Mechanical and shape memory performance of shape memory polyurethane-based aligned nanofibers

In recent years, shape memory polyurethane (SMPU) as a smart material has been used in various applications owing to its desirable shape memory effect and biocompatibility. In this study, unidirectional SMPU nanofibers are innovated by electrospinning to clarify the mechanical and shape memory properties with nanofiber directions. The results showed that when the nanofiber alignment degree is 0° (parallel to the tensile direction), the aligned SMPU nanofibers achieved the obvious improvement of tensile strength (increased to 135%) and elastic modulus (increased to 313%), compared with the random SMPU nanofiber. Moreover, the developed aligned nanofibers exhibited good ability against stress relaxation and creep under constant strain or constant stress conditions in cyclic loading. The aligned SMPU nanofibers with a 0° alignment degree exhibited excellent shape memory properties with shape recovery rates larger than 93% and shape fixity rates larger than 90%, and a dramatic increase of shape recovery stress.     

Enhanced thermal and tensile behaviour of MWCNT reinforced palm oil polyol based shape memory polyurethane

Shape memory polyurethane (SMPU) has received tremendous interest because of its low cost, low density, as well as easy processing. However, its inferior mechanical properties compared to shape memory alloys have constrained its application in a broad range of engineering areas. Nanofillers are commonly added to polymers to overcome the problem associated with low mechanical characteristics. This study aims to examine the effect of various loadings of multiwalled carbon nanotubes (MWCNT) on the thermal stability, soft segment crystallinity, tensile and shape memory behaviour of palm oil polyol based SMPU nanocomposites. The SMPU nanocomposites were synthesised using a two-step polymerisation process. Microphase-separated SMPU nanocomposites obtained as the differential scanning calorimetric analysis showed two melting transitions, which belonged to the soft and hard phase domains. Furthermore, it was found that MWCNT had acted as a nucleating agent, which promoted the crystallisation process of SMPU nanocomposites. The thermal stability and tensile properties of SMPU/MWCNT nanocomposites were enhanced significantly as the MWCNT was added to the SMPU matrix. A considerable enhancement in the shape fixity (SF) value was revealed for PU-30 and PU-40 samples with the addition of MWCNT. The shape recovery (SR) time of SMPU was faster for samples reinforced with MWCNT, whereas SF increased while SR decreased upon increasing the shape memory cycle. The SMPU nanocomposites produced demonstrated enhanced thermal and tensile properties, which has the potential as smart material in many industrial applications.     

Effect of SSL and HSC on morphology and properties of PHA based SMPU synthesized by bulk polymerization method

Searching new shape memory polymer and the associating synthesis technology are critical on the development of smart materials. In this paper, a comprehensive study on Poly(hexylene adipate) PHA being the soft segment of shape memory polyurethane (SMPU) was presented. Bulk polymerization method was employed to synthesize the SMPU with different soft segment length (SSL) and hard segment content (HSC). The influences of SSL and HSC on its morphology and thermomechanical property using DSC, DMA, POM, and shape memory behavior were presented here. The results indicate that the thermal properties, dynamic mechanic properties, and crystal morphology of SMPU are influenced significantly by SSL and HSC. And it is found that the shape fixity increases with SSL but decreases with HSC. On the other hand, the shape recovery decreases with both SSL and HSC, and the associated recovery temperature increases either with the increasing SSL or with decreasing HSC. Lastly, it is concluded that in the PHA‐based‐SMPU, the lower limiting value of SSL for polyurethane having shape memory effect is 2000; their response temperature varied with SSL and HSC, changing from 41.0 to 51.9 °C. Stable hard segment crystal are formed at above 30% HSC sample in bulk polymerization, but shape memory behavior can also be observed when its physical crosslink point are formed in the lower HSC PHA‐based‐SMPU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 444–454, 2007     

Structural relaxation behavior of strain hardened shape memory polymer fibers for self‐healing applications

In this study, shape‐memory polyurethane (SMPU) fibers were strain hardened by cold‐drawing programming (CDP) process. The programmed fibers are experimentally studied on the physical and thermomechanical properties. Structural relaxation, which determines shape memory capability of the SMP fibers, is quantified by conformational entropy change. Based on the entanglement tube theory and reptation theory, the entropic force is derived as a “bridge” to link the stress relaxation and structural relaxation, and thus structural relaxation can be evaluated by stress relaxation. It was found that the CDP SMPU fibers would still have good crackclosing capability after 13 years of hibernation in polymer matrix composite. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 , 51, 966–977     

气相生长碳纤维/形状记忆聚氨酯复合薄膜的力学及形状记忆性能研究

采用溶液混合法制备了不同含量的气相生长碳纤维(VGCF)增强形状记忆聚氨酯(SMPU)的复合材料薄膜,测试分析了纯SMPU及VGCF/SMPU复合材料薄膜的力学性能及形状记忆性能.结果表明,制得的复合材料薄膜在VGCF含量达到9 wt%时,VGCF在SMPU基体中仍具有较好的分散性;SMPU与VGCF复合后,得到的复合材料薄膜的拉伸强度和刚度有较大程度的提高,含量达到9 wt%时复合材料薄膜的拉伸强度比纯SMPU提高66%,弹性模量提高300%,储能模量也有较大程度提高;SMPU与VGCF复合后,形状记忆性能有一定的下降,但经过适当预处理后,其形状记忆性能可以基本接近纯SMPU.     

Gas permeabilities of polyurethane films for fresh produce packaging: Response of O2 permeability to temperature and relative humidity

Thermoplastic shape memory polyurethane (SMPU) polymers were synthesized, cast to films, and their gas barrier properties were characterized. In addition, performance of an optical method was assessed by measuring oxygen permeability (P_O2) of the films. P_O2 of the SMPU film was at least two times higher than that of low density polyethylene (LDPE and increased at higher relative humidity. Permselectivity (P_CO2/P_O2) of the SMPU film was 15, which is approximately three times higher than for LDPE. The film absorbed circa 18% water vapor at 98% relative humidity. The optical method agreed very well (maximum 20% deviation) with a standard carrier gas method in P_O2 measurement. Overall our results show that SMPU is an attractive polymer for fresh produce packaging.     

SHAPE MEMORY EFFECT OF PU IONOMERS WITH IONIC GROUPS ON HARD-SEGMENTS

SMPU （shape memory polyurethane） non-ionomers and ionomers, synthesized with poly（c-caprolactone） （PCL）, 4, 4＇-diphenylmethane diisocyanate （MDI）, 1,4-butanediol （BDO）, dimethylolpropionic acid （DMPA） were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content.     

Investigation on Structures and Properties of Shape Memory Polyurethane/Silica Nanocomposites

In this study, high performance shape memory polyurethane (SMPU)/silica nanocomposites with different silica weight fraction including SMPU bulk, 3%, 4.5%, 6%, 7.5%, 10%, were prepared by sol‐gel process initiated by the solid acid catalyst of p‐toluenesulfonic acid (PTSA). Field emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) observation show that the silica nanoparticles are dispersed evenly in SMPU/silica nanocomposites. Tensile test and dynamic mechanical analysis (DMA) suggest that the mechanical properties and the glass transition temperature (T_g) of the nanocomposites were significantly influenced by silica weight fraction. Thermogravimetric analysis (TGA) was utilized to evaluate the thermal stability and determine the actual silica weight fraction. The TGA results indicate that the thermal stability can be enhanced with the hybridization of silica nanoparticles. Differential scanning calorimetry (DSC) was conducted to test the melting enthalpy (ΔH) and the results suggest that the ΔH was markedly improved for the SMPU/silica nanocomposites. Thermomechanical test was conducted to investigate the shape memory behavior and the results show that the shape fixity is improved by hybridization of silica and good shape recovery can be obtained with the increasing of cycle number for all the samples.     

Shape memory fiber spun with segmented polyurethane ionomer

The effect of cationic groups within hard segments on shape memory polyurethane (SMPU) fibers was studied and the cyclic tensile testing was conducted to assess the shape memory effect. Mechanical properties, hard segment crystallization, and dynamic mechanical properties of SMPU ionomer fibers composed of 1,4‐butanediol (BDO), N‐methyldiethanolamine (NMDA), 4,4′‐methylenebis(phenyl isocyanate) (MDI), and poly(butylene adipate)diol (PBA) were investigated using a universal tensile tester, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results demonstrate that only 2 wt% NMDA can significantly change the glass transition temperature of the soft segment phase. DSC shows that the ionic group within hard segments can facilitate the crystallization of hard segments in unsteamed SMPU ionomer fibers. But for steamed fiber specimens, this effect is insignificant. Moreover, the ionic groups in hard segments with different hard segment contents (HSC) have different effects. In unsteamed fibers with 64 wt% HSC, 2 wt% NMDA increases the glass transition of soft segments from 63.5 to 70.6°C. However, in fibers with 55 wt% HSC, the glass transition temperature is lowered from 46.7 to 33.5°C. The post‐treatment, high‐pressure steaming is an effective way to remove the internal stress and subsequently improve the dimensional stability of SMPU ionomer fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Shape memory polyurethanes based on recycled polyvinyl butyral. I. Synthesis and morphology

Shape memory polyurethanes (SMPUs) were synthesized by 4,4′-diphenylmethane diisocyanate (MDI), hexane-1,6-diol (HD), polypropylene glycol (PPG), and recycled polyvinyl butyral (PVB). Dynamic mechanical analysis, differential scanning calorimetry and Fourier transformation infrared attenuated total reflection spectroscopy was used to characterize the poly (vinylbutyral-urethanes). Micro-phase domain separation of hard and soft segments and phase inversion were investigated. Increasing the hard segment content, i.e., average hard segment molecular weight, leads to an increase in the degree of micro-phase separation, hard domain order and crystallinity. The crystalline hard segment structures combined with the elastic nature of soft segment matrix provide enough physical and chemical crosslinks to have shape memory effect.     

Facile scalable one-step wet-spinning of surgical sutures with shape memory function and antibacterial activity for wound healing

Surgical suture is commonly used in clinic due to its action in accelerating the process of wound healing.However,difficultly handling in minimally invasive surgery and bacteria-induced infection usually limit its use in a wide range of applications.Here,we report a facile scalable strategy to fabricate surgical sutures with shape memory function and antibacterial activity for wound healing.Specifically,a shape memory polyurethane(SMPU) with a transition temperature(T_(trans)) at 41.3℃ was synthesized by adjusting the mole ratio of the hard/soft segment,and then the shape memory surgical sutures containing polyhexamethylene biguanide hydrochloride(PHMB) as a model drug for antibacterial activity were fabricated by a facile scalable one-step wet-spinning approach,in which PHMB was directly dissolved in the coagulation bath that enable its loading into the sutures through the dual diffusion during the phase separation.The prepared sutures were characterized by their morphology,mechanical properties,shape memory,antibacterial activity,as well as biocompatibility before the wound healing capability was tested in a mouse skin suture-wound model.It was demonstrated that the optimized suture is capable of both shape memory function and antibacterial activity,and promote wound healing,suggesting that the facile scalable one-step wet-spinning strategy provides a promising tool to fabricate surgical sutures for wound healing.     

Competing and decisive roles of 1D/2D/3D sp2-carbons in controlling the shape switching,contact sliding,and functional properties of polymers

Stimuli-controllable shape-shifting polymers, such as shape memory polyurethane (SMPU), are promising for robotics, aerospace, sensing, automobiles, and many other applications. However, slow actuation or high shape recovery time, low recovery stress, and inadequate understanding of friction and wear characteristics of SMPU limit its widespread practical uses. Further, SMPU has been engineered with diverse foreign materials but inconsistent results and ambiguous underlying mechanisms, especially when SMPU is modified with sp²-carbon materials, are also major concerns. Here we determine and simultaneously cross-compare the role of 1D/2D/3D graphitic carbons, namely carbon nanotubes, multilayer graphene and graphite, in controlling the properties of SMPU. The designed SMPU-composites display 8–15-folds faster shape recovery in different mediums, higher recoverable stress, faster healing of the dents, 2–3-folds lower friction, better wear resistance, and improved thermal, wettability, and dielectric properties than pristine SMPU. Further, while the introduction of 2D/3D graphitic carbons massively degrade the elongation, 1D carbon nanotubes maintains the stretchability of SMPU. Eventually, we develop a novel heat alarm device employing SMPU-composite as a major component that acts as a heat sensor, an actuator, and enables the closure of the circuit. Our results uncover many unknown phenomena of engineered SMPU and pave the way for the development of smart-technologies.     

Triple shape memory effect in multiple crystalline polyurethanes

Remembering more than one permanent shape is an attractive research topic for shape memory materials (SMMs). In this paper, multiple crystalline shape memory polyurethanes (SMPUs) are prepared with PCL10000 and PTMG2900 by a three‐step polymerization method. DSC and WAXD results show that the obtained polyurethane contains, simultaneously and independently, two kinds of crystals. In addition, it is confirmed through DMA analysis that reversible soft phase and hard domains are formed in the PCL‐PTMG based SMPU system; and two‐step modulus decreases at low temperature range can be obtained in the SMPU with suitable mass proportion of PCL to PTMG, e.g., 1:7. Thus, shape memory effect (SME) can be achieved in this system. Moreover, it is found that the PTMG soft segment dominates the shape memory effect when the PCL mass is lower than that of PTMG; while the PCL soft segment dominates the SME when PCL mass is higher than that of PTMG; and a two‐step programing shape recovery can be achieved when the mass proportion of PCL/PTMG reaches a balance value, e.g., 3:5. Copyright © 2009 John Wiley & Sons, Ltd.     

芳纶纤维/SMPU-SiO2复合材料的界面性能研究

选用形状记忆聚氨酯(SMPU)和正硅酸乙酯(TEOS)为前驱体,固体酸对甲基苯磺酸(PTSA)为催化剂,利用空气中的水分为水解水源,通过溶胶-凝胶法原位制备了形状记忆聚氨酯与二氧化硅( SMPU-SiO2)杂化材料,并将杂化材料应用于芳纶纤维增强的柔性复合材料中,以期改善芳纶纤维与基体的界面性能.同时,针对芳纶纤维表面...     

表面改性对VGCF分散性质的影响

针对气相生长碳纤维极易团聚及与树脂基体界面结合能力较差的难题,采用双氧水-浓硝酸二步法对VGCF进行表面改性处理。利用X射线衍射仪、热重分析仪、傅立叶红外光谱仪、紫外可见分光光度计等测试分析了改性前后VGCF的表面结构和在溶剂中的分散性,并以形状记忆聚氨酯为基体,采用溶液混合法制备了气相生长碳纤维/形状记忆聚氨酯的复合材料,测试了复合材料的力学性能。经过改性后,VGCF的石墨晶型结构几乎没有改变,VGCF表面的含氧官能团浓度得到较大提高,且其在有机溶剂中的分散性及分散稳定性也得到很大提高;在气相生长碳纤维/形状记忆聚氨酯的复合材料截面中,扫描电镜观察表明表面改性使得VGCF在基体中的分散性及与基体的界面结合能力都得到一定程度的提高;经二步法改性处理后的气相生长碳纤维比未处理气相生长碳纤维对复合材料的力学性能的增强效果更为明显。     

Investigation into stress recovery behavior of shape memory polyurethane fiber

In this work, the stress recovery behavior of shape memory polyurethane (SMPU) fiber was investigated. The as‐spun SMPU fibers were subjected to various programing‐recovery conditions. It was observed that recovering at 100 °C generated higher recovery stress than recovering at 150 °C. It was also found that, while hot‐drawn programed fiber has higher recovery stress than cold‐drawn programed fiber if recovered at 100 °C, cold‐drawn programed fiber has higher stabilized recovery stress than hot‐drawn programed counterpart when recovered at 150 °C. A morphological model was proposed based on the results from differential scanning calorimetry, Fourier transform infrared spectrometry, and X‐ray diffraction to understand the physics behind the different stress recovery behaviors. It is found that SMPU experiences different phase transitions and phase separations under different programing and stress recovery conditions. It is concluded that the two sequential phase separations taking place at 100 and 150 °C are primarily responsible for the differences in the stress recovery behavior. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1429–1440     

聚酯的序列结构对聚氨酯弹性体形貌的影响

以己二酸(AA),1,4-丁二醇(BDO),乙二醇(EG)分别采用一步法、二步法合成分子量为3000的聚酯PAEB-R和聚酯PAEB-A.再分别与二苯基甲烷二异氰酸酯(MDI)、扩链剂1,4-丁二醇(BDO),乙二醇(EG)反应分别合成固含量30%与粘度为20000的聚氨酯(PAEB-R)-MDI-TPU和聚氨酯(PAEB-A)-MDI-TPU.SEM、AFM表明不同工艺所合成的聚氨酯均存在微相分离,且聚氨酯(PAEB-R)-MDI-TPU微相分离程度高于(PAEB-A)-MDI-TPU.     

An investigation into compressive responses of shape memory polymeric cellular lattice structures fabricated by vat polymerization additive manufacturing

A combination of additive manufacturing techniques with shape memory materials, so that the shape, property, or functionality of a 3D printed structure can change as a function of time, has recently created new progress in 4D printing. Low-density lattice structures, due to their unique mechanical properties and engineering characteristics, have been candidates for lightweight structures and energy absorbing applications. In the present work, Rhombic and Body-Centered Cubic (BCC) cellular lattice structures, as well as cylindrical bulk samples, were designed and fabricated with Digital Light Process (DLP) by using shape memory resin. The energy absorption of SMP samples was studied in terms of the capabilities of absorption and recovery. In addition, deformation mechanisms of the structures, the influence of strain rate, cyclic behavior and the strain recovery of the structures after each cycle were investigated. All the studies were done in three different cold, warm and hot programming schemes to evaluate the effects of temperature on shape memory effect of the products. Although both structures showed nearly the same strain recovery rates at all conditions, Rhombic structure was found to possess better functional and structural behaviors than BCC lattice in terms of strength, stiffness, and absorption as well as recovery of the induced energy.     

可生物降解多嵌段聚(酯-氨酯)的合成及其热致形状记忆性质

以端羟基L-丙交酯/乙交酯共聚物(PLLG-diol)和端羟基ε-己内酯/乙交酯共聚物(PCG-diol)为硬段和软段,通过与二异氰酸酯反应制得了软、硬分子量和组成均可调的多嵌段聚(酯-氨酯),表征了它们的形状记忆行为.多嵌段聚(酯-氨酯)具有良好的形状记忆性质,应变固定率达98%~99.5%,应变恢复率达93%~98.5%;通过转变温度的调节,可使多嵌段聚(酯-氨酯)在37℃体温下不发生形状变化,而在稍高于体温的温度(40~50℃)下恢复原始形状,其形状恢复速率可通过温度和升温速率来调节.     

基于激发态分子内质子转移的新一代荧光探针

对被誉为多参数、多功能的第二代荧光探针3-羟基黄酮类衍生物的光物理特性及其在微环境极性、微相变和相分离、膜电位测定等方面的实际应用做了比较详尽的介绍.