Testing of Foam Plastics

RIGID FOAM TEST METHODS 14.2.1. Density (ASTM D 1622, ISO 845) 

The density of foam plastics is of considerable interest to parts designers since many important physical properties are related to foam density. The procedure to determine the density of cellular plastics is very simple. Basically, it requires conditioning a specimen of a shape whose volume can easily be calculated. The speci- 

Handbook of Plastics Testing and Failure Analysis, Third Edition, by Vishu Shah Copyright 2007 by John Wiley Sons, Inc. 

The test is primarily intended for determination of apparent overall density and apparent core density of rigid cellular plastics. Apparent overall density is defined as the weight in air per unit volume of a sample, including all forming skins. Apparent core density is defined as the weight in air per unit volume of a sample, after all forming skin has been removed. 

Cell size and cell orientation are very important since several physical properties of rigid cellular plastics depend upon them. For example, determining the water absorption and open-cell content requires knowledge of surface cell volume, which uses cell size values in the calculations. 

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A general rule is that the compressive strength of plastics is greater than its tensile strength. However, this is not generally true for reinforced TSs. The compression testing of foamed plastics provides the designer with the useful recovery rate (see Fig. 3-19). 

According to an ASTM test [10], foamed plastics are classified as rigid or flexible. A flexible foam is one that does not rupture when a 20 x 2.5 x 2.5 cm piece is wrapped around a 2.5 cm mandrel at a uniform rate of 1 lap per 5 s, at 15-25 °C. Rigid foams rupture under this test. This classification is used here. 

ASTM E 84 Steiner Tunnel Test. This test, which uses very large samples (20 ft x 20 1/4 in.) is referenced in all model building codes for evaluating flame spread and smoke emission of foam plastic insulation. The test apparatus consists of a chamber or tunnel 25 ft. long and 17 3/4 X 17 5/8 in. in cross section, one end of which contains two gas burners. The test specimen is exposed to the gas flame for ten minutes, while the maximum extent of the flame spread and the temperature down the tunnel are observed through windows. Smoke evolution can also be measured by use of a photoelectric cell. The flame spread and smoke evolution are reported in an arbitrary scale for which asbestos and red oak have values of 0 and 100, respectively. More highly fire-retardant materials have ratings of 0-25 by this method. 

In 1974, the Federal Trade Commission brought it forcibly to the attention of 26 manufacturers of foamed plastics, raw material suppliers, and The Society of the Plastics Industry that, among other things, the tunnel test did not correctly evaluate the actual fire hazards of these materials. The building codes responded accordingly, and the first code language... 

Since the mechanical properties of foamed plastics are functions of their densities, however, and since test specimens cut from the same large sample will show variations in density, comparison of the properties of different specimens can only be made after accounting for this variation. Manufacturers literature gives mechanical properties of different types of plastic foams either as an exponential function or as... 

The effect of the outdoor environment on foam plastics is not clearly known owing to a lack of data from either the material suppliers or the end users. In general, the resistance of foamed plastics to the outdoor environment is usually similar to that of the base polymer. The test methods described in Chapter 5 are applicable to foam plastics. 

Because of their superior insulating properties, foam plastics have found numerous applications in the construction and packaging industries. Along with increased use, a considerable amount of concern has been expressed in regard to the flammability of foam plastics. A detailed discussion of various tests used in the industry to determine the flammability of cellular and noncellular plastics and their limitations is included in Chapter 8. 

Flammability. The results of small-scale laboratory tests of plastic foams have been recognized as not predictive of their tme behavior in other fire situations (205). Work aimed at developing tests to evaluate the performance of plastic foams in actual fire situations continues. All plastic foams are combustible, some burning more readily than others when exposed to fire. Some additives (131,135), when added in small quantities to the polymer, markedly improve the behavior of the foam in the presence of small fire sources. Plastic foams must be used properly following the manufacturers recommendations and any appHcable regulations. 

Quahty control testing of siUcones utilizes a combination of physical and chemical measurements to ensure satisfactory product performance and processibihty. Eor example, in addition to the usual physical properties of cured elastomers, the plasticity of heat-cured mbber and the extmsion rate of TVR elastomers under standard conditions are important to the customer. Where the siUcone appHcation involves surface activity, a use test is frequently the only rehable indicator of performance. Eor example, the performance of an antifoaming agent can be tested by measuring the foam reduction when the sihcone emulsion is added to an agitated standard detergent solution. The product data sheets and technical bulletins from commercial siUcone producers can be consulted for more information. 

The extent of bleeding in a plastic is evaluated with a test known as the sandwich method. The test sample is placed between a white, smooth surface of plasticized PVC on the top and a standardized sheet of filter paper underneath. The resulting sandwich is then placed between layers of foam material, which in turn are covered by glass plates. The resulting sandwich is allowed to remain in an exposure chamber at 50°C for 72 hours [48]. 

Creep - [PLASTIC TESTING] (Vol 19) -of plastic foams [FOAMED PLASTICS] (Vol 11) -in tire cord [TIRE CORD] (Vol 24)... 

In some cases, it is not possible to evaluate a material or product (combination of materials) in a bench-scale test in a manner that is representative of its end-use. For example, it is difficult to use a bench-scale test method to evaluate the effect of joints on the fire performance of a thick sandwich panel that consists of a plastic foam core and metal skins. In this case, a room test is used to assess the reaction to fire of the materials. It is also very difficult to assess the fire performance of complex objects such as upholstered furniture based on the reaction-to-hre characteristics of the object s components. Large-scale reaction-to-hre tests have been developed to evaluate these complex objects. 

In terms of fire safety, there are no fire resistance requirements and all interior surfaces must comply with the FSI of 200 in the Steiner tunnel test, ASTM E 84,114 or a radiant panel index of 200 in the radiant panel test, ASTM E 162.55 Thermal insulation materials, other than foam plastics, must meet an ASTM E 84 Class A requirement (i.e., FSI < 25 and SDI < 450) and loose-fill insulation must meet the same requirements as the building codes, which are mostly based on smoldering tests (as the materials tend to be cellulosic). Foam plastic insulation must be treated as in the building codes as well (see Table 21.13) it cannot be used exposed (expensive foam that meets the NFPA 286 test is not used in manufactured housing) and must meet an ASTM E 84 Class B requirement behind the thermal barrier. 

NFPA 274 Standard Test Method to Evaluate Fire Performance Characteristics of Pipe Insulation NFPA 275 Standard Method of Fire Tests for the Evaluation of Thermal Barriers Used Over Foam Plastic Insulation... 

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