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Abstract

Shape memory polymers (SMPs) are stimuli-responsive materials, which are able to retain an imposed, temporary shape and recover the initial, permanent shape through an external stimulus like heat. In this work, a novel manufacturing method is introduced for thermoresponsive quick response (QR) code carriers, which originally were developed as anticounterfeiting technology. Motivated by the fact that earlier manufacturing processes were sometimes too time-consuming for production, filaments of a polyester urethane (PEU) with and without dye were extruded and processed into QR code carriers using fused filament fabrication (FFF). Once programmed, the distinct shape memory properties enabled a heating-initiated switching from non-decodable to machine-readable QR codes. The results demonstrate that FFF constitutes a promising additive manufacturing technology to create complex, filigree structures with adjustable horizontal and vertical print resolution and, thus, an excellent basis to realize further technically demanding application concepts for shape memory polymers.

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... When exposed to heat, the one-way shape memory effect DOI: 10.1002/mame.202100619 is triggered and the polymer almost completely returns to its permanent shape. [1][2][3][4][5] The advantageous shape-memory behavior of polymers has already been utilized, among others, in connection with the development of biomedical devices, [6][7][8][9][10][11][12][13] the counterfeit-proof marking of goods susceptible to plagiarism, [14][15][16][17][18][19] and for active assembly [20][21][22][23] and disassembly, [22,[24][25][26][27][28] which both requires a rethinking of classical design processes. ...
... [30] A few studies have been reporting on FFF with SMPs, in particular with thermoplastic polyurethanes (TPUs). [19,[31][32][33][34][35] Most importantly, in the past few years, it has become known how to implement internal stresses during AM, which is the so-called "4D printing," [36,37] addressing timeevolving structural functions as unattainable by conventional 3D printing. [38][39][40] The main advantage of such function integration is that the finished objects can be removed directly from the printer without the need for an additional thermomechanical treatment. ...
... For this purpose, the same extrusion line was used as recently reported. [19,49] The obtained filament had a smooth surface and a diameter of 2.85 ± 0.10 mm. The narrow tolerance range ensured that an important processing criterion was fulfilled. ...
Article
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Four-dimensional (4D) printing of shape memory polymers enables the production of thermoresponsive objects. In this contribution, a facile printing strategy is followed for an in-house synthesized thermoplastic poly(ether urethane). Processing by means of fused filament fabrication (FFF), in which the difference between nozzle temperature and material-specific glass transition temperature of the polymer is kept as low as possible, allows to obtain highly shrinkable objects whose shape and thermoresponsiveness can be precisely controlled. The effectiveness of the method also applies to the printing material polylactic acid. One possible application lies in highly shrinkable objects for assembly purposes. As proof-of-concept, lightweight hands-free door openers for healthcare applications are functionally simulated and developed. Once printed, such devices shrink when heated to fit on door handles, allowing an easy assembly. At the end-of-use, a heating-initiated disassembling and mechanical recycling are proposed. In perspective, a reuse of the materials in 4D printing can contribute to the emergence of a circular economy for highly functional materials. This article is protected by copyright. All rights reserved
... Material jetting 3DP has also been used to print a mixture of commercially available photosensitive resins resulting in a TSE [36]. Among different 3DP techniques, material extrusion (MEX) is the most commonly used technique to print 4D objects due to its simple operation and troubleshooting, low cost of equipment and raw materials, high speed, and the capability to print large parts [37,38]. Here, we have explored whether filament-based MEX (i.e., Fused Filament Fabrication (FFF)) can print TSPs, enabling an electrically triggered TSE. ...
... Therefore, blending polyurethanes (PUs) with PLA was investigated as an effective way to obtain multiphase SMPs with improved strength and elasticity. The PEU selected was a phase-segregated PEU consisting of a crystallizable soft phase based on poly(1,4-butylene adipate) (PBA) and a 4,4′-methylenediphenyl diisocyanate (MDI)/1,4-butanediol (BD)-based hard segment [38,42,43]. The morphology of the composites was explored by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). ...
Article
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Triple-shape polymers can memorize two independent shapes during a controlled recovery process. This work reports the 4D printing of electro-active triple-shape composites based on thermoplastic blends. Composite blends comprising polyester urethane (PEU), polylactic acid (PLA), and multiwall carbon nanotubes (MWCNTs) as conductive fillers were prepared by conventional melt processing methods. Morphological analysis of the composites revealed a phase separated morphology with aggregates of MWCNTs uniformly dispersed in the blend. Thermal analysis showed two different transition temperatures based on the melting point of the crystallizable switching domain of the PEU (Tm~50 ± 1 °C) and the glass transition temperature of amorphous PLA (Tg~61 ± 1 °C). The composites were suitable for 3D printing by fused filament fabrication (FFF). 3D models based on single or multiple materials were printed to demonstrate and quantify the triple-shape effect. The resulting parts were subjected to resistive heating by passing electric current at different voltages. The printed demonstrators were programmed by a thermo-mechanical programming procedure and the triple-shape effect was realized by increasing the voltage in a stepwise fashion. The 3D printing of such electroactive composites paves the way for more complex shapes with defined geometries and novel methods for triggering shape memory, with potential applications in space, robotics, and actuation technologies.
... Semi-crystalline thermoplastic polyurethanes (TPU) are materials with outstanding structural flexibility giving rise to a wide variety of applications from biomaterials [1,2] to additive manufacturing [3]. The elastomeric nature derives from its blocky structure where polymer chains are composed of alternating sequences of soft and hard segments. ...
... The elastomeric nature derives from its blocky structure where polymer chains are composed of alternating sequences of soft and hard segments. The soft segments are generally amorphous or crystallizable polyesters such as poly(butylene adipate) (PBA) [3], polycaprolactone (PCL) [4] and their mixtures [5,6], poly-L-lactide [7], poly(1,10-decylene adipate) [8], polycarbonate [9], polypropylene glycol [10], poly(tetramethylene ether) [10], polyhexamethylene carbonate [11], etc., with specific thermal, mechanical and biodegradable properties. The urethane hard segments are formed by the isocyanate and the chain extender moieties. ...
Article
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A series of semi-crystalline multi-block thermoplastic polyurethanes (TPU), containing poly(butylene adipate) (PBA), polycaprolactone (PCL) and their equimolar mixture (PBA/PCL) as a soft segment was synthesized. The changes in the physical-mechanical and thermal properties of the materials observed in the course of a 36-month storage at room temperature were related to the corresponding structural evolution. The latter was monitored using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXS) and mechanical tests (tensile strength test). The effects of the composition of the soft segment on the phase separation and crystallization of the soft segment were analyzed in detail. It was found that the melting temperature of the crystalline phase increases with storage time, which is associated with hindering of the phase separation of the hard and soft segments of the TPU samples as it was detected by FTIR.
... Shape memory polymers (SMPs) are stimuli-responsive materials that can recover the initial, permanent shape after an imposed, temporary shape during programming (training), by exposure to an external stimulus like heat [1,2]. Among the SMPs, thermoplastic polyurethanes received most of the attention [3], due to their competitive shape memory and mechanical properties compared to other polymers, e.g. ...
... Although there is a broad discussion on the thermomechanical behavior of conventionally produced SMPs [7,8], there is lack of information of SMP materials handled in the era of digital manufacturing. There are only few findings in the literature of fused filament fabrication (FFF) applied as a printing method of shape memory polyurethane [2], unlike to the well documented printing of other thermoplastics in terms of printing strategy and mechanical properties [9,10]. Even in these cases, the focus is on the printability [11À13]. ...
Article
Unique thermal shape recovery and chemical stability make Shape Memory Polymers (SMPs) attractive for critical applications in biomedical, aerospace and energy sectors. While additive manufacturing (AM) of SMPs allows fabrication of functionally-graded structures with tailored, intricate design features, the effect of AM on shape recovery characteristics has not received much attention. To demonstrate that shape recovery characteristics can be significantly enhanced through a variation of AM building strategies and process parameters beyond tuning of material compositions alone, an experimental study was developed. In-situ thermo-micro-mechanical testing was applied to capture the shape memory properties, both during shape programming and post that.
... exceeding e.g., 30 mm, without significantly releasing internal stresses. Another advantage of FFF is that when selecting a 100 µm nozzle, even filigree structures can be manufactured as demonstrated five years ago when printing machine-readable quick response codes using a pristine and a dyed SMP [42]. ...
Article
Although several force application concepts are known that can be used to deform shape memory polymers (SMPs) within the scope of programming, controlled deformation is challenging in the case of samples with a cylinder-like shape, which need to be homogeneously compressed starting from the lateral surface. To solve this problem, this contribution follows a material approach that takes advantage of four-dimensional (4D) printing. Fused filament fabrication (FFF) was used as an additive manufacturing (AM) technique to produce a thermoresponsive tool in a cylindrical shape from a polyether urethane (PEU) having a glass transition temperature (T g) close to 55 • C, as determined by differential scanning calorimetry (DSC). Once it was 4D-printed, a sample of laser cut polyester urethane urea (PEUU) foam with a cylindrical wall was placed inside of it. Subsequent heating to 75 • C and keeping that temperature constant for 15 min resulted in the compression of the foam, because the internal stresses of the PEU were transferred to the PEUU, whose soft segments were completely molten at 65 • C as verified by DSC. Upon cooling to −15 • C and thus below the offset temperature of the soft segment crystallization transition of the PEUU, the foam was fixed in its new shape. After 900 days of storage at temperatures close to 23 • C, the foam recovered its original shape upon reheating to 75 • C. In another experiment, a 4D-printed cylinder was put into hibernation for 900 days before its thermoresponsiveness was investigated. In the future, 4D-printed tools may be produced in many geometries, which fit well to the shapes of the SMPs to be programmed. Beyond programming SMP foams, transferring the forces released by 4D-printed tools to other programmable materials can further expand technical possibilities.
... When applying a suitable stimulus, SMPs are able to almost completely recover the initial shape. In other words, the so-called 'one-way (1W) shape-memory effect (SME)' is triggered (Liu et al., 2007;Dietsch and Tong, 2007;Ratna and Karger-Kocsis, 2008;Pretsch, 2010;Sun et al., 2012;Chalissery et al., 2019). Here, shape recovery is an entropically driven process based on entropy elasticity according to the theory of rubber elasticity (Holme, 1806). ...
Article
Full-text available
Shape-memory polymers can be used to develop thermoresponsive programmable materials that can take on sensory and actuator tasks as their ambient temperature changes. In this contribution, a self-synthesised poly(1,10-decylene adipate) diol-based polyester urethane (PEU) was used for their fabrication. After processing the PEU into filaments, programmable materials, including a gear-like object, the teeth of a ‘bevel gear’ and a unit cell, were additively manufactured by fused filament fabrication. In any case, a thermomechanical treatment was conducted that involved the deformation of the polymer at 75°C. After cooling to 15°C, the programmable materials were unloaded and the thermoresponsiveness between 23°C and 58°C was investigated. A maximum thermoreversible change in height of about 39% was detected for the ‘gear’. With regard to the ‘bevel gear’, proof of feasibility was provided for use as overheating protection, so that a force transmission could be switched off when heated and switched on when cooled down. The unit cell actuated under a weak external load of 0.01 N, thus exhibiting thermoreversible length changes of about 45%.
... Once characterized, the PEU was melt-extruded into a filament as essential for further processing via fused filament fabrication (FFF). For this purpose, the same extrusion line was used as reported recently [42]. The obtained filament had a homogenous diameter of 2.85 ± 0.08 mm, so that an important attribute for further processing was fulfilled. ...
Article
For soft robotics and programmable metamaterials, novel approaches are required enabling the design of highly integrated thermoresponsive actuating systems. In the concept presented here, the necessary functional component was obtained by polymer syntheses. First, poly(1,10-decylene adipate) diol (PDA) with a number average molecular weight M n of 3290 g·mol-1 was synthesized from 1,10-decanediol and adipic acid. Afterward, the PDA was brought to reaction with 4,4'-diphenylmethane diisocyanate and 1,4-butanediol. The resulting polyester urethane (PEU) was processed to the filament, and samples were additively manufactured by fused-filament fabrication. After thermomechanical treatment, the PEU reliably actuated under stress-free conditions by expanding on cooling and shrinking on heating with a maximum thermoreversible strain of 16.1%. Actuation stabilized at 12.2%, as verified in a measurement comprising 100 heating-cooling cycles. By adding an actuator element to a gripper system, a hen's egg could be picked up, safely transported and deposited. Finally, one actuator element each was built into two types of unit cells for programmable materials, thus enabling the design of temperature-dependent behavior. The approaches are expected to open up new opportunities, e.g., in the fields of soft robotics and shape morphing.
... The combination of the materials shape memory effect allows the QR code to be distorted and unscannable when the part is deformed, and scannable once the part has returned to its original shape. Challisery et al. [37] demonstrated this by 3D printing a QR code on a shape memory polymer material. In this work, the applicability of this authentication technique is addressed on the printed Diaplex 9020 SMP. ...
Article
Full-text available
Shape memory polymers (SMPs) are materials capable of changing their structural configuration from a fixed shape to a temporary shape, and vice versa when subjected to a thermal stimulus. The present work has investigated the 3D printing process of a shape memory polymer (SMP)-based polyurethane using a material extrusion technology. Here, SMP pellets were fed into a printing unit, and actuating coupons were manufactured. In contrast to the conventional film-casting manufacturing processes of SMPs, the use of 3D printing allows the production of complex parts for smart electronics and morphing structures. In the present work, the memory performance of the actuating structure was investigated, and their fundamental recovery and mechanical properties were characterized. The preliminary results show that the assembled structures were able to recover their original conformation following a thermal input. The printed parts were also stamped with a QR code on the surface to include an unclonable pattern for addressing counterfeit features. The stamped coupons were subjected to a deformation-recovery shape process, and it was observed that the QR code was recognized after the parts returned to their original shape. The combination of shape memory effect with authentication features allows for a new dimension of counterfeit thwarting. The 3D-printed SMP parts in this work were also combined with shape memory alloys to create a smart actuator to act as a two-way switch to control data collection of a microcontroller.
... They have high curing rate, good toughness but defects of high volume shrinkage and oxygen inhibition. 4,[26][27][28] Hybrid photopolymers are composed of free radical and cationic resins, which concurrently obtain the advantages of two types of photopolymers and show high curing rate, insensitivity to oxygen, and relatively low volume shrinkage. Hybrid photopolymers have been considered as ideal printing materials for vat photopolymerization in several reports. ...
Article
Full-text available
3D Printing has become a powerful technology for future advanced manufacturing, however the choice of materials with good performance is still limited. In this research, a type of hybrid photopolymer resin based on silicone epoxy with high UV curing rate and low viscosity was applied in stereolithography (SLA) technology. First, aliphatic silicone epoxy was synthesized through hydrosilylation reaction, and then compounding with acrylates, cycloaliphatic epoxy and photo‐initiators, finally the hybrid photopolymer system for SLA was obtained. The features of UV curing process were studied through photo‐differential scanning calorimetry and real‐time Fourier transform infrared measurements. Scanning electron microscopy test showed interpenetrating polymer network structure was formed in 3D objects. The performances of 3D printed sample such as mechanical properties, thermal mechanical and stability properties were also investigated in detail. Moreover, the 3D printed objects with complicated structures showed high printing accuracy. This new type of hybrid photopolymer system based on aliphatic silicone epoxy was with fabrication ease, good mechanical properties, good thermal stability and high printing resolution and has great potential of applications in industrial design and models making fields.
... In segmented polyurethane (PU), the exact chemical composition has a significant influence on phase morphology while the ratio of hard to soft segments affects phase separation [6][7][8]. Today, physically cross-linked, phase segregated block copolymers like poly(ester urethanes) (PEUs) belong to the most promising SMP families [9][10][11][12][13][14][15][16][17][18]. Here, switching can be accomplished when passing the glass transition (Ttrans = Tg) or the melting transition (Ttrans = Tm) of the polyester soft segment [19,20]. ...
Article
Full-text available
In this work, a novel type of polyester urethane urea (PEUU) foam is introduced. The foam was produced by reactive foaming using a mixture of poly(1,10–decamethylene adipate) diol and poly(1,4–butylene adipate) diol, 4,4′-diphenylmethane diisocyanate, 1,4–butanediol, diethanolamine and water as blowing agent. As determined by differential scanning calorimetry, the melting of the ester-based phases occurred at temperatures in between 25 °C and 61 °C, while the crystallization transition spread from 48 °C to 20 °C. The mechanical properties of the foam were simulated with the hyperplastic models Neo-Hookean and Ogden, whereby the latter showed a better agreement with the experimental data as evidenced by a Pearson correlation coefficient R² above 0.99. Once thermomechanically treated, the foam exhibited a maximum actuation of 13.7% in heating-cooling cycles under a constant external load. In turn, thermal cycling under load-free conditions resulted in an actuation of more than 10%. Good thermal insulation properties were demonstrated by thermal conductivities of 0.039 W·(m·K)−1 in the pristine state and 0.052 W·(m·K)−1 in a state after compression by 50%, respectively. Finally, three demonstrators were developed, which closed an aperture or opened it again simply by changing the temperature. The self-sufficient material behavior is particularly promising in the construction industry, where programmable air slots offer the prospect of a dynamic insulation system for an adaptive building envelope.
... Dans ce cas, c'est le fait que la transition vitreuse se produise sur une large gamme de température qui permet cette mémorisation multiple.ii. Propriétés de mémoire de forme dans les PUs La propriété de mémoire de forme est une caractéristique connue pour les PUs, et a largement été décrite dans la littérature.20,24,[33][34][35][36][37][38][39][40][41][42][25][26][27][28][29][30][31][32] En effet, grâce à leur T g aisément modulable ainsi que leur biocompatibilité, les PUs sont des systèmes particulièrement prometteurs pour des applications biomédicales. ...
Thesis
Cette thèse porte sur l’application du procédé d’extrusion réactive à la synthèse, sans solvant, de polyhydroxyuréthanes (PHUs). D’une part, des PHUs thermoplastiques ont été synthétisés à partir de trois biscarbonates cycliques à 5 chaînons, activés ou non par des fonctions ester ou éther en béta du cycle, et différentes diamines. La conversion totale des fonctions réactives a été atteinte dans la majorité des cas en des temps courts (quelques heures), malgré le caractère très cohésif des substrats biscarbonates employés et notamment ceux comportant un lien amide. D’autre part, via ce même procédé d’extrusion réactive, différents PHUs réticulés qui présentent des propriétés de mémoire de forme ou encore de reprocessabilité ont été synthétisés. En parallèle, une étude via des réactions modèles menées hors extrudeuse a permis de mettre en évidence les conditions expérimentales permettant de fortement limiter la formation d’un produit secondaire de type urée. Dans le cas particulier du dicarbonate de diglycerol (DGDC), un protocole de purification par recristallisation a été mis au point de façon à séparer ses deux formes énantiomères. La polymérisation des deux énantiomères séparés, avec différentes diamines, a révélé que la stéréochimie du monomère biscarbonate joue un rôle déterminant sur les dimensions et les caractéristiques thermomécaniques des PHUs finaux.
... A full shape memory cycle includes two steps, namely programming, which is to fix the temporary shape, and recovery, which is to apply the stimulus to active the SME. From a real engineering application point of view, such as in active disassembly [31,32], deployable structures [33] and anti-counterfeit applications [34][35][36][37][38][39][40], activation of the SME may not be carried out right after programming, but after a period of storage. As such, we need to consider the influence of aging at around room temperature after programming [41], which is a topic that has been less explored so far [42,43], but that is utterly important from an engineering application point of view. ...
Article
Full-text available
In this paper, we experimentally investigate the influence of storage at 40 °C on the shape memory performance and mechanical behavior of a pre-stretched commercial poly(methyl methacrylate) (PMMA). This is to simulate the scenario in many applications. Although this is a very important topic in engineering practice, it has rarely been touched upon so far. The shape memory performance is characterized in terms of the shape fixity ratio (after up to one year of storage) and shape recovery ratio (upon heating to previous programming temperature). Programming in the mode of uniaxial tension is carried out at a temperature within the glass transition range to one of four prescribed programming strains (namely 10%, 20%, 40% and 80%). Also investigated is the residual strain after heating for shape recovery. The characterization of the mechanical behavior of programmed samples after storage for up to three months is via cyclic uniaxial tensile test. It is concluded that from an engineering application point view, for this particular PMMA, programming should be done at higher temperatures (i.e., above its Tg of 110 °C) in order to not only achieve reliable and better shape memory performance, but also minimize the influence of storage on the shape memory performance and mechanical behavior of the programmed material. This finding provides a useful guide for engineering applications of shape memory polymers, in particular based on the multiple-shape memory effect, temperature memory effect, and/or low temperature programming.
... It is known that smart devices, used for biomedical application, can be prepared using shape memory polyurethane and its composites. However, with expanding knowledge, there is a growing need for advanced technologies such as additive manufacturing or 3D printing techniques for the development of smart devices and information carriers [97][98][99][100]. Several applications in the biomedical field require complex and personalized dimensions and shapes for smart devices which are difficult to produce using conventional manufacturing techniques. ...
Article
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The inherent capability to deform and reform in a predefined environment is a unique property existing in shape memory polyurethane. The intrinsic shape memory ability of the polyurethane is due to the presence of macro domains of soft and hard segments in its bulk, which make this material a potential candidate for several applications. This review is focused on manifesting the applicability of shape memory polyurethane and its composites/blends in various domains, especially to human health such as shielding of electromagnetic interference, medical bandage development, bone tissue engineering, self-healing, implants development, etc. A coherent literature review highlighting the prospects of shape memory polyurethane in versatile applications has been presented.
... The advantages of SMPs have resulted in great potential applications in many areas. For instance, smart fabrics, strain sensors, biomedical materials, and aerospace applications [12][13][14]. Nevertheless, some obstructions still exist that prevent SMPs' widespread application. ...
Article
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In this work, a fast water-responsive shape memory hybrid polymer based on thermoplastic polyurethane (TPU) was prepared by crosslinking with hydroxyethyl cotton cellulose nanofibers (CNF-C) and multi-walled carbon nanotubes (CNTs). The effect of CNTs content on the electrical conductivity of TPU/CNF-C/CNTs nanocomposite was investigated for the feasibility of being a strain sensor. In order to know its durability, the mechanical and water-responsive shape memory effects were studied comprehensively. The results indicated good mechanical properties and sensing performance for the TPU matrix fully crosslinked with CNF-C and CNTs. The water-induced shape fixity ratio (Rf) and shape recovery ratio (Rr) were 49.65% and 76.64%, respectively, indicating that the deformed composite was able to recover its original shape under a stimulus. The TPU/CNF-C/CNTs samples under their fixed and recovered shapes were tested to investigate their sensing properties, such as periodicity, frequency, and repeatability of the sensor spline under different loadings. Results indicated that the hybrid composite can sense large strains accurately for more than 103 times and water-induced shape recovery can to some extent maintain the sensing accuracy after material fatigue. With such good properties, we envisage that this kind of composite may play a significant role in developing new generations of water-responsive sensors or actuators.
Article
Ongoing breakthroughs in the development of functional printing materials are leading to rapid and widespread industrialization of three-dimensional (3D) printing, accompanied by increasingly urgent requirements for methods to prevent problems such as tampering, counterfeiting and destruction of 3D printed products. Anti-counterfeiting of 2D printed products has a long history, but its methods are not suitable for application to 3D printed products, as the latter products have embedding that is substantially different to that of the former products. This review article analyses anti-counterfeiting techniques for 2D printed products, proposes two embedding strategies for 3D printing based on material-responsive properties and 3D digital information, and summarizes the progress and performance of the corresponding anti-counterfeiting methods. It is shown that among the embedded anti-counterfeiting methods that exploit the responsive properties of materials, methods based on optical properties, spectral properties and deformation properties of 3D printing materials are the focus of research on embedding anti-counterfeiting materials into 3D printed objects. In addition, it is demonstrated that state-of-the-art embedding-based anti-counterfeiting methods use 3D digital information interactions and depend on 3D digital watermarks, 3D identification codes and radio-frequency tagging. Finally, a detailed discussion is provided on the generation, integration, extension, detection and prediction of embedded security features that can be printed synchronously with a functional structure. This offers a unique perspective on standardization of embedding-based anti-counterfeiting methods used in 3D printing.
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Material extrusion printing of reactive resins and inks present a unique challenge due to the time-dependent nature of the rheological and chemical properties they possess. As a result, careful print optimization or process control is important to obtain consistent, high quality prints via additive manufacturing. We present the design and use of a near-infrared (NIR) flow through cell for in situ chemical monitoring of reactive resins during printing. Differences between in situ and off-line benchtop measurements are presented and highlight the need for in-line monitoring capability. Additionally, in-line extrusion force monitoring and off-line post inspection using machine vision is demonstrated. By combining NIR and extrusion force monitoring, it is possible to follow cure reaction kinetics and viscosity changes during printing. When combined with machine vision, the ability to automatically identify and quantify print artifacts can be incorporated on the printing line to enable real-time, artificial intelligence-assisted quality control of both process and product. Together, these techniques form the building blocks of an optimized closed-loop process control strategy when complex reactive inks must be used to produce printed hardware.
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Additive manufacturing (AM) offers a great potential for the production of objects with a tailor‐made inner structure especially in combination with material development in the field of polymer compounds. However, the design possibilities for the inner structure depends on printing resolution, accuracy and reproducibility. The quality of small filigree objects printed by additive manufacturing processes for polymer materials like fused filament fabrication (FFF) depends on the polymer material itself as well as of the processing parameters in the additive manufacturing technology used. Here, the production of small porous structures by FFF with an Ultimaker 3 is analyzed using polylactic acid (PLA) as well as polymer compounds of PLA containing carbon nanotubes (CNT) and polyvinyl alcohol (PVA) containing titanium dioxide (TiO2). The influences of the calibration of the building plate, the height of the 1st, 2nd and 3rd layer, and of particulate additives on the printing behaviour of the polymer compound, and hence the resulting accuracy of the width of single printed lines, are studied. Additionally, the printing of lattice‐like scaffold structures using PLA/CNT forming the structure and PVA/TiO2 as soluble support structure is described. This article is protected by copyright. All rights reserved
Article
Thermoresponsive objects can be manufactured from shape memory polymers (SMPs) via fused filament fabrication (FFF). Here we introduce a new technological approach to obtain thermally actuating objects using an in‐house synthesized, phase segregated polyester urethane (PEU). Under almost stress‐free conditions of a dynamic mechanical analysis, the cuboid objects obtained from FFF shrank when heated to 62°C and expanded when cooled to 15°C with a maximum thermoreversible strain of 7.2%. Actuation can be traced back to the phenomena of melting‐induced contraction and crystallization‐induced elongation of the PEU's soft segment, supported by internal stresses as implemented in course of FFF. To translate small changes in shape to a next larger scale, an artificial butterfly was developed in which the movements of two actuator elements were transferred to the wings with the aid of a lever concept. Following a different concept, additive manufacturing of cylindrical samples implied application potential as self‐sufficient gripper, enabling a programmable material behavior in the sense of temperature‐controlled gripping, transport and release of exemplarily selected smooth surfaced objects in the form of vials. This article is protected by copyright. All rights reserved
Article
Development of fiber-spinning technologies and materials with proper mechanical properties is highly important for manufacturing of aligned fibrous scaffolds mimicking structure of the muscle tissues. Here, we report touch spinning of a thermoplastic poly(1,4-butylene adipate)-based polyurethane elastomer, obtained via solvent-free polymerization. This polymer possesses a combination of important advantages such as (i) low elastic modulus in the range of a few MPa, (ii) good recovery ratio and (iii) resilience, (iv) processability, (v) non-toxicity, (vi) biocompatibility and (vii) biodegradability that makes it suitable for fabrication of structures mimicking extracellular matrix (ECM) of muscle tissue. Touch spinning allows fast and precise deposition of highly aligned micro and nanofiber without use of high voltage. C2C12 myoblasts readily align along soft polymer fibers and demonstrate high viability as well as proliferation that makes proposed combination of polymer and fabrication method highly suitable for engineering skeletal muscles. This article is protected by copyright. All rights reserved
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Poly(ester urethane)s represent a widely investigated class of thermoplastic polymers that exhibit a thermally triggered dual shape memory effect. This behavior is the result of urethane‐rich hard segments that define the permanent shape, while domains formed by the crystallizable polyester segments act as the memory switch. We show here that blending poly(ester urethane)s with a second polyester having a different melting temperature is a straightforward and possibly general approach to create triple‐shape memory polymers, in which two different temporary shapes can be programmed. To demonstrate this, we blended a poly(ester urethane) containing crystallizable poly(1,4‐butylene adipate) segments with poly(butylene succinate) or poly(hexamethylene dodecanoate). The blends microphase separate and the different polyester segments form separate semicrystalline domains, which serve as switching elements that can be activated at different temperatures. The blends retain attractive mechanical properties and the shape memory characteristics are characterized by high fixities (70%–96%) and recovery rates (82%–94%).
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Extrusion-based additive manufacturing (EBAM) or 3D printing is used to produce customized prototyped parts. The majority of the polymers used with EBAM show moisture sensitivity. However, moisture effects become more pronounced in polymers used for critical applications, such as biomedical stents, sensors, and actuators. The effects of moisture on the manufacturing process and the long-term performance of Shape Memory Polyurethane (SMPU) have not been fully investigated in the literature. This study focuses primarily on block-copolymer SMPUs that have two different hard/soft (h/s) segment ratios. It investigates the effect of moisture on the various properties via studying: (i) the effect of moisture trapping within these polymers and the consequences when manufacturing; (ii) and the effect on end product performance of plasticization by moisture. Results indicate that higher h/s SMPU shows higher microphase separation, which leads to an increase of moisture trapping within the polymer. Understanding moisture trapping is critical for EBAM parts due to an increase in void content and a decrease in printing quality. The results also indicate a stronger plasticizing effect on polymers with lower h/s ratio but with a more forgiving printing behavior compared to the higher h/s ratio.
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Candidate materials for next generation neural recording electrodes include shape memory polymers (SMPs). These materials have the capability to undergo softening after insertion in the body, and therefore reduce the mismatch in modulus that usually exists between the device and the tissue. Current SMP formulations, which have shown promise for neural implants, contain ester groups within the main chain of the polymer and are therefore prone to hydrolytic decomposition under physiological conditions over periods of 11–13 months in vivo, thus limiting the utility for chronic applications. Ester free polymers are stable in harsh condition (PBS at 75°C or NaOH at 37°C) and accelerated aging results suggest that ester free SMPs are projected to be stable under physiological condition for at least 7 years. In addition, the ester free SMP is compatible with microfabrication processes needed for device fabrication. Furthermore, they demonstrate in vitro biocompatibility as demonstrated by high levels of cell viability from ISO 10993 testing.
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Material choice is a fundamental consideration when it comes to designing a solid dosage form. The matrix material will ultimately determine the rate of drug release since the physical properties (solubility, viscosity, and more) of the material control both fluid ingress and disintegration of the dosage form. The bulk properties (powder flow, concentration, and more) of the material should also be considered since these properties will influence the ability of the material to be successfully manufactured. Furthermore, there is a limited number of approved materials for the production of solid dosage forms. The present study details the complications that can arise when adopting pharmaceutical grade polymers for fused-filament fabrication in the production of oral tablets. The paper also presents ways to overcome each issue. Fused-filament fabrication is a hot-melt extrusion-based 3D printing process. The paper describes the problems encountered in fused-filament fabrication with Kollidon® VA64, which is a material that has previously been utilized in direct compression and hot-melt extrusion processes. Formulation and melt-blending strategies were employed to increase the printability of the material. The paper defines for the first time the essential parameter profile required for successful 3D printing and lists several pre-screening tools that should be employed to guide future material formulation for the fused-filament fabrication of solid dosage forms.
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The rapid development of additive manufacturing and advances in shape memory materials have fueled the progress of four-dimensional (4D) printing. With the right external stimulus, the need for human interaction, sensors, and batteries will be eliminated, and by using additive manufacturing, more complex devices and parts can be produced. With the current understanding of shape memory mechanisms and with improved design for additive manufacturing, reversibility in 4D printing has recently been proven to be feasible. Conventional one-way 4D printing requires human interaction in the programming (or shape-setting) phase, but reversible 4D printing, or two-way 4D printing, will fully eliminate the need for human interference, as the programming stage is replaced with another stimulus. This allows reversible 4D printed parts to be fully dependent on external stimuli; parts can also be potentially reused after every recovery, or even used in continuous cycles—an aspect that carries industrial appeal. This paper presents a review on the mechanisms of shape memory materials that have led to 4D printing, current findings regarding 4D printing in alloys and polymers, and their respective limitations. The reversibility of shape memory materials and their feasibility to be fabricated using three-dimensional (3D) printing are summarized and critically analyzed. For reversible 4D printing, the methods of 3D printing, mechanisms used for actuation, and strategies to achieve reversibility are also highlighted. Finally, prospective future research directions in reversible 4D printing are suggested.
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Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting. The range of polymers used in AM encompasses thermoplastics, thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Aspects of polymer design, additives, and processing parameters as they relate to enhancing build speed and improving accuracy, functionality, surface finish, stability, mechanical properties, and porosity are addressed. Selected applications demonstrate how polymer-based AM is being exploited in lightweight engineering, architecture, food processing, optics, energy technology, dentistry, drug delivery, and personalized medicine. Unparalleled by metals and ceramics, polymer-based AM plays a key role in the emerging AM of advanced multifunctional and multimaterial systems including living biological systems as well as life-like synthetic systems.
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Tissue engineering needs innovative solutions to better fit the requirements of a minimally-invasive approach, providing at the same time instructive cues to cells. The use of shape memory polyurethane has been investigated by producing 4D scaffolds via 3D printing technology. Scaffolds with two different pore network configurations (0/90° and 0/45°) were characterized by dynamic-mechanical analysis (DMA). The thermo-mechanical analysis showed a Tg at about 32 °C (Tg = Ttrans), indicating no influence of the fabrication process on the transition temperature. In addition, shape recovery tests showed a good recovery of the permanent shape for both scaffold configurations. When cells were seeded onto the scaffolds in the temporary shape and the permanent shape was recovered, cells were significantly more elongated after shape recovery. Thus, the mechanical stimulus imparted by shape recovery is able to influence the shape of cells and nuclei. The obtained results indicate that a single mechanical stimulus is sufficient to initiate changes in the morphology of adherent cells.
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This work demonstrates that phase-segregated poly(ester urethane) (PEU) with switching segments of crystallizable poly(1,4-butylene adipate) (PBA) can be programmed to generate two separate stress recovery events upon heating under constant strain conditions. For programming, two elongations are applied at different temperatures, followed by unloading and cooling. During the adjacent heating, two-step stress recovery is triggered. The results indicate that the magnitude of the stress recovery signals corresponds to the recovery of the two deformation stresses in reverse order. As demonstrated by further experiments, twofold stress recovery can be detected as long as the elongation at higher temperature exceeds the strain level of the deformation at lower temperature. Another finding includes that varying the lower deformation temperature enables a control over the stress recovery temperature and thus the implementation of so-called "temperature-memory effects". Moreover, exerting only one elongation during programming enables a heating-initiated one-step stress recovery close to the deformation temperature. Based on these findings, such polymers may offer new technological opportunities in the fields of active assembly when used as fastening elements and in functional clothing when utilized for compression stockings.
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The fourth dimension in 4D printing refers to the ability of materials to alter its form after they are produced, thereby providing additional functional capabilities and performance-driven applications. Stimuli materials provide this capability through the use of shape memory polymers. For this research, the property of programming the determined shape is achieved through controlled heat under laboratory conditions. This paper shows the potential to process and experiment with thermoplastic polyurethane as a shape memory material. Taking a step further, we ascertain the properties of this material through extrusion-based additive manufacturing processes and produce parts for testing. The results show that the characteristics of the 3D printed parts successfully retain the property of the shape memory and the recovery force allows this to be utilised as a mechanical actuator. The recovery stress has been recorded to be between 0.45 and 0.61 MPa (at feed rate 990 mm/min). The maximum level of recovery stress is similar to the same material being processed through conventional compression moulding. Lastly, we designed and produced a coil as an actuator to demonstrate that the same material can be extended to other applications.
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In this study, a series of novel shape memory polyurethanes (SMPUs) containing tertiary amine groups are prepared by designing hexamethylene diisocyanate (HDI)–N-methyldiethanolamine (MDEA) as soft segments and HDI-BDO as hard segments. The structure and properties of the MDEA-based SMPUs are investigated using FT-IR, NMR, DSC, TGA, DMA, POM and AFM. The results demonstrate that the MDEA-based SMPU is composed of an amorphous soft phase and hard phase. The hard phase is amorphous below 20 wt% hard segment content (HSC), whereas the HDI-BDO segments form a semi-crystalline hard phase above 30 wt% HSC. This morphology exhibits good thermally induced SMEs with 100 % shape fixity and more than 80 % shape recovery. Moreover, the MDEA-based polyurethanes are expected to be further multifunctionalized for antibacterial activity, biocompatibility, multi-responsiveness and many other properties. This work provides a new strategy for designing multifunctional shape memory polymers with amine-containing polyurethanes.
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This article presents a novel method of shape memory polymer (SMP) processing for additive manufacturing, in particular, fused-deposition modeling (FDM). Critical extrusion process parameters have been experimented to determine an appropriate set of parameter values so that good-quality SMP filament could be made for FDM. In the FDM process, effects of different printing parameters such as extruder temperature and scanning speed on object printing quality are also studied. In all the process studies, we aim to achieve good-quality parts by evaluating part density, tensile strength, dimensional accuracy, and surface roughness. Based on these studies, sample SMP models have been successfully built. Due to the thermal sensitive nature of the printed SMP parts, they can potentially be used as fasteners in active assembly/disassembly, smart actuators, deployable structures for aero-space applications, etc.
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Fused deposition modeling (FDM) is one of the most popular additive manufacturing technologies for various engineering applications. FDM process has been introduced commercially in early 1990s by Stratasys Inc., USA. The quality of FDM processed parts mainly depends on careful selection of process variables. Thus, identification of the FDM process parameters that significantly affect the quality of FDM processed parts is important. In recent years, researchers have explored a number of ways to improve the mechanical properties and part quality using various experimental design techniques and concepts. This article aims to review the research carried out so far in determining and optimizing the process parameters of the FDM process. Several statistical designs of experiments and optimization techniques used for the determination of optimum process parameters have been examined. The trends for future FDM research in this area are described.
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Two design approaches for multifunctional information carriers are introduced. In the first one, quick response (QR) code carriers, which were composed of poly(ester urethane) (PEU) and microencapsulated thermochromic pigments (T-PIGs), differing in color and color switching temperature (CST), were prepared. The obtained material systems exhibited machine-readable QR codes at 23 [degree]C and a two-stage decolorization when heated, culminating in unreadable QR codes at temperatures above the highest CST of the employed T-PIGs. In the second scenario, information carriers were sealed with a dark, thermochromic PEU layer. As a result, the QR codes were hidden at 23 [degree]C and became readable upon heating due to color fading. Beyond the characterization of the employed components, preparation methods, functionality analyses and durability investigations are reported. When heated after thermo-mechanical programming, pronounced shape memory properties could be verified. The thermo-responsiveness of such
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Stimuli-responsive polymers (SRPs) are smart materials which can show noticeable changes in their properties with environmental stimulus variations. Novel functionalities can be delivered to textiles by integrating smart SRPs into them. SRPs inclusive of thermal-responsive polymers, moisture-responsive polymers, thermal-responsive hydrogels, pH-responsive hydrogels, and light-responsive polymers have been applied in textiles to improve or achieve textile smart functionalities. The functionalities include aesthetic appeal, comfort, textile soft display, smart controlled drug release, fantasy design with color changing, wound monitoring, smart wetting properties and protection against extreme variations in environmental conditions. In this review, the applications of SRPs in the textile and clothing sector are elucidated; the associated constraints in fabrication processes for textiles and their potential applications in the near future are discussed.
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The shape memory behavior of a series of polycaprolactone/methane diisocyanate/butanediol (PCL/MDI/BDO) segmented polyurethanes of different composition was studied. The molecular weight of PCL diols was in the range of 1600–7000, and the hard segment content varied from 7.8 to 27% by weight. Film specimens for shape memory measurements were prepared by drawing at temperatures above the melting temperature of the soft segment crystals and subsequent quick cooling to room temperature under constrained conditions. The shape memory process was observed and recorded in a heating process. Parameters describing the recovery temperature, ability, and speed were used to study the influence of structure and processing conditions on the shape memory behavior of the sample. It was found that the high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical crosslinks in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented copolymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals. The final recovery rate and the recovery speed are mainly related to the stability of the hard segment domains under stretching and are dependent on the hard segment content of the copolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1511–1516, 1997
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Shape-memory polymers (SMPs) have attracted significant attention from both industrial and academic researchers due to their useful and fascinating functionality. This review thoroughly examines progress in shape-memory polymers, including the very recent past, achieved by numerous groups around the world and our own research group. Considering all of the shape- memory polymers reviewed, we identify a classification scheme wherein nearly all SMPs may be associated with one of four classes in accordance with their shape fixing and recovering mechanisms and as dictated by macromolecular details. We discuss how the described shape- memory polymers show great potential for diverse applications, including in the medical arena, sensors, and actuators.
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Shape memory polymers (SMPs) are an emerging class of active materials whose response can be easily tailored via modifications of the molecular parameters and optimization of the transformation processes. In this work, we originally demonstrated that a correct coupling of polymer transformation processes (co-extrusion with chemical blowing agents, salt co-extrusion/particulate leaching, solvent casting/particulate leaching) and SMPs allows one to obtain porous structures with a broad spectrum of morphological properties resulting in tunable thermo-mechanical and shape recovery properties. Such a wide range of properties could fulfil the specifications of medical applications in which the use of SMP-based foams can be envisaged.
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Additive manufacturing, commonly referred to as 3D printing (3DP), has ushered in a new era of advanced manufacturing that is seemingly limited only by imagination. In actuality, the fullest potentials of 3DP can only be realized through innovative breakthroughs in printing technologies and build materials. Whereas equipment for 3DP has experienced considerable development, molecular-scale programming of function, adaptivity, and responsiveness in 3DP is burgeoning. This review aims to summarize the state-of-the-art in stimuli-responsive materials that are being explored in 3DP. First, we discuss stimuli-responsiveness as it is used to enable 3DP. This highlights the diverse ways in which molecular structure and reactivity dictate energy transduction that in turn enables 3D processability. Second, we summarize efforts that have demonstrated the use of 3DP to create materials, devices, and systems that are in their final stage stimuli-responsive. This section encourages the artistic license of advanced manufacturing to be applied toward leveraging, or enhancing, energy transduction to impart device function across multiple length scales.
Article
Hierarchically structuring materials open the door to a wide range of unexpected and uniquely designed properties. This work presents a novel mechanical metamaterial unit cell with strain‐dependent solid–solid phase changes resultant from hierarchically structured “mechanisms” built into an auxetic unit cell, and further presents a realization of this kind. The interaction of auxetic structure and mechanism allows stable or metastable elastic energy states to be reached as a result of mechanical deformation. The result is a principally elastic analog to a shape memory material with a functional dependency on its negative Poisson's ratio. Prototypes are additively manufactured using direct laser writing, and are subsequently subjected to uniaxial compression with a customized micromechanical test set up. Experimental results depict reversible states initially triggered by deformation; the unit cell is a building block for a programmable material with a nonlinear “if… then…” relationship. Implementing interior mechanisms as a hierarchical level unlocks new directions for mechanical metamaterials research, and the authors see potential impacts or applications in multi‐scale modeling, medicine, micro‐actuation and ‐gripping, programmable matter/materials. The work presented herein depicts an auxetic metamaterial unit cell displaying a time‐dependent deformation behavior analogous to conventional shape memory materials, but achieves this through the structurally hierarchical embedding of a “mechanism”. This proof‐of‐concept paper is a step in the direction of programmable materials, which are materials with reversible, functionalized properties triggered by external stimuli such as a force.
Article
Four-dimensional (4D) printing has great potential for fabricating patient-specific, stimuli-responsive 3D structures for the medical sector. Porous Shape memory polymers have high volumetric expansion and enhanced biological activity, which make them as ideal candidates for implant materials through minimally invasive surgical procedures. The objective of the present work is to develop a radiopaque, porous, and custom shaped shape memory polyurethane (SMPU) for its application in endovascular embolization. In this paper, the porous SMPU was fabricated by combining extrusion, fused filament fabrication (FFF) and salt leaching. The filament for FFF was produced by extruding the mixture of SMPU, NaCl, and Tungsten at the desired composition. The 3D printed and salt leached porous SMPU was observed to have the porosity in the range of 32.7 - 36% and pore sizes of <250 µm with the interconnected network. The porous Tungsten SMPU showed the improved radiopacity, increased storage modulus, and also, excellent shape holding and shape recovery up to 100%. The feasibility of combining fused filament fabrication and salt leaching technique was established for fabricating the radiopaque porous SMPU having the required characteristics for embolization, which can be explored by the Interventional Radiologist.
Article
Purpose Material extrusion additive manufacturing, also known as fused deposition modeling, is a manufacturing technique in which objects are built by depositing molten materials layer-by-layer through a nozzle. The use and application of this technique has risen dramatically over the past decade. This paper aims to first, report on the production and characterization of a shape memory polymer material filament that was manufactured to print shape memory polymer objects using material extrusion additive manufacturing. Additionally, it aims to investigate and outline the effects of major printing parameters, such as print orientation and infill percentage, on the elastic and mechanical properties of printed shape memory polymer samples. Design/methodology/approach Infill percentage was tested at three levels, 50, 75 and 100 per cent, while print orientation was tested at four different angles with respect to the longitudinal axis of the specimens at 0°, 30°, 60° and 90°. The properties examined were elastic modulus, ultimate tensile strength and maximum strain. Findings Results showed that print angle and infill percentage do have a significant impact on the manufactured test samples. Originality/value Findings can significantly influence the tailored design and manufacturing of smart structures using shape memory polymer and material extrusion additive manufacturing.
Article
The continuously increasing demand for oil and gas and the depleting number of new large reservoir discoveries have made it necessary for the oil and gas industry to investigate and design new, improved technologies that unlock new sources of energy and squeeze more from existing resources. Shape memory materials (SMM), with their remarkable properties such as the shape memory effect (SME), corrosion resistance, and superelasticity have shown great potential to meet these demands by significantly improving the functionality and durability of offshore systems. Shape memory alloy (SMA) and shape memory polymer (SMP) are two types of most commonly used SMM's and are ideally suited for use over a range of robust engineering applications found within the oil and gas industry, such as deepwater actuators, valves, underwater connectors, seals, self-torqueing fasteners and sand management. The potential high strain and high force output of the SME of SMA can be harnessed to create a lightweight, solid state alternative to conventional hydraulic, pneumatic or motor based actuator systems. The phase transformation property enables the SMA to withstand erosive stresses, which is useful for minimizing the effect of erosion often experienced by downhole devices. The superelasticity of the SMA provides good energy dissipation, and can overcome the various defects and limitations suffered by conventional passive damping methods. The higher strain recovery during SME makes SMP ideal for developments of packers and sand management in downhole. The increasing number of SMM related research papers and patents from oil and gas industry indicate the growing research interest of the industry to implement SMM in offshore applications. This paper reviews the recent developments and applications of SMM in the offshore oil and gas industry.
Article
Novel fast response shape-memory polyurethanes were prepared from bio-based polyols, diphenyl methane diisocyanate and butane diol for the first time. The bio-based polyester polyols were synthesized from 9-hydroxynonanoic acid, a product obtained by ozonolysis of fatty acids extracted from soy oil and castor oil. The morphology of polyurethanes was investigated by synchrotron ultra-small angle X-ray scattering, which revealed the inter-domain spacing between the hard and soft phases, the degree of phase separation, and the level of intermixing between the hard and soft phases. We also conducted thorough investigations of the thermal, mechanical, and dielectric properties of the polyurethanes, and found that high crystallization rate of the soft segment gives these polyurethanes unique properties suitable for shape-memory applications, such as adjustable transition temperatures, high degree of elastic elongations, and good mechanical strength. These materials are also potentially biodegradable and biocompatible, therefore suitable for biomedical and environmental applications.
Poster
The selective compression of quick response (QR) and Data Matrix code carriers based on shape memory polymer (SMP) with a freely configurable steel ball type indenter and adjacent thermo-mechanical shape fixing gave notched, room temperature (23 °C) stable, temporary shapes with non-decipherable codes. The microscopic investigation of cryomicrotome sections unveiled indentation-related shape fixities of about 90%. Independent of the selected two-dimensional code, the triggering of the SM effect resulted in sufficient shape recoveries to restore the code readability so that a maximum number of characters including 122 for a QR code (version 7) and 112 in case of a Data Matrix code (version 12) could be read with a scanning and decoding device. Due to the large number of difficult to copy shapes with on demand releasable information, SMPs may serve as viable information carriers for product and brand protection applications.
Article
Shape memory polymers (SMPs) are smart materials that can change their shape in a pre-defined manner under a stimulus. The shape memory functionality has gained considerable interest for biomedical applications, which require materials that are biocompatible and sometimes biodegradable. There is a need for SMPs that are prepared from renewable sources to be used as substitutes for conventional SMPs. In this paper, advances in SMPs based on synthetic monomers and bio-compounds are discussed. Materials designed for biomedical applications are highlighted.
Article
A series of thermoplastic poly(ester urethane)s (PUs) containing poly(butylene 1,4-cyclohexanedicarboxylate) (PBC) as a soft segment were prepared for shape memory materials via a two-step synthesis, with isophorone diisocyanate and 1,4-butanediol as its hard segments. The isomerization of the 1,4-cyclohexylene ring moiety (CHRM) happened during the preparation of PBC oligomers with molecular weight of 1700, 2300 and 3300 g mol⁻¹, but such phenomenon was not observed during the reaction for the synthesis of PU. The three PBC oligomers could all crystallize, but their crystallization ability was depressed after incorporation of PUs. Thermo, thermo-mechanical and mechanical properties of the corresponding PUs were studied to understand their structural information. It was found that the PU containing PBC1700 was an elastomer at elevated temperatures, and its shape memory properties were evaluated by DMA procedures. Regardless of its low degree of micro-phase separation, it was very interesting to find that the shape recovery ability of such PU was excellent, which was in contrast to traditional findings.
Article
Shape-memory polymers (SMPs) as stimuli-responsive shape-changing polymers are of great interest for fundamental research and technological innovation. In this contribution, a brief review of the recent trends in the field of SMPs is presented with particular focus on their structure, shape-memory effects and working mechanism. A special attention is paid to smart multi-responsive and multi-functional SMP materials as emerging technological class. They are mainly described as shape-memory nanocomposites (SMCs) where the incorporation of functional (in)organic nanofillers in the SMP matrices is purposely carried out. Potential applications of the SMCs-based materials as medical and biomimetic devices, self-healing systems, self-deployable structures, actuators, sensors etc. or their direct implementation in the industry are finally outlined.
Article
Medical devices such as implants, surgical instruments, extracorporal devices, and wound covers, as well as controlled drug delivery systems (CDDS) require a specific combination of material properties and functions including, for example, mechanical stability, biocompatibility, and biofunctionality. Polymeric biomaterials are of high relevance for such applications, as properties and functions can be tuned in a wide range by only small defined variations of their chemical or morphological structure. The rapid progress in surgical techniques, especially in minimally invasive surgery, requires smart materials, which are capable of an active on-demand movement and which do not need to be removed in a second surgery. These challenges can be addressed by shape-memory polymers (SMPs) described in this chapter. SMPs are of high technological significance for biomedical applications as they enable on-demand predefined changes in the shape of a device upon exposure to a suitable stimulus. Multifunctional materials are obtained when the shape-memory effect is combined with an additional function such as hydrolytic degradability, biofunctionality, and controlled drug release. Selected biomaterials with shape-memory capability are presented, including data on their biocompatibility. The potential of SMPs as a platform technology for biomedical applications is sketched by an overview on SMP-based medical devices being developed and the potential use of SMPs as matrix for CDDS.
Article
Material extrusion additive manufacturing (MEAM), also known as three-dimensional (3D) printing, is a popular additive manufacturing technique suitable for producing 3D shapes using thermoplastic materials. The majority of companies that design and test 3D printing machines work with thermoplastic acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) filaments. It is, however, crucial to utilize different types of filaments for a broader range of applications with different mechanical property requirements. Shape memory polymers (SMPs) are smart materials that react to an applied stimulus in order to recover large strains. MEAM techniques may be used for the production of SMP-based parts, allowing for smart structures to be created in a wide variety of geometries. In this work, a commercial 3D-printer was used to produce 3D printed polyurethane-based SMP specimens. An annealing heat treatment was applied to some of the specimens. Mechanical and thermomechanical testing was conducted to study the effects of testing temperatures and annealing heat treatments on the tensile and shape memory properties of the samples. 3D printing was shown to be a suitable technique for producing SMP parts capable of retaining good shape memory characteristics. Different annealing heat treatments and test temperatures were found to have considerable effects on the SMP specimen properties. In particular, annealing the specimens at 85. °C for 2. h helped to improve the rate of shape recovery and the consistency of mechanical test results.
Article
Shape memory polymers (SMP) were first developed in the mid 1980s, and interest in these "smart" polymers continues to grow today. The momentum of development over the last two decades for this class of polymers is reflected in the broad range and versatility discovered in SMP. At the university research level and in commercial businesses, SMP's functions and possibilities are being explored. SMP offers dynamic shape "memory" properties. It can change from a rigid polymer to an elastic state and then return to a rigid state again. In its elastic state, SMP will recover its "memory" shape if left unrestrained, or while pliable, it can be stretched, folded, or conformed to other shapes. These unique characteristics lend themselves for use in a myriad of fields, including clothing manufacturing, deployable space applications, morphing aircraft, and medical treatment, to name only a few. The opportunities of SMPs continue to expand as a researchers gain a full understanding of the material's capabilities and limitations. With the development of tailorable properties and new activation mechanisms, SMPs benefits are only now being realized.
Article
Temperature-memory polymers are able to generate a substantial mechanical response when heated above the temperature, at which a preceding deformation was carried out. Here we show how to design the temperature-memory effect (TME) by thermomechanical treatment. As a model polymer, phase segregated poly(ester urethane) (PEU) containing crystallizable segments of poly(1,4-butylene adipate) (PBA) was used. For programming, strain elongation was applied at temperatures within the PBA melting transition area, before temperature holding, unloading and cooling were carried out. Upon heating under stress-free or constant strain recovery conditions, precisely set temperature-memory onsets could be witnessed. Most importantly, strain fixities and recoverabilities the same as maximum recovery stresses turned out to be controllable by strain rate and temperature holding time after deformation, while transition temperatures remained largely unaffected. The tailoring of thermoresponsiveness was structurally enabled by different PBA crystallinities in the programmed state as verified by wide-angle X-ray scattering (WAXS). The reported studies intend to design TMEs in semicrystalline polyurethanes according to user-defined needs to make this technology broadly applicable.
Article
Shape memory polymers (SMPs), as a class of programmable stimuli-responsive shape changing polymers, are attracting increasing attention from the standpoint of both fundamental research and technological innovations. Following a brief introduction of the conventional shape memory effect (SME), progress in new shape memory enabling mechanisms and triggering methods, variations of in shape memory forms (shape memory surfaces, hydrogels, and microparticles), new shape memory behavior (multi-SME and two-way-SME), and novel fabrication methods are reviewed. Progress in thermomechanical modeling of SMPs is also presented.
Article
Stimulus-responsive materials are able to response to a particular stimulus, such as, heat, chemical, and light. As such, they are smarter and more intelligent than ordinary materials. While in most stimulus-responsive materials, the result is limited to a change in their certain physical/chemical properties, stimulus-responsive shape memory materials (SMMs) are able to recover their original shape, after being quasi-plastically distorted. SMMs are ideal for an integrated intelligent system, in which “The material is the machine” that can sense and then generate reactive motion as pre-programmed.This paper presents a brief review on the current progress in stimuli-responsive SMMs, from recent development in traditional shape memory alloys (SMAs) and shape memory polymers (SMPs) to newly emerged shape memory hybrids (SMHs), which open the door for ordinary people to design their own SMMs in a do-it-yourself (DIY) manner.The focus of this review is on twofold, namely phenomena, in particular those newly observed ones, and novel applications with great potential at present and in near future.
Article
We demonstrate that phase-segregated poly(ester urethane) (PEU) with crystallizable switching segments of poly(1,4-butylene adipate) (PBA) excels as high-performance temperature-memory polymer. Temperature-memory effects (TMEs) with regard to strain and stress recovering could be programmed by polymer elongation at temperatures below or within the PBA melting transition, followed by cooling under constant stress below the PBA crystallization transition and unloading. Beyond that conventional approach, a novel TME programming route was designed, mostly consisting in specimen elongation and unloading at the same temperature. As a result, an enhanced control over the onsets of strain and stress recovering could be achieved. With these findings, the TME could be exploited to switch quick response (QR) codes in recently developed information carriers from unreadable to readable. We conjecture that such behavior can be programmed into virtually all semicrystalline elastomers and anticipate applicability as label technology to monitor temperature abuse of food and pharmaceuticals.
Article
The polyurethane shape-memory polymer (SMP) developed by Mitsubishi Heavy Industry, Japan is not only thermo-responsive, but also moisture-responsive as recently found. The moisture-responsive ability atop the well-known thermo-responsive feature could open a new dimension for applications of this fantastic material. This paper presents a concise review of the thermo- and moisture-responsive properties and thermomechanical behaviors of this SMP and its composites, and potential applications utilizing these features, in particular in biomedical engineering.
Article
The swelling, viscoelastic, and mechanical behavior of phase-segregated poly(ester urethane) (PEU) block copolymers, composed of 4,4-methylenediphenyl diisocyanate, 1,4-butanediol as a chain extender, and crystallizable poly(1,4-butylene adipate) (PBA) with molecular weights between 1330 and 4120 g mol(-1), are investigated. Wide-angle X-ray scattering (WAXS) is employed to study the overall PEU crystallinity, which increases from 8.6 to 13.6% at higher PBA contents. The existence of two crystalline, polymorphic PBA phases, a thermodynamically stable phase and a metastable phase, is confirmed by further WAXS measurements. Calorimetric and thermomechanical investigations give evidence for controllable PBA polymorphic behavior. The crystallization conditions, like the cooling rate, affect the emerging polymorphic mixture, whereas the storage conditions either promote or inhibit the polymorphic ( to ) transition. The introduced concepts represent a new approach for gaining control over programmable thermoresponsiveness, which may be transferable to other shape-memory polymers with polymorphic switching segments.
Article
A series of polyester urethanes (PEUs) comprising poly(lactic acid‐co‐polydiol) copolymers as a soft segment, 4,4′‐diphenylmethane diisocyanate (MDI) and 1,4‐butanediol (BDO) as a hard segment were systematically synthesized. Soft segments, which were block copolymers of L‐lactide (LA) and polydiols such as poly(ethylene glycol) and poly(trimethylene ether glycol), were prepared via ring opening polymerization. Glass transition temperatures (T g) of the obtained PEUs were found strongly dependent on properties of copolymer soft segments. By simply changing composition ratio, type and molecular weight of polydiols in the soft segment preparation step, T g of PEU can be varied in the broad range of 0–57°C. The synthesized PEUs exhibited shape memory behavior at their transition temperatures. PEUs with hard segment ratio higher than 65 mole percent showed good shape recovery. These findings suggested that it is important to manipulate molecular structure of the copolymer soft segment for a desirable transition temperature and design optimal soft to hard segment ratio in PEU for good shape recovery. Copyright © 2011 John Wiley & Sons, Ltd.
Article
As a new class of smart materials, shape memory polymers and their composites (SMPs and SMPCs) can respond to specific external stimulus and remember the original shape. There are many types of stimulus methods to actuate the deformation of SMPs and SMPCs, of which the thermal- and electro-responsive components and structures are common. In this review, the general mechanism of SMPs and SMPCs are first introduced, the stimulus methods are then discussed to demonstrate the shape recovery effect, and finally, the applications of SMPs and SMPCs that are reinforced with fiber materials in aerospace are reviewed. SMPC hinges and booms are discussed in the part on components; the booms can be divided again into foldable SMPC truss booms, coilable SMPC truss booms and storable tubular extendible member (STEM) booms. In terms of SMPC structures, the solar array and deployable panel, reflector antenna and morphing wing are introduced in detail. Considering the factors of weight, recovery force and shock effect, SMPCs are expected to have great potential applications in aerospace.
Article
Solvent-cast films from shape memory poly(ester urethane) (PEU) containing different weight contents of microencapsulated thermochromic pigments (T-PIGs) were prepared by drying in air. Spectrophotometric investigations unveiled that gradual loading with T-PIG black resulted in continuous darkening of the films up to filler contents of 20 wt%, accompanied by a steady enhancement of thermochromic properties. Taking this composition as standard, PEU films equipped with T-PIG black, blue and red were deposited atop PEU plaques to obtain laminate structures. Herein, the cover layer thickness (100 ± 5 μm) and the good dispersion of T-PIGs inside the polymer matrix were verified by scanning electron microscopy. Machine-readable information carriers were prepared by laser engraving quick response (QR) codes into the cover layer of the laminates and subsequently cutting cuboidal samples therefrom. Finally, thermo-mechanical programming of the QR code carriers was applied to randomly distort the code patterns, thus rendering them unreadable. Upon heating, surface decolorization and shape recovering occurred; during the ensuing cooling, the surface color and contrast reappeared whereupon the QR codes could be read out. Spectrophotometric, calorimetric and thermo-mechanical investigations gave evidence that the color switching temperature of the T-PIGs roughly coincided with the melting temperature of the ester-based switching segment and thus with the activation temperature of the shape memory effect. Apart from that unique functionality, manifold design concepts may render information carriers difficult-to-copy. Therefore, we anticipate tremendous potential as anti-counterfeiting technology.
Article
Following a guest diffusion approach, the surface of a shape memory poly(ester urethane) (PEU) was either black or blue colored. Bowtie-shaped quick response (QR) code carriers were then obtained from laser engraving and cutting, before thermo-mechanical functionalization (programming) was applied to stabilize the PEU in a thermo-responsive (switchable) state. The stability of the dye within the polymer surface and long-term functionality of the polymer were investigated against UVA and hydrolytic ageing. Spectrophotometric investigations verified UVA ageing-related color shifts from black to yellow-brownish and blue to petrol-greenish whereas hydrolytically aged samples changed from black to greenish and blue to light blue. In the case of UVA ageing, color changes were accompanied by dye decolorization, whereas hydrolytic ageing led to contrast declines due to dye diffusion. The Michelson contrast could be identified as an effective tool to follow ageing-related contrast changes between surface-dyed and laser-ablated (undyed) polymer regions. As soon as the Michelson contrast fell below a crucial value of 0.1 due to ageing, the QR code was no longer decipherable with a scanning device. Remarkably, the PEU information carrier base material could even then be adequately fixed and recovered. Hence, the surface contrast turned out to be the decisive parameter for QR code carrier applicability.
Article
Shape memory polyurethane (PU) block copolymers composed of 4,4 ' -methylenebis-(phenylisocyanate), poly(tetramethylene glycol), and 1,4-butanediol as a chain extender were synthesized by a two-step process. FT-IR spectra showed that carbonyl peak appearing at 1700 cm(-1) increased with higher hard segment content, whereas another carbonyl peak at 1730 cm(-1) decreased. It suggests that hard segments get more aggregated to form domains in the PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of PU, such as maximum stress, tensile modulus, and elongation at break. Especially, maximum stress, tensile modulus, and elongation at break increased significantly at 30 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content. Finally, 80-95% of shape recovery was obtained at 30-45 wt % of hard segment content, and the control of hard segment content in PU block copolymers is very important in determining their physical properties.
Article
In two hydrolytic degradation studies the tensile (mechanical) and functional (thermo-mechanical) properties of a hydrolysis-stabilized shape memory poly(ester urethane) and its non-stabilized analog were investigated. Hydrolytic degradation was enforced by specimen immersion in de-ionized water at 80 °C. Significant differences in the fundamental shape memory parameters were monitored as function of aging time for the stabilized and non-stabilized polymer. This included the ability to recover strain (shape recoverability) and stress (stress recoverability) on heating after shape programming. Hydrolysis-related mechanical and functional changes were correlated with morphological ones, detected by differential scanning calorimetry (DSC). The shape memory poly(ester urethane), which was protected by a carbodiimide-based hydrolysis stabilizer, revealed significantly improved resistance towards hydrolysis with respect to various mechanical and shape memory parameters.
Article
The shape memory functionality of a segmented poly(ester urethane) and its hydrolytically aged specimens has been studied by cyclic thermo-mechanical measurements with an imposed strain of 100%. The shape memory effect was triggered by a melting transition in the soft segment phase. Aging was enforced by immersion in hot de-ionized water. In the course of the immersion the tensile properties (secant moduli, stress and strain at yield and break) were impaired by hydrolysis. Advanced specimen embrittlement finally led to rupture during the first thermo-mechanical cycle. This happened after 68days of aging at 55°C and correspondingly after 8days at 80°C. The residual strain after the first cycle, which was about 25%, increased significantly with aging time. Therefore, the total strain recoverability became ever smaller: aged specimens needed conditioning by at least two cycles for a full development of shape recoverability. Likewise the recovery force decreased continuously. Despite these degradation effects, it was observed that the shape fixity and the cycle-related shape recovery of appropriately conditioned specimens (number of cycles N>2) remained on a constant high level (at round 100% and between 90% and 100%, respectively) throughout the whole aging period. These observations are discussed within the framework of a simplified model of the behavior of crystallizable shape memory polymers. The amorphous state of the polymer is described by the equation of the linear visco-elastic solid. As for the semi-crystalline state the material is assumed to react elastically with respect to deviations from the configuration, which was frozen up under constraint conditions. The curves of the dependence of the material behavior on aging time at 55°C match perfectly those at 80°C when the time axis is adjusted by a factor of 8.5, from which the apparent activation energy for hydrolytic aging in the amorphous state of 82kJmol−1 could be deduced.
Article
The feasibility of laboratory-synthesized polyurethane-based shape-memory polymer (SMPU) actuators has been investigated for possible application in medical pressure bandages where gradient pressure is required between the ankle and the knee for treatment of leg ulcers. In this study, using heat as the stimulant, SMPU strip actuators have been subjected to gradual and cyclic stresses; their recovery force, reproducibility and reusability have been monitored with respect to changes in temperature and circumference of a model leg, and the stress relaxation at various temperatures has been investigated. The findings suggest that SMPU actuators can be used for the development of the next generation of pressure bandages.
Article
A segmented poly(ester urethane) shape-memory polymer with poly(ε-caprolactone) (PCL) soft segment and urethane hard segment was studied by FTIR to investigate the structural evolution in the shape-memory cycle. It was revealed that in the cold drawing programming process, first the amorphous PCL chains start to orient along the drawing direction, and then, the hard segment and the crystalline PCL chains orient upon further extension, accompanied by the weakening of the hydrogen bonds along the drawing direction between the hard segments and stress-induced disaggregation and recrystallization of the crystalline PCL. In the recovery process, the hard segments restore first with the parallel hydrogen bonds strengthening and then the amorphous PCL chains restore the original random orientation, and finally the crystalline PCL chains lose their alignment to a less-oriented state.
Article
Understanding the relationship between the number-average molecular weight (Mn) and the shape memory behavior of polymers is crucial for a complete picture of their thermomechanical properties, and hence for the development of smart materials, and, in particular, in textile technology. We report here on the study of shape memory properties as a function of Mn of polymers. Shape memory polyurethanes (SMPUs) of different Mn were synthesized, with various catalyst contents or molar ratio(r = NCO/OH) in the composition. In particular, two types of SMPU, namely Tm and Tg types according to their switch temperature type, were synthesized to compare the influence of Mn on their shape memory behavior. X-ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and shape memory behavior results for the SMPUs are presented. The results indicate that the melting temperature (Tm), the glass transition temperature (Tg), the crystallinity, and the crystallizability of the soft segment in SMPUs are influenced significantly by Mn, before reaching a critical limit around 200 000 g mol−1. Characterization of the shape memory effect in PU films suggests that the Tm-type films generally show higher shape fixities than the Tg-type films. In addition, this shape fixity decreases with increasing Mn in the Tg-type SMPU, but the shape recovery increases with Mn in both types of SMPU. The shape recovery temperature, in contrast, decreases with Mn as suggested by the result of their thermal strain recovery. It is concluded that a higher molecular weight (Mn > 200 000 g mol−1) is a prerequisite for SMPUs to exhibit higher shape recovery at a particular temperature. Copyright © 2007 Society of Chemical Industry
Article
Additive processing technologies are rapidly growing in all fields of application. A large number of scientific publications were investigated in order to provide a comprehensive overview of rapid prototyping methods for polymers and their applications, of currently available materials and research concerning additive processes. The current problems of additive processes are described, together with their potential solutions. Furthermore, this article delivers an insight into possible future trends of additive technologies. magnified image
Article
Segmented polyurethanes containing soft segments with lower molecular weight exhibit shape-memorizing properties. Structure and properties of shape-memorizing polyurethanes (S-PUs) were studied. S-PUs are characterized by a rather high glass transition temperature: Tg of S-PUs is usually in the range of 10–50°C. A Pplot of 1/Tm against–In XA is approximately linear, indicating that the hard segments are randomly distributed along the molecular chain. S-PUs with a hard segment of 67–80 mole % form negative spheruiites; they give a faint scattering maximum in a small-angle X-ray diffraction pattern. On the other hand, S-PUs with a hard segment of 50 mole % form fine birefringent elements, giving diffuse scattering in its SAXD pattern. A cyclic test of an S-PUs above Tg indicates that the residual strain increases and the recovery strain decreases with increasing cycle and maximum strain. It has been suggested by dynamic mechanical investigation that the shape-memorizing property of the S-PUs may be ascribed to the molecular motion of the amorphous soft segments. © 1996 John Wiley & Sons, Inc.