Page 363 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

PLASTICS ADDITIVES 5.43

research and development. Real fires occur under such a variety of conditions that they are
very difficult to correlate with laboratory data. And legal problems have arisen from lay-
men’s misunderstanding of technical terminology, greatly limiting our ability to record
and communicate test data.
Laboratory testing has gone through a series of fads: burning/nonburning, rate of burn-
ing, oxygen index, radiant panel, char formation, smoke generation, toxicity of combus-
tion gases, calorimetry, and thermal degradation. Practical testing has been governed by
Underwriters Laboratory pass/fail, building industry tunnel tests, insurance company
room-corner tests, and review of actual fires.

5.7.2 Flammability of Plastics
For simple laboratory evaluation, oxygen index is the percentage of oxygen in air that is
just sufficient to support burning (see Table 5.32).

TABLE 5.32 Oxygen Index of Common Polymers

Oxygen Oxygen
Polymer index, % Polymer index, %
Polyoxymethylene 15 Nylon 22
Polyethylene 17 (Wood 24)
Polypropylene l7 Polyphenylene ether 26
Polymethyl methacrylate 17 Polycarbonate 26
Cellulose acetate 17 Polysulfone 30
Polystyrene 18 Silicone 30
ABS 18 Polyvinylidene fluoride 44
Phenol-formaldehyde 18 Polyvinyl chloride 45
Epoxy 18 Polyvinylidene chloride 60
Polyesters 20 Polytetrafluoroethylene 95

Normal air is 21 percent oxygen. Polymers with an oxygen index below 21 will burn.
Polymers above 21 can be burned in a strong flame but may self-extinguish if left alone.
Thus, it is possible to choose a polymer to meet most flame-retardant requirements.
However, in terms of other properties, especially economics, it is more common to use ad-
ditives to increase the flame retardance of the commonly used polymer.

5.7.3 Flame Retardants
There are certain ingredients that definitely increase flame retardance: organic phospho-
rus, organic bromine, organic chlorine, antimony oxide as synergist for the halogens, and
water of hydration.

5.7.3.1 Organic Phosphorus. This is the most flame-retardant element in the periodic
table. It is generally used as phosphate ester plasticizers or built into polyols for polyesters

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