Shape-memory effects of polyurethane copolymer cross-linked by dextrin
2008
The effects of the dextrin cross-linking and hard-segment content on the shape-memory property of a polyurethane (PU) block copolymer were investigated. Although dextrin was selected due to its large number of free hydroxyl groups and ubiquitous availability, it is unfortunately insoluble in most organic solvents. The insolubility of dextrin was resolved by attaching a phenyl group onto the dextrin to reduce its hydrophilicity. The phase separations of hard and soft segments were not dependent on the dextrin cross-linking and hard-segment content, as per the results obtained from FTIR, DSC, and XRD analysis. An increased content of chemically cross-linked dextrin increased the maximum stress, but did not decrease the strain for most cases. The cross-linking density increased with increasing dextrin content, as expected. After dextrin cross-linking, the shape recovery rate was generally over 90%, and remained the same after four cyclical tests, while a low shape retention rate was observed for most cases. The best shape-memory effect, considering both the shape recovery and retention rate, was found for a PU consisting of 35 wt.% hard segment and 2 wt.% dextrin. Finally, dextrin was compared to other cross-linking compounds, such as glycerol and pentaerythritol, in this investigation.
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