Dynamic Mechanical Analysis Results Research Articles

Facile synthesis of a reactive P/N/S-containing compound toward highly effective flame retardancy of epoxy resin with high transparency and improved mechanical strength

It is still a great challenge to develop flame-retardant epoxy resins (EP) with high transparency. Herein, a reactive P/N/S-containing compound (DOPT) was designed and synthesized by the Atherton-Todd reaction between p-toluenesulfonamide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. The addition of DOPT simultaneously improved the flame retardancy, fire safety and mechanical strength meanwhile kept the better transparency of the EP At 5 wt% DOPT loading, the modified EP (FREP-5) achieved a LOI value of 37.5% and UL-94 V-0 rating, with maintaining almost the same transmittance of the pure EP. Meanwhile, the FREP-5 also gave the lowest values of the peak heat release rate, total heat release, total smoke production and fire growth rate, revealing the enhanced fire safety of the flame-retardant EP. The significant improvement of flame retardancy of FREP thermosets was ascribed to the physical barrier effect of phosphorus-rich char in condensed phase, and the quenching and diluting effects of abundant phosphorus-containing free radicals and nitrogen/sulfur-containing inert gases in gaseous phase. Furthermore, the results of dynamical mechanical analysis and mechanical performance test revealed that the incorporation of DOPT improved the tensile and flexural strength of epoxy thermoset. In summary, DOPT is a novel highly efficient flame retardant for EP, which enables EP to maintain its potential application in the optical fields.

Skin-core structure of thermally aged epoxy resin: Roles of oxidation and re-crosslinking

The skin-core structure of thermally aged epoxy resin consisting of the aged surface-layer and the unaged inner-layer, was studied in this paper. A new tanδ peak appeared in the results of dynamic mechanical analysis (DMA) after the specimens were thermally aged. It steadily diminished when the surface of the specimens was gradually removed, which indicates that the newly detected peak arose from formation of surface-layer during ageing. Thickness of the surface-layer could reach up to 0.09 mm after thermal ageing for 480 h. According to Fourier transform infrared spectroscopy (FTIR) results, formation of the surface-layer was found to closely correlated with thermal oxidation and re-crosslinking processes. The former induced oxidized molecular chains while the later might be related to the production of carboxylic acid dimers and etherification reactions to result in strengthened networks. This was further ascertained by the results of dielectric spectroscopy and isothermal surface potential decay (ISPD) tests. The relaxation process of aged epoxy resin displayed higher relaxation time, strength, and activation energy than unaged specimens, and evident growths of both deep and shallow level traps densities were also observed after thermal ageing. This casts new light on the thermal ageing mechanism of epoxy resin and could provide a feasible method for its insulation degradation assessment.

Design of an Impact Absorbing Composite Panel from Denim Wastes and Acrylated Epoxidized Soybean Oil based Epoxy Resins

The focus of this work is to make a significant contribution to solid waste management by designing impact-absorbing bio-composite panels using bio-resin and denim wastes. In this context, composite panels are produced by vacuum infusion technique using both epoxy and acrylated epoxidized soybean oil (AESO) based hybrid resins while denim wastes are utilized as reinforcement materials in fiber and fabric forms. Both physical (fiber density and fiber weight ratio) and mechanical analyses (drop-weight impact resistance and dynamic mechanical analysis (DMA)) of the composites are performed. The outcomes of the study prove that the increase in the AESO ratio of the resin system improves the ductility of the composite and consequently the impact resistance. On the other hand, dynamic mechanical analysis results indicate that the AESO plug-in reduces the storage module and increases the damping factor.

Dynamic mechanical analysis of Silk and Glass (S/G/S)/Pineapple and Glass (P/G/P)/Flax and Glass (F/G/F) reinforced Lannea coromandelica blender hybrid nano composites

Hybrid composites are formed by the combination of natural fibers (pineapple, silk, flax etc.) and synthetic fibers (glass) reinforced polymer or hybrid or natural resin matrix composites which have specific mechanical properties due to contents of renewability, recyclability, and biodegradability compared to synthetic fibers. Lannea coromandelica (LC, Anacardiaceae plant gum) is blended with Epoxy (synthetic polymer matrix resin) to form hybrid Lannea Coromandelica Blender Epoxy matrix (LCE) resin composites for the replacement of epoxy resin to improve the biodegradability and environmental friendly nature. NaOH treated and untreated hybrid Composites (Pineapple (PGP)/Silk (SGS)/Flax (FGF) fiber mats with 2%, 4%, 6% volume fraction of Bentonite nanoclay (BNC) nano filler loading in each composition reinforcement in hybrid LCE resin) and hybrid LCE resin are prepared by Compression hand molding technique method. The maximum mechanical properties are observed for treated P/G/P fiber mats with 2%, 4%, 6% volume fraction BNC filler reinforced LCE resin matrix. Mechanical properties such as tensile properties, flexural properties and impact strength of hybrid composites have improved three to four times compared to hybrid LCE resin. Results of dynamic mechanical analysis (DMA) show that untreated and treated hybrid composites have the highest storage modulus (stiffness and adsorption energy) and the lowest damping factor (Tan δ) when compared to hybrid LCE resin. Biodegradability testing has revealed that adding 4 percent volume fraction of nano filler to treated P/G/P fiber mats reinforced LCE resin composite resulting in minimal weight loss over a long period of time.

Dynamic mechanical analysis performance of pure 3D printed polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS)

Dynamic mechanical analysis (DMA) is a technique that is used to study the viscoelastic behaviour of polymeric materials. 3D printing is one of the well-known applications of additive manufacturing techniques which has wide areas of application. In that, Fusion Deposition modelling (FDM) has very fine outcomes with better printing qualities to execute good products. In this research work, the 3D printed samples of pure ABS and PLA were examined under dynamic mechanical analysis to study the various temperature heat, absorbing, storing, and dissipating behaviour of these samples. The results show, both ABS and PLA performed well under the heat flow categories. While comparing to conventional manufacturing technologies, these 3D printed DMA results are showing some excellent results. These polymeric samples may prepare as composites and used for various applications, for better outcomes and capabilities. Storage modulus, while taking the temperature values of ABS to 90 °C maximum and for PLA about 48 °C. This will happen, but this pure form of materials printed through FDM also has such a very good energy storing capacity. Considering the loss modulus energy dissipation in the form of heat started from 110 °C, this is one of the good signs on the fabricated technique and build quality of ABS. The continues decrease in the degree of crystallinity of the PLA and ABS increases the meshing strength noted in the damping factor.

Dynamic Mechanical Analysis during polyurethane foaming: Relationship between modulus build-up and reaction kinetics

The modulus build-up and relative density evolution during the reactive foaming of four standard polyurethane formulations was monitored in-situ by Dynamic Mechanical Analysis (DMA) with a customised set-up in parallel plate geometry. The modulus increased from 0.01 MPa in the first minutes to over 1.2 MPa within 20 min. The set-up also enabled the recording of vitrification followed by curing times. These typically occur within 3 min of each other. The results of DMA are corroborated by measurements of the reaction kinetics with Infrared Spectroscopy. This goes to show that the modulus remains nearly unchanged during the stage of swiftest isocyanate conversion, while the point of gel conversion is accompanied by their increase.

Dynamic mechanical response of ZrCu-based bulk metallic glasses

The thermal stability and the dynamic mechanical relaxation behavior of (Zr50Cu40Al10)100-xDyx (at.%) (x = 0 or 2) metallic glasses were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). In the case of the (Zr50Cu40Al10)100-xDyx (x = 0 or 2) metallic glasses, atomic mobility increases by introduction of the Dy element. The activation energy of the the main a relaxation process and fragility index were discussed according to the DMA measurements. With the help of the time-temperature superposition (TTS) principle, the master curves of the model alloys were established, the Kohlrausch-Williams-Watts (KWW) function and quasi-point defects (QPD) theory were used to descirbe the master curves of the metallic glasses. The characteristic parameters related to microstructural heterogeneity in the KWW equation and the QPD model, Kohlrausch exponent βKWW and the correlation factor χ were evaluated. In parallel, the elastic, viscoelastic and viscoplastic responses of the model alloys have been analyzed based on the DMA results. Our investigations demonstrated that introduction of the Dy increases the structure heterogeneity of the (Zr50Cu40Al10)100-xDyx (x = 0 or 2) glassy system, which plays an important role in tailoring the dynamic relaxation behavior and mechanical properties of the metallic glasses.

Copper slag as a potential waste filler for polyethylene-based composites manufacturing

The present study aimed to analyze the application of waste material from copper production– copper slag (ŻŻL) as filler for composites based on the high-density polyethylene (HDPE). Copper slag filler was introduced in the amounts of 1–20 wt%, and its influence on the appearance (color analysis), chemical structure (Fourier-transform infrared (FTIR) spectroscopy), microstructure (optical microscopy), as well as static (tensile tests) and dynamic (dynamical mechanical analysis (DMA)) mechanical properties of composites were investigated. Proper dispersion of filler implicated that the incorporation of up to 5 wt% of filler caused only slight, 5% drop of tensile strength, with the simultaneous 16% rise of Young’s modulus. Further increase of filler loading resulted in higher values of porosity and the rise of the adhesion factor, determined from DMA results, which led to the deterioration of mechanical performance. Moreover, spectroscopic analysis of PE-ŻŻL composites indicated that the analyzed filler might be applied as a coloring agent, and the appearance of composites may be engineered by adjustment of filler loading.
 Keywords: polyethylene, copper slag, mechanical properties, structure, composite, particle reinforced composite

Quantifying inter- and intra-ply shear in the deformation of uncured composite laminates

Understanding the bending mechanics of uncured carbon fiber prepreg is vital for modeling forming processes and the formation of out-of-plane wrinkling defects. This article presents a modification of standard dynamic mechanical analysis (DMA) to characterize the viscoelastic bending mechanics of uncured carbon fiber prepreg using Timoshenko beam theory, along with an updated model describing inter-ply shear in uncured laminates. By post-processing DMA results, the analysis provides temperature and rate-dependent values of inter and intra-ply shear stiffness for a carbon fiber laminate and each individual ply with experimental results for AS4/8552 presented. The new methodology provides a means to parametrize process models, and also gives an indication of optimal manufacturing conditions to enable defect-free forming and consolidation processes.

Effect of different lengths of side groups on the thermal, crystallization and mechanical properties of novel biodegradable poly(ethylene succinate) copolymers

To explore the effect of different lengths of side groups, the thermal, crystallization, and mechanical properties were systematically investigated for three novel poly(ethylene succinate) (PES) based copolyesters containing methyl, butyl, and octyl as side groups, respectively, in this research. Relative to linear PES, the presence of side groups did not modify the crystal structure, while increasing the length of side groups slightly decreased the crystallinity of the copolymers. Despite the length of side groups, they all displayed high thermal decomposition temperatures. Increasing the length of side groups gradually decreased the melting point temperatures of PES copolymers. The glass transition temperature of poly(ethylene succinate-co-1,2-propylene succinate) slightly increased; however, those of poly(ethylene succinate-co-1,2-hexamethylene succinate) and poly(ethylene succinate-co-1,2-decamethylene succinate) gradually decreased with an increase in the length of side groups. PES and its copolymers displayed the same crystallization mechanism; however, the crystallization time increased as the length of side groups increased at the same degree of supercooling. The elongation at break increased while the Young's modulus decreased with increasing the length of side groups. The dynamic mechanical analysis results revealed that the storage modulus and tan δ gradually decreased as the length of side groups increased. In brief, the length of side groups significantly influenced the thermal, crystallization, and mechanical properties of PES based copolymers.

Mechanical Characterization of Core-Shell Rubber/Epoxy Polymers for Automotive Structural Adhesives as a Function of Operating Temperature

Automotive structural adhesives must show a steady toughness performance in the temperature range of −40 °C to 80 °C, considering their actual usage environments. Core-shell rubber (CSR) nanoparticles are known to enhance the toughness of epoxy systems. In this study, a CSR, pre-dispersed, diglycidyl epoxy of bisphenol A (DGEBA) mixture at 35 wt % (KDAD-7101, Kukdo Chemical, Seoul, Korea) was used as a toughener for an automotive structural epoxy adhesive system. A simple, single-component, epoxy system of DGEBA/dicyandiamide with a latent accelerator was adopted, where the CSR content of the system was controlled from 0 to 50 phr by the CSR mixture. To determine the curing conditions, we studied the curing behavior of the system by differential scanning calorimetry (DSC). Modulus variations of the cured bulk epoxies were studied using a dynamic mechanical analyzer (DMA) in the dual cantilever mode. The flexural modulus of the cured epoxies at various temperatures (−40, −10, 20, 50, and 80 °C) showed the same tendency as the DMA results, and as the flexural strength, except at 0 phr. On the other hand, the strain at break exhibited the opposite tendency to the flexural modulus. To study the adhesion behavior, we performed single-lap joint (SLJ) and impact wedge-peel (IWP) tests. As the CSR content increased, the strength of the SLJ and dynamic resistance to the cleavage of the IWP improved. In particular, the SLJ showed excellent strength at low temperatures (32.74 MPa at 50 phr @ −40 °C (i.e., an 190% improvement compared to 17.2 MPa at 0 phr @ −40 °C)), and the IWP showed excellent energy absorption at high temperatures (21.73 J at 50 phr @ 80 °C (i.e., a 976% improvement compared to 2.07 J at 0 phr @ 80 °C)). The results were discussed in relation to the changes in the properties of the bulk epoxy depending on the temperature and CSR content. The morphology of the fracture surface was also provided, which offered useful information for composition studies using the CSR/epoxy system.

Dielectric Performance of Silica-Filled Nanocomposites Based on Miscible (PP/PP-HI) and Immiscible (PP/EOC) Polymer Blends

This study compares different polymer-nanofiller blends concerning their suitability for application as insulating thermoplastic composites for High Voltage Direct Current (HVDC) cable application. Two polymer blends, PP/EOC (polypropylene/ethylene-octene copolymer) and PP/PP-HI (polypropylene/ propylene - ethylene copolymer) and their nanocomposites filled with 2 wt.% of fumed silica modified with 3-aminopropyltriethoxysilane were studied. Morphology, thermal stability, crystallization behavior dynamic relaxation, conductivity, charge trap distribution and space charge behavior were studied respectively. The results showed that the comprehensive performance of the PP/PP-HI composite is better than the one of the PP/EOC composite due to better polymer miscibility and flexibility, as well as lower charging current density and space charge accumulation. Nanosilica addition improves the thermal stability and dielectric properties of both polymer blends. The filler acts as nucleating agent increasing the crystallization temperature, but decreasing the degree of crystallinity. Dynamic mechanical analysis results revealed three polymer relaxation transitions: PP glass transition ( $\beta$ ), weak crystal reorientation ( $\alpha 1$ ) and melting ( $\alpha 2$ ). The nanosilica introduced deep traps in the polymer blends and suppressed space charge accumulation, but slightly increased the conductivity. A hypothesis for the correlation of charge trap distribution and polymer chain transition peaks is developed: In unfilled PP/EOC and PP/PP-HI matrices, charges are mostly located at the crystalline-amorphous interface, whereas in the filled PP/EOC/silica and PP/PP-HI /silica composites, charges are mostly located at the nanosilica-polymer interface. Overall, the PP/PP-HI (55/45) nanocomposite with 2 wt.% modified silica and 0.3 wt.% of antioxidants making it $a$ promising material for PP based HVDC cable insulation application with $a$ reduced space charge accumulation and good mechanical properties.

Enhanced multiphase interfacial interaction of impact polypropylene copolymer by in-situ introducing polyethylene

Impact polypropylene copolymer (IPC) is utilized in various commercial products worldwide due to its excellent physical properties and low production costs. Introducing polyethylene (PE) into IPC is known to improve the impact properties with little rigidity loss, but little is known about the influence of the multiphase interfacial interaction on these properties. In this work, we investigate this matter through fabricating a series of in-reactor alloys with multi-stage polymerization. Morphology observations revealed that introducing PE into IPC in-situ can promote the phase structure without the external force. Dynamic mechanical analysis results revealed that the introduction of well-dispersed PE in-situ could strengthen the interface interaction between PP matrix and EPR dispersed phase, which is conducive to the dissipation of impact energy. Atomic force microscopy-infrared results suggested that the in-situ introduction of PE promotes the enrichment of the ethylene-propylene block copolymers (EbP) to the multiphase interface. This work offered a new insight into the rational design of the next generation IPC with improved properties.

One-pot synthesis of isosorbide-based copolycarbonate with good flexibility and tunable thermal property

In this article, we reported a new strategy to synthesize of isosorbide-based copolycarbonates with good flexibility and tunable thermal property via one-pot direct melt polycondensation of isosorbide (ISB), dimethyl carbonate (DMC) and 1,4-benzenedimethanol (BDM). The effect of different feed ratio on the chemical structure, molecular weight, thermal and mechanical property of copolycarbonates was in-depth studied. A series of metal ion-containing compounds as catalysts were used, and the copolycarbonates was synthesized with weight average molecular weight (Mw) of 80,300 and dispersity index below 1.78 by sodium tert-butoxide catalyst, and the reaction time was shorted to only 3.5 h with the ISB conversion up to 99.0%. Meanwhile, the Tg values realized controllable and tunable from 69 to 164 °C by varying the ratio of two diol monomers, and the influence of the structure of carbonyl carbon in repeating units of copolycarbonates on the thermal properties were demonstrated. Moreover, the results of dynamic mechanical analysis (DMA) implied that the flexibility of copolycarbonates was increased with increasing BDM content, and the results of scratch resistance and melting index of the copolycarbonates provided enormous prospect for the industrial application.

Improved mechanical responses of GFRP composites with epoxy-vinyl ester interpenetrating polymer network

Present investigation deals with development of glass fiber reinforced polymer (GFRP) composite with a matrix composed of a polymer blend of epoxy and vinyl ester. The evolved Interpenetrating polymer network (IPN) formed due to blending of the polymers resulted in improved tensile, flexural and interlaminar shear properties of the hybrid composite than that of both glass fiber/epoxy (GE) and glass fiber/vinyl ester (GVE) composites. Resin burn-off test revealed that the glass fiber volume fraction to be almost identical in all three composite laminates, which was ~45%. The role of curing temperatures (140, 170, 200 and 230 °C) on the cure kinetics of the composites was examined based on the flexural properties of the composites, which is also supported with the dynamic mechanical thermal analysis (DMTA) results. The glass fiber reinforced epoxy-vinyl ester interpenetrating polymer network (GEVIPN) composite led to 21.83%, 22.54% and 13.43% improvement in interlaminar shear strength (ILSS), tensile and flexural strength respectively, over GE composite at optimal post cure temperature. Further, chemical restructuring of GEVIPN composite was analysed by Fourier transform infrared spectroscopy (FTIR). From scanning electron microscopy (SEM), it was comprehended that strong interfacial bonding between the matrix and fiber made GEVIPN composite exhibit better mechanical properties.

Silane-modified low molecular weight ‘liquid’ polymers in sulfur cured mixtures of styrene-butadiene copolymers and silica

Silane coupling agents are used in silica filled rubber compounds to increase the filer-polymer interactions and to lower the filler-filer interactions. In addition, silane functionalized polymers can be used. Special types of polymers are low molecular weight ‘liquid’ polymers. The goal of this paper is to obtain more understanding about the uses and effects of these low molecular weight ‘liquid’ polymers in combination with silanes and other compound components. Three different silane coupling agents and six different low molecular weight ‘liquid’ polymers were selected, evaluated and comparatively introduced in mixtures of a SSBR/silica compound. The Payne effect was measured to evaluate the strain dependence of the mixtures. It was used to evaluate the filler-filler interactions and estimate the micro dispersion. This provides information about the interactions and the building of additional networks that comprises the low molecular weight ‘liquid’ polymer together with the silica, silane and main polymer. Results of dynamic mechanical analysis are discussed. The microstructures and silane-functionalizations show clear dependences on the glass transition temperatures, loss moduli and tan δ values.

Ionic Liquid/Sulfonated Polyimide Composite Membranes: Effect of Polyimide Sequence on CO2 Transport Properties

The carbon dioxide capture and storage (CCS) plays an important role in reducing greenhouse gases, but its high energy cost is a critical issue. The CO2 separation is recognized as a key process for reducing cost, and a membrane separation method is one of the promising candidates with a low energy cost. Ion gels comprising polymer networks and ionic liquids (IL), which exhibit unique properties such as non-volatility and CO2 absorption selectivity, have attracted attention as environmentally friendly separation membranes. Previous work in our group has shown that sulfonated polyimide (SPI) with an imidazolium cation exhibits good compatibility with an IL. SPI can hold high content of IL (~75 wt%) and form a uniform, flexible, tough (~10 MPa of Young’s modulus) and thin composite membrane.[1-3] This SPI was synthesized by random copolymerization of a sulfonated ionic monomer and a non-ionic monomer. The composite membranes separated into bicontinuous two phases of ionic and non-ionic domains, which contribute to the formation of gas diffusion path and mechanically tough network, respectively. By using multiblock copolymers of SPI, it is expected that the size and connectivity of each domain are improved, which could lead to the increase of the CO2 permeability and mechanical toughness of the membrane. In this study, we fabricated an 1-buty-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim][NTf2])/SPI composite membranes composed of multiblock-type SPI (mb-SPI) and compared their property with those of random-type SPI (r-SPI).75 wt%[C4mim][NTf2]/mb-SPI composite membranes exhibited higher CO2 permeability (372 barrer) than the corresponding r-SPI (235 barrer) while the gas selectivity (CO2/N2) is 26, which is of the same magnitude as that of r-SPI (CO2/N2 is 28). The mb-SPI can hold higher IL content up to 80 wt% than r-SPI, resulting in higher CO2 permeability (480 barrer; CO2/N2 is 27). The higher ionic conductivity also suggested the higher connectivity of ionic domains in mb-SPI system. On the other hand, from tensile tests, it was found that the mb-SPI membrane was less ductile than the r-SPI membrane. The result of dynamic mechanical analysis (DMA) indicates that the difference of internal structure between the membranes composed of mb-SPI and r-SPI is one of the reasons of the poor mechanical property.To fabricate more strong membrane, we used SPI with more rigid polymer backbone. Rigid mb-SPI exhibits high CO2 permeability (450 barrer) and gas selectivity (CO2/N2 is 24), comparable with the conventional one, and the mechanical property was superior to the conventional one. From these results, we concluded that the mb-SPI membrane having high CO2 permeability and toughness was successfully fabricated.

Dynamic Mechanical Analysis Investigations of PLA-Based Renewable Materials: How Are They Useful?

Interest in renewable polymers increased exponentially in the last decade and in this context poly(lactic acid) (PLA) became the leader mainly for practical reasons. Nevertheless, it is outstanding also from a scientific point of view, because its thermal and morphological properties are offering challenging new insights. With regard to dynamic mechanical analysis (DMA), PLA does not have the classical behavior of a thermoplastic polymer. Often, overlapping events (enthalpic relaxation, glass transition and crystallization) that occur as the temperature increases make the DMA result of a PLA look inexplicable even for polymer scientists. This review offers a perspective of the main phenomena that can be revealed in a DMA experiment and systematizes the information that can be obtained for every region (glassy, glass transition, rubbery, cold-crystallization and melting). Also, some unusual patterns registered in some cases will be commented upon. The review intends to offer indices that one should pay attention to in the interpretation of a DMA experiment, even if the investigator has only basic skills with DMA investigations.

Design of heat‐triggered shape memory polymers based on ethylene‐acrylic acid copolymer/nitrile‐butadiene rubber thermoplastic vulcanizates

AbstractHeat‐triggered shape memory polymers (HSMPs) consisting of ethylene‐acrylic acid copolymer (EAA) and nitrile‐butadiene rubber (NBR) were fabricated by peroxide‐induced dynamic vulcanization; meanwhile, in order to realize rapid and reconfigurable shape fixity and shape recovery, a facile and effective strategy was designed. Morphological structure and interface interaction are decisive factors for HSMPs, the FE‐SEM images showed the average diameter of NBR particles in EAA/NBR TPVs was 5 to 8 μm and the strong interface interaction between EAA matrix and NBR particles provided critical assistance in keeping the temporary shape of deformed rubber particles and storing stronger elastic driving force. The shape memory behavior of EAA/NBR TPVs was characterized and the result demonstrated that excellent shape‐fixity (>91%), shape‐recovery (>93%), and fast recovery speed (<30 s) could be obtained at suitable deformation temperature of 95°C. The results of dynamic mechanical analysis and shape memory research showed that the high modulus value supported the improvement of shape‐fixity ratio and the appropriate ratios of EAA/NBR TPVs were the key factors for excellent shape memory performance. The novel HSMPs expected to open up potential applications in the field of sensors and self‐assembling smart devices.

Designing a polymer blend nanocomposite with triple shape memory effects

In this work, a polymer blend nanocomposite containing two widespread natural biopolymers (poly (l-lactic acid) and polyvinyl acetate) and nanohydroxyapatite (nHA) was manufactured. Triple-shape memory behavior was observed when 10 wt% of nHA was incorporated to the polymer blends. In contrast, adding lower content of nHA (1 and 5 wt% of nHA) did not bring about this behavior but only led to an increase in glass transition temperature (Tg). The triple-shape memory behavior was attributed to the phase separation in the polymer nanocomposites, which was confirmed by Atomic Force Microscope (AFM) and Dynamic Mechanical Analysis (DMA). The thermal responsive dual- and triple-shape memory behavior was thoroughly examined. According to the DMA results, the addition of nHA improved the thermal stability of nanocomposites, which in turn led to an increase in storage modulus. Subsequently, the results of the shape memory test indicated that the interaction between the matrix and the nanofiller could improve the shape memory properties of the nanocomposites. However, further increasing the nanofiller content (e.g., to 15 wt%) led to formation of aggregation in the polymers and consequently degraded shape recovery ratio. Further research also demonstrated that increasing thermomechanical cycles had a significant effect on shape memory behavior. In other words, there is a synergistic effect of adding nanofiller and increasing thermomechanical cycles on improving the shape memory properties.