Improved Dispersion of Carbon Nanoparticles Modified by Poly(Sodium 4-Styrenesulfonate) and Its Influence on the Properties of Natural Rubber Latex

A novel strategy of radical polymerization of sodium 4-styrenesulfonate on the surface of carbon black (CB) in the solid state was developed to prepare hydrophilic carbon nanoparticles (PNASS-CB). A high performance natural rubber latex (NRL)/PNASS-CB composite was produced by the latex compounding technique. Scanning electron microscope shows considerable improvement in the dispersion of PNASS-CB in rubber matrix. The lower degree of filler–filler networks and the stronger filler–rubber interaction of PNASS-CB in rubber matrix were confirmed by dynamic mechanical thermal analysis. Rheometric properties of NRL/PNASS-CB, like scorch time and optimum cure time, decreased. Tensile strength, tear strength, and elongation at break increased due to stronger interaction between the PNASS-CB and rubber matrix. Dynamic mechanical properties of the modified carbon nanoparticles further corroborated a significant contribution from the better dispersion and efficient load transfer of PNASS-CB on the static and dynamic mechanical properties of composites.     

The effect of accelerator contents on the vulcanizate structures of SSBR/silica vulcanizates

Physical properties of rubber compounds are affected by the filler–rubber interaction, filler dispersion in the rubber matrix, and cross-link structure formed during vulcanization. In particular, the cross-link structure is closely related to the physical properties of vulcanizates and has been analyzed using the swelling test and Flory-Rehner equation. However, the relationship between the structure and physical properties of vulcanizates cannot be explained by the cross-link density obtained using these methods. The cross-link density obtained from the swelling test is a complex result of the filler–rubber interaction occurring during the compounding as well as the chemical cross-link structure formed by sulfur during the vulcanization. Moreover, the rubber vulcanizates that use silica need to be separately analyzed for each factor as its physical properties are affected more by the filler–rubber interaction than by carbon black. Therefore, this study determines the factors that contribute to the total cross-link density of vulcanizates into chemical cross-link density and filler–rubber interaction via quantitative analysis using the swelling test results and Flory-Rehner and Kraus equations. The vulcanizates used for the analysis were carbon black-filled and silica-filled non-functionalized SSBR compounds with varying cure accelerator for each filler loading. Their chemical cross-link density was measured and the effect of the filler–rubber interactions on their mechanical and dynamic viscoelastic properties was investigated. Furthermore, the relationship between the structure and physical properties of rubber vulcanizates was elucidated.     

Interface tailoring of layered silicate/styrene butadiene rubber nanocomposites

To improve the interfacial interaction in clay/SBR nanocomposites prepared by latex compounding method, a novel clay modification for the nanocomposites was introduced before latex compounding with SBR using three kinds of organic modifiers, namely, hexadecyl trimethyl ammonium bromide (C16), bis(hexadecyl) dimethyl ammonium bromide (DC16) and 3-aminopropyl triethoxy silane (KH550). On the other hand, bis(triethoxysilylpropyl)tetrasulfide (Si69) was added into the KH550 modified clay/SBR nanocomposite during later mechanical blending, and was designed to interact with both KH550 and rubber and thus improve the interface. Structure changes of the nanocomposites were followed by study of X-ray diffraction, transmission electron microscopy and rubber process analyzer. Dynamic mechanical analysis and tensile tests were carried out to obtain information about the mechanical properties of the nanocomposites. The results revealed that, with the organic modification, clay was dispersed finely in the rubber matrix with part rubber-intercalated or part modifier-intercalated structure. Compared with the unmodified nanocomposite, the tensile strength, the stress at 300% strain, and the tear strength of modified SBR–clay nanocomposites were significantly improved. Moreover, the type of modifiers and strength of interfacial interaction determined the properties of the nanocomposites. The incorporation of KH550 and Si69 brought the best modification effect among all the modification methods.     

Ecofriendly latex films from cassava starch-filled radiation pre-vulcanized natural rubber latex

ABSTRACT

The demands of the usage of hazardous ingredients for sulfur curing system in latex industries decrease with an increase in health-conscious and environmental awareness. This work demonstrates the incorporation of cassava starch (CS) as biodegradable fillers with natural rubber latex (NRL) through a sulfur-free crosslinking technique using radiation pre-vulcanization natural rubber latex (RVNRL) in comparison to sulfur pre-vulcanized natural rubber latex (PvNRL). The 20% CS dispersion was prepared, and 5–25?phr of dispersed CS content were compounded with NRL and formed into films by the coagulant dipping method. Microstructures and crystallinity of the films were analyzed by scanning electron microscopy (SEM) and X-ray diffraction, and their mechanical properties of NRL/CS films were characterized by tensile and tear tests. The result revealed that the crystallinity of RVNRL films was lower than PvNRL films. The total bond of S?C from PvNRL contributes to high tensile strength compared to C?C intermolecular rubber bond from radiation vulcanization system. The trend of decrement of tensile properties from sulfur crosslinking was larger than radiation crosslinking, and both systems gave similar tensile behavior at 25?phr of CS content. This attributed to the better dispersion of CS in RVNRL as confirmed by SEM micrographs. It was found that the optimum tear strength of RVNRL/CS and PvNRL/CS films was obtained at 10 and 5?phr of filler content, respectively. The result presented in this study may facilitate a contribution to the current literature on the development of latex film by radiation pre-vulcanization for rubber industry in the future.     

Effect of the amounts of glycidyl methacrylate on the mechanical and dynamic properties of styrene–butadiene–glycidyl methacrylate terpolymer/silica composites

GMA-SBRs with GMA contents in the range of 0.06–0.71 wt.% were synthesized and used to evaluate the properties of the silica composites for fuel-efficient tires. The chemical structures of the GMA-SBRs were analyzed using Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance (¹H NMR), size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). GMA-SBRs can enhance filler–rubber interaction through covalent bond formation between the silica filler and rubber molecules. After compounding, the cure characteristics and mechanical and dynamic properties of the GMA-SBR silica-filled composites were analyzed. The mechanical properties, including the Mooney viscosity, bound rubber, swelling ratio, and moduli, exhibited obvious differences with increasing GMA content. However, the optimum content of GMA in the GMA-SBR, in terms of dynamic properties such as the Payne effect which represents the change in dynamic modulus against the strain to determine the extent of filler flocculation and tan δ at 60 °C representing tire rolling resistance, was ~0.6 wt.%. These results are due to improved silica dispersion, resulting from increased covalent bond formation between GMA-SBR and the silica surface. This approach assists in the determination of functional group contents in functionalized emulsion styrene–butadiene rubber for fuel-efficient tires, leading to a decrease in vehicular greenhouse gas emission.     

Styrene-butadiene-glycidyl methacrylate terpolymer/silica composites: dispersion of silica particles and dynamic mechanical properties

Styrene-butadiene-glycidyl methacrylate terpolymer (GMA-SBR) was synthesized by emulsion polymerization for the fuel efficient tire tread composite. The chemical structure of the GMA-SBR was analyzed using infrared spectroscopy, ¹H NMR, gel permeation chromatography, and differential scanning calorimetry. The GMA-SBR/silica composite is the first instance introduced covalent bonds between silica filler and rubber molecules by in-chain modification of styrene-butadiene molecules. After compounding, the curing characteristics, the mechanical and dynamic mechanical properties of the composites were analyzed. The GMA-SBR/silica composite exhibited higher wear resistance of 32.9% and lower rolling resistance of 25.7% than the styrene-butadiene rubber 1721/silica composite. These results are due to the improvement of silica dispersion in the composite as the covalent bonding increased the filler–rubber interaction and the countervailing effects of less filler flocculation. The proposed approach assists in finding a solution to improve the performances of tires for fuel efficiency and the reduction of greenhouse gases from the vehicles.     

Natural Rubber/Graphene Oxide Nanocomposites Prepared by Latex Mixing

Natural rubber/graphene oxide (NR/GO) nanocomposites were prepared by latex mixing. The dispersion state of GO and the mechanical properties of the nanocomposites were studied. It was found that a uniform dispersion of GO in the NR matrix was achieved with the latex mixing method. The well-distributed GO was remarkably effective in improving the tensile strength and storage modulus of NR at very low filler contents, without sacrificing the ultimate strength. The percolation point of GO in the nanocomposites took place at a content of less than 0.1 parts by weight per hundred parts of rubber. The Halpin-Tsai model was used to analyze the reinforcement effect of GO for NR.     

Characterization of Filler-rubber Interaction,Filler Network Structure,and Their Effects on Viscoelasticity for Styrene-butadiene Rubber Filled with Different Fillers

For styrene-butadiene rubber (SBR) compounds filled with the same volume fraction of carbon black (CB), precipitated silica and carbon–silica dual phase filler (CSDPF), filler-rubber interactions were investigated thru bound rubber content (BRC) of the compounds and solid-state ¹H low-field nuclear magnetic resonance (NMR) spectroscopy. The results indicated that the BRC of the compound was highly related to the amount of surface area for interaction between filler and rubber, while the solid-state ¹H low-field NMR spectroscopy was an effective method to evaluate the intensity of filler-rubber interaction. The silica-filled compound showed the highest BRC, whereas the CB-filled compound had the strongest filler-rubber interfacial interaction, verified by NMR transverse relaxation. The strain sweep measurements of the compounds were conducted thru a rubber process analyzer; the results showed that the CSDPF-filled compound presented the lowest Payne effect, which is mainly related to the weakened filler network structure in polymer matrix. The temperature sweep measurement, tested by dynamic mechanical thermal analysis, indicated that the glass transition temperature did not change when SBR was filled with different fillers, whereas the storage modulus in rubbery state and the tanδ peak height were greatly affected by the filler network structure of composites.     

Carbon nanotubes as reinforcement of styrene-butadiene rubber

This study reports an easy technique to produce cured styrene-butadiene rubber (SBR)/multi-walled carbon nanotubes (MWCNT) composites with a sulphur/accelerator system at 150 °C. Significant improvement in Young's modulus and tensile strength were achieved by incorporating 0.66 wt% of filler without sacrificing SBR elastomer high elongation at break. A comparison with carbon black filled SBR was also made. Field emission scanning electron microscopy was used to investigate dispersion and fracture surfaces. Results indicated that the homogeneous dispersion of MWCNT throughout SBR matrix and strong interfacial adhesion between oxidized MWCNT and the matrix are responsible for the considerable enhancement of mechanical properties of the composite.     

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.     

Interface effect in the silicone rubber/mineral powder composites

Silicone rubber/mineral powder composites have been prepared by surface modification and ultrafinecrashing of mineral powder, mixing and vulcanizing with silicone rubber resin. The surface and interface energy for mineral filler and silicone rubber matrix were investigated. It was found that there is a correlation between W _a/σ_SL (interfacial adhesive work/interfacial tension) and the tensile strength of the corresponding composite, especially for unmodified ultrafine mineral filler. On the other hand, the chemical modification of the surface changes the surface group on the mineral filler and results in improvement of the interfacial interaction between silicone rubber matrix and mineral filler, consequently, altering the reinforcing effect of the mineral filler.     

Reinforcing mechanism of a novel hydrophilic nano-carbon black in natural rubber latex

Novel water-dispersible carbon nanoparticles (PNASS-CBs) were produced by radical polymerization of sodium 4-styrenesulfonate (NASS) on the surface of carbon black (CB) in the solid state. Scanning electron microscopy (SEM) and the Payne effect results showed that the modified CBs were less likely to form particle networks and thus dispersed better in the natural rubber (NR) matrix, with an average size of 90 nm that was much less than that of the aggregated pristine CBs. We propose that the appropriate modification of CBs mitigates filler-filler interaction and enhances the filler-rubber interaction, which can also be proved by the higher bound rubber contents of the NRL/PNASS-CB composites. When a NRL/PNASS-CB composite is subjected to an outside force, e.g. tensile, more physically absorbed rubber chains (bound rubber) slip and self-adjust their absorbed spots on the CBs’ surface (stress redistribution) in order to jointly share the applied stress. This has a positive effect on the resistance to damage of the rubber molecular chains. Therefore, the addition of the hydrophilic CBs in NR latex leads to significant improvements in the mechanical properties of the NRL/PNASS-CB composites.     

Influence of peroxide curing systems on the performance of natural rubber-based magnetic composites

Rubber magnetic composites were prepared by incorporation of strontium ferrite into natural rubber-based continuous matrix. The prepared rubber compounds have model character and besides the rubber and the filler, they contained only ingredients of peroxide curing system, dicumyl peroxide as curing agent, and ethylene glycol dimethacrylate as co-agent. The work was focused on the evaluation of curing system composition and magnetic filler content on curing process, cross-link density, physical–mechanical and magnetic properties of tested materials. The achieved results revealed that the evaluated properties are dependent on the composition of curing system and on the content of ferrite too. Ferrite incorporated in the rubber matrix imparts magnetic properties to the composites considerably. In addition, the improvement of physical–mechanical properties with doping content of ferrite was observed.     

Thermal Properties and Fire Resistance of Jute-Reinforced Composites

The thermal behaviour, fire resistance and mechanical properties of jute-reinforced composites with vinylester and resol matrix were studied. Organically modified clay was added to the polymeric matrix in order to enhance the properties of the composites. An inhomogeneous distribution of the nanoreinforcement in the polymer was observed by X-ray diffraction. Thermogravimetric analyses revealed that the addition of clay to the resol resin by sonication enhanced the thermal resistance of the jute-reinforced composite at temperatures higher than 300°C. The fire resistance of the composites was evaluated by means of a cone calorimeter. A diminution in the peak of the heat release rate was observed when clay was added to the polymeric matrix. On the other hand, neither the time to ignition nor the total heat evolved was significantly reduced by the clay addition. Additionally, an increment in the flexural modulus as well as in the flexural strength of the resol composites was observed when the clay was added to the matrix. The fiber–matrix interface of the composites was studied by scanning electron microscopy. It was observed that as the clay dispersion degree was increased the interface quality was diminished in the resol composites.     

Reduced filler flocculation in the silica-filled styrene–butadiene–glycidyl methacrylate terpolymer

This study presents a method to improve the dispersion of silica in rubber compounds using a styrene-butadiene-glycidyl methacrylate terpolymer (GMA-SBR) synthesized by cold emulsion polymerization. It has been demonstrated that silica particles in conventional rubbers tend to agglomerate during storage, as well as at the onset of vulcanization, because of their polarity. GMA-SBR can improve the compatibility with silica by the formation of covalent bonds between the epoxy groups of GMA-SBR and silanol groups on the silica surface. SBR 1721 and GMA-SBR silica-filled compounds were prepared without curatives by a kneader and a two-roll mill. After compounding, the reaction of the epoxy group, filler flocculation, and morphology of the compounds were analyzed using infrared spectroscopy, a rubber process analyzer, and transmission electron microscopy, respectively. In addition, the content of bound rubber in the compounds was determined by extracting the unbound rubber material with toluene. The GMA-SBR silica-filled compounds had a higher bound rubber content and exhibited significantly different filler flocculation and silica dispersion behaviors compared with the SBR 1721 silica-filled compounds.     

Mechanical and dielectric properties of SEBS modified by graphite inclusion and composite interface

Tough and flexible dielectrics were prepared using graphite (G), a natural and low-cost resource, as filler in polystyrene-b-(ethylene-co-butylene)-b-polystyrene (SEBS) and maleinized SEBS (SEBS-MA) matrices. The disintegration of graphite in submicron particles was accomplished by the shear forces during the melt processing step and it was highlighted by atomic force microscopy. Simultaneous increase of tensile strain, strength and Young's modulus was noticed for SEBS/G and SEBS-MA/G composites compared to unfilled matrices, this remarkable feature being previously reported only for some nanocomposites. Moreover, an exponential variation of the dielectric permittivity with the volume fraction of G was obtained. Higher reinforcing efficiency and better dielectric properties were observed in SEBS-MA/G composites, compared to the corresponding SEBS/G composites, due to the stronger polymer–filler interface and better dispersion of graphite. This study brings new insights into nanolevel properties of SEBS composites and it opens new perspectives on high performance composites by using graphite instead of expensive graphene and efficient melt mixing process.     

Properties of Natural Rubber Vulcanizates/Nanosilica Composites Prepared Based on the Method of In-situ Generation and Coagulation

Using the characteristics of silica sol dispersing well in water and easy formation of silica gel when the silica sol is heated, by mixing a system of concentrated natural rubber latex and silica sol, the silica sol can in-situ generate SiO₂ particles when heated. After coagulation of the mixed system, natural rubber/nanosilica composites C(NR/nSiO₂) were obtained. The composites C(NR/nSiO₂) and their vulcanizates were studied using a rubber processing analyzer (RPA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The influence of silica contents on the C(NR/nSiO₂) vulcanizates mechanical properties, cross-linking degree, Payne effect, dissipation factor (tanδ), and the particle size and dispersion of SiO₂ in NR were investigated. The results obtained were compared with the NR/SiO₂ composites based on traditional dry mixing of bale natural rubber and precipitated silica (white carbon black). The results showed that when using a sulfur curing system with a silica coupling agent (Si69) in C(NR/nSiO₂), the vulcanizate had better mechanical properties, higher wet resistance, and lower rolling resistance than those without Si69. In the composites C(NR/nSiO₂) and their vulcanizates, the SiO₂ particles’ average grain diameter was 60 nm, and the good-dispersion of the in-situ generated SiO₂ in the rubber matrix were a significant contribution to the satisfactory properties of C(NR/nSiO₂) composites and their vulcanizates.     

Thermodynamic Description of Strain-Induced Crystallization of Natural Rubber by a Combination of the Tube Model and a Scaling Argument

The addition of nanoparticles remarkably improves the mechanical properties and strain-induced crystallizability of natural rubber. To reveal the underlying mechanism for the enhancement of these physical properties, we analyzed the microstructural changes of rubber due to the inclusion of clay and carbon black by using the tube model. The rubber filled with clay exhibited a stronger confinement effect of entanglements on the chain conformation compared with the pure rubber and that filled with carbon black. As a result, we propose a new thermodynamic approach to the entropic elasticity of entangled rubber by a combination of the blob scaling argument and the tube model. The thermodynamic analysis demonstrated that the restriction effects of both entanglements and the filler network led to a reduction of the conformational entropy in clay-filled rubber, resulting in the decrease of the onset strain of crystallization. These results revealed the mechanism of the strain-induced crystallization and filler reinforcement from the viewpoint of thermodynamics.     

Reinforcement effects of multiwall carbon nanotubes in elastomeric matrices: Comparison with other types of fillers

Mechanical and electrical properties of composites based on butyl rubber and multiwall carbon nanotubes (MWNTs) are investigated. Gradual increases in elastic moduli are observed with the filler content. It was found that the degree of strain affects the electrical resistivity. Finally, the level of reinforcement imparted to a rubbery matrix by carbon nanotubes is compared with that provided by other types of fillers such as carbon black, clay fibers or layered silicates.     

Synthesis of spin labelled silica and EPR molecular dynamics study at silica–polymer interfaces

Information concerning the interface structure in filler/polymer composites is of key importance for the rationalization of reaction mechanisms in mechano‐chemical (extrusion, blending, etc.), thermal or radiation induced free radical processes and for elucidating the factors underlying the reinforcing mechanism. The analysis of the chain dynamics is a suitable tool for undertaking such investigations because any reactivity parameter (rate constants, collisional frequencies, activation energies) and bonding interactions are strictly related to the mobility of the interacting centres. EPR spectroscopy coupled with specific spin labelling at the filler/polymer interface is a tool for making such novel perspective available. In this work, a spin labelling study of the molecular motion at the filler–rubber interface in a silica–SBR blend is reported. Spin labels of different length, spanning a 9–11 Å depth and linked to the surface of silica particles, were prepared and used for determining the rotational diffusion tensors, the T₅₀ and order parameter in silica/SBR interfaces. The measurements carried out as a function of the temperature in comparison with unbound spin probes dispersed in the rubber matrix have afforded information consistent with the structure of the interfaces predicted by molecular–level theoretical models. Copyright © 2010 John Wiley & Sons, Ltd.