Static decay

This section is based on descriptions of tests set out in the publication Principles of flame retardancy and test methods by Anzon Limited (Technical Memorandum 1 2 and ITRI Ltd (Technical Bulletin No 4)). 

Flame retardants take effect only during the early stages of a fire. Criteria are therefore  

Because of the difficulty of precise measurements, testing of flame retarded plastics in the past has used classifications such as self-extinguishing and nonburning , which can give misleading interpretations regarding actual fire performance. Some rationalization of test methods has been attempted by (for 

Specification Orientation of specimen Ignition source Time of Similar tests application of ignition source Comments 

ANSI/ASTM D635-77 Horizontal Bunsen burner 30 s BS2782 508A 1 For self-supporting plastics 2 Used in US Building Codes 3 Similar test used in UK Building Regulations  

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Statexan ITA Static control agents Static decay Static decay times Static dissipation Static drying Static electricity Static eliminating devices Static mixers Static phenomena... 

Fig. 2. Measuring static charge, (a) Field voltage measurement (b) Faraday cage (c) surface resistivity measurement and (d) static decay test.

The static decay test is a good measure of the static dissipative nature of an object. However, the test is controlled by the object s resistance to ground. Objects that have a high resistance, such as insulators, will not readily accept an induced charge or decay an induced charge. The static decay test is most suited for objects with resistances of 10 or less (52). 

Varying the fatty acid portion of the surfactant can have an effect on antistatic performance. In the example given in Table 5, ethoxylated coconut amine results in the shortest static decay time, whereas ethoxylated stearyl amine results in the longest static decay time (135). 

Table 5. Static Decay Times of Ethoxylated Fatty Amines in High Density Polyethylene...

Table 6. Effect of Ethoxylated Oleyl Amines on Static Decay in Polyolefins...

Pilling and Rice [39, 134] have shown that these static decay expressions (100) are applicable over times, tD... 

Calibration of FAGE1 from a static reactor (a Teflon film bag that collapses as sample is withdrawn) has been reported (78). In static decay, HO reacts with a tracer T that has a loss that can be measured by an independent technique T necessarily has no sinks other than HO reaction (see Table I) and no sources within the reactor. From equation 17, the instantaneous HO concentration is calculated from the instantaneous slope of a plot of ln[T] versus time. The presence of other reagents may be necessary to ensure sufficient HO however, the mechanisms by which HO is generated and lost are of no concern, because the loss of the tracer by reaction with whatever HO is present is what is observed. Turbulent transport must keep the reactor s contents well mixed so that the analytically measured HO concentration is representative of the volume-averaged HO concentration reflected by the tracer consumption. If the HO concentration is constant, the random error in [HO] calculated from the tracer decay slope can be obtained from the slope uncertainty of a least squares fit. Systematic error would arise from uncertainties in the rate constant for the T + HO reaction, but several tracers may be employed concurrently. In general, HO may be nonconstant in the reactor, so its concentration variation must be separated from noise associated with the [T] measurement, which must therefore be determined separately. 

Figure 4.18 shows the kinetics of the tunnelling luminescence growth after the step-like temperature increase observed for F, Vk centres in pure KBr crystal (for the static decay the kinetics is described well by the Becquerel s law with a 0.8). Unlike the case of rotation, Fig. 4.17, it is obviously delayed with the distinctive r which becomes shorter, as temperature is raised (for more details see [18, 51]). This delay arose directly due to the transient period resulting in the formation of the quasi-steady-state recombination profile. (The same behaviour has been observed for Ag°, centres in KCl-Ag). 

One single property of filler - electric conductivity - affects many properties of the final products. These properties include electric insulation, conductivity, superconductivity, EMI shielding, ESD protection, dirt pickup, static decay, antistatic properties, electrocatafysis, ionic conductivity, photoconductivity, electromechanical properties, thermo-electric conductivity, electric heating, paintability, biocompati-bilify, etc. Possession of one of these properties in a polymer can make it useful in industiy and eveiyday use. Examples are given in Chapter 19. Here, the electrical... 

Standard methods, electric resistance - ASTM D 257, shielding effectiveness -ASTM ES 7, BS 6667 (part 1 and 2), static decay - ASTM F 365, BS 2783 (part 2),... 

Static decay, s 0.01-10 State liquid or solid color clear to black... 

The compound s static decay time should also be reduced to less than a few seconds. These properties depend on the test specification and requirement called out (such as the military specification MIL-B-81705 or the National Fire Protection Association (NFPA) 99 specification) [1-1, 6-1, 6-2, 6-28]. 

Polymer Antistat Composition (Pius Form, and Supplier Designation) Tested Antistat Loading Level (and Typical Loading Range) Static Decay Time (Seconds) After Various / Ing Periods (Days) Surface Resistivity Exponent (lO ohms/ sq) After Various Aging Periods (Days) ... 

Speed Surface resistivity and static decay wilues require time after processing to reach optimum wilues while the additives migrate to the surface. In some cases, more than a few days may be required for major... 

Form An antistat in liquid form may provide more immediate and lower static decay and resistivity properties than the same chemical composition used in powder form, likely because of differences in migration rate or dispersion. PO film forms also matter for instance, winding a film into a roll using high tension delays the migration of the antistat to the film surface, compared with an unwound film. 

Effectiveness over time Static decay times may start to increase several weeks after processing as antistats become consumed, removed from the surface, or otherwise deactivated. (Overall effectiveness also depends on having enough moisture in the air with which to form a thin surface layer of water.)... 

Static decay rates of carbon or metal-filled versus metal-painted or neat polycarbonate are shown in Table 18.6. All the filled polycarbonates performed similarly, a charge of 5 kV decayed in less than 0.06 s compared to more than 100 s for neat PC [63]. Metal-filled composites may show ohmic behavior in the interior but appear nonohmic overall due to surface depletion of the conductive species [68]. 

TABLE 8.1 Static decay-times for electrostatic dissipation (ESD) of batch-mixed and twin-screw extruded composites, measured at 1% cutoff and 50% relative humidity. 

Yang et al. [245] have used TG for the study of the thermal weight loss of low-MW surfactants, used as antistatic agents in HDPE containers. In a typical example of product development Ward et al. [246] have reported the use of TG in combination with static decay and optical measurements for evaluation of the effectiveness of some 13 internal antistatics. With fail/pass criteria of a weight loss of 5% (up to 250°C) and a static decay time of less than 0.5 s at 70% r.h., none of the commercially available surfactants did meet all critical criteria developmental PMMA antistats were reported. 

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