Synergistic fire- and mechanical effect of biochar and ammonium polyphosphate in epoxy composite

Abstract: Polymer composites are used in a varying extent and are challenging the use of traditional materials due to the push towards sustainable development. They have replaced steels and aluminum alloys in applications. Polymer composites are used in load-bearing and semi-load bearing applications in automotive, transport and aerospace industry due to their good characteristics. Polymer poses beneficial characteristics such as chemical stability, corrosion resistance, attractive strength-to-weight ratio, and be processed with ease. However, many polymers are highly flammable, making them a fire hazard. The fact that polymer composite is highly flammable, they need to undergo fire safety treatment that are sustainable towards the environment and humans. In this study biochar and ammonium polyphosphate (APP) were added in different combinations to epoxy resin. The purpose was to evaluate the synergistic effects that biochar and APP has on epoxy composite and how it will affect the fire- and mechanical properties. Additionally, developing a composite that retains a high compressive strength while increasing its thermal stability. Lastly, evaluate if the best performing composite could be recommended for load/semi-load‑bearing applications along with being sustainable towards the environment and humans. This thesis was conducted through literature study and laboratory work where three different tests were done such as cone calorimeter (CC), thermogravimetric analysis (TGA) and compressive test. The CC and TGA test were done to analyze the synergistic effect APP and biochar had on epoxy composites fire properties, but also determine which composition obtained the best fire properties. The compressive test was done to analyze the synergistic effect APP and biochar had on the epoxy composites mechanical properties. From the CC- and TGA tests it was observed that biochar and APP individually improved the fire properties of the epoxy where a decrease in peak heat release rate per unit area (PHRRPUA) and a decrease in mass loss was obtained. Additionally, it was noticed that the addition of only APP had a greater impact in improving the fire properties compared to only biochar. However, a combination of 15 wt.% biochar and 20 wt.% APP improved the fire properties the most. The compression tests indicated that biochar reduced the compressive strength drastically compared to the neat epoxy, since the biochar-based samples exhibited a porous structure. The addition of only APP in the epoxy showed a minimal reduction in compressive strength compared to neat epoxy. In conclusion, biochar and APP were improving the fire properties of epoxy composite whereas the compressive strength decreased. Overall, by an addition of only APP to the epoxy, the fire properties were enhanced where the compressive strength was conserved compared to neat epoxy. Since the composition with only APP performed the best overall, this composition can thereby be recommended for development in load/semi-load-bearing applications.