|M.Sc Student||Potashnik Avishai|
|Subject||Aging Dynamic of Polyurethane|
|Department||Department of Chemical Engineering||Supervisor||Professor Emeritus Moshe Narkis|
Amorphous polymers, such as polyurethane, change their mechanical characteristics with time. Physical aging takes place when an amorphous matter is held below its glass transition temperature (Tg). In this state, relaxation processes originating in the unstable state material (namely, an overcooled liquid with entropy, enthalpy and free volume, all above the corresponding equilibrium values) are taking place. In parallel, other processes resulting from exposure to environmental conditions including radiation, humidity, oxygen and various solvents cause additional changes in the material, described as chemical aging. Moreover, non-chemical mechanisms such as solvent swelling may be also involved.
This thesis focuses on the aging behavior of commercial TDI-based elastomeric polyurethane (PU). Natural aging experiments (room conditions for different durations) were done, along with accelerated aging experiments in which the temperature, relative humidity and time were controlled. The aging phenomenon was investigated using the following techniques: DETA, FTIR, DMTA, DSC and SEM. Different mechanisms (physical aging, isocyanate to urea, isocyanate to urethane and urethane to isocyanate reactions) were observed at different aging conditions and by using the above techniques. The aging behavior of the investigated polyurethane was studied by electrical, chemical, mechanical, thermal and morphological means, and a reasonable agreement among the results was obtained. It was found that when aging conditions vary, different aging mechanisms take place, resulting in a different aging behavior. A generalized model to describe this effect has been suggested.