In the microcapsule-based self-healing methodology, the liquid self-healing agent must be polymerized under optimal cure kinetics and the polymerized healing agent be a strong adhesive to matrix for a successful healing agent system. The dynamic cure kinetics were investigated for endo-dicyclopentadiene (endo-DCPD) containing two comonomers, norbornene carboxylic acid (NCA) and norbornene methanol (NM), during polymerization via the ring-opening metathesis polymerization (ROMP) in the presence of the 1st and 2nd generation Grubbs'' catalysts by means of Differential scanning calorimetry (DSC). The experimental DSC data obtained were analyzed to evaluate kinetic parameters using model-fitting and model-free isoconversional methods. The model-free isoconversional method was found to predict better than the model-fitting method. Activation energy was determined from the model-free isoconversional method in a whole conversion range, showing different trends under the 1st and 2nd generation Grubbs'' catalysts. The addition of the NCA (or NM) leads to the shift of the peak temperature to higher temperature and the reduction of total enthalpy and activation energy from the analysis. Single lap shear adhesion tests were made for the healing agents with comonomers. It revealed that bond strength to epoxy resin was enhanced by ∼50% when 5 wt% of comonomers was added to endo-DCPD. The enhancement of the adhesion may be attributed to the formation of hydrogen bondings between epoxy resin and endo-DCPD with the comonomers.
The epoxy formulation with low viscosity and fast curing for Resin Transfer Molding (RTM) was developed using DSC, viscosity measurements, and mechanical tests. Two different DGEBA type epoxy resins, high viscous (YD128) and low viscous (YD115), were used as base resins, and diethylenetriamine (DETA) and isophorone diamine (IPDA) as hardeners, and tertiary amines and mercaptans as accelerators. From the DSC and flexural tests, a YD115/YD128=7/3 blend with 5 phr of 4-mercaptan accelerator and 3 phr of diluent was found to be a suitable formulation for the low viscosity and fast curing epoxy system.
Blends of endo-DCPD with high toughness and epoxy resin with high thermal/mechanical properties were fabricated and characterized using DSC, DMA (dynamic mechanical analysis) and tensile tests in this work. Two epoxy resins, DCPD-epoxy dissolved in methyl ethyl ketone (DES) and DCPD-epoxy (DE), were used as base resin. ROMP reaction of endo-DCPD was initiated with the 2nd generation Grubbs'' catalyst and cure reaction of DES (or DE) was with nadic methyl anhydride (NMA). The two cure reactions from endo-DCPD and epoxy were observed in the blends at two different temperatures during dynamic DSC scans. From DMA, it was found that a endo-DCPD/DE=9:1 blend was compatible but 7:3 became incompatible. Tensile tests showed that toughness was deceased but the modulus and strength were increased with increase of the DE content.