Decomposition and combustion of EVA and LDPE alone and when fire retarded with ATH

133

Naturally occurring mixtures of hydromagnesite and huntite have found important industrial use. Their endothermic decomposition over a temperature range similar to that of commonly used polymers and their release of water and carbon dioxide, has led to such mixtures being successfully used as fire retardants. They have replaced aluminium hydroxide and magnesium hydroxide in many applications. The current understanding of the thermal decomposition mechanism of both minerals and their combination in natural mixtures has been reviewed and related to their fire retardant action. Both minerals contribute to the reduction in flammability of polymers although the extent of these interactions has not been fully investigated. However, the fire retardant mechanism of these minerals appears more complicated than either aluminium hydroxide or magnesium hydroxide. This paper critically examines the literature on the fire retardant behaviour of mixtures of hydromagnesite and huntite, providing information of particular use to formulators of fire retardant polymers using these minerals. It also highlights the gaps in understanding of the fire retardant mechanisms of mixtures of hydromagnesite and huntite and areas that require further research.

Section: Decomposition Of Hydromagnesite and Huntite When Incorporatementioning

confidence: 95%

“…McGarry [86] has shown that as pure EVA decomposes it forms a charred skin layer slowing the degradation of the underlying polymer. This layer can be disrupted by the release of water vapour from the decomposition of ATH increasing the rate of decomposition.…”

Section: Decomposition Of Hydromagnesite and Huntite When Incorporatementioning

confidence: 99%

The fire retardant behaviour of huntite and hydromagnesite – A review

Hollingbery

Hull

2010

133

“…For example, ATH normally decomposes at 190°C, whereas, when in an ethylenevinyl acetate copolymer (EVA) in a common cable industry formulation, water does not start to be lost until the temperature reaches 250°C 29 . The loss of water can also have a deleterious effect, rupturing protective layers formed, for example, by the cross-linking of the conjugated polyene in EVA/ATH composites 30 .…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

Fire retardant action of mineral fillers

Hull

Witkowski

Hollingbery

2011

285

144

Endothermically decomposing mineral fillers, such as aluminium or magnesium hydroxide, magnesium carbonate, or mixed magnesium/calcium carbonates and hydroxides, such as naturally occurring mixtures of huntite and hydromagnesite are in heavy demand as sustainable, environmentally benign fire retardants. They are more difficult to deploy than the halogenated flame retardants they are replacing, as their modes of action are more complex, and are not equally effective in different polymers. In addition to their presence (at levels up to 70%), reducing the flammable content of the material, they have three quantifiable fire retardant effects: heat absorption through endothermic decomposition; increased heat capacity of the polymer residue; increased heat capacity of the gas phase through the presence of water or carbon dioxide. These three contributions have been quantified for eight of the most common fire retardant mineral fillers, and the effects on standard fire tests such as the LOI, UL 94 and cone calorimeter discussed. By quantifying these estimable contributions, more subtle effects, which they might otherwise mask, may be identified.

“…Figure 2 shows the effect of the ratio of huntite to hydromagnesite on the rate of heat release. Each sample shows an initial peak in rate of heat release on ignition due to the ignition of acetic acid [54], as previously described for the samples shown in Figure 1. This peak is followed by a declining rate of heat release dependant on the ratio of huntite to hydromagnesite.…”

Section: Effect Of Mineral Ratios On Combustion In the Cone Calorimetermentioning

confidence: 96%

“…When a char forms it slows the combustion of the underlying polymer leading to a decrease in heat release rate, following an initial peak, as the fire progresses through the polymer compound. The initial peak in rate of heat release on ignition is believed to result from the ignition of acetic acid [54] released during the early decomposition stages of the EVA. Clearly the calcium carbonate filled compound has a high, steady, rate of heat release and a short burning time as would be expected for a compound containing no active fire retardant additive.…”

Section: Effect Of Mineral Ratios On Combustion In the Cone Calorimetermentioning

confidence: 99%

The fire retardant effects of huntite in natural mixtures with hydromagnesite

Hollingbery¹,

Hull²

2012

The fire retardant effects of natural mixtures of huntite and hydromagnesite have been investigated. As well as being entirely natural these mixtures of minerals can be considered "greener" and more environmentally friendly, in their production methods, than alternatives such as aluminium hydroxide and magnesium hydroxide. It has been shown that the release of water and carbon dioxide from hydromagnesite helps to increase the time to ignition and peak heat release in cone calorimeter testing. Huntite has been shown to decrease the average rate of heat release and increase the strength of the residue. Electron microscopy has shown that the huntite particles maintain their platy morphology during combustion in the cone calorimeter. The morphology of these particles helps to reduce the rate of heat release by slowing the release of flammable decomposition products to the flame. The platy shape of the huntite particles increases the strength of the residue containing higher proportions of this mineral. Huntite is shown to play an active part in improving fire retardancy when used in a mixture with hydromagnesite, giving performance for typical mixtures comparable to those of aluminium hydroxide.