Viscoelastic properties of alkoxy silane-epoxy interpenetrating networks

A model epoxy-silane interpenetrating network (IPN) was synthesized to simulate the molecular structure found at the fiber-matrix interphase. The Youngʹs modulus ( E ) of the epoxy-silane IPN was determined through micromechanical analysis both quasi-statically and in the frequency domain. The epoxy-silane IPN was synthesized by diffusion of uncured diglycidyl ether of bisphenol A (DGEBA) epoxy resin and bis (p-aminocyclohexyl) methane (PACM) curing agent into spherical particles of condensed and crosslinked 3-glycidoxypropyltrimethoxysilane (GPS). This IPN composition was chosen to simulate the typical properties of a silane modified interphase found in glass reinforced composites. Differential scanning calorimetry (DSC) showed that the glass transition temperature ( T g ) of the initial crosslinked siloxane network increases upon cure of the DGEBA and PACM, but was still significantly lower than that of the neat epoxy matrix. Additionally, dynamic mechanical analysis (DMA) was used in conjunction with the micromechanical C-Combining Rule to show that the Youngʹs modulus of the epoxy-silane IPN spherical inclusions ( E i ) is decreased in comparison to the Youngʹs modulus of the matrix epoxy ( E m ) at all temperatures. The time-temperature superposition (tTsp) principle was successfully applied to the epoxy-silane IPN to determine viscoelastic properties at high frequencies. The viscoelastic properties of the epoxy-silane IPN may have implications with respect to the ballistic impact resistance of composite structures used for Army applications.