Thermomechanical Characterization of Shape Memory Polymers

Shape memory polymers (SMPs) are evolving intensively in smart materials research. SMPs can undergo large deformations, hold a temporary shape and then recover their original shape upon exposure to a particular external stimulus. The emerging development of fibre reinforced shape memory polymer composites (SMPCs) has improved SMPs’ mechanical properties to be comparable to modern fibre reinforced composites. Moreover, the inclusion of nanoparticles has enhanced the diversity in activation mechanisms and improved structural properties and durability.
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\nToday, the SMPCs are generally viewed as promising substances for engineered applications that have raised intensive interest among the scientists and engineers. Interestingly, stimulation by light enables unique and advanced shape memory effects (SMEs) in SMPCs that can fulfill the sophisticated demands of engineering. The ability to vary the light wavelength, intensity, periodicity, polarization and the irradiated position on the SMP component enables wavelength selective, reversible, sequential and multiple SMEs. Furthermore, light travel long distances in a vacuum, can be focussed onto a certain area, is safe to humans and, can be a control signal carrier and most notably, can be sent through optical fibres to extremely inaccessible areas.
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\nIncorporation of metallic, carbon and organic based photothermal fillers into a SMP matrix is a convenient proven method to prepare light activated shape memory polymer composites (LASMPCs). These photothermal fillers convert electromagnetic radiation into thermal energy that triggers the SMP matrix. The current study comprehensively reviewed the performances, mechanisms, challenges and limitations of the existing LASMPC systems and associated optical technologies. Predominantly this research was intended to develop reinforced LASMPC systems and allied optical technologies applicable for large scale structural engineering applications.
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\nIn this study, styrene and bisphenol A epoxy based thermosets and polylactic acid (PLA) based thermoplastic SMPs were used as polymer matrix materials. Carbon fibre, glass fibre, multiwalled carbon nanotube (MWCNT) and rare earth organic complexes of Nd(TTA)3Phen and Yb(TTA)3Phen were used as reinforcement and photothermal fillers. The samples were produced by means of vacuum bagging, mould casting and 4D printing. Morphological investigations were conducted to identify the microstructure and manufacturability of the LASMPCs. The samples’ mechanical and physical properties were tested by standard test methods for polymer matrix composites. Dynamic mechanical analysis was carried out to determine the thermomechanical characteristics. The photothermal effect was investigated through thermal imaging and associated shape memory behaviours were studied through shape fixing and recovery experiments. A finite element analysis was performed with ABAQUS to simulate the photothermal heating behaviour.
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\nThe current study established a material development framework for LASMPC materials and presented apt manufacturing methods for structural and large scale engineering applications. Different modes of light diffusion such as scattered low intensity light, focussed laser beams and light delivery through fibre optics were proved for structural LASMPCs. Sequential and selective wavelength activation of structural LASMPCs are presented. The FEA simulation provided additional understanding on light exposed LASMPCs’ 3-dimensional heating behaviour. Embedding a D-shaped optical fibre in an LASMPC created a single unit smart actuator, which was remotely activated by light. It was proven that flexible radiation shields can reduce the unanticipated shape recovery of LASMPCs components and protect the LASMPCs from polymer degradation due to radiation.
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\nThe improvements to their structural properties and innovative remote activation methodologies have justified LASMPCs’ aptness for space engineering applications. This study has proven its successful completion by three selected case studies of space applications. An LASMPC solar panel array model was sequentially deployed in four recovery steps. In a vacuum, a space habitat structure model was compressed to a third of its volume and then recovered its original shape. A 4D printed boom structure model was tested, proving customized LASMPC structures for sophisticated space equipment fabrication. The deployable LASMPC structures can reduce the occupied room in spacecraft. The improvements to the structural properties of LASMPCs while keeping the SME, understanding on thermomechanical and photothermal behaviours, remote actuation through optical fibres, radiation shields and the insight to space applications are the most significant novel outcomes of this study. This thesis opens up windows of opportunity for the scientific and engineering communities to provide innovative solutions to realize the sophisticated large scale engineering demands in aerospace and space applications and beyond.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 181361, “Advancement in Openhole Sand-Control Applications With Shape-Memory Polymer,” by Xiuli Wang and Gbenga Osunjaye, Baker Hughes, a GE company, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed. Conventional openhole sand-control techniques include standalone screens, expandable screens, and openhole gravel packing (OHGP). In some cases, the uniformity, size, and level of compressive strength of the formation dictate the use of an OHGP completion. However, OHGP is not always feasible or practical for some reservoirs and geographic locations. Shape-memory-polymer (SMP) technology can fill the gaps that exist with current OHGP techniques. This paper summarizes a technology using SMP to provide downhole sand control in openhole environments. Introduction The SMP conformable sand-control system consists of an engineered polymer material compacted onto a retainer cartridge (outer shroud, plain Dutch-weave mesh, and inner shroud). The assembly is then installed onto a perforated base pipe by mechanical means to provide a simple modular system for openhole sand-control applications. SMP Principle and Engineered Behaviors. The SMP typically has two different states: the glass state at low temperatures and the rubber state at higher temperatures. The point of change of state (the transition from the glass state to the rubber state), and the associated temperature, is referred to as the glass transit temperature (Tg). The engineered SMP has a defined Tg—the point where shape recovery starts. The initial SMP is first heated to the Tg of the polymer. Then, a mechanical force is applied to compact it to a smaller diameter and onto a retainer cartridge. The condensed SMP is then cooled below its Tg, and the force is removed. The SMP retains its compacted size until the surrounding temperature of the SMP reaches the Tg, at which point shape recovery begins. The bottomhole temperature (BHT) of the candidate reservoirs needs to be lower than the Tg to ensure that the SMP is rigid under the downhole conditions during the production phase. After the SMP sand-control system is installed in a wellbore, to expand the SMP under a BHT that is lower than the Tg, an activation fluid must be introduced. This activation fluid serves as a catalyst and temporarily reduces the Tg below the BHT so the SMP will be recovered to its initial shape. After the SMP is deployed, the activation fluid is flushed out. The SMP retains its recovered shape that conforms to the wellbore, and it is ready for production.

Shape memory polymer (SMP) systems exhibiting semicrystalline- elastomer blends, such as thermoplastic polyurethane and polylactic acid have been well studied, but their use in biomedical shape memory applications has been limited by their high activation temperature. SMPs are capable of deformation and recovery through the activation of an external stimuli, such as temperature. Critical criteria for SMPs used in biomedical applications is achieving a stimulus temperature close to 37°C while still experiencing sufficient shape recovery. A polymer’s glass transition temperature has been well defined as the SMP system’s activation temperature and therefore should be decreased to achieve a decreased activation temperature. In this work, a well-known, biocompatible plasticizer, polyethylene oxide (PEO), was added to thermoplastic polyurethane (TPU) – polylactic acid (PLA) SMP blends to observe the plasticizing effect on the structural, thermal, mechanical, and shape memory properties of the polymer blends. Additionally, the geometry of the fabricated SMP samples was tailored to further enhance the shape memory effect through a bowtie honeycomb structure. Our results suggest that the addition of PEO into the SMP system may be an effective method for decreasing the polymer’s glass transition temperature through the alteration of the polymer chain structure. With the addition of 30% PEO, the glass transition temperature of the TPU/PLA blend was successfully decreased from 62.4°C to 34.6°C while achieving 86.5% shape recovery when activated at 37°C, which is only a 5% decrease in shape recovery when activated at 50°C. These results suggest that the addition of a biocompatible plasticizer may overcome the limitation of employing temperature activated SMP systems in biomedical applications, and enhances the potential of these materials for reconfigurable structures, energy dissipation systems, and SHM in civil engineering applications.

Reconfigurable mesostructures with prestressing, reverse stiffness and shape memory effects

Shape memory alloys (SMAs) have the disadvantage that cooling is difficult and the actuating speed during cooling is slow. To resolve this problem, shape memory material actuators that operate only with heating is required. SMAs are characterized by a low apparent Young's modulus below the transformation temperature and a strong shape recovery force above the reverse transformation temperature. Alternatively, shape memory polymers (SMPs) have two properties: shape fixability and shape recovery. The SMPs are hardened below the glass transition (Tg) temperature and the material is recovered to memorized shape above the Tg temperature. The other hand, 3D printer is a machine that can directly output a 3D-designed product designed by a computer in 3D, and molded materials such as polymer, resin, metal, and ceramics. In this research, we developed the SMC of SMA wire and SMP sheet using adhesive that develops actuates into two shapes only by heating.

Shape memory polymers (SMPs) is a type of smart polymers. Shape-memory polymers (SMPs) allow for the development of stimuli-responsive polymer-based materials that can undergo substantial recoverable deformation in response to an external stimulus. Shape-memory effects (SMEs) of these SMP-based materials for task-specific applications are picking the interest of academic and industrial researchers. Significant progress has been gained in the field of shape memory polymers (SMPs) in recent years, with the discovery of new compositions for property tweaking, the discovery of new processes for shape fixing and recovery, and the initiation of phenomenological modelling. The current review will provide a brief account of the history of SMPs, their qualities, their structure and mechanism, classification, biodegradable SMPs and use of SMPs in various fields. Recent advancements in shape memory polymer composites (SMPCs) and shape-memory polymer blends (SMPBs) are also emphasized. This review explains distinct classification criteria of SMPs with a view of polymer type and structure and external stimulation.

The glass transition temperatures of epoxy-based shape memory polymers (SMPs), which contain a flexibilizer at various contents of 0%, 5%, 10% and 15% respectively, are determined through DMA tests. The shape memory effect of such materials is investigated through shape recovery experiments. Experimental results show that the content of flexibilizer has much influence on the shape memory effect of epoxy-based SMP. A shape recovery equation is developed based on the results of shape recovery experiment. Numerical calculations show that the developed shape recovery equation well predicts the shape recovery behaviors of epoxy-based SMP.

Shape memory polymers (SMPs) are uniquely suited to a number of applications due to their shape storage and recovery abilities and the wide range of available chemistries. However, many of the desired performance properties are tied to the polymer chemistry which can make optimization difficult. The use of foaming techniques is one way to tune mechanical response of an SMP without changing the polymer chemistry. In this work, a novel thiol–epoxy SMP was foamed using glass microspheres (40 and 50% by volume Q-Cel 6019), using expandable polymer microspheres (1% 930 DU 120), and by a chemical blowing agent (1% XOP-341). Each approach created SMP foam with a differing density and microstructure from the others. Thermal and thermomechanical analysis was performed to observe the behavioral difference between the foaming techniques and to confirm that the glass transition (Tg) was relatively unchanged near 50 °C while the glassy modulus varied from 19.1 to 345 MPa and the rubbery modulus varied from 0.04 to 2.2 MPa. The compressive behavior of the foams was characterized through static compression testing at different temperatures, and cyclic compression testing at Tg. Constrained shape recovery testing showed a range of peak recovery stress from 5 MPa for the syntactic Q-Cel foams to ∼0.1 MPa for the chemically blown XOP-341 foam. These results showed that multiple foaming approaches can be used with a novel SMP to vary the mechanical response independent of Tg and polymer chemistry.

A constitutive model of shape memory polymers based on glass transition and the concept of frozen strain release rate

Thermomechanical characterization of a shape memory polymer based self-repairing syntactic foam

Shape memory polymers (SMPs) have attracted significant research interest in robotic applications due to their tunable thermomechanical properties and ability to change shape and recover their original form upon exposure to external stimuli, primarily temperature. One‐way SMPs require reprogramming for each cycle, whereas two‐way SMPs (2W‐SMP) intrinsically exhibit shape memory behavior without additional programming. This study develops a cross‐linked polycaprolactone/dicumyl peroxide (PCL/DCP) based 2W‐SMP composite. The thermomechanical and thermal properties are characterized using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). To create a freestanding 2W‐SMP capable of shape change and recovery solely through temperature variations, without relying on external loads for actuation, the SMP is embedded in a low‐stiffness elastomeric matrix. The resulting composite material exhibits an intrinsic two‐way shape memory effect, enabling reversible shape transformations during heating and cooling cycles. The one‐way and two‐way shape memory behaviors are systematically investigated using DMA. The one‐way shape memory effect demonstrated exceptional shape fixity and strain recovery values of 96% and 96.8%, respectively, confirming the material's ability to fix a temporary shape and recover its permanent form upon external stimulus. The practical potential of the 2W‐SMP is demonstrated by testing it as a gripper device, which exhibited repeatable opening and closing responses during heating and cooling cycles, illustrating its reversible shape transformations and durability over multiple actuation cycles.

Shape-memory polymers (SMPs) are synthesized with adjustable glass transition temperature (Tg) ranging from 299 to 322 °C, higher than those reported previously. The polyimide containing thermal stable but flexible linkages within the backbone act as reversible phase, and high molecular weight (Mn) is necessary to form physical cross-links as fixed phase of thermoplastic shape-memory polyimide. The critical Mn is 21.3 kg/mol, and the relationship between Mn and Tg is explored. Thermoset polyimides show higher storage modulus and better shape-memory effects than thermoplastic counterparts due to covalent cross-linking, and the effective cross-link density with the influence on their physical properties is studied. The mechanism of high-temperature shape-memory effect of polyimide on the basis of chain flexibility, molecular weight, and cross-link density is proposed, which will benefit further research on high-temperature SMPs.

The shape memory effect (SME) does not only concern the macroscopic structure. It concerns also the polymer structure at morphological, macromolecular, and molecular scales. This effect may depend on different physicochemical properties like morphology heterogeneity, chain rigidity, steric hindrance, chain polarity, free volume, cross‐linking or entanglement density, molecular shape and weight, and so on. Hence, finding the relationship between the SME and these properties is very important. This can help to obtain the knowledge about the phenomenon origin and mechanism. One of the basic polymer properties, which can have direct SME, may be the molecular weight (Mw). The question here is: If the Mw of a shape memory polymer (SMP) changes, for different reasons like degradation, what will be the effect of this change on its SME. In order to answer to this question, the investigation is focused on an SMP blend of 40% poly(ɛ‐caprolactone) (PCL) and 60% styrene‐butadiene‐styrene (SBS). Then, enzymatic hydrolysis is performed on this blend to change its Mw. It is shown that this change is only related to the variation in the Mw of PCL. After that, different samples with a distinct average Mw are prepared and characterized by various experimental methods. Shape memory tests are performed on these blends, and the recovery rate (Rr) for each of them is determined. It is found that when Mw of PCL decreases, its degree of crystallinity, its glass transition, and its melting temperatures, corresponding to the PCL phase, increase. However, the elongation at break of the blend declines with the reduction in Mw. The tests show that the alteration in the blend's Mw influences its SME. Indeed, Rr of the (PCL/SBS) mixture drops with the decrease in Mw of PCL.

As humanity's exploration of cosmic space becomes more and more in-depth, aerospace technology, as a critical cornerstone supporting this endeavor, is constantly facing new challenges and opportunities. Aerospace engineering has extremely stringent requirements for materials, which require high strength and toughness to withstand extreme environmental conditions, such as high temperature, low temperature, high radiation, etc., and meet the complex needs of lightweight, high reliability, and multi-functional integration. Traditional materials often face many limitations in meeting these requirements, and the emergence of shape memory polymers (SMPs) has provided new ideas and possibilities for the design and application of aerospace materials. As an emerging class of intelligent materials, SMPs, due to their unique shape memory effect, lightweight and high strength, good designability, and other characteristics have gradually demonstrated excellent application potential in several aspects of the aerospace field. Application potential in many aspects of the aerospace field. Based on this, this paper first explains the shape memory effect (SME). Then, SMPs under different actuation conditions are explored, including light, heat, electricity, and magnetic field stimulation conditions. Finally, the paper highlights the application of SMPs in wing deformation structures, space deployable structures, thermal protection systems, etc. This will provide new solutions for the lightweight and multifunctional design of spacecraft.

Shape memory polymer (SMP), which has attracted lots of attentions recently, is a kind of smart material. The thermally induced SMPs can remember two different shapes because of the combined functions of polymers molecular architecture, morphology and the specific multi-step processing technology named shape memory creation programming. This paper aims to analyze Polyurethanes shape memory properties based on the viscoelastic theory. First, the Polyurethanes creep and relaxation performances are simulated using Maxwell-Weichert model. The simulated results of relaxation process are found in good agreement with the experimental results. Later, same model is used to describe Polyurethanes shape memory effects in strain-controlled situation. As the results show, Polyurethanes shape recovery ratios are almost 100%, whereas shape fixing properties are relatively poor. Moreover, as shown by the simulated results of recovery time under different recovery temperatures, recovery time shortens along with the increase of recovery temperature.