Carbon fiber reinforced polymer (CFRP) materials have gained prevalence in high-performance aerospace applications due to their excellent environmental stability and strength-to-weight ratio. These composite materials contain a large volume fraction of interphase between the carbon fibers and surrounding epoxy matrix. Due to the chemically dissimilar nature of the carbon fiber and surrounding matrix, there exists an energetic driving force for interphase formation, which has been studied extensively in the literature. We postulate, however, that the constrained space in the vicinity of an additive acts to influence interphase morphology as well. To study this, fully cured tetraglycidyl ether of diaminodiphenylmethane (TGDDM), isophorone diamine (IPDA) microspheres were synthesized by precipitation polymerization. After purification, the microspheres were post cured to ensure that no reactive functionality remained on their surface, which was confirmed <i>via</i> Fourier transform infrared spectroscopy. The microspheres were then dispersed in the self-same matrix formulation at 1, 5, and 10 weight percent utilizing a high shear twin-screw extruder. The resulting material was investigated using optical microscopy to ensure uniform dispersion, and absence of microsphere agglomerates within the system. Dispersion into the selfsame matrix eliminates the energetic driving force for interphase formation that exists in other composite materials and allows for direct observation of the impacts of constrained space on interphase properties. Microsphere properties were observed to be comparable to those of the bulk matrix material in all cases; therefore, any change in the composite material behavior is due to the formation of an interphase in the vicinity of the microspheres. The cure reaction was studied using differential scanning calorimetry to establish the impact of microspheres on the onset and final extent of reaction. The network homogeneity and thermomechanical properties of the microcomposites were quantified using dynamic mechanical analysis, in order to probe the homogeneity of the interphase and compare it to a control network. The mechanical properties were analyzed in both compression and tension, and the fracture toughness was measured by a notched-edge bend technique.

Ghost particles: Effect of constrained space on glassy polymer network formation and mechanics

2019 Spring National Meeting

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