Technical Concept – Aerosols: Principle, Techniques and Application
Aerosol is filled in a can which contain propellant and specific solvent under pressure. The mixture is enforced out from container through a small opening present at the top which is under higher pressure, when the container’s valve is opened. As a result of higher pressure inside the can and sudden pressure release, a aerosol mist is formed.
Road Of Evolution Of Aerosols
1790 : Self- Pressurized carbonated beverage introduced in france
1943 : Department Of Agriculture researchers Goodhue & Sullivan develop a small aerosol can pressurized by a liquefied gas in USA
1949 : The first one inch aerosol valve is introduced.
1953 : Aerosol industry quickly developed in United States and around the world
Components Of Aerosols:
An aerosol canister is actually a complex piece of machinery that helps deliver a steady, concentrated stream of whatever product that is filled inside the tin which is encompassed of following components ;
• Product concentrate
• Aerosol container
• Valve and actuator
Types of Propellants:
- Liquefied gas propellants
2. Compressed gas propellant
When liquefied gas is used as propellant, under pressure propellant exist in liquid and at head space, it exist as gas. When valve of container is opened, some of the liquid propellant turns to gas but pressure remains unchanged as time passes. Liquid propellant helps in blending the dissolvable solvent with it completely. For example LPG, CFC etc
1. Liquefied Petroleum Gas:
Features of LPG:
• LPG has fundamentally bring down cost when contrasted with different fuels, for example, Dimethylether (DME) and Chlorofluorocarbons etc.
• LPG is a steady and pure propellant compound.
• LPG is an odourless, non-corrosive and non-toxic gas.
• LPG offers an extensive variety of appropriate vapor pressure and boiling points. The impediment of Hydrocarbon propellants are flammability and explosive. So the use is lessened propellant.
Chloro Fluro Carbon:
2. Compressed gas propellant:
Compacted gas fuels occupy the head space over the fluid in the tin. When the aerosol valve is opened the gas drives the fluid out of the can. In the head space the amount of gas stays constant which on usage pressure decreases because most of the gas escapes the can. For example Carbon dioxide, Nitrous oxide and Nitrogen.
Carbon dioxide: It has high vapor pressure which is less toxic compared to hydrocarbon propellants. Since because of low cost, it is mostly used in most of aerosol sprays which is normally used in a concentration of 2-4%. While preparation of Carbon dioxide propellant, often Co2 from air is used by fractional distillation and it does not add extra carbon dioxide to atmosphere. Because of their low expansion ratio, the sprays are rather wet and the froths are not as steady as created by liquefied gas propellants.
Nitrogen: An ideal propellant which helps in keeping up flow of the most viscous fluid through any container. It also eliminates oxygen and carbon dioxide from container completely reducing the possibility of fire catch or acid formation in case of flammable solvents. Since it is of very high cost and is high pressure with low solvency in numerous solvents, it is normally not used in aerosol spray.
Nitrous Oxide: At room temperature, Laughing gas is a colorless non-flammable gas, which is mainly approved to use for food grade product and it is highly soluble in most of the solvents. When pressure inside the canister is released, the liquid nitrous instantly turns to gas, expanding the volume to 4 times than that of the solvents.
Types of Container:
1. Unlined Metal Containers
It is mainly used for solvent based aerosol and used for water based concentrates which contain corrosion inhibitor.
2. Double Lined Metal containers:
This can be used for Water Based Aerosols where added corrosion protection is required. Interior coatings are made up of – phenolic resin, urethane, or epoxy which are normally applied before container fabrication.
3. Lined Metal containers:
This can be used mainly for a water-based application. Solvents will usually dissolve lining in them. If water-based formulation contains more than 19% of Dimethyl Ether then use Unlined Can with good corrosion inhibitor package. Dimethyl Ether at this level will penetrate the can lining allowing attack of tin plate. Some of the two-piece containers only come lined, therefore stability must run for the solvent blends.
The product concentrate is the active drug combined with additional ingredients or co-solvents essential to formulate a steady and effective product. The concentrate can be a solution, suspension, emulsion, semisolid, or powder. For aerosols, it is important to completely study the kind of concentrate or formulation, choice of the propellant gas, concentrate/gas proportion and managing the gas pressure in agreement with the discharged state, method for utilize and utility of their contents.
• Solvent Based (Water in Oil, Dispersions): – Unlined containers are normally used because most solvents will dissolve the interior coating of the can. – If you have a moisture content of greater than 0.1% present in the concentrate, a corrosion inhibitor will most likely be necessary. In certain situations, even a moisture content less than 0.1% could cause interior can corrosion. – Propellants used in solvent formulas are Hydrocarbons, Hydrocarbon blends, Hydrofluorocarbons. – Solvent Formulas will normally require a higher level of the liquified gas propellant. Propellant levels as high as 1/3 of the Net Content of the product may be necessary to completely discharge the can. It is normal for the DME, Hydrofluorocarbon and Hydrocarbon propellants to act as solvents in these formulas. – Carbon Dioxide levels in solvent formulas will run between 2 to 7% and Nitrogen will run about 0.5 to 2%. – The saturation level of Carbon Dioxide in the concentrate is greater than that of Nitrogen.
Valve and Actuator:
Components of Valve:
Operating Principle Of Valve
Pressure on the actuator depresses the stem. This movement interrupts the sealing action of the gasket and exposes the stem orifice to the pressurized flow of the product in the container, thereby opening the valve. When the actuator is released, the spring returns the stem orifice to the sealed position, closing the valve.
Actuators: Actuators and spouts form the outlets through which the aerosol contents are discharged.
• Mechanical Break Up: Incorporates a swirl chamber results in discernible pattern & shape.
• Non Mechanical Break Up: Direct flow through the actuator usually results in a stream.
Characteristics Of Aerosols:
The pressure of the propellant discharges the contents. If the contents are a solubilized system containing 40-70% liquefied gas, they are sprayed out as a mist, but if they are an emulsion system containing 5-15% liquefied gas, the contents are discharged as a foam.
• Extension tube which is attached to actuator make product flow easier and helps in reaching difficult crevices.
• The bottom part of container is not flat which helps in controlling increased pressure inside the canister.
• To empty out the liquid inside the can completely, the dip tube it aligned with the colour marking on valve plate.
Advantages & Disadvantages Of Aerosols:
• Long Lasting
• Particle size/pattern control
• Continuous spray
• Easy to Use/Immediate Use
• Controlled Application
Applications Of Aerosols:
• Automobile ( Starter Motors, Drive Chains, Car locks, Spark plugs, Door Hinges, Push back and tilting systems)
• Industrial (Overhauling machinery, crane hook bearings and wheels, Lubricates and opens jammed bearings, Loosens jammed nuts and bolts, Power tools, Jigs & fixtures).
• Ordnance ( Guns, Precision fitting, Linkages )
• Electrical Equipment (Alternators, Motors, Relays, Circuit Breakers, Fuses, Potentiometer Relays, Switch gears etc.)
• Pneumatic Systems (Sticky solenoid valves, Clogged needle valves, Automatic valves & cylinders)
• Household (Drawers, Hinges, Pins, Sliding Contact at Windows, Sewing Machines, etc.)
• Domestic (Mixers and Grinders, Hand Tools, Washing Machines, Collapsible Grills, Folding Chairs and Tables, TV, Radio and Tape recorder tuners etc.)
• General Purpose (Sliding Windows and door channels, Locks, Switches, Bicycle chains and sprockets, rolling shutters, elevator doors etc.)
Steps Towards The New Frontiers Of Aerosols:
• Special aerosol containers: Special aerosol containers comprise different types of compartment can using either an inner bag or piston system.
• Inner bag system: This type of compartment can has a soft inner bag (made from PE or soft aluminum) which is filled with the aerosol contents while the outer part of the container is filled with the gas. The pressure of the gas squeezes the inner bag causing the aerosol contents to be discharged.
• Piston system: In this type, there is a piston inside the container. The part of the container above the piston is filled with the aerosol contents and that below it with gas, the pressure of which pushes up the piston valve discharging the contents from the container.