AbstractThe effect of introduction of a silane coupling agent and absorbed moisture (i.e., equilibrium hygroscopic state) on the tensile properties of a thermoplastic reinforced reaction injection molding (RRIM) composite, having a fiber volume fraction of 0.33, was evaluated. The composite was produced by anionically polymerizing caprolactam monomer within a continuous strand (swirl) glass fiber mat using a RRIM method. In addition to the expected strong dependence of the composite tensile stiffness and strength on introduction of 1.5 wt (based on the total weight of glass fibers) of γ‐amino propyl triethoxy silane coupling agent, the effect of the mode of application of the coupling agent on the resultant composite properties, under tensile loading, was observed to be insignificant in the dry state but quite important in the wet state. Microscopic examination of the fracture surfaces revealed a three‐stage tensile failure mechanism that is associated with debonding at low strains of the fibers, fiber failure (at the weakest point), and pull‐out of the fibers resulting in catastrophic failure, at the ultimate tensile strain, of the com
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