EAA基热致型热塑性形状记忆高分子弹性体的制备与性能研究

采用乙烯-丙烯酸共聚物(EAA)热塑性弹性体制备了热致型形状记忆高分子材料,并对其力学性能、微观取向结构、结晶行为和不同变形模式下的形状记忆效应进行了研究,还对变形温度与回复温度对其形状记忆效应的影响进行了探讨。结果表明,EAA样品拉伸表面存在明显取向结构,为其形状回复提供了驱动力;根据EAA样品的熔融、结晶和粘弹行为可确定其形状记忆变形温度和回复温度范围;在拉伸、旋转和卷曲模式下,EAA样品均表现出良好形状记忆效应;当变形温度接近EAA熔点且为95℃时,EAA样品同时具备优异的形状固定率(98.7%)和良好的形状回复率(91.5%);升高回复温度可提高EAA样品形状回复速率。     

EVA热致型形状记忆高分子材料的制备与性能研究

采用乙烯-醋酸乙烯共聚物(EVA)热塑性弹性体制备了热致型形状记忆高分子材料,研究了其力学性能、取向结构、结晶性能及不同变形模式下的形状记忆性能,探讨了变形温度和回复温度对形状记忆效应的影响。结果表明,EVA拉伸试样表面存在明显的取向结构,这为形状回复提供了驱动力;拉伸作用促进了试样结晶,变形回复后试样DSC曲线存在双峰;在拉伸、螺旋和卷曲模式下,EVA试样均呈现良好的形状记忆效应;当变形温度接近EVA熔融温度76℃时,试样可同时获得良好的形状固定率(其值95%)和优异的形状回复率(其值95%);升高回复温度可显著加快EVA试样形状回复速率。     

基于EMA热塑性弹性体的热致型形状记忆高分子的制备与性能

以乙烯-丙烯酸甲酯共聚物(EMA)制备热致型形状记忆高分子,通过伺服控制拉力试验机、差示扫描量热分析、拉伸夹具和电热恒温水浴锅研究了其力学行为、取向结构、结晶行为及不同变形模式下的形状记忆行为,并研究了形状记忆效应受到预热温度和回复温度的影响规律。结果表明,EMA拉伸样品的表面存在明显的取向结构,这为其形状回复提供了驱动力;EMA具有良好的结晶性能,且熔融温度为98℃;拉伸、螺旋和卷曲模式下,EMA样品均呈现出良好的形状记忆效应;当变形温度接近EMA的熔融温度时,EMA样品的形状固定率大于95%且形状回复率大于90%;EMA样品的形状回复速率会随着温度的升高而加快。     

高反式—1,4—聚异戊二烯形状记忆材料的研究

低度交联反式－１,４－聚异戊二烯（ＴＰＩ）是一种交联度控制在一定范围,室温下可结晶,加热后具有热弹性,从而具有形状记忆功能的材料。本文研究了有机过氧化物硫化体系及填料对低度交联ＴＰＩ力学性能、电性能以及热刺激变形温度等的影响,并和硫磺硫化体系进行了对比。结果表明,有机过氧化物硫化比硫磺硫化ＴＰＩ形状记忆材料具有更高的硬度、拉伸强度,更低的回复残率,更大的体积电阻率,适合电绝缘性能要求较高的制品。     

SMA智能结构在形状控制领域的研究进展

形状记忆合金(Shape Memory Alloy,简称SMA)拥有其他金属或合金所不具备的形状记忆效应及超弹性。对形状记忆合金材料进行一定的预变形,在其形状回复过程中会产生较大的回复力。将预变形的SMA埋入结构中或连接于结构表面,当其受热回复时即可使结构形状改变。基于此原理,国内外已对智能梁结构、机翼、旋翼叶片、智能进气道、发动机舱后缘结构、可变发动机喷嘴等的形状控制进行了研究。本文在综述基于SMA结构形状控制研究的基础上,提出了若干需要进一步研究的问题。     

生物降解PPC/HA复合材料的制备与性能研究

将羟基磷灰石（HA）用硅烷偶联剂KH570处理，然后与聚碳酸亚丙酯（PPC）进行共混，制备了一种可生物降解、生物相容性好的PPC／HA复合材料，研究了其在不同混合比例时的力学性能、玻璃化转变温度及其内部结构。该复合材料力学强度介于塑料和橡胶之间，具备良好的力学回复特性和一定的形状记忆效应，HA为20％（质量分数，下同）时，断裂伸长率达到315％，弹性回复率可达98％。DSC分析表明，复合材料的玻璃化转变温度受姒的影响不大，在35℃左右，随HA含量的不同略微有一些变化。SEM观察到在拉伸过程中，复合材料内部出现一种板块与微纤复合结构，这种结构对材料的力学性能变化有一定影响，可能也是力学回复特性产生的原因。     

杜仲胶/聚乳酸形状记忆热塑性硫化胶的制备及性能

将生物基高分子材料杜仲胶（EUG）和聚乳酸（PLA）通过动态硫化技术制备了具有形状记忆性能的热塑性硫化胶（EUG/PLA TPV）。通过扫描电子显微镜、差示扫描量热、动态力学和力学性能测试及热机械循环分析等手段分别考察了EUG/PLA TPV的微观形貌、相容性、热性能、动态力学和力学性能及形状记忆性能。结果表明,增容剂腰果酚有效改善了EUG相与PLA相之间的相容性,从而提高了EUG/PLA TPV的力学性能。当橡塑质量比为5/5时,拉伸强度为10.5 MPa,扯断伸长率达到286%,是纯PLA的约48倍。EUG/PLA TPV具备特殊的双连续相结构,可以赋予其良好的形状记忆性能,形状固定率最高达到93%左右,形状回复率最高达到98%左右。     

纤维增强形状记忆复合材料及其应用

纤维增强形状记忆复合材料及其应用，它涉及一种形状记忆复合材料及其应用。本发明解决了目前形状记忆聚合物材料的刚度和强度等力学性能较差、变形回复时输出的外力较小、运动稳定性和可靠性较差的问题。本发明由形状记忆聚合物材料和纤维增强相材料组成。本发明各组分材料的体积分数为：形状记忆聚合物材料20％～95％，     

反式-1，4-聚异戍二烯／炭黑导电复合材料的形状记忆性能

采用熔融共混法及适度硫化工艺制备了反式-1．4-聚异戊二烯／炭黑导电复合材料．研究了该复合材料的力学性能、导电性、热致及电致形状记忆性能。结果表明．随炭黑用量的增加,复合材料的拉伸强度先增加后减少．拉断仲长率逐渐降低。100％定伸应力和300％定伸应力呈升高趋势;高导电炭黑可大幅提高复合材料的导电性,复合材料的热刺激响应回复温度逐渐升高．热致形变回复率和热致回复速度均降低,热致形状记忆性能降低。复合材料具有良好的电致形状记忆性能．高导电炭黑的用量和外加电压对复合材料的电致形状记忆性能有重要影响．电致形变回复率和回复速度随外加电压或高导电炭黑用量的增加而增加。     

铝—硅低共熔合金对沥青结合的镁碳耐火材料的影响

本研究使用了含量达１４％（重量）的铝－硅低共熔合金加到沥青结合的ＭｇＯ－Ｃ耐火材料中，而加６％（重量）的合金，在１４００℃下其显气孔率、常温耐压强度和高温抗折强度达到最佳。加入Ａｌ－Ｓｉ合金还可明显地减小总的透气性。Ｘ射线衍射和显微结构分析结果揭示出，在ＭｇＯ－Ｃ耐火材料中生成了ＭｇＡｌ２Ｏ４和ＡｌＮ相。这些相可能与８００℃以上耐火材料性能得以提高密切相关。     

Influence of uniaxial compression on the shape memory behavior of vitrimer composite embedded with tension-programmed unidirectional shape memory polymer fibers

Tension programmed shape memory polymer (SMP) fibers have been used as sutures for closing wide-opened cracks per the close-then-heal strategy. However, the composite may be subjected to compression loading during service. These compression loads can reduce the amount of recoverable strain in these pre-tensioned fibers, limiting their ability to close cracks. The purpose of this study is to investigate the effect of in-service compression loading on the shape memory effect (SME) of composites consisting of SMP fiber and SMP matrix. To this end, pre-stretched shape memory Polyethylene Terephthalate (PET) fibers were embedded into a shape memory vitrimer to obtain composite samples with different fiber volume fractions. The SME of both the PET fiber and the vitrimer was investigated. The effect of compression load on the SME of the composite was studied. It is found that, uniaxial compression on the composite along the fiber direction significantly reduced the shrinking ability of the embedded pre-tensioned SMP fibers. Hence, this is a factor that needs to be considered when designing such types of self-healing composites.     

Shape memory composites based on a thermoplastic elastomer polyethylene with carbon nanostructures stimulated by heat and solar radiation having piezoresistive behavior

A thermoplastic elastomer polyethylene (TEPE) based on an ethylene/1‐butene copolymer having shape memory effect (SME) without any chemical modification is presented and the effect of adding either carbon nanotubes or thermally reduced graphite oxide is analyzed. For electrical percolated samples, the development of a polymer sensor that changes its electrical conductivity under solar radiation triggered by SME is further presented. Our results showed that programmed samples recovered their permanent shape showing SME under a direct heating stimulus at 60 °C. The addition of carbon nanostructures increased the times needed to reach 100% recovery as compared with pure TEPE. Noteworthy, the SME was also stimulated remotely by solar radiation increasing the sample temperature. Composites presented a faster SME under this remote radiation process as compared with pure TEPE due to their higher radiation absorption. Percolated TEPE/carbon nanotube composites displayed further a decrease in the electrical resistivity during SME under this solar radiation. Finally, our results showed that the glass transition also triggered the SME in these samples allowing the development of triple shape memory polyethylenes without any chemical crosslinking process. Based on these findings, a simple route was developed to produce double, or even triple, shape memory piezoresistive polyethylenes that can be activated remotely by solar radiation. © 2018 Society of Chemical Industry     

Modeling shape memory effect in uncrosslinked amorphous biodegradable polymer

Shape memory effect (SME) is critical for minimally invasive surgical procedures in medicine. In this paper, the shape memory behavior of amorphous biodegradable polymer, poly(d,l-lactide-co-glycolide), is experimentally investigated. Based on the experimental observations and the understanding of the underlying mechanism of SME, a one-dimensional constitutive model is derived to describe the shape memory behavior in the context of (1) the stress-strain behavior in deformation, (2) the isothermal recovery and (3) the recovery at constant heating rate, by using a set of model constants. By fine tuning the model constants, a good agreement between the experimental results and computer predictions was achievable.     

Fabrication of poly(ε‐caprolactone) (PCL)/poly(propylene carbonate) (PPC)/ethylene‐α‐octene block copolymer (OBC) triple shape memory blends with cycling performance by constructing a co‐continuous phase morphology

In this paper, a triple shape memory material was prepared by ultra‐simple melt blending from poly(ε‐caprolactone) (PCL), poly(propylene carbonate) (PPC) and ethylene‐α‐octene block copolymer (OBC). The obtained material possessed a co‐continuous phase morphology and presented an excellent triple shape memory effect (triple‐SME). Theoretical prediction demonstrated that a special continuous phase morphology could be constructed by adjusting the proportions of the blend. Moreover, the results indicated that a close relationship existed between the phase morphology and the triple‐SME of PCL/PPC/OBC. The sample with 35 vol% PPC content contributed to the formation of a continuous phase morphology and exhibited the optimal triple‐SME. Additionally, the sample PCL/PPC/OBC (32.5/35/32.5) showed outstanding structure and performance stability during cycle loading–unloading tests, which evidenced the prominent cycling shape memory property (nearly 100% shape fixing and recovery of temporary shape). Overall, this work could provide an efficient, convenient and recyclable method to obtain high‐performance shape memory materials. © 2020 Society of Chemical Industry     

Microwave-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) interpenetrating polymer networks chemically linked to SiC nanoparticles

Microwave (MW)-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) interpenetrating polymer networks (SMP-IPNs) were prepared through in situ polymerization. Silicon carbide (SiC) nanoparticles were modified by 3-(methacryloyloxy) propyltrimethoxysilane (KH570). 3-(Methacryloyloxy) propyltrimethoxysilane was covalently bonded on the surface of SiC through the reaction of silanol and the methoxy groups. The polymerization of acrylic acid (AA) using N,N′-methylenebis (2-propenamide) (MBA) as cross-linker in PVA solution was initiated through the double bonds of KH-570 grafted on SiC, leading to a PAA polymer network cross-linked with MBA. The PVA molecular chains run through the PAA cross-linking network and form an IPN structure. Therefore, SiC as a strong MW absorbing material could be chemically cross-linked into polymer matrix. The effect of composition on the properties of SMP-IPN was studied using dynamic mechanical analysis, dielectric properties and shape memory effect (SME) test. The results showed that the introduction of SiC in IPNs not only provided samples with excellent MW-induced shape memory effect (SME), but also caused a higher equilibrium temperature under MW irradiation. Moreover, both SiC content and applied MW power affected the shape recovery properties of PVA/PAA interpenetrating composites. MW-induced SMPs offered great advantages such as fast recovery, high recovery rate, and remote actuation. This study provides the potential applications of the fast and environmentally friendly SMPs used as MW-responsive sensors, implantable devices, etc.     

Nanoindentation of NiTi shape memory thin films at elevated temperatures

The shape memory effect and nanoindentation response of various phases of sputtered NiTi shape memory thin films were investigated as a function of temperature. The phase transformation temperatures of NiTi films were observed to be sensitive to a compositional shift. The mechanical properties of NiTi thin films also presented a significant response to phase transformations. At the same load, the maximum indentation depth for austenite is smaller than for martensite, indicating that martensite is softer than austenite. A martensite thin film was converted to austenite via in situ heating nanoindentation and displayed the mechanical properties similar to the austenite film at room temperature. These results underscore the validity of elevated temperature nanoindentation methods as a means of interrogating the mechanical properties of materials that undergo thermally-induced phase transformations. The details of the load–displacement curves are also described.     

Recent progress in shape memory polymer: New behavior,enabling materials,and mechanistic understanding

Shape memory polymers (SMPs), as a class of programmable stimuli-responsive shape changing polymers, are attracting increasing attention from the standpoint of both fundamental research and technological innovations. Following a brief introduction of the conventional shape memory effect (SME), progress in new shape memory enabling mechanisms and triggering methods, variations of in shape memory forms (shape memory surfaces, hydrogels, and microparticles), new shape memory behavior (multi-SME and two-way-SME), and novel fabrication methods are reviewed. Progress in thermomechanical modeling of SMPs is also presented.     

Fabrication of Shape‐Memory Aerogel Based on Chitosan/Poly(ethylene glycol) Diacrylate Semi‐Interpenetrating Networks via a Facile and Eco‐Friendly Strategy

While the field of shape memory polymers (SMPs) has developed rapidly, it is still highly challenging to obtain SMPs in the form of aerogels (SMPAs) due to the unique technique used for the fabrication of the aerogels and their high porosity. Herein, a thermally induced SMPA based on chitosan/poly(ethylene glycol) diacrylate (CS/PEGDA) semi‐interpenetrating networks is reported that are produced using an eco‐friendly strategy. The main network is responsible for the shape memory effect (SME) and can be easily tuned by varying the feed ratio of the two PEGDA precursors, which have different molecular weights. The crystalline segment in poly(ethylene glycol) diacrylate (PEGDA) with higher molecular weight acts as the molecular switch, and the PEGDA with lower molecular weight endows the network with an efficient degree of crosslinking. Meanwhile, the chitosan (CS) is interpenetrated into the main network to enhance the aerogel. The SME is realized both at the macroscale and the microscale, as is further demonstrated for three different models with various shapes.     

Influence of annealing-induced phase separation on the shape memory effect of graphene-based thermoplastic polyurethane nanocomposites

Thermoplastic polyurethane (TPU) is a multiblock copolymer that exhibits an attractive shape memory effect (SME). Its morphology consists of a soft segment (SS), which corresponds to the polyol or a long-chain diol, while the hard segment involves the intercalation of a diisocyanate and a chain extender. Due to the distinct thermodynamic parameters of each monomer, these segments are not miscible with each other, resulting in a phase-separated structure in their morphology. This structure is characterized by the formation of soft and hard domains (SD and HD), respectively. When incorporating 0.1 wt% of graphene nanoplatelets (GNP) or 0.1 wt% of multilayer graphene oxide (mGO) into the TPU matrix using solution casting process, a contribution to the phase separation of these domains is observed. This phenomenon becomes even more pronounced when graphene-based nanocomposites are subjected to annealing at 110°C for 24 hours, indicating a good interaction between the GO and GNP with the HD and SS, respectively. After annealing, the nanocomposites (TPU + GNP and TPU + mGO) exhibit improved performance in SME, as evidenced by an approximately 9% increase in the shape recovery ratio compared to the nonannealed TPU. Additionally, all nanocomposites maintained a high strain during SME programming, surpassing that of pure TPU, both before and after annealing. This suggests a direct influence of the graphene-based nanoparticles on the shape memory effect.     

Two‐Way Reversible Shape Memory Properties of Benzoyl Peroxide Crosslinked Poly(ethylene‐co‐vinyl acetate) under Different Stress Conditions

Two‐way (reversible) chemically crosslinked semicrystalline shape memory polymers are synthesized using poly(ethylene‐co‐vinyl acetate) (PEVA) with benzoyl peroxide (BPO). The two‐way shape memory effect (2W‐SME) is achieved under both constant stress and stress‐free conditions. It is found that the stress‐free 2W‐SME can be achieved by the relationship between the initial prestretching strain (R_prestretch) and recovery strain (R_rec). Under the same prestretching stress, the stress‐free two‐way shape memory behavior can be controlled by variation of R_rec using a different setting temperature (T_set) in the recovery process. More importantly, the driving force and recovery force, as one of the key indicators for two‐way shape memory materials, are investigated, and they significantly change depending on the BPO content. The sample with high BPO content shows excellent high‐temperature creep resistant performance. A highly crosslinked structure can suppress viscous flow and provides sufficient force to allow the sample to recover its initial shape after crystal melting. Therefore, the PEVA/BPO samples are able to contract during heating. The presence of an oriented crystal structure with high applied stress that causes sample elongation during cooling is also investigated. These findings for PEVA/BPO two‐way shape memory polymers will contribute to their applications as soft actuators in various fields.