A sustainable sol-gel approach for the preparation of self-extinguishing hybrid epoxy nanocomposites containing coffee-derived biochar

The improper recycling of polymeric wastes is causing several issues. More waste-to-wealth routes are needed to prepare functional polymer-based products with low contents of flame retardants (FRs). Limiting the concentration of phosphorus (P) in the manufacturing of FR epoxy systems counteracts the rising depletion of natural resources. The use of industrial biowastes (e.g., spent coffee grounds (SCGs)) in combination with other synergists allows for the exploitation of low P loadings (i.e., 1 wt.%) to obtain self-extinguishing epoxy composites, whose matrix undergoes proper sol-gel modification. Herein, we demonstrate that the pyrolysis of SCGs enables the preparation of hybrid epoxy materials showing no dripping V-0 rating in UL 94 tests and a significant decrease (up to ~65%) in the peak heat release rate.