10. Effect of Thermal and Mechanical Damage on Phase Separation, Crosslink Density, and Polydispersity of Polyurea Variants

Comprehensive experimental studies are performed to comprehend further the effects of thermal and mechanical aspects of cavitation on polyurea (PU) variants microstructure and molecular transitions. Different polyurea formulations are distinguished by the difference in their pre-polymer mixing ratios, including the chain length distribution of diamines. Virgin, cavitation-erosion damaged, and undamaged (exposed to water) along with annealed polyurea samples are tested for their crosslink density and molecular weight using swelling experiments and gel permeation chromatography (GPC). Additionally, FTIR spectra can be utilized to evaluate crystallinity (in formation and ordering of hydrogen bonds followed by their destruction). Furthermore, FTIR spectra for mechanically damaged samples under cavitation erosion can be related to water absorption and oxidation. It is understood that formulations with a higher hard segment (HS) to soft segment (SS) ratio tend to be more crosslinked. It is also observed that the swelling capacity is decreasing for polyurea with higher HS/SS ratio. It is concluded that the polyurea nanostructure can substantially affect its resistivity against thermal and mechanical damages.