Components of Aerosol Package

Sponsored Links

Components of Aerosol

1) Components of Aerosol Package 2, 3, 14, 15

The following components / parts require for aerosol product:

1) Propellant

2) Product concentrate

3) Container

4) Valve and Actuator

Aerosol components

5.1) Propellants:

Propellants are responsible for developing the pressure in the aerosol container and also it expel the product from the container when the valve is opened and helps in expels the product by atomization of contents or foam production of the product.

When the propellant/s is a liquefied gas or a mixture of liquefied gases, it frequently serves the propellant and solvent or vehicle for the product concentrate.

Types of propellant

Depending on the route of administration and use, the propellant can be classified as

I) Type-I Propellant A- Liquified Gas

1) For oral and inhalation (Fluorinated hydrocarbons)

Tri-chloro-mono-flouro methane (propellant 11)

Di-chloro di-fluro methane (propellant 12)

Di-chloro tetra-fluro ethane (propellant 114)

2) Topical Pharmaceutical aerosols (Hydrocarbons)




II) Type-II Propellant B - Compressed Gas Propellants

3) Compound gases


Carbon di-oxide

Nitrous oxide


The basic characteristics of propellants are chemically inert, free from toxicity, inflammability and explosiveness. Due to these characteristics, the chlorofluorocarbon (CFC) propellants P-11, P-12 and P-114 etc., are using in aerosol products from several years. Now-a-days their usage is reduced, as they cause the depletion of ozone layer. The CFCs are using in some aerosol products, due to their low toxicity and inflammability. They are still use in small quantities in the treatment of asthma and chronic obstructive pulmonary disease (COPD). P-134a and P-227 are now been developed and are being incorporated in aerosol formulations in place of P-12.

P-11, P-12 and P-114 etc. are the CFCs suitable for oral, nasal and inhalation aerosols. These chlorofluorocarbon propellants are generally accepted due to their relatively low toxicity and inflammability. The chlorofluorocarbons as classes are inert, but P-11 is undergo hydrolysis and it will form hydrochloric acid in the presence of water. The developed acid increases the corrosion of the container and may irritate when applied to membranes. If water content is there in product P-12 or a mixture of P-12 and P-114 are generally used.

The CFCs are gases at room temperature that can be liquefied by cooling them below their boiling point or by compressing them at room temperature. For example, dichlorodifluoromethane (P-12) will form a liquid (when cooled to - 21.6degF or compressed to 84.9 psia at 70degF) (psia = pounds per square inch). Some liquefied gases also have a very large expansion ratio compared to the compressed gases (e.g., nitrogen, carbon dioxide). The usual expansion ratio for liquefied gases is about 240 which mean that 1 ml of liquefied gas will occupy a volume of approximately 240 ml (it allowed to vaporize). Compressed gases expansion ratio is about 3 - 10.

Physical Properties of some Fluorinated Hydrocarbon / Chlorofluorocarbon Propellants 1, 5, 10

Chemical Name

Chemical formula

Numerical Designation a

Vapor pressure (psiab) 70 0C

Boiling point (1 ATM) 0F

Liquid density (g/mL) 70 0F











- 21.6












- 37.7












- 11.2








a The numerical designations for fluorinated hydrocarbons propellants have been designed so the chemical structure of the compound can be determined from the number.

The system consists of three digits.

  • The digit at the complete right refers to the number of fluorine atoms in the molecule.
  • The second digit from the right represents one greater in the number of hydrogen atoms in the molecule.
  • The third digit from the right indicates one less the number of carbon atoms in the molecule, if this third digit is 0, it is omitted and a two digit number is used.
  • The capital letter "C" is used before a number to indicate the cyclic nature of a compound.
  • The small letters following a number are used to indicating decrease in symmetry of (isomeric) compounds. The most symmetrical compounds are given the designated number and all other isomers are assigned a letter (i.e., a, b, etc.) in descending order of symmetry.
  • The number of chlorine atoms in a molecule determined by subtracting the total number of hydrogen and fluorine atoms from the total number of atoms required to saturate the compound.

b psia (pounds per square inch absolute) which equals to psig (pounds per square inch gauge + 14.7)

When a liquefied gas propellant/s mixture is sealed in an aerosol container with the product concentrate is establish equilibrium between the propellant which remains liquefied and a portion that vaporizes and occupies the upper portion of the container. The developed pressure at this equilibrium is referred to as the "vapor pressure" (expressed as psia) and it is a characteristic of each propellant at a given temperature. So the vapor pressure is exerted equally in all directions and is independent of the quantity of liquefied phase present and the pressure forces the liquid phase up the dip tube and out of the container when the valve is opened or actuated. As the propellant reaches to the atmosphere or air, it evaporates due to the drop in pressure and leaves the product concentrate as airborne liquid droplets or dry particles.

As some content of the liquid is removed from the container through the dip tube, then the equilibrium between the propellant's liquefied phase and vapor phase is rapidly re-established. The pressure within the container remains constant and the product may be continuously released at same rate and with the same proportion.

In the case, when there is no dip tube in the container, the container is used in the reverse position so that the liquid phase is in direct contact with the valve. When the valve is opened or actuated, the liquid phase is emitted and immediately reverts to the vapor phase in the atmosphere.

Aerosol components with propellant

Hydrochlorofluorocarbons (HCFC) and Hydrofluorocarbons (HFC)

The HydroChloroFluoroCarbons (HCFC) and HydroFluoroCarbons (HFC) differ from CFCs. These may not contain chlorine and contains one or more hydrogens. These compounds break down in the atmosphere at a faster rate than the CFCs resulting in a lower ozone depleting effect.

P-22, 142b, and 152a are used in topical pharmaceutical preparations. These three propellants have a greater miscibility with water and therefore are more useful as solvents compared to the other propellants.

They are also slightly more flammable than the other propellants but this is not perceived as a disadvantage.

Properties of Hydrochlorofluorocarbon and Hydrofluorocarbon Propellants 1, 5, 10




@70degF (psia)

degF (1 ATM)

Liquid Density
@70degF (g/ml)




- 135.7

- 41.4






- 15.0












- 12.5









  • The environmental acceptance, low toxicity and nonreactivity are the characteristics of hydrocarbons propellants allowing them to be used as the propellant.
  • Hydrocarbons are used in the preparation of water based aerosols as they are stable to hydrolysis due to the absence of chlorine. Since they are immiscible with water, they retain on the top of water.
  • Hydrocarbons will develop good pressure to push the contents out of the container.
  • The disadvantage of Hydrocarbon propellants are flammability and explosive. So the usage is reduced as propellant.
  • Hydrocarbons do not contains halogens and therefore hydrolysis does not occur making these good propellants for water based aerosols.

Properties of Hydrocarbon Propellants 1, 5, 10




@70degF (psia)

degF (1 ATM)

Liquid Density
@68degF (g/ml)





- 43.7














Propane, butane and isobutane are the most commonly used hydrocarbons as propellants. They are used alone or as mixtures or mixed with other liquefied gases to get the desired vapor pressure and degree of flammability. The flammability has been substantially reduced by using mixture of propellants and with the development of newer types of aerosol dispensing valves (i.e., valve with vapor tap).

Vapour pressure of Hydrocarbons 1, 5, 10


Pressure (psig) 70 0C

Composition (mol %)

n = Butane





108 +- 4




Traces of ethane

A- 70

70 +- 2




A- 52

52 +- 2




A- 46

46 +- 2





40 +- 2





31+- 2





24 +- 2




0.1 each neopentane and isopentane

A- 17

17 +- 2




Traces of isopentane


The use of compressed gas like Nitrogen, Nitrogen dioxide and Carbon dioxide as propellant/s, which emits contents in the form of fine mists, foams, fine mists or semisolid. It produces fairly wet sprays and the foams are not as stable as produced by the liquefied gas propellant. Unlike the aerosol prepared with liquefied gas propellant, there is no propellant reservoir. The compressed gas propellant is contained in the headspace of the aerosol container which forces the product concentrate to emit contents out of the container. For this higher gas pressure is require in this aerosol. This aerosol finds its application to dispense food products, dental creams, hair preparation and ointments.

Properties of Compressed Gases 1,5,10



@70degF (psia)

degF (1 ATM)

Gas Density
@70degF (g/ml)




- 320


Nitrous Oxide



- 127


Carbon Dioxide



- 109


Aerosol components with propellant as compressed Gas

Difference between Liquefied Propellant and Compressed Gas Propellant

Difference between Liquefied Propellant and Compressed Gas Propellant


Gas molecules follow in random paths and collide with each other and the walls of the container. These collisions of gas molecules exert a pressure per unit area and also cause the gases to occupy a volume. Both the volume and pressure are affected by temperature.

The interrelationships of these variables find out by Boyle, Charles or Gay-Lussac's law and can be applied to pharmaceutical aerosols.

Boyle's Law states that:

P a 1 / V when temperature does not change and PV = K

Where, V= The volume (ml or L)

P = The pressure (atm)

K = The proportionality constant

Charles's Law or Guy-Lussac's Law states that:

V a T when pressure does not change and V = KT

Where, T = the absolute temperature (degK)

If two sets of conditions (i.e., P, V, and T) are being considered, from above equations can be combined to obtain the relationship:

P2V2 / T2 = PV / RT

Where the subscripts 1 and 2 refer at two different conditions. The P, V and T of each condition may be different, the ratio V1/V2 is constant and mathematically can be expressed as PV= RT, Where, R = the constant value of the ratio.

To above equation, consider only 1 mole (i.e., one gram molecular weight) of ideal gas.

If n moles of gas were to be considered, it becomes:

PV = nRT

This is also known as the "Ideal Gas Law". Where 'R' is the molar gas constant and is used with many different units depending on the mathematical application. (8.314 J/degK/mole or 0.08205 L atm/degK/mole or 1.987 cal/degK/mole).

By blending of proper proportions of propellants to get the desired vapour pressure in the container.

Vapour pressure of mixtures of propellants can be calculated according to "Dalton's Law" and "Rault's Law".

Dalton's Law: Total vapour pressure in any system is equal to the sum of the individual or partial pressures of the various components.

P = p1 + p2 + p3

Rault's Law: It is regards lowering of the vapour pressure of a liquid by the addition of another substance.

Ideal behavior is the vapour pressure of a mixture consisting of two individual propellants is equal to sum of the mole fraction of each component present is multiplied by vapour pressure of each pure propellant at desired temperature.

This relationship can shown mathematically as:

pa = (na / na + nb) PAo = NA PAo

Where: pa = partial vapour pressure of propellant A

pAo = vapour pressure of pure propellant A

na = moles of propellant A

nb = moles of propellant B

NA = mole fraction of component A

To calculate the partial vapour pressure of propellant B:

pb = (nb / nb + na) PBo = NB PBo

The total vapour pressure of the system is obtained from

P = pa + pb

Where: P = Total vapour pressure of system

pa = partial vapour pressure of propellant A

pb = partial vapour pressure of propellant B

Blends / Mixture of Fluorocarbon Propellants for Pharmaceutical Aerosols 10

Propellant Blend *


Vapour pressure (psig) 70 0C

Density (g/mL) 70 0F

























* It is generally understood that the designation "Propellant 12/114 (70:30)" indicates of 70 % by weight of propellant 12 and 30 % by weight of propellant 114.

5.1) Product concentrate: 10

Simply the product concentrate is the active ingredient of the aerosol is combined with the required adjuncts,

  • The Active drug (for therapeutic activity)
  • Propellant/s (to expel the contents from the container)
  • Antioxidants (to prevent degradation of product)
  • Surface active agents/ Surfactants (to Increase Miscibility)
  • Solvent/s (to prepare a stable and efficacious product and to retard the evaporation of the propellant)
  • Other excipients like Vehicles, suspending agents etc.

Solution Aerosols are two phase systems consisting of the product concentrate in a propellant or mixture of propellants or a mixture of propellant and solvent. Some solvents may also be added to the formulation to retard the evaporation of the propellant.

Solution aerosols can be difficult to formulate because many propellant or propellant-solvent mixtures are nonpolar in nature and these are poor solvents for the aerosol product concentrate. Few solvents can be used. E.g: Ethyl alcohol (most commonly used solvent), dipropylene glycol, propylene glycol, ethyl acetate, hexylene glycol and acetone.

Solution aerosols are used to make foot protective preparations, local anesthetics, anti-inflammatory preparations, spray on protective films and for oral and nasal applications. They contain 50 to 90% propellant for topical aerosols and up to 99.5% propellant for oral and nasal aerosols. If the percentage of propellant increases, the degree of dispersion and spray also fine form. The percentage of propellant decreases, the wetness of the spray will get increases. The particle sizes of the sprays can vary from 5 to 10 mm in inhalation aerosols and 50 to 100 mm for topical sprays.

Suspension Aerosols can prepare, when the product concentrate is insoluble in the propellant or mixture of propellant and solvent or when a co-solvent is not desirable. Eg: Anti-asthmatic drugs, steroids and antibiotics are prepared in suspension aerosols.

  • When the valve is opened or actuated, the suspension formulation is emitted to atmosphere and the propellant rapidly gets vaporizes and leaves a fine dispersion of the product concentrate.
  • For formulation of suspension aerosols are not necessary with solution aerosols includes agglomeration, particle size growth, moisture content, valve clogging and particle size of the dispersed aerosolized particles.
  • Lubricants such as isopropyl myristate, light mineral oil and surfactants such as oleic acid, sorbitan trioleate and lecithin have been used to overcome the difficulties of particle size agglomeration and growth which are directly related to the clogging problems.
  • The moisture content of the entire formulation should be kept below 200 to 300 ppm so all of the ingredients need to be the anhydrous form of the chemical or be capable of becoming anhydrous after a drying process.
  • The particle size of the insoluble ingredients of product concentrate should be in the 1 to 10 um range for inhalation aerosols and between 40 to 50 um for topical aerosols.

Emulsion Aerosols consists of the active ingredient, surfactant/s, nonaqueous and/or aqueous vehicle/s. Depending on the components, the emitted product can be a stable foam (shaving cream type) or a quick breaking foam. A quick breaking foam creates a foam form, when emitted from the container, which collapses in a relatively short time. This type of foam is used to apply on large area without manual rubbing or spread the product. In these the active drug is more rapidly available to affected area, because the foam quickly collapses.

Foams can be produced when the product concentrate is dispersed in throughout the propellant and the propellant acts as the internal phase. Here o/w type of emulsion will form. When the propellant is in the external phase (like a w/o emulsion), foams are not created but results in to sprays or wet streams. When surfactants are used which have limited solubility in both the organic and aqueous phases stable foams are produced. Surfactants concentrate at the interface between the propellant and the aqueous phase forms a thin film as the "lamellae." It is the specific composition of lamellae that indicates the structural strength and general characteristics of the foam.

Surfactants used in emulsion aerosols have included fatty acids saponified with anionic surfactants, triethanolamine and some nonionic surfactants like polyoxyethylene fatty esters, alkyl phenoxy ethanols, polyoxyethylene sorbitan esters and alkanolamides. The nonionic surfactants are less compatibility problems because no electronic charge.

Basic principle to release product concentrate from container

Basic principle to release product concentrate from container

Liquefied propellant or propellant mixture exists in equilibrium with the product concentrate in a sealed aerosol container. The liquefied propellant vapourises and occupies the upper portion of the aerosol container. As the liquefied propellant exists in equilibrium with the propellant in the

vapour phase in an aerosol container, so a constant pressure is maintained within the aerosol container. Hence, it is called as "a pressurised aerosol container".

The pressure exerted by the propellant is called as "vapour pressure", measured in psig, is the characteristic of specific propellant. Upon the actuation of the valve, the pressure exerted by the propellant is distributed equally in all direction in the aerosol container, forcing the product concentrate up the dip tube and out of the aerosol container. As the vapour pressure of the propellant in air is lower than inside the aerosol container, so the propellant evaporates on reaching the air and product concentrates dries up as dry particles.

5.1) Aerosol Containers: 2, 3, 14, 15

They must be stand at pressure as high as 140 to 180 psig (pounds per sq. inch gauge) at 1300 F. The glass or metal containers are generally used. Glass disadvantage is brittleness, so restricted usage of glass. If the pressure is less than 25 psig and propellant content is less than 15% then glass can be used. It should be coated with plastic coating in two layers if pressure is less than or equal to 33 psig. For linings Epoxy and vinyl resins can be used. Vinyl resins can form strong lining but it will get damaged by steam. But the epoxy resins can be used, as they are resistant to steam. The products which have less pH, vinyl coating on the epoxy coating is most suitable.

Choice of the material is depend on- Pressure of the system, whether product is aqueous or not, pH of the product, physicochemical properties of preparation.

Different types of materials for aerosol containers are:

5.3.1) Metals

- Tin plated steel (Side-seam or Three, Two piece or Drawn, Tin-free steel)

- Aluminum

- Stainless steel

5.3.2) Glass

- Uncoated glass

- Plastic coated glass

5.3.3) Plastics

5.3.1) Metals:

Tinplated steel:

It is used for most aerosols as it is light inexpensive and durable. It is steel that has been plated on both side with tin.

Tin plated steel containers are of two types-

(a) Two pieces container body, consisting of a drawn cylinder, the base of the container, is held in place with double seam.

(b) The three piece container has aside seam the base being attached as for two piece container, the top has a 1 inch opening and is joined to body by double seaming to protect container from corrosion and also to prevent the interaction between the tin and the formulation. Oleoresin, phenolic, vinyl, or epoxy coatings are used as the coating materials. The tin plated steel containers are used in topical aerosols.


  • The aerosol cylinders are seamed and soldered to provide a sealed unit.
  • Special protective coatings are applied within the container to prevent corrosion and interaction between the container and formulation if necessary.


  • The main disadvantage of stainless steel containers is high cost.
  • For small sized container only.
  • Leak of container due to flaws in the seam or welding.
  • Corrosion with some preparations.


The aluminium containers are light weight and are less prone to corrosion than other metals. Aluminium is used in most metered dose inhalers (MDIs) and many topical aerosols. Epoxy, vinyl, or phenolic resins coatings are done on aluminium containers to reduce the interaction between the aluminium and the formulation. The seamless aerosol containers manufactured by an impact extrusion process have no leakage, incompatibility and corrosion.

The container themselves available in different sizes ranging from 10 ml to over 1,000 ml.


  • These are manufactured by extrusion or by any other methods that make them seamless.
  • Against leakage the seam type of container is of greater safety.
  • No incompatibility and corrosion.


  • High cost.

Stainless steel:


  • It is resistant to corrosion.
  • No coating is required.
  • It can withstand high pressure.


  • Expensive.
  • Which restricts its sizes to small sized containers.

5.3.2) Glass:

One of the materials is glass, limited usage because of its brittleness. So glass containers are used in lower pressure and when low amount of propellant are in use such as if the pressure is less than 25psig and propellant content is less than 15%. In order to protect the glass containers against breakage due to high pressure, it is to be coated with plastic coating in two layers. Epoxy and vinyl resins can be used as linings. Vinyl resins are not resistant to high temperature of the steam about 200 0F. But epoxy resins are resistant to steam. These coatings are suitable for low pH water based products. Used for some topical and MDI aerosols.


  • Glass has less chemical compatibility than metal containers.
  • No corrosion.
  • Glass can be molded to different design.
  • Glass containers preferred for aerosols.


  • Glass containers must be precise to provide the maximum in pressure safety and impact resistance.
  • More chances for accidental breakage.
  • Not suitable for photosensitive preparations.

5.3.3) Plastic:

Plastics are more permeable to vapours and atmospheric air (like oxygen), so it may interact with the formulation and also may lead to oxidative degradation of the formulation.

Polyethylene tetra phthalate (PET) container as used for some non pharmaceutical products.


  • Cheap.
  • Malleable and ductile.
  • Easy to mold.


  • Incompatibility between drug- plastic and may lose its efficiency and potency.

Summary for Pressure Limitations for Aerosol Containers 1,15

Container Material

Max. Pressure (psig)

Temperature (0F)

Tin plated steel






Stainless steel



Un Coated glass



Coated glass






5.2) Actuators:

  • It ensures that aerosol product is delivered in the proper and desired form.
  • It allows easy opening and closing the valve.
  • The actuator or adaptor which is fitted to the aerosol valve stem is a device which on depression or any other required movement opens the valve and directs the spray to the desired area.
  • The design of the actuator which incorporates an orifice of varying size and shape and expansion chamber is very important in influencing the physical characteristics of the foam or spray. Particularly in the case of inhalation aerosols, the active ingredient/s must emit with proper range of particle size.
  • A proportion of the active ingredient/s is usually deposited on the inner surface of the actuator and the amount available is less than the amount released by actuation of the valve.
  • Following types of actuators available.

Types of Actuators

a) Spray actuators: These are having capable of dispersing the stream of product concentrate and propellant into relatively small particles by allowing the stream to pass through various openings 0.016 to 0.040 inches. It breaks stream into fine particles.

These actuators used for topical use such as spray-on bandages, antiseptics, local anesthetics and foot preparations.

b) Foam actuators: It consists of relatively large orifices ranges from 0.070 to 0.125 inches.

c) Solid steam actuators: Similar to foam type of actuators. Used for semisolid products like ointments.

d) Special/ Mist actuators: These are designed for special purpose, to deliver the contents of medicaments at site of action like throat, eye or vaginal tract.

Types of Actuators 1

5.1) Valve and Valve Assembly: 1

Valves deliver the drug in desired form and regulate the flow of product concentrate from the container. The valve should be able to withstand the pressure encountered by product concentrate and the container, should be corrosion resistant.. They also provide proper amount of medication. Dispersing of potent medication at proper dispersion/ spray approximately 50 to 150 mg +-10 % of liquid materials at one time use of same valve.

There are two types of valves are available a) Continuous spray valve and b) Metering valve.

a) Continuous spray valves: To deliver the contents in spray or foam or solid stream continuously with or without measuring and for continuously. These types of valves are used for all types of pharmaceutical aerosols.

b) Metering valves: For potent medication and exact amount of medicament will be dispensed at one time application. Approximately 50 to 150 mg +- 10% at one time application.

Valve Assembly

Valve Assembly 11

Valve Assembly and its components: 1, 3


Valve stem


Valve Spring

Ferrule/Mounting cup/Valve cup

Valve Body/ Housing

Dip tube

Valve Assembly components


It ensures that aerosol product is delivered in the proper and desired form. It allows easy opening and closing the valve. The actuator or adaptor which is fitted to the aerosol valve stem is a device which on depression or any other required movement opens the valve and emits the spray to the applied area. The design of the actuator which incorporates an orifice of varying size and shape and expansion chamber is very important which influences the physical characteristics of the foam or spray, particularly in the case of inhalation aerosols, where the active ingredient/s must emit in the proper particle size range. Some proportion of the active ingredient/s is usually deposited on the inner surface of the actuator, the amount available which released by actuation of the valve.

Stem: The actuator is supported by the stem and the formulation is delivered in the proper form to the chamber of the actuator by the stem. It is made up of Nylon, Delrin, Brass and Stainless steel.

Gasket: The stem and valve are placed tightly in their place by the gasket and the leakage of the formulation is prevented by gasket. It is made up of Buna N and Neoprene rubber.

Spring: The gasket of aerosol container is held in its place by the spring and also helps to keep the valve in closed position when the pressure is released upon actuation of the formulation.

Mounting Cup or Ferrule: The Mounting cup or Ferrule is generally made up of aluminum which serves to place the valve in its position and then attached to the aerosol container. So the underside of the mounting cup/ Ferrule is exposed to the contents of the container. So it is to be compatible with the contents to prevent interaction/s. It may be coated with an inert material such as vinyl coating as it prevents any interaction with the contents also corrosion of aluminum is prevented.

Housing or Valve body: The Housing or Valve body located directly below the Mounting cup or Ferrule is made up of Nylon or Delrin work, which uses to connect dip tube, stem and actuator of aerosol container.

The size of orifice will determine the rate of delivery of product and the desired form in which the product is to be emitted. (Size is 0.013 to 0.080 inches)

Dip Tube: The dip tube is made up of polyethylene or polypropylene extends from the housing body or valve body down into the product concentrate works to bring the formulation from the container to the valve. The inner diameter of the dip tube depends on the viscosity and the desired rate of delivery of the product. The inner diameter of the dip tube increases with an increase in the viscosity of the formulation. For less viscous solutions the inner diameter ranges from 0.12 inch to 0.125 inch. For viscous solutions the inner diameter is 0.195 inch.

Generally the actuator, stem, housing and dip tube are made up of plastic. The mounting cup and spring made up of metal. The gasket made up of rubber or plastic resistant to the formulation.

About the Author

Naseeb Basha Shaik's picture

Working as Assistant Professor, Pharmaceutics Department at G.Pulla Reddy College of Pharmacy, Mehdipatnam, Hyderabad.

You May Also Like..