Cardanol-derived anhydride cross-linked epoxy thermosets with intrinsic anti-flammability, toughness and shape memory effect

With the increasing awareness of environmental protection, the development of high-performance bio-based epoxy resins has attracted more and more attention to reduce the dependence on the petroleum-based 4,4′-diaminodiphenylmethane (DDM). In this work, we synthesized two kinds of cardanol-based curing agents (Car-DCP-MAH and Car-DPC-MAH) as alternatives for petroleum-based DDM. The chemical structures of Car-DCP-MAH and Car-DPC-MAH were confirmed by 1H and 31P NMR. Compared with the traditional DGEBA/DDM thermoset, the cured DGEBA/Car-DCP-MAH and DGEBA/Car-DPC-MAH thermosets both displayed good intrinsic fire resistance in terms of higher LOI values (29% and 28%, respectively, versus 24.5%) and V-0 rating in the UL-94 test. Furthermore, the results of the cone calorimeter test showed a significant reduction in the peak heat release rate (PHRR) values of the cured DGEBA/Car-DCP-MAH and DGEBA/Car-DPC-MAH which were 42.3% and 47.7%. The flame retardancy of these two systems was mainly due to the great carbonization ability and the formation of the intact and compact char layer. Owning to the flexible long alkyl chain in the crosslinking network, the toughness of the cured DGEBA/Car-DCP-MAH and DGEBA/Car-DPC-MAH products was greatly improved with the higher elongation at break and impact strength. Additionally, the cured DGEBA/Car-DCP-MAH and DGEBA/Car-DPC-MAH thermosets both showed preferable shape memory properties with a high shape recovery efficiency of 98.6% and 96.3%. This study provides a novel strategy to achieve bio-based epoxy thermosets with intrinsic anti-flammability, toughness and shape memory effect.