Thermal and flame-retardant epoxy vitrimers based on disulfide bonds

Thermosets and thermoset composites are used in a wide range of applications in the plastics industry. However, the recyclability of these materials is limited and challenging. Vitrimers and vitrimer-based composites offer significant potential in terms of recyclability through the incorporation of covalent dynamic bonds in the polymer network. However, flame-retardant properties are mandatory for many potential applications of these materials.
In this work, the flame-retardant properties of an epoxy vitrimer based on bisphenol A diglycidyl ether (DGEBA) and 4-aminophenyl disulfide were studied. In total, the influence of 16 different phosphorous-based flame-retardant additives and reactive flame retardants with different oxidation numbers of the phosphorus were investigated by DSC, TGA and TG-MS measurements and the flame-retardant tests UL94, limiting oxygen index (LOI) and cone calorimetry. The most promising flame-retardant vitrimers were mechanically recycled and tested again.
LOIs up to 38 % O2 and UL94 V-0 classification were achieved.