Thermal decomposition of polymeric materials

Most of unwanted fires are fuelled by polymeric materials, ranging from natural polymers found in wood, cotton or wool, to synthetic polymers (“plastics”) derived from crude oil, showing much greater flammability. Polymer molecules are too large to be volatile, but break down thermally, by chain scission and chain stripping, to release fuel to the vapour phase prior to ignition. Experimental and numerical methods for investigating polymer decomposition are reviewed, followed by a description of the chemical decomposition of individual polymers. In order to use flammable synthetic polymers in high risk applications, fire retardants are frequently added to meet regulatory requirements. The range of available fire retardants is described in relation to their different modes of action. This is followed by a description of the more common test methods used to assess the flammability of polymeric materials, including ignitability, flame spread and heat release rate, together with a summary of the importance of physical properties and char formation on their burning behaviour.