Flammability ratings

For physical, thermal, electrical, and mechanical properties, ASTM test methods are employed (28). Flammability ratings are often based on Underwriters Laboratories (UL) standards (29). UL flammabiUty ratings given ia this article are aot iateaded to reflect the hazards preseated by the resias uader use coaditioas. Typical properties are givea ia Table 3. More details and additional properties are given ia Refereaces 5 and 31—33. 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

The UL flammability ratings describe the relative ease of ignition and combustibiUty of plastics. Tests include the measurement of flame propagation, time to self-extinguish, melt and drip with and without flame, and oxygen indexes. Some engineering plastics, eg, polyetherimides, are, as ranked by this test, inherently nonflammable. Others can be made nonflammable by compounding with flame retardants (ERs) such as bromine... 

Process lines 3 in (7.62 cm) and larger, containing material with a health or reactivity rating of two, three, or four, or a flammability rating of three or four. Lines containing materials with lower ratings can also be marked if desired. 

Greater attention is usually paid to the results of a vertical test, in which the sample is clamped at the top end and a bunsen flame of height 19 mm is applied to the lower end at a point 9.5 mm above the top of the bunsen burner (i.e. halfway along the flame). The material is classified as V-2, V-1 or V-0 in increasing order of flammability rating by reference to the conditions given in Table 5.14. 

Some UL94 flammability ratings are given by way of example in Table 5.15. 

Table 5.15 Some collected UL94 flammability ratings...

Good dimensional stability, partially as a consequence of the low water absorption but also because of a low coefficient of thermal expansion. Capability of compounding to give UL94 V-0 flammability ratings. 

The hexahydrate is used in the preparation of deodorant and antiperspi-rant. Also, it is apphed in textile finishing to improve the antistatic characteristics and flammability ratings of various textile materials. Commercially, it is sold as crystalline powder or as a 28% solution in water. 

Numerous housings, electrical enclosures, and cabinets are injection-molded from rigid PVC. These take advantage of PVC s outstanding UL flammability ratings and easy molding into thin-walled parts. 

It has been shown that the required loading levels of metal hydroxides to flame retard polyolefins can be reduced by the addition of transition metal oxides as synergistic agents. For example, a combination of 47.6% MH modified with nickel oxide in PP gave a UL94 V-0 flammability rating, which would require -55% of unmodified MH.4 These systems, however, can only be used where the color of the product is not important. 

The addition of very small amounts of fine carbon fibers73 or polyacrylonitrile fibers74 can reduce the level of inorganic hydroxide required to achieve UL94 V-0 flammability ratings in polyolefin compounds. These secondary additives are thought to function as char promoters. 

Injection-Molded Products. Numerous housings, electrical enclosures, and cabinets are injection-molded from rigid PVC. These take advantage of PVC s outstanding UL flammability ratings and easy molding into thin-walled parts. PVC has developed melt flow capabilities to the point where it competes with essentially any other flame-retarded engineering thermoplastic and molds easier than most. 

Flammability and gas emission V-0 flammability rating down to 1.45 mm without the use of additives. 

The outstanding characteristics of this material are its UL 94 V-0 and 5V flammability rating, heat-deflection temperature of 420 F (216 C) at 66 psi (0.45 MPa), high flexural strength and modulus, and excellent chemical and solvent resistance. PBT resins are especially suitable for applications requiring a combination of high heat endurance, sti ess, chemical resistance, and moderate creep (7) (9). 

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