  A series of recyclable epoxy resin (REP) composites are successfully prepared
in this study, aiming to improve flame retardancy while keep good recyclability
and mechanical properties. The commercial
9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide (DOPO) with high reactive
P-H bond is used as highly-efficient flame retardant in this work. Compared
with pure epoxy resin with a limited oxygen index of 21.7 % and no rating in
vertical burning test, recyclable epoxy resin only with 3 wt% DOPO acquires a
limited oxygen index value of 27.8% and V-0 rating. In addition, REP composites
containing 4 wt% DOPO displays quick self-extinguishing behavior, which shows
the 43.5% drop of the peak heat release rate. The main reason might be that
traditional phosphorous-containing flame retardant existing in REP composites
can play a positive role in both condensed phase and gas phase when burning. On
the other hand, both scanning electron microscopy and Raman results also
further affirm the improved flame retardancy. Moreover, flame-retardant REP
composites can also maintain good transparency and mechanical properties. As
well as the favorable recyclability originated from the special exchangeable
disulfide crosslinks. High-Performance REP composites possessing expected flame
retardancy, recyclability and good mechanical properties pave the way to
broaden applications of thermoset epoxy materials.
