Research On Low Viscosity Bisphenol F Epoxy Curing System

To meet the requirements of Vacuum Assisted Resin Transfer Molding, the modification and curing formulation of low viscosity Bisphenol F epoxy was studied. The curing characteristics and the properties of cured products were investigated, cured respectively by NT-1(modified aromatic amine), A40(epoxy curing agent), DDM(4,4'-diaminodiphenylmethane)and A-40/DDM complex. Their advantages and disadvantages used in the VARTM were also analyzed. An reactive diluents DEAD with designed structure was selected, and its effect on the viscosity of the curing system and the properties of products was studied. The epoxy system was modified with tri-functional organic silane. The curing system was confirmed, which could resolve the inconsistency between room-temperature curing and prolonging the pot life, and the inconsistency of room-temperature curing and high thermal endurance of cured products.It was showed that , the tensile strength of the NT-1 cured products was up to 90.61MPa, the flexural strength 132.76MPa, the glass transition temperature(Tg) 139.6℃, when the cure schedule was 30℃/2h + 80℃/3h. But the pot life of this system at room temperature was only about 45 minutes, which couldn't meet the demand of VARTM. Activated diluents DEAD had little effect on the properties of the cured products, but greatly decreased the viscosity of the resin system. When the ratio of DEAD and Bisphenol F epoxy was 1:10, the viscosity dropped from 3550mPa·s to 1300mPa·s. And compared with Non-DEAD system, the tensile strength , the flexural strength, and Tg decreased only about 5%. As excellent reactive diluents, DEAD could provide high properties holding ratio.The DDM cured Bisphenol F epoxy performed high thermal endurance. When the cure schedule was 60℃/4h + 90℃/3h, Tg could reach 157℃. But DDM was difficult to disperse homogeneously in resin at room temperature. A40 cured bisphenol F epoxy had a long pot life as 8 hours at room temperature, meanwhile high resolving ability of DDM. So matching A40 and DDM could resolve the inconsistency of room-temperature curing and prolonging the pot life, and the inconsistency of room-temperature curing and high thermal endurance of cured products. When the ratio of A40 to DDM was 8:18, the pot life of the system was 3.5 hours at room temperature. While the cure schedule was 50℃/4h + 120℃/2h, the tensile strength of the cured products was 85.99MPa, flexural strength 117.01MPa, Tg 123.6℃. The mechanical properties of this matched system could reach the same level as the DDM cured bisphenol F epoxy system, and were better than that of A40 cured system.When A40-DDM cured Bisphenol F epoxy system was modified with tri- functional organic silane, the optimal ratio of organic silane to Bisphenol F epoxy was1:4. Compared with Non-organic silane system, the tensile strength was improved by 12.2%, flexural strength 9.4%, meanwhile Tg could hold the formerly line.