A series of shape memory polyurethanes (SMPUs) was prepared from polycaprolactone diol (PCL) 4000, 1,4‐butanediol (BDO), dimethylol propionic acid (DMPA), triethylamine, and 4, 4′‐diphenylmethane diisocyanate (MDI), to which excess MDI or glycerin were added to obtain crosslinked shape memory polyurethanes. Their mechanical, thermomechanical, thermal and shape memory properties were investigated by using differential scanning calorimetry (DSC), Fourier‐transform (FT‐IR) spectroscopy, dynamic mechanical analysis (DMA) and tensile testing. The results showed that crosslinked SMPUs have better thermal and thermomechanical properties than those prepared from linear polyurethanes and display good shape memory effects. Copyright © 2005 Society of Chemical Industry

In this study, a series of smart polymer fibers with a shape memory effect were developed. Firstly, a set of shape memory polyurethanes with varying hard-segment content were synthesized. Then, the solutions of the shape memory polyurethanes were spun into fibers through wet spinning. The thin films of the polyurethanes were considered to represent the nature of the polyurethanes. Differential scanning calorimetry tests were performed on both the thin films and the fibers to compare their thermal properties. Wide angle x-ray diffraction and small angle x-ray scattering techniques were applied to investigate the structure of the thin films and the fibers, and the structure change taking place in the spinning process was therefore revealed. The spinning process resulted in the polyurethane molecules being partially oriented in the direction of the fiber axis. The molecular orientation prompted the aggregation of the hard segments and the formation of hard-segment microdomains. The mechanical properties of the fibers were examined through tensile tests. The shape memory effect of the thin films and the fibers was investigated through a series of thermomechanical cyclic tensile tests. It was found that the fibers showed less shape fixity but more shape recovery compared with the thin films. Further investigations revealed that the recovery stress of the fibers was higher than that of the thin films. The smart fibers may exert the recovery force of shape memory polymers to an extreme extent in the direction of the fiber axis and therefore provide a possibility for producing high-performance actuators.

Polyurethane (PU) nanofibers were prepared by the electrospinning method. The process parameters, including the applied voltage, feeding rate, and solution concentration, were investigated carefully. The results showed that the resultant nanofibers, electrospun from PU/N,Ndimethylformamide (DMF) solutions, had ultrafine diameters ranging from about 700 to 50 nm. In addition, it was found that the diameters and morphology of the nanofibers were influenced greatly by the process parameters. In particular, the solution concentration played a main role in influencing the transformation of the polymer solution into ultrafine fibers, and the diameters increased with the solution concentrations increasing. Finally, it was concluded that uniform PU nanofibers without beads or curls could be prepared by electrospinning through good control of the process parameters, such as 5.0-7.0 wt % PU/DMF solutions, 10-15-kV applied voltages, and 0.06-0.08 mm/min feeding rates.

Subtle interaction between shape-memory polymer and cellulose fibers within fabrics remains a critical issue for understanding their thermal-mechanical properties and thus the shape-memory behavior in cotton fibers. We demonstrate here the efficacy of Raman spectroscopy to probe the induced stresses in warp and weft fibers, presenting physicochemical features for cellulose fibers finished with macromolecule polyurethane and small-molecule dimethyloldihydroxyethyleneurea. Accordingly, a possible mechanism for transfer of the shape-memory effect to fabrics is proposed. Forming as a coating on the fiber surface after the finishing process, the shape-memory polymer takes a critical role in reducing the residual stress in weft fibers, establishing the prerequisite for reserving the shape-memory effect to fabric. In addition, this work has demonstrated that Raman spectroscopy is able to probe the residual stresses in cotton fabrics after being treated by chemicals in addition to that due to physical deformation. Our result provides clear evidence that in the finishing process strength reduction in fibers in general is not only caused solely by a chemical reaction, but also by a physical modification of the cotton structure.

In this paper, an electro-active shape memory fibre was fabricated successively by incorporating multi-walled carbon nanotubes (MWNT). The shape memory polyurethane (SMP-MWNT) composite was prepared by in situ polymerization and the SMP-MWNT fibre was prepared by melt spinning. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations of the morphology revealed that the MWNTs are axially aligned and homogenously distributed in the SMP matrix, which is helpful for the fibre's electrical conductivity improvement and for the electro-active shape memory effect. At 6.0 wt% MWNT content, the prepared shape memory fibre shape recovery ratio was 75% and the fixing ratio was 77%.