propellants used in aerosol systems and the principle behind their selection

1. SEMINAR 9
AEROSOL: PROPELLANTS
Presented by ,
Ms. Aparna Ivon
M. Pharm 2 nd semester
Department of Pharmaceutics
APSC Pariyaram

2. INDEX
• Introduction
• Components of aerosol
• Propellants
• Principle behind selection of propellant
• Conclusion
• Bibliography
2

3. INTRODUCTION
• Aerosol is defined as a system that depends on the power of a compressed
or liquefied gas to expel the contents from the container.
• Aerosols are pressurized systems. The term pressurized system is used
commonly when referring to the aerosol container or complete product.
• Pressure is applied to the aerosol system through the use of one or more
liquefied or gas propellants’ upon actuation of the valve assembly of the
aerosol, the pressure exerted by the propellant forces the contents of the
package out through the opening of the valve
Advantages
1. A dose can be removed without contamination of remaining material.
2. The medication can be delivered directly to the affected area in a desired
form such as spray, stream, quick breaking foam or stable foam.
3. Irritation produced by the mechanical application of topical medication is
reduced or eliminated.
3

4. 4. Rapid onset of action circumvention of the first pass effect and avoidance
of degradation in the GI tract is achieved.
5. Dose lowering in case of steroid therapy and dose titration to individual
needs can be achieved by using metered dose and dry powder inhalers.
• The propellant is generally regarded as the heart of the aerosol package.
• It is responsible for development of pressure within the container,
supplying the necessary force to expel the product when the valve is
opened.
• The physical form in which the contents are emitted is dependent upon
the formulation of the product and the type of the valve employed.
• The physical form selected for a given aerosol is based on the intended
use of that product.
• Aerosol products were intended for topical administration for the treatment
of burns, minor cuts, infection and various dermatologic conditions
4

5. COMPONENTS OF AEROSOL
An aerosol product consists of the following components
• Propellant
• Container
• Valve and actuator
• Product concentrate
5

6. PROPELLANTS
• The propellant is responsible for developing the proper pressure
within the container, and it expels the product when the valve is
opened and aids in the atomization or foam production of the product.
• Various types of propellants are used which can be classified into
1. Liquefied gases
2. Hydrocarbons
3. Hydrocarbon ether
4. Compressed gases
6

7. • They are gases at room temperature and atmospheric pressure and can
be liquefied easily by lowering the temperature or by increasing the
pressure.
• They also maintain a constant pressure within the container.
• When they are placed in a sealed container, they immediately separate
into a liquid and a vapour phase.
• They have wide spread use as propellent, since they are very effective in
dispersing the ingredients into a fine mist or a foam.
• They are relative inert, non toxic and non-flammable.
• They also have an advantage of maintaining a constant pressure within
the container
• E.g. chlorofluorocarbon (CFC), hydrochloroflurocarbon (HCFCs),
and hydroflurocarbons (HFCs)
Liquefied gases
7

8. All the fluorinated propellants are identified by a numerical designation. The
rules governing this nomenclature system is as follows.
1. All the propellants are designed by three digits(000)
2. The first digit represents the one less than the number of carbon
atoms(‘c’-1)in the compound
3. The second digit represents the one more than the number of hydrogen
atoms(‘H’+1)in the compound
4. The last third digit represents the number of fluorine atoms in the
compound
5. The number of chlorine atoms in the compound can be found by
subtracting the sum of the fluorine and the hydrogen atoms from the total
number of atoms that can be added to saturate the carbon chain.
6. In the case of isomers the most symmetrical one is indicated by the
number alone. As the isomer becomes more and more asymmetrical, the
letter a, b, c, etc. follows the number.
7. For cyclic compound, a C is used before the number.
8

9. Fluorinated hydrocarbons
• They are widely used in most aerosol for oral and inhalation use. E.g.
1. Trichloromonofluromethane CCl3F 11
2. Dichlorodifluromethane CCl2F2 12
3. Dichlorotetrafluroethane CClF2CClF2 114
9

10. Hydrocarbons
• Hydrocarbon propellants have replaced CFCs for topical pharmaceutical
aerosols.
• Hydrocarbons are flammable, less toxic, less dense, more economic,
more soluble, and chemically more stable.
• They also have a wide range of solubility.
• Hydrocarbons have a density of less than 1 and their immiscibility with
water makes them useful in the formulation of a three phase system
aerosols.
• Being lighter than water, the hydrocarbon remains on the top of the
aqueous layer and serves to push the contents out of container.
• Not being halogenated, hydrocarbons generally possess better solubility
characteristics than the fluorinated hydrocarbon.
10

11. • Hydrocarbons are characterized by their extreme chemical stability. They
are not subjected to hydrolysis, making them useful with water based
aerosols. They will react the halogen but only under server condition.
• Examples: butane(propellant A-17) ,isobutene(propellant 31),
propane(propellant A-108)
11

12. Compressed gas
• Compressed gas are used in products like hair preparations, ointments,
dental creams, aqueous germicidal and antiseptic aerosols, contact
lenses cleaner and food products.
• Compressed gas has little expansion power and will produce a fairly wet
spray and less stable foam as compared to liquefied gas.
• The compressed gas such as nitrogen, nitrous oxide, and carbon
dioxide has been used as propellant.
• Depending on the nature of the formulation and the valve design, the
product can be dispensed as a fine mist, foam or semisolid
12

13. Hydrocarbon ether
• Example: Dimethyl ether-This is an alternative liquefied propellant, and
is more common in personal care products, and some air fresheners.
• It is significantly higher in price than hydrocarbon propellants.
• An advantage of DME is its solubility in and compatibility with aqueous
formulas.
13

14. PRINCIPLE BEHIND SLECTION OF
PROPELLANTS
• The vapour pressure of a mixture of propellant can be calculated
according to Dalton’s law.
• Dalton’s law states that the total pressure in any system is equal to the
sum of the individual or the partial pressure of the various components.
Total vapour pressure =partial pressure of A +partial pressure of B
Where; A and B are two different propellants
• The pressure exerted by an individual gas in a mixture is known as
its partial pressure.
14

15. • Raults law which regards lowering of the vapour pressure of a liquid by
the addition of another substance, states that the depression of the
vapour pressure of a solvent upon the addition of a solute is proportional
to the mole fraction of the solute molecules in the solution.
• Given ideal behavior, the vapour pressure of a mixture consisting of two
individual propellant is equal to the sum of mole fraction of each
component present multiplied by the vapour pressure of each pure
propellant at the desired temperature
• This relation can be shown mathematically;
Where, Pa = partial vapour pressure of propellant A
PA0 = vapour pressure of pure propellant A
na and nb = mole fraction of propellant A andB respectively
NA= mole fraction of component A
15

16. • To calculate the partial vapour pressure of propellant B,
• Total vapour pressure of the system is obtained from;
Where, P is the partial vapour pressure of the system
16

17. • When the mole fraction of one component is large and the other is small
then it does not affect the vapour pressure, this system approaches ideal
behavior.
• For practical purpose, however the calculated pressure is sufficiently
accurate for most determinations.
• When the components are of similar physical and chemical nature, the
experimentally determined values and the calculated values are
approximately the same.
• In the case of fluorinated hydrocarbon the deviation from the ideal
behavior is not great. And the results are approximately equal or within
5%.
• When other solvents are present, such as alcohols, the vapour pressure
can be determined in a similar manner.
17

18. CONCLUSION
• Aerosol is a non invasive pulmonary drug delivery system which is
considered to be one of the best methods as compared to other
routes of administration.
• It is useful to treat asthma, COPD etc.
• Various types of propellants are used in the formulation of aerosol
which will create a pressure inside the containers and helps to expel
the contents from the container.
• Propellants are important in formulation of aerosols.
18

19. BIBLIOGRAPHY
• Leon Lachman, H A. Lieberman. The theory & practice of industrial
pharmacy. 4th edition.CBS publishers and distributors, 2013. Chapter21:
Pharmaceutical aerosol, 770-774
• Howard C Ansel, Loyd V Allen,Nicholas G Popovich. Pharmaceutical
dosage forms and drug delivery systems.7th edition. Pheladelphia:
Lippincot Williams and Wilkins: 2000.chapter 13. Disperse systems, 384-
386.
• Remington. The science &practice of pharmacy, 20th edition. Indian:
Lippincot Williams and Wilkins: 2000. Chapter 50:aerosol,1006-1008
19

20. COPY RIGHT MESSAGE
The manuscript contains portions of Copyrighted works. These items are
included under the fair use exemption of the Copyright law and have
been prepared according to the educational fair use guidelines. They
are restricted from further use other than at Academy of
Pharmaceutical Sciences, Pariyaram. ©
20