Curing kinetics and mechanical properties of magnetocured epoxy adhesive doped with magnetic nanoparticles

The curing kinetics as well as the corresponding tensile properties of magnetocured epoxy adhesive doped with magnetic nanoparticles (MNPs) is investigated in this article, where the curing reaction process is depicted using an isoconversional model. It is found that the tensile modulus and strength strongly depend on the curing degree (CD) and mass fraction of MNPs when curing degree varies from 0.7 to 1.0. When curing degree is 0.7, the tensile modulus of the adhesive with 15%wt and 30%wt MNPs increases by 46% and 592% compared to that with 10%wt MNPs, respectively, but the increase is not obvious when curing degree is higher than 0.9. This difference is more significant in the tested tensile strength, where the samples with 15%wt and 30%wt MNPs are 7.08 and 20.83 times higher than the one with 10%wt MNPs under 0.7 curing degree. However, the corresponding tensile strength with 1.0 curing degree is reduced by 4% and 35%, respectively. Scanning electron microscopy observation reveals different fracture mechanisms caused by curing degree variation. Failure occurs in the adhesive region for curing degree below 0.9, while failure initiates and propagates at the interface between adhesive and MNPs for curing degree above 0.9. It can be concluded that the intrinsic property of the adhesive determines the tensile properties when the curing degree is lower than 0.9, while the weak interfacial interaction between adhesive and MNPs introduces reverse effect when the curing degree is higher than 0.9. This competitive relationship should be considered in the design of magnetocuring process.Highlights Enhancement in adhesive modulus from MNPs addition degrades as CD approaches 1. Intrinsic property of adhesive determines the tensile strength with CD < 0.9. Weak interface dominates the failure mechanism in adhesive with CD > 0.9.