Temperature sensitive water vapour permeability and shape memory effect of polyurethane with crystalline reversible phase and hydrophilic segments

Polyurethanes based on poly(caprolactone) (PCL) diol, hexamethylene diisocyanate, 4,4′‐diphenylmethane diisocyanate and hexamethylene diamine were modified by hydrophilic segments, diol‐terminated poly(ethylene oxide) or dimethylol propionic acid (DMPA). Differential scanning calorimetry, dynamic mechanical tests, tensile tests, and measurement of water vapour permeability were carried out to characterize these polyurethanes. Temperature sensitive water vapour permeability, that is, the abrupt increase of water vapour permeability at the melting temperature of the PCL phase, was enhanced by modification with hydrophilic segments. Fatigue in shape memory effects was minimized by introducing some amount of DMPA units into the polyurethane chain. © 2000 Society of Chemical Industry     

Mechanical and shape‐memory properties of polyamide/maleated polyethylene/linear low‐density polyethylene blend

Novel polymer blends of polyamide and linear low‐density polyethylene with maleated polyethylene as compatibilizers were prepared in a modular intermeshing corotating twin‐screw extruder. Polymer blends with different contents of polyamide in polyethylene matrix were obtained. The mechanical properties were studied in terms of the tensile strength and elongation‐to‐break. The shape‐memory properties of the blended materials were characterized using three‐point bending test in a temperature‐controlled chamber. The results show that the incorporation of maleated polyethylene has a strong effect on the tensile properties and the morphology of the blends. The shape‐memory effect of blended materials is affected by polyamide weight fraction, and 60 wt % polyethylene, 20 wt % polyamide, and 20% maleated polyethylene have an acceptable performance. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal,mechanical, and shape‐memory properties of nanorubber‐toughened,epoxy‐based shape‐memory nanocomposites

Epoxy‐based shape‐memory polymers (ESMPs) are a type of the most promising engineering smart polymers. However, their inherent brittleness limits their applications. Existing modification approaches are either based on complicated chemical reactions or done at the cost of the thermal properties of the ESMPs. In this study, a simple approach was used to fabricate ESMPs with the aim of improving their overall properties by introducing crosslinked carboxylic nitrile–butadiene nanorubber (CNBNR) into the ESMP network. The results show that the toughness of the CNBNR–ESMP nanocomposites greatly improved at both room temperature and the glass‐transition temperature (T_g) over that of the pure ESMP. Meanwhile, the increase in the toughness did not negatively affect other macroscopic properties. The CNBNR–ESMP nanocomposites presented improved thermal properties with a T_g in a stable range around 100 °C, enhanced thermal stabilities, and superior shape‐memory performance in terms of the shape‐fixing ratio, shape‐recovery ratio, shape‐recovery time, and repeatability of shape‐memory cycles. The combined property improvements and the simplicity of the manufacturing process demonstrated that the CNBNR–ESMP nanocomposites are desirable candidates for large‐scale applications in the engineering field as smart structural materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45780.     

Morphology and water vapor permeability of temperature‐sensitive polyurethanes

A series of segmented polyurethanes (PUs) were prepared, in which five different polyols and hexamethylene diisocyanate were used as soft segments, and 4,4′‐diphenylmethane diisocyanate, hydrophilic segment poly (ethylene glycol) 200 (PEG 200), and chain extender 1,4‐butanediol were used as hard segment. Morphology of the PUs was investigated using differential scanning calorimetry, wide angle X‐ray diffraction, polarizing microscopy, and transmission electron microscopy. Water vapor permeability of the membranes as a function of temperature was tested accordingly. Results show that the presence of PEG200 interferes the crystallization of hard segment in these PUs, and at the same time, increases phase compatibility between soft and hard segment in the PET‐PU. It leads to a lower crystal melting temperature and degree of crystallinity of soft segment in the segmented PU than those of pure polyols, and no crystallization existing in hard segment. A morphological model is proposed, that is, aggregated soft‐segment‐rich domains can be observed clearly in the PUs with high crystallinity in soft segment, while identifiable hard domains are well‐distributed in the soft segment domains in the PU with low crystallinity. Within the temperature range of crystal melting, water vapor permeability of the PU membranes increases significantly with increase of temperature. Such temperature‐sensitive property is triggered by crystal melting of soft segment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Water vapor permeability of the polyurethane/TiO2 nanohybrid membrane with temperature sensitivity

A novel thermal‐sensitive polyurethane (TSPU)/TiO₂ nanohybrid membrane was successfully prepared via in situ process and used for controllable water vapor permeation. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) were employed to reveal the nanohybrid mechanism between TSPU and TiO₂ and the thermal sensitive characteristics of TSPU/TiO₂ nanohybrid membranes. FTIR analysis demonstrates that the highly active nano‐TiO₂ particles produced by the hydrolysis of the nanoprecursor (tetrabutyl titanate) have reacted with the active groups of TSPU. And some new peaks assigned to the Ti? O? C, Ti? C, and Ti? O? Ti bonds occur in the FTIR spectra of TSPU/TiO₂ nanohybrid membrane; these chemical bonds are believed to contribute to the higher mechanical properties of nanohybrid samples. DSC study indicates that nanohybridization does not disrupt the intrinsic phase‐separated structures and thermal‐sensitive characteristics of pure TSPU, the difference in behavior is the phase transition temperature (defined as switch temperature, T_s) of the reversible phase shifting from 50.1 to 53.4°C. SEM analysis shows that the nano‐TiO₂ particles are evenly distributed in TSPU and the size of the nano‐TiO₂ is lower than 100 nm. In addition, the water vapor permeability (WVP) of nanohybrid membrane is found to depend on the TiO₂ content. To be specified, when TiO₂ content is lower than 5.0 wt %, the nanohybrid samples show lower WVP at low temperatures and higher WVP at high temperatures than pure TSPU. Especially, when the temperature exceeds the T_s, for example from 50 to 60°C, the WVP of pure TSPU show improvement by 114%, whereas the WVP of the nanohybrid TSPU with 5.0 wt % TiO₂ content shows improvement by 145%, the latter shows more sensitivity to thermal stimuli. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Wet‐driven shape‐memory behaviors and thermal adaptability of cotton knitted fabrics containing crosslinked poly(ethylene glycol) moieties

Cotton knitted fabrics were treated with poly(ethylene glycol) (PEG) in the presence of polyhydric alcohol etherified dimethylol dihydroxy ethylene urea as the crosslinker and magnesium chloride hexahydrate as the catalyst. In wet–dry cycles, the fabrics treated with 30% PEG1500 in the presence of 15% crosslinker and 3% catalyst showed obvious wet‐driven shape‐memory behaviors in terms of a 12% shrinkage rate in the wet state and a 80% shrinkage‐recovery rate in the dry state. The results of weight gain, morphological structures, Fourier transform infrared spectra, and X‐ray diffraction pattern tests confirmed PEG deposits on the surface of the treated fabrics, demonstrated the crosslinking of cotton cellulose with PEG and crosslinker, and also explained the wet‐driven shape‐memory mechanism. The results from differential scanning calorimetry show that the treated fabrics with wet‐driven shape‐memory behaviors had a phase‐change enthalpy and heat‐storage capacity. The crosslinking of cotton cellulose with PEG had a strong influence on the mechanical performance and air permeability of the cotton knitted fabrics. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43473.     

Dependency of the shape memory properties of a polyurethane upon thermomechanical cyclic conditions

The relationship between the shape memory properties and thermomechanical cyclic conditions was investigated with a type of shape memory polyurethane (SMPU). The thermal and dynamic mechanical properties of the polyurethane were examined by using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). It was found that the SMPU exhibited good shape memory effects (SMEs) at deformation temperatures ranging from T_g to T_g + 25 °C. The strain recovery ratios increased with the increase of deformation speed and with the decrease in maximum strain. The recovery ratios also increased with increasing fixing speed. Therefore, in practical applications, in order to obtain better SMEs, the SMPU should be cooled to its frozen state as soon as possible after being deformed at a high temperature. The ‘fixity’ dramatically increased with the decrease in fixing temperature. To obtain optimal SMEs, the polymer has to be reheated up to the temperature at which the polymer deformed. In addition, the recovery ratios of the SMPU could increase slightly with the increase of recovery time. Copyright © 2004 Society of Chemical Industry     

Mechanical and shape‐memory behavior of shape‐memory polymer composites with hybrid fillers

Shape‐memory polymer (SMP) materials have several drawbacks such as low strength, low stiffness and natural insulating tendencies, which seriously limit their development and applications. Much effort has been made to improve their mechanical properties by adding particle or fiber fillers to reinforce the polymer matrix. However, this often leads to the mechanical properties being enhanced slightly, but the shape‐memory effect of reinforced SMP composites being drastically reduced. The experimental results reported here suggested that the mechanical resistive loading and thermal conductivity of a composite (with hybrid filler content of 7.0 wt%) were improved by 160 and 200%, respectively, in comparison with those of pure bulk SMP. Also, the glass transition temperature of the composite was enhanced to 57.28 °C from the 46.38 °C of a composite filled with 5.5 wt% hybrid filler, as determined from differential scanning calorimetry measurements. Finally, the temperature distribution and recovery behavior of specimens were recorded with infrared video in a recovery test, where a 28 V direct current circuit was applied. The effectiveness of carbon black and short carbon fibers being incorporated into a SMP with shape recovery activated by electricity has been demonstrated. These hybrid fillers were explored to improve the mechanical and conductive properties of bulk SMP. Copyright © 2010 Society of Chemical Industry     

Bio‐based thermoplastic polyurethane and polyamide 11 bioalloys with excellent shape memory behavior

Bio‐based blends of commercially available polyester based bio thermoplastic polyurethane (TPU) and castor oil based polyamide 11 (PA11) of different ratios are prepared by melt processing. The blends properties such as shape memory behavior through unconstrained and constrained recovery, interfacial interaction, morphology, dynamic mechanical, rheological, and mechanical behavior are studied. A strong interface between the two polymeric phases due to hydrogen bonding observed through morphology indicates that TPU and PA11 are well compatible. The complex viscosity of blends ranges between that of neat PA11 and TPU. Thermal analysis shows that higher the TPU content lower the melting point (T_m ) corresponding to PA11 and the crystallization temperature (T_c ) remains unaltered. Adding TPU to PA11 ductility and impact strength of the blends increases significantly with the small reduction in their tensile strength. Shape memory behavior investigation reveals that, blends recover almost 95% of the applied deformation when heated at zero load and they recovered a stress of 1.8–3.2 MPa in constrained recovery during three consecutive thermomechanical cycles. The reported results on bioalloys promotes the usage in multidisciplinary field of intelligent devices, such as ergonomic grips and sports shields. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44794.     

Effects of superfine silk protein powders on mechanical properties of wet‐spun polyurethane fibers

Mechanical measurements were employed to investigate the effects of three types of superfine silk protein powder on tensile strength, elongation, and elasticity of wet‐spun Pellethane^® 2363‐80AE polyurethane (PU) fiber. These superfine silk protein powders included undegummed silk (with both native silk fibroin and sericin, water insoluble), native silk fibroin (with native silk fibroin only, water insoluble), and regenerated silk fibroin (with regenerated silk fibroin only, water soluble) in powder form. Experimental data derived from the mechanical measurements illustrated that the miscibility between the PU and regenerated silk fibroin were superior to that between PU and the other two silk proteins. This may be attributed to the similar chemical structure and microphase separation of PU and regenerated silk fibroin with lower molecular weight than native silk fibroin. This preliminary work may provide some information for biomimetic processing of silk‐inspired PU biofibers, which combine elasticity of synthetic PU with biofunction of natural silk fibroin for special biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improved mechanical properties of shape‐memory polyurethane block copolymers through the control of the soft‐segment arrangement

High‐performance shape‐memory polyurethane block copolymers, prepared with two types of poly(tetramethylene glycol) (PTMG) used as soft segments, were investigated for their mechanical properties. Copolymers with a random or block soft‐segment arrangement had higher stresses at break and elongations at break than those with only one kind of PTMG. Random copolymers with fewer interchain interactions showed higher elongation than block copolymers. All the copolymers had shape‐recovery ratios higher than 80%. In dynamic mechanical testing, the glass‐transition behavior clearly depended on the soft‐segment arrangement: random copolymers had only one glass‐transition peak, whereas block copolymers showed two separate glass‐transition peaks. Overall, the control of the soft‐segment arrangement plays a vital role in the development of high‐performance shape‐memory polyurethane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2410–2415, 2004     

A simulation method to analyze chemo‐mechanical behavior of swelling‐induced shape‐memory polymer in response to solvent

A network of thermally responsive shape‐memory polymers (SMPs) could imbibe a quantity of solvent molecules to swell, and subsequently induces a chemical potential change in polymer. When an equilibrium is reached between the mechanical load and the chemical potential of polymer network and solvent, the SMP polymer usually swells with a field of inhomogeneous and anisotropic deformation, which is considered to be equivalent to a hyperelastic field. We implement this theory in the free‐energy function equation, and analyze examples of swelling‐induced deformation and shape recovery behavior. This work may provide a powerful tool to study complex swelling‐induced shape‐memory behavior of SMPs in response to the immersing solvents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crosslinked polyurethanes with shape memory properties

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     

Biodegradable polyurethane based on random copolymer of L‐lactide and ϵ‐caprolactone and its shape‐memory property

A series of biodegradable polyurethanes (PUs) are synthesized from the copolymer diols prepared from L ‐lactide and ε‐caprolactone (CL), 2,4‐toluene diisocyanate, and 1,4‐butanediol. Their thermal and mechanical properties are characterized via FTIR, DSC, and tensile tests. Their T_gs are in the range of 28–53°C. They have high modulus, tensile strength, and elongation ratio at break. With increasing CL content, the PU changes from semicrystalline to completely amorphous. Thermal mechanical analysis is used to determine their shape‐memory property. When they are deformed and fixed at proper temperatures, their shape‐recovery is almost complete for a tensile elongation of 150% or a compression of 2‐folds. By changing the content of CL and the hard‐to‐soft ratio, their T_gs and their shape‐recovery temperature can be adjusted. Therefore, they may find wide applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4182–4187, 2007     

Mechanically strong shape memory polyurethane for water vapour permeable membranes

Water vapour permeable polymeric thin films possess significant importance in miscellaneous applications such as packaging, medical devices, controlled‐release systems, electronics and biosensors. In this work, a series of shape memory polyurethanes (SMPUs) were synthesized by a two‐step pre‐polymerization technique with variations in hard to soft segments and molecular weight of macroglycol. DSC, Fourier transform infrared spectra, dynamic TGA and tensile testing were carried out to characterize and evaluate the properties of these synthesized SMPUs. The effect of the soft segment and the molecular weight of macroglycol on the thermal properties, mechanical properties and water vapour permeability of the synthesized SMPUs were investigated to achieve a good water vapour permeable membrane. We found that the synthesized SMPUs demonstrated a good water vapour transmission rate of over 1460 g m^?2 day^–1 as well as robust mechanical properties with tensile strength 19.8 MPa indicating a promising permeable polymeric thin film for many potential applications, especially as protective clothing. © 2018 Society of Chemical Industry     

Microstructural and mechanical property evolutions of shape memory polyurethane during a thermodynamic cycle

To better understand the shape memory behaviors of synthesized shape memory polyurethane (SMPU) sealant with a tailored transition temperature (T_t) for concrete pavement joints, the thermal and dynamic mechanical properties of SMPU were first characterized to determine the shape memory switching temperature of SMPU. Then the microstructural and mechanical property evolutions of SMPU in the original, programmed, and recovered states during a five‐step thermodynamic cycle were discussed, respectively. The results indicate that the tailored T_t of prepared SMPU can be used as the shape memory switching temperature to match its working temperature. Further, the programming causes the phase separation in SMPU, leading to an obvious anisotropy. The SMPU has satisfactory shape memory performance. The orientation of molecular chains in soft segments is confirmed along the stretching direction. The oriented molecular chains can restore to the naturally curled state during the free recovery. Finally, the programming improves the mechanical properties of SMPU. The recovered SMPU shows a slight decrease in mechanical properties because of the partially impaired crystal structures and broken molecular segments during the programming and recovery. It is concluded that the synthesized SMPU with the specially tailored T_t is suitable to use as a sealant of concrete pavement joints. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45703.     

交联型与线形水性聚氨酯的形状记忆性能比较

由聚酯多元醇、2,4–甲苯二异氰酸酯、二羟甲基丙酸等合成了水性聚氨酯乳液,对乳液性能进行了研究;对制得的聚氨酯胶膜进行了红外分析、DSC测试和形状记忆性能测试;用丙三醇和三羟甲基丙烷作为扩链制得的交联水性聚氨酯与用1,4–丁二醇制得的线形水性聚氨酯进行了性能比较,结果表明:不同扩链剂对水性聚氨酯的性能有一定的影响,与线形水性聚氨酯相比,交联型水性聚氨酯具有较好的形状记忆性能,形状恢复率可达92%～97%。     

智能防水透湿聚氨酯研究进展

简要介绍了实现形状记忆聚氨酯(SMPU)的智能透湿机理,综述了SMPU在智能透湿性方面的研究进展及智能防水透湿膜和织物研究中存在的问题,提出了研究开发具有创新功能的智能防水透湿织物是未来纺织工业发展的趋势。     

TPU/PLA nanocomposites with improved mechanical and shape memory properties fabricated via phase morphology control and incorporation of multi-walled carbon nanotubes nanofillers

Shape memory polymer nanocomposites based on thermoplastic polyurethane (TPU)/polylactic acid (PLA) blends filled with pristine multi-walled carbon nanotubes (MWCNTs) and modified MWCNTs─COOH were fabricated by direct melt blending technique and investigated for its morphology, mechanical, thermal, electrical, and shape memory properties. Morphological characterizations by using transmission electron microscope (TEM) and field emission scanning electron microscope (FESEM) revealed better dispersion of MWCNTs─COOH in the polymer blend, which is attributed to the improved interfacial interactions between the polymer blends and MWCNTs-COOH. Loading of the MWCNTs-COOH in the TPU/PLA blends resulted in the significant improvements in the mechanical properties such as tensile strength and elastic modulus and these effects are more pronounced on increasing the MWCNTs─COOH loading amount, when compared to the pristine MWCNTs filled system. Thermal analysis showed that the glass transition temperature of the blends increases slightly with increasing loading of both pristine and modified MWCNTs in the system. The resistance of nanocomposites decreased from 2 × 10¹² Ω to 3.2 × 10¹⁰ Ω after adding 3% MWCNTs─COOH. The shape memory performance tests showed that the enhancement of shape recovery by 252% could be achieved at 3% MWCNTs loading, when compared to that of TPU/PLA blends.     

Thermal induced shape‐memory and self‐healing of segmented polyurethane containing diselenide bonds

Herein, we synthesized a series of polyurethane copolymers (PUs) with poly(1,4‐butylene adipate) glycol as soft segment and 2,4‐toluene diisocyanate as well as extenders including 1,4‐butanediol and di(1‐hydroxyethylene) diselenide as hard segment. The chemical structure, thermal property, crystallization behavior, shape memory, and self‐healing performances of the PUs were systematically characterized by a series of experiments. It was found that the PU2 containing a higher diselenide component (～33 mol %) exhibited both shape memory and self‐healing behaviors under a moderate temperature (～57 °C). Meanwhile, the PUs showed a good repeatability of shape memory function, and their fixity and recovery ratios were all above 90%. Additionally, the dynamic exchangeable feature of diselenide bonding endues the PUs chains with an acceptable reprocessability and self‐healing performances, and the PU2 sample could be healed for five times by thermal treatment with the healing efficiencies above 70%. This work provides a heuristic perspective for the development of shape memory and self‐healing materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46326.