|Plastics materials are used in large volumes in major applications such as buildings, vehicles and electronic appliances. In each of these areas fire safety is critical. Fire is a big menace. As per estimates from USA, there are approximately 400,000 residential fires each year, 20% involving electrical distribution and appliances; another 10% concerning upholstered furniture and mattresses. These fires kill about 4,000 people, injure another 20,000 people and result in property losses amounting to about US$4.5 bln. The use of flame retardant plastics can reduce deaths by 20%. Flame retardants can act in a variety of ways: by raising the ignition temperature, reducing the rate of burning, reducing flame spread and reducing smoke generation. Hence flame retardants have been developed to improve the properties of plastics under the different conditions of processing and use. Flame retardants are an important part of fire protection as they not only reduce the risk of a fire starting, but also the risk of the fire spreading. The increasing demands in the electrical and electronic sector for miniaturisation and faster injection moulding cycles exerts additional demand on flame retardant technology. The faster injection speeds require higher processing temperature stability and increased flow performance; while miniaturisation leads to increasing property performance for a given resin system as less material is used in each part. Flame retardants in commodity polymers are growing exceptionally well since the inherent flame retardant polymers are relatively more expensive. Environmental, health and technical concerns and regulations like REACH, RoHS, WEEE will change the market of flame retardants along with other additives used in polymers.
In all, over 175 different types of FRs exist, commonly divided into four major groups: inorganic FRs, organophosphorus FRs, nitrogen-containing FRs and halogenated organic FRs.
Inorganic FRs comprise metal hydroxides (e.g. aluminium hydroxide and magnesium hydroxide), ammonium polyphosphate, boron salts, inorganic antimony, tin, zinc and molybdenum compounds, as well as elemental red phosphorous. Inorganic FRs are added as fillers into the polymers and are considered immobile, in contrast to the organic additive FRs. Organophosphorous FRs are primarily phosphate esters that may also contain bromine or chlorine. Organophosphorous FRs are widely used both in polymers and textile cellulose fibers. Nitrogen-containing FRs inhibit the formation of flammable gases and are primarily used in polymers containing nitrogen, such as polyurethane and polyamide. The most important nitrogen-based FRs is melamine and melamine derivatives.
The main flame retardant systems currently in use are polymeric based brominated solutions which have a range of performance characteristics offering a choice of solutions depending on specific critical performance requirements. Brominated additives will continue to lead the flame retardant additive market in total value. Phosphorus-based flame retardants will grow at the fastest pace, driven by increasing trends towards non-halogenated products. Rapid gains are also expected in inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide which are finding more use in polyolefins. Halogen-free and phosphorous-free route is the most difficult, and also the most environment friendly, with a limited choice of FR additives.
The newer technologies being developed include flame retardants combining nanoclays with another major class of flame retardants based on metal hydroxides. The nanoclays synergistically improve how the metal hydroxide retardants perform, improve how the plastics are processed, as well as their material properties. Nanoclays are appealing to use because they can be added in relatively small amounts. Some nanomaterials, especially carbon nanofibers, appear to have promise for use in polyurethane foam.
Flame retardants can interfere, inhibit or even suppress the combustion process during a particular stage of the fire: heating, decomposition, ignition or flame spread. There are two types of action, chemical or physical. Generally chemical actions are more efficient than physical ones. The chemical actions can be:
• Reaction in the gas phase: The radical gas phase combustion process is interrupted by the flame retardant, resulting in cooling the system, reducing and eventually suppressing the flammable gas flux.
• Reaction in the solid phase: The flame retardant builds up a char layer protecting the polymer against oxygen and heat.
The physical actions can be:
• Cooling: Endothermic processes cool the polymer to a temperature inhibiting the fire.
• Formation of a solid or gaseous protective layer against heat and oxygen needed to sustain the combustion.
• Dilution effects: Inert fillers reduce the combustible carbon content, and additives releasing inert gases dilute the fuel in the solid and gaseous phases.
Organic and inorganic phosphorous compounds have a good fire safety performance and are fast developing to meet halogen free requirements. Nitrogen-containing flame retardants are of lower efficiency and are combined with phosphorous compounds to boost their efficiency. Inorganic compounds, particularly aluminum and magnesium hydroxides, must be used at high levels to compensate for their lower efficiency and meet high fire safety performances. HFFR polymers with increasing oxygen index values are Polysulfones, PEEK, Liquid crystal polymers (LCP), Melamines (MF), Polyamides (PI), Polyamide-imide (PAI), Polyetherimide (PEI), Polyphenylenesulfide (PPS), Polybenzimidazole (PBI).
US demand for flame retardants will rise 3.8% pa to 1 bln lbs in 2013, reflecting more stringent fire codes and flammability requirements, especially in building materials and consumer products, as per Freedonia. Additionally, an improved economic outlook in key applications, such as wire and cable insulation and jacketing, and motor vehicles, will fuel demand. Nonetheless, overall gains will be limited by cost sensitivity in price-competitive markets such as motor vehicles and textiles, as well as environmental and health concerns over several flame retardant chemicals. In value terms, flame retardant demand will advance nearly 4% pa to US$1.1 bln in 2013. This represents a deceleration from the 2003-2008 period, which was characterized by rapid price increases for flame retardants as a result of high raw material and energy costs. Phosphorus-based flame retardants will grow at the fastest pace, driven by increasing trends toward non-halogenated products. However, brominated compounds will continue to lead the market in total value, as the regulatory climate in the US is unlikely to undergo dramatic changes in the near future. Rapid gains are also expected for smaller-volume flame retardants, such as magnesium hydroxide, which is finding increased use in polypropylene and engineering resins. Alumina trihydrate (ATH) will remain the largest volume flame retardant through 2013, comprising 46% of demand and growing slightly faster than the overall market