Influence of a crosslinked system on the morphology and properties of TPVs based on PA/NBR

The mechanical properties of thermoplastic vulcanizates (TPVs), depend strongly on their morphologies, which themselves depend on the properties of the primary polymers, the composition of the TPV, and the crosslink system and crosslink process. The morphology is defined during the dynamic vulcanization. This work deals with the study of the influence of crosslink systems on TPVs based on PA/NBR (copolyamide PA6/6‐6 and nitrile rubber) in a 40/60 composition. Dicumyl peroxide, bismaleimide, phenolic resin, a sulfur‐accelerated system, and dicumyl peroxide with two coagents were used as crosslinkers. TPVs were characterized by taking into account their mechanical strength, solvent resistance, compression set, and morphology. The curing system constituted by dicumyl peroxide and sulfur/bismaleimide as coagents resulted in a more defined morphology, and therefore the TPV exhibited the best properties. For these TPVs, a morphology consisting of spherical domains of rubber distributed homogeneously on the polyamide matrix could be observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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.     

The effect of selective location of carbon nanotubes on electrical properties of thermoplastic vulcanizates

Three types of conductive thermoplastic vulcanizates (TPVs) were prepared by blending polypropylene (PP), carbon nanotubes (CNT), and carboxylic acrylonitrile butadiene ultrafine full‐vulcanized powdered rubber (xNBR‐UFPR). The CNT locations were different in these three types of TPVs, i.e., CNTs were localized in PP matrix, in the xNBR‐UFPR phase, or mainly in the interface. It had been found that TPV with CNTs localized mainly in the interface had the lowest conductive percolation threshold among these three types of TPVs. The volume resistivity of the TPV with 2 phr CNTs was as small as 220 Ω?cm. Moreover, the conductive TPV possessed good mechanical properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

丁基橡胶及卤化丁基橡胶阻尼材料的研究进展

介绍了丁基橡胶的阻尼性能及应用,阐述了丁基橡胶、氯化丁基橡胶及溴化丁基橡胶阻尼材料的研究进展。指出提高损耗因子和拓宽阻尼温域是丁基橡胶基高性能阻尼材料的研究方向,丁基橡胶与其他橡胶共混、开发合适的硫化体系和填料是提高丁基橡胶基阻尼材料性能的重要手段。     

Experimental and statistical study of the effects of material properties,curing agents,and process variables on the production of thermoplastic vulcanizates

A comprehensive experimental study together with statistical analysis was performed to identify the optimal process conditions, materials selection, and curing system for the production of thermoplastic vulcanizates (TPVs) based on EPDM rubber and polypropylene. Two types of curing systems were studied together with five different types of EPDM rubber. The TPV products were assessed according to elastic modulus and degree of swelling (indicators of crosslink density), ultimate tensile strength, ultimate elongation, tear strength, and compression set. A design of experiments method was applied to minimize the number of experiments and to obtain response surface and regression models for this complex and highly interactive system. From the modeling results, optimum values for the influential factors were obtained to achieve the target end product properties. It was found that a phenolic resin‐based curing system gave the best product properties and that the most influential factors were the rubber characteristics (ethylene content, ethylidene norbornene content, and molecular weight) and the polypropylene content in the formulation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

硫化体系对动态硫化EPDM/POE热塑性弹性体性能的影响

采用动态硫化的方法在Haake转矩流变仪上制备了三元乙丙橡胶/聚烯烃(EPDM/POE)热塑性弹性体(TPV),并分别对不同硫化体系和硫化剂用量对TPV交联密度和性能的影响进行了研究。结果表明,随硫化剂用量的增加,TPV的交联密度增大,其中硫黄硫化体系的TPV变化最明显;采用硫黄硫化体系和酚醛树脂硫化体系制备的TPV性能优于过氧化物硫化体系,并且DCP和硫黄分别在用量为0.5份,酚醛树脂在1.0份时性能较佳。     

Influences of blend proportions and curing systems on dynamic,mechanical, and morphological properties of dynamically cured epoxidized natural rubber/high‐density polyethylene blends

Thermoplastic elastomers (TPEs) based on dynamically cured epoxidized natural rubber/high‐density polyethylene (ENR/HDPE) blends were prepared. Influence of the process oil, blend proportion, and curing systems were investigated. It was found that the oil‐extended thermoplastic vulcanizates (TPVs) exhibited better elastomeric properties and improved ease of the injection process. Increasing the proportion of ENR caused increasing elastic response of elongation at break, tension set properties, and tan δ. It was also found that the TPV treated with phenolic resin exhibited superior mechanical properties and the smallest vulcanized rubber domains. The TPV treated with the conventional peroxide co‐agent curing system showed superior strength properties but had poor elastomeric properties. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Automotive applications of thermoplastic vulcanizates

Thermoplastic vulcanizates (TPVs) are special classes of thermoplastic elastomers, in which dynamic vulcanization of the rubber phase takes place during melt mixing with a semicrystalline thermoplastic matrix phase at elevated temperature. This review article focus on the different types of thermoplastic vulcanizates (TPVs) from various elastomer and thermoplastic blends that are suitable for the automotive applications purpose. A detailed study of the various TPVs based on polypropylene-ethylene propylene diene rubber (PP-EPDM) and polypropylene-ethylene α-olefin has been focused and their application in the automobile sector has been summarized. Most of the commercially available TPVs are PP-EPDM based. Limited applications of that TPVs in high heat and oil resistant application purposes requires new generation of TPVs. High performance TPVs or super TPVs are new generation TPVs that exhibit high heat resistance as well as excellent oil resistance property suitable for automotive under-the-hood applications. Therefore TPVs based on XNBR-PA12, HNBR-PA12 and FKM-PA6 system has also been explored in details in this study and the possibility of the use of those TPV system has been focused for the high temperature application purpose in the automobile sector where high and oil resistant application properties is the prime concern.     

Shear flow behavior and oil distribution between phases in thermoplastic vulcanizates

The high rate shear flow behavior and the morphology of five different oil‐extended polypropylene (PP)/ethylene‐propylene‐diene monomer (EPDM) thermoplastic vulcanizate blends were investigated with the melt flow rate (MFR) of the PP varying from 0.7 to 20. The ratio of rubber to PP is 70 : 30 in three of the thermoplastic vulcanizates (TPVs) and 50 : 50 in the other two TPVs. The distribution of the high‐temperature oil between the PP melt and the rubber is a key parameter because this will affect the viscosity of the PP/oil medium. The object of this study was to estimate the matrix composition in each of the TPVs at processing temperatures and to compare the shear viscosity of the effective matrix with that of the TPV. To this end, several PP/oil mixtures were prepared and their viscosity curves were correlated with the neat PP melt viscosity curves by means of shift factors varying with oil concentration. The oil distribution between the PP and rubber phases was estimated from TEM micrographs of the TPV blends. The results show that the PPs are mixed with oil to different proportions in the different TPVs and the viscosity curves of these mixtures exhibit the same trends in magnitude as the corresponding TPV viscosity curves. Hence, the shear flow of TPVs can be understood more readily in terms of the effective PP/oil medium flow behavior than in terms of the neat PP melt flow. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 113–121, 2004     

Molecular design of damping rubber based on polyacrylate‐containing silicone

A series of damping rubbers based on poly(meth)acrylate and poly(meth)acrylate‐containing silicone rubbers has been prepared. The dynamical mechanical properties were evaluated by using a dynamic mechanical viscoelastometer (DMA). A detailed investigation is reported on the relationship of the damping capability of the poly(meth)acrylate rubbers with their composition and macromolecular architecture. Also discussed is the effect of two kinds of silicone elastomers on the damping performance of the polyacrylate‐containing silicone rubber. The results indicate that, in vulcanized rubber systems, both statistical copolymerization for multiple monomers and blending between immiscible polymers with close T_gs facilitate broadening the glass transition peaks. Furthermore, the molecular design is quite an effective approach in which the multiple monomers whose polymers have a ladder‐changing T_g are used to synthesize the damping rubber with the broad effective functional area. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 746–751, 2002     

Selectively located aluminum hydroxide in rubber phase in a TPV: Towards to a halogen‐free flame retardant thermoplastic elastomer with ultrahigh flexibility

Novel thermoplastic vulcanizate (TPV) based on two EVAs with different VA contents, ethylene vinyl acetate rubber (VA content =50 wt%; EVM) and ethylene VA copolymer (VA content =28 wt%; EVA₂₈), has been successfully prepared by dynamic vulcanization in our previous work. In this study, we have incorporated aluminum hydroxide (ATH) into the TPV based on EVM/EVA₂₈ for the purpose to fabricate halogen‐free flame retardant TPVs with high flexibility. The morphology and the properties of the ATH filled TPVs have been investigated. It was found that the ATH particles were finely dispersed into the crosslinked EVM phase, while few ATH particles were observed in the EVA₂₈ matrix. The fabricated TPVs with 45% ATH exhibit LOI of 30.2%, significantly prolonged ignition time, and drastically reduced heat release rate. At the same time, the TPVs show excellent stretchability (>300% elongation at break), nice elasticity (only about 30% remnant strain at 100% stretching), high strength, and good flexibility as well. We have attributed the multifunctional performance of the ATH filled TPVs to both the fine phase structure of the base TPVs and the selective dispersion of ATH fillers in the rubber phase. POLYM. COMPOS., 36:1258–1265, 2015. © 2014 Society of Plastics Engineers     

Relationship between the rheology and morphology of dynamically vulcanized thermoplastic elastomers based on EPDM/PP

Relationship between the rheological properties and morphology of dynamically vulcanized thermoplastic elastomers (TPVs) based on Ethylene Propylene Diene Monomer (EPDM) and Polypropylene (PP) blends containing 20, 40 and 60% of EPDM were studied. The samples were prepared in a laboratory internal mixer at a rotor speed of 60 rpm. We performed morphological studies on the cryogenically fractured samples using scanning electron microscopy (SEM). The rheological behavior and melt viscoelastic properties of the samples were studied by rheometric mechanical spectrometry (RMS) at a temperature of 220°C. The TPV samples showed a significant viscosity upturn and a strong storage modulus that tended to plateau at low shear rates, with the highest extent for the sample containing 60% of EPDM. These results were attributed to a network structure resulting from agglomerates formed between the cured rubber particles, as evidenced by the morphological features of the samples. The multiple elastic response, expressed in terms of relaxation time distribution, H(λ), exhibited by the molten TPV sample containing 60% of EPDM suggests that apart from the contribution of flow‐induced molecular orientation of the PP matrix, there may also exist some elastic response induced by agglomerates formed between the cured rubber particles. The results predicted from the linear viscoelastic model proposed in the present work were found to be in good agreement with the experimental results. POLYM. ENG. SCI. 45:84–94, 2005. © 2004 Society of Plastics Engineers.     

Effects of compounding procedure on morphology development,melt rheology,and mechanical properties of nanoclay reinforced dynamically vulcanized EPDM/polypropylene thermoplastic vulcanizates

New nanocomposite thermoplastic vulcanizates (TPVs) comprising dynamically cross‐linked nanoscale EPDM rubber particles dispersed throughout the polypropylene (PP) matrix have been prepared by both batch and continuous melt blending of PP with EPDM in the presence of vulcanizing ingredients, nanoclay and maleated EPDM (EPDM‐g‐MA) as compatibilizer. X‐ray diffraction, linear melt viscoelastic measurement, and tensile mechanical behavior results revealed that the developed microstructure is strongly affected by the type of the melt compounding process as well as the route of material feeding. When EPDM phase was precompounded with a vulcanizing agent, nanoclay, and EPDM‐g‐MA prior to the melt blending with PP, not only nanosize cross‐linked rubber particles appeared uniformly throughout the PP continuous phase, but also the melt blending leads to the significant enhancement of the mechanical properties compared with counterpart samples prepared by one‐step melt mixing process. Also better dispersion of nano layers in the rubber compound before melt blending with PP results in higher mechanical properties of the resulted TPV. POLYM. ENG. SCI., 56:914–921, 2016. © 2016 Society of Plastics Engineers     

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     

Assessment of crosslink network and network defects of unfilled and filled ethylene‐propylene‐diene terpolymer using solid state nuclear magnetic relaxation spectroscopy

Reinforced rubbers are complex compared to unfilled systems. There are differences in the mechanisms affecting network molecular structure as well as properties of the rubber materials. In this article investigation of crosslink network and untied network defects on a molecular level of unfilled and carbon black filled ethylene‐propylene‐diene terpolymer was carried out using proton solid‐state double‐quantum NMR spectroscopy. The results show that the filled system demonstrates lower cure efficiency in conjunction with more noncoupled network defects than the unfilled one. In addition, the filled system yields the greater spatial heterogeneity because of the localization of the free radicals at the rubber–filler boundary. These strongly influence the mechanical properties of the filled rubber. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44224.     

Kaolin modified with sodium salt of rubber seed oil as a reinforcing filler for blends of natural rubber,polybutadiene rubber and acrylonitrile–butadiene rubber

Blends of natural rubber (NR) and synthetic rubbers are widely used in the rubber industry to meet specific performance requirements. Further, the emerging field of organomodified clay/rubber nanocomposites could provide a host of novel materials having a unique combination of properties to meet various stringent service conditions. Previous studies have shown that at very low dosages, china clay (kaolin) modified with sodium salt of rubber seed oil (SRSO) improved the cure characteristics and physico‐mechanical properties of NR. Results of the present study show improved cure characteristics and physico‐mechanical properties for blends of NR with butadiene rubber and nitrile rubber containing 4 phr of SRSO‐modified kaolin as indicated by reduction in optimum cure time along with higher tensile strength, tensile modulus and elongation at break for their vulcanizates as compared to those containing unmodified kaolin. The SRSO‐modified kaolin/rubber nanocomposites showed improved flex resistance, reduced heat build‐up, tan delta and loss modulus and higher chemical crosslink density index, indicating a reinforcing effect of the SRSO‐modified kaolin, enabling the nanocomposites to have potential industrial applications. © 2015 Society of Chemical Industry     

Effect of grafted maleic anhydride content and recyclability of dynamically cured maleated natural rubber/polypropylene blends

Maleated natural rubbers (MNRs) were prepared using various levels of maleic anhydride (MA) at 4, 6, 8, 10, and 12 phr. Dynamically cured 60/40 MNR/PP blends with phenolic‐modified polypropylene (Ph‐PP) compatibilizer at a loading level of 5 wt % of PP were prepared by melt mixing process using sulfur vulcanization system. The influence of the level of MA on properties of the thermoplastic vulcanizates (TPVs) was studied. It was found that the mixing torque, apparent shear stress, shear viscosity, tensile strength, and hardness properties increased with increasing levels of the MA or grafted succinic anhydride groups in the MNR molecules. This is attributed to an increase in chemical interaction and reaction between methylol groups in the Ph‐PP molecules and polar functional groups in the MNR molecules upon increasing levels of the grafted succinic anhydride groups. As a consequence, compatibilizing block copolymers of MNR and PP blocks were formed. The block copolymers were capable of compatibilizing with MNR and PP blend components via the respective blocks. Recyclability of the MNR/PP TPVs was also studied. It was found that, after processing through a number of cycles by injection molding and extrusion processing, the TPV exhibited marginal decreases in mechanical properties. This corresponded to slightly increasing size of the dispersed vulcanized rubber domains. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

NR/PP thermoplastic vulcanizates: Selection of optimal peroxide type and concentration in relation to mixing conditions

Thermoplastic vulcanizates (TPVs) from natural rubber (NR) and polypropylene (PP) were studied, prepared by dynamic vulcanization during melt mixing, using various peroxides to crosslink the rubber phase. The objective was to find a proper balance between degree of crosslinking of the rubber and degradation of the PP‐phase, and the tendency of the peroxide to form smelly by‐products, in particular acetophenone. Four types of peroxides were investigated: 2,5‐dimethyl‐2,5‐di(tert‐butyl‐peroxy) hexyne‐3 (DTBPHY), 2,5‐dimethyl‐2,5‐di(tert‐butyl‐peroxy) hexane (DTBPH), di(tert‐butylperoxyisopropyl) benzene (DTBPIB), and dicumyl peroxide (DCP), at two mixing temperatures: 160 and 180°C for a 60/40 NR/PP TPV. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 160°C, whereas the other two require a higher temperature of 180°C. The best mechanical properties, tensile strength, elongation at break and compression set are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the NR and PP. Unfortunately, these two peroxides form more smelly by‐products than DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these NR/PP TPVs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Influence of phenolic curative on crosslink density and other related properties of dynamically cured NR/HDPE blends

Dynamically cured 60/40 NR/HDPE blends with various amounts of phenolic curative were prepared in an internal mixer at 160°C. A simple blend (i.e., the blend without curative) was also prepared using the same materials and blend proportion for comparison purposes. Mechanical, dynamic, and morphological properties; swelling resistance and crosslink density of the blends were investigated. It was found that the thermoplastic vulcanizates (TPVs) gave superior mechanical and dynamic properties than the simple blend. Furthermore, the mechanical properties in terms of elongation at break, modulus and tensile strength and elastic response in dynamic test in terms of storage modulus increased with increased loading amount of the curative. The complex viscosity also increased but the tan δ and tension set decreased with increased loading level of the curative. The crosslink density of the TPVs was estimated based on the elastic shear modulus. It was found that the crosslink density of the blends increased with increased loading levels of the curative while the degree of swelling decreased. This correlated well with the trend of mechanical and dynamic properties. SEM micrographs were used to confirm the level of mechanical and dynamic properties. It was found that the simple blend at a given blend ratio exhibited co‐continuous phase morphology. However, the TPVs showed micron scale of vulcanized rubber domains dispersed in a continuous HDPE matrix. The size of vulcanized rubber domains decreased with increasing amounts of the curative. This led to greater interfacial adhesion between the phase and hence superior mechanical and dynamic properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of recyclable polybutadiene rubber based on acid–base complexation

Thermoreversible polybutadiene (PB) rubber is prepared by the self‐assembly of thiol‐ene functionalized PB oligomers containing amine and carboxylic acid groups, respectively, via acid–base reaction. The as‐formed ionic hydrogen bonds between the amine and carboxylic acid groups function as the crosslinking points to construct the polymer network. By controlling the crosslinking density, a series of materials ranging from soft gel to stiff solid with different physical properties can be obtained. The thermal reversibility of the ionic hydrogen bonds is evidenced by rheometry and temperature‐dependent FTIR spectra. In contrast to conventional covalently crosslinked rubbers, the thermoreversible PB rubbers prepared exhibit the capability of thermally reshaping and recycling. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45280.