Influence of mixing procedures and curing time on molecular and topological structures of NR/BR vulcanizate

A rubber compound containing butadiene rubber (BR), natural rubber (NR), and carbon black was investigated by thermomechanical analysis (TMA). A difference in dynamics of the formation of molecular and topological structures of a vulcanizate were found to be dependent on the mixing technology and curing time. Separation of the topological structure of cured rubber into two blocks with differing transition temperatures was visible after 20 min of vulcanization, when a share of a low‐temperature block is minimal and M̄_n(n) reaches a stable value of about 2400. A low‐temperature block had a predominant concentration of covalent branching junctions, independent of the mixing procedures, whereas the high‐temperature block had covalent and topological junctions in concentrations that were dependent on the mixing method. For curing times longer than 20 min, the characteristic changes in values of M̄_n(n) are dependent on the procedure of rubber compound mixing. After additional homogenization of compounds and vulcanization, the rubbers are characterized by a diblock structure with the same qualitative structure of the branching junctions as for nonhomogenized ones. In some cases, the homogenization increases the relative concentration of the covalent junctions in the high‐temperature block. When a preblend of BR and carbon black was prepared first, and then mixed with NR, this technology makes rubber compounds less sensitive to additional homogenization during further processing. A mechanism of creation and transformation of rubber–carbon black junctions during compounding and vulcanization of rubber compounds with two raw rubbers that differed in adsorption ability was proposed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 660–669, 2000     

Rice‐husk‐ash‐filled natural rubber. II. Partial replacement of commercial fillers and the effect on the vulcanization process

In a previous investigation, we observed that in the presence of a conventional vulcanization system, the addition of white rice husk ash (WRHA) to natural rubber (NR) compounds increased the rate of crosslinking and lowered the apparent activation energy (E_a) of the vulcanization reaction more strongly than the other fillers used. In this work, commercial fillers, such as precipitated silica (Zeosil‐175) and carbon black (N762), were partially replaced by black rice husk ash and WRHA. Cure studies were carried out on a TI‐100 curometer at 150, 160, 170, and 180°C, and the overall rates and the E_a's for the vulcanization process were calculated for each compound, with the assumption that vulcanization followed first‐order kinetics. Again, WRHA showed some catalytic effect on the NR vulcanization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1405–1413, 2003     

Interfacial interactions and properties of natural rubber–silica composites with liquid natural rubber as a compatibilizer and prepared by a wet‐compounding method

Natural rubber–silica [W(NR–SiO₂)] composites were prepared by wet‐compounding technology with liquid natural rubber (LNR) as a compatibilizer. The effects of the LNR content and wet‐compounding technology on the filler dispersion, Payne effect, curing characteristics, mechanical properties, and interfacial interactions were investigated. The results show that the incorporation of LNR promoted vulcanization and decreased the Payne effect of the W(NR–SiO₂) composites. With the addition of 5 phr LNR, the remarkable improvements in the mechanical properties of the W(NR–SiO₂) vulcanizates were correlated with the improved silica dispersion and strengthened interfacial bonding. Furthermore, the W(NR–SiO₂) vulcanizates containing LNR exhibited improvements in both the wet‐skid resistance and rolling‐resistance performance. The interfacial interactions, quantitatively evaluated by the Mooney–Rivlin equation and Lorenz–Park equation on the basis of the rubber elasticity and reinforcement theory, were strengthened in the presence of LNR. Accordingly, an interfacial structural model was proposed to illustrate the improvements in the mechanical properties of the W(NR–SiO₂) composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46457.     

Premature vulcanization behaviors of rubber compounds under high shear rates processing

The premature vulcanization behaviors of six kinds of common rubber (NR, BR, SBR, NBR, CR, and EPDM) compounds containing curing agents were studied in a wide processing temperature range (100–140°C) and rotor speed range (30–70 rpm) using a Brabender torque rheometer, which can supply the rubber compounds a high shear rates processing condition. After comparison with the Mooney scorch time (MSt₅), it is shown that Mooney scorch time cannot predict the premature vulcanization time under high shear rate processing. Six models were put forward based on the data obtained from the Brabender mixing head. The regression analysis and variance analysis showed that these models could simulate the premature vulcanization time very well. An explanation was given based on the reactivity and of rubber chain segments: the increasing reactivity and the impact probability of reactive rubber chain segment under high shear rate is the main reason of shorter scorch time of rubber compounds under high shear rate internal mixing. © 2006 Wiley Periodicals, Inc. JAppl PolymSci 102: 5414–5420, 2006     

Vulcanization of chlorobutyl rubber. III. Reaction mechanisms in compounds containing combinations of zinc dimethyldithiocarbamate,tetramethylthiuram disulfide,sulfur, and ZnO

Poly(isoprene‐co‐isobutylene) (IIR or butyl) and chlorinated poly(isoprene‐co‐isobutylene) (CIIR or chlorobutyl) compounds containing combinations of zinc dimethyldithiocarbamate [Zn₂(dmtc)₄], tetramethylthiuram disulfide (TMTD), sulfur, and ZnO were vulcanized at 150°C, the reaction was stopped at various points, crosslink densities were determined by swelling, and the concentrations of residual curatives and extractable reaction intermediates and products were determined by high‐performance liquid chromatography and atomic absorption (ZnCl₂). In compounds that did not contain zinc, CIIR crosslinked more slowly than IIR and crosslinking could be explained by the same mechanism as applies to the vulcanization to highly unsaturated rubbers like polyisoprene. In zinc containing compounds, CIIR crosslinked faster because of dehydrohalogenation reactions that led to carbon–carbon crosslinks. As found with ZnO/ZnCl₂ formulations, both ZnCl₂ and conjugated diene butyl are essential precursors to crosslink formation. Zn₂(dmtc)₄ can trap HCl, thus preventing reversion and may also initiate dehydrohalogenation. When the equilibrium crosslink density is reached, 50% of the chlorine originally present in the rubber is extractable as ZnCl₂ and the remainder as dimethylthiocarbamic acid chloride. A mechanism to account for dehydrochlorination and crosslinking in the presence of Zn₂(dmtc)₄ is presented. In compounds with sulfur, crosslinking occurs via accelerated sulfur vulcanization and chlorine abstraction, leading to higher crosslink densities than is achieved with either curative system on its own. Carbon–carbon crosslinks predominate, the slower, accelerated sulfur reaction, making a lesser contribution to the overall reaction. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1309–1316, 2001     

Analysis of network structure formed in styrene–butadiene rubber cured with sulfur/TBBS system

Several styrene–butadiene rubber (SBR) compounds were prepared with different cure systems based on sulfur and TBBS (N‐t‐butyl‐2‐benzothiazole sulfenamide), varying the amount of sulfur and accelerator between 0.5 and 2.5 phr in the formulation. Torque curves, measured with a moving die rheometer at temperatures at 433 K, were used to characterize the vulcanization. The time to achieve the maximum torque, t_100%, was evaluated for each sample, and this time was set to vulcanize sheets at 433 K. The density and type of elastically active crosslinks of each cured sample were evaluated by means of swelling measurements and were related to the vulcanizing system. Finally, the rheometer data were analyzed considering the network structure formed during vulcanization. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1105–1112, 2007     

Effects of modified silica on the co-vulcanization kinetics and mechanical performances of natural rubber/styrene–butadiene rubber blends

Rubber blends are widely used for combining the advantages of each rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co-vulcanization process is still a challenge. Herein, high-resolution pyrolysis gas chromatography–mass spectrometry (HR PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene–butadiene rubber (SBR) in NR/SBR blends filled with modified silica (SiO₂). The reaction rates of crosslinking of each rubber phase in NR/SBR were calculated, which showed that the crosslinking rates of NR were much lower than those of SBR phase in the unfilled blends and blends filled with unmodified and silane modified silica. Interestingly, the vulcanization rates of NR and SBR phase were approximately same in the vulcanization accelerator modified silica filled blends, showing better co-vulcanization. In addition, the vulcanization accelerator modified silica was uniformly dispersed and endowed rubber blends with higher mechanical strength compared to the untreated silica. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48838.     

THE COMPARISON PROPERTIES OF RECYCLE RUBBER POWDER,CARBON BLACK,AND CALCIUM CARBONATE FILLED NATURAL RUBBER COMPOUNDS

The effects of filler loading on the curing characteristics, swelling behavior, and mechanical properties of natural rubber compounds were studied using a conventional vulcanization system. Recycle rubber powder (RRP), carbon black (CB) (N550), and calcium carbonate (CaCO₃) were used as fillers and the loading range was from 0 to 50 phr. Results show that the scorch time, t ₂, and cure time, t ₉₀, decrease with increase in filler loading. At a similar filler loading, RRP shows shortest t ₂ and t ₉₀ followed by CB and calcium carbonate. The tensile strength, tensile modulus, and hardness increase with increase in CB loading, whereas elongation at break, resilience, and swelling properties show opposite trend. For RRP and calcium carbonate filled natural rubber compounds, the tensile strength increases up to 10 phr and starts to deteriorate at higher filler loading. The other properties such as tensile modulus, hardness, elongation at break, resilience, and swelling percentage show a small change (increase or decrease) with increase in RRP and calcium carbonate loading in natural rubber compounds. Overall results indicate that RRP can be used as a cheapener to replace calcium carbonate in natural rubber compounds where improved mechanical properties are not critical.     

Effects of palm oil fatty acid on curing characteristics,reversion and fatigue life of various natural rubber compounds

The effects of palm oil fatty acid concentration (0, 1, 3, 5, 7 phr) and epoxidation on curing characteristics, reversion and fatigue life of carbon black filled natural rubber compounds have been studied. Three different types of natural rubber, SMR L, ENR 25 and ENR 50 having 0, 25 and 50 mol% of epoxidation and conventional sulphur vulcanization were used. The cure time t₉₀, scorch time t₂, M_HR − M_L (maximum torque − minimum torque) and fatigue life of all rubbers were found to increase with increasing palm oil fatty acid concentration. However, the reversion of all rubbers decreases with increasing palm oil fatty acid concentration. At similar concentrations of palm oil fatty acid, ENR 50 compounds exhibit the shortest scorch and cure times followed by ENR 25 and SMR L compounds. For reversion, SMR L compounds show the lowest value followed by ENR 50 and ENR 25 compounds, whereas for fatigue life, the highest value is obtained with ENR 50 compounds followed by ENR 25 and SMR L compounds. © 1999 Society of Chemical Industry     

Evidence of ionic components in vulcanization mixtures by means of electric current measurements: Investigations with natural rubber/sulfur/zinc bis(dimethyldithiocarbamate) and comparison mixtures

Continuous low‐level current (CLLC) measurements for detecting ionic species in the course of vulcanization reactions were applied to investigate the vulcanization of a mixture of natural rubber (NR), sulfur (S), and zinc bis(dimethyldithiocarbamate) (ZnDMTC). A dc voltage was applied to the reaction mixture in a special vulcanization mold and the current (e.g., in the range of 10⁻⁹ A) was measured. Temperature‐dependent current maxima were found after reaction times t_max. The simplest explanation is that transitory ionic species occur during vulcanization. An activation energy (E_a ) = 116.4 kJ/mol, similar to that obtained in previous chemical investigations, was determined from the decrease of t_max with increasing temperature. The maxima corresponded to reaction times where a strong increase of polymer crosslinking was observed, as measured using vulcametry. For comparison, dc measurements were carried out with the corresponding mixture without elemental sulfur (NR/ZnDMTC) and mixtures containing zinc stearate (ZnST) instead of zinc bis(dimethyldithiocarbamate) (NR/S/ZnST and NR/ZnST). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2206–2212, 2000     

Cure behavior and antimicrobial performance of sulfur‐cured natural rubber vulcanizates containing 2‐hydroxypropyl‐3‐piperazinylquinolinecarboxylic acid methacrylate or silver‐substituted zeolite

This work used 2‐hydroxypropyl‐3‐piperazinylquinolinecarboxylic acid methacrylate (HPQM) or silver‐substituted zeolite (SSZ) as antibacterial agents for natural rubber (NR) compounds vulcanized by conventional vulcanization (CV), semi‐efficient vulcanization, and efficient vulcanization (EV) systems. The cure behavior and antibacterial performance of the NR vulcanizates were studied by varying the loadings of HPQM or SSZ, contact times, and vulcanization systems. The antibacterial performance of the rubber compounds was examined by halo test and plate‐count‐agar methods against Escherichia coli (E. coli, ATCC 25922) and Staphylococcus aureus (S. aureus, ATCC 25923) as the testing bacteria. The cure time and crosslink density were dependent on the vulcanization recipe used but were not affected by the addition of HPQM or SSZ. Diphenylguanidine at the level of 1.0 phr (parts by weight per hundred parts of resin) in NR vulcanized by the EV system had the ability to kill the E. coli and S. aureus bacteria. The NR vulcanized by the CV system showed the most pronounced antibacterial performance, as compared with the other two vulcanization systems, via migration and diffusion of HPQM or SSZ onto the NR surfaces, this being identified by the relatively large reduction of contact angle values. The HPQM showed the most preference for NR compounds vulcanized with the CV system with a contact time of 120 min or longer to achieve a bacteria‐killing efficacy of 99.0–99.9%, the efficacy being more pronounced for E. coli bacteria. J. VINYL ADDIT. TECHNOL., 19:123–131, 2013. © 2013 Society of Plastics Engineers     

Sorption and diffusion of acrylonitrile monomer through crosslinked nitrile rubber

As the first step for the preparation of interpenetrating polymer networks from nitrile rubber and polyacrylonitrile, the sorption and diffusion of acrylonitrile monomer through nitrile rubber crosslinked by three different vulcanization systems—conventional (CV), dicumyl peroxide (DCP), and a mixture consisting of sulfur and peroxide (mixed)—were studied in the temperature interval of 30–70°C. Kinetic curves have been generated for these systems to compute diffusion and sorption coefficients. The equilibrium sorption is found to be maximum for the CV system. The molar mass between crosslinks (M_c) has estimated and compared with affine and phantom models. It was found that the M_c values follow the affine model. The diffusion coefficient values are highest for DCP and lowest for CV. It was observed that the kinetics of liquid sorption followed an anomalous behavior. The temperature dependence of the transport parameters was followed by an Arrhenius relationship, from which the activation energy for diffusion, permeation, and sorption were calculated. It is found that temperature activates diffusion in all cases. The polymer–solvent interaction parameter was determined. The amount of polysulfidic linkages in the rubber network was also estimated. The experimental results were compared with theoretical predictions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 941–952, 2000     

Utilization of silane functionalized carbon nanotubes‐silica hybrids as novel reinforcing fillers for solution styrene butadiene rubber

Carbon nanotubes‐silica (CNTs‐SiO₂) nanohybrid filler was fabricated by coating inorganic silica on multi‐wall CNTs through a sol–gel process. The CNTs‐SiO₂ nanohybrids were then functionalized by 3‐methacryloxypropyltrimethoxysilane (3‐MPTS) followed by compounding to solution styrene butadiene rubber (S‐SBR) through mechanical mixing. The Fourier‐transform infrared spectroscopy showed that the CNTs were coated by inorganic SiO₂, and grafted with 3‐MPTS successfully. The functionalized CNTs‐SiO₂ nanohybrids had a rough surface as revealed by transmission electron microscope images. After hybridization and grafting, the functionalized CNTs‐SiO₂ nanohybrids still maintained the crystal structure of CNTs, which was determined by X‐ray diffraction and Raman spectrum. The addition of nanohybrids accelerated the vulcanization process and improved the crosslinking degree of vulcanizates. With adding 10 phr (parts per hundred of rubber) functionalized CNTs‐SiO₂, the mechanical properties of S‐SBR vulcanizates were improved significantly. The tensile moduli at 100% elongation (M₁₀₀) and tensile strength had 54% and 28% increase, respectively. The incorporation of functionalized CNTs‐SiO₂ nanohybrids also largely enhanced the storage modulus, and slightly increased the thermal conductivity of vulcanizates. POLYM. COMPOS., 00:000–000, 2013. © 2013 Society of Plastics Engineers POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Effect of electron-beam irradiation on the thermal vulcanization of a natural rubber compound

The influence of electron-beam irradiation on the thermal vulcanization curing kinetics of a natural rubber compound was investigated by means of rheometric tests [moving die rheometry (MDR)] and differential scanning calorimetry (DSC). Differences in the storage moduli of compounds with different radiation doses were observed and assigned to a plasticizer effect by the zinc stearate mainly formed in the mixing stages; this compound migrated to the interphase region. This fact was confirmed by Fourier transform infrared spectroscopy. From the measurements performed by MDR and DSC testing, the induction time (t_o) was analyzed in the frame of the Claxton–Liska model, whereas the kinetic behavior of the nonirradiated and pre-irradiated compounds were satisfactorily fitted with the Isayev–Deng and Kamal–Ryan models. Additionally, both curing characterization techniques corroborated the fact that the pre-irradiated rubber compound showed an earlier t _o and a lower activation energy in comparison with the nonirradiated compound. These facts were attributed to the effect of irradiation on the free sulfur content present in the rubber compound, which promoted more activated precursor species to crosslink with rubber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47216.     

Investigation of crystallization behavior in dynamically vulcanized EPDM–nylon copolymer blends

A thermoplastic vulcanizate (TPV) of a ethylene–propylene–diene terpolymer (EPDM) and nylon copolymer (PA) was prepared by dynamic vulcanization. Maleic anhydride (MAH)–grafted EPDM (EPDM–g–MAH), MAH‐grafted EPR (EPR–g–MAH), and chlorinated polyethylene (CPE) were used as compatibilizers. The effect of dynamic vulcanization and compatibilizer on the crystallization behavior of PA was investigated. Differential scanning calorimeter measurement results showed no pronounced shift in the crystallization temperature for PA in EPDM–PA TPV compared to that for PA in the neat state, whereas the crystallization temperature increased after adding compatibilizer. The decrease in the crystallinity of TPVs was a result of the crystallization occurring in confined spaces between rubber particles. The equilibrium melting temperature (Tm⁰) of the PA copolymer was measured and was determined to be 157°C. The isothermal crystallization kinetics of PA in the neat and TPV states also was investigated. The crystallization rate was highest in the compatibilized TPV and lowest in the neat PA, whereas it was intermediate in the uncompatibilized TPV unvulcanized blends. Compared with unvulcanized EPDM–PA blends, the dynamic vulcanization process seemed to cause an obvious increase in the crystallization rate of the PA copolymer, especially when a suitable compatibilizer was used. This occurred because the dynamic vulcanization introduced fine crosslinked rubber particles that could act as heterogeneous nucleating centers. In addition, the use of a suitable compatibilizer permitted the formation of finely dispersed vulcanized rubber particles and therefore increased the density of the nucleating centers. The complex morphology of the blends was investigated by atomic force microscopy to evaluate the effect of compatibilizer on the size of the dispersed rubber particles. Compared with the morphology of TPVs with the same dosage of EPDM–g–MAH compatibilizer, the morphology of TPVs using EPR–g–MAH as compatibilizer showed much smaller dispersed rubber particles, which may have contributed to the higher crystallization rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 824–829, 2003     

Rice husk ash filled natural rubber. III. Role of metal oxides in kinetics of sulfur vulcanization

In preceding investigations the overall rate and apparent activation energy for the vulcanization process were calculated for natural rubber compounds, assuming that vulcanization follows first‐order kinetics. It was observed that the addition of white rice husk ash (WRHA) increased the rate of crosslinking and lowered the apparent activation energy more profoundly than commercial fillers, precipitated silica (Zeosil‐175) and carbon black (N762), with a conventional vulcanization system. In this work, a specific model for the vulcanization process accelerated by N‐cyclohexylbenzothiazole sulfenamide was used to investigate the real role of WRHA in crosslink formation. Cure studies were carried out at 150°C, and the kinetics constants were evaluated. In relation to the other fillers, WRHA seems to develop catalytic activity, resulting in a positive effect on the specific rate of crosslink formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1519–1531, 2003     

Synthesis of Zn/Mg oxide nanoparticles and its influence on sulfur vulcanization

To reduce the ZnO levels in rubber compounds, mixed metal oxide nanoparticles of zinc and magnesium (Zn_1−xMg_xO) have been synthesized and used as activator. The aim is to obtain better curing properties due to its nanosize and to take advantage of the behavior of both ZnO and MgO in sulfur vulcanization. The model compound vulcanization approach with squalene as a model molecule for NR and CBS as accelerator has been used to study the role of the mixed metal oxide along the reaction. The results found show that with Zn_1–xMg_xO nanoparticles the reaction of CBS becomes faster, higher amounts of MBT are formed at shorter reaction times, and the consumption of sulfur occurs faster in comparison with standard ZnO. Furthermore and more important, an increased crosslink degree calculated as the total amount of crosslinked squalene is obtained. All these findings indicate that Zn_1−xMg_xO is a promising candidate to reduce the ZnO levels in rubber compounds. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Nano ZnO as cure activator and reinforcing filler in natural rubber

Zinc oxide (ZnO) nanoparticles of size 20–90 nm and surface area 9.56 m²/g were synthesized from ZnCl₂ and Chitosan and characterized by X‐ray diffraction, high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). Natural rubber (NR) vulcanizates containing nano ZnO was prepared by mill mixing and characterized by SEM, energy dispersive X‐ray analysis (EDAX), and HRTEM. Cure characteristics, free volume studies, bound rubber, crosslink density, and dynamic mechanical properties were evaluated and compared with that of NR vulcanizate containing conventional micro ZnO. Considering the cure characteristics, it was found that NR vulcanizate with 0.5 phr (parts per 100 g rubber) of nano ZnO showed low values of optimum cure time (t₉₀) and very high cure rate index compared with 5 phr of conventional micro ZnO. The study shows that micro ZnO can be successfully replaced with nano ZnO for accelerated sulfur vulcanization process in NR, and preparation of vulcanizate containing nano ZnO with better properties as that of micro ZnO. The optimum dosage of nano ZnO as a cure activator in NR vulcanization was found to be 0.5 phr compared with conventional grade micro ZnO. This will lead to substantial cost reduction in the manufacture of rubber products and alleviate environmental pollution due to excess ZnO in rubber compounds. POLYM. ENG. SCI., 2013 © 2013 Society of Plastics Engineers     

A new approach for kinetic modeling and optimization of rubber molding

Although extensive research has been carried out on the understanding of the complex vulcanization process, the influence of reversion through exposure time and temperature on the vulcanization degree remains unclear. Therefore, the main aim of this study was a novel optimization approach that can help the industrial practitioners to select the optimal operating parameters, exposure time, and molding temperature, to achieve desired vulcanization degree of selected product. Spheres of four different diameters (2.5, 5, 10, and 20 cm) were selected as test geometry for simulation and optimization of rubber molding. Obtained vulcanization rheometer data for commercially available rubber blend (NR/SBR) were fitted by a new modeling approach, dividing vulcanization curve into two fitting sets: curing and reversion. The heat transfer equations for chosen geometry were coupled with proposed kinetic model. A new temperature-dependent kinetic parameter x, as the maximal reversion degree, was introduced, enabling determination of the lowest operating molding temperature (T_min = 132.36 °C), preventing high reversion and overheating of the rubber product. The final optimization goal was assessment of the optimal temperature and vulcanization time dependence on the rubber products dimensions. Proposed models have precise prediction with R² values greater than 0.8328 and MAPE less than 2.3099%.     

Thermal aging properties and chemical resistance of blends of natural rubber and epoxidized low molecular weight natural rubber

Studies into solvent resistance and aging properties of blends of natural rubber and epoxidized low molecular weight natural rubber were carried out. Vulcanization of the blends using the semi‐efficient vulcanization (semi‐EV) system was found to have curing advantages over conventional vulcanization (CV) and efficient vulcanization (EV) systems. The rheological properties (cure time, t₉₀, and scorch time, t₂), solvent resistances, and aging properties of the vulcanizates were found to improve as the level of epoxidized low molecular weight natural rubber in the blends increases. The mechanical properties of the blends were also found to be within the accepted level for NR vulcanizates. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1733–1739, 2005