Shape Memory Performance Research Articles

Modulation of shape memory properties of trans-polyisoprene by sulfur

Abstract In this paper, TPI/S composites were prepared by a simple physical melt blending method, and the composites were hot-pressed and molded using a vulcanization system. The effect of cross-linking on the vulcanization properties, mechanical properties, crystalline properties, and shape memory properties of trans-1-4 polyisoprene (TPI) was investigated by varying the amount of sulfur (S). It was shown that with the increase of sulfur dosage, both TPI scorch time and orthoclave time were shortened and the mechanical properties decreased; The melting peak area and melting temperature of the crystalline region of TPI decreased with the increase of sulfur content, and the cross-linking density increased while the crystallinity tended to decrease and the heat resistance deteriorated; In addition, with the increase of sulfur content, the shape return rate of TPI/S composites was increasing and the shape fixation rate was decreasing. When the TPI/S composites were used as shape memory materials, the sulfur dosage of 1 phr had the best shape memory performance, at which time the shape fixation rate of the composites reached 96.9% and the shape recovery rate reached 86.2%. When the sulfur content was elevated to 2 phr, the shape memory fixation rate was significantly decreased, indicating that the shape memory properties were severely compromised. This study reveals that the quantity of sulfur exerts a significant influence on the application of TPI/S composites. An appropriate amount of sulfur can facilitate the preparation of thermoplastic elastomers for utilization in shape memory materials. Nevertheless, an excessive amount of sulfur will substantially enhance the internal cross-linked structure of the composite and deteriorate the shape memory performance.


Investigation on Polyether Sulfone Toughening Epoxy Vitrimer: Curing and Dynamic Properties.

Diglycidyl ether of bisphenol A crosslinking with glutaric anhydride is used to form the conventional "covalent adaptive network", polyether sulfone (PES) by coiling and aggregating on the adaptive network is used to significantly increase the uncured resin viscosity for improving the processability of epoxy resin, but inevitably affecting the curing reaction and dynamic transesterification reaction. This study investigates the crucial roles of PES in curing dynamics and stress relaxation behavior. The results indicate that although PES does not directly participate in the crosslinking reaction of polyester-based epoxy vitrimers. Moreover, the isothermal curing studies reveal that the addition of PES can greatly bring forward the reaction rate peak from conversion α = 0.6 to α = 0.2, meaning that the curing mechanism transfers from chemical control to diffusion control. Dynamic property analysis shows that the addition of PES significantly accelerates stress relaxation, especially at lower temperatures, leading to low viscous flow activation energy Eτ and relatively insensitive stress relaxation behavior to temperature. Introducing PES into vitrimer resin greatly improves crosslinking density (2.31×10⁴molm- 3), enhancing glass transition temperature (82.68°C), tensile strength (68.66MPa), and fracture toughness (6.25%). Additionally, the modified vitrimer resin exhibits satisfying shape memory performance and reprocessing capability.

Phosphorus/boron-containing, flame-retardant polyurethane elastomers with great mechanical, shape-memory, and recycling performances

Based on sustainable development strategy and practical application requirement, it is crucial to develop high-strength, recyclable, and flame-retardant polyurethane (PU) elastomers. Hence, a flame-retardant, reprocessable, high-performance polyurethane elastomer (PU-DP 1–7) with dynamic boronic ester bonds and phosphorus-containing groups was well-designed and prepared. The chemical structure of PU-DP 1–7 was confirmed by Fourier transform infrared spectrometry (FTIR) and X-ray photoelectron spectroscopy (XPS). PU-DP 1–7 shows a transmittance of about 60 % at the wavelength of 900 nm, and phosphorus and boron elements are evenly distributed within its surface, confirming the formation of uniform cross-linking network. The inclusion of phosphorus-and boron-containing groups endows PU-DP 1–7 with a vertical combustion (UL-94) V-0 rating, indicative of desired flame retardancy. In addition, PU-DP 1–7 exhibits a tensile strength of 42.7 MPa and an elongation at break of 616.9 %, with high adhesion strengths towards various substrates due to abundant hydrogen bonds within its network. Furthermore, the dynamic borate ester bonds endow PU-DP 1–7 with superior physical recycling and shape-memory properties. After hot-pressing at 130 °C, the reformed PU-DP 1–7 film shows an 83.6 % recovery efficiency in terms of elongation at break. This work presents an integrated strategy to create flame-retardant, recyclable polyurethane elastomers with great mechanical and shape-memory performances by introducing phosphorus-containing segments and dynamic boronic ester bonds.

Fabrication of highly carboxylated nanofibrous aerogels under mild conditions and their protein adsorption performance

The development of high-performance media for protein adsorption in bio-purification is highly desired, particularly in biological pharmaceuticals. In this study, we demonstrate a simple, versatile and mild strategy to construct a nanofibrous aerogel (NFA)-based adsorption media for protein purification. Pyromellitic dianhydride (PMDA) was selected to in-situ graft onto poly(ethylene-co-vinyl alcohol) (PE-co-PVA) nanofibers in aerogels through liquid phase grafting. The obtained PE-co-PVA/PMDA NFAs (PPNAs) possessed superb underwater elasticity, compression fatigue resistance and shape-memory performance. With an open porous network, abundant adsorption ligands, and surface hydrophilicity, the PPNAs exhibited a significant adsorption capacity of 1019.71 mg/g and a short equilibrium time of 3.0 h, surpassing that of commercial and reported nanofiber-based adsorbents. Additionally, the PPNAs demonstrated good dynamic adsorption performance for protein driven solely by gravity. Furthermore, the PPNAs showed reusability, selectivity, acid and alkaline resistance, and practical potential of extracting lysozyme form egg white solution. The successful scale-up of such aerogel-based adsorbents can open up new way for the development and design of next-generation protein adsorption media for bio-purification applications.

Investigating the Shape Memory Effect and Corrosion Resistance of the Fe-(17-2x) Mn-6Si-xNi-yCr-0.3C Alloys (x = 0, 1, 2, 3, 4; y = 0, 1, 3, 5)

In this study, low Mn content Fe-Mn-Si-based shape memory alloys [Fe-(17-2x) Mn-6Si-xNi-yCr-0.3C (x = 0, 1, 2, 3, 4; y = 0, 1, 3, 5)] were prepared via vacuum arc remelting. The alloys were hot-rolled and solid-solution-treated at 1150 °C for 1 h followed by aging at elevated temperatures. The effects of Cr and Ni addition on the shape memory performance and corrosion resistance of the alloys in 3.5 wt% NaCl solutions were investigated using bending test and potentiodynamic polarization, respectively. It was revealed that the recoverable strain of the alloys remains larger than 2% when 1Ni is replaced with 2Mn and Cr is added. However, it becomes less than 2% in 11Mn and 9Mn alloys because of the easy formation of the α’ martensite. The shape memory effect of alloys is highly improved due to the precipitation of fine carbides in the grains by the addition of Cr and after aging treatment at elevated temperatures (≧700 °C). The highest shape recovery ratios of 88.3% for 17Mn0Ni3Cr, 94.0% for 15Mn1Ni3Cr, 94.4% for 13Mn2Ni5Cr, 88.1% for 11Mn3Ni5Cr, and 86.8% for 9Mn4Ni7Cr, respectively, were achieved after 800 °C aging treatment. The strip-like second phase (carbides) forms at the grain boundaries in the Cr-free alloys after 600 °C aging treatment. There are lots of fine carbides (M23C6 and M7C3) precipitated in the interior of the grains at the aging treatments ≧ 700 °C. However, M7C3 is eliminated at 900 °C aging treatment. The corrosion resistance results showed that the corrosion resistance of the alloys is improved by adding Cr. The maximum corrosion potentials (−0.474 V) have been observed for 13Mn2Ni5Cr, and similar mechanisms have been analyzed in all series of alloys.

Self-Healable, Transparent, Biodegradable, and Shape Memorable Polyurethanes Derived from Carbon Dioxide-Based Diols.

A series of CO2-based thermoplastic polyurethanes (TPUs) were prepared using CO2-based poly(polycarbonate) diol (PPCDL), 4,4'-methylenebis (cyclohexyl isocyanate) (HMDI), and polypropylene glycol (PPG and 1,4-butanediol (BDO) as the raw materials. The mechanical, thermal, optical, and barrier properties shape memory behaviors, while biocompatibility and degradation behaviors of the CO2-based TPUs are also systematically investigated. All the synthesized TPUs are highly transparent amorphous polymers, with one glass transition temperature at ~15-45 °C varying with hard segment content and soft segment composition. When PPG is incorporated into the soft segments, the resultant TPUs exhibit excellent self-healing and shape memory performances with the average shape fixity ratio and shape recovery ratio as high as 98.9% and 88.3%, respectively. Furthermore, the CO2-based TPUs also show superior water vapor permeability resistance, good biocompatibility, and good biodegradation properties, demonstrating their pretty competitive potential in the polyurethane industry applications.

Shape memory cyclic behavior and mechanical durability of woven fabric reinforced shape memory polymer composites

The shape memory cyclic behavior and mechanical durability of the shape memory polymer (SMP) and three woven fabrics (plain, twill, and satin weaves) reinforced shape memory polymer composite (WFR-SMPCs) are characterized to investigate the effect of woven textures on the mechanical and shape memory properties of WFR-SMPCs. Shape memory cycle test, shape memory durability test, and microscopic observation for SMP and WFR-SMPCs were carried out. Experimental results show that the SMP is temperature-sensitive, and higher temperature facilitates the shape memory performance of the material. The woven fabric reinforcements can significantly enhance the mechanical properties of the SMP matrix while still maintaining good shape recovery ratios above 98 % and shape fixation ratios above 90 % even though there is a slight decrease in these values. The twill WFR-SMPC displays the best mechanical performance. The satin WFR-SMPC has the highest shape recovery ratio. The twill WFR-SMPC performs the best in load-bearing capacity and recovery stress. The microscopic observations show that the rotational misalignment and bending of the fiber tows, and damage to the matrix are the main failure modes of the WFR-SMPCs at high shear strain.

Self-recovery and self-conducting epoxy-based shape memory polymer microactuator

This paper introduces a self-conducting microactuator based on carbon black (CB) -embedded SMP, offering prospects for more precise and controllable microelectronic devices. CB doping allows adjustment of the overall resistance of SMP (approximately 70 Ω), ensuring efficient and uniform heating performance. However, the incorporation of a significant amount of CB particles adversely affects the mechanical properties. The successful doping of carbon nanotubes (CNTs) allows for an overall improvement in performance while maintaining electrical properties. The prepared CB-CNT-SMP (CC-SMP) composite material exhibited rapid deformation (25 s), thermal stability (uniform heating), and outstanding shape memory performance. Notably, this CC-SMP achieves dual triggering through both electrical and thermal stimuli. The shape change rate of the CC-SMP at 4 V aligns with the results obtained at 70 °C, indicating that the doped particles do not compromise the deformation ability. We have fabricated shape memory-based self-driven electronic devices by controlling the voltage and structural design. The proposed CC-SMP can change its morphology on the basis of voltage and temperature, demonstrating reliable self-recovery capabilities.

4D printed Electroactive carbon fiber and carbon nanotube synergistically reinforced composites for supporting personalized insole

Smart footwear plays a vital role in walk correction, with mechanical behavior and shape memory effect (SME) being essential aspects. To create personalized smart insoles, we developed a novel blend of polylactic acid (PLA), thermoplastic polyurethane (TPU), and carbon nanotubes (CNT) via melting-extrusion for a continuous-fiber 3D printer. Diverse insole support unit-cell structures (triangular, rhombus, grid) were fabricated with PLA/TPU/CNT filaments, incorporating continuous carbon fibers (CFs) in the front, middle, and back parts of a particular orthopedic insole. The compressive strength and modulus of samples unexpectedly decreased upon CNT incorporation. However, CNT in the TPU phase improved the shape memory performance, shortening the recovery time by 58 %. CF-reinforced composites exhibited excellent mechanical properties and SME; the front triangular structure showed a 13.4 times increase in compressive strength and a 22.6 times increase in modulus compared to free-fiber composites. The printed samples demonstrated remarkable electro-induced shape memory properties due to the dual conductive network formed by CF and CNT. Our PLA/TPU/CNT/CF (nano-) composite is well-suited for personalized shape-memory insole applications, offering enhanced mechanical performance and electro-induced shape-memory capabilities.

Influence of curing temperature on shape memory performance of polyethylenimine‐based shape memory polymer coated cotton fabric

AbstractThis research investigates the effect of curing temperature on the shape memory behavior and coating adhesion of polyethylenimine‐based shape memory polyurethane (PEI‐SMPU) to cotton fabric. The study utilized a dip‐coating process to apply a PEI‐SMPU solution to cotton fabrics, followed by curing at temperatures ranging from 100 to 160°C. Scanning electron microscopy confirmed uniform coating, and significant adhesion, and surface roughness was substantially reduced as evidenced by atomic force microscopy. The fabric's shape memory performance improved with increasing cure temperature, exhibiting excellent recovery (90%) at lower SMPU concentrations (1%). The results indicated that the tear strength of the fabric decreased with increasing curing temperature, attributed to constrained yarn mobility due to increased SMPU cross‐linking. The study successfully correlates the thermal and mechanical properties of SMPU‐coated fabrics with the interaction between SMPU and fabric, emphasizing the preservation of their laundering durability after multiple wash cycles. These findings contribute to the development of smart textiles with improved performance and longevity.

Enhanced shape memory performance and numerical simulation of knitted‐fabric reinforced polymer composites with weft yarns

AbstractFabric‐reinforced shape memory polymeric composites (SMPC) have shown great potential in the design of intelligent deformation structures. In this work, the weft‐knitted fabric inserted with weft yarns was developed as reinforcement to fabricate the shape memory epoxy polymer (SMEP) composites. The effects of weft yarn, loop density and direction on the shape memory performance of SMPC under different bending radii were experimentally investigated. The results show that the SMPC have good shape fixity ratios and shape recovery ratios of around 98%. As compared with those of SMPCs without inserting weft yarns, the SMPCs with weft yarns have shorter shape recovery time, and the recovery force of SMPCs with weft yarns in the 0° and 90° directions shows an increase of 86.4% and 79.5%, respectively. The recovery force of SMPC improve 3.7 times compared to SMEP. The multiscale models of SMPC were established with basis of the results of micro‐computed tomography scanning of specimens and viscoelastic theory. The surface buckling behaviors of SMEP and SMPC specimens after U‐bending load were discussed. Finally, the deformation of loops and weft yarns of SMPC were analyzed to reveal the shape memory mechanism.Highlights Shape memory polymeric composites (SMPC) with weft yarns has shorter shape recovery time. Recovery force of SMPC with weft yarns was obvious enhanced. Multi‐scale viscoelastic models of SMPC were established. Surface buckling behaviors of SMPC after U‐bending load were revealed.

Development of shape memory epoxy resin/polyethylene glycol film based on molecular dynamics simulation and performance investigation

AbstractBased on the molecular dynamics (MD) simulation of glass transition temperature (Tg) and hydrogen bonding in the composite system of epoxy resin (Ep) and polyethylene glycol (PEG), this work developed shape memory Ep/PEG (EpP) films with controllable thermal response, recycling and reprocessing functions using melt dispersion and polymerizing‐pressing processes. EpP films with different PEG contents exhibit excellent shape memory performance, among which the shape recovery rate of EpP‐5 film can reach 92.7%, which can recover from complex structures to the initial shape. The PEG in the composite system can effectively regulate the thermal and mechanical properties of EpP, especially increasing the strain at break and reducing the Tg. Compared with EpP‐0 film. The Tg of EpP‐15 film increased by 40°C and the strain at break increased by 18.56%. Furthermore, compared with the EpP‐0 film, the recycling‐reprocessing temperature of EpP‐15 film has been reduced by 75°C. In summary, based on MD simulation, shape memory EpP films with controllable thermal response, recycling, and reprocessing functions have been successfully developed, and have shown considerable application prospects in the field of intelligent materials.

Biobased photothermal responsive shape memory polythioether/MXene nanocomposites with self-extinguishing performance

Thermosetting shape memory polymers (TS-SMPs) have a higher shape fixity ratio (Rf) and shape recovery (Rr) due to their structure integrity and thermal stability, and the glass transition temperature (Tg) usually influences the transition temperature (Ttrans) of TS-SMPs. Therefore, it is significant to tailor the Tg range and mechanical properties for TS-SMPs. In this work, the inherently flame-retarding bio-based MXene-reinforced polythioether nanocomposites with excellent shape memory performance, driven by photothermal response, were designed. Firstly, a photopolymerizable MXene nanomonomer (MPS-MXene) was obtained by introducing 3-(methacryloxy) propyltrimethoxysilane onto the surface of the MXene monolayer. Then, the bis(4-allyl-2-methoxyphenyl) phenyl phosphonate (BEP) was synthesized by eugenol (a lignin derivative) with phenyl phosphonic dichloride. The polythioether/MXene composites (BEP-T-xM) were synthesized through in-situ thiol-ene photopolymerization of MPS-MXene, BEP, and tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate. Surprisingly, compared with neat polythioether, the Tg of BEP-T-0.2 M composite increased from 19.6 to 34.6 °C, when only 0.2 wt% MPS-MXene was added. The photothermal conversion efficiency (η = 73.8 %) and shape memory performance with Rr (>98 %) were greatly improved. Consequently, the interesting phenomena such as “sunflowers growing towards the sunlight” and “thermal shrinkage” can be observed. Meanwhile, the tensile strength and Young’s modulus increased significantly by 141 % and 91 %, respectively, due to the good dispersion of rigid MPS-MXene nanosheets. Furthermore, all the polythioether/MXene composites showed self-extinguishing performance. This study will provide a novel strategy for designing biobased photothermal-responsive TS-SMPs.

High‐performance shape memory characteristics by integrating urea linkages into the polyurethane elastomer

AbstractShape memory polymers have been widely researched to develop multifunctional materials that respond smartly to external stimulations and programmed signals. Among them, shape memory polyurethane (SMPU) is drawing great attention owing to its highly tunable properties and ease of integrating new functions. However, the effect of urea bonds on SMPU elastomers has rarely been investigated because of the extreme reactivity of amine crosslinkers. In this study, we used diethanolamine (DEOA), which contains a secondary amine, as the crosslinker for SMPU synthesis. Unlike other crosslinkers containing primary amines, they can form urea bonds in a more gentle manner. The urea bonds reinforce the intermolecular interactions between the hard segments with strong hydrogen bonding, thus increasing the phase separation and degree of crystallization. Consequently, the urea‐containing SMPU exhibits improved mechanical strength and shape memory abilities for both fixing and recovery. Moreover, the transcarbamoylation reaction, which enables the reconfiguration of the original shape, is observed. The introduction of the urea bonds into the SMPU elastomer can be beneficial in achieving flawless shape memory performances in various sensitive applications.

4D printed NiTi variable-geometry inlet for aero engines

ABSTRACT In modern aerospace engineering, the demand for innovative and adaptable solutions is paramount. This study focuses on enhancing aircraft engine components, specifically variable-geometry inlets, to meet evolving aviation technology requirements. We utilise custom Ni51Ti alloy powder to create 4D printed variable-geometry inlets. A comprehensive examination of thermal history and residual stress reveals differences in the behaviour of NiTi alloys at various points of the 4D printed inlet. After post-treatment, the printed inlet demonstrates stable two-way shape memory effects, undergoing adaptive deformation with temperature changes, mimicking the operational conditions of a commercial aircraft. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) tests confirm that the 4D printed NiTi alloys maintain very stable phase transformation temperatures and two-way shape memory performance. Fluid dynamics simulations further reveal that the variable-geometry inlet design is potentially more efficient in certain operational scenarios with a total pressure recovery factor of 0.9919.

Novel 4D-printing pellets with infrared-light responsive shape memory effect

Four-dimensional (4D)-printing technology is attractive to researchers since it combines 3D printing with smart materials to produce 3D structures with various shapes and change shapes under specific external stimuli. Herein, novel shape memory polymer (SMP) pellets with infrared-light responsive shape memory effect were developed for 4D printing applications. The structures, properties, and infrared-light responsive shape memory performances of the resulting (SMP) pellets were thoroughly investigated. The results showed PDA/SMP pellets prepared by direct loading of polydopamine (PDA) particles on SMP pellets displayed less influence on the basic properties of SMP while fluidity was enhanced. The obtained PDA/SMP pellets employed as feed materials for particle 3D printers revealed good thermal-induced shape memory performance and photo-responsive shape memory performance in printed 3D structures. Under infrared-light irradiation, the curled shape recovered to straight splines within 60 s due to the strong absorption and good photo-thermal conversion of the loaded PDA nanoparticles under infrared light. Overall, the as-prepared PDA/SMP pellets look promising for use in biomedical fields and smart devices, as well as remote control deformation with 4D printing technology.

Understanding the shape-memory mechanism of thermoplastic polyurethane by investigating the phase-separated morphology: A dissipative particle dynamics study

Shape-memory polyurethanes (SMPUs) are promising materials that change shape in response to external heat. These polymers have a dual-segment structure: a hard segment for netpoint and a soft segment for molecular switch. Understanding the molecular behavior of each segment and microphase-separated morphology is crucial for comprehending the shape-memory mechanism. This study aimed to understand the shape-memory behavior by observing the phase separation of SMPU using mesoscale models based on dissipative particle dynamics (DPD) simulations. The SMPU copolymer was modeled using 4,4′-diphenylmethane diisocyanate (MDI, hard segment) and poly(ethylene oxide) (PEO, soft segment). By calculating segment solubility and repulsion parameters, we found that the hard-segment domain changes from isolated form to a lamellar and interconnected structure and eventually to a continuous form as its content increases. Combining these insights with shape-memory performance models can enhance our understanding of better SMPU design and contribute significantly to the optimization of smart stimuli-responsive materials.

Ultra-hydrophobic Eucommia gum coating with temperature-responsive and shape-memory performance

The intelligent and multifunctional composites offer important applications in many fields. However, the fabrication of intelligent and multifunctional composites still faces limitations due to complicated processes, high costs, and restricted area coverage. Here, we present a new approach for creating a micro/nano-hybrid hierarchical Eucommia ulmoides gum (EUG) coating with outstanding superhydrophobic, temperature-responsive and shape-memory characteristics. The intelligent EUG coating prepared in this study can regulate the change and recovery of the microstructure of the coating surface by altering temperature and external force, thereby achieving control of the surface properties and memory performance of the coating. These EUG hydrophobic shape-memory coatings are obtained through the preparation of superhydrophobic sepiolite particles, spin coating, and chemical cross-linking processes. In addition to its performance advantages, the outstanding advantage of these composites is the simple and easy preparation process, regardless of the substrate surface topography. These novel superhydrophobic and temperature-responsive shape-memory EUG composites can achieve contact angle and thickness regulation. These superhydrophobic and temperature-responsive shape-memory EUG composites are highly expected to be applied in medical devices and intelligent textiles fields.

Self-driven intelligent curved hinge based on shape-morphing composites

The space deployable structures based on shape memory polymer composites (SMPCs) possessed excellent self-deployable performance, which effectively avoided the impact and electromagnetic pulse (EMP) caused by the explosion of pyrotechnic devices. In this work, two types of self-driven curved hinges with different angles of 80° and 115° (Type 80 and Type 115) were designed based on SMPCs. The thermomechanical properties and time–temperature-dependent viscoelastic behaviors of SMPCs were systematically investigated. The three-point bending performance and cyclic shape memory performance of the developed hinges were also characterized. In addition, the deployment performances of Type 80 driven 350 g object under different heating powers were investigated in the environment of ± 70 °C and 103 Pa atmospheric pressure. A staircase-like heating strategy was proposed to achieve precise and controllable deployment under this environment. The developed self-driven curved hinges were expected to have tremendous application potential on the flap actuators and optical payload rotating platforms of the satellites.

4D-printed PLA-PETG polymer blends: comprehensive analysis of thermal, mechanical, and shape memory performances

4D-printed PLA-PETG polymer blends: comprehensive analysis of thermal, mechanical, and shape memory performances