Triple-shape Memory Polymers Research Articles

Magnetic-responsive triple shape memory polymer from bio-based benzoxazine/urethane polymer alloys with iron oxide nanoparticles

Novel magnetic-responsive triple shape memory polymers (SMPs) derived from bio-based benzoxazine-urethane (V-fa/PU) polymer alloys containing iron oxide nanoparticles (Fe3O4 NPs) were developed in this work. Shape memory effect and curing behavior of the alloys were investigated at various bio-based PU contents. The polymerization of V-fa/PU polymer alloys with a heterogeneous network generated a broad glass transition temperature, which is a crucial feature for the development of triple SMPs. The influence of Fe3O4 NPs incorporation into the polymer nanocomposites on the SMP performance triggered by magnetic fields was also investigated. It was found that the addition of Fe3O4 NPs can enhance the dynamic mechanical properties and magnetic characteristics of the V-fa/PU polymer alloys thanks to the superparamagnetic property of Fe3O4 NPs. Moreover, the performance of the SMPs based on V-fa/PU polymer nanocomposites filled with Fe3O4 NPs showed high shape fixity of up to 98%, a shape recovery of 98%, and a recovering time of 8 s. Furthermore, bio-based V-fa/PU polymer alloys containing Fe3O4 NPs were developed as magnetic responsive triple SMPs with shape fixity in the range of 95–97% and shape recovery in the range of 85–95%. The results suggested that magnetic responsive triple SMPs from bio-based V-fa/PU polymer alloys filled with Fe3O4 NPs are promising candidate for advanced applications.

A thermo-mechanical constitutive model for triple-shape and two-way shape memory polymers

Semicrystalline polymers often have diverse molecular configurations in response to the variation of temperature, making it easier to realize multiple or two-way shape memory effects (SMEs). In order to provide guidance for the design of relevant smart structures, it is necessary to develop corresponding constitutive models to better characterize the thermal-mechanical behavior of such shape memory polymers (SMPs). For the first time, a thermo-mechanical finite deformation constitutive model is presented to reveal the deformation mechanism of the triple-shape two-way SME of semicrystalline SMPs in our work, based on the theory of thermodynamics with internal state variables. To verify the validity of the model, the model results are compared with the test data for a typical shape memory cycle. It is found that the model can be employed to describe the non-equilibrium response of semicrystalline SMPs with two types of crystallites in the vicinity of crystallization and melting. Since the model results fit well with the test data, the effectiveness of the model in predicting the triple two-way shape memory behavior is demonstrated.

Kinetic criterion for triple-shape memory effect in amorphous polymers undergoing heterogeneous glass transitions

The triple-shape memory effect (triple-SME) in amorphous polymers arises from the heterogeneous glass transitions of different components. However, due to the complex composition and structural relaxation of triple-shape memory polymers (triple-SMPs), existing models struggle to characterize the shape memory temperature range for each component and its dependence on thermal history. This presents a challenge in developing a kinetic criterion to judge the occurrence of the triple-SME. To address this issue, we propose a kinetic phase transition model to predict the shape memory temperature range for each transition phase in triple-SMPs under different thermal histories. By combining the Tool-Narayanaswamy-Moynihan (TNM) model with the Adam-Gibbs theory, the effect of cooling rate during programming on subsequent triple-SME is investigated. Subsequently, the effectiveness of the proposed model is evaluated by applying it to predict the shape memory performance and thermomechanical behavior of SMPs with dual- and triple- SMEs under different thermal histories. Using this modeling strategy enables the calculation of the critical isothermal shape recovery time for each transition phase under different thermal histories, effectively preventing shape recovery overlap. Consequently, the proposed model is expected to provide theoretical guidance for designing SMPs with triple-SME and promoting their application in engineering.

Photoresponsive triple shape memory polymers with a self-healing function based on poly (lactic acid)/polycaprolactone blends

Self-healing shape memory polymers (SMPs) have considerablepotential in advanced manufacturing and biomedical fields. Polypyrrole (PPy) exhibits excellent photoconversion properties, which may be utilized in SMP formulation; however, its application in this regard has not been explored. In this study, PPy-filled polymer nanocomposites were prepared to investigate their shape memory and self-healing characteristics. First, poly(lactic acid) (PLA) and polycaprolactone (PCL) were blendedto form PLA/PCL shape memory matrices. An 80:20 PLA/PCL blend showed excellent triple-shape memory performance with shape recovery rates (Rr1, Rr2, and Rr3Rr) of 92%, 87%, and 93%, respectively PPy nanoparticles were then incorporated into the blend as photothermal conversion fillers to develop photoresponsive SMPs. SMPs. The resulting PLA/PCL/PPy nanocomposites exhibited elevated surface temperatures during near-infrared (NIR) irradiation, thus demonstrating the photoconversion effect. In addition, these nanocomposites showed reversible triple-shape change behavior and excellent self-healing efficiencies upon NIR exposure, owing to the controllable melting and recrystallization of the PLA and PCL phases. Furthermore, the material properties of severed nanocomposites were restored after self-healing. These results, in addition to the biocompatibility and simple fabrication process of these materials, therefore demonstrate the potential utility of PPy-filled SMPs in several applications, including soft robotics and biomedical devices.

Thermo-mechanical modeling of viscoelastic crystallizable shape memory polymers

Shape memory polymers (SMPs) are a class of soft active materials that have the ability to retain one or multiple temporary shapes and exhibit deformation as a response to stimuli. The temporary shapes involved can be very complex but SMPs can recover large amounts of strains as compared to other smart materials. They have a wide range of applications in fields as diverse as healthcare, transportation, energy generation, etc. and their mechanism can be easily altered. Hence, there is an increasing need to model their behavior. This paper discusses the behavior of a thermally activated subclass of SMPs in which the temporary shape is fixed by a crystalline phase and the return to original shape is due to the transition of this crystalline phase. We simulate its thermo-mechanical behavior using a framework based on the theory of multiple natural configurations. Viscoelastic effects have been incorporated using a rate type model along with the anisotropy of the crystalline phase. The model has been applied to boundary value problems of homogeneous deformations such as uniaxial extension of dual shape and triple shape memory polymers under controlled stress and strain conditions. The model has also been applied to boundary value problems related to inhomogeneous deformations such as circular shear, inflation, and extension of a hollow cylinder. The effects of parameters such as temperature, external stress, crystallinity, shear modulus and relaxation time on the nonlinear deformation have been studied. The results are found to be consistent with the experimental data and show how the complicated thermo-mechanical behavior and shape memory effect are influenced by these parameters.

Designing self-crosslinkable ternary blends using epoxidized natural rubber (ENR)/poly(ethylene-co-acrylic acid)(EAA)/poly(ε-caprolactone) (PCL) demonstrating triple-shape memory behavior

The aim of this work is developing a facile and versatile route for preparing chemically crosslinked triple-shape memory polymers (SMPs). Hence, epoxidized natural rubber(ENR)/poly(ethylene-co-acrylic acid)(EAA)/poly(ε-caprolactone) (PCL) ternary blends were fabricated using the facile melt-mixing method. Interestingly, it was observed that the resultant ternary blends could self-crosslink during molding at high temperature without need for any crosslinking agents. Differential scanning calorimeter (DSC) and dynamic mechanical analyzer (DMA) analyses revealed that all of the ternary blends have two well-separated thermal transitions (Tm, PCL and Tm, EAA) and, as a result, they exhibited triple-SM behavior. Moreover, the mechanical properties as well as shape memory effect of ternary blends were improved with carboxylation of PCL. The developed ternary blends can be considered as a promising SM material in many in-vivo and aerospace applications.

Micro buckling of carbon fiber in triple shape memory polymer composites under bending in glass transition regions

Abstract Micro buckling of carbon fiber reinforced in triple shape memory shape polymer composites subjected to large bending strain is presented in the two distinct thermal regions through the minimum energy method. The properties of triple shape memory polymers are formulated by Boltzmann superposition principle, which are substituted in the formulation to obtain micro buckling behavior of carbon fiber in temperature dependent soft matrix. Total strain energy and half buckling wavelength of fiber are presented for the wide range of temperature encompassing the two thermal transitions. Temperature significantly regulate the behavior the volatile modulus property of the matrix in the glass transition regions. Parametric study is also presented to understand the effect of thickness and volume fraction along with the temperature. The maximum half wavelength of the fiber is obtained at the values of thickness and volume fraction as 1.75 mm and 0.4 respectively for all the thermal conditions.

Recyclable, Self-Healing, Thermadapt Triple-Shape Memory Polymers Based on Dual Dynamic Bonds

Fabricating a single polymer network with a combination of multi-shape memory effect (multiple-SME), solid-state plasticity, recyclability and self-healing behavior remains challenges. We designed imine bonds and ionic hydrogen bonds dual crosslinked polybutadiene (PB) networks. The resultant PB networks showed triple-shape memory effect (triple-SME), where imine bonds could be used to fix the permanent shape and ionic hydrogen bonds and glass transition acted as the transition segments for fixing/releasing the temporary shapes. Additionally, the dual dynamic bonds offered PB networks outstanding solid-state plasticity, recyclability and self-healing behavior. This strategy provides some insights for preparing shape memory polymers integrating multiple-SME and multi-functionality.

External Stress-Free Reversible Multiple Shape Memory Polymers.

The present work is focused on developing external stress-free two-way tripleshape memory polymers (SMPs). Accordingly, a series of innovative approaches are proposed for the material design and preparation. Polyurethane prepolymers carrying crystalline polytetrahydrofuran (PTMEG) and poly(ε-caprolactone) (PCL) as the switching phases are respectively synthesized in advance and then cross-linked to produce the target material. The stepwise method is believed to be conducive to manipulation of the relative contribution of PCL and PTMEG. Moreover, the chain extender, 2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol (UPy), is incorporated to establish hydrogen bonds among the macromolecules. By straightforward stretching treatment at different temperatures, the hydrogen bond networks are successfully converted into an internal stress provider, which overcomes the challenge of stress relaxation of the melted low melting temperature polymer (i.e., PTMEG) and increases the efficiency of stress transfer. Meanwhile, the contraction force of the switching phases is tuned to match the internal tensile stress. As a result, the internal stress provider can closely collaborate with melting/recrystallization of the crystalline domains, leading to the repeated multipleshape memory effects. The cross-linked polyurethane is thus able to reversibly morph among three shapes and displays its potentials as soft robot and actuator. The strategy reported here has the advantages of easily accessible raw materials, simple reaction, and facile programing/deprograming/reprograming, so that it possesses wide applicability.

High-Temperature Triple-Shape Memory Polymer with Full Recovery through Cross-Linking All-Aromatic Liquid Crystalline Poly(ester imide) under Reduced Molding Temperature

High thermal transition temperature, good processing feature, and full recovery of two temporary shapes are three necessary properties of triple-shape memory polymers (Tri-SMPs) for cutting-edge fields such as aerospace deployable structures, high temperature sensors, and actuators; however, it is still an interesting project with great challenges to prepare these functional polymers. Herein, without using solvent and high curing temperature (>300 °C), a new kind of thermally resistant Tri-SMP (LCPEI-EPEA) with two distinct glass transition temperatures (Tg = 93 and 218 °C) and 100% shape recovery ratios of two recovery processes was developed, which was prepared through building cross-linked networks based on acetylene terminated all-aromatic liquid crystalline poly(ester imide) (LCPEI) and reactive epoxy oligomer with acetylene side groups (EPEA). The relationship between cross-linked structures and integrated properties is intensively discussed. Unique copolymer molecular structures and chemical cross-...

Design and Characterization of Novel Potentially Biodegradable Triple-Shape Memory Polymers Based on Immiscible Poly(l-lactide)/Poly(ɛ-caprolactone) Blends

In this study, covalently cross-linked network strategy has been applied to prepare new triple-shape memory polymers (TSPs) based on poly(l-lactide) (PLA)/poly(ɛ-caprolactone) (PCL) blends. The TSPs were fabricated by adding di-cumyl peroxide, with triallyl isocyanurate as a coagent for performing the cross-linking reaction. The differential scanning calorimetry (DSC) analysis demonstrated that all the PLA/PCL blends show two melting points (Tm,PCL and Tm,PLA), which can be employed as the transition temperature (Ttrans) to induce triple-shape memory behavior. The scanning electron microscopy (SEM) analysis indicated that there are two immiscible morphologies: co-continuous structure and matrix-droplet. The influence of temperature on the crystalline phase changes was analyzed by X-ray diffraction at various temperatures. The results revealed that during the heating–cooling cycle, the degree of crystallinity decreased when the temperature increased and at higher temperature, the crystallization peaks of PCL disappeared. Multiple thermal–mechanical tests were performed and the results showed that the composition ratio of the two phases plays an important role in the triple-shape memory behavior. The results confirmed that the excellent shape memory behavior was obtained for the sample containing 50 wt% PCL.

The design of triple shape memory polymers with stable yet tunable temporary shapes by introducing photo-responsive units into a crystalline domain

A desirable triple-shape memory effect showing stable yet easily tunable temporary shapes is achieved using a physically crosslinked network with photo-responsive coumarin-containing poly(ε-caprolactone) as soft segments and poly(l-lactide) as hard segments.

A thermodynamic framework for the modeling of crystallizable triple shape memory polymers

Triple shape memory polymers (TSMPs) can be programed to remember and switch between three distinct shapes with the use of external stimuli, typically an increase in temperature. In this work, constitutive equations have been developed to model the thermo-mechanical behavior of crystallizable TSMPs. In these materials the transient shapes are fixed by the formation of crystalline phases, whereas the switching between the temporary and permanent shapes is due to the melting of the crystalline phases. The model is developed using a framework based on the theory of multiple natural configurations. Constitutive equations have been formulated for the original amorphous phase, the intermediate semi-crystalline phases, and transition of the crystalline phases, during the shape fixation and recovery cycles of TSMPs. These models have been developed within a full thermodynamic framework, extending our previous work in which the models were developed within a mechanical setting (Moon, Cui, & Rao, 2015; Moon, Rao, & Chester, 2016). The model has been applied to solve for the problems of inflation and extension of a hollow cylinder and uniaxial extension. The results are consistent with experimental observations.

Triple shape memory polymers by 4D printing

This article aims at introducing triple shape memory polymers (SMPs) by four-dimensional (4D) printing technology and shaping adaptive structures for mechanical/bio-medical devices. The main approach is based on arranging hot–cold programming of SMPs with fused decomposition modeling technology to engineer adaptive structures with triple shape memory effect (SME). Experiments are conducted to characterize elasto-plastic and hyper-elastic thermo-mechanical material properties of SMPs in low and high temperatures at large deformation regime. The feasibility of the dual and triple SMPs with self-bending features is demonstrated experimentally. It is advantageous in situations either where it is desired to perform mechanical manipulations on the 4D printed objects for specific purposes or when they experience cold programming inevitably before activation. A phenomenological 3D constitutive model is developed for quantitative understanding of dual/triple SME of SMPs fabricated by 4D printing in the large deformation range. Governing equations of equilibrium are established for adaptive structures on the basis of the nonlinear Green–Lagrange strains. They are then solved by developing a finite element approach along with an elastic-predictor plastic-corrector return map procedure accomplished by the Newton–Raphson method. The computational tool is applied to simulate dual/triple SMP structures enabled by 4D printing and explore hot–cold programming mechanisms behind material tailoring. It is shown that the 4D printed dual/triple SMPs have great potential in mechanical/bio-medical applications such as self-bending gripers/stents and self-shrinking/tightening staples.

Dual-responsive triple-shape memory polyolefin elastomer/stearic acid composite

Triple-shape memory polymers (triple-SMPs) have one permanent and two temporary shapes, which enable more complex actuation than traditional dual-SMPs. This work reports a novel polyolefin elastomer (POE)/stearic acid (SA) composite with excellent triple-shape memory and dual-responsive properties. SA displays two well-separated thermal transitions when melt-blending with POE, and is capable of memorizing two temporary shapes under different temperatures. It is found that the robust “house of cards” structure formed by the flake-like SA crystals in the composite is the key player behind the unique behavior. In addition, the actuation of the POE/SA composite can also be triggered upon exposing the material to the appropriate chemical vapor at room temperature. The triple-shape memory and dual-responsive ability atop the simple preparation process dramatically widen the applications of this fantastic material.

Thermally and Electrically Triggered Triple-Shape Memory Behavior of Poly(vinyl acetate)/Poly(lactic acid) Due to Graphene-Induced Phase Separation.

This work aimed to develop a facile and broadly applicable method for fabricating multistimuli responsive triple-shape memory polymers (SMPs). Hence, herein the SMPs were prepared through the simple physical blending of two commercially available biopolymers, poly(lactic acid) (PLA) and poly(vinyl acetate) (PVAc), in the presence of robust and conductive graphene nanoplatelets. Interestingly, atomic force microscopy observations and thermal analyses revealed that the presence of nanofillers led to phase separation and appearance of two well-separated transition temperatures in the blend of these two miscible polymers. Consequently, shape memory results showed that the unfilled blend of PLA/PVAc with a single thermal transition can only show moderate heat triggered dual-shape memory behavior. While, PLA/PVAc/graphene nanocomposite blends demonstrated excellent thermally and electrically actuated triple-shape memory effects besides their remarkable dual-shape memory behavior. In addition, electrical conductivity of the blend was enhanced by ∼14 orders of magnitude in the presence of graphene. More interestingly, electroactive shape recovery experiments exhibited that depending on the applied voltage, temporary shapes in each region of sample can be either individually or simultaneously recovered.

Triple Shape Memory Polymers: Constitutive Modeling and Numerical Simulation

Recently, triple shape memory polymers (TSMPs) have been discovered; these materials can be programmed to switch between three distinct shapes. Previously, we introduced a model to describe the mechanical behavior of TSMPs; however, the earlier study was limited in scope to simple cases of uniaxial deformation. In this work, we build upon our prior work, and develop robust numerical methods and constitutive equations to model complex mechanical behavior of TSMPs in inhomogeneous deformations and loading conditions using a framework based on the theory of multiple natural configurations. The model has been calibrated to uniaxial experiments. In addition, the model has been implemented as a user material subroutine (UMAT) in the finite element package abaqus. To demonstrate the applicability of the developed constitutive model, we have numerically simulated two cases of three-dimensional bodies undergoing triple-shape cycles; triple-shape recovery response of a complex TSMP geometry and the triple-shape recovery response of a stent when it is inserted in an artery modeled as a compliant elastomeric tube.

A Facile Strategy To Construct PDLLA-PTMEG Network with Triple-Shape Effect via Photo-Cross-Linking of Anthracene Groups

Covalently cross-linked network has been widely applied in triple-shape memory polymers (TSPs), and fabricating triple-shape memory networks with the optional shapes through a facile and fast way is highly expected in the real applications. In this study, a “preshaped and post-cross-linking” strategy has been put forward to fabricate the triple-shape networks via fast photo-cross-linking in solid state. The photoresponsive anthracene group was first employed to develop a poly(d,l-lactide)–poly(tetramethylene oxide) glycol (PDLLA-PTMEG) network via UV light irradiation. Two steps were involved in network fabrication: first, linear copolymers (AN-PDLLA-PTMEG) containing anthracene groups on the side chains with different mass ratio of PDLLA segments were synthesized, and then PDLLA-PTMEG networks (NW-PDLLA-PTMEG) were formed by 365 nm UV light irradiation under an argon atmosphere. The structures of all the precursors were determined by 1H NMR, and all networks were evaluated by swelling tests. The results ...

Triple-shape memory effects of bismaleimide based thermosetting polymer networks prepared via heterogeneous crosslinking structures

A series of bismaleimide based triple shape memory polymers with heterogeneous crosslinking structures were synthesized, and their shape memory behaviours are characterized.

Constitutive modeling of the mechanics associated with triple shape memory polymers

Shape memory polymers (SMPs) are smart materials that alter their shape in response to external stimuli. Dual-shape SMPs are widely recognized and are characterized by two shapes involved in a typical shape memory cycle. Recently, triple-shape memory polymers (TSMPs) have been introduced that have the ability to remember three shapes. Thermo-sensitive TSMPs can perform two sequential shape changes in response to heat, which were programed previously in a triple-shape creation process (TSCP). TSMPs are technologically significant as their development of has led to emergence of many complex potential applications that cannot be achieved by dual-shape polymers (Zhao et al., 2013). Crystallizable TSMPs are a class of thermo-sensitive TSMPs, where the shape creation is due to formation of crystalline phases. Different TSCPs have been reported which enable to control the triple shape capability of these materials. In this work the mechanical behavior of TSMPs has been modeled using a framework that has been developed recently for studying crystallization in polymers (Rao, 2003; Rao and Rajagopal, 2001, 2002, 2004). The framework has been used successfully to model SMPs (Barot and Rao, 2006; Barot et al., 2008), light activated SMPs (Sodhi and Rao, 2010) and is based upon the theory of multiple natural configurations. The model has been used to simulate a uni-axial deformation cycle for different types of TSCPs and the results have been compared with experimental data.