed tends to become the external phase
Droplet size measurement
Laser Particle Analyser
Opticalmethod
Laser method
Use of sound waves (Malvern)
Audio method
Microscopy
• Uses • Droplet size and size distribution• Quality of manufacturing process e.g.
undispersed thickener• Detecting unwanted crystallisation • Early indications of instability e.g.
flocculation, coalescence, synerisis• Comparison of different emulsions• Liquid crystals
What does an emulsion look like?
What does an emulsion look like?
What does an emulsion look like?
What don’t you want to see?
Is it Stable?
What are the stability risks associated with emulsions?
Take a few minutes in your tables to come up with some possible answers
Is it Stable?
What are the stability risks associated with emulsions?
•Creaming•Sedimentation•Flocculation•Coalescence•Phase Inversion•Ostwald Ripening
Is it Stable?
Why is that?
•Emulsions are thermodynamically unstable•Their natural tendency is to revert to a state of least energy i.e. separated into two layers•The process of emulsification is to produce droplets but also to maintain them in this state over a reasonable shelf life
Creaming / Sedimentation
• No change in droplet size• Reversible• Driven by density difference• Usually results from gravitational forces
Creaming Sedimentation
Coalescence
• Not reversible• May lead from flocculation, creaming /
sedimentation or Brownian motion• Involves 2 drops coming together
• May lead to complete separation
Stokes’ Law
Defined as:-
Velocity of droplet (v) = (2a2 g (ρ1 – ρ2)) / 9η
Wherea = Radius of dispersed phase dropletρ1= Density of continuous (external) phaseρ2 = Density of continuous (internal) phaseg = Acceleration due to gravityη = viscosity of the continuous (external) phase
Van der Waals forces
Defined as
F = - Aa12H
Where
F = Van der Waals forces of attractionsA = Hamaker constanta = Radius of dispersed phase dropletsH = Distance between two adjacent dispersed
phase droplets
Is it Stable?
What can these two equations tell us that will help us make formulating decisions to improve stability?
Take a few minutes in your tables to come up with some possible answers
• From Stokes’ Law• Thicken the continuous phase. This increase η
and reduces the velocity• Reduce the particle size by greater or more
effective mixing.This has a major effect as a is squared
• Reduce the difference in specific gravity between the phases
• Additionally from Van der Waal• Increase the distance between droplets either
through thickening the water phase to reduce mobility, reducing particle size, or introducing materials that avoid droplets getting too close e.g. polymers
Improving emulsion stability
• Charge stabilisation• Interfacial film strengthening
• with powders
• with polymers
• With non-ionic emulsifiers• Steric stabilisation• Continuous phase viscosity• Droplet size• Co-emulsifiers / polar waxes• Liquid crystals
Improving emulsion stability
Charge stabilisation
--
-
----
--
--
-
----
--
--
-
----
--
--
-
----
--
--
-
----
--
--
-
----
--
--
-
----
--
+
+
+
+
+ ++
+
++
+
+
+
+++
++
++
++
+
+++
+
++
+
++
+
+
+
+
+
+ +
+ ++
Negatively charged oil droplets repel each other
Stability affected by quantity of electrolyte and whether M+ or M++
Improving emulsion stability
• Interfacial film strengthening• Reduces the probability of coalescence
when droplets collide
Interfacial film strengthening with powders
Powder particle size must be very small
Powder must have an affinity for both the oil and water phase
Improving emulsion stability
Interfacial film strengthening with polymers
Polymer sits at emulsion interface
Polar groups orient into the water phase
e.g. Cetyl PEG/PPG-10/1 Dimethicone Acrylates/vinyl isodecanoate crosspolymer
Improving emulsion stability
Interfacial film strengthening with non-ionic emulsifiers
Oil
Tighter packingat interface
Interface strengthening is dependent on the number of molecules that are packed into the interface
Improving emulsion stability
• Polymer molecules adsorb on the surface of oil droplets, leaving tails and loops extending into the water phase
• Polymer molecules must be strongly adsorbed at interface
• There must be high coverage of droplet surface with polymer
• The 'tails and loops' must be soluble in the water phase
• e.g. Cetyl PEG/PPG-10/1 Dimethicone
Improving emulsion stabilitySteric stabilisation
• Continuous phase viscosity• Thickening the water phase restricts
movement of oil droplets• Thickeners with yield points are most
effective
• Droplet size
Increasing stability
Improving emulsion stability
• Co-emulsifiers / polar waxes• e.g. Cetyl alcohol
• Co-emulsifiers have weaker surface activity than primary emulsifiers
• Adds body and helps prevent coalescence
Improving emulsion stability
Is it Safe?
What are the key components of an emulsion that contribute to safety risk?
Is it Safe?
What are the key components of an emulsion that contribute to safety risk? Here are some possibilities
•Preservatives•Fragrance•Actives•Emulsifiers
What is an emulsifier?
Water lovinghead
Oil lovingtail
'Hydrophilic''Lipophobic'
'Lipophilic''Hydrophobic'
Potential irritation
• Emulsifiers, since they are surface active, may be a factor in increasing the risk of irritation
therefore
• Excessive levels of emulsifier should be avoided
• The most appropriate type of emulsfier should be chosen
Types of emulsifiers
• Anionics
The emulsifier carries a negative charge e.g. Sodium Stearate soap
C H COO Na3517
- +
Types of emulsifiers
Pros and Cons
• Were very common• Old fashioned• Not as versatile• Cheap• Limitations for actives due to high pH• Give negative charge to the oil droplet
Types of emulsifiers
• Cationic
The emulsifier carries a positive charge e.g. Palmitamidopropyl Trimonium Chloride
_ClCH3(CH2)14C NH(CH2)3
O
CH3
CH3
N CH3+
Types of emulsifiers
Pros and Cons
• Usage is not high in Skincare • Good barrier• Excellent silky skin feel• Give positive charge to oil droplet• Can be used at lower pH
Types of emulsifiers
• Non-ionic
Emulsifier carries no overall charge and can be made to form both Water-in-oil or Oil-in-water emulsifiers e.g. Steareth-2
CH3 (CH2 )16 CH2 (OCH2 CH2)2 OH
Types of emulsifiers
• Most common• Wide range• Versatile• Strengthen the emulsion interface• HLB system to predict choice
HLB system
0 10 20
LipophilicOil lovingNon polarOil soluble
HydrophilicWater lovingPolarWater soluble
HLB system
Emulsifier HLB 5
Emulsifier HLB 10
Emulsifier HLB 15Oilphase
Waterphase
Determining HLB values
Source: Croda ( Taken from Croda’s time saving guide to emulsifier selection” - training course available from Croda PLC)
How can you tell the difference?
• Measure conductivity – conductivity is higher with an O/W emulsion than a W/O emulsion
• Dye uptake - a water soluble dye will be taken up by an O/W emulsion
• Dispersion – an O/W emulsion will easily disperse in water
Required HLB for oil-in-water emulsion
Benzophenone-3Mineral oil Caprylic/Capric triglycerideCetyl alcoholVitamin E
710 - 11 515 - 16 6
HLB system
Required HLB for water-in-oil emulsion
Mineral oil 4
• Oil phase components can be given required HLB values
• Required HLB and emulsifier HLB are matched up
• Each oil will have 2 required HLB’s, one for oil-in-water emulsions, the other for water-in-oil emulsions
• The required HLB is published for some oils
Emulsifier selection using HLB
HLB Summary
• Pros– Empirical system
giving starting position
– Can be assessed practically
• Cons– Not good for anionics and
cationics– Need to know HLB of oil
which can vary– Can be time consuming
working out or measuring– Does not determine the
amount of emulsifier needed
Emulsifier blends
In the HLB system the HLB of the emulsifier blend is additive for example if an oil system had a required HLB of 10 you could use either
EmulsifierHLB 10
EmulsifierHLB 5
EmulsifierHLB 15or
Emulsifier blendsFor a given blend of non-ionic emulsifiers, where Emulsifier A is more lipophilic than Emulsifier B
Emulsifier A Emulsifier B
Oil Oil Tighter packingat interface
Considerations when choosing an emulsifier
• Type of emulsion• Oils to be emulsified• Processing - hot or cold• Effect on skin• Properties of the emulsion• Cost• Level of electrolyte
Can you make it on a larger scale consistently?
What are the differences that would impact on the manufacture of an emulsion between lab and factory?
Take a few minutes in your tables to come up with some possible answers
Can you make it on a larger scale consistently?
What are the differences that would impact on the manufacture of an emulsion between lab and factory?
Heating/ Cooling ratesStirring/ Shear rates
How are emulsions formed?• In order to overcome the barrier between the oil
and water we need to add energy• This is derived from two sources:-
• For long term stability both forms are needed
Chemical energy + Mechanical energy (emulsifier) (homogeniser)
Two key requirements for creating a stable emulsion
• Apply enough energy to the two phases to create a dispersion
• Stabilise the created dispersion
• Maintain a small droplet size• Increase the external phase viscosity to
reduce movement• Reduce phase density difference
Two stages of creating an emulsion
• Stage 1 – apply energy to the two phases to create a dispersion
• Generally heat to 70 - 75°C
• Stage 2 – stabilise the created dispersion• Maintain the small droplet size• Increase the external phase viscosity• Reduce phase density difference
Emulsion manufacture• Heating to this temperature can change the
level of the oil phase e.g. Cyclomethicone• If you need to add sensitive ingredients hot e.g.
sunscreens, then do it just prior to emulsification
• Avoid post emulsification addition of preservatives etc that partition between oil and water
Emulsion manufacture• After cooling the remaining ingredients are
added e.g. heat sensitive preservatives, perfumes.
• For W/O emulsions if you have to add preservatives these MUST be added prior to emulsification
• Only Oil-in-water emulsions can be made to weight easily
• BUT you must start thinking about scale up from the first formulation attempt
Emulsion manufacture• Laboratory
– Oil phase added with Silverson mixing
– Beaker placed in bowl of cold water and stir cooled
Takes approx 30 min
• Factory– Oil phase added with gate stirring followed by homogeniser mixingSize and distance
– Cold water passed through water jacket with gate stirring
Can take hours!
Emulsion manufacture
Phase Inversion Temperature(PIT)
• Occurs in some non-ionic emulsifier systems
• Linked to solubility of emulsifier in the respective phases • At different temperatures• In the presence of electrolyte
• Mostly used to transition water in oil to oil in water at a given temperature to produce desired small particle size
Phase Inversion Temperature(PIT)
• Unique for any given emulsifier or blend of emulsifiers
• Useful for explaining behaviour of emulsion systems
• Helps to understand formation of differing types of emulsion observed for a given blend of emulsifiers
Phase Inversion Temperature• Within the marked band a complex three phase mixture
is found• Above TU a W/O emulsion exists, below TL O/W• This temperature and band will be different for different
systems
0o
75o
0 20% emulsifier blend
Tem
per
atur
e oC TU
T
TL
2 phase
1 phase
2 phase
3 phase
Source: Kahlweit M: Microemulsions, Science 29 April 1998, p671-621
Phase Inversion Temperature• Why might this be the case?
• Solubility of ethoxylated emulsifiers increases with increasing ethoxylation
8 20
Sol
ubil
ity
Number of ethoxylate groups
Phase Inversion Temperature• Bancroft’s rule suggests that the emulsion formed
will depend on where the emulsifier is most soluble
• Oil in water where most water soluble
(hydrophilic)
• Water in Oil where most lipid soluble (lipophilic)
• Consequently changes the effective HLB
observed
• By correct choice of emulsifier conversion from a W/O to an O/W is possible