Effects of Bismaleimide Resin on Dielectric and Dynamic Mechanical Properties of Epoxy-Based Laminates

Effects of bismaleimide (BMI) resin on dielectric properties e.g., permittivity (e''), loss factor (e"), and ionic conductivity (σ) of two different epoxy-amine resin systems were measured during dynamic curing (over a temperature range 20-300°C) by using dielectric analysis (DEA). Dynamic mechanical properties, e.g., flexural storage and loss moduli (E'' and E") and shear storage and loss moduli (G'' and G") of the glass-fabric reinforced composites (laminates) of the above mentioned resin matrices were carried out by dynamic mechanical analysis (DMA) technique. Double exothermic curing peaks were observed for the formulations with DDS as curing agent. For each system, that region of the curve in which the values for ionic conductivity are frequency dependent, indicates that the measurement is strongly influenced by dipole relaxations. At temperatures near or below Tg, dielectric properties of resins are dominated by the molecular dipoles (frequency-dependent response). Ionic conductivity increases largely on using DDS as curing agent for DGEBPA over MDA however; addition of BMI to DDS- and MDA-cured thermosets decreases the ionic conductivity in the former and increases it in the later resin systems. Addition of bismaleimide (BMI) resin in three different concentrations tothe glass-fabric DGEBPA/MDA and DGEBPA/DDS laminates, increases Tg, Tg∞, and flexural and shear storage moduli (E'' and G'') considerably.