The curing of unsaturated polyester resin is the process of linear macromolecules forming a three-dimensional network through the crosslinking agent, but the curing process cannot consume all the active double bonds in the resin and achieve a curing degree of 100%. In other words, the degree of curing of the resin is difficult to achieve. The reason is that in the late stage of the curing reaction, the viscosity of the system increases sharply, which hinders the diffusion. Generally, it can only be considered that the curing is complete when the material properties tend to be stable. The degree of resin curing has a great influence on the performance of FRP. The higher the degree of curing, the mechanical properties, physical and chemical properties of FRP products are fully exerted. (Someone has done experiments to test the physical properties of UPR resin at different stages after curing, and the results show that its bending strength does not increase with time, and it does not stabilize until one year later. In fact, for FRP products that have been put into use, one year later, due to the effects of heat, light and other aging and corrosion of the medium, the mechanical properties began to gradually decline.)
There are many factors that affect the degree of curing. The composition of the resin itself, the amount of initiator and accelerator, curing temperature, post-curing temperature and curing time can all affect the degree of curing of the polyester resin.