Fire Retardancy of Mineral Fillers in EVA Copolymers - ACS Publications

Chapter 7

Downloaded by NORTH CAROLINA STATE UNIV on December 20, 2012 | http://pubs.acs.org Publication Date (Web): December 18, 2012 | doi: 10.1021/bk-2012-1118.ch007

Fire Retardancy of Mineral Fillers in EVA Copolymers Artur Witkowski,*,1 Luke Hollingbery,1,2 and T. Richard Hull1 1Centre

for Fire and Hazards Science, University of Central Lancashire, Preston PR1 2HE, U.K. 2Minelco Ltd., Raynesway, Derby DE21 7BE, U.K. *E-mail: [email protected]

A simple numerical model quantifies the four contributions made by mineral fillers to fire retardancy. This model has been applied to samples of EVA filled with calcium carbonate (as a control), aluminium hydroxide, magnesium hydroxide, hydromagnesite, and naturally occurring mixtures of huntite and hydromagnesite in various ratios. The model shows good correlation between the magnitude of the endotherm and the ignition behavior, in both limiting oxygen index test and cone calorimeter. The heat release rate, measured by oxygen depletion, masks the contribution of the endotherm in the cone calorimeter. The intial peak derives from chain stripping EVA, releasing acetic acid in the molten polymer, which reacts with the hydroxides to form acetates, which are subsequently converted to acetone, and volatilized as fuel, but delayed, relative to the release of acetic acid by EVA.

Mineral Filler Fire Retardants Mineral fillers are an important class of fire retardants with many inherently sustainable attributes, including cleaner manufacture, reduction in polymer (hence hydrocarbon) use, no reported environmental hazards, and no adverse effect on the biggest causes of death and of injury in fire, smoke and toxicity (1). However, mineral fillers are more difficult to incorporate into a polymer and to achieve the required level of fire retardancy than halogenated flame retardants, so better © 2012 American Chemical Society In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


understanding of the details of their mode of action is required. Incorporation of any non-combustible filler will reduce the flammability of a polymer, by reducing the total amount of fuel, the rate of diffusion of oxygen into, and fuel from, the polymer bulk while increasing the heat capacity, thermal conductivity, reflectivity and emissivity. There may also be synergistic or antagonistic catalytic (2) or other surface effects associated with the filler, and effects on the polymer melt rheology (3). To date, a fairly simplistic view of their mode of action has been generally assumed. Mineral filler fire retardants (FRs) decompose endothermically, with the release of inert gases or vapour, resulting in a fire retardancy effect. In order to be effective, this decomposition must occur in a narrow window above the polymer processing temperature, but at, or below, its decomposition temperature. In practice most of the suitable materials are group II or III carbonates or hydroxides. Four effects can be considered to contribute to its fire retardancy. • • •

•

Heat capacity of the filler prior to decomposition. Endothermic decomposition, absorbing heat and therefore keeping the surrounding polymer cooler. Production of inert diluent gases absorbing heat from the flame. Flaming reactions require a critical concentration of free radicals to be self-sustaining. If this concentration falls sufficiently, through temperature reduction or dilution, for example by the release of water or carbon dioxide, flame extinction will occur. Accumulation of an inert layer of inorganic residue on the surface of the decomposing polymer. This will shield it from incoming radiation, and act as a barrier, to oxygen reaching the fuel, flammable pyrolysis products reaching the gas phase, and radiant heat reaching the polymer.

For example, the most widely used FR, aluminium hydroxide (Al(OH)3), (commonly referred to as alumina trihydrate (ATH) and incorrectly formulated as Al2O3.3H2O, even though it is neither an alumina, nor a hydrate (4)), decomposes to form alumina (Al2O3) with the release of water. Al(OH)3 breaks down endothermically forming water vapour, diluting the radicals in the flame, while the residual Al2O3 builds up to form a protective layer.

It is worth noting that the heat capacity of organic polymers (5) vary from 1.6 to 3.0 J K-1g-1, over the temperature range ambient to decomposition, thus the decomposition enthalpy of an FR mineral filler is around the same as that required to heat 2 g of polymer between 250 and 500 °C – the decomposition enthalpy of 1 g Al(OH)3 is equal to the heat (q) required to raise the temperature of a mass (m) of 1.2 g of polypropylene from ambient temperature to decomposition (424°C)(Δθ), assuming constant heat capacity (c) during heating, (q = m c Δθ, so q = 1.2 x 2.8 x 400 = 1.3 kJ). 98 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Production methods for both ATH and another mineral filler FR, magnesium hydroxide (MH) involve the use of minerals (bauxite or lime) followed by a chemical process, and in the case of ATH, the storage and disposal problems of a caustic red sludge by-product. As well as ATH and MH, naturally occurring mixtures of hydromagnesite (Mg5(CO3)4(OH)2.4H2O) and huntite (Mg3Ca(CO3)4) have similar potential as FRs, some of which are sold as UltraCarb®. Commercially exploited natural reserves of huntite and hydromagnesite mixtures, are already very pure and do not need chemical processing, or precipitation of the final product. This makes production of fine particle size mixtures of huntite and hydromagnesite much less energy intensive. The only by product is a small quantity of dolomite, MgCa(CO3)2, a mineral closely related to huntite, Mg3Ca(CO3)4, that occurs naturally in the mixture and is removed during the grinding process. Previous authors have discussed the decomposition of huntite and hydromagnesite (6–8). Natural hydromagnesite particles have a blocky morphology (7, 9) and once processed, the majority of the particles are usually between 1 and 10 µm in diameter, depending on the processing. It thermally decomposes (1, 3), between about 220 °C and 550 °C in two stages, initially releasing water then carbon dioxide, leaving a solid residue of magnesium oxide.

Huntite particles have a platy morphology and the particles are usually about 1 µm or less in diameter, much smaller than hydromagnesite particles. It thermally decomposes between about 450 °C and 750 °C in two stages, releasing only carbon dioxide, leaving a solid residue of magnesium oxide and calcium oxide.

The thermal decomposition of mixtures of these minerals, through endothermic release of carbon dioxide and water, has led to several studies showing their potential applications, including FR additives for polymer compounds. The endothermic decomposition of hydromagnesite coincides with the temperature range at which polymeric materials, such as ethylene vinyl acetate and polyethylene, thermally decompose. This is a good indicator that hydromagnesite has potential to perform well as an FR. Huntite decomposes between about 450 °C and 750 °C, a temperature range where most of the polymer has completely volatilised. This has led to a suggestion that huntite has little more influence than an inert diluent filler in terms of fire retardancy. It has been argued by the current authors (9) that the evidence in the literature does not back up this assertion. Recent work (10) demonstrates that both huntite and hydromagnesite contribute significantly to the FR properties of polymer compounds. Ethylene-vinyl acetate (EVA) is an elastomeric copolymeric material capable of maintaining its flexibility at filler loadings as high as 70% by weight. In combination with metal hydroxide or carbonate FRs, it makes an ideal alternative 99 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


to polyvinyl chloride for fire retarded communication and power cable sheathing. The FR behaviour of combinations of EVA with ATH and MH have been widely reported (11, 12). In studies reported elsewhere (13), for samples containing ATH, water is evolved around 250 °C, and for samples containing MH around 300 °C. At about 320 °C the acetate groups are released as acetic acid and the resulting polyene cross-links to form a protective layer. Of greater interest and significance are the more recent studies (14) of the trapping of acetic acid by M(OH)x, as aluminium or magnesium acetate, followed by a catalytic conversion occurring on the oxide surface, forming acetone, carbon dioxide (CO2) and water, delaying and diluting the fuel released from the decomposing polymer. The early peak of HRR for EVA formulations gives high peak HRRs, and FIGRA (fire growth rate) values, giving an initial boost to flame spread. These early peaks were eliminated by trapping of acetic acid by aluminium or magnesium hydroxide, which is only released after dehydration, with the formation of aluminium or magnesium oxide, following the ketonic decarboxylation of acetic acid to acetone, carbon dioxide and water. Thermochemically, the heat of combustion of two moles of acetic acid (2 x -876.1= -1752 kJ) is sufficiently similar to the heat of combustion of 1 mole of acetone product (-1785.7 kJ) that the process is unlikely to have a noticeable impact on the total heat release. The four contributions to fire retardancy have been crudely calculated for some mineral fillers (8). The heat absorbed by the filler from ambient to its decomposition temperature was calculated from the heat capacity over that range; the heat absorbed by the inorganic residue was determined from its representative heat capacity from the decomposition temperature to the final residue temperature (estimated as 600 °C), for the fraction remaining in the condensed phase; the heat absorbed by endothermic decomposition was obtained from DSC studies and published data; the heat absorbed by the water or carbon dioxide released to the gas phase is their representative heat capacity from the filler decomposition temperature to the maximum flame temperature (estimated as 900 °C) (8). While the temperature of premixed flames of typical hydrocarbon fuels in air, and the adiabatic flame temperature (corresponding to the maximum temperature attainable from thermodynamic considerations without loss of heat) can reach 2000 °C (15), and a candle flame has been reported to have a peak temperature of 1400 °C, polymer diffusion flames have only been reported to reach a peak temperature of around 900 °C (16, 17). These data, together with the average values of heat capacities of the filler, its residue, and its gaseous decomposition products have been used to estimate the heat absorption by the filler, the residue, the evolved water vapour and carbon dioxide and the decomposition endotherm, shown in Figure 1. The selection of mineral fillers is matched to the current work, including those fillers for which experimental data is reported. As the data have been calculated in energy units, the contribution to the individual fillers may be compared in absolute terms. Figure 1 shows the energy absorption per gram of each of the processes undergone by the filler.

100 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 1. Absolute estimation of heat absorbed by potential FR mineral fillers (labels such as HU40HM60 show the % huntite (HU) and hydromagnesite (HM) in the mixture).

The higher decomposition temperature of MH and particularly the greater contribution of the filler, increase its energy absorbing capacity by about 250 J g−1, compared to aluminium hydroxide. Comparing aluminium and magnesium hydroxide, it is evident that the difference between their relative effects arises from the higher decomposition temperature of Mg(OH)2, giving a larger contribution to the heat capacity of the undecomposed filler, but a smaller contribution from the heat capacity of the residue, and from the heat capacity of the greater volume of water vapour released by the Al(OH)3 – even though the energy for such a release is almost identical for both fillers. For the hydromagnesite, huntite and HU43HM57 mixture, which has been proposed as an alternative to Al(OH)3, it can be seen that the higher decomposition temperature of huntite gives a greater filler contribution, although overall HU43HM57 absorbs less energy than either ATH or MH. This approach is deliberately simplistic, and involves the following assumptions: •

•

The thermal conductivity of the polymer composite is unaffected by the presence of the filler. This is not realistic, particularly if incorporation of the filler results in significant changes to the melt flow behaviour. The final temperature reached by the solid residues and the CO2 and water in the gas phase do not vary significantly from one filler to another. This is discussed further. 101

In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

• • •


•

•

The heat capacity of the filler, and residue is not affected by the presence of polymer. The decomposition endotherm of the filler is unaffected by incorporation into the polymer. The only effect of the solid residue is its ability to act as a heat sink (in practice it will also change the reflectivity and the absorption of radiant heat). The only effect of the gas phase diluent is an absorber of heat, neglecting any effects reducing the free radical concentration below a critical threshold, by collisional quenching. It takes no account of particle size or morphology of the filler, which have been shown to be important in experimental studies.

It might be that the greatest value of simple models, such as the one presented here, is to observe deviations from the predicted behaviour in order to identify other properties, obscured by the physical effects of the filler, which also contribute to (improvements in) the burning behaviour. For example, the superior performance of mixtures of huntite and hydromagnesite compared to aluminium hydroxide reported here, or the unexpected FR performance of the micro and nano-boehmites.

Experimental Materials Mixtures of huntite and hydromagnesite with different ratios of the two minerals were supplied by Minelco Ltd. The samples are labelled throughout this work according to the ratio of the two minerals. For example HU43HM50 signifies that the sample contained a mixture of the minerals in the ratio: 43% huntite and 50% hydromagnesite. The remaining percentage comprises of closely related minerals, such as dolomite. For simplicity, in the calculation described earlier and in comparisons with it, the remaining percentage is taken to be huntite (which is closely related to dolomite). The actual HU:HM ratios, and those used in the calculations are shown in Table 2. In addition, natural calcium carbonate was supplied by Minelco under the name MicroCarb ST10H; aluminium hydroxide supplied by Nabaltec under the name Apyral AP40; magnesium hydroxide supplied by Martinswerk under the name Magnifin H5A; The following polymer formulation referred to as “EVA” (Table 1) was chosen as a typical, general purpose, halogen free compound found in the wire and cable industry. It has been used throughout this study to investigate the effects of huntite and hydromagnesite. Limiting oxygen index (LOI) tests were carried out according to BS EN ISO 4589-2:1999, using a Stanton Redcroft instrument with a total gas flow of 18 L min−1. Samples of 10 x 125 x 3 mm were cut from compression moulded plaques, and measurements were taken to the nearest 0.5% O2. A Fire Testing Technologies (FTT) cone calorimeter was used in accordance with ISO 5660, in triplicate, with a heat flux of 50 kW m-2, and samples of 100 x 100 x 6 mm. Py-GC-MS experiments 102 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


were carried out on a CDS-5200 Pyrolyser (Chemical Data Systems Co.) coupled with a PerkinElmer TurboMass gas chromatography-mass spectrometry (GC-MS) system. Around 0.8 mg of polymer in a quartz tube was inserted into a platinum coil on the probe tip, connected to a temperature programmer. The pyrolyzer, under helium, was heated from 50 to 450°C at 10°C min-1, and the decomposition products collected on Tenax TA trap at 50 °C. The trap was then heated at 280 °C for 2 min, the desorbed vapour transferred at 310 °C to the GC-MS.

Table 1. Typical wire and cable formulation Tradename

Description

Supplier

Quantity (phr)

Escorene UL00328

Exxon

Ethylene vinyl acetate (28%)

55

Exact 8201

ExxonMobil

Polyolefin elastomer

30

Fusabond MB226D

DuPont

Maleic anhydride grafted polyethylene

10

Borealis BS2581

Borealis

High density polyethylene

5

Irganox 1010

Ciba (BASF)

phenolic antioxidant

1

Mineral filler

Various

metal hydroxide / carbonate

160

Total

261

Results The limiting oxygen index (LOI) values in Table 2, show a significant improvement for all the FR additivies considered, with the exception of HU93HM5, which shows a similar value to the calcium carbonate. Other studies (18) have reported that increasing the proportion of hydromagnesite from 0% up to 40% increases the oxygen index, but further increase in the proportion of hydromagnesite has no further benefit to the LOI. Figure 2 shows the correlation between the calculated effects of the filler and the measured LOI. The clearest correlation is with the endotherm, which increases the LOI as it increases. The only significant exception to this is the HU77HM18 material, which may form a more strongly adherent residue, as described by Rothon (19), who showed the influence of a resilient inorganic residue on the tip of the burning LOI specimen. The heat release rate (HRR) of EVA compounds filled with ATH, MH, hydromagnesite and the various blends of huntite and hydromagnesite was measured using cone calorimetry at applied heat fluxes of 30, 50 and 70 kW m-2, as shown in Figure 3. As the time to ignition increases as the heat flux is reduced, direct comparison is less apparent. Therefore, the HRR has been plotted against 103 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

time following ignition, rather than time from the start of the test. Unfortunately data is only available for MH at 50 kW m-2, and this is plotted from the start of the test.

Table 2. Effect of huntite/hydromagnesite ratio on limiting oxygen index Ratios used for calculation


FR additive

LOI

Aluminium hydroxide

30.0

Magnesium hydroxide

31.5

Calcium carbonate

23.0

Hydromagnesite

29.5

HU24HM67

HU33HM67

29.5

HU41HM57

HU43HM57

29.0

HU43HM50

HU50HM50

28.0

HU77HM18

HU82HM18

29.5

HU93HM5

HU95HM5

24.5

Figure 2. Comparison of calculated FR contributions and measured LOI values.





Figure 3. HRR at varying heat fluxes of diferent samples of FR EVA.



Calcium carbonate, as may be expected, and as predicted by the calculation, makes only a small contribution to reducing the flammability, despite being present at a high loading (160 phr or 61%), particularly at the higher heat fluxes. Relative to calcium carbonate, ATH, MH, hydromagnesite and huntite-hydromagnesite mixtures reduced the rate of heat release over the entire burning period. The hydromagnesite filled compounds behave in a very similar manner to the ATH filled compound, showing an initial peak, followed by a second fairly sharp peak associated with movement and collapse of the residue. The compounds filled with a blend of huntite and hydromagnesite have a lower rate of heat release than the ATH or hydromagnesite filled compounds for most heat fluxes for most of the burning time, showing benefit from almost half of the hydromagnesite being replaced by huntite. As reported elsewhere (10), the use of a mixture of huntite and hydromagnesite leads to a stronger more stable char which does not collapse during the test period and gave a longer slower burn. This is particularly evident in the samples containing a higher proportion of huntite, and not addressed in the simple calculation model described earlier. The heat release characteristics of the magnesium hydroxide filled compound were different to the ATH or huntite-hydromagnesite filled compounds. The compound shows a much slower reduction in rate of heat release following the initial peak. It was quite clear that the formation of the residue from this compound was different to that of the ATH and hydromagnesite filled compounds.

Table 3. Summary of Cone Calorimeter data at 30, 50 and 70 kW m-2 Sample Applied Heat Flux /kW m-2 ATH

Time to iginition /s 30 226

MH

50 98

Average HRR /kW m-2

Peak HRR /kW m-2

70

30

50

70

30

50

70

54

117

169

208

81

84

102

125

163

88

CaCO3

210

83

43

186

257

251

107

129

187

Hydromagnesite

302

101

48

117

168

197

83

89

106

HU24HM67

249

93

44

139

162

190

73

74

90

HU41HM57

88

168

71

HU43HM50

219

81

40

130

154

191

68

56

84

HU77HM18

227

90

40

135

138

189

64

41

85

HU95HM5

236

78

43

154

174

202

52

57

103

EVA-huntite-hydromagesite mixtures also show similar sharpness and intensity of the initial peak of heat release with increasing heat flux. The cone calorimeter has been shown (20) to heat the surface of a ceramic board to about 500 °C, 610 °C, and 700 °C when heat fluxes of 30 kW m-2, 50 kW m-2 and 70 kW m-2 are used. Huntite and hydromagnesite go through a series of 107 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


decompositions (21) commencing at about 220 °C and completing at about 750 °C. ATH decomposes over a temperature range of about 180 – 350 °C. Therefore a heat flux of 30 kWm-2 is sufficient to ensure total decomposition of ATH, at higher heat fluxes the decomposition of the ATH will remain the same as at 30 kW m-2. As hydromagnesite and huntite have stages of decomposition that occur at higher temperatures these will be activated sooner at the higher heat fluxes. The additional heat flux activates the higher temperature decompositions in the hydromagnesite and huntite which means that it actually becomes more efficient at higher heat fluxes and keeps the rates of heat release closer that which was measured at 30 kW m-2. Table 3 provides a summary of numerical data which is used as the basis for comparing the behaviour of the formulations to the simple model. For HU41HM57 (and MH) data are only available at 50 kW m-2.

Figure 4. Relationship between individual energy contributions to FR effect, and time to ignition in the cone calorimeter at 50 kW m-2.

Figure 4 shows a reasonable correlation between the time to ignition and the magnitude of the decomposition endotherm. This fits with the general principle that the LOI, as an ease of extinction test (with the same criteria as ignition, that the heat feedback from the flame must equal or exceed the heat required to gasify the fuel), is driven by the same material parameters as the time to ignition. 108 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 5. Relationship between Peak Heat Release Rate, measured in the cone calaorimeter, and the contribution from the endothermic decomposition of the filler.

In contrast to Figure 4, Figure 5 shows only a very modest contribution of the filler decomposition endotherm to the magnitude of the peak HRR. In part, this is due to the method of measurement of HRR by oxygen depletion calorimetry (13.1 kJ released for every gram of oxygen consumed). Endothermic decomposition, and the production of water and CO2 will have no effect on the magnitude of the HRR when measured in the cone calorimeter, whereas in a real fire, or in experiments measuring the HRR using a thermometric device, this heat absorption would reduce the overall HRR. The slight trend showing reduction in peak HRR at 30 kW m-2 probably results from the cooling effect of the endotherm, resulting in a reduction of the rate of gasification of the pyrolysed EVA.

Figure 6. Pyrolysis GC-MS traces showing distribution between acetone and acetic acid from decomposition of EVA containing ATH, MH,and EXFR 0044, a commercial HU-HM blend containing roughly equal proportions of each mineral. 109 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 6 shows the acetone (2.15) and acetic acid (~2.7) peaks from the GC traces of the pyrolysis products of FR filled EVA, identified by MS. Under these pyrolysis conditions, the conversion of acetic acid to acetone is most efficient for HU-HM and least efficient for EVA-ATH. As described earlier, the acetone:acetic acid ratio is impotant, as acetic acid or acetone release is considered responsible for the first sharp peak in the HRR curve. As acetic acid is trapped on the hydroxides as an acetate, then subsequently released as acretone, this will delay the initial peak until the decomposition of the hydroxide. This explains the longer time to ignition of the EVA-MH sample, though is hidden behind the axis in the plots in Figure 3.

Conclusions Different tests for quantifying flammability focus disproportionately on particular aspects of burning behaviour. Thus, the LOI, which shows the least correlation to other tests, seems to be more strongly influenced by the presence and resilience of the inorganic residue (19); only the side effects of the endotherm decomposition, not the endotherm itself, are quantified in cone calorimetry (the time to ignition may be delayed and peak heat release lowered and delayed by endothermic decomposition of the filler, but the measured value of the total heat release, or effective heat of combustion will be unaffected by the endothermic event). The model analysis (8) described here shows reasonable correlation with overall flammability parameters, and particularly the magnitude of the endotherm to the ignition behaviour. However, it is limited in its scope, and some effects of filler, such as the reduction of dripping (UL94) and action as a radiant heat shield the inorganic residue (cone calorimeter), are not included. This simple model also fails to address the enhanced FR effects achieved from incorporation of huntite into EVA, reinforcing the barrier layer with a platy resilient mineral. The UltraCarb mixture can outperform both hydromagnesite, and aluminium hydroxide as an FR. This indicates that the FR mechanism of huntite is not simply the endothermic release of inert diluent vapour typical of other mineral fillers, since it has been shown that mixtures of huntite and hydromagnesite perform similarly to aluminium hydroxide in measurements involving cone calorimetry. Huntite certainly has much greater effect than an inert diluent filler, such as calcium carbonate (Figure 3). The endothermic release of water and carbon dioxide from hydromagnesite at temperatures between 220 °C and 500 °C helps to reduce the initial peak of heat release and increase the time to ignition. It shows that the partial decomposition of huntite at temperatures between 450 °C and 600 °C helps to reduce the rate of heat release during the later stages of combustion by providing a physical barrier, slowing the release of combustible gases to the flame. This has been ascribed to the platy morphology of huntite, reinforcing the barrier properties of the residual layer (9). The additional heat absorbed during the endothermic, partial decomposition, of huntite also reduces the heat transferred to the underlying polymer and further dilutes the gas phase with non-combustible carbon dioxide. In summary the FR action of mixtures of huntite and hydromagnesite comes from a combination of the actions of the two minerals. 110 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

References 1.

2.


3.

4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

Hull, T. R.; Wills, C. L.; Artingstall, T.; Price, D.; Milnes, G. J. In Fire Retardancy of Polymers: New Applications of Mineral Fillers; Royal Society of Chemistry: Cambridge, U.K., 2005; Chapter 28, p 372−384. Hull, T. R.; Quinn, R. E.; Areri, I. G.; Purser, D. A. Polym. Degrad. Stab. 2002, 77, 235–242. Rothon, R. N. Effects of Particulate Fillers on Flame Retardant Properties of Composites. In Particulate-Filled Polymer Composites, 2nd ed.; Rothon, R. N., Ed.; Rapra Technology: Shawbury, U.K., 2003; Chapter 6. Horn, W. E. Inorganic hydroxides and hydroxycarbonates: Their function and use as flame retardants. In Fire Retardancy of Polymeric Materials; Grand, A., Wilkie, C. A., Ed.; Marcel Dekker: New York, 2000; Chapter 9. Stoliarov, S. I.; Safronava, N.; Lyon, R. E. Fire Mater. 2009, 33, 257–271. Ozao, R.; Otsuka, R. Thermochim. Acta 1985, 86, 45–58. Hollingbery, L. A.; Hull, T. R. Thermochim. Acta 2010, 509, 1–11. Hull, T. R.; Witkowski, A.; Hollingbery, L. A. Polym. Degrad. Stab. 2011, 96, 1462–1469. Hollingbery, L. A.; Hull, T. R. Polym. Degrad. Stab. 2010, 95, 2213–2225. Hollingbery, L. A.; Hull, T. R. Polym. Degrad. Stab. 2012, 97, 504–512. Hull, T. R.; Price, D.; Liu, Y.; Wills, C. L.; Brady, J. Polym. Degrad. Stab. 2003, 82, 365–371. Rothon, R. N.; Hornsby, P. R. Polym. Degrad. Stab. 1996, 54, 383–385. Zilberman, J.; Hull, T. R.; Price, D.; Milnes, G. J.; Keen, F. Fire Mater. 2000, 24, 159–164. Witkowski, A.; Stec, A. A.; Hull, T. R. Polym. Degrad. Stab. 2012, in press. Bradley, J. N. Flame Combustion and Phenomena; Methuen’s Monographs on Chemical Subjects; Methuen & Co. Ltd.: London, 1969; p 29. Audoin, L.; Kolb, G.; Torero, J. L.; Most, J. M. Fire Safety J. 1995, 24, 107–130. Yuan, L.-M.; Cox, G. Fire Safety J. 1997, 27, 123–139. Kirschbaum, G. Ind Miner. 2001, 61–67. Ashley, R. J.; Rothon, R. N. Plast. Rubber Process. Appl. 1991, 15, 19–21. Schartel, B.; Hull, T. R. Fire Mater. 2007, 31, 327–354. Hollingbery, L. A.; Hull, T. R. Thermochim. Acta 2010, 509, 1–11.


Fire Retardancy of Mineral Fillers in EVA Copolymers - ACS Publications

Recommend Documents