The role of thiophosphoryl disulfide on the co‐cure of CR‐EPDM blends

Bis(diisopropyl)thiophosphoryl disulfide (DIPDIS) has been used as a coupling cum curing agent for the compatibilization of blends of ethylene propylene diene monomer rubber (EPDM) with chloroprene rubber (CR). Electrical and mechanical properties of the blend vulcanizates have been studied to find the efficiency of the vulcanizing cum coupling activity of DIPDIS. The study reveals that CR in the presence of DIPDIS greatly improves the physical properties of EPDM. It is noted that the physical properties of the vulcanizates obtained from CR‐EPDM blend depend upon CR:EPDM ratio. The scanning electron microscopy (SEM) study reveals that it is possible to form a coherent blend of CR and EPDM in the presence of DIPDIS. Copyright © 2004 John Wiley & Sons, Ltd.     

Plasma polymerization of acetylene onto silica: an approach to control the distribution of silica in single elastomers and immiscible blends

Surface modification of silica by acetylene plasma polymerization is applied in order to improve the dispersion in and compatibility with single rubbers and their blends. Silica, used as a reinforcing filler for elastomers, is coated with a polyacetylene (PA) film under vacuum conditions. Water penetration measurements show a change in surface energy due to the PA‐film deposition. The weight loss measured by thermo‐gravimetric analysis (TGA) is higher for the PA‐coated silica compared to the untreated filler, confirming the deposition of the PA film on the silica surface. Time of flight‐secondary ion mass spectrometry (ToF‐SIMS) shows the well‐defined PA cluster peaks in the high mass region. Scanning electron microscopy (SEM) measurements show silica aggregates, coalesced by the coating with smooth and uniform surfaces, but without significant change in specific surface area. Elemental analysis by energy dispersive X‐ray spectroscopy (EDX) measurements also confirms the deposition of the polymeric film on the silica surface, as the carbon content is increased. The performance of single polymers and their incompatible blends based on S‐SBR and EPDM, filled with untreated, PA‐ and silane‐treated silica, is investigated by measurements of the bound rubber content, weight loss related to bound rubber, cure kinetics, reinforcement parameter, Payne effect, and mechanical properties. The PA‐ and silane‐modified silica‐filled pure S‐SBR and EPDM samples show a lower filler–filler networking compared to the unmodified silica‐filled elastomers. Decrease in the reinforcement parameter (α_F) for the plasma‐polymerized silica‐filled samples also proves a better dispersion compared to silane‐modified and untreated silica‐filled samples. On the other hand, the PA‐silica‐filled samples show a higher bound rubber content due to stronger filler–polymer interactions. Finally, the PA‐silica‐filled pure EPDM and S‐SBR/EPDM blends show high tensile strength and elongation at break values, considered to be the result of best dispersion and compatibilization with EPDM. Copyright © 2008 John Wiley & Sons, Ltd.     

Fly ash particles and precipitated silica as fillers in NR/CR vulcanizates under thermal and thermal‐oil ageing

The loading effect of precipitated silica (PSi) and fly ash‐based silica (FASi) on mechanical properties of natural rubber/chloroprene (NR/CR) under thermal and thermal‐oil ageing was investigated with variation in NR content in the NR/CR blends. The selected results were compared with vulcanized NR/nitrile rubber (NR/NBR) blends. The cure time of CR vulcanizate was found to decrease with increasing NR content, but increased with silica fillers. The Mooney viscosity for CR vulcanizates reduced with increasing NR content. The addition of NR had no effect on tensile modulus and tensile strength for the FASi filled NR/CR, but the opposite trend was observed for the PSi filled NR/CR. The post‐curing effect was more significant in PSi filled NR/CR than in FASi filled NR/CR. The tensile strength of the NR/CR vulcanizates was slightly reduced after thermal ageing especially at high NR content, more extreme reduction being found by thermal‐oil ageing. The elongation at break of NR/CR with both silica fillers ranged from 400 to 900%. The hardness results were similar to the tensile modulus. The addition of PSi in NR/CR considerably increased the tear strength, but less pronounced effect was found for FASi. The resilience properties of NR/CR tended to decrease with increasing silica content. The compression set became poorer when NR content was increased. The PSi showed higher improvement in compression set than the FASi. The effects of silica and ageing on the mechanical properties for NR/CR vulcanizates were similar to those for NR/NBR vulcanizates. Copyright © 2009 John Wiley & Sons, Ltd.     

Ductile–brittle‐transition phenomenon in polypropylene/ethylene‐propylene‐diene rubber blends obtained by dynamic packing injection molding: A new understanding of the rubber‐toughening mechanism

For a more complete understanding of the toughening mechanism of polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, dynamic packing injection molding was used to control the phase morphology and rubber particle orientation in the matrix. The relative impact strength of the blends increased at low EPDM contents, and then a definite ductile–brittle (D–B) transition was observed when the EPDM content reached 25 wt %, at which point blends should fail in the ductile mode with conventional molding. Wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the shear‐induced crystal structure, morphology, orientation, and phase separation of the blends. WAXD results showed that the observed D–B transition took place mainly for a constant crystal structure (α form). Also, no remarkable changes in the crystallinity and melting point of PP were observed by DSC. The highly oriented and elongated rubber particles were seen via SEM at high EPDM contents. Our results suggest that Wu's criterion is no longer valid when dispersed rubber particles are elongated and oriented. The possible fracture mechanism is discussed on the basis of the stress concentration in a filler‐dispersed matrix. It can be concluded that not only the interparticle distance but also the stress fields around individual particles play an important role in polymer toughening. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2086–2097, 2002     

Reinforcement of compatibilized NR/NBR blends by fly ash particles and precipitated silica

Effects of precipitated silica (PSi) and silica from fly ash (FA) particles (FASi) on the cure and mechanical properties before and after thermal and oil aging of natural rubber (NR) and acrylonitrile–butadiene rubber (NBR) blends with and without chloroprene rubber (CR) or epoxidized NR (ENR) as a compatibilizer have been reported in this paper. The experimental results suggested that the scorch and cure times decreased with the addition of silica and the compound viscosity increased on increasing the silica content. The mechanical properties for PSi filled NR/NBR vulcanizates were greater than those for FASi filled NR/NBR vulcanizates in all cases. The PSi could be used for reinforcing the NR/NBR vulcanizates while the silica from FA was regarded as a semi‐reinforcing and/or extending filler. The incorporation of CR or ENR enhanced the mechanical properties of the NR/NBR vulcanizates, the ENR being more effective and compatible with the blend. The mechanical properties of the NR/NBR vulcanizates were improved by post‐curing effect from thermal aging but deteriorated by the oil aging. Copyright © 2008 John Wiley & Sons, Ltd.     

Difference in bound rubber formation of silica and carbon black with styrene‐butadiene rubber

Formation of bound rubber is affected by the physical structure and surface chemistry of filler and the property of rubber. Variation of the bound rubber formation in styrene‐butadiene rubber compounds filled with silica and/or carbon black was studied. Influence of temperature on extraction of loosely bound rubber was also investigated. For the both silica and carbon black‐filled compounds, the bound rubber content increases with increase in the silica content ratio. The bound rubber content decreases with increasing the extracting temperature. The loosely bound rubber content of the silica‐filled compound is higher than that of the carbon black‐filled one. Activation energy for the extraction of the unbound and loosely bound rubbers becomes higher as the total filler content increases. The activation energy of the silica‐filled compound is higher (almost double the value) than for the carbon black‐filled one. Copyright­© 2002 John Wiley & Sons, Ltd.     

Studies on the properties of EPDM–CSE blend containing HTPB for case‐bonded solid rocket motor insulation

Elastomeric blends based on ethylene propylene diene (EPDM) rubber as a primary polymer have been investigated for the thermal insulation of case‐bonded solid rocket motors (SRMs) cast with composite propellant containing hydroxy terminated polybutadiene (HTPB) as a polymeric binder. EPDM rubber found as an attractive candidate for the thermal insulation of case‐bonded SRM due to the advantages such as low specific gravity, improved ageing properties, and longer shelf life. In spite of these advantages, EPDM, a non‐polar rubber, lacks sufficient bonding with the propellant matrix. Bonding properties are found to improve when EPDM is blended with other polar rubbers like polychloroprene, chlorosulphonated polyethylene (CSE), etc. This type of polar polymer when blended with EPDM rubber enhances the insulator‐to‐propellant interface bonding. In the present work, an attempt has been made to study the properties of EPDM–CSE based insulator by incorporating HTPB, a polar polymer as well as a polymeric binder, as an additive to the EPDM–CSE blend by varying the HTPB concentration. Blends prepared were cured and characterized for rheological, mechanical, interface, and thermal properties to study the effect of HTPB addition. This paper reports the preliminary investigation of the properties of EPDM–CSE blend containing HTPB, as a novel and futuristic elastomeric insulation for case‐bonded SRM containing HTPB as propellant binder. Copyright © 2007 John Wiley & Sons, Ltd.     

Structure and properties of star‐shaped solution‐polymerized styrene‐butadiene rubber and its co‐coagulated rubber filled with silica/carbon black‐I: morphological structure and mechanical properties

The morphological structure and mechanical properties of the star‐shaped solution‐polymerized styrene‐butadiene rubber (SSBR) and organically modified nanosilica powder/star‐shaped SSBR co‐coagulated rubber (N‐SSBR) both filled with silica/carbon black (CB) were studied. The results showed that, compared with SSBR, silica powder could be mixed into N‐SSBR much more rapidly, and N‐SSBR/SiO₂ nanocomposite had better filler‐dispersion and processability. N‐SSBR/SiO₂/CB vulcanizates displayed higher glass‐transition temperature and lower peak value of internal friction loss than SSBR/SiO₂/CB vulcanizates. In the N‐SSBR/SiO₂/CB vulcanizates, filler was dispersed in nano‐scale resulting in good mechanical properties. Composites filled with silica/CB doped filler exhibited more excellent mechanical properties than those filled with a single filler because of the better filler‐dispersion and stronger interfacial interaction with macromolecular chains. N‐SSBR/SiO₂/CB vulcanizates exhibited preferable performance in abrasion resistance and higher bound rubber content as the blending ratio of silica to CB was 20:30. Copyright © 2008 John Wiley & Sons, Ltd.     

Great improvement of low‐temperature impact resistance of isotactic polypropylene/ethylene propylene diene monomer rubber blends by traces of carbon nanotubes and β‐nucleating agents

In this work, a considerable low‐temperature toughness enhancement of isotactic polypropylene (iPP) was achieved by adding 30 wt% ethylene propylene diene monomer rubber (EPDM) as well as traces of β‐nucleating agent (β‐NAs) and carbon nanotubes (CNTs). The impact strength of the iPP/30 wt% EPDM blend with 0.1 wt% β‐NAs reached 6.57 kJ/m² at ?20°C, over 2.5 times of pure iPP. A slightly improved impact strength was further found in the β‐nucleated iPP/30 wt% EPDM at the presence of 0.05 wt% CNTs. The presence of traces of CNTs, β‐NAs, and EPDM displayed synergistic low‐temperature toughness reinforcement effect on the iPP blends. The underlying toughening mechanism was attributed to the formation of a great amount of voids and plastic deformation of iPP matrix affected by CNTs, β‐NAs, and EPDM. Our work provided a feasible strategy to significantly increase the low‐temperature toughness of iPP.     

Uncross‐linked polypropylene (PP)/ethylene‐propylene‐diene (EPDM)/multi walled carbon nanotube (MWCNT) and dynamically vulcanized PP/EPDM/MWCNT nanocomposites

In this study, relatively large amounts of polypropylene (PP), ethylene‐propylene‐diene (EPDM), and multi‐walled carbon nanotube (MWCNT) were melt‐mixed with and without DCP. Dynamically vulcanized PP/EPDM (TPV)/MWCNT nanocomposites were prepared by two methods: the MWCNTs were added either before or after the dynamic vulcanization of the blends. The effects of composition, rotor speed, and dynamic vulcanization on their surface resistivity were investigated. The surface resistivity of uncross‐linked PP/EPDM/MWCNT nanocomposites increases with increasing the content of EPDM. At PP/EPDM (70/30 wt%) nanocomposite with 1.5 phr MWCNT, slightly lower surface resistivity is obtained by increasing the rotor speed during mixing. However, for PP/EPDM (50/50 wt%) and PP/EPDM (30/70 wt%) nanocomposites, surface resistivity decreases with increasing the rotor speed from 30 to 60 rpm. But further increase in rotor speed (90 rpm) leads to an increase of surface resistivity. When the MWCNTs were added after the dynamic vulcanization of the blends, the surface resistivity of TPV70/MWCNTnanocomposite is lower than that of uncross‐linked PP/EPDM/MWCNT nanocomposite. However, when the MWCNTs were added before the dynamic vulcanization of the blends, the surface resistivity of TPV70/MWCNT nanocomposite is >10¹² Ω/square. Copyright © 2010 John Wiley & Sons, Ltd.     

Three‐Dimensional Structure of Olefinic Thermoplastic Elastomer Blends Using Electron Tomography

Summary: The present communication reports the first use of electron tomography in reconstructing the three‐dimensional morphology in thermoplastic elastomer blends. The blends investigated were dynamically vulcanized blends of ethylene‐propylene‐diene (EPDM) rubber/poly(propylene)/oil and polystyrene‐block‐(ethylene‐co‐butylene)‐block‐polystyrene (SEBS)/poly(propylene)/oil. An easy identification of blend morphology could be carried out at blend compositions, where conventional transmission electron microscopic imaging gives misleading information. This technique gives a higher resolution than any other microscopic technique, and is applicable to blends with dispersed as well as co‐continuous morphologies.

Example of a tomographic model of partially co‐continuous SEBS phases in a SEBS/PP/oil thermoplastic blend. Only the contours of the SEBS phase are shown.     

Influence of reaction parameters on the structure of in situ rubber/silica compounds synthesized via sol–gel reaction

In situ silica was synthesized in three non‐vulcanized rubber matrices, namely natural rubber, styrene‐butadiene rubber, and EPDM (ethylene‐propylene diene ter‐polymer), using the sol–gel method with tetra‐ethoxysilane (TEOS) as silica precursor and hexylamine as catalyst. The effect of the reaction parameters such as the amount of TEOS, the reaction time (15–120 min), and the type of rubber was explored. Transmission electron microscopy was used to study the gradient in silica content and particle size over the sample thickness. The diffusion gradient of TEOS and catalyst solution in the rubber matrix responsible for the gradient was studied with Fick's law. An excellent dispersion of silica was obtained for all rubbers, even for the very non‐polar EPDM, without the use of any additives to improve the dispersion. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 967–978     

Preparation and characterization of vinyltriethoxysilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM‐g‐VTES/LLDPE) blends

Graft polymerization of vinyltriethoxysilane (VTES) onto ethylene‐propylene‐diene terpolymer (EPDM) was carried out in toluene using dicumylperoxide (DCP) as initiator. Effects of various parameters (EPDM content, VTES content, reaction time, reaction temperature and initiator concentration) on the grafting efficiency of VTES onto EPDM were investigated. At the optimum grafting efficiency conditions, EPDM‐g‐VTES was developed by melt mixing in a twin screw extruder and then linear (l), statically vulcanized (s) and dynamically vulcanized (d) blends of EPDM‐g‐VTES with linear low‐density polyethylene (LLDPE) with varying percentage compositions were prepared by melt mixing in the twin screw extruder. The grafting of VTES onto EPDM and its crosslinking was confirmed by FT‐IR. The characterization of mechanical properties such as tensile strength, elongation at break, Young's modulus and hardness, differential scanning calorimetry (DSC) analysis and morphology were studied and compared for the EPDM‐g‐VTES/LLDPE blends. The study reveals that the dynamically vulcanized blend improves the mechanical and thermal properties due to the presence of efficient interaction between component polymers when compared with other blends. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal stability of CR/CSM rubber blends filled with nano- and micro-silica particles

The properties of filled polymers depend on the properties of the matrix and the filler, the concentration of the components and their interactions. In this research we investigated the rheological and mechanical properties and thermal stability of polychloroprene/chlorosulfonated polyethylene (CR/CSM) rubber blends filled with nano- and micro-silica particles. The density of the nano-silica filled CR/CSM rubber blends was lower than that of the micro-silica filled samples but the tensile strength and elongation at break were much higher. The nano-silica filled CR/CSM rubber blend has higher V _r0/V _rf values than micro-silica composites and show better polymer–filler interaction according to Kraus equation. The nano-silica filled CR/CSM rubber blends were transparent at all filler concentration, and have higher glass transition values than micro-silica filled compounds. The higher values of the glass transition temperatures for the nano- than the micro-filled cross-linked systems are indicated by DMA analysis. The nano-filled cross-linked systems have a larger number of SiO–C links than micro-filled cross-linked systems and hence increased stability.     

Filler–polymer interactions in both silica and carbon black‐filled styrene–butadiene rubber compounds

Bound rubber in a filled rubber compound is formed by physical adsorption and chemisorption between the rubber and the filler. Styrene–butadiene rubber (SBR) is composed of four components of styrene, cis‐1,4‐, trans‐1,4‐, and 1,2‐units. Filler–polymer interactions in both silica and carbon black‐filled SBR compounds were studied by analyzing microstructures of the bound rubbers with pyrolysis‐gas chromatography. Differences in the filler–polymer interactions of the styrene, cis‐1,4‐, trans‐1,4‐, and 1,2‐units were investigated. The filler–polymer interactions of the butadiene units were found to be stronger than that of the styrene unit. The interactions of the cis‐1,4‐ and trans‐1,4‐units were stronger with carbon black than with silica, whereas the 1,2‐unit interacted more strongly with silica than with carbon black. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 439–445, 2001     

Effect of silane coupling agent on the polymer‐filler interaction and mechanical properties of silica‐filled NR

The effects of filler loading and a new silane coupling agent 3‐octanoylthio‐1‐ propyltriethoxysilane (NXT silane) on the polymer‐filler interaction and mechanical properties of silica‐filled and carbon black‐filled natural rubber (NR) compounds were studied. Silica (high dispersion silica7000GR, VN2, and VN3) and carbon black (N330) were used as the fillers, and the loading range was from 0 to 50 phr. The loading of NXT silane was from 0 to 6 phr. Experimental results show that the maximum and minimum torques of silica and carbon black‐filled NR increase with increasing filler loading. With increasing filler loading, the scorch time and optimum cure time decrease for carbon black‐filled NR, but increase for silica‐filled NR. The minimum torque, scorch time, and optimum cure time decrease because of the presence of NXT silane. For the carbon black and silica‐filled NR, the tensile strength and elongation at break have maximum values, but the hardness, M300, M100, and tear strength keep increasing with filler loading. The mechanical properties of silica‐filled NR were improved in the presence of NXT silane. With increasing filler loading, the storage modulus of filled NR increases, but the loss factor decreases. Carbon black shows the strongest polymer‐filler interaction, followed by VN3, 7000GR, and VN2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 573–584, 2005     

Effects of nucleating agents on microstructure and fracture toughness of poly(propylene)/ethylene‐propylene‐diene terpolymer blends

The effects of nucleating agents (NAs) on fracture toughness of injection‐molded isotactic poly(propylene)/ethylene‐propylene‐diene terpolymer (PP/EPDM) were studied in this work. Compared with PP/EPDM blends without any NA, PP/EPDM/NA blends show very small and homogeneous PP spherulites. As we expected, PP/EPDM blends nucleated with β‐phase NA aryl amides compound (TMB‐5) present not only a significant enhancement in toughness but also a promotion of brittle‐ductile transition. However, the addition of α‐phase NA 1,3:2,4‐bis(3,4‐dimethylbenzylidene) sorbitol (DMDBS) has no apparent effect on the toughness of the blends. The impact‐fractured surface morphologies of such samples were analyzed via scanning electronic microscope (SEM). More detail work about the toughening mechanisms of elastomer and NA based on elastomer particles size and matrix crystal structures were carried out. Our results suggest that, besides the crystal structures of matrix, the elastomer particles size and size distribution plays an important role in controlling the toughening effect of nucleated PP/elastomer blends. The smaller the elastomer particles size and lower the polydispersity, the more apparent the synergistic toughening effect of NA and elastomer is. This investigation provides a fresh insight into the understanding of toughening mechanism of elastomers in PP blends and facilitates to the design of super toughened PP materials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 46–59, 2009     

Preparation of polypropylene/ethylene‐propylene‐diene terpolymer/nitrile rubber ternary thermoplastics vulcanizates with good mechanical properties and oil resistance by core‐shell dynamic vulcanization

As the most successful commercialized thermoplastic vulcanizates (TPVs), polypropylene (PP)/ethylene propylene rubber (EPDM) TPVs exhibit poor oil resistance. In this work, we prepared PP/EPDM/butadiene acrylonitrile rubber (NBR) ternary TPVs with good oil resistance using core‐shell dynamic vulcanization. According to the theoretical analysis of the spreading coefficient and the transmission electron microscopy results, the rubber phases exhibited a special core‐shell structure, in which the cross‐linkedNBR‐core was encapsulated by the EPDM‐shell. The core‐shell structure effectively improved the interfacial compatibility between PP and NBR phase as the EPDM‐shell could avoid the direct contact of them, thus improving the mechanical properties of the TPVs. For example, the PP/EPDM/NBR (40/30/30) ternary TPV showed enhanced tensile strength of 12.57 MPa, compared with 10.71 MPa of PP/EPDM (40/60) TPV and 11.11 MPa of PP/NBR (40/60) TPV, respectively. Moreover, the oil resistance of the TPVs was also improved. Compared with PP/EPDM TPV, the change rates in mass, volume, tensile strength and elongation at break of PP/EPDM/NBR TPV after oil immersion decreased by 42.18%, 48.69%, 52.68% and 28.77%, respectively.     

Filler‐polymer interactions of styrene and butadiene units in silica‐filled styrene–butadiene rubber compounds

Styrene–butadiene rubber (SBR) is a copolymer of styrene and butadiene, and the butadiene unit is composed of cis‐1,4‐, trans‐1,4‐, and 1,2‐components. Filler‐polymer interactions of each component of SBR in silica‐filled SBR compounds were examined by microstructure analysis of the bound and unbound rubbers. The composition ratio of butadiene and styrene units (butadiene/styrene) of the bound rubber was higher than that of the compounded rubber. Of the butadiene units, the 1,2‐component of the bound rubber was more abundant than the cis‐1,4‐ and trans‐1,4‐components. The filler‐polymer interaction of the butadiene unit with silica was stronger than that of the styrene unit, and the interaction of the 1,2‐component was stronger as compared with the others. The butadiene–styrene ratio of the bound rubber of the compounds containing the silane coupling agent was lower than for the compounds without the silane. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 577–584, 2004     

高疲劳寿命氯丁橡胶基减振材料的结构与性能

以氯丁橡胶(CR)为基体材料, 将新型反式-1,4-丁二烯-异戊二烯共聚橡胶(TBIR)引入传统CR减振基体中, 探讨TBIR在减振材料中的应用前景. 研究发现, 随着TBIR用量的增加, CR/TBIR混炼胶的强度及模量明显提升; CR/TBIR硫化胶的拉伸强度、 撕裂强度、 压缩永久变形、 动静刚度比及耐疲劳性能均得到改善, 特别是一级疲劳寿命提高了50%~400%(未填充体系)及40%~180%(填充体系), 六级疲劳寿命提高了60%~500%(未填充体系)及30%~120%(填充体系). 与未填充CR/TBIR硫化胶相比, 填充CR/TBIR硫化胶由于炭黑补强作用及填料-聚合物相互作用的引入, 屈挠疲劳寿命、 撕裂强度及拉伸性能均显著提高. 与填充CR硫化胶相比, 填充CR/TBIR质量比为90/10的并用胶能够在保持硫化胶的损耗因子基本不变的基础上, 实现综合性能的平衡提升.