Heat transfer effects in polymer flame retardancy

Abstract

Product flammability is of particular concern because polymer use in, homes, and industrial premises keeps increasing at a rapid pace. To mitigate the inherent flammability hazard carried by polymers, flame retardant additives are the preferred way to ensure that products can resist ignition for longer and reduce the rate at which fire spreads, thus increasing the evacuation time allowed for people. Most research in the field focusses on the chemical action pathways of the flame retardant additives, with not much research on the role of heat transfer. This thesis studies the heat transfer effects in polymer flame retardancy. All three modes of heat transfer, radiation, convection, and conduction, are studied and quantified. Experimental and numerical methods are combined to complement each other to give a more complete understanding. The effective absorption coefficient of thermal radiation in polybutylene terephthalate (PBT) is studied with systematic additions of flame retardants. It was found that some flame retardants affect the absorption coefficient more than others, but thermal degradation has the strongest effect shown to be likely caused by inducing porosity in the material which increases the absorption coefficient. In convective ignition of flame retarded PBT the time to ignition can be increased by the use of flame retardants. The degradation leading up to ignition reduces the thermal diffusivity of polymers. The reduction in thermal diffusivity was largely unaffected by the flame retardants. Increasing the thermal diffusivity through additives in epoxy showed that the time to ignition increases as the conduction rate increases, reducing the surface temperature. Modelling modifications in thermal diffusivity through additives in PBT showed that there is a trade-off between flammability variables, namely time to ignition and mass loss rate. This thesis shows how heat transfer can be used to reduce flammability and complement the current approaches.