Investigation of modified SEBS‐based thermoplastic elastomers by temperature scanning stress relaxation measurements

Thermoplastic elastomers (TPEs) based on poly(styrene‐b‐ethylene/butylene‐b‐styrene) (SEBS), modified with poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE), were investigated by a new testing method. The development and characterization of TPEs with improved temperature and oil resistance is a current area of research to extend the applications of TPEs, especially in the automotive industry. Thermal scanning stress relaxation (TSSR) was used to investigate the relaxation behavior of compounds containing SEBS, blended with extender oil, various amounts of PPE and in some cases with a thermoplastic polymer. Polyamide 12 (PA12) or polypropylene (PP) were used as the thermoplastic component. TSSR measurements were applied to detect relaxation changes in the glass transition region of the polystyrene blocks mixed with PPE. It was shown that the glass transition temperature increased with addition of PPE to the compound up to a limit of approximately 150°C, which corresponded to a weight fraction of PPE in the polystyrene (PS)‐block of 0.5. The increased glass transition temperature lead to SEBS‐based thermoplastic elastomer compounds with improved upper service temperatures. Phase images obtained by atomic force microscopy showed that the addition of PPE results in an increase of hard phase dimension. The addition of a thermoplastic polymer improved the mechanical properties and temperature resistance, but naturally decreased the elasticity of the compounds. Compounds containing PA12 exhibited an improved oil resistance. POLYM. ENG. SCI., 45:1498–1507, 2005. © 2005 Society of Plastics Engineers     

Exploring the thermomechanical properties of peroxide/co-agent assisted thermoplastic vulcanizates through temperature scanning stress relaxation measurements

Temperature scanning stress relaxation (TSSR) measurement of peroxide vulcanized polymer blends of polypropylene (PP) and ultrahigh molecular-EPDM (UHM-EPDM) rubber has been performed to study the thermomechanical behavior of thermoplastic vulcanizates (TPVs). Co-agents play crucial roles in the enhancement of properties of TPVs. Different types of co-agents (Triallyl cyanurate-TAC; N, N-m-phenylene-dimaleimide-HVA2; zinc dimethacrylate-ZDMA; and in-situ formed zinc dimethacrylate-ZMA) have been explored in this work. TSSR study shows that higher T₅₀ and T₉₀ values have been achieved in ZMA co-agent assisted-TPV. Higher TSSR-index (RI) value was also found for the same co-agent ZMA, indicating higher elastic behavior. TSSR result supports the mechanical and rheological properties, and it is found that the ZMA and ZDMA show higher mechanical strength. Cross-linked-density calculated by modified Flory–Rehner equation and the cross-link-density as obtained from TSSR method have been compared and the trend was found to be the same. Stress relaxation study shows the slow relaxation-phenomena of the ZMA-TPV with slowest relaxation-time (θ_r) than the other TPVs, which correlates with superior material strength. Thermogravimetric analysis proves that there is a difference in degradation temperature of the blends at approximately 5–10°C. Ultrahigh molecular weight-EPDM/PP based TPVs reveal superior thermomechanical and physico-mechanical properties with ZMA and ZDMA co-agent over TAC and HVA2. These ultrahigh molecular weight-EPDM based TPVs can be used in automotive seals/strips, hoses, bellows, and 2 K-molds for automotive applications.     

Design and properties of a series of high‐temperature thermoplastic elastomeric blends from polyamides and functionalized rubbers

A series of high‐temperature thermoplastic elastomers (TPEs) and thermoplastic vulcanisates (TPVs) were successfully developed based on two different types of heat resistant polyamide (PA) (25 parts by weight)—PA‐12 and PA‐6, in combination with three different functionalized rubbers (75 parts by weight) of varying polarity, e.g., maleic anhydride grafted ethylene propylene diene terpolymer (MA‐g‐EPDM), sulphonated ethylene propylene diene terpolymer, and carboxylated acrylonitrile butadiene rubber, by melt mixing method. These rubbers have low level of unsaturation in its backbone, and the plastics showed high melting range. Thus, the developed TPEs and TPVs were expected to be high temperature resistant. Resol type resin was used for dynamic vulcanization to further increase the high temperature properties of these blends. Interestingly, initial degradation temperature of the prepared blends was much higher (421 °C for MA‐g‐EPDM/PA‐12) than the other reported conventional TPEs and TPVs. Fourier transform infrared analysis described the interactive nature of the TPEs and TPVs, which is responsible for their superior properties. The maximum tensile strength with lowest tension set was observed for the carboxylated acrylonitrile butadiene rubber/PA‐12 TPV. Mild increase in mechanical properties without any degradation was observed after recycling. Dynamic mechanical analysis results showed two distinct glass transition temperatures and indicated the biphasic morphology of the blends, as evident from the scanning electron microscopy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45353.     

Rheological behavior and morphological and interfacial properties of PLA/TPE blends

Rheological and interfacial tension data were employed to predict the morphology and thermal and mechanical properties of noncompatibilized and compatibilized poly(lactic acid) (PLA)/thermoplastic elastomer (TPE) blends. PLA was melt blended with thermoplastic polyurethane (TPU) and ethylene elastomer (EE) and compatibilized by ethylene–butyl acrylate–glycidyl methacrylate (EBG) in an internal mixer chamber. Both TPU and EE TPEs have higher viscosities than PLA, and the interfacial properties evaluated have revealed better adhesion between domains of PLA–TPU. The efficiency of the compatibilizer agent EBG depended on the TPE type inferred by modifications in the scanning electron microscopy images of PLA/TPE blends and by the Izod impact strength (improved by 23%). The EBG was more effective in the PLA/TPU blend. The TPEs and EBG did not affect the PLA thermal stability, and no thermal event was observed in the usual PLA extrusion and injection temperature range. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47962.     

Influence of phase modifiers on morphology and properties of thermoplastic elastomers prepared from ethylene propylene diene rubber and isotactic polypropylene

A series of thermoplastic elastomers (TPEs) were prepared from a binary blend of ethylene propylene diene rubber (EPDM) and isotactic polypropylene (iPP) using different types of phase modifiers. The influence of sulphonated EPDM, maleated EPDM, styrene‐ethylene‐co‐butylene‐styrene block copolymer, maleated PP, and acrylated PP as phase modifiers showed improved physico‐mechanical properties (like maximum stress, elongation at break, moduli, and tension set). Scanning electron and atomic force microscopy studies revealed better morphologies obtained with these phase modified EPDM‐iPP blends. The dependence of the phase modifier type and concentration was optimized with respect to the improvement in physical properties and morphology of the blends. Physical properties, dynamic mechanical properties, and morphology of these blends were explained with the help of interaction parameter, melt viscosity, and crystallinity of the blends. Theoretical modeling showed that Kerner, Ishai‐Cohen, and Paul models predicted the right morphology–property correlation for the prepared TPEs. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Temperature scanning stress relaxation behavior of water responsive and mechanically adaptive elastomer nanocomposites

The decrease of stress at constant strain, that is, the stress relaxation process as a function of temperature, is a central mechanical characteristics of elastomer nanocomposites for their potential applications. However, in the conventional stress relaxation test, the relaxation behavior is usually determined as a function of time at constant temperature. The present work reports the temperature scanning stress relaxation (TSSR) characteristics of a new kind of mechanically adaptive elastomer nanocomposite by monitoring the nonisothermal relaxation behavior as a function of temperature. This kind of adaptive elastomer nanocomposite was prepared by introducing calcium sulfate (CaSO₄), as the water-responsive phase into the hydrophilic elastomer matrix. The influence of water-induced structural changes on TSSR behavior was investigated. Water treatment had a strong effect on the shape of the relaxation spectrum of the nanocomposite. It was revealed that the in situ development of hydrated nano-rod crystal structures of CaSO₄ in the elastomer matrix was responsible for the changes in the mechanical relaxation behavior of the composites. Atomic force microscopy was used to verify this nano-rod crystal morphology in the elastomer matrix. The mechanism of water-induced mechanical reinforcement of the composite was explored from dynamic mechanical analysis of the material and correlated with its stress relaxation behavior. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48344.     

Toward superior applications of thermoplastic elastomer blends: double Tg increase and improved ductility

With the aim of curbing air pollution and addressing climate change, the use of low density thermoplastic elastomers (TPEs) in transportation could be a useful way to lighten the vehicle weight. For that, melt blending of high performance rubber and thermoplastics is an attractive way of preparing high performance TPEs. In this work, several TPEs have been prepared by melt blending of hydrogenated acrylonitrile butadiene rubber (HNBR) with polyamide 6 (PA6), adding different amounts of carboxylated HNBR (XHNBR) as compatibilizer: 40/60/0, 40/42/18, 40/30/30 and 40/18/42 (PA6/HNBR/XHNBR). The resulting blends were investigated using melt rheological measurements, morphological observations (scanning electron microscopy and polarized optical microscopy), dynamic mechanical analysis, differential scanning calorimetry analysis and mechanical tests. A biphasic morphology was noted for all TPEs. An increase in XHNBR amount changes the morphology from dispersed to co‐continuous. This evolution is explained by the change in the melt rheological properties of the HNBR/XHNBR rubber phase. Moreover, the introduction of 42% XHNBR resulted in an increase in the glass transition temperature of both rubber and PA6 phases. This double T_g increase phenomenon was attributed to the interfacial interactions between the carboxyl groups in XHNBR and the amine end groups in PA6. Additionally, thermal analysis revealed a reduced crystallinity of PA6 in the blend, which corresponds to enhanced interfacial interactions. The interfacial adhesion and the co‐continuous morphology resulted in an improved ductility. This study reveals the possibility of obtaining TPE blends with tunable thermal and mechanical properties by controlling both interfacial interactions and morphology. © 2019 Society of Chemical Industry     

Crystallization behavior and spherulite growth rate of isotactic polypropylene in isotactic polypropylene/natural rubber based thermoplastic elastomers

The melting and crystallization behavior of isotactic polypropylene/natural rubber (PP/NR) based thermoplastic elastomers (TPEs) were investigated using differential scanning calorimetry. The samples were scanned at a heating rate of 10°C/min under nitrogen atmosphere. The effects of blend ratio on the melting and crystallization characteristics of the blends were analyzed. Normalized crystallinity is unchanged by the addition of small amount of NR, but as the amount of rubber increases crystallinity increased for the 30/70 NR/PP and lowered for the 50/50 NR/PP blend system. Morphology of the blend was analyzed using scanning electron microscopy (SEM). Blend ratio showed a pronounced influence on the phase morphology of the NR/PP TPEs. As the amount of NR increases more than 50 wt % the system changes from dispersed to cocontinuous structure. Hot‐stage polarizing optical microscopy (POM) was used to study the radial growth of spherulite as a function of blend ratio, cooling rate, and crystallization temperature. Spherulite growth rate is marginally influenced by the rubber inclusions. The spherulite morphology observed under polarized optical microscopy is influenced by the blend morphology. It was found that for the cocontinuous 50/50 blend system, spherulites are much different from the usual appearance under polarized light. Attempts have been made to correlate the crystallization behavior with the morphology of the blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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

Shape 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.     

Comparative deformational characteristics of poly(styrene-b-ethylene-co-butylene-b-styrene) thermoplastic elastomers and cross-linked natural rubber

Three poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) thermoplastic elastomers (TPEs) are studied mechanically and compared to cross-linked natural rubber. It is observed that subtle alterations in the mid-block of the TPEs affect their mechanical properties significantly. The stress relaxation at room temperature is significantly altered indicating a reduced flow in systems where the ratio of ethylene to butylene segments in the mid-block is greater than one. The cyclic behavior of these systems also shows significant hysteresis. Differential scanning calorimetry suggests that these TPEs crystallize at low temperatures, similar to the observed behavior in cross-linked natural rubber. Results of internal energy changes from deformation calorimetry provide evidence for strain-induced crystallization occurring in certain SEBS systems, similar to the internal energy changes observed for cross-linked natural rubber. Simultaneous WAXD/SAXD measurements on deformed SEBS samples highlight deformation at the nanometer and the molecular length scales. In situ WAXD at different strains further reinforces the evidence for formation of strain-induced crystallites in the selected systems. Strain-induced crystallization occurring in certain TPEs provides a mechanism for reduction of flow at high strains and accounts for the retention of their highly elastic behavior.     

Mullins effect and its reversibility for compatibilised thermoplastic elastomers based on high-density polyethylene/waste ground rubber tyre powder under compression mode

Thermoplastic elastomers (TPEs) based on high-density polyethylene (HDPE)/waste ground rubber tyre (WGRT) powder blends were prepared by melt-compounding where styrene–butadiene–styrene block copolymer (SBS) was used as compatibiliser. Mullins effect and its reversibility of the prepared TPEs under compression mode were investigated systematically. The results showed that the stress softening, residual deformation and hysteresis could be observed obviously during the cyclic uniaxial loading–unloading tests. Compared with that of the HDPE/WGRT blends, the compatibilised TPEs had a slight stress softening. Increasing the heat treatment temperature and the SBS dosage could strengthen the reversibility of the Mullins effect remarkably.     

Thermoplastic elastomers from rubber and recycled polyethylene: chemical reactions at interphases for property enhancement

Recycled low density polyethylene (R‐LDPE) has been reactively compatibilized with butadiene rubber (BR) by using small additions of reactive polyethylene copolymers and reactive BRs to produce thermoplastic elastomers (TPEs). TPEs were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), rheology measurements, wide‐angle X‐ray scattering (WAXS) and mechanical testing. WAXS results show that the presence of BR and reactive modifiers does not completely prevent the crystallization of R‐LDPE during the TPE formation. Depression of the melting point has been found in all cases. Also in all cases, compatibility is provided by formation of interfacial layers. The best mechanical characteristics are obtained for R‐LDPE + BR blends compatibilized with poly(ethylene‐co‐acrylic acid) (PE‐co‐AA) and polybutadiene terminated with isocyanate groups (PB‐NCO) for PB‐NCO = 7.5 wt% per PB and COOH/NCO ratio = 1/1. The stress at break and elongation at break are respectively improved by 31 % and 63 %. The PB‐NCO modifier participates in co‐vulcanization with BR in the rubber phase and reacts at the interface with the PE‐co‐AA dissolved in the polyolefin phase. As a result, the amorphous phase of R‐LDPE is dissolved by the rubber phase and a morphology with dual phase continuity is formed, assuring an improvement of mechanical properties of TPEs. Copyright © 2004 Society of Chemical Industry     

Viscoelastic effects on the phase separation in thermoplastics modified cyanate ester resin

A high temperature thermosetting bisphenol-A dicyanate, BADCy was blended with a thermoplastic poly(ether imide) (PEI). The phase separation behavior of the blend was investigated by scanning electron microscopy (SEM) and time resolved light scattering (TRLS). It was found by SEM that the blend with 20 and 25 wt% PEI had a phase inversion structure. The results of TRLS displayed clearly that the phase separation took place according to a spinodal decomposition (SD) mechanism and the evolution of both scattering vector q_m and the maximum scattering intensity I_m followed Maxwell-type relaxation equation. The temperature-dependent relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in PEI/BADCy blends were affected by viscoelastic effect.     

Thermal properties of a thermoplastic polyimide blend

Differential scanning calorimetry and dynamic mechanical analysis of blends of a new thermoplastic polyimide (TPI) and poly(ether imide) (PEI) have confirmed the full miscibility of the system over the whole composition range. Annealing of the blends above the glass transition temperature of TPI, but below its crystallization temperature, did not produce a shift in the glass transition, while physical ageing of the annealed blends also failed to reveal any indication of phase separation. The rate of crystallization of TPI was slowed by the addition of PEI, and the temperature of the maximum crystallization rate shifted upwards. The β‐relaxation behavior of the blends followed a linear trend between the response of the component polymers, while the low‐temperature γ‐relaxation was unchanged by blending. The time scale of physical ageing of the blends did not behave in a linear fashion, and the enthalpy loss on ageing also deviated from the average. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 543–552, 1999     

共混工艺条件对EPDM/PP热塑性弹性体力学性能的影响

本文探讨了开炼机和单螺杆挤出机两种简单的共混设备制备的 EPDM/PP热塑性弹性体( TPES)性能差别 ,实验结果表明 ,单螺杆挤出机制备的 TPES具备更好的力学性能 ,170℃制备的 TPES的拉伸强度和 10 0 %定伸应力优于 190℃制备的 TPES,而断裂伸长率则相反     

Morphology and properties of poly(ethylene terephthalate) and thermoplastic polyester elastomer blends modified in the melt by a diisocyanate chain extender and filled with a short glass fiber

The structural features and rheological, mechanical, and relaxation properties of poly(ethylene terephthalate) (PET) blends with 7–50 wt % polyester thermoplastic polyester elastomer (TPEE), a block copolymer of poly(butylene terephthalate) and poly(tetramethylene oxide), chemically modified by a diisocyanate chain extender (CE) and reinforced with 30% glass fibers (GF) were studied. The composites were obtained by reactive extrusion with a twin‐screw reactor–mixer with a unidirectional rotation of screws. The molecular–structural changes in the materials were judged against data provided by differential scanning calorimetry, scanning electron microscopy, relaxation spectrometry, and rheological analysis of the melts. Regardless of the TPEE concentration in the blends with GF‐reinforced PET, the addition of CE resulted in the growth of the indices of the mechanical properties at straining, bending, and impact loading and an increase in the melt viscosity. In addition, an increase in the average length of short GFs in the composites and an intensification of interphase adhesion in the polyester binder–GF surface system were observed. The introduction of CE promoted a slowdown in PET crystallization in the composites and intensified the interphase adhesion in the binder–GF system at temperatures higher and lower than the PET glass‐transition temperature. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45711.     

Polypropylene/natural rubber thermoplastic elastomer: Effect of phenolic resin as a vulcanizing agent on mechanical properties and morphology

The aim of this study is to characterize thermoplastic elastomers (TPEs) from polypropylene and natural rubber with and without phenolic resin as a vulcanizing agent. The blends containing 40–60 wt % of polypropylene were mixed in an internal mixer and pressed with a compression molding machine. TPEs without rubber vulcanization, named as unvulcanized thermoplastic natural rubber (uTPNR) were compared to TPEs containing dynamic vulcanized rubber, referred as vulcanized thermoplastic natural rubber (vTPNR). The uTPNRs illustrated cocontinuous phase morphology, whereas the vTPNRs displayed dispersed phase of vulcanized natural rubber. Tensile properties, tear strength, thermal ageing resistance, ozone resistance, tension set, hardness and swelling test in toluene, IRM 903 oil and engine oil were carried out according to ASTM. It was found that tensile and tear strength, hardness and tension set of the uTPNRs increased with increasing polypropylene content. Dynamic vulcanization improved tensile strength, elongation at break, tension set and degree of swelling of the TPEs, whereas hardness and tear strength did not show significant change after dynamic vulcanization. The vTPNRs exhibited higher ozone resistance and swelling resistance than the uTPNRs. Reprocessability of the vTPNRs was investigated and showed that tensile strength decreased at 20 and 30% and elongation at break decreased at 13 and 27% for the first and the third reprocessing respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

聚合物共混体系中分散相在物理老化过程的尺寸变化

文章研究了退火过程对乙烯-辛烯共聚物/热塑性聚氨酯不相容共混物的相聚集现象的影响,利用扫描电子显微镜分析分散相的粒径,结果表明,随着退火温度的提高和时间的延长,分散相的粒径变大、分布变宽,聚集长大机理起关键作用。     

Cure kinetics and morphology of blends of epoxy resin with poly (ether ether ketone) containing pendant tertiary butyl groups

The cure kinetics and morphology of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin modified with a poly (ether ether ketone) based on tertiary butyl hydroquinone (PEEK-T) cured with diamino diphenyl sulphone (DDS) were investigated using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dynamic mechanical thermal analysis (DMTA). The results obtained from DSC were applied to autocatalytic and diffusion controlled kinetic models. The reaction mechanism broadly showed autocatalytic behaviour regardless of the presence of PEEK-T. At higher PEEK-T concentration, more diffusion controlled mechanism was observed. The rate of curing reaction decreased with increase in thermoplastic content and also with the lowering of curing temperature. The activation energies of the blends are higher than that of the neat resin. The blends showed a phase separated morphology. The dispersed phase showed a homogeneous particle size distribution. The T_g of the neat resin decreased with the decrease in cure temperature. Two T_g's corresponding to the epoxy rich and thermoplastic rich phases were observed in the dynamic mechanical spectrum. The storage modulus of 10 and 20 phr PEEK-T blends are found to be greater than the neat resin.