Qinghao Meng

Morphology, phase separation, thermal and mechanical property differences of shape memory fibres prepared by different spinning methods

In this paper, the mechanical properties, especially the shape memory properties, of shape memory fibres (SMFs) prepared by the melt spinning method and the wet spinning method were studied. It was observed that the melt-spun SMFs had higher tenacity, breaking elongation and shape memory effect compared with those of wet-spun SMFs. The results from differential scanning calorimetry (DSC), x-ray diffraction (XRD) and dynamic mechanical analysis (DMA) were used to understand the underlying physics behind these property differences. It is concluded that the melt-spun SMFs have higher phase separation, which results in both better soft segment and hard segment crystallization. To obtain higher-performance SMFs in general, the melt spinning method is preferred.

An electro-active shape memory fibre by incorporating multi-walled carbon nanotubes

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 fibres 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%.

Effect of steaming on shape memory polyurethane fibers with various hard segment contents

To illustrate the effect of post-treatment high-pressure steaming and hard segment content on shape memory polyurethane (SMPU) fiber, a series of shape memory polyurethane having various hard segment contents was synthesized with the pre-polymerization method, spun with a wet spinning process and treated with high pressure saturated water vapor. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), wide angle x-ray diffraction (WAXD), mechanical testing and cyclic tensile testing were conducted to investigate the particular thermal/mechanical properties, crystallization of hard segments and shape memory properties of SMPU fibers. In addition, in the light of a comparison between the original and the treated SMPU fiber, the effect of steaming post-treatment in SMPU fibers with various hard segment contents was illustrated. The steaming treatment gives rise to a higher elongation ratio at break, lower tenacity and initial modulus. Hard segment crystallization can be induced, especially in fiber with higher hard segment content after treatment. The glass transition temperature of the soft segment of SMPU fibers was decreased after steaming and the trends are most likely significant in high hard segment content specimens. Steaming with high pressure saturated water vapor can eliminate the thermal shrinkage and provide dimensional stability to the original SMPU fibers. The recoverability remains well in all treated specimens, but the fixity ability decreases with the decrease of hard segment content.

Properties of shape memory polyurethane used as a low-temperature thermoplastic biomedical orthotic material: influence of hard segment content

A series of PCL-based shape memory polyurethanes was synthesized via bulk pre-polymerization. Their thermal, mechanical properties, shape memory properties, softening and hardening processes were investigated by the experimental approach and made comparison with a commercially available orthotic material. The cytotoxicity of the low-temperature thermoplastic polyurethane was tested. The results suggest that the soft segment phase of the shape memory polyurethanes has a melting transition at about 36–46°C, which makes them possible low-temperature thermoplastic materials. The hard segment phase has a two-fold effect on the shape memory polyurethane as a low-temperature thermoplastic orthotic material: increasing tensile mechanical strength at room temperature, which enables it to be used in circumstances where high tensile strength is required; and reducing low-temperature malleability and fixity ratio, which make it difficult to fabricate orthortic devices. To obtain a shape memory polyurethane with excellent low-temperature thermoplastic properties for orthopaedical surgical use, the hard segment content should not be above 22 wt%. At last, a prototype wrist orthosis was easily fabricated at 60°C with hand using a shape memory polyurethane with 16 wt% hard segment content. Cytotoxicity tests indicate that the wrist orthotic material is not cytotoxic.

Biological Evaluations of a Smart Shape Memory Fabric

A shape memory fiber was prepared and a corresponding shape memory fabric was fabricated by knitting using the prepared shape memory fiber. Both the fiber and fabric showed good shape memory properties. The prepared fiber had much higher mechanical strength than that of corresponding shape memory films due to molecular orientation caused by the spinning process. The biological evaluations of the prepared shape memory fabric were preliminarily assessed in terms of cytotoxicity, hemolysis, sensitization and dermal irritant. The test results show that the shape memory fabric is not cytotoxic, hemolytic, sensitive, or irritant. Due to the special format of shape memory fiber/fabric being more compatible with human bodies compared with shape memory films or bulks, the shape memory fiber/fabric may find broad application in biomedical areas such as artificial tendon, artificial cornea, hernia repair, artificial bone joints, orthodontics, scaffold material, and wound dressing.