I tried to "program" pure polyurethane (Tg is minus 44 degrees, Tm is about 170 degrees) to check its ability to fix and recover shape. The temperature cycle was 1) 90 degr., bend in half; 2) minus 15 degr., removed load; 3) heating of non-loaded sample to 90 degr. The bended in half shape was fixed at minus 15, not ideal, but about 90%, and after heating at 60 degrees the recovery rate was about 80% and than not any changes were visible in recovery process while heating to 90 degr.
So I want to ask: why I didn't reach any of critical temperatures (Tg, Tm), my sample had not any thermal transition, but it was still able to work as a material with shape memory effect? What is a physical basis of this effect?
Dear Anastasiia Kashirina,,
Over Tg, the deformation of the polymeric materials may have an elastic, plastic and viscoelastic (time dependent) components. Their ratio depends mainly on the type of polymer, the temperature and possible processes of chemical or physical crosslinking. The elastic or plastic deformation should not be confused with the notion of "shape memory"
Dear Anastasiia Kashirina, if I understood well the question, Tg is -44, and you experimental temperatures are all above Tg, so what is the problem since above it many thermal transitions are possible. My Regards
@ Abdelkader BOUAZIZ
Thank you for reply.
According to the DSC data, there is no any thermal transition in the temperature range -44~170 (between Tg and the crystalline part melting temperature), so this is why I can't understand the mechanism of that type of shape memory effect. Can it be possible just because of the chemical bonds in my PU?
Dear Anastasiia Kashirina, I think this is due to a pure elastic recovery due mainly to entaglements if PU is lineaire or to crosslinks if PU is partially cured. My Regards
Dear Mr Bouaziz, thank you for suggestions, they are really useful for me!
Dear Anastasiia Kashirina,,
Over Tg, the deformation of the polymeric materials may have an elastic, plastic and viscoelastic (time dependent) components. Their ratio depends mainly on the type of polymer, the temperature and possible processes of chemical or physical crosslinking. The elastic or plastic deformation should not be confused with the notion of "shape memory"
Dear @ Galina Zamfirova , thank you for reply! I really appreciate your comment. The "shape memory"-like behavior of my PU can be explained by elastic deformation during heating-cooling process. I won't confuse it with shape memory effect in future.
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