Shape Fixity Rate Research Articles

Space-deployable device based on shape memory cyanate ester composites

Shape memory cyanate ester is a class of shape memory polymers with high thermal stability and excellent space environmental adaptability. In this study, a space-deployable device based on cyanate ester-based shape memory polymer composite (CE-SMPC) was proposed, and its thermomechanical properties and shape memory behavior were experimentally evaluated. The space-deployable device maintained a high shape fixity rate even after prolonged exposure to high or low temperatures, which ensured its locking reliability in space applications. The results of self-deployment experiments indicated that the space-deployable device exhibited good shape recovery performance in both atmospheric and vacuum environments. The SMPC-based space-deployable device presented in this study was applied to China's first Mars exploration mission to achieve autonomous locking and release of the deployable engineering measurement subsystem on the probe.

Synthesis of a self-healing polymer blend containing dynamic diels-alder and h-bond crosslinks

Introduction: It is unquestioned that self-healing polymers are being applied in numerous applications due to their indiscernible advantages, such as the extension of materials’ life span. Not surprisingly, researchers throughout the world concentrate on boosting the progression of the polymer. However, it takes 24 h or 48 h for the self-healing process of polymer-based materials in manifold studies to be efficacious. This can be thought of as a problematic hurdle slowing its advancement and application. Therefore, our research was conducted in an attempt to create a blended structure through hydrogen interplay between (thio)urethane bonds and H-acceptor heterocyclic moieties. Method: The integration of 5 wt%, 10 wt% and 20 wt% blended copolymer capable of forming H-bonds into the network structure was performed to gain a network blend. Furthermore, ATR-FTIR spectroscopy, shape-memory and self-healing tests were employed for the determination of hydrogen bond formation coupled with various properties. Result: From the ATR-FTIR results, the occurrence of H-bonds was proven. In addition, the blends’ rates of shape recovery and shape fixity rates were more than 99%. It contributes to the mechanical recovery at 82.75% with the addition of 10 wt% of the blended copolymer after 10 h at 70 °C, surpassing those of the 5 wt% and 20 wt% blends. Conclusion: This study will pave the way for self-heling polymers to be utilized in different fields in the future.

Heat-Stimuli Shape Memory Effect of Poly (ε-Caprolactone)-Cellulose Acetate Composite Tubular Scaffolds.

Small-diameter artery disease is the most common clinical occurrence, necessitating the development of small-diameter artificial blood vessels. In this study, seven types of poly(-caprolactone)-cellulose acetate (PCL-CA) composite nanofiber membranes were prepared with different proportions of PCL and CA. The adhesion and growth of Mc3t3-e1 cells were considered to confirm the in vitro cytocompatibility of PCL-CA membranes. A smooth stainless-steel mandrel with a diameter of 4 mm was used to roll up the prepared nanofiber membranes to produce the tubular scaffold with 50 °C hot water. The tubular scaffolds were subjected to axial and circumferential tensile tests. The mechanical performance of the PCL-CA tubular scaffold could be improved by increasing the layers. In addition, the burst pressure (BP) of the tubular scaffolds was increased with the layers, and the BPs of six-layer (2380 ± 36.8 mmHg) and eight-layer (3720 ± 80.5 mmHg) tubular scaffolds were much higher than that of the human saphenous vein (2000 mmHg). The compression shape memory performances of the PCL-CA tubular scaffold with different layers were also investigated to simulate and analyze the contraction and expansion of tubular scaffolds. The experimental results showed that the compression strain of the tubular scaffold in the diameter direction reached 35%, and the ultimate shape recovery rate reached 87%. However, the shape fixity rate and shape recovery rate increased, demonstrating that the optimum number of layers can improve the compression shape memory performance of the tubular scaffold. The results of this study, including comprehensive morphological and mechanical properties and cytocompatibility, indicated the potential applicability of PCL-CA tubular scaffolds as tissue engineering grafts.

The cooperative effect of short-cut carbon fiber and carbon black on the performance of electric-driven morphing skins

Shape memory polymers (SMPs) with variable stiffness properties become the most promising candidate materials for morphing skins. Due to the influence of external environment, electric-driven composite skin is becoming the trend of development. In this paper, rubber toughed hydro-epoxy morphing skins filled with conductive carbon black (CB) and short-cut carbon fiber (SCF) were prepared. The total mass fraction of CB and SCF was fixed at 2.6 wt %. By adjusting the content ratio of CB and SCF (CB/SCF), the in-plane mechanical property, fracture morphology, thermal-mechanical behavior, electronic resistivity, and out-of-plane shape memory behavior of five types of skin were investigated. These results showed that the addition of CB and SCF had a synergistic effect on skin performance. When CB/SCF was 5:5, the composite skin had the highest tensile strength and the lowest glass transition temperature (Tg). In the thermo-active shape memory test, the composite skin presented good shape fixity rate (Rf) and shape recovery rate (Rr). Due to the bridging effect of SCFs on CB particles, the composite skin with CB/SCF ratio of 5:5 has the minimum resistivity and can return to its initial shape within 29 s at 60 V.

Thermal, mechanical and shape fixity behaviors of shape memory cyanate under γ-ray radiation

Smart materials and structures have developed rapidly, especially their application in the aerospace field has been widely valued and recognized in recent years. Shape memory cyanate ester (SMCE) resin as a class of smart polymers has a broad application prospect in space deployable structure due to the high glass transition temperature (Tg ) and excellent mechanical properties. In this work, the SMCE resins were prepared by regulating cyanate prepolymer with small molecules, showing high Tg (> 218 °C) and high storage modulus (E' > 3.15 GPa). The SMCE resins maintained a high shape fixity rate (Rf > 95%) at high operating temperatures (100 °C and 120 °C) for 30 d, providing a great potential application for active deformation structures. Moreover, the synergy of carboxyl (–COOH) functionalized multi-walled carbon nanotubes and short carbon fiber enhanced the thermodynamic properties and shape-changing function of the SMCE composites. The spring made by SMCE composite exhibits 360° freedom rotation, which can be used as smart structures in the aerospace field.

An electric‐driven variable stiffness morphing skin: Preparation and properties

AbstractWith variable stiffness properties, shape memory polymers (SMPs) become the most promising materials of morphing skins. In this article, based on hydro‐epoxy resin/carboxyl‐terminated butadiene acrylonitrile/maleic anhydride matrix, composite morphing skins are prepared by doping conductive carbon black (CB). By adjusting the content of CB, in‐plane and out‐of‐plane properties of skins can be adjusted. Because of the in‐plane tensile stress acting on the skin during flight, tensile test is required. The results indicate that in‐plane tensile strength of skin decreases as the CB content increases. In electrical resistivity test, the electronic resistivity of skin decreases sharply at a low‐percolation threshold (1.9 wt%) and then maintains a low and steady level. As for out‐of‐plane properties, thermo‐ and electro‐active shape memory test are studied. All of the selected typical composite skins have 100% thermo‐driven shape recovery rate. Some skins have 100% thermo‐driven shape fixity rate and fast electro‐active shape recovery speed. When the CB content is 2.6 or 3 wt%, the skin can recover its out‐of‐plane deformed shape completely at 150 V. Benefit from easy control and remote drive, the composite SMP skins are proved to be a promising candidate material for morphing skins.

A variable stiffness morphing skin: preparation and properties

In the course of flight, morphing skins play an important role in morphing aircrafts. Shape memory polymer (SMP) with variable stiffness performance is a good candidate material for skin. In this paper, a series of SMP morphing skins were prepared from hydro-epoxy resin, carboxyl-terminated butadiene acrylonitrile (CTBN) and maleic anhydride. By adjusting molecular weight and content of CTBN, in-plane properties and out-of-plane properties of morphing skins can be adjusted. Due to the in-plane tensile stress acting on the skin during flight, tensile test was carried out to study its in-plane performance. After testing, skin can resist maximum in-plane tensile strength of 63.7 MPa. As for the out-of-plane performance of the skin, shape memory test was studied in this paper. All morphing skins have 100% shape fixity rate (Rf) and fast shape recovery rate (Rr). When toughened by CTBN of 10% of 4000 molecular weight with a mass fraction, the skin can recover its out-of-plane deformed shape in 33 s. The SMP skins were proved to be a promising candidate for morphing skins.

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.

Near infrared-induced shape memory polymer composites with dopamine-modified multiwall carbon nanotubes via 3D-printing

A simple modification process was developed to improve the mechanical and thermal properties of near-infrared (NIR) induced shape memory polymer composites without compromising their shape memory properties. A combination of 3D printing technology and polyurethane/polycaprolactone blends with dopamine/multi-walled carbon nanotubes (PMWCNTs) filler was used in preparing NIR-induced shape memory composites. The X-ray photoelectron spectroscopy, Fourier transformed infrared (FTIR), thermo gravimetric analysis (TGA), and transmission electron microscopy imaging results showed that the MWCNTs were successfully modified. The tensile strength of composites reached 46.1 MPa when PMWCNTs content was 3 wt%. The scanning electron microscopy imaging results revealed a good dispersibility of PMWCNTs in composites. FTIR results showed that PMWCNTs formed hydrogen bonds with composites matrix. The X-ray diffraction (XRD), TGA, and Differential scanning calorimetry results illustrated that PMWCNTs were beneficial for improving the crystallinity and thermal properties of composites, further proving the existence of hydrogen bonds. The addition of PMWCNTs made composites to have higher thermal conductivity. The high thermal conductivity of 1.901 W m−1 K−1 was achieved at a relatively low content of PMWCNTs (5 wt%), which was 3.6 times higher than that of the composites without fillers. When the PMWCNTs’ content was 3 wt%, the composites still showed that the shape fixity rate was over 90% and the shape recovery rate was over 75% after three shape memory cycles, indicating that the good shape memory property was retained. The shape memory behavior of NIR induced 3D printed models was successfully achieved and is obviously demonstrated.

High glass transition temperature shape‐memory materials: Hydroxyl‐terminated polydimethylsiloxane‐modified cyanate ester

ABSTRACTHydroxyl‐terminated polydimethylsiloxane (HTPDMS) and hydrogenated bisphenol A‐type epoxy resin (AL‐3040) were coreacted with a silane coupling agent (KH‐550) to form an AL‐3040 epoxy resin–HTPDMS block copolymer. Then, the copolymer was used as a compatibilizer to modify cyanate ester with different mass ratios. Subsequently, the blend was cured to form HTPDMS‐modified shape‐memory cyanate ester. The soft Si─O─Si segments of HTPDMS act as a flexible unit that can be grafted with the crosslinked triazine structures of cyanate ester. It was excellent for the toughening modification of cyanate ester. With increasing mass ratio of compatibilizer and cyanate ester, the tensile strength and glass transition temperature (T g) of HTPDMS‐modified cyanate ester were decreased, whereas impact strength and elongation at break were increased. The shape‐memory tests exhibited that HTPDMS‐modified cyanate ester systems have excellent shape‐memory properties with a shape recovery rate of >96% and shape fixity rate of >97% and a recovery time of less than 110 s. Furthermore, Thermo‐Gravimetric Analyzer (TGA) tests showed that HTPDMS‐modified cyanate ester exhibited good thermal stability; the temperature of 10% mass loss was high at 365 °C. The char yield was increased with increasing contents of compatibilizer at 800°C. Therefore, HTPDMS modified cyanate ester exhibited much better heat resistance at high temperature. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48641.

High energy proton irradiation stability and damage mechanism of shape-memory epoxy resin

The effects of 1 MeV proton beam irradiation at 70 °C on shape-memory epoxy resin (SMEP) were investigated from the perspective of shape memory properties, dynamic thermomechanical properties and chemical structures in this paper. Results illustrated that the degradation of SMEP’s shape recovery rate was staged in contrast to the negligible degradation of shape fixity rate. The shape recovery rate reduced relatively slowly from 98.59% to 91.16% in the initial stage before the fluence reached 5 × 1014 cm−2 and then came down sharply to 38.82% after the fluence reached 1 × 1015 cm−2 and eventually reduced slowly to 36.29%. Moreover, the degradation of SMEP’s dynamic mechanical properties was also staged with the increasing of irradiation fluence. When the fluence was 2 × 1014 cm−2, there was still one peak in the tan δ spectrum shifting to higher temperature, indicating that the network of SMEP was still homogeneous and crosslinking instead of chain scissions took place mainly and homogeneously. When the fluence reached 5 × 1014 cm−2, the network of SMEP turned to be heterogeneous since there were 3 peaks split from one peak, implying that crosslinking and chain scissions coexisted simultaneously and to a similar extent. After the irradiation fluence reached 1 × 1015 cm−2, the two peaks in higher temperature merged into one peak and the intensity of this peak decreased quickly, revealing that chain scissions turned to be prominent. Structural analysis demonstrated that the chain scissions induced by 1 MeV proton irradiation mainly took place at the sites of aliphatic ether C–O groups on the surface layer, which was responsible for the significantly reduced shape recovery rate after the irradiation fluence reached 1 × 1015 cm−2.

Degeneration and damage mechanism of epoxy-based shape memory polymer under 170 keV vacuum proton irradiation

Shape memory polymers are the promising candidates for the next generation space deployable structures. However, to design highly reliable, long-life space deployable structures, it is essential to study the performance of shape memory polymers in the harsh space environments. In this work, the epoxy-based shape memory polymer was irradiated by 170 keV proton beam in vacuum condition. Multiple characterization techniques including dynamic mechanical analysis, electron paramagnetic resonance spectra, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to study the properties and microstructure changes after irradiation. Experimental results showed that the shape fixity rate remained almost unchanged at approximately 99.6% after proton irradiation while the shape recovery rate decreased sharply from its original 98.6% to 76.3% with increasing fluence up to 10 × 1015 cm−2. Moreover, the decrease of glass transition temperature and the accelerated growth of free radical concentration indicated dominant chain scissions. Further research found that the cleavage of aliphatic chemical bonds, especially C–N and C–O groups of aromatic ether and aliphatic ether were responsible for the significant drop of the shape recovery rate, suggesting that epoxy-based shape memory polymers with more aromatic rings are thought to be better choices when designing the materials for applications in space deployable structures.

Degeneration and damage mechanism of epoxy-based shape memory polymer under 1 MeV electron irradiation

The degradation behaviors of epoxy-based shape memory polymer (SMP) after 1 MeV electron irradiation were investigated in the paper. It was founded that the shape fixity rate remained almost no changed at approximately 99.6% while the shape recovery rate decreased rapidly from its original 98.6% to 85.9% with increasing fluence up to 200 × 1014 cm−2, which could be owned to the partial cleavage of the crosslinked network of epoxy-based SMP after irradiation. Further research found that the irradiation-induced scissions of the crosslinked network took place as a result of the debonding of the weak aliphatic C-O and C-N groups.

Effects of accelerated aging on thermal, mechanical and shape memory properties of cyanate-based shape memory polymer: I vacuum ultraviolet radiation

Shape memory polymers (SMPs) are novel intelligent materials. Evaluation of the durability of SMPs in the complex environment of future space applications helps to optimize their incorporation in space-deployable structures. In this paper, we performed vacuum outgassing and ultraviolet (UV) radiation exposure tests on a cyanate-based SMP with a glass transition temperature of 206 °C. The cyanate-based SMP shows 1.04% of total mass loss and 0.01% of collected volatile condensable matter, as determined by vacuum outgassing tests. Vacuum UV radiation deepened the color of the surface, shown little effect on the thermal stability of the SMP sample. The irradiation induced some instability of the molecular structure within the material, and this effect was gradually strengthened with the increase of exposure time. However, UV radiation did not detectably change the mechanical properties of the cyanate-based SMP; the tensile strength and elastic modulus remained essentially constant at 66 ± 2 MPa and 1940 ± 80 MPa, respectively. The average shape fixity rate and average shape recovery rate before and after UV radiation were all above 97.6%, and the repeatability was satisfactory.

Thermoset shape memory polymers and their composites

This article reviews the main progress in the development of typical thermoset shape memory polymers. Thermoset polymers are usually stronger in their microstructure than thermoplastic polymers due to their covalently crosslinked three-dimensional networks. The virtues of thermoset polymers make them great source materials for shape memory polymers. However, their three-dimensional networks endow thermoset shape memory polymers with not only high shape fixity rates and shape recovery rates but also low deformation abilities and brittleness. In the past decade, many breakthroughs have been made regarding thermoset shape memory polymers. Typical thermoset materials, such as epoxy resin, cyanate resin, thermoset polyurethane, polyimide, and polystyrene, have been studied as raw materials for shape memory polymers. Studies on thermoset shape memory polymers have been carried out to not only improve their fundamental properties (i.e. broadening of their operating temperatures and service environments and enhancing their thermal stabilities and mechanical properties) but also introduce functional performance properties (e.g. responsiveness to light, electricity, magnetism, and chemical stimuli). This article aims to present a brief review of the development of thermoset shape memory polymers, including the selection and preparation of materials, the improvement of properties, the functionalization of their composites, and their potential applications.

Lignin valorization by forming toughened thermally stimulated shape memory copolymeric elastomers: Evaluation of different fractionated industrial lignins

ABSTRACTLignin‐based thermal responsive dual shape memory copolymeric elastomers were prepared with a highly branched prepolymer (HBP, A2B3 type) via a simple one‐pot bulk polycondensation reaction. The effect of fractionated lignin type (with good miscibility in the HBP) on copolymer properties was investigated. The thermal and mechanical properties of the copolymers were characterized by DMA, DSC, and TGA. Tensile properties were dominated by HBP <45% lignin content while lignin dominated >45% content. The copolymers glass transition temperature (Tg) increased with lignin content and lignin type did not play a significant role. Thermally stimulated dual shape memory effects (SME) of the copolymers were quantified by cyclic thermomechanical tests. All copolymers had shape fixity rate >95% and >90% shape recovery for all compositions. The copolymer shape memory transition temperature (Ttrans) increased with lignin content and Ttrans was 20°C higher than Tg. Lignin, a renewable resource, can be used as a netpoint segment in polymer systems with SME behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41389.

Shape memory thermoplastic elastomer from maleated polyolefin elastomer and nylon 12 blends

Semicrystalline maleated polyolefin elastomer (mPOE) and nylon 12 were melt blended in an internal mixer at 200 °C with proportions of 90/10, 80/20, and 70/30 wt/wt, respectively. Molau test, melt viscosity measurement, differential scanning calorimetry, dynamic mechanical analysis and tensile testing were conducted to characterize the structure and properties of the blends. The results revealed that POE-graft-nylon 12 copolymer was formed during the mixing, and the blends show two melting transitions at 57–60 and 174–178 °C attributed to mPOE and nylon 12, respectively, which are dependent on the blend composition. The blends exhibit typical thermoplastic elastomeric behavior and their tensile modulus, strength and hardness increase with increasing nylon content. It was also observed that the blends form a physically crosslinked structure until the melting transition of nylon 12. The blends exhibit excellent thermally triggered shape memory effect, i.e., almost 100 % shape fixity rate and 100 % shape recovery rate, and the recovery occurs in a few seconds when the temporarily fixed shaped sample is heated just above the Tm of mPOE phase in the blends.

Influence of blocked polyisocyanate on thermomechanical, shape memory and biodegradable properties of poly(lactic acid)/poly(ethylene glycol) blends

A series of shape memory biodegradable blends from poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were prepared by solution casting method. Ethyl cellosolve-blocked polyisocyanate (EC-bp) was synthesized and used as a cross-linker to obtain cross-linked PLA/PEG blends. The chemical structure of the prepared composite was confirmed by Fourier transform infrared spectra. Thermomechanical, thermal and shape memory properties of the blends were investigated and compared by dynamic mechanical analysis, thermogravimetric analysis and shape memory testing. The results showed that EC-bp cross-linked PLA/PEG blends had better thermal and thermomechanical properties than non-cross-linked blends and displayed good shape memory effects in both shape fixity rate and shape recovery rate. Moreover, the effect of EC-bp addition on the rate of biodegradable degradation in a phosphate buffer solution (pH 7.4) was studied at 37 °C. The prepared cross-linked PLA/PEG blends demonstrated better degradation resistance compared to the non-cross-linked blends.

Shape-Memory Properties of Nanocomposites based on Poly(ω-pentadecalactone) and Magnetic Nanoparticles

ABSTRACTMagneto-sensitive shape-memory polymers (SMP) obtained by incorporating magnetic nanoparticles in a SMP matrix are an emerging class of multifunctional materials. The incorporation of the nanoparticles enhanced the mechanical properties and in addition enabled remote actuation by exposure to alternating magnetic fields. Here, we report on the thermallyinduced shape-memory properties of such magneto-sensitive nanocomposites based on poly(ω- pentadecalactone) (PPDL) switching segments and magnetic nanoparticles. A series of nanocomposites were prepared by crosslinking of poly(ω-pentadecalactone)dimethacrylate (Mn = 2800 g·mol-1and 5100 g·mol-1) in the presence of silica encapsulated magnetic nanoparticles. The silica shell of the nanoparticles was selected to enhance the distribution and compatibility of the nanoparticles with the polymer matrix. Thermal and mechanical properties of the nanocomposites were explored as a function of PPDL chain length and nanoparticle weight content. All nanocomposites exhibited excellent shape-memory properties with shape fixity rates between 86% and 93% and shape recovery rates above 97%. Potential applications for such shape-memory nanocomposites include smart implants, medical instruments, which could be controlled on demand by thermal or indirect magnetic heating.

Shape-Memory Properties of Electrospun Non-wovens Prepared from Amorphous Polyetherurethanes Under Stress-free and Constant Strain Conditions

ABSTRACTThe shape-memory properties of electrospun polyetherurethanes (PEU) non-wovens with a single fiber diameter of around 1 μm were explored. In uniaxial cyclic, thermomechanical tensile tests a dual-shape shape-memory creation procedure (SMCP) was applied and the shape recovery was examined under stress-free and constant strain conditions. The thermal properties of the electrospun PEU non-wovens were found to be similar to those obtained for bulk PEU samples, whereas the mechanical properties revealed differences with respect to the elongation at break (εb) at increased temperatures. Excellent dual-shape properties were achieved for the PEU non-wovens with a high shape fixity rate (Rf) and shape recovery rate (Rr). A significant higher recovery stress (σmax) was obtained under constant strain recovery conditions for the electrospun non-wovens compared to the bulk PEU samples, which might be attributed to the higher degree of orientation of the polymer chains in the microfibers. Therefore the influence of different (single) fiber diameters as well as the variation of the programming elongation εm and temperature Tprog on σmax is an interesting issue for future investigations.