Extra strong Cu2+-doped intumescent char to protect epoxy resin against fire.

The intumescence, compactness, and strength of char are the key points to the intumescent flame retardant system. However, the char residues of flame retardant polymers rarely exhibit all three characteristics, especially strength. Herein, a novel Cu2+-doped intumescent flame retardant (Cu–CHP) was prepared without producing any waste. When Cu–CHP was exposed at a high temperature (∼1400 °C), it can rapidly expand and carbonize to form dense char. Surprisingly, the intumescent char residue of Cu–CHP can hold up more than 2000 times its own weight. Benefitting from the excellent intumescent charring capacity of Cu–CHP, the resultant EP/Cu–CHP 18% composite can withstand around 600 s penetrating of butane flame (∼1400 °C) because of strong dense char protection, and only 0.9 wt% Cu2+ content resulted in the limiting oxygen index (LOI) of EP/Cu–CHP 18% increases to 31% and the vertical burning (UL-94) reaches V-0 rating. Additionally, its peak heat release rate, total smoke production, and fire growth rate are significantly reduced by 70%, 53%, and 75%, respectively, compared with neat epoxy resin. Especially, the smoke density of EP/Cu–CHP 18% was dramatically dropped by more than 68%. Because a Cu2+-doped intumescent, compact, and strong char residue was produced during burning. This work provides a new strategy to impart excellent flame retardancy and smoke suppression to highly flammable polymers by building metal-doped strong intumescent char residues. [Display omitted] • Cu2+-doped flame retardant was prepared without producing any wastes. • Cu2+-doped intumescent, compact, and strong char residue was produced. • Excellent flame retardancy and smoke suppression were imparted to epoxy resin. • The intumescent flame retardant mechanism was proposed. [ABSTRACT FROM AUTHOR]