| This work was focused on two important parts including the cyanate ester modified epoxy resin system and epoxy3221system. In the first part, the effects of cyanate ester/epoxy resin ratio and curing cycles on the properties of cured resins were investigated. The curing mechanism also was study by FTIR. Base on this the best formulation was selected. In the second part, bisphenol A type epoxy CYD-128and tetraglycidyl4,4’-diaminophenylmethane were selected as the main resin and the anhydride (THPA) and dicyandiamide were selected as the curing agent respectively. Tertiary amine and substituted urea were acted as the accelerators. The epoxy system3221was estimated as the best system by compared the properties of different system. The detailed information is showed as followes:1. Cyanate ester modified epoxy resin systemThe results showed that the ratio of cyanate ester (CE) to epoxy resin (EP) was one of the major factor that controlled the hot deformation temperature (HDT), water absorption and diffusion and the dielectric properties of cured products. The HDT gained its highest value when the ratio of CE to EP was40to60and absorption content got its lowest values when the ratio of CE to EP was30to70. The dielectric properties of cured products, however, were enhanced by increasing the ratio of cyanate ester. Not only the dielectric constant and dielectric loss decreased with the increase of CE content in the system, but also the stabilization under higher temperature and wet conditions was increased. Based on these analyses, the CY40system was estimated as the best formulation which composed of40wt%cyanate ester HY-1,60wt%epoxy resin CYD-128and0.5wt%isocaprylic cobalt. The hygrothermal properties of CY40system were also enhanced. The using temperature of CY40system was at least50℃higher than that of unmodified system. The CY40/EW220composites still has excellent properties under wet conditions at130℃.FTIR results confirmed that the trimerization of cyanate ester was prior to formation when the reaction temperature was below160℃. Then cyanate ester reacted with epoxy group directly to formation the oxazoline, oxazolidinone and isocyanurate. At the same time, oxazoline also involved in the reaction with epoxy groups. The reaction involved in the isocyanurate was the dominating reaction in the system when the reaction temperature was below180℃. It must be notified that the content of cyanurate, oxazolidinone and isocyanurate depend on the cyante ester/epoxide functional ratio.The reaction kinetic parameters of CY40system are as followes:Activation energy Eal=89.0kJ.mol-1, Ea2=88.5kJ.mol-1Frequency factor A1=5.70×109, A2=3.11×108Rate constant of activation k125℃=1.43×10-6, k1180℃=3.11×10-1k225℃=9.5×10-8, k2180℃=1.94×10-2The changes of rate constant activation indicated the parallel effects of reaction temperature on the two reactions. The reaction rate of trimerization of cyanate ester was enhanced by increasing content of cyanate ester. Cyanate ester has the characteristic of latent curing agent for epoxy resins.2. Epoxy system3221The optimized epoxy system3221is of the best integrated properties including the heat resistance, hygrothermal properties, dielectric properties and processing techniques. The activation energy of3221system is84.2kJ.mol-1and the storage life is more than one month at ambient temperature.The results showed that the curing temperature had a great influence on the physical properties. An elevated curing temperature can result in an enhancement of extent and, in turn, enhance the glass transition temperature. The system investigated in this study, epoxy system3221/RH glass fabric composites, an increasing equilibrium moisture content can be incurred by both the excessively high curing temperature(above130℃) and low curing temperature(below120℃). The following result was that the lowering in Tg and interlaminar share strength were promoted and the maintenance of relative stiffness and stability of dielectric properties were degraded. Furthermore, the excessively elevated curing temperature also resulted in a broad split in tan8peaks and degradation of compatibility of the system. All these are unfavorable for the use of materials. Based on the above results, a range of curing temperature from120℃to130℃with a curing time for2hours was recommended for the cure of epoxy system3221/RH glass fabric reinforced composites. |
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