Shape Memory Polymer Composites Research Articles

Experimental investigations of temperature-sensitive shape memory polymer composites for 4D printing

Shape memory polymers (SMPs) and their composites (SMPCs) have emerged as popular materials in a variety of industries due to their unique properties of shape-changing behavior in response to external stimuli. The inclusion of reinforcement may modify the SMPs to enhance their thermal and shape memory properties. Different types of bio ceramics have already been used to alter the thermal and shape memory behavior of SMPs. However, using bioactive glass (BG) as filler to modify these properties has not yet been explored. Despite the significant advantages that shape-memory polymers (SMPs) offer when combined with 3D/4D printing technology, their potential in 3D printing has been explored only to a limited extent. This work created a solvent-based 4D-printed temperature-sensitive shape memory polymer composites (SMPCs) system using polylactic acid (PLA) and bioactive glass (BG). The influence of BG on the thermal as well as shape-memory capabilities of composites was further examined. An increase in the degree of crystallinity and viscoelastic characteristics of PLA/BG composites led to improved shape memory properties, like shape fixity and shape recovery. These findings suggest the potential for using the developed SMPC printed through 4D printing technology, to develop complex shapes for self-foldable structures and smart biomedical devices in the future.

Matrix‐phase material selection for shape memory polymer composites: A comparative analysis of multi‐criteria decision‐making

AbstractIn the present study, the selection of suitable shape memory polymers (SMPs) to be used as the matrix‐phase material with various (In)organic filler materials to achieve the required optimum multi‐stimuli response in shape memory polymer composites (SMPC) systems is analyzed. The selection of these materials is based on their mechanical and physical properties as well as other underlying factors such as cost, availability, shape recovery rate, and aesthetic characteristics. In this study, the entropy method was applied to estimate the weightages of the various criteria while the gray relation analysis (GRA) and the technique for order preference by similarity to ideal solution (TOPSIS). Multi‐criteria decision‐making (MCDM) approaches have been used to rank the suitable matrix‐phase polymer materials for manufacturing shape memory polymer composites (SMPC) system. A total of eight alternative SMP matrix‐phase materials based on a set of nine criteria were analyzed and ranked. The proposed methodology and the result obtained thereof have been illustrated in detail. The results obtained from TOPSIS and GRA methods have been compared to conclude the effects of the material properties on the ranking and the selection of the SMP materials. Among all the eight alternatives considered, thermoplastic polyurethane (TPU) was found to be the best material in both the MCDM methods. The material cost, resistivity, % elongation, and hydrophobicity present the most influencing properties on the SMP material selection, whereas density presents no effect on the SMP matrix material selection. The robustness of the results for the comparative analysis was verified using TOPSIS methodology to validate its reliability. It was revealed that the TPU, polycarbonate, polypropylene, and epoxy‐resin/poly(lactic acid) are the most dominant matrix‐phase SMP material alternatives when a deviation in the entropy weights of the primary evaluation criteria is applied. The novelty of this study is the exploration and application of statistical MCDM methods of engineering material selection problems based on a set of decision criteria, which can be time‐consuming and costly while using experimental analysis methods.Highlights SMPCs are applicable engineering materials thus making their research viable. SMPC systems can undergo various shape changes under external stimuli. Selection of matrix‐phase polymer is critical in achieving desired objectives. GRA and TOPSIS MCDM approaches have been applied in the selection process. TPU was found as the best material in both methods.

Design, fabrication and experimental verification of a drag sail based on thermal-driven controllable bi-stable shape memory polymer composite booms

Deployable drag sails are used for passively deorbiting defunct satellites and other spacecraft. Designing the deployable boom is the main challenge in this technology. We present a bi-stable shape memory polymer composite (Bi-SMPC) boom with high stiffness, a high unfolding/folding ratio, and consistent roll-out deployment. It was designed and fabricated by a strategy of controlling the gradual release of elastic energy stored in a bi-stable composite structure through thermal-driven SMP matrix. Two heating layer strategies were investigated experimentally to determine the optimal driving layer and driving parameters. Based on these parameters, verification tests of a four-stage deployment Bi-SMPC boom were conducted. Meanwhile, a proof-of-concept prototype of a four-stage deployment drag sail based on the Bi-SMPC booms was designed and fabricated. Tests were conducted to verify the effectiveness of the drag sail deployed by the booms. It was found that SMPs can effectively control the deployment of bistable composite structures. The nickel-chromium alloy heating layer offers a more uniform driving temperature field compared to carbon fiber. The drag sail can be deployed successfully under the driving of four Bi-SMPC booms.

Effect of the LEO space environment on the functional performances of shape memory polymer composites

For the first time, shape memory polymer composites (SMPCs) have been exposed in LEO environment by the MISSE-FF platform: two carbon-fiber reinforced laminates with an SMP interlayer were retrieved after 1 year of exposure, and tested on Earth. Microscopy, DSC, FTIR and mechanical tests were carried out on flight and backup samples. Results show that flight samples behaved differently, because of their different orientation on MISSE-FF. The applied deformed shape was partially recovered on the sample with zenith orientation during its exposure, but both flight samples did not show any additional shape recovery on-Earth. The other sample, with wake orientation, froze the non-equilibrium shape permanently.

Shape memory behaviors of three-dimensional five-directional braided composites with different axial yarns arrangements

The effect of braided structure on shape memory behaviors of 3D braided composites is critical to design the responses of the composite under external fields. Here we report the effect of axial yarn on shape memory behaviors of three-dimensional five-directional (3D5d) braided shape memory polymer composites (SMPCs) under bending. It was found that the axial yarns will improve bending stiffness and electro-thermal behaviors significantly. The thermomechanical deformation and shape memory effect of SMPCs are influenced by the braiding structural parameters. Specifically, the 3D5d SMPCs exhibits a 53.6% increase in bending recovery force and a faster shape recovery speed than those of 3D four-directional SMPCs. We found from finite element analyses (FEA) that the axial yarns positions influence the inner stress distribution and shape memory behaviors of SMPCs. The axial yarns distributed on both sides of SMPC influence the shape memory behaviors more than those of the middle layer.

4D printing and programming of continuous fibre-reinforced shape memory polymer composites

This study demonstrates the use of fused filament fabrication (FFF) 4D printing (4DP) to print programmable continuous fibre-reinforced composite (CFRC) structures with exceptional strength and eco-friendly features. This research focuses on bio-shape memory polymer composites (SMPCs) and employs experiments to fabricate lightweight CFRC parts using FFF technology. Different types of continuous fibres, including carbon fibre (CF), aramid fibre (AF), and fibreglass (FG), are incorporated into a biopolymer matrix made of biodegradable polylactic acid (PLA). The study evaluates microstructure, mechanical properties, and shape memory properties of SMPCs, employing techniques like cold and hot programming. Continuous fibres significantly enhance mechanical properties, increasing strength by over 1027.5 % in tensile tests and nearly 497.3 % in three-point bending tests. The research also addresses shape recovery and fixity ratios in 4D-printed SMPCs, finding a decrease when continuous fibres are incorporated into PLA. Notably, FGPLA specimens achieve the highest shape recovery ratio of approximately 95 ± 1 % after pure PLA. These findings highlight the potential of 4D-printed CFRCs in various applications, from human-material interaction to mechanical and biomedical fields. They contribute to sustainability by reducing material consumption and waste, demonstrated through the creation of reusable and lightweight items like hooks, lockers, finger splints, and meta-composites.

Equivalent plate model of shape memory polymer composite based variable height corrugated structure

In this work, an equivalent plate model for a shape memory polymer composite based corrugation structure with varying height, for morphing application, is developed. A thermodynamically consistent constitutive relation based on temperature dependent phase transformation concept for shape memory polymer matrix is used in the composite model. The homogenization model is based on the equivalence of strain energy of a representative unit volume. Following validation, as an application, commonly used airfoil profile NACA 63210 was considered to demonstrate the model utility. Parametric studies have been undertaken to investigate the influence of corrugation parameters like thickness and number of corrugations.

Dynamic mechanical response and deformation mechanism of poly (ε-caprolactone) (PCL) / epoxy resin(EP) shape memory polymer composites

The dynamic mechanical response and deformation mechanism of poly (ε-caprolactone) (PCL) and epoxy resins shape memory polymer (SMP) composites were investigated in this paper. The SMP composites were a blend of PCL and epoxy resins by using the facile melt-mixing method. The distribution of PCL in the composites was observed by SEM, which was in from microparticle morphology to continuous morphology with the increasing PCL content. And the dynamic mechanical analyzer (DMA) tests were performed to demonstrate the viscoelastic properties and shape memory effect of the PCL/EP composites. Based on the above characterization of PCL/EP composites, the split Hopkinson pressure bar (SHPB) tests were performed to study the dynamic mechanical properties at the strain rates of 4000/s to 7000/s. The results showed that the flow stress increased with the increasing strain rate, which exhibited an obvious sensitivity to strain rate. However, the flow stress of PCL/EP decreases with the increasing PCL content due to the low strength of PCL. And PCL/EP composites failed in a typical ductile failure mode under quasi-static loading, whereas an excellent plastic deformation ability was observed at high strain rates, which was attributed to the heat generated by the plastic work during the adiabatic compression. Combining with the experimental results, the corresponding deformation mechanism was also discussed.

PLLA/(MWCNTs-ZnO)@PDA composite with NIR-light induced shape memory effect, antibacterial properties and 3D printability

PLLA based shape-memory polymer composites with multifunctions have attracted growing attention in biomedical applications. Generally, a single nanofiller has the problem of insufficient functionalization and easy aggregation. Therefore, we design and fabricate polydopamine (PDA) surface modified MWCNTs-ZnO hybrid nanostructure ((MWCNTs-ZnO)@PDA). The dispersion of (MWCNTs-ZnO)@PDA in PLLA is improved in comparison with the pristine MWCNTs or ZnO. The results indicate that the (MWCNTs-ZnO)@PDA nanosystem shows a synergistic effect on the mechanical properties and photothermal properties of the composites. Comparative analysis with neat PLLA demonstrates a remarkable 17% increase in tensile strength and a 19% increase in elongation at break for PLLA/(MWCNTs-ZnO)@PDA composite. Additionally, the composites exhibit excellent NIR light-induced shape memory effects with a shape recovery ratio reaching 100%. Moreover, PLLA/(MWCNTs-ZnO)@PDA composites show favorable antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Furthermore, the polymer composites display good 3D printability, and the 3D-printed porous scaffold possesses high compressive strength and modulus. Also, the PLLA/(MCNTs-ZnO)@PDA scaffold can be compressed into a compact size and recover its original shape under NIR light irradiation. This work provides an approach to prepare novel shape-memory polymer composites with multifunctions including high strength, light-induced shape-recovery, antibacterial properties and printability.

4D printed continuous fiber reinforced shape memory polymer composites with enhanced mechanical properties and shape memory effects

Multi-material four-dimensional (4D) printing has gathered significant interest among researchers as an emerging manufacturing technique. In this study, continuous carbon fibers are integrated into shape memory polymers (SMPs) using multi-material co-extrusion 4D printing. This process results in the creation of shape memory polymer composites (SMPCs) characterized by high load-bearing capacity and stimulus responsiveness. Micro-CT scanning is employed to evaluate the internal porosity of SMPCs, based on which the three-dimensional (3D) reconstruction images are generated. Meanwhile, various mechanical tests are implemented, including tensile, three-point bending, and compression tests, to explore the mechanical properties and fracture modes of the 4D printed SMPCs. In addition, the shape memory effect of the 4D printed SMPCs is verified by experiments and finite element simulations. The results demonstrate shape recovery rates higher than 96%. This study offers valuable insights into the fabrication and testing of smart composites with compatible deformation and high load-bearing capacity.

Shape memory polymer composite fabrics with high recovery force and excellent electrothermal drive deformability

AbstractFabric‐reinforced shape memory polymer composites are lightweight, strong, formable, controllable, and suitable for various engineering and innovative applications. This study aims to fabricate and characterize electrothermal dual drive shape memory polymer composite fabrics (SMPCFs) of different densities with three‐dimensional (3D) angle‐interlock structures. The tensile properties, electrothermal properties, recovery forces (both tensile and bending), and shape recovery properties of SMPCFs were evaluated. The SMPCFs exhibited a tensile elongation of over 20% at the transition temperature. SMPCFs can reach transition temperatures when loaded with 2 V. The recovery forces are up to 225 N in tensile recovery force and 3.6 N in bending recovery force. In the shape recovery test, the recovery ratio exceeded 97%. Finally, the demonstration of recovery properties can stimulate the possibilities of SMPCFs in innovation and applications.Highlights Core‐shell structured composite filaments were prepared. 3D angle‐interlock composite fabrics: high strength, electrothermal drive. Tensile recovery force of composite fabrics can be up to 225 N. Elongation at transition temperatures was up to 20%.

Self-Unfolding Properties of Smart Grid-Reinforced Membrane Origami

Origami-based membrane structures have shown great potential to revolutionize the construction of deployable and lightweight space structures in the future. However, the efficient unfolding mechanism puts forward major challenges to the practical realization of space-deployable structures. Here, a smart grid-reinforced membrane origami (SGRMO) is presented. The unfolding action hinges upon the application of forces facilitated by shape memory polymer composites (SMPCs). Subsequent locking action ensues through the restoration of the initial rigidity, accomplished via cooling mechanisms. This novel structure achieves the required lightweight and functionality by employing the grid design concept and effectively reduces the decline in unfolding extent caused by irreversible plastic deformation at the crease. Its recovery properties, including unfolding angle, distance, and surface precision, are experimentally and analytically investigated under different conditions. The results indicate that the structure can be reliably unfolded into the predefined shapes. In the case of Miura-SGRMO, the optimal surface precision is attained when the angle-ψ registers at 30°. The results of this study are expected to serve as the design of ultra-large flexible solar arrays and deployable antenna structures.

Effect of kenaf fiber loading on mechanical and morphological properties of polyurethane shape memory polymer composites

Shape memory polymers (SMPs) have captivated researchers and engineers with their unique ability to recover their original shape after deformation. Among SMPs, shape memory polyurethane (SMPU) is promising due to its easy processing, cost-effectiveness, and biocompatibility. Despite its potential, SMPU faces limitations in strength and modulus, hindering structural applications. This study investigates the sustainable improvement of shape memory polymer composites (SMPCs) by integrating kenaf fibers (KF) as a reinforcing material at different percentages, specifically 5%, 10%, 15%, 20%, 30%, and 40% of the composite’s weight. A combination of hand lay-up technique and compression moulding technique was employed for the fabrication process to achieve the desired shape. The results reveal a clear correlation between the KF content and the mechanical properties. Tensile testing reveals improved strength and strain up to 20% KF, peaking at this level but declining at 30% and 40% due to fiber agglomeration and void formation. Scanning electron microscope (SEM) analysis highlights favourable fiber-matrix adhesion at optimal level. By shedding light on the mechanical behaviour of SMPC with KF reinforcements, this study paves the way for developing high-performance composites tailored for shape memory applications.

4D printed biocompatible magnetic nanocomposites toward deployable constructs

Herein, an alternating magnetic field-triggered shape memory polymer composite has been 3D printed as a tissue scaffold that can be remotely deployed at physiological temperatures and can be extended to soft robotics.

Recent Advances in Shape Memory Polymers: Multifunctional Materials, Multiscale Structures, and Applications

AbstractShape memory polymers (SMPs) are one of the primary directions in the development of modern high‐tech new materials, which are integrated with sensing, actuation, information processing, and autonomous deformation. Here, multifunctional shape memory polymers are focused and a detailed introduction to the characteristics of self‐deformation, self‐sensing, self‐healing, and self‐learning is provided. Integrating with other functional materials to form shape memory polymer composites (SMPC), designing and controlling the material structure and organization at the microscale, thereby achieving more precise and controllable shape memory effects and expanding the potential of material applications. Ultimately, it is shown that SMPs and their composites have a wide range of fascinating applications in the fields of robotics, smart clothing, smart textiles, biomedical devices, and wearable technology. SMPs will thus continue to play a significant role in future deeper exploration.

Axial and radial reversibility and energy absorption behaviors of braided shape memory composite thin-walled tubes

Braided shape memory polymer composites (SMPCs), which integrate braided structures with shape memory polymers, are well-known for their superior mechanical properties, reversible deformation, and recovery capabilities. This study focused on exploring the reusable energy absorption capacity of intelligent braided SMPC tubes. The effects of braiding structure on compression modes, mechanical properties, energy absorption, shape memory performance, and repeatability under axial and radial compression have been comprehensively investigated. The results show that SMPC tubes have a shape recovery ratio exceeding 94 % after four cycles. As the number of compressions increased, both the mechanical and energy absorption properties decreased, particularly during the first compression. Higher energy absorption capacity has been observed in SMPC tubes with larger braiding angles, up to 32.51 J, 2.3 times that of pure TPU tubes. These findings offer potential approaches for the development of high-performance reusable protective devices and lightweight intelligent structures.

Design and Optimization of 4D Printed Carbon Fiber Reinforced Poly Lactic Acid Parts Using Fused Deposition Modeling for Shape Memory Applications: A Taguchi Approach

The manufacturing industry has witnessed substantial interest in the advancement of 4D printing technology in recent years. This technology has enabled the production of complex structures with enhanced functionality and adaptability. Fused Deposition Modeling (FDM) has become a preferred technique for 4D printing due to its ease of use, affordability, and versatile nature. To achieve efficient and effective 4D printing, the process parameters must be optimised to ensure the desired shape recovery behaviour of the printed parts. The main objective of this study is to optimize the process parameters for the production of 4D printed components using FDM technology and Carbon Fiber reinforced Poly Lactic Acid (CF/PLA) Shape Memory Polymer Composites (SMPCs). This study examines the shape recovery properties of the printed components by modifying the process parameters, including Infill Density (ID), Geometrical Thickness (GT), and Bending Angle (BA), through the implementation of Design of Experiments (DOE) L9 Orthogonal Array (OA). Utilizing Analysis of Variance (ANOVA) to determine the significant factors and their optimum levels, the process parameters are statistically analysed. The results indicate that ID and GT are the statistically significant parameters, and the optimum levels for parameters includes 20% ID, 1.5mm GT, and 300 BA led to faster shape recovery. This study demonstrates the effectiveness of the Taguchi approach in the design and optimization of the process parameters for 4D printed parts using FDM.

A three-dimensional constitutive equation for shape memory polymer composites considering energy dissipation under single loading–unloading condition

Shape memory polymer composites (SMPCs), composed of shape memory polymers (SMPs) and fabrics, can recover their deformed shapes to initial configurations by changing temperature. The shape recovery energy of the SMPs and the elastic energy of the fabrics are regarded as key points to predict the restored configuration of the SMPCs. In this research, a three-dimensional constitutive equation for SMPCs is newly developed, considering the energy dissipation of fabrics under a single loading–unloading condition. The constitutive equation is derived from Mooney–Rivlin, viscoelastic, and stored strain energy models for SMPs, as well as polynomial functions for fabrics. The Mooney–Rivlin and viscoelastic models describe the time- and temperature-dependent hyperelastic properties, and the stored strain energy model can explain the shape recovery. The polynomial functions are newly proposed to take into account the dissipated energy of fabrics, such as residual deformation and hysteresis effect. Because the elastic energy of fabrics considerably influences the shape recovery of SMPCs, the proposed constitutive equation can accurately predict the recovered configuration. Analyses of SMPCs are conducted using the finite element method and validated by comparing them with the results obtained from experiments. The constitutive equation is used to analyze the shape recovery behaviors of an SMPC skin. The skin can be largely stretched, and the deformed shape can be restored to its initial shape by applying electricity. The SMPC skin is applied to a morphing flap, and its shape-changing behaviors are demonstrated experimentally.

4D printed and multi-stimulus responsive shape memory polymer nanocomposites developed on hydrogen bonding–metal-phenolic sacrificial network: Application for hazardous chemical operations soft robots

Designing 4D printed shape memory polymers (SMPs) with mechanical robust and multi-stimulus responses applied in soft robot holds vast promise. While significant progress has been made in this area, implementing SMP composites with multi-stimulus response capabilities for fused filament fabrication (FFF) 4D printing typically sacrifices the inherent mechanical properties of the materials, limiting the requirements for robust and tough applications of SMP in soft robotics. In this work, Fe3O4 nanoparticles are employed as functional particles, and the "hydrogen bonding–metal-phenolic" sacrificial network in the nanoparticles and polymer is designed to achieve NIR light and magnetic stimulation response without sacrificing the maximum strength and toughness of the 4D printable SMP. The SMP nanocomposite developed from the sacrificial network has a tensile strength of 18.98 MPa and an elongation at break of 897 %, a 40 % increase in strength and 196 % increase in elongation at break compared to SMP nanocomposites with direct Fe3O4 addition. In addition, the shape-programmable soft robot with NIR light and magnetic stimulation response is developed based on 4D printing. The remote precision control and drugs release demonstrates the potential application of 4D printed soft robots in hazardous chemical operations.

Smart Composite Booms for Solar Sails

Composite booms for solar sails have been prototyped by using innovative smart materials. Shape memory polymer composites (SMPCs) have been manufactured by interposing SMP layers between carbon-fiber-reinforced (CFR) plies. A polyimide membrane has been embedded into the CFR-SMPC frame of the sail during lamination. The sail’s size has been limited to 250 × 250 mm2 to allow its testing on Earth. The feasibility of large sail deployments has been shown by prototyping small CFR-SMPC elements to insert only in the folding zones. Numerical simulation by finite element modeling allowed for predicting the presence of wrinkles close to the frame’s vertexes in the cases of large sails under solar radiation pressures. Nevertheless, the frame’s configuration, with SMPC booms at all the edges of the sail membrane, seems to be suitable for drag sails instead of propulsion. On-Earth recovery tests have been performed on 180° folded sails by using flexible heaters. After an initial induction time, the maximum rate was reached with a following drop. In the case of two heaters per folding zone, the angular recovery rate reached the maximum value of about 30 deg/s at the power of 34 W, and full recovery was made in 20 s.