SMOULDERING COMBUSTION OF PHASE CHANGE MATERIALS WITHIN A POROUS HEMP MATRIX

Modern buildings increasingly include innovative materials aimed at reducing energy consumption and embedded carbon. One group of energy saving additives are known as Phase Change Materials (PCMs) which are present in the form of microencapsulated paraffin wax, whilst hempcrete has emerged as an innovative porous insulation material. Consequently, PCMs are combustible and may modify the combustion behavior of the substrate material. The aim of this research is to investigate the combustion behavior of a novel construction material with and without the addition of PCMs. The change of combustion characteristics caused by the introduction of PCMs into novel insulation material has been quantified when exposed to different heat fluxes. Combustion characterisation is conducted in the cone calorimeter at low heat fluxes and with no pilot ignition source. This promotes a one-dimensional opposed smoulder followed by a period of forward smoulder when the reaction front reaches the bottom of the sample. The critical heat flux for the onset of smouldering was observed to be reduced from 8kW.m-2 to 3kW.m-2 when PCM was added into the hempcrete matrix. Thermogravimetric Analysis (TGA) is used to identify pyrolysis and oxidative reactions for each of the major components of the final PCM hempcrete material, and is applied in the interpretation the combustion. TGA identified that the PCM ignited at a lower temperature than the hemp. Coupled with the resulting increase in the effective heat of combustion, ignition was more easily achieved. The PCM also acted to enhance the smoulder reaction resulting in a higher mass loss rate (0.052 compared to 0.028g.s-1 at 16kW.m-2), both initially and throughout the test. Addition of PCM was also found to increase the smoulder temperature and propagation rate. The transition between opposed and forward smolder generated in this set-up is also investigated.