Synthesis of shape memory polyurethane/clay nanocomposites and analysis of shape memory,thermal, and mechanical properties

In this study, shape memory polyurethane/clay nanocomposites were synthesized by using two‐step in situ polymerization. The effects of nanoparticle content on mechanical, thermal, and shape memory properties were studied. Soft and hard segments of polyurethanes were based on polycaprolactone (PCL) diol and 4,4′‐diphenylmethane diisocyanate/1,4‐butanediol molar ratio with 70/30, respectively. The differential scanning calorimetry, tensile test, dynamic mechanical thermal analysis, parallel plate rheometer, and X‐ray diffraction were used to evaluate the properties of the nanocomposites. To evaluate shape memory properties, a tensile device equipped with a thermal chamber was used. Glass transition temperature of soft segments has been increased by nanoclay loading. Addition of nanoclay to polyurethane matrix caused to disrupt ordering in hard domains, decrease in elongation and tensile strength. The results show that crystallinity of soft segments and dispersion of nanoparticles affect on the mechanical properties and shape memory behavior of nanocomposites, distinctly. Nanocomposite containing 1 wt% shows the best shape memory properties. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

The influence of heat treatment on the properties of shape memory fibers. II. Tensile properties,dimensional stability,recovery force relaxation,and thermomechanical cyclic properties

Shape memory fibers (SMFs) were prepared via a melt spinning process. The fibers were subject to different heat treatments to eliminate internal stress and structure deficiency caused during the melt spinning process. The influences of heat treatments on the SMF thermal properties, molecular orientation, tensile properties, dimensional stability, recovery force relaxation, and thermomechanical cyclic properties were studied. It was found that the heat treatments increased soft segment crystallinity and phase separation while decreased molecular orientation. The low‐temperature heat treatment increased the breaking elongation, shape fixity ratios, and decreased boiling water shrinkage while shape recovery ratios were decreased. High‐temperature treatment increased both the shape recovery ratios, fixity ratios, recovery stress stability and at the same time decreasing the fiber mechanical strength. The results from differential scanning calorimetry, molecular orientation apparatus, and cyclic tensile testing were used to illustrate the mechanism governing the mechanical properties and shape memory effect. To obtain comprehensive outstanding properties, the SMF is expected to be treated at a high temperature because of the hard segment high glass transition temperature. Unfortunately, the heat treatment could not be conducted at a too high temperature because the SMF became too tacky and soft due to the melting of the soft segment phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Evaluation of nanoparticulate fillers for development of shape memory polyurethane nanocomposites

The effects of nano-size fillers on shape memory (SM) properties of polyurethane (PU) nanocomposites were evaluated. Organoclay, carbon nanofiber (CNF), silicon carbide (SiC), and carbon black (CB) were selected as the fillers in an attempt to reinforce the PU and to obtain significantly increased shape recovery stress. The shape memory PU was synthesized from diphenylmethane diisocyanate, 1,4-butanediol, and poly(caprolactone)diol, the latter with a molecular weight of 4000 g/mol. The composites were prepared by melt mixing of extended chain PU with the fillers. The shape memory behavior was triggered by heating the specimen above the melting point of the crystalline soft segment. Our results indicate that exfoliated organoclay significantly augments SM performance, while CNF and SiC diminish it by interfering with crystallization of the soft segment. CB destroys the shape memory properties beyond a certain loading. Better SM performance with organoclay can be attributed to mechanical reinforcement without much interference with the soft segment crystallinity. The reduction of soft segment crystallinity in the presence of CNF and SiC was analyzed. It was found that the extent of crystallinity, as well as the crystallization temperature, was significantly reduced in the presence of these fillers.     

Influence of heat treatment on the properties of shape memory fibers. I. Crystallinity,hydrogen bonding,and shape memory effect

Shape memory fibers (SMFs) were prepared via melt spinning. The fibers underwent different heat treatments to eliminate internal stress and structure deficiency caused during melt spinning. The influences of heat treatments on the SMF crystallinity, molecular orientation, hydrogen bonding, and shape memory behavior were studied. It was found with increasing heat‐treatment temperature, the soft segment crystallinity, crystallite dimension, and microphase separation increased, and the hydrogen bonding in the hard segment phase increased. Low temperature heat treatments decreased the shape recovery ratios while increasing the shape fixity ratios as a result of internal stress releasing and molecules disorientation. High temperature heat treatments increased the hard segment stability. Increasing heat‐treatment temperature resulted in the improvement of both the shape recovery and fixity, because it promoted the phase separation. The results from DSC, DMA, XRD, and FTIR were used to illustrate the mechanism governing these properties difference. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

双重激发聚氨酯形状记忆泡沫制备与性能研究

以聚乙二醇、聚丙交酯-co-己内酯二醇(PCLA)、液化MDI和水为主要原料,制备了具有可双重激发形状记忆性能的聚氨酯泡沫.通过红外光谱、差示扫描量热、形状记忆、质量损失率和拉伸强度测试,研究了形状记忆聚氨酯泡沫(SMP F)的组成、结晶、形状记忆和在水溶液中的降解性能.结果表明:SMP F结晶熔融温度为41～45℃,...     

Shape memory segmented polyurethanes: dependence of behavior on nanocellulose addition and testing conditions

The response of synthesized shape memory segmented polyurethanes (PUs) was affected by the addition of cellulose nanocrystals, as well as by the various conditions selected to carry out thermomechanical cyclic tests. The PUs were synthesized from an α‐hydro‐ω‐hydroxy‐poly(ethylene oxide), tolylene‐2,4‐diisocyanate and 1,4‐butanediol as chain extender. Nanocomposites were prepared by mixing a suspension of cellulose nanocrystals in N,N‐dimethylformamide with the thermoplastic PU dissolved in the same organic solvent. The thermal properties of the neat PU and resulting composites were examined using differential scanning calorimetry. It was found that cellulose addition increases the PU soft segment melting and crystallization temperatures and the degree of crystallinity of this phase. Shape memory behavior was studied using cyclic thermal tensile tests. Both neat PU and composites exhibit shape memory properties, with fixity and recovery values that depend on heating temperature, imposed deformation, deformation rate and nanofiller addition. Copyright © 2011 Society of Chemical Industry     

Studies on thermally stimulated shape memory effect of segmented polyurethanes

The shape memory behavior of a series of polycaprolactone/methane diisocyanate/butanediol (PCL/MDI/BDO) segmented polyurethanes of different composition was studied. The molecular weight of PCL diols was in the range of 1600–7000, and the hard segment content varied from 7.8 to 27% by weight. Film specimens for shape memory measurements were prepared by drawing at temperatures above the melting temperature of the soft segment crystals and subsequent quick cooling to room temperature under constrained conditions. The shape memory process was observed and recorded in a heating process. Parameters describing the recovery temperature, ability, and speed were used to study the influence of structure and processing conditions on the shape memory behavior of the sample. It was found that the high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical crosslinks in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented copolymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals. The final recovery rate and the recovery speed are mainly related to the stability of the hard segment domains under stretching and are dependent on the hard segment content of the copolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1511–1516, 1997     

聚已内酯/聚氨酯共聚热致形状记忆材料的合成与表征

以聚己内酯（PCL）为软段,甲苯2,4-二异氰酸酯（TDI）为硬段,通过预聚合和扩链反应制得含结晶软段的聚氨酯形状记忆材料（SMPU）,通过差热分析、红外分析及X射线衍射对其微结构进行了表征。结果表明,随着硬段含量的增加,SMPU的结晶熔融温度上升,结晶度下降,形状回复率减小,形状固定率始终保持在98 %左右;随着PCL相对分子质量的提高,SMPU的结晶熔融温度减小,结晶度增大,回复响应温度逐渐降低。     

A smart hollow filament with thermal sensitive internal diameter

In this work, a thermoplastic shape memory polyurethane was prepared via melt polymerization and a corresponding shape memory hollow fiber was fabricated via melt spinning. The fiber mechanical properties, especially shape memory effect, were characterized by static tensile, thermo‐mechanical cyclic tensile testing. The hollow fiber switching temperature was the melting transition temperature of the soft segment phase at about 41°C. The tenacity of the hollow fiber was about 1.14 cN/dtex, and breaking elongation was 682%. The shape fixity ratio was above 87% and the recovery ratio was above 89%. The internal diameter of the hollow fiber could be noticeably changed and the deformed fiber cross‐section could be well fixed. Once heated above the soft segment phase melting transition temperature, the hollow fiber internal hole recovered to its original diameter. The results from differential scanning calorimetry, X‐ray diffraction, and dynamic mechanical analysis were used to illustrate the mechanism governing the mechanical properties and shape memory effect especially. Due to the changes of the hollow fiber and the internal diameter affect of the physical properties of the prepared products, this fiber may be used in smart textiles for thermal management, or as stuffing of pillows and mattresses, which can adjust to body contours. Furthermore, the findings suggest that this kind of hollow fiber with thermal sensitive internal diameter could be used in smart filtration, drug‐controlled release, and liquid transportation in vivo. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of Graphene Oxide on Thermally Induced Shape Memory Behavior of PLA/TPU Blends: Correlation with Morphology,Creep Behavior,Crystallinity, and Dynamic Mechanical Properties

In this study, shape memory is thermally induced in a series of graphene oxide (GO) filled poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) blends, prepared via melt mixing process, and their shape recovery and shape fixity are measured, and the results are correlated with morphology, dynamic mechanical properties, crystallinity and creep recovery behavior. Morphological analysis by scanning and transmission electron microscopy reveals that the blends are immiscible, and GO platelets are mainly localized in the TPU phase of the blends, which lead to smaller and more elongated TPU droplets with improved interfacial adhesion being responsible for the improved shape recovery performance compared to the unfilled blend. A systematic enhancement found in storage and Young's modulus, tensile strength, creep resistance and creep recovery, and cold crystallinity as a result of GO inclusion are in agreement with the improved shape recovery, shape fixity and overall shape memory performance of the filled systems. The developed PLA/TPU/GO nanocomposites with highly improved mechanical properties can be utilized as a new class of environmentally friendly shape memory materials for a broad range of applications.     

Carbonaceous fillers for shape memory actuation of polyurethane composites by resistive heating

The effectiveness of carbonaceous, electrically conductive fillers in shape memory actuation of polyurethane composites by resistive heating was evaluated. Specifically, the dependence of electrical resistivity on specimen temperature and imposed tensile strains encountered in shape memory test cycles was determined for shape memory polyurethane (SMPU) composites of carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), and carbon black (CB). The SMPU composites with crystalline soft segments were synthesized from diphenylmethane di-isocyanate, 1,4-butanediol, and poly(caprolactone)diol in a low-shear chaotic mixer and in an internal mixer. The materials synthesized in the chaotic mixer showed higher soft segment crystallinity and lower electrical percolation threshold. A reduction in soft segment crystallinity was observed in the presence of CNF and ox-CNF; the reduction was smaller in the case of ox-CNF. Only the composites of CB showed pronounced positive temperature coefficient (PTC) effects. The observed PTC effects bore a close relationship with non-linear thermal expansion during heating. The composites of CNF and ox-CNF did not show PTC effects due to low levels of soft segment crystallinity. The resistivity of composites of CB increased by several orders of magnitude with imposed tensile strain while composites of CNF and ox-CNF showed weak dependence on strain.     

Characterization of nanocellulose‐ reinforced shape memory polyurethanes

BACKGROUND: Shape memory polymers are capable of fixing a transient shape and of recovering their original dimensions by the application of an external stimulus. Their major drawback is their low stiffness compared to smart materials based on metals and ceramics. To overcome this disadvantage, nanocellulose was utilized as reinforcement. RESULTS: Composites were prepared by casting stable nanocellulose/segmented polyurethane suspensions. The heat of melting of the polyurethane soft segment phase increased on cellulose addition. Composites showed higher tensile modulus and strength than unfilled films (53% modulus increase at 1 wt% nanocellulose), with higher elongation at break. Creep deformation decreased as cellulose concentration increased (36% decrease in 60‐minute creep by addition of 1 wt% nanocellulose). The nanocomposites displayed shape memory properties equivalent to those of the neat polyurethane, with recoveries of the order of 95% (referred to second and further cycles). CONCLUSIONS: It is possible to markedly improve the rigidity of shape memory polymers by adding small amounts of well‐dispersed nanocellulose. However, this improvement did not have substantial effects on the material shape fixity or recovery. Shape memory behavior seems to continue to be controlled by the polymer properties. Copyright © 2007 Society of Chemical Industry     

Enhanced shape memory effect of poly(L-lactide-co-ε-caprolactone) biodegradable copolymer reinforced with functionalized MWCNTs

Data from comprehensive thermomechanical tests of poly(L-lactide-co-ε-caprolactone) biodegradable shape memory polymer (SMP) reinforced with pristine and functionalized multiwalled carbon nanotubes (MWCNTs) are reported. The SMP specimens tested up to 500% strain and between 25 °C and 70 °C temperatures. The incorporation of functionalized MWCNTs leads to the best overall reinforcing effect in tensile modulus, yield stress, tensile strength and elongation at failure. Thermo mechanical experiments resulted that the functionalized MWCNTs increased the glass transition range of composites and changed the melting point of composites slightly. The crystallinity of composites was increased with increment of MWCNTs in composites. The shape fixity and shape recovery of composites increased slightly, while the recovery stress increased 46%. It is found that the functionalized MWCNTs prepare an effective physical cross linking and switching segments in polymer composites.     

Synthesis and characterization of poly(carbonate urethane) networks with shape‐memory properties

In this study, a series of shape‐memory polyurethanes were prepared from polycarbonate diol (PCDL) with a molecular weight of 2000, trimethylol propane, and isophorone diisocyanate (IPDI). The properties of crosslinked poly(carbonate urethane) (PCU) networks with various compositions were investigated. The chemical structures and thermal properties were determined with Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. FTIR analysis indicated that PCU had the structures of IPDI and PCDL and the amido formyl ester in polyurethanes. The gel content of PCU showed that PCU could be effectively formed as crosslinked polyurethane networks. The glass‐transition temperatures of the PCU networks increased slightly with decreasing soft‐segment content in the networks. The values of Young's modulus in the networks at 25°C increased with decreasing soft‐segment content, whereas the tensile stress and breaking elongation decreased significantly. PCU showed shape‐memory effects with a high strain fixity rate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Composites of carbon nanofibers and thermoplastic polyurethanes with shape‐memory properties prepared by chaotic mixing

Composites of carbon nanofibers (CNFs), oxidized carbon nanofibers (ox‐CNFs), and shape‐memory thermoplastic polyurethane (TPU) were prepared in a chaotic mixer and their shape‐memory properties evaluated. The polymer was synthesized from 4,4′‐diphenylmethane diisocyanate, 1,4‐butanediol chain extender, and semicrystalline poly(ε‐caprolactone) diol soft segments. The shape‐memory action was triggered by both conductive and resistive heating. It was found that soft segment crystallinity and mechanical reinforcement by nanofibers produced competing effects on shape‐memory properties. A large reduction in soft segment crystallinity in the presence of CNF and stronger mechanical reinforcement by well‐dispersed ox‐CNF determined the shape‐memory properties of the respective composites. It was found that the maximum shape recovery force, respectively, 3 and 4 MPa, was obtained in the cases of 5 and 1 wt% CNF and ox‐CNF, respectively, compared with ～1.8 MPa for unfilled TPU. The degree of soft segment and hard segment phase separation and thermal stability of the composites were analyzed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.     

Vegetable Oil-Based Hyperbranched Thermosetting Polyurethane/Clay Nanocomposites

The highly branched polyurethanes and vegetable oil-based polymer nanocomposites have been showing fruitful advantages across a spectrum of potential field of applications. Mesua ferrea L. seed oil-based hyperbranched polyurethane (HBPU)/clay nanocomposites were prepared at different dose levels by in situ polymerization technique. The performances of epoxy-cured thermosetting nanocomposites are reported for the first time. The partially exfoliated structure of clay layers was confirmed by XRD and TEM. FTIR spectra indicate the presence of H bonding between nanoclay and the polymer matrix. The present investigation outlines the significant improvement of tensile strength, scratch hardness, thermostability, water vapor permeability, and adhesive strength without much influencing impact resistance, bending, and elongation at break of the nanocomposites compared to pristine HBPU thermoset. An increment of two times the tensile strength, 6 °C of melting point, and 111 °C of thermo-stability were achieved by the formation of nanocomposites. An excellent shape recovery of about 96–99% was observed for the nanocomposites. Thus, the formation of partially exfoliated clay/vegetable oil-based hyperbranched polyurethane nanocomposites significantly improved the performance.     

A study of structure and tensile properties of polyamide 12/clay nanocomposites

The nanocomposites are multiphase materials where at least one phase is in nanoscale, less than 100 nm, whereby a higher specific interfacial area is achieved. Due to their characteristic properties, the nanocomposites are nowadays being increasingly used for the engineering applications, and certainly will have a significant role in the materials production in the future. An important class of nanocomposite materials are polymer layered silicates, in which the layered filler (mostly modified natural clay minerals) is dispersed in the polymer matrix. Many of parameters (i.e., type of polymer matrix, type and amount of nanofiller, and a number of process parameters as melting temperature, screw speed, number and shape of mixing screws, etc) affect properties of nanocomposites. As part of the paper, the samples of PA12/nanoclay nanocomposite mixture were made by adjusting various parameters (content of nanoclay, the screw rotation frequency and mixture temperature). Afterward, the tensile properties of obtained specimens were analysed. The mathematical models that show dependence of tensile properties on the mixture parameters were obtained as the result of analysis. POLYM. COMPOS., 37:684–691, 2016. © 2014 Society of Plastics Engineers     

Development of shape memory polyurethane based on polyethylene glycol and liquefied 4,4′‐diphenylmethane diisocyanate using a bulk method for biomedical applications

In this study, a series of shape memory polyurethanes (SMPUs) were synthesized successfully by the bulk polymerization method from liquefied 4,4′‐diphenylmethane diisocyanate (L‐MDI), 1,4‐butanediol (BDO) and polyethylene glycol (PEG). The influence of the hard segment content (HSC) on the structure, morphology, properties and biocompatibility of PEG based SMPUs (PEGSMPUs) was carefully investigated. The results show that a microphase separation structure composed of a semicrystalline soft phase and an amorphous hard phase is formed in the PEG6000/L‐MDI/BDO system. Crystallization of the PEG soft segment is influenced by the hard segments. The PEG semicrystalline soft phase serves as a reversible phase while the L‐MDI?BDO hard segment acts as physical netpoints. Finally, a cyclic tensile test shows that all PEGSMPUs have good shape recovery (e.g. above 80%), whereas good shape fixity can only be achieved when the HSC is less than 35 wt%. The Cell Counting Kit 8 assay also demonstrates that only PEGSMPUs containing less than 40 wt% HSC have low cytotoxicity. It is thus concluded that PEGSMPUs bearing both good shape memory effects and good biocompatibility can be used as shape memory materials for biomedical applications when the HSC is less than 35 wt%. © 2014 Society of Chemical Industry     

The role of branching architecture in shape memory semi-IPNs: Shape memory effect and tube model analysis

The impact of branching architecture of one continuous uncrosslinked phase on properties of classic shape memory semi-interpenetrating polymer networks (semi-IPNs) was explored. Crosslinked poly (methyl methacrylate) (PMMA)/star-shaped polyethylene glycol (PEG) (PMMA/SPEG) semi-IPNs and PMMA/linear PEG (PMMA/LPEG) semi-IPNs were synthesized with the same PEG content. Mechanical properties, phase structure, thermal properties, dynamic mechanical properties, and shape memory properties of these two semi-IPNs systems were compared. Due to the better compatibility of SPEG in the PMMA network, which was derived from little crystallization compared with PMMA/LPEG semi-IPNs, PMMA/SPEG semi-IPNs exhibited a combination of large tensile strength and high elongation at break. PMMA/SPEG semi-IPNs, which had little crystallization exhibited superior shape recovery versus PMMA/LPEG semi-IPNs, which had more crystallization. Moreover, the higher the crystallinity in PMMA/PEG semi-IPNs was the worse long-term temporary shape retention. Based on tube model theory, the high shape recovery capacity of PMMA/SPEG semi-IPNs is mainly ascribed to the retraction of free PEG arms, which is entropically favorable and thermally activated due to the fluctuations of the path length. This result is supported by stress relaxation analysis and the influence of long shape fixity time on shape fixity ratio for these two systems.     

固相法制备有机黏土改性聚丙烯

采用固相法对黏土进行有机化插层改性,制备出有机黏土;通过熔融插层法制备聚丙烯/有机黏土纳米复合材料。X射线衍射分析表明,固相法改性黏土可以与聚丙烯形成纳米复合材料。利用DSC研究了纳米复合材料的结晶和熔融过程,结果表明:聚丙烯/有机黏土纳米复合材料的结晶温度提高,熔融过程、熔点及结晶度没有明显变化。力学性能测试结果表明:有机黏土含量在3%～5%范围内,纳米复合材料的力学性能最佳。