Abstract
Triple-shape memory epoxy (EP)/polycaprolactone (PCL) systems (PCL content: 23 wt %) with different structures (PCL nanoweb embedded in EP matrix and EP/PCL with co-continuous phase structure) were produced. To set the two temporary shapes, the glass transition temperature (Tg) of the EP and the melting temperature (Tm) of PCL served during the shape memory cycle. An attempt was made to reinforce the PCL nanoweb by graphene nanoplatelets prior to infiltrating the nanoweb with EP through vacuum assisted resin transfer molding. Morphology was analyzed by scanning electron microscopy and Raman spectrometry. Triple-shape memory characteristics were determined by dynamic mechanical analysis in tension mode. Graphene was supposed to act also as spacer between the nanofibers, improving the quality of impregnation with EP. The EP phase related shape memory properties were similar for all systems, while those belonging to PCL phase depended on the structure. Shape fixity of PCL was better without than with graphene reinforcement. The best shape memory performance was shown by the EP/PCL with co-continuous structure. Based on Raman spectrometry results, the characteristic dimension of the related co-continuous network was below 900 nm.
Highlights
Shape memory polymers (SMPs) change their shapes reversibly from temporary to permanent under combined action of mechanical load and external stimulus, which is in most cases heat
scanning electron microscopy (SEM) images of the morphology of the electrospun nanofibers with and without graphene can be seen in Figures 1 and 2
The fibers tended to form bundles with diameters of 1–5 μm after post curing conducted above the melting temperature of PCL; EP/PCL nanoweb with graphene: graphene nanoplatelets, located between the fibers, likely acted as spacers and strengthened the nanoweb structure during impregnation
Summary
Shape memory polymers (SMPs) change their shapes reversibly from temporary to permanent under combined action of mechanical load and external stimulus, which is in most cases heat. The transformation temperature is the glass transition temperature (Tg). The temporary shape is set by deformation above Tg followed by cooling under load. During this procedure, the segments between the crosslinks adapt to the external load via conformational rearrangements. The strain energy, stored by this way, is released when the material is unloaded and heated above its Tg whereby the permanent shape is restored. The related SMPs are termed one-way, dual-shape memory systems because the reversible shape change occurs only from temporary to permanent
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