There are many kinds of ammonium orthophosphate, they are used as chemical fertilizers, food additives, flame retardants and dye leveling agents.
2.6.1 Mechanism of Reac tion of Tri ammonium Orthophosphate as a flame retardant
When plastics or other materials which contain tri ammonium orthophosphate are exposed to accidental fire or heat, the flame retardant starts to decompose into phosphoric acid and ammonia following t his reaction [47,48]:
(NH4)3 PO4 . 3H2O (HPO3)n + 3NH3 + 3H2O
Phospheric acid
(HPO3)n + Polymer
Char
+ H3PO4
A carbon foam is built up on the surface against the heat source (charring). The carbon barrier acts as an insulation layer preventing further decomposition of the material.
(NH4)3 PO4 . 3H2O 3NH3 + H3PO4 + 3H2O
Ammonia and water vapour acts as diluents in the vapour phase.
2.7 Polyurethane foam
Polyurethane is one of the foam polymers that have gained overwhelming importance in the foam industries and in the synthetic polymer technology. Other foam products include polyethylene (PE), polyvinylchloride (PVC), polypropylene and styrene buta rubber ( S BR) and polystyrene and so on.
As synthetic plastic they h ave two desirable properties, easily malleable or shapeable and capable of stretching and returning to its original shape, those contribute to their vitality in the society [51].
Today a number of foam materials are known and are all around us in our daily lives, in our homes, vehicles, schools and businesses. It is the cushioning materials of choice in nearly all upholstered furniture and mattresses. These foam materials are also use in car and truck seats, beddings, roof liners and sound proofing [52].
In medical setting foam provides adaptable support as needed. As packaging materials, it protects delicate objects and helps in the flow of ink in our printer cartridges. Foam can also be incorporated in wood and metals in the construction of buildings under water constructions, automobile bodies and electronic gadgets because of their inherent properties which includes corrosion resistance, resistance to water, resilience, toughness, high tensile strength and elongation, flex and moderate to high creep resistance and high temperature moulding characteristics. It can also be made into many different colours and shapes [53].
Polyurethane foam is one of the most versatile materials ever created. Its formulations cover a wide range of stiffness, hardness and den sities, which contributes to its numerous uses and applications. Low – density polyurethane foams with a density less than 0.1gcm 3 is used in upholstery, bedding and automotive and truck seating.
The medium density polyurethane foams have a density of 0.1gcm3 to 0.4gcm3 while high density polyurethane foams have a density higher than 0.4gcm 3 [54].
The market for polyurethane foam has witnessed innovations and improvements especially in attempts to lower the general costs and the obvious high flammability tendency, without detracting the desirable characteristics.
One major modification made in an effort to reduce the high flammability properties has been the incorporation of flame retardants in the production of polyurethane foams.
2.7.1 History of Polyuret hane Foams
Otto Bayer and his coworkers did the pioneer work on polyurethane polymers in 1937 at the laboratories of T.G Farbeir in Leverkusen, Germany [52]. They used polyaddition principles to produce polyurethane from liquid diisocyanates and liqu id polyether or polyester diols. The new monomer combination circumvented existing patents obtained by Wallace Carothers on polyesters. The initial work was focused on the production of fibres and flexible foams.
Owing to the constrains of the World War II, flex ible polyurethane was produced in commercial quantity in 1954, based on toluene and diisocyanate (TDI) and polyester polyols. The invention of these foams was possible because water was accidentally introduced in the reaction mix. These raw materials were also used to produce rigid foams, gum rubber and elastomers.
The first commercially available polyether polyol (poly – tetramethylene ether) glycol, was introduced by Dupont in 1956 by polymerizing tetrahydrofuran. The cheaper polyalkylene glycols were in troduced by BASE and Dow Chemical the following year, 1957 [52]. The polyether polyols offered technical and commercial advantages such as low cost, ease of handling, and better hydrolytic stability and quickly supplanted polyester polyols in the manufactu re of polyurethane goods. Other polyurethane pioneers were Union Carbide and the Mobay Corporation, a U.S Monsanto / Bayer J oint Venture [52].
In 1960, more than 45,000 tons of flexible polyurethane foams were produced. As time went on, the availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) made possible the development and use of polyurethane rigid foams as high performance insulation materials.
In 1967, urethane modified poly – isocyanurate rigid polyurethane foams were introduced, with better thermal stability and flammability resistance to low density insulation products.
In 1969, Bayer A.G exhibited an all plastic car in Dusseldorf, Germany. Parts of car were manufactured using a new process called RIM, Reaction Injection Molding. Rim technology uses high – pressure impingement of liquid components followed by the rapid flow of the reaction mixture into a mould cavity. Large parts, such as automotive fascia and body panels, can be moulded in this manner.
Polyurethane RIM leads to the production of other numerous products and processes. The use of diamin e chain extenders and trimerization technology gave poly(urethane isocyanurate ) and poly urea RIM. This technology allowed production of first plastic – body automobile in the United States, the Pontiac Fiero, in 19 83.
In early 1980s, water blown microcellular flexible foam was used to mould gaskets for panel and radial seal air fillers in the automotive industry. Since then, increasin g energy process and the desire to eliminate PVC plastisol from automotive applications have greatly icreased market share. Highly filled polyurethane elastomers and more recently unfilled polyurethane foams are used in high temperature oil filter applications.
Polyurethane foam (including foam rubber) is often made by adding small amounts of volatile materials ‘blowing agents’ to the reaction mixture. These simple volatile chemical s yield important performance characteristics, primarily thermal insulation. In early 1990s, the Montreal Protocol led to the reduction in the use of chlorine containing blowing agents such as trichlorofluromethane (CFC – 11), owing to their impact on ozone depletion. Other haloalkanes, such as the hydrochlorofluorocarbon 1,1 dic hloro – 1- fluoroethane (HCFC – 141b) were used as interim replacement until they were phased out under IPPC directive on green house gases in 1994 and by Volatile Organic Compounds (VOC) directives of the European Union (EU) in 1997.
By the late 1990s, th e use of blowing agents such as carbon dioxide, pentane, 1,1,1,2 – tetrafluoroethane and 1,1,1,3,3 – pentafluoropropane became more widespread in North America and Europe, although chlorinated agents remained in use in many developing countries [55].
In 1990s, the development continue s with building on the existing polyurethane spray coating technology and polyetheramine chemistry, and the production of two – component polyurea spray elastomers. Their fast reactivity and relative insensitivity to moisture make them useful coating for large surface area projects, such as secondary containment, manhole and tunnel coatings, and tank liners. Excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. It was in the same period that the new two-component polyurethane and hybrid polyurethane – polyurea elastomer technology was used in the spray -in-place load bed liners.
In 2004, the use of polyols derived from vegetable oils to make polyurethane products began. This was partl y due to the rising costs of petrochemical feedstocks and partially due to an enhanced public desire for environmentally friendly green products.
2.7.2 Definition of P olyurethane foams
Polyurethane is derived from a chemical reaction of a diisocyanate with a polyol. Once this reaction has occurred, a substance is created that is safe and extremely versatile. It
