Green one-step modification of spent coffee grounds as synergistic bio-based flame retardant for waterborne epoxy resin

Fire retardant coatings are moving towards environmentally friendly products, and the development of green flame retardants is gradually attracting the attention of researchers. In this work, spent coffee grounds (SCG) were modified with m-xylylenediamine phosphonate ammonium (MAP) to create a bio-based flame retardant (SCG-g-MAP) for waterborne epoxy resin (WEP). The structure and composition of SCG-g-MAP were analyzed by a range of characterization tests, and the effects of SCG-g-MAP on the thermal stability, flame retardancy and fire resistance of WEP composite coatings were discussed. It revealed that WEP composite coating with 10 % SCG-g-MAP and partial conventional intumescent fire retardant fillers, resulted in a LOI value of 29.5 % and self-extinguishing capability. Moreover, the coating exhibited significantly improved fire resistance and thermal insulation properties due to its better thermal stability and excellent barrier function of forming carbon layer. This work presents a new attempt and inspiration for the application of biomass waste such as SCG for green flame retardant fillers.