Tailored Polyurea-Glass Interfaces and the Characterization by the Single-Fiber Fragmentation

Polyurea is an elastomer that has been intensively researched due to its excellent thermal and mechanical properties. Polyurea based composite material has recently become a research interest to further explore what this polymer has to offer. In order to better understand the overall static or dynamic mechanical properties of the polyurea based composites, how to tailor and characterize the polyurea-filler interface has become a crucial problem. This study focuses on one of the filler materials, glass. Three types of polyurea-glass interfaces are studied by using silane reagents that have similar molecular structures but with different end functional groups to modify the glass surfaces. Accordingly, bonds with different strengths are formed between the glass and the polyurea through the different chemical character of the reagent molecules. The polyurea-glass interfacial properties are tested by the single-fiber fragmentation, which is a widely used method to test the shear properties of the interface between the fiber and the polymer. Single-fiber fragmentation samples are fabricated by casting a single glass fiber along the axial direction of the dogbone-shaped polyurea tension test sample. Tension tests are conducted and the continuous photoelastic videos are taken to observe the single fiber fragmentation process until the fragmentation reaches its saturation state. Meanwhile, stress-strain data are recorded. By analyzing the single-fiber fragmentation data, the polyurea-glass interfacial shear strengths are calculated. The observation of the debonding zones at the interface is used to find the approximate models for the interfacial shear adhesion of polyurea-glass interfaces for different reagents, hence proving the potential for tailoring of the interfacial strength using surface treatment.