Investigation Of Effects Of Two Flame Retardants On The Fire Characterisit Ics Of Flexible Poly Ether Foam

2.7.7.1    Morphology of the polyurethane foam
The physical properties of flexible polyurethane foam are a function of both, the cellular structure, and the phase separated morphology of the polymer comprising the struts of the foam [57]. These two factors are intimately related because both are influenced by the forces exerted during the expansion and stabilization of the foam. There has been considerable effort to try and understand how these two factors influence the physical properties of the foam such as load bearing, compressive stress -relaxation, creep, and how those properties are a function o f varied temperature and humidity conditions [57]. While testing polyurethane foams, workers have often found it difficult to separate the effects of cellular structure and the solid state polymer morphology on the foam properties. For this reason, some in vestigators have worked on flexible polyurethane foam formulations with an attempt to deconvolute the effect of polymer morphology on foam properties .
2.7.7.2    Cellular Structure    of the polyurethane foam
The cell structure is the presence or absence of win dows in the cell or the number of windows per cell. As stated earlier, the properties of flexible polyurethane foams are strong function of its cellular structure. A complete knowledge of the cellular structure of a foam would require the exact size, shape and location of each cell [7 8]. Since obtaining this information is difficult, and impractical, certain approximations are employed. Mean cell diameters and average cell volumes are often used to characterize cell size, since a distribution in cell size i s always noted. Earlier researchers described the shape of foam cells similar to that of a pentagonal dodecahedron, which has twelve five -sided faces. However some four -and six-sided faces is also observed in real polyurethane foams, and thus the cell geometry might be better approximated using the fourteen - faced tetrakaidecahedron space filling model [57]. Another variable of importance for flexible foams is the degree of cell openness. This is usually characterized using air -flow measurements [71].
2.7.7.3    Applications of polyurethane [7 9]
Polyurethane foam is one of the most versatile materials eve created, and is applied in several areas of needs. These include our homes, vehicles, schools and business.
Polyurethane products have many uses, over three q uarters of the global consumption of polyurethane products in the form of foams, with flexible and rigid types being roughly equal in market size. In both  cases the foam is usually behind other materials; flexible foams are behind upholstery, fabrics in co mmercial and domestic furniture, rigid foams are inside the metal and plastic walls of most refrigerators and freezers, or behind paper, metals and other surface materials in the case of thermal insulation panels in the construction sector. Its use in garm ents, is growing, for example, in lining the cups of brassier s. Polyurethane is also used for moulding which includes door frames, columns, balusters, windows headers, pediments, medallions and rosettes.
The precursors of expanding polyurethane foam are available in many forms, for use in installation, sound deadening, floatation, industrial coatings, packing material and even cast – in – place upholstery padding. Since they adhere the most surfaces and automatically fill voids, they have become quite popular in these applications. The uses of polyurethane foams are show n in Table 2: