A Comparative Study of the Dynamic-Mechanical Properties of Styrene Butadiene Rubber/Epoxidized Natural Rubber Dual Filler Nanocomposites Cured by Sulfur or Electron Beam Irradiation

The properties of (50/50?wt%) styrene butadiene rubber/epoxidized (50%) natural rubber (SBR/ENR50) blends containing nanoclay (NC, 5 or 10phr) without and with carbon black (CB 20phr) cured by sulfur or by electron beam (EB) irradiation (50 and 100kGy), were compared. A sulfur cured compound containing 35phr CB was prepared as a reference sample. Dynamic mechanical thermal analysis (DMTA) indicated that the sulfur cured sample containing 10phr NC and 20phr CB and the 100kGy irradiated sample with 5phr NC and 20phr CB had higher crosslink density, storage modulus, and tensile strength, and less loss factor and loss modulus, compared to the reference sample. Scanning electron microscopy (SEM) images of cryo- fractured surfaces confirmed the DMA and crosslink density results. We suggest a light weight 100kGy irradiated sample containing the lowest amount of NC and 20phr CB with a uniform distribution of the –C–C– bonds crosslinks, for high thermal stability applications and also for passenger cars tire treads, for its ice grip and wet skid properties especially for icy and wet roads, with improvements of 23% and 20%, respectively as compared to the reference sample.     

Structure and Mechanical Properties of 50/50 NR/SBR Blend/Pristine Clay Nanocomposites

A blend/clay nanocomposites of 50/50 (wt%) NR/SBR was prepared via mixing the latex of a 50/50 NR/SBR blend with an aqueous clay dispersion and co‐coagulating the mixture. The structure of the nanocomposite was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Nanocomposites containing less than 10 phr clay showed a fully exfoliated structure. After increasing the clay content to 10 phr, both nonexfoliated (stacked layers) and exfoliated structures were observed in the nanocomposites. The results of mechanical tests showed that the nanocomposites presented better mechanical properties than clay‐free NR/SBR blend vulcanizate. Furthermore, tensile strength, tensile strain at break, and hardness (shore A) increased with increasing clay content, up to 6 phr, and then remained almost constant.     

Mechanical and Flame Retardant Properties and Microstructure of Expandable Graphite/Silicone Rubber Composites

Flame-retardant expandable graphite (EG)/silicone rubber (SR) composites were prepared using nano-CaCO₃ particles as reinforcement filler. In addition to mechanical measurements, limited oxygen index (LOI), UL-94 and cone calorimeter tests (CCT), the thermal properties were tested by thermogravimetric analysis (TGA). The results showed that the content and particle size of the EG both had large effects on the flammability and mechanical properties of the EG/SR blends. The composites that contained 25 phr EG (50–80 mu) had excellent LOI values, 47–48, and achieved the UL-94 V-0 level while the pure SR sample had the LOI value of 25 and achieved the UL-94 V-2 level. The data obtained from the CCT indicated that the addition of EG decreased remarkably the heat release rate, smoke emission, and mass loss rate of the composites. SEM microphotographs of the EG/SR composites before and after combustion demonstrated that EG underwent a large volume expansion, and the multiporous char structure blocked heat transfer and protected the substrate from fire.     

Microstructure and Properties of Polypropylene/Clay Nanocomposites

Nanocomposites of polypropylene (PP) containing various contents of Cloisite 15A nanoclay particles were prepared by one-step melt compounding in a twin screw extruder. Tensile and impact properties of the nanocomposite systems were investigated and correlated with their microstructures. The tensile modulus increased with an increase in Cloisite 15A content but the tensile strength, elongation at break, and impact strength were decreased. WAXS and TEM studies showed almost exfoliated structures. There was a decrease in permeability values with an increase in nanoclay content up to 5 wt. %. Exceeding this content of nanoclay had no significant effect on permeation due to the aggregation phenomenon at high concentrations of the nanoparticles. Most of the examined micromechanical models for prediction of the tensile modulus of the nanocomposite were successful despite being based on fiber-shaped fillers. An exfoliated structure of clay within the nanocomposite was assumed for the modeling using a molecular dynamics simulations approach, employing Dreiding, Forcite, and COMPASS force fields, in order to investigate the best one for a successful estimation of elastic modulus. Relative to the experimental modulus values of the nanocomposites, which were around 1100–1200 MPa, the COMPASS force field had the best correlation with the values with a slight departure of about 10%.     

The Role of Organoclay on Microstructure Development and Rheological Properties of Poly(Butylene Terephtalate)/Epoxy/Organoclay Hybrid Systems

The main objective of the present work was to study the role of organoclay on the microstructure development and rheological properties of poly(butylene terephtalate)/ epoxy/organoclay (Cloisite® 30B) hybrid nanocomposites. The effects of feeding order and curing of the epoxy were also investigated. The hybrid nanocomposite samples were prepared by melt compounding in a laboratory internal mixer at a temperature of 240°C. The samples were prepared by three feeding routes; (1) simultaneous feeding, (2) PBT/organoclay based master batch feeding, and (3) epoxy/organoclay based master batch feeding. The XRD results evidenced a highly intercalated microstructure for all the samples. The linear viscoelastic results obtained for uncured samples, prepared by the first and second feeding routes, exhibited a pronounced low-frequency nonterminal behavior whose extent was found to be increased in the cured samples. These results suggested that the major part of the nanoclay tactoids and/or platelets were dispersed in the PBT matrix, with higher nanoclay concentration in the sample prepared by the second feeding route. However, the samples prepared through epoxy/organoclay based master batch did not exhibit an appreciable low-frequency solid body response. This suggests that the process of migration of the nanoclay tactoids and/or platelets from epoxy droplets to PBT matrix was the time consuming process due to the high aspect ratio of the nanoclay and the high viscosity of the PBT matrix. From linear and nonlinear viscoelastic measurements, it could be deduced that the curing process does not play an important role in determining the extent of intercalation and dispersion of the nanoclay, but it can enhance the interfacial interaction between the two phases in the nanocomposite.     

Investigation of Cell Structure and Expansion Ratio of Microcellular Polypropylene Nanohomocomposites Prepared by a Solid-State Process

Microcellular poly(propylene-ethylene) random copolymer (r-PP-PE)/nanoclay (nanocomposite) and r-PP-PE/nanoclay/polypropylene fibers (nanohomocomposite) were autoclave-foamed via a solid-state microcellular foaming process using supercritical N₂ as a foaming agent. Polypropylene grafted with maleic anhydride (PP-g-MA) was used as a compatibilizer. Amount of PP-g-MA to nanoclay was 3:1. This study investigated the effects of clay content and the presence of polypropylene fiber on the expansion ratio and cell morphology of the samples. The results indicated that nanoclay increased the expansion ratio of the samples, but the expansion ratio for nanohomocomposites was slightly lower than the nanocomposites. In addition, scanning electron microscopy (SEM) observation showed that the nanoclay decreased the cell size and increased the cell density, except for the nanocomposite with the highest nanoclay content, 3 wt%, which had larger cell size compared to the samples with 1.5 wt% nanoclay and less. On the other hand, the simultaneous presence of nanoclay and polypropylene fibers synergistically increased the cell nucleation effect; thus there was a dramatic increase in cell density. The Differential scanning calorimetry (DSC) analysis showed that the microcellular foaming process decreased the crystallinity of both types of samples.     

Study on the Reinforcing Effect of Milled Carbon Fibers in a Natural Rubber Based Composite

Milled carbon fibers (MCF) have been tested at 2, 4, and 6 phr in a standard natural rubber compound with 45 phr of N375 carbon black. A dramatic increase in the low elongation moduli was observed even with only 2 phr of MCF. The presence of MCF confers anisotropic properties to the rubber compounds that can be measured by an anisotropic factor σ, defined as the ratio between the modulus parallel to the MCF prevalent direction over the modulus orthogonal to the MCF prevalent direction. It has been shown that the presence of MCF is able to reduce the mechanical hysteresis and also the compression set of the natural rubber compound. However, the tear strength properties are affected negatively. The present study demonstrates the feasibility and the advantages derived by the utilization of the carbon fibers as extra reinforcing filler in rubber compounds.     

Carbon Black–Filled Styrene Butadiene Rubber Masterbatch Based on Simple Mixing of Latex and Carbon Black Suspension: Preparation and Mechanical Properties

An improved process was developed for the production of carbon black (CB)–filled styrene butadiene rubber masterbatch (SBR-CB-MB) using a simple latex/CB mixing technology; the improvement comprised processing the CB as an emulsifier-free aqueous suspension by high-rate shearing. Tensile and tear strength, dynamic compression behaviors, the Payne effect, equilibrium swelling and bound rubber of the SBR-CB-MB and dry mixing CB filled SBR (SBR-CB-DM), covering a wide range of CB loading (45–70 phr), were investigated and compared. It was found that the tensile and tear strength, heat buildup and compression set, abrasion volume loss, and the Payne effect of the SBR-CB-MB were lower than those of the SBR-CB-DM, while the bound rubber content were higher, indicating good CB/rubber interaction in the SBR-CB-MB. SEM analysis showed that no free CB could be found on the surface or inside of the granular SBR-CB-MB particles, indicating good CB dispersion in the rubber matrix.     

Surface properties of polypropylene/organoclay nanocomposites

Influence of nanoclay amount on surface properties of the nanocomposites was investigated using Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), contact angle measurement, scanning electron microscopy (SEM) and transmission spectroscopy (TS). Polypropylene based nanocomposites containing various loads of nanoclay were prepared by melt compounding. X-ray diffraction (XRD) characterized the dispersion of nanoclay in polymer matrix. AFM and SEM studies have shown increase in surface roughness by raising the amount of nanoclay. Contact angle measurements of the resultant nanocomposites have also shown improvement in wettability related to disperse part of surface tension. POM images illustrated an increase in the number of spherulite simultaneously with a decrease in their size; this result was also supported by differential scanning calorimetry (DSC).     

Preparation of Silicon Carbide Nanoparticle/Butadiene Rubber/Silane Nanocomposites; Structural,Mechanical, Tribological and Thermal Properties

Silicon carbide nanoparticles (nano-SiC), in the amounts of 0, 3, and 5 parts per hundred of rubber (phr), were employed in a butadiene rubber (BR) based compound as a potential commercial rubber and the structure, mechanical, tribological and thermal properties of the samples were investigated. The use of 3 phr of nano-SiC, especially in the presence of silane, increased the crosslink density and improved the tensile strength (35%) and elongation at break (64%) of the BR. In addition; the abrasion resistance of the BR was improved about 120% and the coefficient of friction increased. Scanning electron microscopy (SEM) images revealed the use of silane resulted in an appropriate dispersion of the nano-SiC and improvement of its interaction with the matrix. The use of nano-SiC, especially with silane, increased the initial thermal decomposition temperature of the BR and decreased its rate of degradation.     

Dynamic Fatigue Behavior of Natural Rubber Reinforced with Nanoclay and Carbon Black

The dynamic fatigue behaviors of natural rubber (NR) filled with carbon black (CB) and both nanoclay (NC) and CB at same hardness was evaluated using the stepwise increasing strain test (SIST) and long-term testing. Compared with NR/CB composites, NR/CB/NC nanocomposites exhibited higher fatigue-limited strain, stronger dynamic stress relaxation, and longer compression fatigue life. By examining the fracture morphologies, nonlinear viscoelastic behavior, and hysteresis loss of filled NR, it was found that NR, synergisticly reinforced by NC and CB, exhibited improved anti-fatigue ability than NR filled with CB due to stronger filler–filler interactions between NC and CB (a local filler network) and the high aspect ratio and typical lamellar structure of NC.     

Polyvinyl Alcohol/Na-Montmorillonite Nanocomposite Hydrogels Prepared by Freezing–Thawing Method: Structural,Mechanical, Thermal,and Swelling Properties

Physically crosslinked nanocomposite hydrogels based on polyvinyl alcohol (PVA) containing Na-montmorillonite were prepared by the cyclic freezing–thawing method. The primarily exfoliated morphology of prepared nanocomposite hydrogels was confirmed by X-ray diffractometry (XRD) and transmission electron microscopy (TEM) as complementary techniques. It is shown that some interactions developed between the hydroxyl groups of PVA chains and Na-montmorillonite silicate layers in the nanocomposite hydrogels. Differential scanning calorimetry (DSC) results indicated some shifting in the glass transition temperature of the PVA hydrogel in the presence of the nanoclay. Swelling measurements showed that the swelling ratios of the nanocomposite hydrogels were increased either by decreasing the Na-montmorillonite content or by increasing the swelling medium temperature. Dynamic mechanical–thermal properties results showed higher storage modulus for nanocomposite hydrogels in temperature ranges both below and above 0°C. It was also found that the hardness of the nanocomposite hydrogels increased by increasing the nanoclay loading level.     

The Effect of Structure of the Clay Modifier on the Morphology and Properties of Polystyrene/Clay Nanocomposites Prepared via In Situ Suspension Polymerization

Polystyrene (PS)/organoclay nanocomposites were prepared via free radical suspension polymerization. Two kinds of organoclay were used, labeled KT and KD, modified by trimethyloctadecyl ammonium (TM) and dimethyldioctadecyl ammonium (DM) ions, respectively. Nanocomposites containing various amounts of both of the organoclay nanoparticles (1, 3, and 5 wt%) were prepared. The wide angle X-ray diffraction (WAXD) results revealed intercalation in both of the nanocomposites. The greatest improvement in thermal stability of the nanocomposites was achieved with 5 wt% of organo-MMT for both of the clays. The nanocomposite containing 3 wt% of KT organo-MMT showed the greatest improvement of storage modulus. When the organoclay content exceeded 3 wt%, the storage moduli decreased compared to the nanocomposite filled with 3 wt% of the organoclay. D-spacing calculations using Bragg's law and WAXD data showed that the KT and KD nanoparticles were intercalated within the PS matrix, but with different extents of intercalation. The styrene conversions of the as-polymerized nanocomposite samples were obtained by a gravimetric method. The results showed that conversion decreased with incorporation of organoclay in the reaction recipe. Particle size was also increased by increasing nanoclay content.     

Wet Sliding Abrasion of Natural Rubber Composites Filled with Carbon Black at Different Applied Loads

The wet sliding abrasion and abrasion behavior of carbon black (CB)-filled natural rubber (NR) composites were investigated using a Deutsche Industrie Normen (DIN) abrader and compared to their dry abrasion resistance. The results showed that water tended to lubricate the contact between the rubber and the abrader and thus the abrasion loss was reduced. At different applied loads, the abrasion mechanism of the filled vulcanizates was different. When the applied load was below the turning point, the rubber abrasion was mainly fatigue abrasion and the main factor to influence the abrasion was the dynamic loss factor tanδ of the rubber. When the applied load was above the turning point, the rubber abrasion was mainly pattern abrasion and the main factors to influence the abrasion were the mechanical properties, in particular tensile and tear strength.     

Effect of glycidyl methacrylateas compatibilizeron physico-chemical properties of gamma irradiated composites ofethylene propylene diene monomer rubber / styrene butadiene rubber/ground tire rubber

ABSTRACT

Composites of ethylene propylene diene monomer rubber (EPDM)/ styrene butadiene rubber (SBR)/ground tire rubber (GTR)(50/50/20) phr (part per hundred parts of rubber, by weight)loaded with different contents of glycidylmethacrylate (GMA) 2–6?phr. were irradiatedfrom 50 to 250?kGy. The physicochemical properties were investigated.

Irradiation dose and GMA improved physicochemical properties, the optimum content of GMA is 6?phr at a low dose of irradiation. These results were confirmed by scanning electron microscopy (SEM).     

Effect of interfacial bonding on impact properties of chopped glass fiber polymer nanocomposites

This paper aims to presents the investigations made on the effect of impact response of chopped glass fiber–epoxy nanocomposite laminates subjected to low velocity impact using instrumented falling weight impact tests. The laminates were prepared using six layers of chopped strand mat with density of 610 gsm with epoxy resin and nanoclay content varied from 1, 3, and 5 wt%, by hand lay-up method. The nanoclay was dispersed into the epoxy by high shear mixing process in order to obtained uniform distribution of individual nanoclay. Laminates were impacted at constant mass with different impact energies. During these low velocity impact tests, the maximum load, absorbed energy, and deflection at peak load were recorded. It was observed that by dispersion of nanoclay as reinforcement, there was significant improvement in load carrying capacity and energy absorption. When a small amount of nanoclay (1 wt%) was added into the epoxy, the maximum load was enhanced by 20%. The presence of stiffer nanoclay significantly reduced the surface cracks propagation and controlled delamination area. Scanning electron microscopy was performed to characterize the damage progression.     

Sulfonated Aromatic Polymers and Organically Modified Montmorillonite Nanocomposite Membranes for Fuel Cells Applications

Aromatic polymers, such as sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO), sulfonated poly(ether ether ketone) (SPEEK), and sulfonated poly(ether sulfone) (SPES), at the optimum degrees of sulfonation (DS), are suggested and evaluated as alternatives to Nafion for direct methanol fuel cells (DMFCs) applications. To reduce the methanol cross-over, which decreases the efficiency of the cell, organically modified montmorillonite nanoclays (OMMT) were added at 1 wt% to the sulfonated matrices with the optimum DS. The X-ray diffraction (XRD) patterns of nanocomposite membranes proved that the nanoclay layers were exfoliated. The proton conductivity and methanol permeability of the membranes, as well as the ion-exchange capacity (IEC), were measured. The selectivity parameter, ratio of proton conductivity to methanol permeability, was identified at 25°C for the nanocomposite membranes and the results were compared with Nafion117. Finally, the DMFC performance tests were investigated at 70°C and 5 M methanol feed for the manufactured nanocomposite polyelectrolyte membranes (PEMs). The SPEEK-based nanocomposite membrane showed the highest maximum power density in comparison with Nafion 117 and SPES and SPPO nanocomposite membranes. The results indicated that the nanocomposite membranes were promising PEMs for DMFC applications.     

Insights into the Reinforcement of Butyl Rubber by Carbon Black and Silica with the Aid of Their Dynamic Properties

Carbon black (N234) and silica (Vulksail N) with a silane coupling agent Si-69 were chosen as reinforcing fillers in butyl rubber (IIR). The rheological behavior of the IIR compounds and the dynamic mechanical properties of IIR vulcanizates were investigated with a rubber processing analyzer and dynamic mechanical analysis (DMA) to examine the filler dispersion in the rubber matrix and the interaction between filler and matrix. The data indicated that the N234 filled IIR compounds had more filler networks than those filled with silica. Filler networks first appeared at 30 phr N234 and 45 phr silica with silane coupling agent Si-69. The interaction between N234 and IIR was far stronger than that between silica and IIR. However, the silica Vulksail N filled IIR had better wet-grip and lower rolling resistance compared to the carbon black-filled IIR should IIR be chosen as a substitute of styrene-butadiene rubber (SBR) in tire tread. The reinforcing factor, R, R (related to the difference in tan d peak height at T_g for the filled and nonfilled rubbers), also demonstrated that the N234-IIR interaction was stronger than for the silica. IIR with 30 phr N234 exhibited the largest tensile strength, 20.1 MPa, for those vulcanizates examined. The tensile and tear strengths of N234 filled IIR were higher than those of IIR with similar amounts of silica. Thus, it was concluded that N234 is a more active reinforcing filler in IIR than silica (Vulksail N) even with a silane coupling agent (Si-69).     

Carbon Black Filled Powdered Natural Rubber

Carbon black (CB) filled powdered natural rubber [P(NR/N234)] was prepared using a patented method of latex/CB coagulation technology. The influence of curing recipes and CB contents on the curing, mechanical, and dynamic properties were studied in depth, and the results were compared with that of NR/N234 compounds based on traditional dry mixing of bale NR and CB. The results showed that, compared with NR/N234, P(NR/N234) showed higher tensile strength, tear strength, rebound elasticity and flexibilities, and the antiabrasion properties were similar, while the dynamic temperature-build-up and dynamic compression permanent set were about 50% of that of NR/N234. The analysis based on scanning electron micrographs (SEM) and the Payne effect showed that the fine dispersion of CB in the rubber and the enhanced interaction between CB and rubber contributed to the excellent properties of P(NR/N234), sufficient that they make P(NR/N234) a potential material for the tread compounds of heavy-duty all-steel cord radial tires.     

Polyelectrolyte Nanocomposite Membranes,Based on Chitosan-phosphotungstic Acid Complex and Montmorillonite for Fuel Cells Applications

A polyelectrolyte complex (PEC) of chitosan and phosphotungstic acid (PWA) was prepared and characterized as a proton-conducting membrane for direct methanol fuel cell (DMFC) applications. Fourier transform infrared spectroscopy showed the presence of stable PWA in PEC. To reduce the methanol permeability, several amounts of montmorilonite (MMT) nanoclays (trade name: Cloisite Na) were introduced to the system. The X-ray diffraction patterns of nanocomposite membranes proved the nanoclay layers were exfoliated in the membranes at loading weights of MMT lower than 3 wt%. Proton conductivity and methanol permeability were measured. According to the selectivity parameter—ratio of proton conductivity to methanol permeability—PEC containing 2 wt% MMT (PEC/2 wt% MMT) was identified as the optimum composition. Finally, DMFC performance tests were investigated at 70°C and 5 M methanol feed and the optimum membrane showed higher maximum power density in comparison with Nafion 117. The results indicated the optimum nanocomposite membrane is a promising polyelectrolyte membrane (PEM) for DMFC applications.