Flame dripping

No test specimens bum longer than 10 seconds after each removal from the flame. No specimens exhibit flaming drip that ignites dry surgical cotton placed 12" below the test specimen. Nor does afterglow persist for longer than 30 seconds. 

Identical to V-1 except that the flaming drip from some specimens ignites the dry cotton placed below the specimens. 

One of the most stringent and most widely accepted test is UL 94 that concerns electrical devices. This test, which involves burning a specimen, is the one used for most flame-retardant plastics. In this test the best rating is UL 94 V-0, which identifies a flame with a duration of 0 to 5 s, an afterglow of 0 to 25 s, and the presence of no flaming drips to ignite a sample of dry, absorbent cotton located below the specimen. Tlie ratings go from V-0, V-l, V-2, and V-5 to HB, based on specific specimen thicknesses. 

Another aspect of the burning of PBT blends is dripping. When a thermoplastic part is burned, it will begin to melt as it bums. In some cases, the plastic resin will drip away from the sample. If these drips are burning, it can lead to a spread of the fire. The UL-94 test takes this into consideration and, depending on rating, requires little or no flaming drips. 

N6-25A 3% 52.6 7.2 190 5 — 19 Burnt slowly with small flame, dripping occurred... 

For a UL 94 V-l rating the individual bum times are less than 30 s and the total of all bum times is less than 250 s in addition, there should not be any flaming drips. For a UL 94 V-2 rating the same restrictions apply for bum times, but flaming drips are allowed. 

Flame drippings None None Allowed if burns briefly... 

UL94 V-0 Vertical burning stops within 10 seconds after two 10-second flame applications no flaming drips allowed Commonly required for unattended appliance applications... 

Tr 1 (flaming-dripping) if the filter paper catches fire by virtue of the flaming drops within 20 s after the ignition. 

V-0 Individual burn times less than 10 sec total burn time for all samples less than 50 sec no flaming drips that ignite cotton located below sample. 

Poly(tetrafluoroethylene) (FIFE) is used at a very low level (0.01 to 0.5 wt%) in combination with other flame retardants to suppress flaming drips. The flame retardant action of PTFE is not related to any chemical reaction of fluorine or halogen fluoride. During polymer processing at 200 to 300°C, PTFE particles soften, the shear force of extrusion elongates the particles up to 500%, and microfibrils are formed. Upon combustion the microfibrils shrink back when the polymer melts and a network that prevents dripping is formed. This flame retardant action of PTFE is a physical phenomenon. 

Cellulose acetate is an amorphous material with a specific gravity of 1.30. It burns very slowly with a yellow flame, drips, gives off an odor of vinegar, and has black smoke with soot. It is soluble in acetone, furfuryl alcohol, and acetic acid. Cellulose acetate is positively identified by infrared spectroscopy. 

Furthermore, the burning behaviour of the nanocomposites has been visually observed. It was found out that PCL nanocomposites exhibit remarkable flame retardant properties. Although unfilled PCL and PCL-based microcomposites (PCL filled with Cloisite Na ) continuously release burning droplets (flamed dripping) able to propagate the fire to surrounding materials when they are exposed to flame, PCL nanocomposites (obtained... 

Polythene melts and burns with a non-smoky flame, drips of melted material fall from the flame. The vapour smells waxy. 

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