Mechanical Properties Of Thermoplastic Elastomers Research Articles

A mathematical model of thermoplastic elastomers for analysing the topology of microstructures and mechanical properties during elongation

In this study, a mathematical model based on graph theory is developed to analyse the deformed structures and mechanical properties of thermoplastic elastomers (TPEs) using ABA-type triblock copolymers. TPEs exhibit a network structure formed by bridge chains; deformation of this network structure causes stress. During the deformation of TPEs, domain breakage and coalescence occur, accompanied by topological changes in the chains, such as conformational transitions between the bridge and loop chains. By employing the mathematical concepts of harmonic realization of graphs in the physical space and the tension tensor to quantify the stress in the bridge-chain network structure, an effective method for analysing topologicalchanges in microstructures caused by elongation is proposed. As an application of this method, optimal geometric structures of block copolymers with desired functionalities can be determined.

Enhancing the dynamic mechanical properties of thermoplastic elastomers: A study on polypropylene /natural rubber blends

The aim of this study was to investigate the modifications of the mechanical properties of polypropylene (PP) by incorporating elastomers, while considering the impact on its stiffness. Specifically, the research focused on determining the optimal loading of elastomer to achieve desirable properties and exploring the influence of these processes on the morphology and mechanical behavior of the prepared blends. Thermoplastic elastomers (TPEs) consisting of polypropylene and natural rubber (PP/NR) were prepared using a melt-mixing process, and the mechanical properties of the blends were evaluated. The stress-strain properties of the blends revealed a successful modification of PP, transforming it from a stiff and strong thermoplastic into a stiff and tough thermoplastic elastomer when 10% NR was included in the PP matrix. As the loading of NR increased, a reduction in tensile strength (TS) and modulus (E) of the blends was observed, while elongation at break (EB) increased. The flexural strength of unmodified PP was 45.9 MPa, which decreased with increasing NR loading. Similarly, the impact strength of unmodified PP was 25.8 KJ/m2, whereas the values for 10%, 20%, 30%, and 40% NR inclusion were 30.8, 24.3, 20.6, and 15.2 KJ/m2, respectively. The melt flow index (MFI) of unmodified PP was 14.1 g/10 min, while the values for 10%, 20%, 30%, and 40% NR inclusion were 19.4, 15.7, 11.6, and 10.2 g/10 min, respectively. The best combination of mechanical properties was observed at 10% NR inclusion in the PP matrix. The micrograph of the blends, as observed from SEM micrographs, supported the modification of PP, resulting in the production of TPE with observable adhesion sites, indicating good compatibility between the components. In a nutshell, a significant 47% increase in impact strength was achieved through the modification process.

Influence of the Method of Graphene Introduction on Physical and Mechanical Properties of Thermoplastic Elastomers

Influence of the Method of Graphene Introduction on Physical and Mechanical Properties of Thermoplastic Elastomers

Influence of the Method of Graphene Introduction on Physical and Mechanical Properties of Thermoplastic Elastomers

A method for reinforcing a compound based on styrene-butadiene thermoplastic elastomer has been developed. The mechanical characteristics of reinforced compounds have been studied. A comparative analysis of various methods for introducing a nanofiller into a polymer matrix has been carried out. The developed technique shows an increase in the compressive strength of the composition by 50%, as well as tensile strength by 20%.

Improved Elastic Recovery from ABC Triblock Terpolymers.

The promise of ABC triblock terpolymers for improving the mechanical properties of thermoplastic elastomers is demonstrated by comparison with symmetric ABA/CBC analogs having similar molecular weights and volume fraction of B and A/C domains. The ABC architecture enhances elasticity (up to 98% recovery over 10 cycles) in part through essentially full chain bridging between discrete hard domains leading to the minimization of mechanically unproductive loops. In addition, the unique phase space of ABC triblocks also enables the fraction of hard-block domains to be higher (fhard ≈ 0.4) while maintaining elasticity, which is traditionally only possible with non-linear architectures or highly asymmetric ABA triblock copolymers. These advantages of ABC triblock terpolymers provide a tunable platform to create materials with practical applications while improving our fundamental understanding of chain conformation and structure-property relationships in block copolymers.

Nanoscale strain–stress mapping for a thermoplastic elastomer revealed using a combination of in situ atomic force microscopy nanomechanics and Delaunay triangulation

AbstractStyrene block copolymer‐type thermoplastic elastomer (TPE) has a nanoscale phase‐separated structure and undergoes topological changes in response to external stimuli. A typical example is the macroscopic stress relaxation in TPEs while maintaining the elongated state. To understand the influence of structural changes on the mechanical properties of TPEs, in this work, we evaluate a styrene‐ethylene‐butylene‐styrene‐type TPE using an in situ atomic force microscopy (AFM)‐based nanomechanical approach while maintaining 50% strain. According to AFM deformation and modulus maps of the same area at different relaxation times, it is found that the hard polystyrene domain splits in the early stage of relaxation, resulting in a constant rise in the number. At the same time, the modulus of the soft poly(ethylene‐butylene) matrix continues to decrease. Both the domain number and matrix modulus stabilize in the late stage of the relaxation. Further finite element analysis explains the above phenomenon. The distribution of stresses and strains under the material microscopically evolves toward homogenization with relaxation time. The internal stress network achieves an elastic behavior after sufficient relaxation at the expense of hard‐domain splitting.

Morphological and Mechanical Properties of Thermoplastic Elastomers Based on Recycled High Density Polyethylene and Recycled Natural Rubber

Abstract In this work, thermoplastic elastomers (TPE) are produced by melt mixing of recycled high-density polyethylene (RHD) with two types of off-the-road (OTR) ground tire rubber (GTR). Non-regenerated (NR) and regenerated (RR) rubbers are used to investigate the effect of GTR concentration and regeneration on the blends properties containing up to 90 wt.% GTR. The blend morphology is studied by scanning electron microscopy (SEM) to show incompatibility and low interfacial adhesion between RHD and GTR (NR and RR) especially above 40 wt.% RR. This behavior is attributed to the GTR regeneration process and agglomeration of RR particles with lower surface area and affinity toward RHD compared with NR. In all the compounds, the mechanical properties in tension of RR blends were lower than for NR blends, which is attributed to the degradation of the GTR backbone chains lowering the molecular weight (MW) during the regeneration process. Also, NR has a more important effect on impact strength improvement due to its higher crosslinked structure making the particles more deformable/elastic to absorb the mechanical energy before crack initiation. The experimental results also show that 80 wt.% GTR is the optimum concentration for the production of low cost and eco-friendly TPE based on recycled materials.

Relationships between molar mass and fracture properties of segmented urethane and amide copolymers modified by chemical degradation

AbstractThis publication highlights the structure–property relationships in several thermoplastic elastomers (TPEs): one poly(ether‐block‐amide) and two thermoplastic polyurethane elastomers with ester and ether soft blocks. Structural changes are induced by chemical degradation from virgin samples through hydrolysis and oxidation. Molar mass measurements show an exclusive chain scission mechanism for all TPEs, regardless of the chemical modification condition. Mechanical behavior was nevertheless obtained from uniaxial tensile testing and fracture testing while considering the essential work of fracture (EWF) concept. During the macromolecular scission process, elongation at break shows a plateau followed by a drop, while stress at break decreases steadily. Once again, the trend is identical for all TPEs in all conditions considered. The βwp parameter determined using the EWF concept exhibits an interesting sensitivity to scissions (i.e., molar mas decrease). Plotting elongation at break as a function of molar mass reveals a strong correlation between these two parameters. This master curve is particularly remarkable considering the range of TPEs and chemical breakdown pathways considered (hydrolysis and oxidation at several temperatures). Relevant structure–property relationships are proposed, highlighting that molar mass is a predominant parameter for determining the mechanical properties of thermoplastic elastomers.

Influence of silane‐modified coconut shell powder on thermal and mechanical properties of thermoplastic elastomers

AbstractA silane coupling agent (glycidyloxypropyltrimethoxysilane, GPTMS) was used to modify coconut shell powder (CSP), and the influence of the modified coconut shell powder (G‐CSP) on the thermal and mechanical properties of thermoplastic elastomers (TPEs) was investigated. The thermal stabilities of the G‐CSP‐TPEs were studied using TGA; Young's modulus of the G‐CSP‐TPEs was studied by means of the spherical indentation test and the tensile test, and the tensile test was also used to characterize the tensile strength of the G‐CSP‐TPEs. The results revealed that the specific functional groups of GPTMS were efficiently grafted onto the CSP and that G‐CSP enhanced the thermal stability of the TPEs. Under 8% strain, Young's moduli of 0–7.5 wt% G‐CSP‐TPEs obtained by the spherical indentation test and tensile test were almost equal, while the modulus of 10–15 wt% G‐CSP‐TPEs measured by the latter test was greater than that of the former test. The tensile strength of G‐CSP‐TPEs increased up to a threshold limit (10 wt% G‐CSP), followed by a significant decrease. Micro‐images of the fractured surfaces obtained by SEM indicated that the addition of G‐CSP gradually filled the microvoids in the matrix and enhanced the tensile strength of the composite. As the G‐CSP mass percentage exceeded a threshold limit (>10 wt%), the particles started to agglomerate, resulting in weak interfacial adhesion and inferior mechanical properties. Hence, an optimal amount of reinforcing agent G‐CSP should be added to attain desirable thermal and mechanical properties. © 2020 Society of Chemical Industry

The toughening of polymeric glasses using cellulose without sacrificing transparency

The development of cellulose graft copolymers has been intensively studied during recent years. Our previous works have demonstrated that cellulose graft strategy can greatly improve the mechanical properties of thermoplastic elastomers. However, the effect of cellulose graft strategy on glassy polymers is still unknown. Herein, Cellulose-graft-poly(methyl methacrylate) (Cell-g-PMMA) copolymers were synthesized by activators regenerate by electron transfer atom transfer radical polymerization (ARGET ATRP). Two kinds of celluloses, microcrystalline cellulose (MCC) and wood pulp cellulose (Pulp) were used as starting materials. Thermal behavior, transparency, and mechanical properties of these graft copolymers were investigated. Compared with the brittle fracture of PMMA, a typical ductile fracture was observed in both MCC-g-PMMA and Pulp-g-PMMA copolymers, which showed similar transparency as linear PMMA film. The tensile toughness of MCC-g-PMMA copolymers was almost 7 times to that of linear PMMA. Furthermore, the toughness of Pulp-g-PMMA copolymers was even better than that of MCC-g-PMMA copolymers.

Towards understanding the role of peroxide initiators on compatibilization efficiency of thermoplastic elastomers highly filled with reclaimed GTR

Thermoplastic elastomers based on recycled high density polyethylene (rHDPE) and styrene-butadiene-styrene (SBS) block copolymer were highly filled with reclaimed ground tire rubber (RR). The impact of various organic peroxides (dicumyl peroxide (DCP), benzoyl peroxide (BP) and di-tert-butyl peroxide (DB)), applied as free-radical initiators, on the processing, structure and performance properties of rHDPE/SBS/RR blends was investigated. It was found that, regardless of peroxide type, their application resulted in decrease of the sol fraction, which indicated increase of cross-link density. This was confirmed by the reduced flowability of material, expressed by noticeable changes in melt flow index that decreased in the order BP > DB > DCP. The most beneficial changes were observed for application of DCP, which led to 80% increase of tensile strength, 40% reduction of permanent set and 25% increase of hardness. Moreover, thermal stability of analyzed thermoplastic elastomers was significantly improved with onset of thermal decomposition shifted by over 40 °C. Scanning electron microscope images revealed enhancement of interactions at the interphase due to increased cross-link density, which had direct influence on the mechanical properties of thermoplastic elastomers. The results showed that processing and mechanical performance of obtained thermoplastic elastomers can be easily engineered by suitable selection of organic peroxide.

Analytical interpretations of static and dynamic mechanical properties of thermoplastic elastomer toughened PLA blends

ABSTRACTPoly(lactic acid) (PLA) was melt blended with thermoplastic elastomer (TPE) styrene–ethylene–butylene–styrene‐g‐maleic anhydride (SEBS‐g‐MA) copolymer using a micro compounder which used melt recirculation approach for efficient dispersion of SEBS‐g‐MA in PLA. The SEBS‐g‐MA volume fraction (Φd) was varied between 0.07 and 0.48. Dynamic mechanical analysis showed 10.4 °C decrease in glass transition temperature at Φd = 0.48. Differential scanning calorimetry results exhibited shift in cold crystallization temperature to a higher temperature in the presence of SEBS‐g‐MA. Thermogravimetric analysis presented enhanced thermal stability of PLA/SEBS‐g‐MA blends. Tensile strength and modulus decreased while elongation‐at‐break and Izod impact strength increased in the blends. Theoretical models were employed to analyze the tensile properties of the blends in order to evaluate the blend structure. The microstructural attributes were characterized by wide‐angle X‐ray diffraction, Fourier‐transform infrared spectroscopy, and scanning electron microscopy of cryofractured, impact fractured, and tensile fractured surfaces. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45644.

Sustainable poly(ε-decalactone)−poly(l-lactide) multiarm star copolymer architectures for thermoplastic elastomers with fixed molar mass and block ratio

To improve the thermal and mechanical properties of thermoplastic elastomers derived from plant-based monomers, a series of well-defined multiarm star block copolymers was investigated. Controlled bulk ring-opening polymerization of ε-decalactone (DL) with multiarm initiators yielded hydroxyl-terminated (PDL−OH)n, which were subsequently converted to (PDL−PLLA)n using l-lactide (LLA) through a one-pot, two-step process. The multiarm copolymers were designed for targeting on Mn,NMR and fPLLA of 180 kg mol−1 and 0.27, respectively. Structural analysis proved that PLLA hard domains were thinner, and thus, more compact microphase-separated structures with hexagonally packed cylinders were induced by increasing n. Thermal and tensile property measurement demonstrated that, although the copolymers had a lower crystallinity in PLLA due to the shorter chain length, the thermal degradation stability and mechanical strength were enhanced, which was caused by to an amplified pinning effect caused by the more closed packed PLLA domains, in addition to chemical crosslinking of the PDL strands.

Mechanical Properties of Star Block Polymer Thermoplastic Elastomers with Glassy and Crystalline End Blocks

The mechanical properties of thermoplastic elastomers (TPEs) consisting of 6-arm star block polymers with glassy, crystalline, or composite crystalline–glassy physical cross-linking (hard) domains were investigated and compared to the analogous linear triblock or pentablock polymers. The 6-arm stars exhibited qualitatively similar solid-state morphologies and phase behavior to their linear counterparts, as demonstrated by small-angle X-ray scattering and differential scanning calorimetry. Consequently, the architecture had minimal impact on the small-strain behavior in uniaxial extension at room temperature. As the applied strain increased, the star polymers exhibited more pronounced strain hardening than the corresponding linear TPEs, resulting in an increase in the ultimate strength of 20% for the polymers with crystalline end blocks and 30% when the end blocks were glassy. Each of the three star polymers exhibited superior recovery (i.e., lower residual strain) and lower hysteresis than the correspondi...

Characterisation and micromechanical modelling of the elasto-viscoplastic behavior of thermoplastic elastomers

The first objective of this study is to characterise the physico-chemical and mechanical properties of thermoplastic elastomers (TPE) and their constituents. In parallel with the experimental study, a model describing the mechanical behaviour of such materials at room temperature and without damage is proposed. The composite materials studied in the present work are processed by blending particles of vulcanized rubber ethylene-propylene-diene (EPDM) into an isotactic polypropylene (PP) matrix. These particles, obtained from a recycling process, have an average diameter of 70μm. The constitutive equation for TPE composites is developed within the framework of a self-consistent micromechanical approach which considers the mechanical behaviour of each phase. A preliminary analysis of various TPE in linear elasticity justifies the choice of a morphological pattern for the model, which views elastomer particles as embedded in the thermoplastic matrix. In the non-linear domain, the PP matrix is modelled by means of an elastoviscoplastic model whose parameters are fitted using tensile and instrumented spherical micro-indentation tests. The elastomer exhibits viscoelastic behaviour. Having determined the material parameters by inverse analysis, the proposed micromechanical model is compared with tensile and bending tests performed before damage initiation and for various elastomers contents.

Effect of single-walled carbon nanotube on the physical, rheological and mechanical properties of thermoplastic elastomer based on PP/EPDM

Abstract The effect of the incorporation of single-walled carbon nanotubes (SWNT) on the morphological, physical, rheological and mechanical properties of thermoplastic elastomer based polypropylene (PP)/ethylene propylene diene (EPDM) (80/20) is reported. The morphological study showed that the size of the dispersed phase decreased by the addition of SWNT, this effect being more appreciable with 0.5 wt.% of SWNT. The results of differential scanning calorimetry showed that the addition of SWNT increased the crystallinity of PP/EPDM/SWNT nanocomposites. This effect was not linearly dependent on SWNT content, particularly at high SWNT concentrations. The rheological results revealed that addition of SWNT increased the storage modulus and complex viscosity at low frequencies. The Izod impact strength and tensile strength improved when 0.5 wt.% of SWNT was used. Furthermore, the tensile modulus increased remarkably by increasing the SWNT content, but the elongation at break of the material decreased.

Self‐Healing Supramolecular Block Copolymers

Polymer, heal thyself! Supramolecular ABA triblock copolymers formed by dimerization of 2-ureido-4-pyrimidinone (UPy) end-functionalized polystyrene-b-poly(n-butyl acrylate) (PS-b-PBA) AB diblock copolymers have been synthesized, resulting in a self-healing material that combines the advantageous mechanical properties of thermoplastic elastomers and the dynamic self-healing features of supramolecular materials.

Mechanical properties of thermoplastic elastomers based on silicone rubber and an ethylene–octene copolymer by dynamic vulcanization

AbstractThermoplastic vulcanizates (TPVs) are a special class of thermoplastic elastomers that are generally produced by the simultaneous mixing and crosslinking of a rubber with a thermoplastic polymer at an elevated temperature. Novel peroxide‐cured TPVs based on blends of silicone rubber and the thermoplastic Engage (an ethylene–octene copolymer) have been developed. These TPVs exhibit very good overall mechanical and electrical properties. With an increasing concentration of dicumyl peroxide, the tensile strength, modulus, and hardness of the TPVs increase, whereas the elongation at break decreases. Significant correlations have been obtained from oscillating disc rheometer torque values with various physical properties, such as the modulus and tension set of the TPVs. The aging characteristics and recyclability of the silicone‐based TPVs are also excellent. Scanning electron microscopy photomicrographs of the TPVs have confirmed a dispersed phase morphology. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Performance of Dynamically Vulcanized Thermoplastic Elastomer under Vibration Force Field

The mechanism of vibration force field on dynamically vulcanized thermoplastic elastomers (TPE) is studied through the analyses of their mechanical properties, DSC, XRD, and TGA. Experimental results show that the tensile strength, tensile stress at 100%, and elongation at break of TPE increase within a certain range, but shore A hardness decreases with the increase in the vibrational frequency or amplitude. With the increase in the rubber and plastics ratio, the tensile strength, tensile stress at 100%, and shore A hardness of TPE decrease, but elongation at break increases. The mechanical properties of TPE processed in dynamic condition are better than those in steady condition. The interpenetration and entanglement of macromolecular chains between ethylene-propylene-diene terpolymer (EPDM) and polypropylene (PP) under vibration force field strengthen, the influence of amorphous component on the crystallinity of crystalline component increases, and the miscibility of two-phase interface increases. Therefore, introduction of vibration force field can improve the melting temperature, resistance to heat, and thermal stability of TPE, reduce the crystallinity of crystalline component PP, and increase vulcanization rate. Shearing and elongational effect of vibration force field strengthens deformation, fracture, fineness, and dispersion of EPDM in matrix PP, and side effect of over-vulcanization or degradation caused by local high temperature reduces, which enhances phase inversion of blending systems and realizes processing control of dynamic vulcanization, mixing dispersion, and reactant performance.

Motional Heterogeneity in Poly(ether-block-amide) Copolymers As Revealed by Solid-State NMR

An insight into the motional heterogeneity of a series of poly(ether-block-amide) copolymers is presented and discussed in terms of its NMR fingerprints dependent on a content and length of hard and soft segments and a microphase-separated morphology. Local-field dipolar spectra carry a straightforward signature of microphase-separated morphology endowed with a strong mobility gradient. The dipolar features of the poly(tetramethylene glycol) (PTMG) and polyamide-12 (PA) components, besides visualizing the presence of separated PTMG and PA phases, also give evidence for the presence of the dynamic heterogeneity of each component. 1H MAS spectra provide an another fingerprint of phase-separated systems. Although such spectra roughly show increasing line broadening at higher PA/PTMG ratio, they are mainly sensitive to the presence of the most mobile fragments and may give a distorted vision of intrinsic mobility of the soft component in the presence of its dynamic heterogeneity. 13C spectra bearing proton−carbon J-coupling features appear to be more sensitive to the length of the soft blocks and seem to bring a proper visualization of their overall mobility. Special attention has been paid to characterize motional heterogeneity of the soft component by exploiting cross-polarization transfer efficiency combined with indirect T2(1H) relaxation measurements. The cross-polarization inversion experiments provide, from heteronuclear dipolar interaction perspective, a corroborating visualization of the extent of motional distribution of the PTMG component. The revealed fingerprints of the motional heterogeneity of the soft component and the ways exploited in this work for their retrieval might be helpful for a better assessment of its role in the mechanical properties of thermoplastic elastomers.