Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5203200 | Polymer Degradation and Stability | 2010 | 10 Pages |
Abstract
A series of cyclic thermo-mechanical measurements was conducted on segregated poly(ester urethane) to study substantial changes in triple-shape properties as a result of hydrolytic aging (80 °C). Prior to the analysis of aging effects, a concept of triple-shape testing was elaborated, starting with the implementation of two distinct programming units. The first one included a deformation at 60 °C to Ém1 = 100% (temporary shape B) and its fixing through soft segment crystallization by cooling to â20 °C under constant strain. The second one consisted of a deformation at â20 °C to Ém2 = 200% (temporary shape A) and its stabilization through soft segment vitrification as achieved by cooling to â60 °C under fixed strain constraint. Then, gradual heating of the polymer from below to above its thermal transition temperatures gave two independent shape recovery responses in the reverse order of shape fixing: A â B through passing the glass transition by heating from â60 to 23 °C and B â C (back to the permanent shape), when heating the material from 23 to 60 °C and thus above its soft segment melting temperature. In a progressive approach, the storage of loading history through the sequential fixing of two temporary shapes was proven by the development of shape recovery stresses under constrained environment. With the implementation of the two testing methods several aging-related effects could be detected. Good shape fixing abilities â¥90% for both shapes were found and contrasted by significant changes in shape recoverabilities and stress storage capacities. Further insights derived from differential scanning calorimetry (DSC) measurements, indicating an aging-related growth in soft segment crystallinity, and dynamic mechanical analysis (DMA), suggesting a plasticizer effect of water onto the polymer matrix and that aging favoured an increase in cross-linking density.
Related Topics
Physical Sciences and Engineering
Chemistry
Organic Chemistry
Authors
Thorsten Pretsch,