Degradation behavior of shape memory polymer due to water and diesel fuel

Shape memory polymers (SMP) are smart materials, which have the ability to memorize the original or permanent shape. Owing to this characteristic SMP can be used as a sensor, a transplant, as well as structural materials in wide range of applications. Despite its importance, its degradation behavior is still not completely known; and only a limited amount of work has been reported in the literature. In this thesis, the experiments have been carried out to evaluate the degradation behavior of Veriflex- SMP (industry supplied SMP samples) upon exposure to two different types of liquids; water and diesel fuel separately. It has been found that the “glass transition temperature, Tg” decreases due to immersion in water and diesel fuel. The immersion of Veriflex- SMP in water and diesel fuel facilitates the breakage of existing bonds and the formation of new bonds, thereby increasing the mobility of polymeric chains. In addition, water and diesel fuel are found to be effectively plasticize the SMPs, by reducing the storage modulus; and thus decreasing the structural integrity of the SMP. It is also observed that upon exposure to diesel fuel for a couple of weeks, the Tg of Veriflex- SMP goes below the room temperature. As a result, Veriflex- SMP goes back to the original shape without the application of external energy. The stress relaxation tests are also conducted to determine the changes in physical properties of SMP. The decay of the stress is found much faster and eventually to a much lower value in the degraded samples, in comparison to the untreated samples, tested under the similar conditions. It is also found that the stress decay is increased with the increase of immersion time in water and in the diesel fuel. From Fourier Transform Infrared (FTIR) tests it has been found that the formation of hydrogen bonding between the SMP and the solvents (water and diesel fuel) is the main reason for the degradation of SMP; although the hydrogen has a minor effect on the structure of SMP, but it has an obvious influence on the glass transition temperature, Tg