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

CHAPTER FOUR
RESULTS AND DISCUSSION
4.1    After Glow Time (AGT)
•    The results of the after glow ti me produced with the two flame retardants are shown in Table 6, Fig. 3 below. The incorporation of these two flame retardants into the substrate substantially reduced AGT – as much as six – fold at 2.5pph melamine concentration. Glow is an exothermal oxida tive combustion of material without a flame and is known to depend on quantity of carbonaceous char available [47]. Thus, the higher the char, the longer the AGT values. In the Fig. 3 below, at all concentrations after glow is decreased with respect to untreated sample. The significance of this observation becomes clear if it is realized that in fire situation, what is most striking is the flame and that attracts fire combatants. There have been countless cases when after the flame have been dowsed and everybody gone home, and the fire starting all over later. This scenario is because; the usually not perceptible glow was not extinguished. Of cause , the longer the AGT time, the higher the risk of re - enlightenment of a fire. Obviously therefore, reduction of AGT is a very useful technique in fire chemistry.
•    As has been stated, AGT depends on char volume. It is seen in Fig. 3 that the phosphate enhances char formation more than mela mine. Thus it is hardly surprising therefore that the latter is a better AGT reductant. The mechanism by which flame retardants enlarge the formation of more char by burning material is somewhat complicated, but is summarized by statement that they dam up the egress of particulate pyrolysis product.

4.2    Ignition Time
The effects of the flame retardant on the ignition time of the polyurethane foam are in indicated in Table 7, Fig. 4. From the results of the ignition tests, it is evident that incorporation of these flame retardants dramatically increases the ignition time of the foam. The ignition time of the    untreated    sample    is    20sec        while        at    maximum concentration of the phosphate (2.5pph) it is 238sec, a ten- fold increase of the ignition            time of the foam. As the concentration of flame retardants increases, the ignition time of the foam samples also increases.    The impact of the increase in the concentration of the flame retardants    on ignition time was more in the foam samples retarded with tri ammonium    orthophosphate        than    that    retarded    with melamine.
The ignition time is a particularly important characteristic of any combustible or burnable material as its ignition is the onset    of    thermal degration        that        results    in    catastrophic combustion. Any material that has very short ignition time therefore “catches” fire very readily and longer ignition time, or reluctance to burning is favourable. Thus , it is interesting that susceptibility to resist combustion/ burning increases with the concentration of the flame retardant. It is clear that at all concentration, ammonium phosphate performs better than melamine. The reason for this is not easy to fathom. Tri ammonium    phosphate    (in    fact    phosphate        generally    are known to impart fire – resistance characteristics to materials such as timbers, fabrics and plastics [49,50] and owe their performance to the fact that at high temperature they yield some viscous phosphoric acids that prevent the issuance of hot oxidizeable pyrolysates that initiate and sustain combustion. Recently in literature melamine is being developed as a good flame retardant for polyurethane [42- 44]. It is a known fact that nitrogen – containing compounds feature a great deal in flame retardants chemistry becaus e they spit out nitrogen oxy – acids that suppress flame by a mechanism similar to the phosphates.