Thermoplastic Elastomer Nanocomposites Research Articles

High temperature co-polyester thermoplastic elastomer nanocomposites for flexible self-regulating heating devices

Pyroresistive polymer composites are smart materials with great promise in numerous fields of electronic devices, including temperature and strain sensors, self-regulating heating, and over-current/over-temperature protective devices. However, the operational window of these materials is limited by the phase transition temperatures of the polymer matrix and the brittleness of the composites. Herein, a conductive polymer composite based on a co-polyester thermoplastic elastomer reinforced with graphene nanoplatelets (GNPs) was developed, which exhibits a positive temperature coefficient (PTC) switching temperature of 200 °C. This system shows a more gradual increase in resistivity with temperature and a less pronounced drop in resistivity past the critical transition temperature than other PTC composites. Moreover, Joule heating experiments revealed the ability to regulate at a predefined maximum temperature (within 150 – 200 °C), tuneable through parameters such as filler concentration, applied voltage and thermal boundary conditions, as also demonstrated by multiphysics simulations. Due to the more gradual PTC curve, this composite can produce steady state heating far below the PTC peak, unlike almost all other PTC materials: a unique advantage for self-regulating heating devices as the polymer is not in a melt state, reducing polymer degradation, filler mobility and increasing safety margin before onset of NTC behaviour.

Dynamically vulcanized CNC‐reinforced thermoplastic elastomer based on PP/EPDM: Morphology and mechanical properties control via interfacial compatibilization

AbstractIn this study, dynamically vulcanized thermoplastic elastomer nanocomposites consisting of polypropylene (PP) as the thermoplastic matrix, ethylene propylene diene monomer (EPDM) rubber as the dispersed phase, and needle‐like cellulose nanocrystals (CNC) were investigated. The two polymers were melt blended in a ratio of 70/30 (PP/EPDM) and 60/40% w/w (PP/EPDM) together with CNC (2, 3, and 5 phr) and sulfur‐curing system. The potential of EPDM‐g‐MA and PP‐g‐MA's as interfacial compatibilizers for enhancing interfacial interactions between components and partitioning of CNC between the two polymer phases was examined by measuring the decrease in the size of EPDM particles. The resulting thermoplastic vulcanizates (TPV) were characterized using a melt rheometric mechanical spectrometer (RMS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and tensile tests. The inclusion of any type of interfacial compatibilizers led to enhanced tensile properties when compared to the samples lacking compatibilizers in both TPVs and TPEs in different ratios. EPDM‐g‐MA was found to be more effective for 60/40% w/w (PP/EPDM) TPVs, while PP‐g‐MA showed higher potential for 70/30% w/w TPVs. The CNC‐reinforced TPVs displayed higher melt elasticity than their unloaded counterparts. These nanocomposites also showed reduced EPDM particle size, enhanced Young modulus, and a higher degree of crystallinity.Highlights Nanocomposite thermoplastic vulcanizates (TPVs): polypropylene (PP)/ethylene propylene diene monomer (EPDM)/cellulose nanocrystals (CNC) with matrix‐dispersed morphology. Interfacial enhancement: Compared EPDM grafted maleic anhydride (EPDM‐g‐MA) and PP‐g‐MA potentials. Tensile properties: EPDM‐g‐MA is more effective in higher rubber content TPVs. Mechanical enhancements: Improved properties and Young's modulus in CNC‐filled TPVs. Diverse applications: PP/EPDM/CNC nanocomposites in auto, electrical, electronic, and packaging industries.

Automated fabrication of a scalable heart-on-a-chip device by 3D printing of thermoplastic elastomer nanocomposite and hot embossing

The successful translation of organ-on-a-chip devices requires the development of an automated workflow for device fabrication, which is challenged by the need for precise deposition of multiple classes of materials in micro-meter scaled configurations. Many current heart-on-a-chip devices are produced manually, requiring the expertise and dexterity of skilled operators. Here, we devised an automated and scalable fabrication method to engineer a Biowire II multiwell platform to generate human iPSC-derived cardiac tissues. This high-throughput heart-on-a-chip platform incorporated fluorescent nanocomposite microwires as force sensors, produced from quantum dots and thermoplastic elastomer, and 3D printed on top of a polystyrene tissue culture base patterned by hot embossing. An array of built-in carbon electrodes was embedded in a single step into the base, flanking the microwells on both sides. The facile and rapid 3D printing approach efficiently and seamlessly scaled up the Biowire II system from an 8-well chip to a 24-well and a 96-well format, resulting in an increase of platform fabrication efficiency by 17,5000–69,000% per well. The device's compatibility with long-term electrical stimulation in each well facilitated the targeted generation of mature human iPSC-derived cardiac tissues, evident through a positive force-frequency relationship, post-rest potentiation, and well-aligned sarcomeric apparatus. This system's ease of use and its capacity to gauge drug responses in matured cardiac tissue make it a powerful and reliable platform for rapid preclinical drug screening and development.

Enhanced tensile and barrier properties of modified LLDPE with rubbery materials and graphene nanoplatelets for packaging application

AbstractLinear low‐density polyethylene (LLDPE) is widely used in industries. It possesses remarkable characteristics such as low density, easy to process, and recyclable. However, LLDPE‐based products are known to be highly permeable to water and oxygen, thus limiting their application as packaging material. In this study, natural rubber (NR) and graphene nanoplatelets (GNP) were mixed with LLDPE to produce thermoplastic elastomer nanocomposites films as a novel, potential packaging material with the aid of liquid natural rubber (LNR) as compatibilizing agent. The formulation modification of GNP, NR, and LNR components influenced the mechanical and barrier properties of the resulting nanocomposites. The mixing methods, i.e., direct melt‐mixing and masterbatch mixing (MB) were also investigated. Apparently, tensile test for samples prepared from MB mixing method yielded better results compared to samples from direct melt‐mixing. Permeability tests of water vapor (WVP) and oxygen (OTR) demonstrated that LLDPE/GNP/NR/LNR nanocomposites films managed to reduce the permeability rate of WVP and OTR of pure LLDPE by 92.73% and 98.60%, respectively. The tortuous theory had been confirmed that the experimental data best fit the Nielsen model at aspect ratio of 20, 30 and 10, 20, 40, 200 for WVP and OTR, respectively.

Jamming carbonaceous nanofiller in the continuous phase and at the blend interface for phenomenal improvement in the overall physico-mechanical properties of compatibilized thermoplastic elastomer

Reduced graphene oxide (RGO) nanosheets have been selectively jammed in the continuous polypropylene (PP) phase and at the blend interface of random terpolymer of ethylene, acrylic ester and maleic anhydride (EAMAT) compatibilized PP and epichlorohydrin rubber (ECH) based thermoplastic elastomer (TPE). The presumptions from the contact angle studies regarding the preferential localization of RGO in the continuous PP phase and at the blend interface of compatibilized PP/ECH/EAMAT/RGO TPE nanocomposite have been analyzed via field emission scanning electron microscopy and atomic force microscopy. The presence of RGO in the continuous PP phase and at the blend interface results in a phenomenal improvement in the mechanical, rheological and viscoelastic properties of the compatibilized PP/ECH/EAMAT/RGO TPE nanocomposites. X-ray diffraction studies of the strained compatibilized PP/ECH/EAMAT/RGO TPE nanocomposite testify that, during straining, the RGO nanosheets help the PP chains to orient and consequently there is a prominent improvement in the overall physico-mechanical properties.

Loop and Bridge Conformations of ABA Triblock Comb Copolymers: A Conformational Assessment for Molecular Composites

We computationally investigate the conformational behavior, “bridging” chain, between different the phase-separated domains vs “looping” chain on the same domain, for two chain architectures of ABA triblock copolymers, one with a linear architecture (L-TBC) and the other with comb architecture (C-TBC) at various segregation regimes using dissipative particle dynamics (DPD) simulations. The power-law relation between the bridge fraction () and the interaction parameter () for C-TBC is found to be in the vicinity of the order-disorder transition (), indicating a drastic conversion from the bridge to the loop conformation. When further increases, the bridge-loop conversions slow down to have the power law, , approaching the theoretical power law predicted in the strong segregation limit. The conformational assessment conducted in the present study can provide a strategy of designing optimal material and processing conditions for triblock copolymer either with linear or comb architecture to be used for thermoplastic elastomer or molecular nanocomposites.

Wholly Biobased Polyamide Thermoplastic Elastomer‐Cellulose Nanocomposites

AbstractPolymers play a prominent role in daily lives; however, there is a growing concern on the depleting fossil resources triggering the research for sustainable alternatives. Here, novel wholly biobased nanocomposites are prepared from polyamide 36,36 (PA36,36) thermoplastic elastomer and cellulose nanocrystals (CNCs). Further, the influence of CNC addition and CNC loading on the morphological features, thermal and mechanical properties of PA36,36 is studied. The presence of CNC in PA36,36 affects the thermal degradation of PA36,36. The additions of 10 and 30 wt% CNCs to the PA36,36 improve the tensile strength and Young's modulus by up to 700% and 750% to 9.6 and 6.8 MPa, respectively, while still maintaining relatively high elongation at break values. The hardness of the polymer increases significantly after the inclusion of CNC. The PA36,36/CNC nanocomposites also show relatively good resilience when exposed to 100% strain. Overall, these biobased thermoplastic elastomer nanocomposites can be potential alternatives for some existing rubbers with low or medium hardness.

A journey of thermoplastic elastomer nanocomposites for electromagnetic shielding applications: from bench to transitional research

Thermoplastics elastomers, its processing and properties, electrical conductivity and application as EMI shielding materials.

Mechanism and kinetic regularities of crystallization of nanocomposites based on bentonite and polymer mixtures of random polypropylene with butadiene nitrile rubber

The paper presents the results of a study of the dilatometric properties of thermoplastic elastomer nanocomposites based on mixtures of random polypropylene, nitrile butadiene rubber, a compatibilizer - copolymer of polypropylene with maleic anhydride. Nanosized bentonite particles were used as a filler. The concentration of bentonite nanoparticles was varied in the range of 1.0-20 wt %. The values of the free and occupied specific volumes of nanocomposites were determined depending on the temperature and concentration of bentonite. The mechanism and kinetic regularities of the crystallization process of nanocomposites are established.

Synergistic Effects of Thermal and Near-Infrared Radiation Heating on the Self-Healing Effect of Shape Memory Polyethylene Elastomer Nanocomposites

The preparation of commodity polymers that can undergo self-healing of scratched surfaces is still quite challenging without involving complicated synthetic processes and high cost of healing agents. In the research described here, we prepared a self-healing acrylic acid-functionalized metallocene polyethylene elastomer (mPE-g-AA) nanocomposite with the addition of arginine to form supramolecular hydrogen bonding. Thermal characterization, mechanical properties, shape memory effect, and self-healing properties were investigated. The addition of mutilwall carbon nanotubes (MWCNTs) effectively increased the tensile properties of the modified mPE. The acrylic acid-modified mPE greatly improved its shape recovery ratio, up to 94.2 ± 4.7%, and maintained a high shape fixing ratio (91.6 ± 1.3%) due to the hydrogen bonding acting as physical crosslinks. Overall, all modified mPE samples showed good shape memory performance. Besides the conventional thermal heating to heal the scratched surface cracks, MWCNTs were incorporated to permit healing the surface cracks through near-infrared radiation (NIR). However, the MWCNTs-filled samples under the thermal healing process unexpectedly resulted in the crack widths increasing, perhaps due to the effect of the MWCNTs with high recovery stress pushing outward on both sides of the crack during heating. Interestingly, the synergistic approach of combining thermal healing and NIR was found to be the most effective in improving the healing efficiency of the mPE-g-AA-Arg/MWCNTs, close to 50% within a short time, in comparison with the existing literature with required healing times of 60 min to have a self-healing efficiency of 45% for mPE modified with maleic anhydride and 3-amino-1,2,4-triazole. To the best of the authors’ knowledge, no work has been reported on the preparation of self-healing thermoplastic elastomer nanocomposites through this approach so far.

Gamma irradiation influence on mechanical, thermal and conductivity properties of hybrid carbon nanotubes/montmorillonite nanocomposites

A thermoplastic elastomer (TPE) based nanocomposite with the same weight ratio of hybrid nanofillers composed of carbon nanotubes (CNTs) and montmorillonite nanoclay (DK4) was prepared using a melt blending technique with an internal mixer. The TPE composite was blended from polylactic acid (PLA), liquid natural rubber (LNR) as a compatibilizer and natural rubber (NR) in a volume ratio of 70:10:20, respectively. The weight ratio of CNTs and DK4 was 2.5 wt%. The prepared samples were exposed to gamma radiation at range of 0–250 kGy. After exposure to gamma radiation, the mechanical, thermo-mechanical, thermal and electrical conductivity properties of the composites were significantly higher than unirradiated TPE composites as the irradiation doses increased up to 150 kGy. Transmission electron microscopy (TEM) micrographs revealed the good distribution and interaction between the nano-fillers and the matrix in the prepared TPE hybrid nanocomposites. In summary, the findings from this work definite that gamma irradiation might be a viable treatment to improve the properties of TPE nanocomposite for electronic packaging applications.

Exfoliated graphene/thermoplastic elastomer nanocomposites with improved wear properties for 3D printing

Although three-dimensional (3D) thermoplastic elastomer printing has been studied, the unsatisfactory mechanical properties of 3D-printed elastomers, especially their substandard wear characteristics, make it difficult to use them in industrial products or processes. In this study, thermoplastic elastomer nanocomposites with improved wear properties were fabricated using thermoplastic polyether elastomer (TPEE), with surface-modified carbon black (CB), or electrochemically exfoliated graphene through multiple extrusion processes. The surface-modified CB/TPEE composite showed about four times more wear resistance and 26% improvement in tensile strength as compared to bare TPEE resin. The graphene/TPEE composite with only 1 wt% graphene exhibited an elevenfold increase in wear resistance and 43% improvement in the tensile strength owing to the high dispersibility and lubricating effect of the two-dimensional graphene filler. Graphene/TPEE composites were extruded into filaments for 3D printing. Three-dimensional printed products made from the nanocomposites have much higher wear resistance than 3D products of bare TPEE resin, demonstrating that graphene and TPEE nanocomposites are well suited for manufacturing a wide variety of complex electronic and mechanical components with excellent wear characteristics.

Dynamically vulcanized thermoplastic elastomer nanocomposites based on linear low-density polyethylene/styrene-butadiene rubber/nanoclay/bitumen: morphology and rheological behavior

Dynamically crosslinked thermoplastic elastomer nanocomposites were synthesized as modifier for the bitumen binder-based asphalts. Linear low-density polyethylene (LLDPE) and styrene-butadiene rubber (SBR), with the ratio of 80/20, bitumen, and organically modified clay (OC) were all melt mixed in the presence of the sulfur curing system. The proposed mixing was carried out in an internal mixer at 160 °C with a rotor speed of 120 rpm. To enhance the molecular interactions between the polymer phases and the clay silicate layers, maleic anhydride-grafted LLDPE (PE-g-MA) with the maleiation degree of 50% was also incorporated into the mixture. Observation of the composite samples, using the scanning electron microscopy (SEM), revealed the matrix dispersed type of morphology for all dynamically vulcanized samples. X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the exfoliation of the clay silicate layers with good dispersion. Rheomechanical spectrometry (RMS) was performed on the prepared nanocomposites. All dynamically vulcanized nanocomposites comprising 2.5% of OC exhibited shear-thinning behavior and non-terminal characteristics with a low frequency range. These indicate the formation of three-dimensional physical networks by the clay nanolayers throughout the LLDPE matrix. The presence of the bitumen in the composition of the prepared nanocomposites improved the flowability of the samples. This is a promising feature of the prepared nanocomposites to be used as an elastic and resistant modifier in the composition of the bitumen-based asphalts.

Thermo-mechanical behavior of elastomers with dynamic covalent bonds

Natural and synthetic rubbers (networks of polymer chains connected by irreversible chemical cross-links) cannot be repaired after damage, while discarded rubbers cannot be economically recycled and reprocessed. To avoid this shortcoming, a number of elastomers with dynamic covalent bonds have recently been synthesized that demonstrate recyclability, malleability and capability of autonomous self-healing due to thermally triggered bond-exchange reactions.A constitutive model is developed for the thermo-viscoelastic and thermo-viscoplastic responses of elastomers whose chains are bridged by adaptive bonds with the associative mechanism of rearrangement. Material parameters in the governing equations are determined by fitting observations in tensile tests, cyclic tests, relaxation tests and creep tests in a wide range of temperatures on covalently cross-linked rubber, thermoplastic elastomer, several elastomers and elastomer nanocomposites with dynamic covalent bonds, and epoxy vitrimers. Characteristic features are discussed of the thermo-mechanical behavior of elastomers with dynamic bonds and structure–property relations are established for these materials.

Thermal decomposition kinetics of dynamically vulcanized polyamide 6–acrylonitrile butadiene rubber–halloysite nanotube nanocomposites

ABSTRACTThermally stable thermoplastic elastomer nanocomposites based on polyamide 6 (PA6), acrylonitrile butadiene rubber (NBR), and halloysite nanotubes (HNTs) were dynamically vulcanized, and their nonisothermal decomposition kinetics were examined. The Friedman, Kissinger–Akahira–Sunose (KAS), Ozawa–Wall–Flynn (FWO), and modified Coats–Redfern (m‐CR) isoconversional models were used to obtain information about the kinetics of the thermal decomposition of PA6–NBR–HNTs in terms of the activation energy per partial mass loss monitored through thermogravimetric analyses performed at different heating rates. An erratic trend was due to the Friedman model, especially for systems having higher HNT loadings, whereas the KAS, FWO, and m‐CR models revealed very similar meaningful thermal decomposition kinetics. A relatively high activation energy corroborating a reliable thermal stability was obtained by the addition of HNTs to PA6–NBR, and the resistance against decomposition was higher for systems containing more HNT. This signified the role of the HNTs as thermal stability modifiers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47483.

Essential work of fracture and failure mechanisms in dynamically vulcanized thermoplastic elastomer nanocomposites based on PA6/NBR/XNBR-grafted HNTs

A detailed fracture toughness analysis of dynamically vulcanized thermoplastic elastomer nanocomposites based on polyamide-6 (PA6) and nitrile butadiene rubber (NBR) reinforced by various concentrations of carboxylated nitrile butadiene rubber (XNBR)-grafted halloysite nanotubes (HNTs) was monitored through using essential work of fracture (EWF) procedure assisted by microstructure observations. The effect of various rubber phase and nanotube loadings on the morphology and fracture toughness of prepared multiphase polymer systems were investigated. The results of EWF analysis suggested that the dominant fracture mechanism in dynamically vulcanized PA6/NBR thermoplastic elastomers containing various rubber phase loadings was the dilatation shear bands resulted from repeated rubber particle debonding which enhances the shear yielding of PA6 matrix. Whereas, the incorporation of XNBR-grafted HNTs into the dynamically vulcanized PA6/NBR thermoplastic elastomers reduced the essential work of fracture followed by enhancement of non-essential work of fracture. However, the aggregation of nanotubes causes to form active sites for crack initiation. The results suggested that the XNBR-grafted HNTs can act as inhibitor sites for crack propagation when individually dispersed in the PA6/NBR multiphase systems.

Micromechanics of reinforcement of a graphene-based thermoplastic elastomer nanocomposite

In this work, a series of graphene-reinforced thermoplastic elastomers were prepared, with the introduction of graphene nanoplatelets (GNPs) of different particle diameter. Their microstructures were characterised by scanning electron microscopy (SEM) and quantified by polarised Raman spectroscopy. Τhe GNPs were well-dispersed and their orientation across the cross-section of the injection moulded samples was consistent with the shear rate profile of fountain flow mechanism. The mechanical properties of the nanocomposites were evaluated by tensile testing and it was found that the GNPs contributed to significant improvements in both the stiffness and strength. A micromechanical model based on the combination of shear-lag theory and the rule-of-mixtures was introduced to analyse the stiffening mechanisms. Τhe effective aspect ratio of GNPs was in the order of 100 and decreased with increasing filler loading due to agglomeration. Finally, the stress transfer efficiency from the matrix to GNPs was evaluated by observing the Raman band shifts under tension.

Crystallization kinetics study of dynamically vulcanized PA6/NBR/HNTs nanocomposites by nonisothermal differential scanning calorimetry

ABSTRACTInvestigation of crystallization behavior and kinetics of thermoplastic elastomer nanocomposites was the subject of limited works because of complexities associated with semiexperimental modeling of such phenomenon in a system containing components having completely different behavior in the molten state. Nonisothermal crystallization kinetics of dynamically vulcanized PA6/NBR/HNTs thermoplastic elastomer nanocomposites was mathematically modeled applying well‐known Avrami, Ozawa, and Mo theoretical models to the differential scanning calorimetry data gathered at various cooling rates. It was found that HNTs contribute as nucleating agents to the crystallization kinetics and cause acceleration of crystallization. Activation energy of the crystallization was calculated by correlating the crystallization peak temperature with the cooling rate using Kissinger model. It was found that Mo equation could properly describe nonisothermal crystallization kinetics of the PA6/NBR/HNTs thermoplastic elastomer nanocomposites. This was recognized from the obtained parameters of Mo equation in terms of HNTs loading level, which suggested a higher rate for dynamic crystallization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46488.

Tuning the mechanical and dielectric properties of clay‐containing thermoplastic elastomer nanocomposites

In this study, the mechanical strength and the AC short term breakdown strength of polystyrene‐b‐poly(ethylene‐co‐butylene)‐b‐polystyrene (SEBS) thermoplastic elastomer clay‐containing nanocomposites have been investigated as function of their morphologies. The SEBS/clay nanocomposites with tailored morphologies were prepared previously by different processing techniques. They featured different orientations of clay platelets as well as polystyrene (PS) block nanodomains, namely: isotropic, oriented, and partially oriented morphologies. In unfilled SEBS matrices, the mechanical strength was mainly tuned by the orientation of PS block nanodomains. A good correlation between the dielectric breakdown strength and the mechanical stiffness was observed overall: the higher the mechanical strength was, the higher the breakdown strength was. In the nanocomposites, the orientation of clay platelets as well as the degree of order and the characteristic sizes of the block copolymer domains were seen to affect strongly the breakdown strength behavior in addition to the mechanical strength. In particular, the partially oriented morphology achieved by film blowing extrusion exhibited the maximum increase of the breakdown strength by 25% with optimized mechanical stiffness evaluated between that of the oriented morphology as a lower limit and that of the isotropic morphology as an upper limit. POLYM. ENG. SCI., 58:E174–E181, 2018. © 2018 Society of Plastics Engineers

A review of thermoplastic elastomeric nanocomposites for high voltage insulation applications

Thermoplastic elastomer (TPE) has gained acceptance as third generation of polymeric materials for high voltage (HV) insulators. The interesting features showed by TPEs were found to fulfill some particular requirements for HV insulations, at least for the distribution class applications, especially at light contamination environments. Introduction of nanomaterials which widely reported to give significant improvements in the electrical, mechanical, thermal and other properties of polymer has attracted attention to the synergistic properties of combining the two complementary technologies of thermoplastic elastomers and nanocomposites. In this paper, research works on various types of TPEs having promising performance as HV insulators are thoroughly reviewed. The emergence of nanocomposites in the electrical insulation field and the important properties consideration for HV insulators as well as the processing techniques of TPE nanocomposites are also discussed. Finally, some of the past and recent developments of TPE nanocomposites focusing on the electrical insulation properties are highlighted in this article. POLYM. ENG. SCI., 58:E36–E63, 2018. © 2018 Society of Plastics Engineers