Shape-memory Polyurethane/Multiwalled carbon nanotube fibers

Shape-memory polyurethane/multiwalled carbon nanotube (SMP-MWNT) composites with various multiwalled carbon nanotube (MWNT) contents were synthesized, and the corresponding SMP-MWNT fibers were prepared by melt spinning. The influence of the MWNT content on the spinnability, fracture morphology, thermal and mechanical properties, and shape-memory behavior of the shape-memory polymer was studied. The spinning ability of SMP-MWNTs decreased significantly with increasing MWNT content. When the MWNT content reached 8.0 wt %, the fibers could not be produced because of the poor rheological properties of the composites. The melt-blending, extrusion, and melt-spinning processes for the shape-memory fiber (SMF), particularly at low MWNT contents, caused the nanotubes to distribute homogeneously and preferentially align along the drawing direction of the SMF. The crystallization in the SMF was promoted at low MWNT contents because it acted as a nucleation agent. At high MWNT contents, however, the crystallization was hindered because the movement of the polyurethane chains was restricted. The hornogeneously distributed and aligned MWNTs preserved the SMF with high tenacity and initial modulus. The recovery ratio and recovery force were also improved because the MWNTs helped to store the internal elastic energy during stretching and fixing. (c) 2007 Wiley Periodicals, Inc.