Memory Properties Research Articles

Using tannin as a biological curing agent to design fully bio-based epoxidized natural rubber/polylactic thermoplastic vulcanizates with mechanical robustness and multi-stimuli-responsive shape memory properties

To effectively mitigate carbon emissions and promote sustainability in the polymer field, biological macromolecules have emerged as a prominent strategy for fabricating functional materials. Herein, tannin (TA) was used as a biological curing agent to design fully bio-based polylactic/epoxidized natural rubber thermoplastic vulcanizates (PLA/ENR TPVs) with mechanical robustness and multi-stimuli-responsive shape memory properties. A dual cross-linking network, comprising both covalent bonds and hydrogen bonds, was successfully constructed in the ENR phase. A special co-continuous morphology was concomitantly constructed in the TPVs, which promoted effective stress transfer between the PLA and ENR phases, endowing the TPVs with balanced stiffness-toughness and shape memory properties. Moreover, the photothermal effect of TA also made it respond to near-infrared light and sunlight, which achieved the non-contact multistage shape memory performance, revealing the significant potential of the TPVs in the field of actuators.

Exploring synergies between GnP and fiber orientation in enhancing mechanical, thermomechanical, and shape memory properties of carbon fiber polymer composites

Abstract This research investigates the mechanical, thermomechanical, and shape memory properties across 12 configurations of shape memory hybrid composites, varying in carbon fiber orientation: uni-directional (UD), bi-directional-Twill (BDT), and bi-directional-Plain (BDP), and multi-walled carbon nanotube weight percentages of 0.4%, 0.6%, and 0.8% elucidate the synergistic effects of fiber architecture and nanomaterial reinforcement. The fabrication process involves initially preparing GnP-modified epoxy nanocomposites through ultrasonication followed by hand layup techniques to fabricate three-phase shape memory hybrid composites. Optimal tensile performance is observed in GnP-modified UD composites at a 0.6 wt% concentration, achieving a tensile strength of 728.32 MPa and a modulus of 71.29 GPa. Furthermore, enhancements in thermomechanical and shape memory properties are noted in GnP-modified BDT composites and are further improved in GnP-modified BDP composites configurations. These improvements are attributed to enhanced interfacial bonding between the polymer and fiber, with the maximum effect observed at the 0.6 wt% BDP composite, validated by morphological analysis using FESEM. The study demonstrates that despite polymer modification, all configurations maintain high shape recovery ratios, particularly notable at 97.54% for 0.6 wt% GnP modified BDP composite, exceeding 90% across all configurations, indicating robust performance in shape memory capabilities.

Toward Highly Toughened Polylactide/Polycaprolactone‐Based Polyurethane Blends With Shape Memory Property via Reactive Blending

ABSTRACTReactive blending has proven to be a versatile and efficient method for enhancing the impact toughness of polylactide (PLA). PLA/cross‐linked polycaprolactone‐based polyurethane (c‐PCLU) blends are prepared by reactive blending of PLA with PCL triol and hexamethylene diisocyanate (HDI). The reaction mechanism, compatibility, crystallization behavior, rheology behavior, mechanical performance, and shape memory property are thoroughly studied. The FTIR results confirmed that the NCO groups of HDI reacted with the hydroxyl groups of PLA and PCL triol, leading to the in situ formation of c‐PCLU and PLA‐co‐PCLU. The phase morphology exhibits a sea‐island structure, suggesting incompatibility between the two phases. The compatibility of the blends is improved with the increase of the PCL triol feeding ratio. The crystallization ability of PLA is retarded in the reactive blend. Both the elongation at break and the shape recovery ratio increase with c‐PCLU content, reaching up to 94.0% and 92.6%, respectively. These findings show that the formation of c‐PCLU greatly enhanced the toughness and shape memory performance of PLA.

Investigating Melt Pool Dimensions in Laser Powder Bed Fusion of Nitinol: An Analytical Approach

Nitinol (NiTi) has gained popularity across various industries due to its shape memory and superelastic properties. Recently, additive manufacturing (AM) has been increasingly utilized to produce NiTi components. This study focuses on single‐track nitinol samples fabricated via powder bed fusion using laser beam (PBF‐LB). Investigating the effects of laser power and scanning speed on melt pool dimensions reveals that melt pool width increases linearly with laser power and decreases logarithmically with scanning speed. However, melt pool depth exhibits outliers that deviate from these trends. Three analytical models are evaluated to predict melt pool dimensions, generally aligning with experimental trends. Notably, the Eagar–Tsai model delivers the most accurate predictions for melt pool width, with a mean absolute error of less than 10%, while the Gladush–Smurov model is more reliable for melt pool depth predictions, showing a mean absolute error under 20%. In contrast, the Rosenthal equation yields less reliable results for both dimensions. This suggests that a combined approach utilizing the strengths of both the Eagar–Tsai and Gladush–Smurov models may provide the most accurate predictions for the melt pool profile of NiTi in PBF‐LB.

Regulation of Glass Transition Temperature in Thermo‐Responsive Epoxy Shape Memory Polymers: The Roles of Chemical Crosslinking Density and Chain Flexibility

ABSTRACTShape memory polymers (SMPs) are novel kinds of smart materials whose shape can be changed in external conditions such as heat stimulus. Due to their excellent structural versatility and high elastic strain, they have important applications in the field of biomaterials. Here, a series of amorphous shape memory polymer materials are prepared and their shape memory properties and glass transition temperature (Tg) are also investigated. A special kind of epoxy polymer, whose shape can be changed at around physiological temperature, is synthesized by regulating the crosslinking density and introducing flexible aliphatic epoxy chains. The shape memory function of this epoxy polymer is studied by deformation test. In addition, to explore their application in the field of biomedical materials, the biocompatibility of the materials are evaluated, including the effects on the erythrocyte hemolysis rate and cell activity. The experimental results show that this kind of epoxy polymer has good shape memory function and biocompatibility.

Adverse Effects of Aβ1-42 Oligomers: Impaired Contextual Memory and Altered Intrinsic Properties of CA1 Pyramidal Neurons

Aβ1-42 (amyloid beta) oligomers, the major neurotoxic culprits in Alzheimer’s disease, initiate early pathophysiological events, including neuronal hyperactivity, that underlie aberrant network activity and cognitive impairment. Although several synaptotoxic effects have been extensively studied, neuronal hyperexcitability, which may also contribute to cognitive deficits, is not fully understood. Here, we found several adverse effects of in vivo injection of Aβ1-42 oligomers on contextual memory and intrinsic properties of CA1 pyramidal neurons. Male rats underwent behavioral and electrophysiological studies 1 week after microinjections into the dorsal CA1 region, followed by histological analysis. After 1 week, Aβ1-42 oligomers impaired contextual learning without affecting basic physiological functions and triggered training-induced neuronal excitability. Furthermore, riluzole, a persistent sodium current (INaP) blocker, dose-dependently reduced Aβ1-42 oligomer-induced hyperexcitability. Congo red staining, which detects insoluble amyloid deposits, further identified labeling of CA1 pyramidal neurons while immunohistochemistry with lecanemab, which detects soluble Aβ oligomers, revealed immunoreactivity of both pyramidal and non-pyramidal cells in the target area. Therefore, our study suggests that a single injection of Aβ1-42 oligomers resulted in contextual memory deficits along with concomitant neuronal hyperexcitability and amyloid deposition in the CA1 region after 1 week.

Shape memory, reprocessable and photothermal networks of polyurethane with silyl ether bonds and croconaine segments

Organic dyes were integrated into networks of polyurethane (PU) in the form of croconaine segments, in order to bestow photothermal properties on the materials. In addition, the PU networks were crosslinked with polysilsesquioxane (PSSQ) so that the materials can be reprocessed (or self-healing) via the metathesis of silyl ether bonds under catalysis. Toward this end, we synthesized a novel diol bearing croconaine moiety, which was used as one of chain extenders and a series of linear PU telechelics with dihydroxyl termini were synthesized. The α,ω-dihydroxyl PU telechelics were then allowed to react with 3-isocyanatopropyltriethoxysilane to gain α,ω-ditriethoxysilane PU telechelics. Through sol-gel process, α,ω-ditriethoxysilane PU telechelics readily underwent crosslinking with PSSQ as the crosslinkages. The crosslinking of PU was in marked contrast to traditional crosslinking of PU with multifunctional ols (or amines) as the crosslinkers. Owing to the crosslinking, shape memory properties were bestowed on the organic-inorganic PU networks. Thanks to the metathesis of silyl ether bonds under catalysis, the organic-inorganic PU networks were reprocessable (or recyclable). Benefiting from the built-in of dye segments, the PU networks significantly displayed excellent photothermal conversion properties. By leveraging the photothermal properties, the shape shifting of the PU networks can be triggered via the irradiation under infrared laser and in a non-contact fashion. In addition, the PU networks were capable of displaying the light-triggered self-healing properties. Thanks to these excellent properties, we demonstrated a successful application of the PU networks a soft robot.

Harnessing nanostructures and fiber architecture: A synergistic leap in shape memory polymer composites

This research investigates the synergistic effects of carbon fiber orientation and nanostructure reinforcement across 21 configurations of shape memory polymer composites. It examines uni-directional (UD), bi-directional Twill (BDT), and bi-directional Plain (BDP) fiber architectures, along with varying concentrations of MWCNT and GnP at 0.4%, 0.6%, and 0.8%. The fabrication process involves initially preparing nanostructure-modified epoxy nanocomposites through ultrasonication followed by hand layup techniques to fabricate three-phase shape memory polymer composites. Optimal tensile performance is observed in GnP-modified UD composites at a 0.6 wt% concentration, achieving a tensile strength of 728.32 MPa and a modulus of 71.29 GPa. Furthermore, enhancements in thermomechanical and shape memory properties are noted in GnP-modified BDT composites and are further improved in GnP-modified BDP composite configurations. GnP-modified composites outperform MWCNT ones due to GnP’s sheet structure aligning parallel to the load and its larger surface area, which facilitate enhanced interaction with the matrix. These improvements, supported by FESEM analysis, highlight enhanced interfacial bonding and result in high shape recovery ratios, with all configurations exceeding 90%, despite polymer modification.

Optimization of the integro-differential hyperbolic model

We consider a model of processes in viscoelastic media. The force arising inside the body may depend not only on the current values but also on the entire time history of the motion (for example, polymers, emulsions, and suspensions exhibit memory properties). Such processes often lead to the necessity of studying hyperbolic integro-differential equations with Volterra integral term. The main goal is to prove the existence and uniqueness of generalized solutions to the corresponding initial-boundary value problem, as well as to investigate the existence of optimal control for systems described by these models. The main results are obtained using the method of a priori inequalities in negative norms. In particular, we justify inequalities in negative norms for the integro-differential operator in certain functional spaces. The work begins with a short description of relevant results with similar formulations and referencing works with physical justification of the model. Afterwards, we describe the problem statement, constraints on equation parameters, and functional spaces used for the investigation. Below are the main results, in particular definitions of generalized solutions and properties on the well-posed of the initial-boundary value problem as well as the existence of optimal control. Control is carried out through the right-hand side of the equation using a certain special operator. It is possible to examine specific examples of such control operators (illustrating various control mechanisms) and the corresponding control spaces. By utilizing proven inequalities and relying on general results of S.I. Lyashko from the theory of a priori inequalities in negative norms, we establish sufficient conditions for the existence of optimal control. In particular, we impose the restrictions on the admissible set of controls and the quality criterion.

Thermal Cycling Behavior of Aged FeNiCoAlTiNb Cold-Rolled Shape Memory Alloys

Fe–Ni–Co–Al-based systems have attracted a lot of interest due to their large recoverable strain. In this study, the microstructure and thermal cycling behaviors of Fe41Ni28Co17Al11.5Ti1.25Nb1.25 (at.%) 98.5% cold-rolled alloys after annealing treatment at 1277 °C for 1 h, followed by aging for 48 h at 600 °C, were investigated. From the electron backscatter diffraction results, we see that the texture intensity increased from 9.4 to 16.5 mud and the average grain size increased from 300 to 400 μm as the annealing time increased from 0.5 h to 1 h. The hardness results for different aging heat treatment conditions show the maximum value was reached for samples aged at 600 °C for 48 h (peak aging condition). The orientation distribution functions (ODFs) displayed by Goss, brass, and copper were the main textural features in the FeNiCoAlTiNb cold-rolled alloy. After annealing, strong Goss and brass textures were formed. The transmission electron microscopy (TEM) results show that the precipitate size was ~10 nm. The X-ray diffraction (XRD) results show a strong peak in the (111) and (200) planes of the austenite (⁠⁠γ, FCC) structure for the annealed sample. After aging, a new peak in the (111) plane of the precipitate (⁠⁠γ′, L12) structure emerged, and the peak intensity of austenite (⁠⁠γ, FCC) decreased. The magnetization–temperature curves of the aged sample show that both the magnetization and transformation temperature increased with the increasing magnetic fields. The shape memory properties show a fully recoverable strain of up to 2% at 400 MPa stress produced in the three-point bending test. However, the experimental recoverable strain values were lower than the theoretical values, possibly due to the fact that the volume fraction of the low-angle grain boundary (LABs) was small compared to the reported values (60%), and it was insufficient to suppress the beta phases. The beta phases made the grain boundaries brittle and deteriorated the ductility. On the fracture surface of samples after the three-point bending test, the fracture spread along the grain boundary, and the cross-section microstructural results show that the faces of the grain boundary were smooth, indicating that the grain boundary was brittle with an intergranular fracture.

Modulation of shape memory properties of trans-polyisoprene by sulfur

Abstract In this paper, TPI/S composites were prepared by a simple physical melt blending method, and the composites were hot-pressed and molded using a vulcanization system. The effect of cross-linking on the vulcanization properties, mechanical properties, crystalline properties, and shape memory properties of trans-1-4 polyisoprene (TPI) was investigated by varying the amount of sulfur (S). It was shown that with the increase of sulfur dosage, both TPI scorch time and orthoclave time were shortened and the mechanical properties decreased; The melting peak area and melting temperature of the crystalline region of TPI decreased with the increase of sulfur content, and the cross-linking density increased while the crystallinity tended to decrease and the heat resistance deteriorated; In addition, with the increase of sulfur content, the shape return rate of TPI/S composites was increasing and the shape fixation rate was decreasing. When the TPI/S composites were used as shape memory materials, the sulfur dosage of 1 phr had the best shape memory performance, at which time the shape fixation rate of the composites reached 96.9% and the shape recovery rate reached 86.2%. When the sulfur content was elevated to 2 phr, the shape memory fixation rate was significantly decreased, indicating that the shape memory properties were severely compromised. This study reveals that the quantity of sulfur exerts a significant influence on the application of TPI/S composites. An appropriate amount of sulfur can facilitate the preparation of thermoplastic elastomers for utilization in shape memory materials. Nevertheless, an excessive amount of sulfur will substantially enhance the internal cross-linked structure of the composite and deteriorate the shape memory performance.

Investigation of Copper Addition on Corrosion Behavior of a Ferrous Based Shape Memory Alloy for Biomedical Implant Applications

Permanent biomedical implants pose several issues in long term scenarios like infections, inflammation, implant fracture, tissue damage, cancerous tumors formation, and skin allergies. Biodegradable biomedical implants are a new interest that function by degrading internally after achieving the implant goal. Shape memory alloys like Nitinol and Iron based shape memory alloys have applications in biomaterials due to the excellent property of super elasticity and shape memory effect respectively with the ease of small surgery requirement. To achieve biodegradability, the alloy composition is to be set while not compromising other properties such as biocompatibility, mechanical properties, shape memory properties, and magnetic properties. Slow corrosion rates of Fe-Mn alloys are reported and alloying addition, surface modifications, and novel manufacturing techniques are suggested to overcome this problem. In this study, the effect of addition of copper addition effect on the degradation behavior of Fe-30Mn-5Si is investigated. Austenite is the major phase present in both samples and small amounts of martensite are also present. For 10% copper, an additional copper rich phase is formed along the grain boundaries as it was beyond the solubility limit of iron matrix. The electrochemical corrosion test shows that 10% Cu addition resulted in 1.72 times higher corrosion rate than that of 5% Cu addition. As 5% Cu addition is within the solubility limit of iron matrix, and it forms a solid solution with iron that creates a passive layer during corrosion testing results in slower degradation.

Ethylene vinyl acetate/copper sulphide with near-infrared light active shape memory behavior

This thesis presents the preparation of ethylene vinyl acetate (EVA)-based shape memory polymer composites (SMPC) (EVA/CuS) with near-infrared light photo-thermal response. The composites were prepared using EVA as the matrix material and copper sulphide (CuS) particles as the functional phase. The designability of SMPs was considered in the preparation of these composites. The results demonstrated that the incorporation of CuS, as a functional phase, enhanced the cross-linking degree and augmented the shape memory properties of EVA. Additionally, it served as a photo-thermal functional filler, imparting its photo-thermal properties. It can be observed that as the quantity of CuS particles incorporated into the EVA/CuS composite film increases, the photothermal conversion performance of the composite film improves, the shape fixation rate rises, and the rate of recovery of light-responsive shape memory accelerates. The temperature of the composites increased to 116.7°C in 20 s when the CuS addition was 2 wt% and the NIR light intensity was 0.5 W/cm2. At a NIR light intensity of 0.6 W/cm2, the “U” shape of the sample was restored to a straight state in 30 s, and the shape recovery rate reached 100%. In this experiment, optical near-infrared photostimulation-responsive EVA/CuS composites have been successfully prepared. These composites demonstrate the ability to achieve remote control and fast response of EVA shape memory behavior, offering a new avenue for the preparation of photo-responsive EVA-based shape memory materials.

Synthesis of a gallic acid-based self-healing waterborne polyurethane with a thermo-responsive dynamic phenol-carbamate network for enhanced mechanical strength, antimicrobial activity, and shape memory properties

To expedite the advancement of multifunctional next-generation smart materials, it is imperative to create polymers derived from renewable, green bio-based resources. This paper presents a direct synthesis of thermo-responsive aqueous polyurethanes by combining gallic acid (GA) with isocyanate groups to form a dynamic phenol-carbamate crosslinked network and the incorporation of the metal-organic framework Cu-MOF-2 for synergistic effects. The resulting GA-based polyurethane (MOF-GWPU) exhibits excellent thermal stability and mechanical properties, achieving an ideal balance between mechanical strength and self-healing efficiency. The MOF-GWPU film demonstrates strong antimicrobial efficacy against Escherichia coli and Staphylococcus aureus, highlighting its exceptional antibacterial performance. The thermo-responsive dynamic covalent bonds enable the MOF-GWPU film to rapidly revert from a temporary shape back to its original form. Post-processing experiments further indicate that the crosslinked GA-PU polymer can be efficiently recycled through solution casting and hot-pressing techniques. This design offers a novel approach and valuable insights for advancing the development of multifunctional smart polymers derived from bio-based resources.

Development and 4D printing of magneto-responsive PMMA/TPU/Fe3O4 nanocomposites with superior shape memory and toughness properties

This paper introduces 4D printing of composites of polymethyl methacrylate (PMMA) and thermoplastic polyurethane (TPU) reinforced with Fe3O4 particles for the first time. PMMA/TPU blends with 70/30 wt% are selected as matrix with the best compatibility based on dynamic mechanical thermal analysis. Fe3O4 nanoparticles are added to the blends with 10 %, 15 % and 20 % weight ratios. Their addition enables remote actuation of the materials in a high frequency alternating magnetic field. Field emission scanning microscopic images confirms a full dispersion of nanoparticles inside the polymeric matrix. Nanocomposites with 20 wt% of Fe3O4 can perfectly recover the permanent shape within 1.5 min in the magnetic field. They also reveal perfect shape memory properties in the hot water. Moreover, all samples display a perfect shape fixity ratio. The addition of TPU significantly enhances the toughness and flexibility of the PMMA matrix. It is found that Fe3O4 nanoparticles further enhance the mechanical strength by 10 % to 15 %, although they reduce the strain at break from 17 % to 14 %. Finally, a gripper is 4D printed and its excellent performance in the magnetic field is demonstrated.

Cortical, striatal, and thalamic populations self-organize into a functionally connected circuit with long-term memory properties

The human brain is a complex organ with an intricate neuronal connectivity and diverse functional regions. Neurological disorders often disrupt the delicate balance among these anatomical compartments, resulting in severe impairments. The available therapeutic options constitute an incomplete solution as many patients respond partially, highlighting the need for continued research into causes and treatments. Bottom-up approaches, like in vitro models, offer insights into brain functions as they recreate the in vivo microenvironment that allows studying how specific features affect physiological and pathological conditions. In this work, we engineered the cortical-striatal-thalamic (CST) circuit, involved in many brain functions such as action initiation and selection, using a three-compartment polymeric device. We characterized the emerging spontaneous electrophysiological activity by using Micro-Electrode Arrays (MEAs). Cortical neurons exhibited complex bursting activity, which influenced the entire circuit. Striatal and thalamic neurons displayed predominantly tonic firing when isolated, while interconnections with the cortex synchronized and organized their neuronal activity, highlighting the cortical pivotal role in bursting activity and information processing. The CST circuit demonstrated self-organization abilities and displayed high entropy values, indicative of dynamic richness and information encoding potential. Furthermore, we proved the CST’s involvement in learning and memory. Our CST model provides a platform for further exploration into brain circuitry and potential therapeutic interventions, underscoring the necessity of realistic in vitro models to fully understand neurological diseases' pathophysiology.

Controlling Long-Term Plasticity in Neuromorphic Computing Through Modulation of Ferroelectric Polarization.

Electrolyte-gated transistors (EGTs) have significant potential for neuromorphic computing because they can control the number of ions by mimicking neurotransmitters. However, fast depolarization of the electric double layer (EDL) makes it difficult to achieve long-term plasticity (LTP). Additionally, most research utilizing organic ferroelectric materials has been focused on basic biological functions, and the impact on nonvolatile memory properties is still lacking. Herein, we present a polyvinylidene fluoride (PVDF)-based ion-gel synaptic device using PVDF and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) to implement LTP through the introduction of ferroelectric materials. The PVDF-based polymer slows the escape rate of TFSI anions from the electrolyte/channel layer through residual polarization. The fabricated synaptic devices successfully demonstrate LTP by controlling ion adsorption under the influence of PVDF-based polymers. Furthermore, it implements synaptic functions including paired pulse facilitation (PPF), high-pass filtering, and neurotransmitter control. To validate the potential of neuromorphic computing, we successfully achieved high recognition rates for artificial/convolutional neural network (A/CNN) simulations via sequential adsorption and desorption under ferroelectric polarization with long-term potentiation/depression (LTP/D). This study provides a rational ion adsorption strategy utilizing the ferroelectric polarization caused by the introduction of a PVDF-based polymer in the dielectric layer.

Optimising Nanoparticle Dispersion Time for Enhanced Thermomechanical Properties in DGEBA-Based Shape Memory Polymer Composites

Shape-memory polymers (SMPs) are smart materials that can change shape upon an external stimulus. This phenomenon is called the shape memory effect (SME), which is caused by entropy change due to rapid molecular motion in the polymer segments. Due to the inherently weak thermomechanical properties, use of SMPs is limited in many engineering applications. Therefore, SMPs are often reinforced with fibres and nanoparticles (NPs). NPs offered greater flexibility due to their superior physical, chemical, electrical, mechanical, and thermal properties. However, the homogeneous distribution of NPs is crucial for composition’s stability and enhancement of the base material’s properties. Among the different techniques used for dispersing NPs, ultrasonic irradiation has shown excellent emulsifying and crushing performance. The sonication process is essential for mitigating agglomerates; however, prolonged sonication time probably increases epoxy temperature, micro-bubbles, cavitation, breaking apart molecules and finally degrading the epoxy resin performances. This paper provides critical insight of nanoparticle dispersion into diglycidyl ether of bisphenol A epoxies (DGEBA). DGEBA epoxy resin was added to TiO2 NPs and sonicated for 60 min with 5 min intervals while the temperature of epoxy was maintained below 60oC by using a water cooling throughout the sonication process. The process parameters such as amplitude, mode, epoxy volume and the weight percentage of NPs were kept constant. After each sonication step, Fourier-transform infrared spectroscopy (FTIR) was performed using Thermo Scientific™ and analysed through OMNIC™ Professional quantitation software. In accordance with FTIR results, until 30 min of the sonication, DGEBA resin was not degraded. In order to confirm the performances and the reinforcing effect of NPs, thermo-mechanical and shape memory properties were compared with the neat specimen. The outcomes of this research have suggested quick guidance to find optimum NP dispersion time for DGEBA resins, which has been hardly studied before.

Preparation and 3D printing parameters of thermo/electrically shape memory PLA/SEBS-g-MA/CB composites

In this work, novel thermo-responsive shape memory blends PLA/SEBS-g-MA and electro-responsive PLA/SEBS-g-MA/carbon black (CB) composites were prepared by melt blending, and were extruded into filaments for 3D printing. SEM images illustrate that the blends possess co-continuous structure at SEBS-g-MA ratio of 30 wt% and showcase remarkable shape memory properties (Rf 100 %, Rr 85.3 %), which were attributed to effective stress transfer. In the second part, PLA/SEBS-g-MA/CB composites were produced with different amounts of CB nanoparticles. The volume resistivity of composites with CB additions of 13 phr and above is maintained at about 102 Ω cm, and the printed samples showed superior electro-responsive performance, with response completed in about 40 s at 60 V DC. In addition, the effect of printing parameters on the mechanical properties was investigated and it was found that the choice of layer thickness was strongly related to tensile and flexural strength.

Shape memory characteristics of injection molded, cross-linked all-polyethylene composites

In this study, we investigated the shape memory properties of a novel self-reinforced polymer composite (SRPC). Chopped Dyneema® SK76 fibers were mixed with high-density polyethylene (HDPE) resin, and samples were produced by injection molding. To allow the fibers to keep their shape and reinforce effectively, we cross-linked them with gamma irradiation (100, 200, and 300 kGy absorbed doses). In the second step of irradiation, we irradiated the composites with doses of 50, 100, 150, and 200 kGy to give them shape memory properties. Soxhlet extractions, differential scanning calorimetry, and scanning electron microscopy revealed that the fibers cross-linked and kept their structural integrity through processing. We confirmed the reinforcing effect of the fibers with flexural tests and by dynamic mechanical analysis. In free recovery experiments, samples had recovery and fixity ratios above 79%. With the highest dose, recovery stress increased by 26%. We showed the viability of this novel method of self-reinforcement in the production of shape memory polymers (SMPs) with improved characteristics.