Description
Polymer matrix composites currently have a wide range of engineering applications in the aerospace, automotive, and biomedical industries. Their mechanical properties such as strength and stiffness to weight ratios can easily be tailored and enhanced by adjusting the volume fraction of the reinforcement and matrix phases. However; the enhanced strength and stiffness are highly dependent on the quality of the interfacial bonding between the reinforcement and matrix. It is our aim to synthesize and characterize a polyurea matrix composite that is reinforced by polyurea microspheres. For this composite, a hyper- viscoelastic polyurea formed from 4:1 weight ratio of Versalink® P1000 and Isonate® 143L was chosen for its superior moisture resistance, and excellent thermal and impact mitigation properties. We hypothesized that polyurea microspheres fabricated from this hyper-viscoelastic polyurea would inherit the superior hygrothermal properties as well as have enhanced stiffness, thus enhancing the properties of the composite. To fabricate the composite, first polyurea microspheres were fabricated using precipitation polymerization. After synthesis, the microspheres were characterized for their structural, thermal, and mechanical properties. The microspheres displayed a highly textured surface with an average diameter size of 2.4 ± 2.9 μm. It was confirmed through infrared spectroscopy and thermogravimetric analysis that the microspheres inherited the chemical composition and hygrothermal properties of bulk polyurea. Through atomic force microscopy the microspheres were found to be four times stiffer than their bulk counterpart. Once characterization of the microspheres was complete, the polyurea microsphere reinforced polyurea matrix composite was fabricated using one weight percent of the reinforcement phase. The composite was then characterized for its physical, thermal, and mechanical properties. It was found that the microspheres were bonded and well dispersed within the matrix. From thermogravimetric analysis, it was found that the composite shared the same thermal properties as the microspheres and bulk polyurea. From the micro-scale mechanical characterization, the composite displayed an enhanced elastic modulus compared to the bulk counterpart. From the dynamic mechanical characterization the composite was found to be slightly more ductile than the bulk polyurea. From the quasi-static mechanical characterization, it was found that the stress buildup nucleated around the interface causing early failure.
