Journal
HIGH PERFORMANCE POLYMERS
Volume 23, Issue 4, Pages 300-307Publisher
SAGE PUBLICATIONS LTD
DOI: 10.1177/0954008311405245
Keywords
Shape memory polymer; glass transition temperature; physicomechanical properties
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Funding
- Deutsche Forschungsgemeinschaft (DFG) [SFB459]
- State North Rhine Westphalia (NRW)
- Alexander von Humboldt (AvH)
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The present investigations were undertaken to find out whether and how often cycling, processing and programming can be repeated, whether repeated programming affects the one way effect and how much irreversible strain the shape memory polymeric material accumulates at a particular temperature. The effect was investigated in dependence of different stress levels, and the effect of both recovery temperature and recovery time was considered. As a model material the commercially and industrially applicable amorphous shape memory polymer Tecoflex (R) was examined and subjected to 50 programming cycles. Tecoflex (R) is characterized by a glass transition temperature, T-g, of 74 degrees C, above which it looses all its strength. During tensile testing at 20 degrees C (T < T-g), stresses a steady increase to 26 MPa as strains approached the rupture strain of 25%. It is observed that at 60 degrees C (T < T-g, but near T-g) the material can be strained to more than 2500% before rupture occurs while stresses slowly increase to values less than 0.3 MPa. It turns out that programming, cooling, unloading and heating to trigger the one way effect causes an increase of irreversible strain that is associated with a corresponding decrease of the intensity of the one way effect during the first thermomechanical cycles.
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