Properties Of Shape Memory Polyurethane Research Articles

Investigation of the self-healing properties of shape memory polyurethane coatings with the ‘odd random phase multisine’ electrochemical impedance spectroscopy

The aim of this work is to study the physical self-healing properties of shape memory polyurethanes (SMPUs) with cerium ions on top of a pure aluminum substrate. To achieve this, the ‘odd random phase multisine’ electrochemical impedance spectroscopy (EIS) is used. The additional information given by this technique (stochastic noise, non-linear and non-stationary behavior of the sample during the measurement) has been useful to verify the quality of the measurement. Moreover, combined with a fitting algorithm weighted by the stochastic noise, these elements of information proved powerful in rejecting, accepting or improving electrical equivalent circuit models used to fit the impedance spectra. These SMPU consist of two parts: a soft matrix in caprolactone and a hard part in polyurethane. SMPU with 12, 30 and 41% of hard phase were investigated. The results showed that a physical self-healing can be observed for the coating with 12% of hard phase.

Thermomechanical properties of shape memory polymer subjected to tension in various conditions

Thermomechanical and functional properties of shape memory polyurethane are presented. A background of the polymer shape memory effects is described. Elastic modulus at various temperatures and the polyurethane parameters important for the practical applications, called shape fixity and shape recovery, are derived. Taking advantages from the high quality testing machine and infrared camera, mechanical characteristics and temperature changes of the shape memory polyurethane specimens subjected to tension test carried out in various conditions are clarified and analyzed. Stress-strain curves and the relevant temperature changes are recorded both in the elastic and the plastic ranges of deformation. A significant value of a thermoelastic effect is observed. Taking into account the obtained experimental data from the polyurethane tension tests performed at room temperature, followed by the heating above its glass transition temperature, the shape memory polyurethane properties are studied.

Synthesis and properties of shape memory polyurethane nanocomposites reinforced with poly(ɛ-caprolactone)-grafted carbon nanotubes

Nanocomposites of polyurethane (PU) and multi-walled carbon nanotubes (MWNTs) were prepared via in-situ polymerization of poly(ɛ-caprolactone)diol (PCL)-grafted-MWNTs, 4,4′-methylene bis(phenyl isocyanate), and 1,4-butanediol. The grafting of PCL onto MWNTs was confirmed by Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The nanocomposites showed more improved mechanical properties compared to conventional nanocomposites with the same MWNT loading. The thermo-responsive shape recovery as measured in a cyclic tensile test was observed to be approximately 80 % for in-situ nanocomposites, though it showed a reduced trend as the wt% of MWNTs increased. X-ray diffraction investigation also showed that the addition of MWNTs into the polyurethane increased the crystallinity. Scanning electron microscopy and TEM measurements showed better dispersion of MWNTs in the nanocomposites synthesized using in-situ method. Consequently, the presence of PCL-g-MWNTs made an important contribution to the enhancement of the mechanical and shape memory properties of polyurethane.

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.

Enhanced mechanical and shape memory properties of polyurethane block copolymers chain-extended by ethylene diamine

Effect on shape memory and mechanical properties of polyurethane (PU) copolymers by changing the chain extender from 1,4-butanediol (BD) to ethylenediamine (ED) was investigated. PU copolymers composed of the different ratio of hard and soft segment were prepared and characterized by IR, DSC, XRD, and UTM. Glass transition temperature of PU increased to room temperature range by adopting ED as a chain extender. The XRD peak pattern changed with hard segment content. ED type PU achieved the high mechanical properties at lower hard segment content than BD type PU. Especially, strain at break of ED type significantly improved compared to BD type. Shape recovery rates were similar for both types of PU, but ED type showed better shape retention rate than BD type. The reason for the differences between two types of PU is discussed in this paper.

Development of shape memory polyurethane fiber with complete shape recoverability

To illustrate the shape memory properties of shape memory polyurethane (SMPU) fiberand the difference of thermal/mechanical properties between SMPU fiber and other variousman-made fibers, series of shape memory polyurethane having various hard segmentcontent were synthesized with the pre-polymerization method and spun with the wetspinning process. Differential scanning calorimetry (DSC), dynamic mechanicalanalysis (DMA), and mechanical testing were conducted to study the particularthermal/mechanical properties of shape memory polyurethane fiber in comparison withother man-made fibers such as nylon6, polyester, Lycra and XLA. In addition, in thepreparation of shape memory polyurethane fiber, the effect of thermal setting temperaturewas systematically investigated by mechanical properties testing, DMA and cyclic tensiletesting, suggesting that the thermal setting temperature has a huge influence on themechanical properties and shape memory property due to the elimination of internal stress.Thermal setting with a higher temperature will give rise to a lower tensile modulus andtenacity and a higher elongation ratio at break. Through employing the optimal thermalsetting treatment, the complete heating responsive recovery in SMPU fiber can beachieved because of the counteracting effect of the irreversible strain and thermalshrinkage.

Structure and Mechanical Properties of Shape Memory Polyurethane Based on Hyperbranched Polyesters

Hyperbranched shape memory polyurethane (HB-SMPU) were prepared from 4,4’-diphenylmethane diisocyanate, poly (butylenes adipate) glycol, and hyperbranched polyester as chain extender via a two-step process. The morphology of the HB-SMPU films was investigated by the use of wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM), DSC and dynamic mechanical analysis (DMA). It was found that the PBAG soft segments in HB-SMPU with 15–35 wt. % of hard segments were in a crystalline state, however, the PBAG segments were in an amorphous state in the HB-SMPU with 40 wt. % hard segments. The increase of the hard segment content resulted in the decrease of the melt transition temperature of the HB-SMPU. The HB-SMPU with 25 wt. % of hard segment content possessed highest loss tangent. Heat of crystallization was dependent on the content of hard segment in the HB-SMPU. 96–98 wt. % shape recovery could be obtained for the HB-SMPU with 15–35 wt. % of hard segment. The content of hard segments in HB-SMPU was very important in determining their physical properties.