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Hydrolytic aging of crystallizable shape memory poly(ester urethane): Effects on the thermo-mechanical properties and visco-elastic modeling

  • The shape memory functionality of a segmented poly(ester urethane) and its hydrolytically aged specimens has been studied by cyclic thermo-mechanical measurements with an imposed strain of 100%. The shape memory effect was triggered by a melting transition in the soft segment phase. Aging was enforced by immersion in hot de-ionized water. In the course of the immersion the tensile properties (secant moduli, stress and strain at yield and break) were impaired by hydrolysis. Advanced specimen embrittlement finally led to rupture during the first thermo-mechanical cycle. This happened after 68 days of aging at 55 °C and correspondingly after 8 days at 80 °C. The residual strain after the first cycle, which was about 25%, increased significantly with aging time. Therefore, the total strain recoverability became ever smaller: aged specimens needed conditioning by at least two cycles for a full development of shape recoverability. Likewise the recovery force decreased continuously. DespiteThe shape memory functionality of a segmented poly(ester urethane) and its hydrolytically aged specimens has been studied by cyclic thermo-mechanical measurements with an imposed strain of 100%. The shape memory effect was triggered by a melting transition in the soft segment phase. Aging was enforced by immersion in hot de-ionized water. In the course of the immersion the tensile properties (secant moduli, stress and strain at yield and break) were impaired by hydrolysis. Advanced specimen embrittlement finally led to rupture during the first thermo-mechanical cycle. This happened after 68 days of aging at 55 °C and correspondingly after 8 days at 80 °C. The residual strain after the first cycle, which was about 25%, increased significantly with aging time. Therefore, the total strain recoverability became ever smaller: aged specimens needed conditioning by at least two cycles for a full development of shape recoverability. Likewise the recovery force decreased continuously. Despite these degradation effects, it was observed that the shape fixity and the cycle-related shape recovery of appropriately conditioned specimens (number of cycles N > 2) remained on a constant high level (at round 100% and between 90% and 100%, respectively) throughout the whole aging period. These observations are discussed within the framework of a simplified model of the behavior of crystallizable shape memory polymers. The amorphous state of the polymer is described by the equation of the linear visco-elastic solid. As for the semi-crystalline state the material is assumed to react elastically with respect to deviations from the configuration, which was frozen up under constraint conditions. The curves of the dependence of the material behavior on aging time at 55 °C match perfectly those at 80 °C when the time axis is adjusted by a factor of 8.5, from which the apparent activation energy for hydrolytic aging in the amorphous state of 82 kJ mol-1 could be deduced.zeige mehrzeige weniger

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Metadaten
Autor*innen:Werner Müller, Thorsten Pretsch
Dokumenttyp:Zeitschriftenartikel
Veröffentlichungsform:Verlagsliteratur
Sprache:Englisch
Titel des übergeordneten Werkes (Englisch):European polymer journal
Jahr der Erstveröffentlichung:2010
Verlag:Elsevier
Verlagsort:Oxford
Jahrgang/Band:46
Ausgabe/Heft:8
Erste Seite:1745
Letzte Seite:1758
Freie Schlagwörter:Active polymers; Hydrolytic degradation; Poly(ester urethane); Shape memory polymers; Thermo-mechanical properties
DOI:10.1016/j.eurpolymj.2010.05.004
ISSN:0014-3057
ISSN:1873-1945
Verfügbarkeit des Dokuments:Physisches Exemplar in der Bibliothek der BAM vorhanden ("Hardcopy Access")
Bibliotheksstandort:Sonderstandort: Publica-Schrank
Datum der Freischaltung:19.02.2016
Referierte Publikation:Ja
Datum der Eintragung als referierte Publikation:19.08.2010
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