The transition of reaction-to-fire behavior from biomass to corresponding biochar

Abstract: As of now, the environmental issue is very topical and there is also an underutilization of different biological material where these can be used in ways that are typically not thought of. One way to increase the degree of utilization is to convert various biomasses such as natural rubber, olive pits, wood chips, and reed pellets into biochar. These biochars can then be added to materials, such as polymers, to improve their reaction-to-fire properties with a low impact on the environment. The process to convert biomasses into biochars, takes place through so-called pyrolysis, i.e., heating under high temperatures and low oxygen concentrations. During pyrolysis, the volatile substances in the biomasses are released and a material is left behind where the compounds that can sustain fire are minimal and a carbon skeleton consisting of strong C-C covalent bonds is prevalent. This biochar then has significantly different material properties compared to its corresponding biomass, where one of the differences is its improved reaction-to-fire properties. This study aims to investigate whether it is possible to determine the final reaction-to-fire properties of different biochars based on the corresponding biomass and its chemical composition. The basis of this study consists of a literature review, laboratory experiments and an analysis. The literature review has been carried out to find the chemical composition of the various biomasses, the laboratory experiments has been carried out to obtain the reaction-to-fire properties of said biomasses and biochars, and the analysis to determine the possibility of predicting the final reaction-to-fire properties of various biochars. The results obtained in this study are that despite the unfavorable reaction-to-fire properties of natural rubber, biochar made from natural rubber had the most desirable reaction-to-fire properties (i.e., fire safe). Of the seven parameters assessed for its reaction-to-fire properties, natural rubber performed worst in five of these compared to the remaining biomasses. However, after conversion to biochar, rubber had the best parameters in three out of five cases where the two additional parameters could not be assessed as these are based on the specimen igniting, which they did not. The parameters in which biochar made from natural rubber obtained the best results were peak heat release rate (PHRR), total heat released per unit area (THRPUA), and maximum average rate of heat emission (MARHE). However, biochar made from natural rubber also obtained the worst results in terms of time to peak heat release rate (TTPHRR) and fire growth rate (FIGRA), where FIGRA is inversely proportional to TTPHRR. Although the lignocellulosic biomasses showed difference in their chemical composition, no major difference in PHRR, THRPUA, and MARHE could be detected between them when their corresponding biochars were tested in the cone calorimeter. The conclusions that can be drawn from this study are that it is possible to predict the final reaction-to-fire properties of the lignocellulosic biochars since they react almost equally when exposed to fire. However, more tests and studies are required to be able to predict the final reaction-to-fire properties of the non-lignocellulosic biochars. This is to understand the chemical compounds and bonds that are formed during pyrolysis, as well as how these affect the biochar’s reaction-to-fire properties.