Most of the thermoplastics are flammable. The key elements in the process of fire are the availability of combustible material(fuel), oxygen and ignition source. Fire is a gas phase reaction wherein high-energy combustible free radicals are formed which combine with oxygen and the fuel to continue the fire cycle and can spread within minutes if plastics are not formulated to retard this process. For the fire to stop or get retarded, any or all these three elements have to be influenced and that is what different flame retardants do in plastics.
Plastics being used in diverse industries from textiles and furnishings to electrical and electronic switchgear and appliances, building, and construction for residential and commercial and office premises, mass transit systems – are required to be formulated such that in the event of a fire they either extinguish completely or retard the spread of heat, flame, smoke, toxic gases which gives enough escape time for people to safely evacuate from the vicinity of fire as well as minimize damage to the building and property.
Flame retardants are added to plastics to increase their resistance to ignition, reduce the spread of flame and prevent dripping which can cause fire to propagate further. They are based on different chemistries and react either chemically or physically with the process of fire to achieve these objectives. For example, brominated flame retardants along with synergists (such as Antimony Tri Oxide) trap the high energy gaseous free radicals to inhibit the fire cycle to propagate and spread, nitrogen and phosphorous based FRs quench such free radicals and dilute the fuel source (plastics) as well as form a carbonaceous char layer blocking non combusted plastic to add to fire, metal oxides cool down the plastics below their combustion temperature by the endothermic reaction.
A Flame Retardant masterbatch package recommendation is based on various factors, some of them are:
- The Polymer and thickness of the product
- Fire rating to be achieved eg UL 94 V0, V1, V2, VTM0, etc.
- Whether halogenated systems are permissible
- Whether outdoor weathering resistance is required
- Mechanical properties to be achieved
- Flame retardants are added to plastics to increase their resistance to ignition.
- It reduces the spread of flame and prevents dripping.
- For a fire to stop or get retarded, flame retardants used in plastics.