Toughening agents are a class of auxiliaries that have reduced brittleness of composites and improved impact resistance of composites. Can be divided into two types of active tougheners and inactive tougheners. Active tougheners are rich in their molecular chains that can react with the matrix resin. It can constitute a network structure, add a part of the flexible chain, and then Improve the impact resistance of composite materials. Inactive tougheners are tougheners that are well compatible with the matrix resin but do not participate in chemical reactions.
Toughening mechanism: Different types of toughening agents have different toughening mechanisms. The liquid polysulfide rubber can react with epoxy resin, introducing a portion of the soft segment, lowering the modulus of the epoxy resin, improving the resistance, but dedication to heat resistance. As a toughening agent for epoxy resin, liquid nitrile rubber has almost no toughening effect at room temperature curing, and the adhesive strength is rather decreased. As long as the medium and high temperature curing system, the toughening and bonding effect is more significant. The carboxyl-terminated liquid nitrile rubber toughened epoxy resin is compatible before curing, phase separated after solidification, and constitutes an “island structure”, which can absorb impact energy without reducing heat resistance at all.