Flame retardant chloroprene rubbers with high tensile strength and elongation at break via dual cross-linked networks

The tensile strength and elongation at break of rubbers are mutually restrictive factors. Design and preparation of chloroprene rubber (CR) with high tensile strength, high elongation at break and excellent flame retardancy at the same time is challenging. Melamine cyanurate (MCA) is for the first time discovered to be a reactive flame retardant for CR. The tensile strength of C-M36 (with 3 wt% ZnO and 36 wt% MCA) vulcanizate is 2.5 times that of C-M0 (only with 3 wt% ZnO) vulcanizate, while the elongation at break of C-M36 vulcanizate is 1.3 times that of ZnO cross-linked C-M0 vulcanizate. At the same time, the limiting oxygen index of C-M36 (39%) is 1.22 times that of C-M0 (32%). FTIR and the vulcanization tests confirm that the reaction between CR and cyanuric acid occurs under the catalysis of a base (melamine), and the cyanuric acid molecules are grafted onto the molecular chain of CR. Two types of crosslinking networks are formed in CR vulcanizate, namely the traditional covalent bond crosslinks and the triple hydrogen crosslinks formed between cyanuric acid and melamine. Thus, the flame-retardant CR/MCA vulcanizate with high strength and high elongation at break is obtained. This research will strongly promote the industrial application of CR.