Degradation of shape memory polymer due to water and diesel fuels

Abstract

Shape-Memory-Polymers (SMP) is smart materials have the ability to memorize original shape; and can be used as sensors, transplants, and structural materials in engineering applications. Despite its practical importance, limited work is available on its degradation behavior. This study has been carried out to evaluate degradation behavior of Veriflex-SMP on exposures to water and diesel fuels separately. It is found that "glass transition temperature, Tg" decreases due to immersion in liquids; and immersion facilitates acceleration of breakage of the existing bonds and the formation of new bonds, thereby increasing the mobility of polymeric chains; and the immersion medium effectively plasticize SMPs by reducing storage modulus and decreases structural integrity of SMP. Upon exposure to diesel fuel for several weeks, "Tg" goes below room temperature; and SMP goes back to its original shape without the need of the application of external energy. Stress relaxation tests shows that stress decay is found to be much faster and to a much lower value in degraded samples and increases with increase of immersion time. From Fourier Transform Infrared tests formation of hydrogen bonding between SMP and the solvents in which it is immersed, is the main reason for SMP degradation; although hydrogen has a minor effect on SMP structure but has an obvious influence on glass transition temperature, Tg.