Cure Rate Index Research Articles

Sustainable Kerala rice husk ash for formulation of basic tyre tread: Taking first step

From a ‘Waste to Wealth’ standpoint, sustainable conversion of agricultural waste materials into value-added products is of crucial importance. The study compares the BET surface area of 5 different rice husk ash varieties: Jyothi (RHA), Jaya (RHA-1), Kanchana (RHA-2), Uma (RHA-3), and Valichoori (RHA-4). The different rice husk ashes were prepared through the calcination of dried rice husk at 700 °C for 2 h. The resulting rice husk ashes and commercial silica (CS) were characterized using FT-IR, XRD, SEM, TEM, DLS, XRF and BET surface area. For the first time, we report on the potential of Kerala rice husk nanoash (Jyothi variety-RHA) with a high surface area (79.33 m2/g) in the development of a basic tyre tread. Natural rubber (NR) composites were prepared by replacing 5phr of carbon black (CB) with 5phr RHA, and 5phr commercial silica (CS). The different composites prepared were designated as NRCB50 (with 50phr CB), NRCB45RHA5 (with 45phr CB and 5phr RHA), and NRCB45CS5 (with 45phr CB and 5phr CS). A comparative study with NR-NEAT (with no filler) was also conducted. The cure rate index was higher for RHA-filled vulcanizates compared to RHA-free composites. Except for abrasion resistance, mechanical properties of NRCB50 and NRCB45RHA5 composites were comparable. The thermo-gravimetric analysis revealed onset degradation temperature ranking as NRCB45RHA5˃NRCB50˃NRCB45CS5. Moreover, dynamic mechanical analysis (DMA) showed no obvious loss in glass transition temperature (Tg). The loss tangent (tan δ) values at 60 °C and 0 °C suggested that the rolling resistance can be significantly reduced by replacing 5phr CB with 5phr RHA without affecting the ice traction.

Effect of Organomodified Bentonite/Silica Hybrid Filler Compound System on Mechanical Properties and Sealing Performance of NR/NBR Rubber Seal for LPG Tube Valve

Organomodified bentonite and silica were used as hybrid fillers in natural rubber (NR)/nitrile butadiene rubber (NBR) seal for liquified petroleum gas (LPG) tube valve compound to evaluate their interaction and influence on mechanical properties and sealing performance. In this work, the NR-organomodified bentonite were prepared by the in situ organomodified and latex compounding method with varying amounts of bentonite then applied in the silica-NR/NBR rubber seal compounds with mixing process held in two rolls open mill. Silanization reaction, Payne effect, curing characteristics, tensile properties, compression set, hardness, uniaxial compression and sealing performance were assessed. The study obtained that NR/NBR-silica/organomodified bentonite show improved silica dispersion physically, as analyzed by Payne effect. The presence of organomodified bentonite decreases the vulcanization reaction. The cure rate index, apparent crosslink density and hardness tend to decrease with addition of organomodified bentonite, while tensile strength and elongation at break are enhanced with increasing organomodified bentonite. With an appropriate amount of organomodified bentonite (organomodified bentonite below 4 phr), the introduction of organomodified bentonite enhances the elastic response of the material, as shown by increasing of tensile properties. The rubber seal’s sealing performance analysis revealed that B4 (4 phr organomodified bentonite) performed the best, with contact stress higher than the actual working pressure and Misses stress lower than the actual working pressure, making it difficult to crack.

Effect carbon black and modified kaolin hybrid filler on the curing and physic-mechanical properties of natural rubber-styrene butadiene rubber blends

Carbon black is known as an excellent reinforced filler for rubber compounding, this petroleum based product needs to be substituted using renewable or mineral filler due to some negative adverse. In this paper, natural rubber (NR) – styrene-butadiene rubber (SBR) (50/50) phr binary blends based on polyethylene glycol-modified kaolin (PEG-K) and carbon black CB hybrid filler were synthesized. The rubber formulation was designed for idler roller for charcoal conveyor in open peat mining application. The present study investigates the effect of PEG-K and CB composition on curing, physical, tensile and oil, and acid resistance of the binary blends. The effect was examined by varying the composition of PEG-K/CB as follows: 50/0; 40/10; 30/20; 20/30; 10/40; 0/50 phr/phr of the hybrid filler. The rubber compounding was conducted in accordance with the ASTM D3142, and the testing procedures were analyzed based on international standards. The vulcanizates were prepared by heating press at 140 °C for about 25 minutes. The results showed that the processing-ability of a single filler is easier than the higher hybrid filler. The rheological analysis showed that the higher PEG-K may increase the cure rate index, but the lower PEG-K might improve cross-linking density. The higher loading CB improved the specific gravity and hardness, tensile strength slightly, while there is less significant effect on decreasing compression set, abrasion resistance, and elongation at break. Meanwhile, the higher number CB of binary blends has better oil and acid resistance than the PEG-K. Compared to idler roller specification in the market, the vulcanizates in this research have better quality.

Green and sustainable biosynthesis of iron oxide nanoparticle (ION) from pomegranate seed and the development of highly reinforced ION based natural rubber (NR) nanocomposite in presence of epoxidized natural rubber (ENR) as compatibilizer

This research article explores a green and sustainable approach for the biosynthesis of iron oxide nanoparticles (ION) from a natural source of non-edible waste part, seed of pomegranate fruit and the studies its application in natural rubber (NR) as reinforcing filler along with a compatibilizer, ENR. The formation of naturally deep brown colored ION was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM) analysis and Energy dispersive X-ray (EDX) microanalysis. The experimental studies shows that the combination of only 1 part per hundred parts of rubber (phr) of the ION and 3phr of ENR can outstandingly increase the overall tensile strength (TS) by nearly 41% and improve others cure and mechanical properties of the NR composite. The cure properties like the maximum rheometric torque (R∞) and the cure rate index (CRI) are increased and the vulcanization time is saved by nearly 24%. The mechanical properties like the modulus at 100%, 300% elongation and the EB (%) are improved in presence of 1phr ION and 3phr of ENR. The thermal aging resistance and thermal stability of the NR composites are also improved in presence of both the ION and the ENR. The compatibility among the ION, ENR and NR was confirmed by analyzing the thermodynamic parameters ΔG and ΔS. The morphology of the nanocomposite was studied by FESEM analysis which confirms the uniform distribution of ION throughout composite matrix. The improvement in the thermal stability of the NR composite is confirmed by the oxidative thermal aging behavior and thermogravimetric analysis (TGA) & derivative thermogravimetric analysis (DTG).

Evaluation of lignin as potential green filler in an optimally designed solution grade styrene–butadiene rubber (SSBR) based tyre tread compound

ABSTRACT In this study, solution grade styrene–butadiene rubber (SSBR) compound was prepared by partial replacement of silica with lignin. The compounds were designed and optimised using an L9 orthogonal array (using Taguchi method) targeting ‘magic triangle’. Cure rate index (CRI), reinforcement index (RI) and hysteresis loss (loss tangent at 60°C) were considered as the responses. Thermo-gravimetric analysis and Differential scanning calorimeter is used to assess thermal degradation and intramolecular reactivity of lignin. Morphological analysis of the composites has instituted the fact that above 20% replacement of synthetic silica by lignin results in re-agglomeration of filler particles due to inferior dispersion. Response analysis through ANOVA coupled with an experimental study on physico-mechanical and dynamic-mechanical properties has manifested that SSBR with 58% vinyl content with 40:10 silica: lignin compounded at 160°C with 10% silane coupling agent (SCA) with respect to silica at factorial levels furnished a ‘magic triangle’ optimised tyre tread compound.

Using chemical agent in microwave assisted devulcanization of NR/SBR blends: An effective recycling method

The aim of this research was using a new chemical devulcanizing agent (i.e. VitaX) in devulcanization of NR/SBR blend as a model compound of tire rubber by microwave (MW) irradiation. For this purpose, the rubber compounds were prepared at different natural rubber (NR) to styrene butadiene rubber (SBR) ratios (40:60, 50:50, 60:40, 70:30 and 80:20). The rubbers were cured and then ground to particles with different mesh sizes (3, 4, 8, 16 and 30). The effect of irradiation time, stirring speed and particle size on sol/gel fractions, crosslink density (CLD) and devulcanization percent (DP) of the microwave irradiated samples was evaluated. Thereafter, effects of using VitaX and its content (0.3, 0.6, 1, 2, 3 and 4 phr) on devulcanized samples was evaluated. Results showed that using VitaX along with microwave irradiation caused decrease in the CLD and increase in the DP (from 9.51 to 34.85%) compared to the microwave assisted devulcanized samples. Finally, the raw NR/SBR rubber compound were replaced by different contents (10, 20 and 30 phr) of the chemical-microwave assisted devulcanized sample. The mechanical and curing properties of the samples were evaluated by tensile test and Oscillating Disk Rheometer (ODR), respectively. The results showed that at replacing content of 10 wt.%, decrement in the curing time and increment in the scorch time, cure rate index (CRI) and CLD was occurred in the re-vulcanized compound. The chemical-MW irradiation based devulcanization method was found to be a promising method for effective recycling of NR/SBR based rubbers such as tire rubbers.

Smart TPE Materials Based on Recycled Rubber Shred.

Thermo-responsive shape memory materials were developed based on recycled ethylene-propylene-diene (EPDM) rubber shred and thermoplastic elastomers (TPE). Ethylene-1-octene TPEs (Engage 8180, 8411, 8452) with varying degrees of crystallinity and Mooney viscosity were used to prepare the composite materials. To avoid the deterioration of static mechanical properties after mixing recycled EPDM rubber shred (RS) with thermoplastic elastomers, they were partially cured using dicumyl peroxide. The peroxide curing was the most effective for a rubber shred/Engage 8180 blend, where the highest cure rate index (CRI), 1.88 dNm⋅min−1, was observed. The curing caused an approximately 4-fold increase of tensile strength (TS) values for EPDM rubber shred/thermoplastic elastomer blend to the level acceptable for the rubber industry compared with an uncured blend. The incorporation of EPDM rubber shred changed thermoplastic elastomers’ viscoelastic behavior, increasing the values of storage (G′) and loss (G″) modulus. The lowest viscosity of molten Engage 8411 during mixing led to higher compatibility of rubber shred RS/8411 blend, as confirmed by analysis of Cole-Cole plots and the blend morphology. All rubber shred RS/TPE blends showed the shape memory behavior. For the RS/Engage 8452 blend, the highest shape fixity (F) value (94%) was observed, while the shape recovery (RR) was 87%. Studies confirmed that the intelligent materials with shape memory effect could be obtained via selectively chosen thermoplastic elastomers; ethylene-1-octene as a binder for recycled EPDM. Prepared recycled TPE/rubber shred blends can be successfully reused due to their viscoelastic and mechanical properties. Therefore, such a concept can be potentially interesting for the rubber industry.

Significantly reinforced and long serviceable acrylonitrile butadiene rubber/graphitic carbon nitride composites for future industrial applications

The application of graphitic carbon nitride (g-C3N4) as non-black reinforcing filler is very little-known part in rubber technology. In the present study, g-C3N4 filled acrylonitrile butadiene rubber (NBR) composites were prepared by conventional two-roll milling process to investigate the influence of g-C3N4 on the mechanical and thermal performances of NBR formulations. NBR composite with 3 phr (parts per hundred parts of rubber) g-C3N4 presents considerably higher cure rate index, hardness, tensile strength, storage modulus and thermal stability than unfilled NBR composite. Also, the addition of g-C3N4 successfully enhances the thermal oxidative aging resistance and fuel consumption efficiency of NBR composites. Thus, g-C3N4 can be used in the near future as interesting filler for developing long serviceable NBR composites with good mechanical properties.

Impact of α‐cellulose as a green filler on physico‐mechanical properties of a solution grade styrene‐butadiene rubber based tire‐tread compound

AbstractPhysico‐mechanical and dynamic mechanical properties of typical solution grade styrene‐butadiene rubber (S‐SBR) and polybutadiene rubber (PBR) based tire‐tread compound were investigated by partially replacing highly dispersible (HD) silica with naturally occurring α‐cellulose. Fourier transform infrared spectrum detected abundance of hydroxyl group in α‐cellulose, which has created keenness to investigate its reinforcement characteristics in an S‐SBR and PBR based compound. Scanning electron microscope and transmission electron microscope were employed to investigate the microstructure and dispersion of α‐cellulose at higher magnification. Thermo‐gravimetric analysis was performed to understand the degradation behavior of α‐cellulose. Differential scanning calorimeter was engaged to detect phase transition and degree of purity of α‐cellulose. An increase in cure rate was observed with partial replacement of HD silica by α‐cellulose. The cure rate index was increased by 13% over control one at 10% replacement of silica with α‐cellulose. It was noticed that at an optimum level of replacement (10%), α‐cellulose containing compounds exhibited lower viscoelastic energy dissipation (both loss modulus [E″] and loss tangent [tan δ]) at the slight expense of tensile moduli. Beside these, substitution of silica with α‐cellulose found to have no effect on wet grip property of the compounds.

Effect of nano‐silver coated carbon black on curing, mechanical, antimicrobial, and electrical properties of natural rubber composite

AbstractNano‐silver coated carbon black (Ag/CB) was prepared via the green coating process and used as a multifunctional additive in natural rubber (NR). The Ag/CB was mixed with NR in varying amounts of 10, 20, and 30 parts per hundred rubber. Curing characteristics, morphology, mechanical and antimicrobial properties, and electrical conductivity of the rubber composites were investigated. Scorch time and cure time of the rubber compounds decreased, while the curing rate index did not change significantly with increasing amounts of Ag/CB. Hardness, tensile strength, and 100% and 300% moduli of rubber composites increased, while elongation at break decreased with increasing amounts of Ag/CB due to good dispersion of Ag/CB particles in the NR matrix. The Ag/CB particles also enhanced the antimicrobial properties of the NR composites, especiallyStaphylococcus aureusas the gram‐positive bacteria andCandida albicansas the fungus. Addition of Ag/CB also enhanced the electrical conductivity of the rubber composites.

Correlations between natural rubber protein content and rapid predictions of rheological properties, compression set and hardness of rubber compound

In this study the correlations between protein contents of different kinds of natural rubber were considered with rheological behavior, compression set and hardness of rubber compounds based on natural rubber. At the first stage, protein contents were obtained by Kjeldahl method and correlated with normalized absorbance of amine band in NR's attenuated total reflection Fourier transform infrared spectra and shown linear behavior. At the second stage, correlations between the protein contents obtained by the spectra were considered with rheological behavior, compression set and hardness of rubber compounds and shown second order fitting models. The introduced models were applied to predict these features in case studies. Results were shown that Mooney viscosity, torque difference, optimum cure time, scorch time, cure rate index and hardness can be predicted by lower than 10% while compression set can be estimated by lower than 20% error. This significant attitude is a nondestructive and fast technique that uses little quantity of NR for prediction of some NR based compounds properties, before compounding.

Exploration of the role of nanoferrite load and particle size on the rheometric, mechanical, and dielectric properties of (Co0.2Zn0.8Fe2O4/NBR) nanocomposites

AbstractSpinel nanoferrite powder with chemical formula Co0.2Zn0.8Fe2O4 was synthesized by sol–gel citrate method. Moreover, nanocomposites of (Co0.2Zn0.8Fe2O4/Nitrile butadiene rubber [NBR]) with different ferrite filler loads (2, 4, 6, 8, 10, 12, 14, 20, 25, and 30 phr) were prepared aiming to enhance more improvements of the mechanical and dielectric properties of NBR to be used in communication and data transmission applications. Different techniques (XRD, SEM, and TEM) were used to investigate the structural and morphological properties of the ferrite and (ferrite/NBR) nanocomposites. Several properties were measured: rheometric [maximum torque (MH), hardness, scorch (ts2) and cure (tc90) times, cure rate index (CRI)], mechanical [stress at yield (σB), stress at rupture (σR), Young's modulus (E)] and dielectric [electrical resistivity (ρac), real (ε′), and imaginary (ε″) parts of the dielectric constant]. The study concentrated on the effect of both nanoferrite concentration and particle size on the different investigated properties. Generally, the rheometric and mechanical properties were improved with increasing ferrite load while reduced with increasing its particle size. However, the dielectric constant showed an increase with increasing ferrite load as well as particle size. These results were explained according to the interaction between ferrite nanoparticles and rubber matrix.

Influence of n-ZnO Morphology on Sulfur Crosslinking and Properties of Styrene-Butadiene Rubber Vulcanizates.

This paper examines the influence of the morphology of zinc oxide nanoparticles (n-ZnO) on the activation energy, vulcanization parameters, crosslink density, crosslink structure, and mechanical properties in the extension of the sulfur vulcanizates of styrene-butadiene rubber (SBR). Scanning electron microscopy was used to determine the particle size distribution and morphology, whereas the specific surface area (SSA) and squalene wettability of the n-ZnO nanoparticles were adequately evaluated using the Brunauer–Emmet–Teller (BET) equation and tensiometry. The n-ZnO were then added to the SBR in conventional (CV) or efficient (EV) vulcanization systems. The vulcametric curves were plotted, from which the cure rate index (CRI) rate of the vulcanization and the activation energy were calculated. The influence on the mechanical properties of the SBR vulcanizates was stronger in the case of the EV curing system than when the CV curing system was used. Of the vulcanizates produced in the EV curing system, the best performance was detected for n-ZnO particles with a hybrid morphology (flat-ended rod-like particles on a “cauliflower” base) and high SSA. Vulcanizates produced using the CV curing system showed slightly better mechanical properties after the addition of nanoparticles with a “cauliflower” morphology than when the rod-like type were used, irrespective of their SSA. In general, nanoparticles with a rod-like structure reduced the activation energy and increased the speed of vulcanization, whereas the cauliflower type slowed the rate of the process and the vulcanizates required a higher activation energy, especially when using the EV system. The crosslink structures were also more clearly modified, as manifested by a reduction in the polysulfidic crosslink content, especially when n-ZnO activators with a rod-like morphology were applied.

Production of safe and antimicrobial ethylene propylene diene monomer (EPDM) rubber vulcanizates for toys and medical applications

The present work deals to prepare safety rubber goods for medical and kids toys applications. The rubber used in this study was ethylene propylene diene monomer (EPDM). The incorporated additives used to obtain promising results for safety rubber goods are ZnO of particle size 26 nm, potassium alum and tetracycline. Two fillers were used like CaCO3 and bentonite. The rubber and its specified ingredients were mixed through the ordinary industrial mixer applied. The compounded rubber was vulcanized by a hydraulic press according to the time determined from the rheological test. The physico-mechanical properties and the cytotoxicity tests of the EPDM rubber vulcanizates were evaluated. The results showed that rheological properties of the vulcanizates depend on the type of filler; CaCO3 and bentonite used. The scorch time decreased with increasing filler concentrations. The minimum and maximum torque as well as the cure rate index were increased with increasing the filler concentration. The data obtained showed the improvement of the physicomechanical properties of the vulcanizates in presence of 10-20 phr fillers . Moreover, there is no great differences in the rheological and physicomechanical properties of the prepared vulcanizates in the presence of the bioactive materials such as ZnO, potassium alum, and tetracycline due to their good compatibility and distribution of these materials in the vulcanizates as clarified from the results of the scanning electron microscope (SEM). The results of cytotoxicity test on the prepared vulcanizates towards human normal cell lines showed good safety property therefore, the cytotoxicity activity of EPDM/Bentonite at 100 ppm was about -58.5 % , while, the antimicrobial activity of EPDM/Bentonite/2.5 ZnO towards Gram -ve or Gram +ve bacteria was good. These promising results push us to use EPDM rubber vulcanizates for producing safe and antimicrobial rubber goods in various industrial and medical applications.

Studies of carboxylated nitrile butadiene rubber/butyl reclaimed rubber (XNBR/BRR) blends for shoe soles application

Abstract Rising environmental issues and huge disposal of rubber waste have resulted in an increased interest in the usage of reclaimed rubber (RR) to produce sustainable and environmental friendly applications. In this study, incorporation of butyl reclaimed rubber into carboxylated nitrile butadiene rubber (XNBR/BRR) was carried out where the loadings of each XNBR and BRR were varied. The rubber was cured with sulphur during the melt mixing using a two-roll mill. This study is aimed to investigate the applied BRR loading towards the physical and mechanical properties of the XNBRcompounds. The results appeared that the optimum cure time (T90) increased and curing rate index (CRI) showed that a faster curing reaction with the increase in the content of BRR where the T90 had an increment of 89% while the CRI was faster by 89%. As for the crosslink density which indicates the density of chains or segments in polymer network, it decreased about 20% with increasing level of BRR. Also, the compression set which refers to the ability of rubber to resist permanent deformation, had an increase of 73% as the loading ratio of BRR increased. These results were obtained due to the low molecular weight of the BRR where the high shear and temperature during the reclamation process severely breaks down the molecular chains of the BRR into shorter segments. With the results obtained, it is shown that reclaimed rubber has the potential for further development and could increase the interest of researchers all around the world in the incorporation of reclaimed rubber for footwear application.

Influences of Modified Palm Stearin on Vulcanization Properties of Carbon Black-Loaded Epoxidized Natural Rubber

The present research-study investigated the influences of modified palm stearin (MPS) on the vulcanization properties of carbon black (CB)-loaded Epoxidized Natural Rubber with 25% mole (ENR 25). The ENR 25 was loaded by CB at a fixed loading (thirty phr) and the MPS was added into the CB-loaded ENR 25 compounds with varied doses from one to seven phr. The influences of MPS additions on the optimum vulcanization and scorch times and also cure rate index (CRI) of CB-loaded ENR 25 were investigated. It was observed that the MPS caused an enhancement in the rate of the vulcanization process on the ENR 25 compounds. The MPS decreased both the times to scorch and optimum vulcanization time but increased the CRI. The bigger the MPS doses caused in the lower were the scorch and optimum vulcanization times but caused in the higher was the CRI. The enhancement in CRI was attributed to the role of MPS as the supplementary accelerator for the CB-loaded ENR 25 compounds. The amine content of MPS enhanced the CRI.

The presence of stearamide as a rubber chemical in silica loaded-styrene butadiene rubber: The curing properties

This research-study investigated the influences of stearamide on the curing properties of silica-loaded styrene-butadiene rubber (SBR). The SBR was loaded with silica at a fixed loading (thirty phr) and the stearamide was added into the silica-loaded SBR compounds with varied doses from two to eight phr. The influences of stearamide additions on the scorch time, optimum curing time and cure rate index (CRI) of silica-loaded SBR were investigated. It was observed that the stearamide caused an enhancement in the rate of the curing process on the SBR compounds. The stearamide decreased both the times to scorch and optimum curing times but increased the CRI. The bigger the stearamide doses caused in the lower were the scorch time, curing time and CRI. The decreases in CRI was attributed to the role of a reactant that interacted chemically inside the silica-loaded SBR compounds. The amine content of stearamide presumably triggered the chemical reaction between the SBR, silica filler and amine itself.

The incorporations of palmitamide as a rubber chemical into carbon black-loaded styrene-butadiene rubber: cure rate index and torque properties

This study studied the effect of palmitamide as a new rubber chemical on the index of healing rate and torsion properties of carbon black (CB) (CB) charged styrene-butadiene rubber compounds. SBR was loaded with CB at a fixed load (thirty phr) and palmitamide was added to the CB-loaded SBR compound at doses varying from two to eight phr. The effect of palmitamide addition on the healing rate index and torsional properties of SBR CB loads were investigated. It was revealed that palmitamide caused an increase in the speed of the healing process in SBR containing CB. The greater the palmitamide dose, the higher the CRI. The increase in CRI is associated with the role of palmitamide as an additional accelerator for CB-loading SBR. The amine content of palmitamide increases CRI. It was also revealed that palmitamide lowers the minimum torque but increases the maximum torque as well as the torque difference by up to six palmitamide additions. The minimum torque reduction is due to the plasticizing effect of palmitamide. The increase in maximum torque and difference in torque is due to the increased intercalation process due to the action of palmitamide as an acting agent which increases CB dispersion.

The effect of pumice and clay composition in natural rubber-ethylene propylene diene monomer blends towards its curing characteristics and physic-mechanical properties

Since some adverse effects of using carbon black as petroleum-based filler in rubber compounding, mineral fillers may be a feasible alternative filler. This research studied the effect of the composition of pumice and clay as mineral filler in natural rubber (NR) and ethylene propylene diene monomer (EPDM) blending towards its curing characteristics and physical-mechanical properties. The effect of reinforced filled in EPDM-NR (70/30) phr blends was observed by varying 50, 70, and 90 phr of filler. While the filler was designed as the composition of pumice/clay (P/C): 20/80; 50/50; 80:20 (weight/weight). The rubber, fillers, and chemical were compounded based on ASTM D-3182. The results showed that the loading of P/C fillers in EPDM-NR blends increased scorch time and decreased cure rate index. It was found that the optimum number of filler could enhance density, modulus. Remarkably, the higher pumice composition caused the abrasion resistance and compression set improved significantly, whereas the overloading pumice and clay cause the physic-mechanical properties remained stable or evenly drop. FTIR spectra of the binary blends confirmed that the fine fillers dispersion was obtained due to some interaction bonding between silanol, aluminol of fillers with the EPDM-NR.

Investigation on viscoelastic behavior of virgin EPDM/ reclaimed rubber blends using Generalized Maxwell Model (GMM)

The reclaiming process of ethylene-propylene-diene monomer (EPDM) using a twin-screw extruder was studied and the effect of reclaiming conditions including screw speed (40, 80 and 120 rpm) and reclaiming agent content (0, 1.5 and 3 phr) at 280 °C (barrel temperature) on swelling, curing, mechanical properties as well as stress relaxation of virgin EPDM/40 phr reclaimed rubber blends was evaluated. According to the results of swelling test, the reclaiming process led to both crosslinks breakage and main chain scission. The appropriate reclaiming conditions were determined as the highest screw speed (120 rpm) and reclaiming agent content (3 phr). Compared to virgin EPDM vulcanizates, the curing behavior of prepared blends showed that the addition of reclaimed rubber had no effect on the scorch time but increased the optimum cure time and decreased the cure rate index. The results obtained for mechanical properties demonstrated that the tensile strength, modulus at 100% and 200% elongation and hardness decreased while the elongation at break of the blends showed no particular trend. The analysis of stress relaxation behavior using the Generalized Maxwell Model (GMM) revealed that the initial and final moduli of all blends decreased, and surprisingly the relaxation times were shorter or showed no change compared to the reference sample. Further, the Dynamic Mechanical Thermal Analysis (DMTA) results exhibited that the Tg of blends decreased but the maximum loss tangent presents no change following the addition of 40 phr reclaimed rubber to the virgin EPDM. Finally, the frequency sweep test indicated that the storage modulus of all blends was lower than that of the virgin sample.