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.     

Characteristic Frequency of Carbon Black Filled Rubber

Due to the high electrical conductivity of carbon black (CB) particles, the presence of CB improves the conductivity of filled rubbers. The impedance spectra of CB filled rubber were simulated using an infinite resistor‐capacitor (RC) circuit by considering the tunneling conduction mechanism for the CB contact regions. The calculated results had a similar appearance to the experimental results, i.e., the Cole‐Cole plot was a semi‐circle and a peak appeared in a plot of the imaginary component of complex impedance with respect to the frequency from which the characteristic frequency was obtained. For a simple RC circuit in parallel connection, the logarithm of the characteristic frequency should be a linear function of the 1/3 power of the average number of primary particles per aggregate. A slight deviation from the line found in the simulations was attributed to the network contribution. Additionally, low CB loading had little effect on the characteristic frequency, in accordance with the experimental data, while high loading had a marked effect. Furthermore, the calculations showed that the characteristic frequency was affected not only by the distribution of individual CB aggregates, but also by the percentage of agglomerates at high CB loading.     

Simulation of Carbon Black Network in Filled Rubber

Carbon black (CB) is one of the most important fillers for rubber and plastics materials. How to describe the CB network is a fundamental problem for establishing relationships between the CB network and the mechanical properties of filled rubber. In view of the electrical conductivity of CB, an infinite circuit consisting of numerous contact resistors, interconnected with each other, is proposed to simulate the CB network in filled rubber; the resistances were determined by considering the tunneling conduction mechanism and a Gaussian distribution for the CB aggregate junction width. As an example, the electrical resistivity of CB (N330) filled natural rubber during uniaxial deformation was studied. It was found that the logarithm of resistivity was an approximately linear function of the extension ratio, and the resistivity increased with the increase of average number of primary particles per aggregates. Additionally, some published experimental points lie between the curves calculated for five primary particles and for seven primary particles per aggregate at extension ratios below 1.2. The calculations suggested that the average number of primary particles per aggregate for CB type N330 might be between five and seven.     

Simulation of Electrical Resistivity of Carbon Black Filled Rubber under Elongation

It has been known that the carbon black (CB) network is responsible for the electrical and mechanical behaviors of filled rubber. Due to the complexity involved in the filled rubber in relation to the conductive mechanism of the CB network, there has been little work concerned with simulation of the electrical behavior at large strains. Based upon an infinite circuit model, the electrical resistivity of CB filled rubber under elongation is simulated. For CB (N330) filled natural rubber with volume fraction of 27.5%, the simulated electrical resistivity increases with elongation at small stains, corresponding to the breakup of the agglomerates. The reduction in resistivity at larger strains corresponds to the decrease of the junction width, which results in a decrease of the contact resistance. Good agreement is found between the simulations and the experimental data available in the literature. The simulated results confirm the effects of the breakdown of the CB network and the alignment of CB aggregates under strain on the electrical resistivity.     

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.     

Investigation of Carbon Black Network in Natural Rubber with Different Bound Rubber Contents

A new method was applied to modify the surface activity of virginal carbon black (VCB). LA‐57, one kind of hindered amine light stabilizer, was adsorbed onto the carbon black surface through a strong shear force induced by the screws of a HAAKE internal mixer. The modified carbon black (MCB) was characterized by FT‐IR and thermogravimetric analysis (TGA). The bound rubber content of the natural rubber (NR) compounded with MCB and VCB varied with the fraction of LA‐57 on the MCB surface. The nonlinear effect at small strains, generally referred as the Payne effect, was investigated in the rubber compounds based on the different bound rubber contents. The NR compound containing the lowest bound rubber content had an obvious Payne effect. Based on the bound rubber content, the types of filler network varied from direct contact mode to the joint rubber shell mechanism.     

Variation of the Payne Effect in Natural Rubber Reinforced by Graft-Modified Carbon Black

Carbon black (CB) was modified by liquid grafting and used for natural rubber (NR) reinforcement. Payne effects during NR reinforcement by the graft-modified carbon black (GCB) were analyzed in this paper. The results showed a proportional relationship between filler content and the Payne effect. Rubber compounds with GCB presented weaker Payne effects than their non-modified counterparts. Qualitative analysis of the correlation between filler network structure and filler content was conducted according to the relationship between bound rubber of a rubber compound and shear modulus. The impact of the storage period on the Payne effect was further studied, and the results demonstrated that the longer the storage period of the rubber compound, the stronger the Payne effect tended to be. The mechanisms by which the Payne effects were manifested differed according to the content of the filler in the rubber.     

炭黑橡胶复合材料导热逾渗行为

研究了导电炭黑40b2填充天然橡胶复合材料的导热性能和力学性能随炭黑体积分数的变化规律,并采用扫描电子显微镜观察了炭黑橡胶体系内部的炭黑分布状况.结果表明,导热性能随炭黑体积分数的变化规律存在类似于导电逾渗现象的导热逾渗现象,逾渗阈值在8.3%～13.63%之间.在逾渗阈值之后,复合材料的拉伸强度下降.炭黑橡胶复合材料...     

Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds

Nanocomposite vulcunizates based on a SBR/ENR50 (50/50%wt) rubber blend containing nanoclay (5 or 10 phr) with and without carbon black (CB 20 phr) were prepared by melt blending in an internal mixer. The compound containing 35 phr carbon black (only) was prepared as a reference sample. Microstructure of nanocomposite samples was investigated by using X-ray diffraction (XRD), melt rheo-mechanical spectroscopy (RMS), and scanning electron microscopy (SEM). The XRD patterns revealed that the distance between the clay layers were increased by adding CB to the nanocomposite samples; they caused better diffusion of chains between the layers and resulted in an intercalated structure. The RMS results also indicated the formation of the filler-filler networks. SEM images of fracture surfaces showed the presence of much roughness in the samples containing both nanoclay and CB compared to the other samples. The results obtained from application of the Flory–Rhener equation showed a high crosslink density for the sample with 10 phr nanoclay and 20 phr CB. Dynamic mechanical behavior, mechanical properties, and abrasion resistance of the nanocomposites were evaluated. The results indicated that the sample containing 10 phr nanoclay and 20 phr CB had an increased dynamic elastic modulus, reduced maximum loss factor (tanδ)_max,, and an improved tensile strength and abrasion resistance compared to the reference sample. Also, this sample showed the lowest maximum loss factor, at 50–60°C, so it can be a candidate for tire-tread application.     

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).     

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.     

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.     

Influence of Carbon Black on Crosslink Density of Natural Rubber

Vulcanization and reinforcement are two important factors contributing to the properties of vulcanized rubber. In order to investigate the influence of carbon black (CB) on chemical crosslinking, three groups of samples with different crosslink densities were prepared. In each group with the same crosslink density, different amounts of CB were introduced. Data fitting showed that delta torque (ΔM = M _H–M _L, the difference between the highest and lowest torques during curing) in the cure curves of each group had a good linear relationship with CB load and extrapolation of the fitting lines almost intercepted the x coordinate at the same value, which indicated that CB had no influence on the chemical crosslinking of the rubber. To verify the above result, a series of nonfilled natural rubber (NR) vulcanizates with different crosslink densities were studied using equilibrium swelling and the swelling ratios were compared with those of corresponding CB filled rubbers with the same sulfur and accelerator amount. The results of both the equilibrium swelling and NMR relaxation parameter measurements showed that CB filled vulcanizates had higher apparent crosslink densities than those of unfilled ones due to the strong interaction between rubber molecules and the surface of the CB particles. The swelling ratios of filled rubbers had a parallel relationship with those of the unfilled ones which indicated that CB had little influence on chemical crosslink density introduced by chemical vulcanization.     

Comparative Properties of Styrene-Butadiene Rubbers (SBR) Containing Pyrolytic Carbon Black,Conventional Carbon Black,and Organoclay

To evaluate the reinforcing potential of pyrolytic carbon black, styrene-butadiene rubber (SBR) was filled with pelletized pyrolytic carbon black (pCB_p), N660 industrial CB, their blend in a 1/1 ratio, and the latter also in the absence and presence of additional organoclay (OC). The Shore A hardness of the filled SBR gums was 65 ± 2°. Effects of the compositions on the filler dispersion, cure behavior, dynamic mechanical thermal parameters (including the Payne effect), tensile mechanical (including the Mullins effect), and fracture mechanical (making use of the J-integral concept) properties were studied and discussed. Though pCB_p had a higher specific surface weight than CB, the latter proved to be a more active filler with respect to the tensile strength. The opposite tendency was found for the tear strength and fracture mechanics characteristics (J-integral at crack tip opening, tearing modulus, and trouser tear strength). This was traced to an enlargement in the crack tip damage zone supported by the dispersion characteristics of the pCB_p. The performance of pCB_p was similar to that of CB with respect to some other properties. OC supported the filler networking which positively affected the resistance to crack initiation.     

Effects of Carbon Black on Chain Mobility and Dynamic Mechanical Properties of Solution Polymerized Styrene-Butadiene Rubber

The structure of the bound rubber, the ¹H NMR (nuclear magnetic resonance) relaxation time, and the crosslink density of the physical network and the glass transition, were studied for solution polymerized styrene-butadiene rubber (SSBR) filled by carbon black, to investigate the effects of carbon black on the chain mobility and dynamic mechanical properties. It was found by ¹H NMR analysis that the rubber chains were adsorbed on the surface of carbon black to form physical crosslinks and restrict the mobility of the chains, especially for some high-mobility units such as chain ends. It was calculated, according to the molecular weight between adjacent crosslinks, that the main motion units of the tightly adsorbed chains appeared to be similar in size to the chain segments. The glass transition temperature (T _g) obtained by differential scanning calorimetry (DSC) could not be used to judge the effect of carbon black on chain mobility, while the appearance and change of the loss-tangent (tan δ) peak at high temperature in dynamic mechanical thermal spectrometry (DMTS) test showed that there were three chain states: free chains, loosely adsorbed chains, and tightly adsorbed chains. The dynamic rheology test showed that the unfilled SSBR compound had the rheological characteristics of entangled chain networks; however the nonlinear viscoelasticities of the filled SSBR were related to the gradual disentanglement of adsorbed chains and free chains. The peaks in tan δ vs. temperature curves implied that the motion unit size decreased with the increase of bound rubber content, and the modulus vs. temperature curve showed an apparently lower mobility of adsorbed chains than that of free chains through the very low dependence of modulus on temperature for the highly filled compounds. The extremely high tensile modulus of the vulcanizate with 63.6% carbon black at room temperature also implied that the adsorbed chains were in the glass state due to their restriction by the carbon black.     

Effect of Ultrafine Full-Vulcanized Powdered Rubber on the Properties of the Intumescent Fire Retardant Polypropylene

Ultrafine full-vulcanized powdered rubber (UFPR) was added into intumescent fire retardant polypropylene (IFR-PP) composites, and fire retardance, morphology, and properties of the composite were analyzed. Ammonium polyphosphate and pentaerythritol were used as the intumescent fire retardants (IFR). The mechanical properties (elongation at break increased from 70% to 110%) and the melt flowability of IFR-PP improved by adding a small quantity of UFPR (less than 0.5 phr) but decreased when the UFPR was more than 0.5 phr. At the same time, the fire retardance, as measured by the limiting oxygen index and the UL94 vertical test rating, and other mechanical properties decreased appreciably with adding UFPR. The reasons were analyzed by using SEM micrographs, and a model was proposed to explain the reasons.     

In situ Grafting onto Silica Surface with Epoxidized Natural Rubber via Solid State Method

An in situ solid state grafting reaction between epoxidized natural rubber (ENR) and silica was performed in a Haake internal mixer. Resulting ENR‐grafted silica was characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) measurements. Based on these results, it was concluded the silanol groups (Si‐OH) of silica caused the ring opening of ENR oxirane rings so that ENR was grafted onto the silica surface. Transmission electron microscopy (TEM) photographs showed ENR‐grafted silica had better dispersibility and smaller aggregates compared with the original silica. Dynamical mechanical analysis (DMA) of vulcanized rubber compounds contained ENR‐grafted silica showed the glass transition temperature (T _g) of grafted ENR molecules shifted to higher temperature, from ?3°C to 20°C, indicating the mobility of ENR was greatly restricted. As a result, the compounds containing ENR‐grafted silica have higher hysteresis, and can be applied in a much wider field, such as damping materials, tires of racing cars, and so on.     

Influence of In-situ Grafting on the Dispersion of Carbon Black in Solvents and Natural Rubber

In-situ grafting of natural rubber (NR) onto the carbon black (CB) surface by a solid-state method was used to obtain grafted carbon black (GCB). The morphology of the original CB and GCB particles was observed by AFM and TEM. The original CB particles fused together and occurred as large dendritic agglomerates while the GCB particles occurred as small aggregates about 150 nm in diameter. The dispersion and dispersion stability of CB and GCB in toluene and cyclohexene were studied by zeta potential and a spectrophotometer. The results showed that the grafting procedure can improve both dispersion and dispersion stability of CB particles. The dispersion in NR was studied by DMA and observed by SEM. It was shown that GCB has better dispersion than CB in a NR matrix. As expected a weakened filler-filler interaction and enhanced filler-polymer interaction occurred after grafting modification.     

Preparation and Characterization of Grafted Natural Rubber/Graphene Oxide Nanocomposites

Vinyltriethoxysilane (VTES) was grafted onto natural rubber (NR) in latex form, using potassium persulfate (KPS) as initiator. The VTES grafted NR (NR-g-VTES) was then further reinforced with graphene oxide (GO) by a mechanical mixing method with different GO loadings to get the rubber composite (GO/NR-g-VTES). The NR-g-VTES was characterized and confirmed by attenuated total teflectance-Fourier transforms infrared spectroscopy (ATR-FTIR). The effect of GO content on the curing characteristics and resulting mechanical properties of the GO/NR-g-VTES were studied and compared with neat NR filled with GO (NR/GO). The maximum and minimum torque and the tensile and tear strength of the NR-g-VTES/GO composites were higher than that of NR/GO. The samples containing low GO concentration showed maximum torque and tensile and tear strength. Dynamic mechanical analysis showed that the interaction between GO and NR-g-VTES was better than that of the GO-reinforced NR.     

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.