Shape Memory Polymer Blends Research Articles

Thermo-responsive shape memory polymer blends based on polylactic acid and polyethylene glycol

Thermo-responsive shape memory polymer blends based on polylactic acid and polyethylene glycol

4D Printing of novel poly(ethylene-vinyl acetate) / poly(butyl methacrylate-co-isobutyl methacrylate) shape memory polymer blends

4D printing is a technology that combines additive manufacturing with shape memory polymers, aiming to enhance the functionality of 3D printed structures. Filaments made from thermoplastic polymers are commonly used in Fused Deposition Modeling (FDM), which is one of the most prevalent types of 3D printing. Here, novel heat-responsive shape memory polymer blends were produced from ethylene-vinyl acetate copolymer (EVA) and poly(butyl methacrylate-co-isobutyl metacrylate) polymers. The effect of blend composition on the morphological, thermal, mechanical, and shape memory properties was investigated. The blend (60E-40B) containing 60 % by weight EVA and 40 % by weight BMA-co-iBMA exhibited optimum shape memory performance with a shape fixing (Rf) of 94.1 % and a shape recovery (Rr) of 94.5 % at a shape transition temperature (Ttrans) of 55 °C. Filament for the 60E-40B blend was produced for FDM type 3D printers, and 4D parts for various applications were printed using this filament. These 4D printed parts, designed for robotic grippers, self-assemble rivets, movable cog-wheel teeth, surface traps, and finger splints, displayed shape recovery characteristics in both hot oven and hot water environments.

A novel green synthesis approach for shape memory polymer nanocomposites decorated with silver nanoparticles

AbstractA new, low‐cost, and direct green synthesis strategy was developed for the preparation of polymer composites composed of silver nanoparticles (AgNPs) decorated on a shape memory polymer blend using Rubus caesius L. leaves. X‐ray powder diffraction, ultraviolet‐visible spectroscopy (UV–vis), scanning electron microscopy, and energy dispersive X‐ray spectroscopy (EDS) elemental composition were applied to characterize the crystal size, morphology, and elemental composition of Ag‐NPs. UV–vis spectra detected the characteristic absorbance signal of AgNPs at about 430 nm, and the average crystal size of nanoparticles was calculated as about 12.60 nm. When nanocomposite films were characterized by attenuated total reflectance infrared spectroscopy, characteristic polylactic acid, and poly ethylene glycol (PEG) signals were determined. From the thermogravimetric analysis curves, it was determined that the amount of residue of nanocomposites increased as the amount of AgNP increased. It was seen that AgNPs did not affect the Tg temperature of the nanocomposite films, while it was also a proof that the polymer blend was immiscible. It was observed that the shape recovery properties of nanocomposite films were better with increasing AgNPs content. Finally, both green synthesized AgNPs and nanocomposites prepared with shape memory polymers showed very good antibacterial activity against Gram‐positive and Gram‐negative bacteria.Highlights Green synthesis of silver nanoparticles (AgNPs) was carried out with Rubus caesius L. leaves. The synthesized AgNPs were characterized by ultraviolet visible spectroscopy and x‐ray powder diffraction. Composite films were prepared with poly lactic acid/poly ɛ‐caprolactone blend by solvent casting method. The amount of residue of nanocomposites increased with increasing AgNPs percentage. The nanocomposite film containing 10% AgNPs has good activity.

4D printable maleated poly(styrene-b-ethylene/butylene-b-styrene) / Poly(ethylene-co-vinyl acetate) thermoplastic elastomer blends; effects of blend composition on shape memory and mechanical properties

Shape memory polymers are attracting attention in materials science with their responsive properties and their application areas are gradually developing. By adapting these materials to the additive manufacturing process, four-dimensional (4D) printing technology has been developed. In this study, novel thermo-responsive shape memory polymer blends were prepared for high temperature applications from commercially available polymers using maleated poly(styrene-b-ethylene/butylene-b-styrene) (SEBS-g-MA) and poly(ethylene-co-vinyl acetate) (EVA) and their applicability in three-dimensional (3D) printing was explored. The presence of SEBS-g-MA led to an increase in the degree of crystallization and glass transition temperature of EVA, accompanied by a decrease in crystallization temperature. As the EVA content increased, the blend morphology transitioned from droplet to co-continuous structure. Higher EVA content resulted in an increase in Young's modulus, but a decrease in tensile strength. Nevertheless, these blends exhibited exceptional elongation at break, surpassing 1200%. The blend comprising 70 wt% SEBS-g-MA and 30 wt% EVA demonstrated a synergistic effect, yielding the highest values for elastic modulus, creep resistance, and storage modulus. Furthermore, the blend with 60 wt% SEBS-g-MA and 40 wt% EVA exhibited optimal shape memory performance, achieving a shape fixing ratio of 93.1% and a shape recovery ratio of 98.7%. The conducted analyses demonstrated that the shape recovery of the produced blends could be adjusted according to temperature, and the blends were able to consistently replicate the shape memory effect across multiple cycles. A filament was manufactured for a 3D printer from the blend of 60 wt% SEBS-g-MA and 40 wt% EVA. Using this filament, 4D models having complex geometries were successfully printed. The produced models were able to maintain their temporary shapes to a significant degree. When triggered by heat, these models rapidly returned to their original shapes within a very short period.

Development of a Resilience Parameter for 3D-Printable Shape Memory Polymer Blends.

The goal of this paper was to establish a metric, which we refer to as the resilience parameter, to evaluate the ability of a material to retain tensile strength after damage recovery for shape memory polymer (SMP) systems. In this work, three SMP blends created for the additive manufacturing process of fused filament fabrication (FFF) were characterized. The three polymer systems examined in this study were 50/50 by weight binary blends of the following constituents: (1) polylactic acid (PLA) and maleated styrene-ethylene-butylene-styrene (SEBS-g-MA); (2) acrylonitrile butadiene styrene (ABS) and SEBS-g-MA); and (3) PLA and thermoplastic polyurethane (TPU). The blends were melt compounded and specimens were fabricated by way of FFF and injection molding (IM). The effect of shape memory recovery from varying amounts of initial tensile deformation on the mechanical properties of each blend, in both additively manufactured and injection molded forms, was characterized in terms of the change in tensile strength vs. the amount of deformation the specimens recovered from. The findings of this research indicated a sensitivity to manufacturing method for the PLA/TPU blend, which showed an increase in strength with increasing deformation recovery for the injection molded samples, which indicates this blend had excellent resilience. The ABS/SEBS blend showed no change in strength with the amount of deformation recovery, indicating that this blend had good resilience. The PLA/SEBS showed a decrease in strength with an increasing amount of initial deformation, indicating that this blend had poor resilience. The premise behind the development of this parameter is to promote and aid the notion that increased use of shape memory and self-healing polymers could be a strategy for mitigating plastic waste in the environment.

Advancing Shape Memory Polymer Blends: Enhancing Mechanical Properties and Tailoring Shape Recovery

This paper explores the integration of pattern analysis techniques into the study of polymer blends, aiming to enhance our understanding of their microstructure and properties. Polymer blends, combinations of two or more polymers, hold immense potential for tailored material design. However, accurately characterizing their intricate microstructures remains a challenge. Pattern analysis offers advanced tools for uncovering hidden relationships within complex data. This research investigates how pattern analysis can provide insights into the structural features and performance of polymer blends, contributing to advancements in material science and industrial applications.

Influences of Crystallinity and Crosslinking Density on the Shape Recovery Force in Poly(ε-Caprolactone)-Based Shape-Memory Polymer Blends.

Shape-memory polymers (SMPs) show great potential in various emerging applications, such as artificial muscles, soft actuators, and biomedical devices, owing to their unique shape recovery-induced contraction force. However, the factors influencing this force remain unclear. Herein, we designed a simple polymer blending system using a series of tetra-branched poly(ε-caprolactone)-based SMPs with long and short branch-chain lengths that demonstrate decreased crystallinity and increased crosslinking density gradients. The resultant polymer blends possessed mechanical properties manipulable across a wide range in accordance with the crystallinity gradient, such as stretchability (50.5-1419.5%) and toughness (0.62-130.4 MJ m-3), while maintaining excellent shape-memory properties. The experimental results show that crosslinking density affected the shape recovery force, which correlates to the SMPs' energy storage capacity. Such a polymer blending system could provide new insights on how crystallinity and crosslinking density affect macroscopic thermal and mechanical properties as well as the shape recovery force of SMP networks, improving design capability for future applications.

Novel of (PLA/PCL blend)/Gd2O3 rare earth oxide nanocomposites: Shape memory effect, thermal, magnetic, and mechanical properties

AbstractPoly ɛ‐caprolactone (PCL) and poly lactic acid (PLA) stand out as biocompatible polymers. In this study, PCL and PLA were blended in 40:60 ratio, respectively, and then the Gd2O3 compound, which is an important earth element oxide, was mixed in PLA–PCL shape memory polymer (SMP) blend at different rates and polymer blend nanocomposites were obtained. First of all, the effects of Gd2O3 oxide on the thermal properties of the SMP blend were determined with a differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA), and it was determined that Gd2O3 did not have a significant effect on the melting temperature of the blend, while it significantly increased its thermal stability. As a result of the XRD (X‐ray diffraction) analysis of the composites at room temperature, it was determined that the semicrystalline blend, with the addition of Gd2O3, increased its crystalline property. When the shape memory effect was examined, it was understood that the additive did not eliminate the shape memory effect. When the magnetic property of the gadolinium oxide‐doped composite, which is magnetocaloric oxide, was examined, the magnetic property of the composite changed from diamagnetic to paramagnetic with increasing additives. Finally, the mechanical properties of the shape memory blend composite were investigated and no regular changes were observed in the mechanical properties with increasing Gd2O3.

Modeling of viscoelastic behavior of a shape memory polymer blend

AbstractShape memory effect (SME) of polymers is a property that concerns both, macroscopic and microscopic changes. The variation of internal polymer properties such, as molecular weight (Mw), rigidity, and viscoelasticity could alter its SME. In this study, a bi‐parabolic model with six parameters is used to describe the viscoelastic behavior of a shape memory polymer (SMP) blend (40% poly(caprolactone), PCL/60% Styrene–Butadiene–Styrene) with different PCL Mw. These parameters are determined using the Cole–Cole method. Modeling curves (E″ = f (E′)) will be then compared to experimental data from dynamical mechanical analysis (DMA) tests. It is shown that the bi‐parabolic model predicts well the behavior of the SMP mixture for different Mw of PCL. Afterwards, the evolution of the model parameters with the Mw of PCL is investigated. It is revealed that, when Mw of PCL drops, the relaxation modulus E0 increases. This result proves that the rigidity of the SMP blend rises with Mw declines.

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.

Non-woven shape-memory polymer blend actuators

The hierarchical design approach provides various opportunities to adjust the structural performance of polymer materials. Electrospinning processing techniques give access to molecular orientation as a design parameter, which we consider here in view of the shape-memory actuation performance. The aim of this work is to investigate how the reversible strain varepsilon^{prime}_{{{text{rev}}}} can be affected by a morphology change from a bulk material to an electrospun mesh. varepsilon^{prime}_{{{text{rev}}}} could be increased from 5.5 ± 0.5% to 15 ± 1.8% for a blend from a multiblock copolymer with poly(ε-caprolactone) (PCL) and poly(L-lactide) (PLLA) segments with oligo(D-lactide) (ODLA). This study demonstrates an effective design approach for enhancing soft actuator performance, which can be broadly applied in soft robotics and medicine.Graphic abstract

Cross-linked Poly(Octadecyl Acrylate)/Polybutadiene Shape Memory Polymer Blends Prepared by Simultaneous Free Radical Cross-linking, Grafting and Polymerization of Octadecyl Acrylate/Polybutadiene Blends.

A semi-crystalline, shape memory polymer (SMP) is fabricated by free radical cross-linking, polymerization, and grafting in a blend of n-octadecyl acrylate and polybutadiene (PB). Poly(n-octadecyl acrylate) (PODA) is a side-chain crystalline polymer, which serves as the structure-fixing network counterbalancing the elastically deformed, cross-linked polymer network. At a constant 50/50 ratio of monomer and polymer the amount of free radical initiator, dicumyl peroxide (DCP) is varied from 1% to 5%w/w PB. From swelling measurements and calculation of the cross-link density it is determined that DCP produces greater than one cross-link per DCP molecule. It is found that lower cross-linking efficiency is favorable for higher shape fixity. This lower efficiency is found to produce a higher degree of crystallinity of the PODA in the 2-5% DCP samples, which is determined to be the main driver of higher shape fixity of the polymer. A SMP with >90% fixity and 100% recovery at uniaxial strains from 34-79% is achieved. This material should be useful for mold processing of shape memory articles. This approach provides a method to decouple the elastomeric and thermoplastic portions of a SMP to convert commodity elastomers into SMPs and tailor the shape memory response.

Preparation and characterization of electro-active shape memory PCL/SEBS-g-MA/MWCNT nanocomposites

In this work, novel thermally responsive shape memory polymer (SMP) blends of poly(caprolactone) (PCL) and maleic anhydride grafted polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS-g-MA) blends and electro-active PCL/SEBS-g-MA/multi walled carbon nanotube (MWCNT) nanocomposites with different compositions were prepared by melt blending technique. The effects of the PCL content (30-40-50%) on morphological, thermal, mechanical and shape memory properties were investigated. Based on SEM analysis, co-continuous morphology was observed in the blend having the weight ratio of 50:50 (50 PCL-50MA). The thermally triggered shape memory properties which were characterized by a dynamic mechanical analyzer (DMA) showed that the 50 PCL-50MA exhibited the highest fixing (Rf 98.28%) and recovery ratios (Rr 87.97%) among the SMP blends. In the second part of the study, the 50 PCL-50MA blend nanocomposites were produced with different amounts of multiwalled carbon nanotubes (MWCNTs) and their thermal, mechanical, morphological, electrical and electro-active shape memory properties were investigated. The blend nanocomposite including 10 phr CNT indicated the lowest volume resistivity value (3.82 Ω cm). The same nanocomposite also showed elecro-active shape memory property generating Joule heat under 40 V voltage with the shortest recovery time (56 s). The nanocomposite also exhibited sensor behaviour when it was subjected to finger bending deformation.

Molecular weight influence on shape memory effect of shape memory polymer blend (poly(caprolactone)/styrene‐butadiene‐styrene)

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

Shape memory effect of three-dimensional printed products based on polypropylene/nylon 6 alloy

Based on the rapid development of three-dimensional (3D) printing, the fabrication of the 3D printed products which can change their shapes over time has been termed as four-dimensional (4D) printing. Since the functionality is generally limited by available materials, especially for fused deposition modeling (FDM, a trendy technology of 3D printing), it has aroused widespread requirements to develop a novel filament with excellent properties and functionalities. In this study, polypropylene/nylon 6 (PP/PA6) alloy was fabricated as a candidate for FDM and maleic anhydride-grafted poly(ethylene–octene) (POE-g-MAH) was used as a modifying agent as well as a compatibilizer. The results showed that the PP/PA6 alloy with 30 wt% of PA6 on the basis of the certain mass ratio of PP and POE-g-MAH (1.5:1) exhibited a high dimensional stability and appropriate mechanical properties in FDM. In addition, the possibility of PP/PA6 alloy as a shape memory polymer blend and the mechanism of shape memory effect (SME) were investigated. The 3D printed product with 30 wt% of PA6 fabricated by the infill orientation of 45°/− 45° and 100% infill density exhibited a great SME with the deformation temperature (Td) of 175 °C. This simple method for preparation of a novel filament with shape memory performance based on PP/PA6 alloy has a vast potential for the development of 4D printing technology.

Shape Memory Properties of Melt-Blended Olefin Block Copolymer (OBC)/Ethylene-Vinyl Acetate Blends

The completely crosslinked shape memory polymer blends (SMPs) traditionally suffer from recycling problems due to their network structure. In this paper we describe the thermal, mechanical, and shape memory behavior of physical blends of OBC (Olefin block copolymer) and EVA (Ethylene-vinyl acetate copolymer), with and without modification of one or both of the components, prepared using a melt-blending method. These behaviors of the modified blends, based on maleated OBC (OBC-g-MA) and/or vinyltriethoxysilane (VTEOS) modified EVA, included OBC/EVA-g-VTEOS, OBC-g-MA/EVA, and OBC-g-MA/EVA-g-VTEOS blends; they were investigated to compare with the OBC/EVA blend. The SEM (scanning electron microscopy) observations showed that the compatibility of the silane and maleic anhydride modified OBC/EVA blends were better than that of the unmodified OBC/EVA blend. The crystallization temperatures of OBC and EVA in the modified blends were higher than those in the neat blend. The OBC-g-MA/EVA-g-VTEOS blend had the highest modulus and thermal stability of all investigated blend systems due to the numerous interactions between maleic anhydride and silane. The shape memory performance, as defined by the shape fixity ratio (Rf) and shape recovery ratio (Rr), was higher for the modified blends of one or both of the modified components than that for the OBC/EVA blend. These modified blends were readily reprocessible, like thermoplastic vulcanizates, and still retained shape memory behavior, in contrast with the fully crosslinked shape memory polymer blends; thus they were also improved in terms of the environmental aspects of processing.

Exploring heat induced shape memory behaviour of alpha olefinic blends having dual network structure

Temperature dependent shape memory polymer blends of alpha olefins (EOC 8440:EOC 8200) at a fixed blend ratio (50:50) have been developed. Alpha olefins with dual architecture get crosslinked to a different extent upon exposure of electron beam (EB) irradiation. The extent of crosslinking in EOC 8200 copolymer was much more than the EOC 8440 copolymer. In case of EOC 8440 copolymer, tendency of the breakage of the crystalline region is higher than the EOC 8200 copolymer and this is supported by the differential scanning calorimetry (DSC) study. Following the DSC melting endotherm, shape memory study was carried out at 70 °C, which shows that the shape fixity value is reduced and shape recovery value is improved with the application of the increasing radiation dose. Improvement of creep behaviour indicates higher creep recovery of the radiation crosslinked blends which also supports the superior shape memory behaviour of the crosslinked blends.

Temperature scanning stress relaxation measurements: A unique perspective for evaluation of the thermomechanical behavior of shape memory polymer blends

ABSTRACTShape memory polymer has the inherent capability of fixing its shape to a deformed or unconstrained shape that gives the material shape fixity and to revert back to its permanent shape that results shape recovery of the material. Temperature scanning stress relaxation (TSSR) studies of uncrosslinked and radiation crosslinked polymer blends of ethylene octene copolymer and ethylene propylene diene rubber has been carried out over a certain temperature range that gives the idea about the thermomechanical behavior of the material. With increasing radiation dose, TSSR index value of the radiation crosslinked blends increases, which is an indication of the improvement of the elasticity of the crosslinked network and thus results better shape recovery of the crosslinked blends when compared to the uncrosslinked one. Higher elasticity of the crosslinked network is also well supported by higher crosslink density and lower tension set value of the radiation crosslinked blends. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45680.

Unique shape memory behavior of polyolefinic blends with special reference to creep behavior, stress relaxation, and melt rheological study

Creep response, stress relaxation behavior, and melt rheological study of the shape memory polymer blend based on EOC‐EPDM has been studied in details. In this study, especially the effect of the crosslinks formation in presence of electron beam on the creep response, melt rheological study and stress relaxation behavior has been reported. With increase of electron beam dose, creep response becomes lower and the creep compliance value also comes down. Higher resistance creep response of the radiation crosslinked blends indicates the superior shape recovery behavior of the blends. Stress relaxation behavior of the crosslinked blend also shows the lower decay of stress value with time for higher radiation crosslinked blend. The lower relaxation ratio of the highly radiation crosslinked blend also supports the superior shape recovery behavior of the crosslinked blend. Apart from, melt rheological study shows the higher storage modulus value and higher complex viscosity of the radiation crosslinked blend which also supports the formation of higher crosslinked network structure. Tension set value also clearly indicates the better shape recovery behavior of the crosslinked blend. POLYM. ENG. SCI., 58:876–885, 2018. © 2017 Society of Plastics Engineers

Shape memory properties of olefin block copolymer (OBC)/poly(ɛ‐caprolactone) (PCL) blends

ABSTRACTConventionally, the chemically crosslinked shape memory polymer (SMP) blends are hard to recycle due to their network structure. Herein, the environmental SMP blends of olefin block copolymer (OBC), a unique thermoplastic elastomer, and poly(ɛ‐caprolactone) (PCL) were physically crosslinked. Dicumyl peroxide was used as the compatibilizer to improve their miscibility, as evidenced by the reduced dispersed domain size of PCL in the OBC matrix and the increased complex viscosity. The peroxide modified OBC/PCL blend conferred enhanced tensile properties, increased dynamic storage modulus, increased crystallization temperature, and higher recovery stress. The shape memory behaviors of OBC/PCL blends predeformed under two different predeformation temperatures (30 and 65 °C) were investigated. The recovery stress showed respective maximum peak values corresponding to their predeformation temperatures. In addition, the modified blends gave the better shape memory performance at 65 °C. Besides the peroxide modification approach, a precycle training process via prestretching the samples and reducing the mechanical hysteresis was implemented to improve shape memory performance further. This is the first work on the OBC‐based SMP blends to enhance shape memory performance by combining the chemical modification using added peroxide compatibilizer and the process modification using a precycle training process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45475.