Fire-resistant ceramic polymer

Materials World magazine
,
1 Nov 2006

Superman, Batman and Spiderman – ordinary men that transform into superheroes, saving lives and fighting crime. These comic strip characters may be pure fantasy, but a new material appears to encompass ‘superhero’ qualities in a very real sense – it sheds its outer layer, changing from a polymer to a more fire-resistant ceramic with life saving potential.

Polymers typically have low melting points – they start to melt between 100-200ºC and rapidly disintegrate at around 300-400ºC, while ceramics are usually formed at temperatures exceeding 700ºC. Polymers, employed in applications such as electric cable jacketing, would therefore add fuel to a fire and cause short circuits.

Commercialised by Ceram Polymerik, based in Noble Park, Victoria, Australia, the ‘ceramifying polymers’ were developed by scientists at the Commonwealth Scientific Research Organisation (CSIRO) and Cooperative Research Centre for Polymers, both in Australia. The materials comprise a polymer matrix, minerals, inorganic fluxing components and various functional additives.

Dr Kevin Thomson, Chief Technical Officer at Ceram Polymerik, although unable to reveal the precise formulations, explains that ‘the polymer will decompose as the temperature increases. There are thermal gradients in the material in a dynamic fire situation [that help to keep] the structure together until various inorganic reactions commence at about 450ºC. The ceramic product then starts to form through the action of the molten fluxes with the minerals, producing small pools of liquid between the mineral particles. This liquid forms ceramic bridges that hold the structure together.

‘A key [element] is to use a small amount of flux to avoid large liquid phases which cause the ceramic to collapse at high temperatures.’

The resulting solid or semi-porous ceramic material can remain stable at over 1,000ºC.

Vince Dowling of CSIRO adds, ‘The aim is to contain the movement of heat and smoke between floors, rooms or compartments by sealing penetrations, prolonging stability or creating barriers, and also to protect structural components.’

This would allow individuals more time to escape.

A variety of minerals and flux systems can be employed depending on the processing temperatures, ceramic properties required and application area.

The technology has been proven in silicones, epoxies, polyesters, polyurethanes and cross-linked rubbers. Although the only commercial grades currently available use thermoplastics PVC and ethylene propylene diene monomer (EPDM).

These are useful for semi-rigid extruded profiles and static seal applications, respectively, and are manufactured using standard extrusion compounding processes.

‘Ceramification’, however, does not make the material flame retardant – the EPDM grade incorporates a non-halogen flame retardant system, while further research will continue to search for a similar PVC-based product. An agreement has been made between Ceram Polymerik and Olex Cables Australia for the commercialisation of the Pyrolex Ceramifiable flexible electrical cable.

Thomson admits that manufacturing such products might be costly as the company uses ‘highly filled thermoplastic compounds’ (with inorganic components and minerals) that are close to the critical packing fraction limit for processing.

But he is adamant that the products show potential for the passive fire protection market, given the increasingly complex shapes and sizes of modern buildings.

‘Look at the installation cost of alternative systems. A fire rated door seal could involve an intumescent strip as well as a rubber strip. A ceramifying polymer seal could replace [it] with a single plastic extrusion.’

 

Further information:

Ceram Polymerik