Electroactive Shape Memory Property of a Cu-decorated CNT Dispersed PLA/ESO Nanocomposite

Shape memory polymer (SMP) nanocomposites with a fast electro-actuation speed were prepared by dispersing Cu-decorated carbon nanotubes (CNTs) (Cu-CNTs, 1 wt %, 2 wt %, and 3 wt %) in a polylactic acid (PLA)/epoxidized soybean oil (ESO) blend matrix. The shape memory effect (SME) induced by an electrical current was investigated by a fold-deploy “U”-shape bending test. In addition, the Cu-CNT dispersed PLA/ESO nanocomposite was characterized by atomic force microscopy (AFM), dynamic mechanical analysis (DMA) and tensile and electrical measurements. The results demonstrated that the SME was dependent on the Cu-CNT content in the nanocomposites. When comparing the SMEs of the nanocomposite specimens with different Cu-CNT contents, the 2 wt % Cu-CNT dispersed system exhibited a shape recovery as high as 98% within 35 s due to its higher electrical conductivity that results from uniform Cu-CNT dispersion. However, the nanocomposites that contained 1 wt % and 3 wt % Cu-CNTs required 75 s and 63 s, respectively, to reach a maximum recovery level. In addition, the specimens exhibited better mechanical properties after the addition of Cu-CNTs.     

Smart TPE Materials Based on Recycled Rubber Shred

Thermo-responsive shape memory materials were developed based on recycled ethylene-propylene-diene (EPDM) rubber shred and thermoplastic elastomers (TPE). Ethylene-1-octene TPEs (Engage 8180, 8411, 8452) with varying degrees of crystallinity and Mooney viscosity were used to prepare the composite materials. To avoid the deterioration of static mechanical properties after mixing recycled EPDM rubber shred (RS) with thermoplastic elastomers, they were partially cured using dicumyl peroxide. The peroxide curing was the most effective for a rubber shred/Engage 8180 blend, where the highest cure rate index (CRI), 1.88 dNm⋅min⁻¹, was observed. The curing caused an approximately 4-fold increase of tensile strength (TS) values for EPDM rubber shred/thermoplastic elastomer blend to the level acceptable for the rubber industry compared with an uncured blend. The incorporation of EPDM rubber shred changed thermoplastic elastomers’ viscoelastic behavior, increasing the values of storage (G′) and loss (G″) modulus. The lowest viscosity of molten Engage 8411 during mixing led to higher compatibility of rubber shred RS/8411 blend, as confirmed by analysis of Cole-Cole plots and the blend morphology. All rubber shred RS/TPE blends showed the shape memory behavior. For the RS/Engage 8452 blend, the highest shape fixity (F) value (94%) was observed, while the shape recovery (RR) was 87%. Studies confirmed that the intelligent materials with shape memory effect could be obtained via selectively chosen thermoplastic elastomers; ethylene-1-octene as a binder for recycled EPDM. Prepared recycled TPE/rubber shred blends can be successfully reused due to their viscoelastic and mechanical properties. Therefore, such a concept can be potentially interesting for the rubber industry.     

Investigations of Effects of Intermetallic Compound on the Mechanical Properties and Shape Memory Effect of Ti–Au–Ta Biomaterials

Owing to the world population aging, biomedical materials, such as shape memory alloys (SMAs) have attracted much attention. The biocompatible Ti–Au–Ta SMAs, which also possess high X–ray contrast for the applications like guidewire utilized in surgery, were studied in this work. The alloys were successfully prepared by physical metallurgy techniques and the phase constituents, microstructures, chemical compositions, shape memory effect (SME), and superelasticity (SE) of the Ti–Au–Ta SMAs were also examined. The functionalities, such as SME, were revealed by the introduction of the third element Ta; in addition, obvious improvements of the alloy performances of the ternary Ti–Au–Ta alloys were confirmed while compared with that of the binary Ti–Au alloy. The Ti₃Au intermetallic compound was both found crystallographically and metallographically in the Ti–4 at.% Au–30 at.% Ta alloy. The strength of the alloy was promoted by the precipitates of the Ti₃Au intermetallic compound. The effects of the Ti₃Au precipitates on the mechanical properties, SME, and SE were also investigated in this work. Slight shape recovery was found in the Ti–4 at.% Au–20 at.% Ta alloy during unloading of an externally applied stress.     

Shape-memory polymers as stimuli-sensitive implant materials

Shape-memory polymers are stimuli-responsive materials. Upon exposure to an external stimulus, e.g. an increase in temperature, they have the capability of changing their shape. The shape-memory effect results from the polymer's structure and morphology in combination with a certain processing and programming technology. Stimuli-sensitive implant materials have a high potential for applications in minimally invasive surgery. A group of biodegradable implant materials with shape-memory has been developed for applications in biomedicine. These implant materials are not a single polymer but polymer systems that allow the variation of different macroscopic properties over a wide range by only small changes in the chemical structure. In this way, it is possible to implement a variety of different applications with tailor-made polymers of the same family. Two different types of degradable shape-memory polymer systems, covalently cross-linked polymer networks and thermoplastic elastomers, are presented and examples are given for each case.     

In-Vitro Analysis of FeMn-Si Smart Biodegradable Alloy

Special materials are required in many applications to fulfill specific medical or industrial necessities. Biodegradable metallic materials present many attractive properties, especially mechanical ones correlated with good biocompatibility with vivant bodies. A biodegradable iron-based material was realized through electric arc-melting and induction furnace homogenization. The new chemical composition obtained presented a special property named SME (shape memory effect) based on the martensite transformation. Preliminary results about this special biodegradable material with a new chemical composition were realized for the chemical composition and structural and thermal characterization. Corrosion resistance was evaluated in Ringer’s solution through immersion tests for 1, 3, and 7 days, the solution pH was measured in time for 3 days with values for each minute, and electro-corrosion was measured using a potentiostat and a three electrode cell. The mass loss of the samples during immersion and electro-corrosion was evaluated and the surface condition was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). SME was highlighted with differential scanning calorimetry (DSC). The results confirm the possibility of a memory effect of the materials in the wrought case and a generalized corrosion (Tafel and cyclic potentiometry and EIS) with the formation of iron oxides and a corrosion rate favorable for applications that require a longer implantation period.     

Two-Way Bending Properties of Shape Memory Composite with SMA and SMP

A shape memory composite (SMC) was fabricated with a shape memory alloy (SMA) and a shape memory polymer (SMP), and its two-way bending deformation and recovery force were investigated. The results obtained can be summarized as follows: (1) two kinds of SMA tapes which show the shape memory effect (SME) and superelasticity (SE) were heat-treated to memorize the round shape. The shape-memorized round SMA tapes were arranged facing in the opposite directions and were sandwiched between the SMP sheets. The SMC belt can be fabricated by using the appropriate factors: the number of SMP sheets, the pressing force, the heating temperature and the hold time. (2) The two-way bending deformation with an angle of 56 degrees in the fabricated SMC belt is observed based on the SME and SE of the SMA tapes during heating and cooling. (3) If the SMC belt is heated and cooled by keeping the bent form, the recovery force increases during heating and degreases during cooling based on the two-way properties of the SMC. (4) The development and application of high-functional SMCs are expected by the combination of the SMA and the SMP with various kinds of phase transformation temperatures, volume fractions, configurations and heating-cooling rates.     

Siloxane Matrix Molecular Weight Influences the Properties of Nanocomposites Based on Metal Complexes and Dielectric Elastomer

Siloxane-based elastomers are some of the most sought-after materials for the construction of actuators and equipment for energy harvesting devices. This article focuses on changes of the mechanical (breaking stress, breaking strain, Young’s modulus) and dielectric properties for elastomers prepared with silicones, induced by the variation of molecular weight of the matrix, with three different silicone polymers having 60,000 g/mol, 150,000 g/mol, and 450,000 g/mol (from GPC measurements). Multiple siloxane elastomers were crosslinked with methyltriacetoxysilane using the sol-gel route. The dielectric permittivity values of the elastomers were also enhanced with two different complex structures containing siloxane bond and 3d transition metals as filler materials for polydimethylsiloxane polymers with various molecular weights. The dielectric spectroscopy tests demonstrated a small decrease (5%) for the values of the dielectric permittivity in relation to increased molecular weight of the siloxane polymer, both for samples prepared with pure polymer and for samples with metal complexes. The samples of nanocomposites showed a >50% increase of dielectric permittivity values relative to samples prepared of pure siloxane elastomer. The thermal tests demonstrated that the nanocomposites retained thermal stability similar with samples prepared of pure siloxane elastomer. The behavior under controlled conditions of humidity showed a trend of increased water vapor sorption with increasing molecular weight but an overall hydrophobic stable character of nanocomposites.     

Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, T(switch). If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(epsilon-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25 degrees C resulted in temporary fixation of the mechanical deformation by 50-60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kA x m(-1)). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature.     

Shape Memory Properties of PBS-Silica Hybrids

A series of novel Si–O–Si crosslinked organic/inorganic hybrid semi-crystalline polymers with shape memory properties was prepared from alkoxysilane-terminated poly(butylene succinate) (PBS) by water-induced silane crosslinking under organic solvent-free and catalyst-free conditions. The hydrolyzation and condensation of alkoxysilane end groups allowed for the generation of silica-like crosslinking points between the polymeric chains, acting not only as chemical net-points, but also as inorganic filler for a reinforcement effect. The resulting networks were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic-mechanical analysis (DMA) and tensile and shape memory tests to gain insight into the relationship between the polymeric structure, the morphology and the properties. By controlling the molecular weight of the PBS precursor, a fine tuning of the crosslinking density and the inorganic content of the resulting network was possible, leading to different thermal, mechanical and shape memory properties. Thanks to their suitable morphology consisting of crystalline domains, which represent the molecular switches between the temporary and permanent shapes, and chemical net-points, which permit the shape recovery, the synthesized materials showed good shape memory characteristics, being able to fix a significant portion of the applied strain in a temporary shape and to restore their original shape above their melting temperature.     

Polymeric triple-shape materials

Shape-memory polymers represent a promising class of materials that can move from one shape to another in response to a stimulus such as heat. Thus far, these systems are dual-shape materials. Here, we report a triple-shape polymer able to change from a first shape (A) to a second shape (B) and from there to a third shape (C). Shapes B and C are recalled by subsequent temperature increases. Whereas shapes A and B are fixed by physical cross-links, shape C is defined by covalent cross-links established during network formation. The triple-shape effect is a general concept that requires the application of a two-step programming process to suitable polymers and can be realized for various polymer networks whose molecular structure allows formation of at least two separated domains providing pronounced physical cross-links. These domains can act as the switches, which are used in the two-step programming process for temporarily fixing shapes A and B. It is demonstrated that different combinations of shapes A and B for a polymer network in a given shape C can be obtained by adjusting specific parameters of the programming process. Dual-shape materials have already found various applications. However, as later discussed and illustrated by two examples, the ability to induce two shape changes that are not limited to be unidirectional rather than one could potentially offer unique opportunities, such as in medical devices or fasteners.     

Characterization of Nanocomposites by Thermal Analysis

In materials research, the development of polymer nanocomposites (PN) is rapidly emerging as a multidisciplinary research field with results that could broaden the applications of polymers to many different industries. PN are polymer matrices (thermoplastics, thermosets or elastomers) that have been reinforced with small quantities of nano-sized particles, preferably characterized by high aspect ratios, such as layered silicates and carbon nanotubes. Thermal analysis (TA) is a useful tool to investigate a wide variety of properties of polymers and it can be also applied to PN in order to gain further insight into their structure. This review illustrates the versatile applications of TA methods in the emerging field of polymer nanomaterial research, presenting some examples of applications of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA) and thermal mechanical analysis (TMA) for the characterization of nanocomposite materials.     

Production of Agglomerates,Composite Materials,and Seed Coatings from Tannery Waste as New Methods for Its Management

This paper presents methods for managing waste produced by the leather industry, including tanning shavings derived from chrome tanning technologies and collagen preparations. Shavings were classified according to their shape (in accordance with Zingg’s shape classification). The content of individual elements was determined, together with the content of volatile organic compounds. Two new products were developed as part of the completed works: agglomerates (methods of non-pressure granulation) and composite materials were produced on the basis of tanning shavings and mineral fillers. Young’s modulus values classify these composite materials in the group of polymers and certain materials from the group of elastomers. A method for seed coating (on the example of legumes and rape) was also developed using a disc granulator, including collagen preparations in one of the layers as a solution for preventing the effects of droughts (biostimulant). The analyses of selected properties of the new products confirm the wide possible application of waste shavings and collagen preparations in a circular economy, especially in the construction, packaging, and agricultural sectors.     

Design of Shape Memory Thermoplastic Material Systems for FDM-Type Additive Manufacturing

The work presented here describes a paradigm for the design of materials for additive manufacturing platforms based on taking advantage of unique physical properties imparted upon the material by the fabrication process. We sought to further investigate past work with binary shape memory polymer blends, which indicated that phase texturization caused by the fused filament fabrication (FFF) process enhanced shape memory properties. In this work, two multi-constituent shape memory polymer systems were developed where the miscibility parameter was the guide in material selection. A comparison with injection molded specimens was also carried out to further investigate the ability of the FFF process to enable enhanced shape memory characteristics as compared to other manufacturing methods. It was found that blend combinations with more closely matching miscibility parameters were more apt at yielding reliable shape memory polymer systems. However, when miscibility parameters differed, a pathway towards the creation of shape memory polymer systems capable of maintaining more than one temporary shape at a time was potentially realized. Additional aspects related to impact modifying of rigid thermoplastics as well as thermomechanical processing on induced crystallinity are also explored. Overall, this work serves as another example in the advancement of additive manufacturing via materials development.     

Light-Actuated Liquid Crystal Elastomer Prepared by Projection Display

Soft materials with programmability have been widely used in drug delivery, tissue engineering, artificial muscles, biosensors, and related biomedical engineering applications. Liquid crystal elastomers (LCEs) can easily morph into three-dimensional (3D) shapes by external stimuli such as light, heat, and humidity. In order to program two-dimensional (2D) LCE sheets into desired 3D morphologies, it is critical to precisely control the molecular orientations in LCE. In this work, we propose a simple photopatterning method based on a maskless projection display system to create spatially varying molecular orientations in LCE films. By designing different synchronized rotations of the polarizer and projected images, diverse configurations ranging from individual to 2D lattice of topological defects are fabricated. The proposed technique significantly simplified the photopatterning procedure without using fabricated masks or waveplates. Shape transformations such as a cone and a truncated square pyramid, and functionality mimicking the responsive Mimosa Pudica are demonstrated in the fabricated LCE films. The programmable LCE morphing behaviors demonstrated in this work will open opportunities in soft robotics and smart functional devices.     

Effects of Carbon Black and the Presence of Static Mechanical Strain on the Swelling of Elastomers in Solvent

The effect of carbon black on the mechanical properties of elastomers is of great interest, because the filler is one of principal ingredients for the manufacturing of rubber products. While fillers can be used to enhance the properties of elastomers, including stress-free swelling resistance in solvent, it is widely known that the introduction of fillers yields significant inelastic responses of elastomers under cyclic mechanical loading, such as stress-softening, hysteresis and permanent set. When a filled elastomer is under mechanical deformation, the filler acts as a strain amplifier in the rubber matrix. Since the matrix local strain has a profound effect on the material’s ability to absorb solvent, the study of the effect of carbon black content on the swelling characteristics of elastomeric components exposed to solvent in the presence of mechanical deformation is a prerequisite for durability analysis. The aim of this study is to investigate the effect of carbon black content on the swelling of elastomers in solvent in the presence of static mechanical strains: simple extension and simple torsion. Three different types of elastomers are considered: unfilled, filled with 33 phr (parts per hundred) and 66 phr of carbon black. The peculiar role of carbon black on the swelling characteristics of elastomers in solvent in the presence of mechanical strain is explored.     

Additive Manufacturing of Smart Composite Structures Based on Flexinol Wires

3D printing of a composite structure with shape memory materials requires a special approach to the subject, at the stage of the design and printing process. This paper presents the design steps during the development of a 3D-printed composite structure with shape memory material. The connection points between the SMA fibers and the printer filament are developed in the MATLAB environment. Finite element method is used to simulate the shortening of the shape memory material under the influence of temperature and its effect on the printed polymer material is presented. In the MATLAB environment, evolutionary algorithms were used to determine the shape of the SMA fiber alignment. This work demonstrates the use of shape memory effect in 3D printed smart composite structures, where the component takes a predetermined shape. The structure obtained as a result of such printing changes with the heat generated by the current voltage, making it the desired fourth dimension.     

Sustainability of Civil Structures through the Application of Smart Materials: A Review

Every year, structural flaws or breakdowns cause thousands of people to be harmed and cost billions of dollars owing to the limitations of design methods and materials to withstand extreme earthquakes. Since earthquakes have a significant effect on sustainability factors, there is a contradiction between these constraints and the growing need for more sustainable structures. There has been a significant attempt to circumvent these constraints by developing various techniques and materials. One of these viable possibilities is the application of smart structures and materials such as shape memory and piezoelectric materials. Many scholars have examined the use of these materials and their structural characteristics up to this point, but the relationship between sustainability considerations and the deployment of smart materials has received little attention. Therefore, through a review of previous experimental, numerical, and conceptual studies, this paper attempts to draw a more significant relationship between smart materials and structural sustainability. First, the significant impact of seismic events on structural sustainability and its major aspects are described. It is then followed by an overview of the fundamentals of smart material’s behaviour and properties. Finally, after a comprehensive review of the most recent applications of smart materials in structures, the influence of their deployment on sustainability issues is discussed. The findings of this study are intended to assist researchers in properly addressing sustainability considerations in any research and implementation of smart materials by establishing a more explicit relationship between these two concepts.     

Recent Trends and Innovation in Additive Manufacturing of Soft Functional Materials

The growing demand for wearable devices, soft robotics, and tissue engineering in recent years has led to an increased effort in the field of soft materials. With the advent of personalized devices, the one-shape-fits-all manufacturing methods may soon no longer be the standard for the rapidly increasing market of soft devices. Recent findings have pushed technology and materials in the area of additive manufacturing (AM) as an alternative fabrication method for soft functional devices, taking geometrical designs and functionality to greater heights. For this reason, this review aims to highlights recent development and advances in AM processable soft materials with self-healing, shape memory, electronic, chromic or any combination of these functional properties. Furthermore, the influence of AM on the mechanical and physical properties on the functionality of these materials is expanded upon. Additionally, advances in soft devices in the fields of soft robotics, biomaterials, sensors, energy harvesters, and optoelectronics are discussed. Lastly, current challenges in AM for soft functional materials and future trends are discussed.     

Towards Low-Cost Effective and Homogeneous Thermal Activation of Shape Memory Polymers

A typical limitation of intelligent devices based on the use of shape-memory polymers as actuators is linked to the widespread use of distributed heating resistors, via Joule effect, as activation method, which involves several relevant issues needing attention, such as: (a) Final device size is importantly increased due to the additional space required for the resistances; (b) the use of resistances limits materials’ strength and the obtained devices are normally weaker; (c) the activation process through heating resistances is not homogeneous, thus leading to important temperature differences among the polymeric structure and to undesirable thermal gradients and stresses, also limiting the application fields of shape-memory polymers. In our present work we describe interesting activation alternatives, based on coating shape-memory polymers with different kinds of conductive materials, including textiles, conductive threads and conductive paint, which stand out for their easy, rapid and very cheap implementation. Distributed heating and homogeneous activation can be achieved in several of the alternatives studied and the technical results are comparable to those obtained by using advanced shape-memory nanocomposites, which have to deal with complex synthesis, processing and security aspects. Different combinations of shape memory epoxy resin with several coating electrotextiles, conductive films and paints are prepared, simulated with the help of thermal finite element method based resources and characterized using infrared thermography for validating the simulations and overall design process. A final application linked to an active catheter pincer is detailed and the advantages of using distributed heating instead of conventional resistors are discussed.