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Hollingbery L.A.,Minelco Ltd. | Hollingbery L.A.,University of Central Lancashire | Hull T.R.,University of Central Lancashire
Polymer Degradation and Stability | Year: 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. © 2012 Elsevier Ltd. All rights reserved.


Hollingbery L.A.,Minelco Ltd. | Hollingbery L.A.,University of Central Lancashire | Hull T.R.,University of Central Lancashire
Thermochimica Acta | Year: 2012

The thermal decomposition of natural mixtures of huntite and hydromagnesite has been investigated. Hydromagnesite decomposes endothermically giving off water and carbon dioxide, the mechanism is dependent on heating rate. Mass losses measured by TGA are consistent with the loss of four water molecules, from the loss of water of crystallisation, and one water molecule from the decomposition of the hydroxide ion, followed by the loss of four carbon dioxide molecules from the decomposition of the carbonate ions. The magnesium carbonate, remaining after the dehydration of hydromagnesite, recrystallises exothermically in response to higher heating rates. This causes the decomposition of the carbonate ions to split into two stages with the second stage moving to a higher temperature. The magnitude of each stage is dependent on the heating rate. Huntite decomposes endothermically, at a higher temperature, giving off carbon dioxide in two stages. Mass losses measured by TGA are consistent with the loss of three carbon dioxide molecules, from the decomposition the carbonate ions associated with the three magnesium ions, followed by the loss of a single carbon dioxide molecule associated with the decomposition of the carbonate ion associated with the calcium ion. © 2011 Elsevier B.V. All rights reserved.


Hollingbery L.A.,Minelco Ltd | Hollingbery L.A.,University of Central Lancashire | Hull T.R.,University of Central Lancashire
Polymer Degradation and Stability | Year: 2010

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.© 2010 Elsevier Ltd. All rights reserved.


Hollingbery L.A.,Minelco Ltd | Hollingbery L.A.,University of Central Lancashire | Hull T.R.,University of Central Lancashire
Thermochimica Acta | Year: 2010

Naturally occurring mixtures of hydromagnesite and huntite are important industrial minerals. Their endothermic decomposition over a specific temperature range, releasing water and carbon dioxide, has lead to such mixtures being successfully used as fire retardants, often replacing aluminium hydroxide or magnesium hydroxide. The current understanding of the structure and thermal decomposition mechanism of both minerals and their combination in natural mixtures is reviewed. The crystalline structure of both minerals has been fully characterised. The thermal decomposition of huntite has been characterised and is relatively simple. However, the thermal decomposition mechanism of hydromagnesite is sensitive to many factors including rate of heating and the composition of the atmosphere. The partial pressure of carbon dioxide significantly affects the decomposition mechanism of hydromagnesite causing magnesium carbonate to crystallise and decompose at a higher temperature instead of decomposing directly to magnesium oxide. © 2010 Elsevier B.V.


Witkowski A.,University of Central Lancashire | Hollingbery L.,University of Central Lancashire | Hollingbery L.,Minelco Ltd. | Hull T.R.,University of Central Lancashire
ACS Symposium Series | Year: 2012

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. © 2012 American Chemical Society.

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