Recyclable flame-retardant epoxy composites based on disulfide bonds. Flammability and recyclability

TL;DR

This study develops recyclable epoxy composites with enhanced flame retardancy using DOPO, maintaining good mechanical properties and recyclability through disulfide bonds, suitable for broader thermoset applications.

Contribution

Introduces a novel recyclable epoxy composite with improved flame retardancy by incorporating DOPO and disulfide bonds, combining high performance with recyclability.

Findings

Recyclable epoxy with 3 wt% DOPO achieves V-0 rating.

Adding 4 wt% DOPO reduces peak heat release rate by 43.5%.

Composites maintain transparency and mechanical integrity.

Abstract

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.