Structure–property relationships of silica/silane formulations in natural rubber,isoprene rubber and styrene–butadiene rubber composites

The mechanical performance of natural rubber (NR), synthetic poly-isoprene rubber (IR), and styrene–butadiene rubber (SBR) composites filled with various silica/silane systems is investigated. The results are analyzed by referring to micro-mechanical material parameters, which quantify the morphological and structural properties of the polymer and filler network. These are obtained from fits with the dynamic flocculation model (DFM) describing the strongly nonlinear quasi-static stress–strain response of filler-reinforced elastomers as found from multihysteresis measurements of the investigated compounds. We focus on the reinforcement mechanisms of silica compounds with coupling and covering silane, respectively. The fitted material parameters give hints that the coupling silane provides a strong chemical polymer–filler coupling, which is accompanied by improved strength of filler–filler bonds for all three rubbers types. This may result also from the chemical coupling of short chains bridging adjacent silica particles. It implies larger stress values for the coupling silane and, in the case of NR and IR, a more pronounced “Payne effect” compared to the covering silane. In contrast, for SBR, the coupling silane delivers a lower Payne effect, which is explained by differences in the compatibility between rubber type and silane-grafted silica surface. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48435.     

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

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

Kinetics of the phase selective localization of silica in rubber blends

The Fourier transformed infrared (FTIR) spectroscopy on the rubber‐filler gel has been used as a tool for the quantitative characterization of the phase selective silica localization in styrene butadiene rubber (SBR)/natural rubber (NR) blends. The so‐called rubber‐layer L was introduced to describe the selective wetting behavior of the rubber phases to the filler. SBR/NR blends filled with silica were the focus of the experimental investigation. NR shows a higher wetting rate than SBR. Silane addition does not affect the wetting of NR but slowdowns the wetting of SBR. With increasing chamber temperature the value of the rubber‐layer L of all mixtures increases owing to the different thermal activated rubber‐filler bonding processes. Using the wetting concept the kinetics of silica localization in the phases of heterogeneous rubber blends was characterized. Because of the higher wetting rate of the NR component, in the first stage of mixing of NR/SBR blends more silica is found in the NR phase than in the SBR phase. In the next stage, silica is transferred from the NR phase to the SBR phase until the loosely bonded components of NR rubber‐layer are fully replaced by SBR molecules. POLYM. COMPOS., 31:1701–1711, 2010. © 2010 Society of Plastics Engineers.     

Reinforcement effects in fractal-structure-filled rubber

A quantitative morphological analysis has been performed using AFM and SAXS measurements in order to determine the spatial distribution of fillers in silica SBR composites. The proportion of fillers in agglomerates or aggregates of silica has thus been separated. Additional measurements have been carried out to quantify the amount of modified polymer in the vicinity of the filler surface, i.e. the bound rubber. It is shown that the reinforcing phase, constituting both silica particles and bound rubber, can be considered either as the dispersed or the continuous phase depending on the filler content.The linear dynamic mechanical properties of composites are then analysed. The variations of the shear modulus as a function of the filler content are then related to either the reinforcement effect induced by fillers or the development of specific additional interactions between phases, i.e. the interface effects. To separate the respective contribution of these effects from the overall dynamic behaviour of composites, micromechanical modelling is then performed. In a first step, the viscoelasticity of composites reinforced by 5.7 vol% of silica is predicted with the help of Christensen and Lo's model. For composites filled with 10 and 15 vol% of silica, self-consistent modelling, applied in a reverse mode, confirmed that the reinforcing phase, i.e. silica particles and bound rubber, acts as the continuous phase, in agreement with the morphological analysis. From the predicted dynamic mechanical properties of the reinforcing phase, the bound rubber behaviour is thus extracted as a function of the filler content and compared to that of unfilled SBR.     

Chemorheology of crosslinked polyisoprene/poly(butadiene co-styrene) blends

Physical and chemical properties of IR/SBR blend systems crosslinked by dicumyl peroxide were investigated in detail. In order to study physical structure of cross-linked rubber blends, measurement of birefringence of extended samples and observation by scanning electron microscope (SEM) of ones ruptured in liquid nitrogen were also carried out. In the vicinity of IR/SBR = 30/70 (weight ratio) the phase structure of blends was reversed. The size of domain was in about 0.2 to 0.7 μm dependent on the blend ratio. In preparing the cross-linked rubber blends, cross-linking reaction seemed to occur independently in each rubber phase. The birefringence linearly increased with the blend ratio in the range of IR/SBR = 100/0 to 40/60 and then largely increased in IR/SBR < 30/70. Stress relaxation of rubber blends was observed at 373 K in both air and nitrogen. Chemical stress relaxation of these systems could be represented by a combination of rate constant of stress relaxation and volume fraction of each cross-linked rubber, that is, the degradation of the networks of cross-linked rubber blends occurred independently in each rubber phase.     

Influence of the filler type on the rupture behavior of filled elastomers

This work is devoted to the rupture behavior of elastomers filled with carbon black (CB) or silica. Two elastomers have been studied: one which crystallizes under strain, natural rubber (NR), and another one which does not crystallize, styrene butadiene rubber (SBR). The study of the crack propagation of Single Edge Notched specimen (SENT) during stretching at different speeds focuses on the crack initiation and crack deviation phenomenon. This deviation is of main importance in the materials crack resistance as it leads to a large increase in the energy needed for rupture. The deviation in filled or unfilled NR is controlled by crystallization, which is a slow process. In unfilled SBR, deviation is controlled by polymer chain orientation, which is hindered by relaxation mechanisms. The introduction of fillers promotes strain amplification, and strain anisotropy in the crack tip region of the notched samples, and therefore crack deviation. In term of energy density at break of the SBR composites, the SBR filled with silica treated with a covering agent is the most efficient. Thus, a weak interface between the silica and SBR promotes better rupture properties. When comparing Silica and CB filled NR, the highest strain energy to rupture is also obtained with silica. This might be due to the weaker filler‐matrix interface for silica. Thus, these results evidence the kinetic aspect of the rupture, and of the mechanisms it involves: the polymer relaxation, the crystallization (for NR), and the filler‐matrix interaction and decohesion, all of them being strongly interrelated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Multiscale Observation of the Fatigue‐Induced Damage Mechanisms in Carbon‐Black Filled Styrene‐Butadiene Rubber

Filled rubber materials exhibit a complex macroresponse characterized by stress softening, hysteresis, and dissipative heating when they are cyclically loaded. The relationship of these inelastic features to the microstructure changes is far from being fully established. This paper deals with the damage mechanisms in sulfur‐vulcanized styrene‐butadiene rubber (SBR) specimens in the diablo form reinforced with carbon‐black (CB) and zinc‐oxide (ZnO) fillers, and submitted to tension cyclic loading at room temperature. The microstructure alteration is characterized at different relevant scales and at different zones of the diabolo specimen by means of various technologies in the aim to report valuable insights about the mechanisms responsible for the macroresponse of this rubber‐filler material system. IR absorption spectra reveal that increasing filler content induces more interfacial interaction between CB and SBR chains. The environmental scanning electron microscopy (ESEM) observations show relevant altered morphologies of elastomeric chains with a predominant effect of both CB and ZnO fillers. A mesoscale observation of material density variation is presented using X‐ray computed tomography and the results are compared with those issued from ESEM.     

改性膨润土在丁苯橡胶中的应用

改性膨润土吸附有机物后，晶胞中的部分基团发生了变化，但蒙脱石的晶胞形状没有改变。随着丁苯橡胶中改性膨润土粒径的减小，丁苯橡胶硫化胶的拉伸强度、扯断伸长率、３００％定伸应力、撕裂强度都有所增加，硬度下降。其填充效果比碳酸钙的效果好。     

Interface effects in elastomers reinforced by modified precipitated silica

The contributions of the so‐called “interface effects” on the overall viscoelastic behavior of SBR reinforced by precipitated silica modified by model sizing agents are evaluated by using micromechanical models in a reverse mode. According to the nature of the coupling agent, two kinds of “interface effects” can be distinguished: (i) an overall change in the viscoelastic behavior of the polymer matrix, when the sizing agent is a chemical promotor acting as additional ties of the SBR network, and (ii) the formation of an actual mesophase, when direct interactions between SBR chains and silica could occur, as for example, when the coating agent of silica is an organosilane based on short aliphatic chains. With increasing the length of the aliphatic chains of the coating agent (LOS agent), some a plasticisizing effect of the polymer is detected by DSC. It can affect either the entire polymer matrix or a confined region at the close vicinity of silica aggregates. According to this assumption, the bimodal viscoelastic behavior of the LOS‐mesophase revealed by the modeling indicates that in addition to a local plasticisizing effect induced by this agent, some direct interactions could occur between silica surface and SBR constraining the mobility of rubber molecules.     

Influence of PP fiber and SBR latex on the mechanical properties of crumb rubber mortar

This article presents a new kind of rubber mortar modified by polypropylene fiber (PP fiber) and styrene‐butadiene rubber latex (SBR latex). The mechanical properties of this crumb rubber mortar were investigated in the research, including the compressive strength, flexural strength, flexural toughness, and flexural elasticity modulus. The test results showed that the flexural toughness index of the rubber mortar was seen to enhance by about 50–100% with the addition of PP fiber and SBR polymer latex. Due to the addition of PP fiber and SBR latex, the flexural elastic modulus of rubber mortar could further reduce by 4–27%. The three‐phase composite dispersion model of this rubber mortar was put forward. Furthermore, it was observed from scanning electron micrograph that the interfacial transition zone between the rubber particles and cement paste was enhanced by the SBR latex, and the interleaving of polymer films and rubber particles strengthen the flexibility and toughness of the mortar. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40591.     

BIMS/filler interactions. I. Effects of filler structure

Polymer/filler interactions have been found to affect the performance of tire tread, sidewall, innerliner, or carcass and other industrial rubber products that are all based on filled elastomers. Identification of types of various polymer/filler interactions and ranking of their impacts have been elusive. Isobutylene-based polymers have relatively saturated structures and contain very low concentrations of functional group. Examples are BIMS (a brominated isobutylene/p-methylstyrene copolymer) containing p-bromomethylstyrene and p-methylstyrene; bromobutyl rubber containing  Br and olefin; chlorobutyl rubber containing  Cl and olefin; and butyl rubber containing olefin. On the other hand, high diene rubbers, such as polybutadiene rubber, polyisoprene rubber, and styrene/butadiene rubber, have unsaturated backbones and high olefin contents. Hence, different types and extents of interaction with reinforcing fillers, such as carbon black (CB) or silica, are expected in these two classes of elastomer. This work employs bound rubber (solvent extraction), viscoelasticity, stress–strain measurements, and solid state NMR to identify, differentiate, and scale polymer/filler interactions in unvulcanized BIMS/CB, BIMS/silica, SBR/CB, and SBR/silica composites, where SBR denotes a styrene/butadiene rubber. Four different types of CB and one type of silica have been studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4943–4956, 2006     

Shape controlled spherical (0D) and rod-like (1D) silica nanoparticles in silica/styrene butadiene rubber nanocomposites: Role of the particle morphology on the filler reinforcing effect

Silica/styrene butadiene rubber (SBR) nanocomposites were prepared by blending method using shape-controlled spherical and rod-like nanoparticles with different aspect ratios as filler for the rubber reinforcement. The differently shaped silica particles were synthesized by sol–gel method using tetraethoxysilane (TEOS) and (3-mercaptopropyl) trimethoxysilane (MPTSM) as silica precursors, and cetyltrimethylammonium bromide (CTAB) as structure directing agent. This strategy allowed to study the influence of the particle morphology on the reinforcing effect independently of the silica surface chemistry and considering the aspect ratio as the only geometrical variance. Spherical and anisotropic rod-like particles, dispersed in the nanocomposites, formed a network of particles bridged by thin rubber layers throughout the SBR matrix. Moreover, differently oriented domains of aligned rods are observed when the aspect ratio of particles increases and is ≥2. Dynamic-mechanical properties demonstrated that the rod-like particles with the higher aspect ratio provided stronger reinforcement of the rubber. This was related to the self-alignment of the anisotropic particles and to the consequent larger filler/polymer interface, compared to that of spherical ones.     

Oil absorbents based on styrene–butadiene rubber

Four oil absorbents based on styrene–butadiene (SBR)—pure SBR (PS), 4‐tert‐butylstyrene–SBR (PBS), EPDM–SBR network (PES), and 4‐tert‐butylstyrene‐EPDM‐SBR (PBES)—were produced from crosslinking polymerization of uncured styrene–butadiene rubber (SBR), 4‐tert‐butylstyrene (tBS), and ethylene–propylene–diene terpolymer (EPDM). The reaction took place in toluene using benzoyl peroxide (BPO) as an initiator. Uncured SBR was used as both a prepolymer and a crosslink agent in this work, and the crosslinked polymer was identified by IR spectroscopy. The oil absorbency of the crosslinked polymer was evaluated with ASTM method F726‐81. The order of maximum oil absorbency was PBES > PBS > PES > PS. The maximum values of oil absorbency of PBES and PBS were 74.0 and 69.5 g/g, respectively. Gel fractions and swelling kinetic constants, however, had opposite sequences. The swelling kinetic constant of PS evaluated by an experimental equation was 49.97 × 10^?2 h^?1. The gel strength parameter, S, the relaxation exponent, n, and the fractal dimension, d_f, of the crosslinked polymer at the pseudo‐critical gel state were determined from oscillatory shear measurements by a dynamic rheometer. The morphologies and light resistance properties of the crosslinked polymers were observed, respectively, with a scanning electron microscope (SEM) and a color difference meter.     

Multiphase polymer processing: Controlled-ingredient-distribution mixing and its effect on some properties of styrene-butadiene (SBR)/butadiene-acrylonitrile copolymer rubber blend compounds

The flex-crack-growth resistance and oil-swelling resistance of a styrene-butadiene (SBR)/butadiene-acrylonitrile co-polymer (NBR) rubber blend are studied as a function of the distribution of ingredients in the individual rubber phases. The blends consist of 70:30 weight ratio of SBR:NBR with incorporation of 82.5 phr carbon black and other ingredients via the controlled-ingredient-distribution mixing procedure. The results show that flex crack growth is affected by the distribution of carbon black. Better flex crack growth resistance could be achieved by adding 10 percent of carbon black to the NBR rubber phase and 90 percent to the SBR phase. The swelling of these rubber blends in ASTM #2 oil is also affected by the location of carbon black and by the mixing history. The blends with more black initially preloaded in the SBR phase have lower swelling, as have blends with shorter cross-mixing time or the mill. A simple equation based on the permeation/moduli of composite materials is proposed to describe the swelling of this rubber blend in terms of the swelling of the constituent rubber phases, the distribution of ingredient in the individual rubber phases, and the blend morphology. One of the key assumptions is to consider the individual black preloaded rubber as a continuum. The quantitative correlation with the observed swelling data is reasonably good.     

Silica‐modified SBR/BR blends

The purpose of this article is that the silica‐modified SBR/BR blend replaces natural rubber (NR) in some application fields. The styrene‐butadiene rubber (SBR) and cis‐butadiene rubber (BR) blend was modified, in which silica filler was treated with the r‐Aminopropyltriethoxysilane (KH‐550) as a coupling agent, to improve mechanical and thermal properties, and compatibilities. The optimum formula and cure condition were determined by testing the properties of SBR/BR blend. The properties of NR and the silica‐modified SBR/BR blend were compared. The results show that the optimum formulawas 80/20 SBR/BR, 2.5 phr dicumyl peroxide (DCP), 45 phr silica and 2.5 mL KH‐550. The best cure condition was at 150°C for 25 min under 10 MPa. The mechanical and thermal properties of SBR/BR blend were obviously modified, in which the silica filler treated with KH‐550. The compatibility of SBR/BR blend with DCP was better than those with benzoyl peroxide (BPO) and DCP/BPO. The crosslinking bonds between modified silica and rubbers were proved by Fourier transform infrared analysis, and the compatibility of SBR and BR was proved by polarized light microscopy (PLM) analysis. The silica‐modified SBR/BR blend can substitute for NR in the specific application fields. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Different preparative modes for the incorporation of additives in NR/SBR blends

Rubber goods usually require a combination of properties that cannot be provided by one elastomer only and then two or more polymer components have to be mixed to meet specific requirements. In such cases, the additives normally employed in rubber formulations are unevenly distributed, depending on the affinity of each compound to each polymeric phase. Thus, the dispersion of each one of these ingredients in the different rubbers will influence the rate and degree of vulcanization and, in consequence, the performance of the final composite. In this work, natural rubber (NR) and styrene butadiene rubber (SBR) were mixed in a 1 : 1 ratio. The compositions were obtained according to ASTM D 3182, by using four different preparative modes for the incorporation of the additives. After vulcanization, morphological, and dynamic mechanical thermal analysis, tensile strength, hardness, and tear resistance of each composition were investigated. The results show that the best properties were found when the NR/SBR mixture was prepared in such a way as to favor the vulcanization of the SBR phase while preserving the NR phase from excessive vulcanization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 483–489, 2004     

Effect of carbon‐based nanoparticles on the cure characteristics and network structure of styrene–butadiene rubber vulcanizate

The network structure of styrene–butadiene rubber (SBR) in the presence of carbon black (CB) with two different structures and multi‐walled carbon nanotubes (MWCNTs) was investigated. Swelling behaviour, tensile properties at various strain rates and cure kinetics were characterized. Experimental data were analysed using the Flory–Rehner model as well as the tube model theory. It is found that the network structure of CB‐filled SBR follows a three‐phase composite model including rigid particles, semi‐rigid bound rubber and matrix rubber. This bound rubber is postulated to be critical for the mechanical and deformational properties, development of crosslinking density in matrix rubber and polymer–filler interaction. For MWCNT‐filled SBR, the bound rubber does not show a substantial contribution to the network structure and mechanical performance, and these properties are greatly dominated by the higher aspect ratio and polymer–filler interaction. Additionally it is deduced that the crosslinking density of matrix rubber increases on incorporation of the fillers compared to unfilled matrix rubber. Copyright © 2012 Society of Chemical Industry     

Comparing the dynamic behaviour of several rubbers filled with silanized silica nanofiller

BACKGROUND: The effect of the same amount of precipitated silica nanofiller on the curing and dynamic properties of different rubbers, including natural rubber (NR) without and with the addition of elemental sulfur (NR with S), synthetic polyisoprene (IR), polybutadiene (BR) and poly(styrene‐co‐butadiene) copolymer (SBR), was investigated. The silica surfaces were pre‐treated with bis(3‐triethoxysilylpropyl)tetrasulfane (TESPT) to chemically bond the silica to the rubber. The rubbers were primarily cured by using sulfur in TESPT with the addition of optimum accelerator (TBBS) and activator (ZnO), which helped to form sulfur chemical bonds between the rubber and filler. RESULTS: Cure properties, Mooney viscosity, glass transition temperature, bound rubber and crosslink density along with dynamic properties of the filled rubbers, including tan δ, loss modulus (G″) and storage modulus (G′), were measured as a function of double oscillation amplitude (DSA) from 15 to 1000 µm, temperature from ?130 to 100 °C and frequency from 1 to 100 Hz. The results with emphasis on potential for tyre tread applications are discussed. It emerged that SBR along with BR filled rubbers had the highest rolling resistance while IR filled rubber had the least. Moreover, it was found that SBR filled rubber had the best skid resistance and BR filled rubber the worst. CONCLUSION: Interestingly, the variation of G′ with DSA showed a complicated behaviour for different filled rubbers. It emerged that in some DSA ranges the Payne effect was observed, and in the remaining ranges increments of G′ with DSA were seen. Because the bound rubber of most of the filled rubbers was more than 92%, there should be another predominant mechanism in the systems studied rather than simply de‐agglomeration or filler network breakdown, which is proposed by the Payne model. In addition, the nanoscale of the filler may be effective for this behaviour. Copyright © 2008 Society of Chemical Industry     

Thermal and scanning electron microscopy/energy‐dispersive spectroscopy analysis of styrene–butadiene rubber–butadiene rubber/silicon dioxide and styrene–butadiene rubber–butadiene rubber/carbon black–silicon dioxide composites

Silica as a reinforcement filler for automotive tires is used to reduce the friction between precured treads and roads. This results in lower fuel consumption and reduced emissions of pollutant gases. In this work, the existing physical interactions between the filler and elastomer were analyzed through the extraction of the sol phase of styrene–butadiene rubber (SBR)–butadiene rubber (BR)/SiO₂ composites. The extraction of the sol phase from samples filled with carbon black was also studied. The activation energy (E_a) was calculated from differential thermogravimetry curves obtained during pyrolysis analysis. For the SBR–BR blend, E_a was 315 kJ/mol. The values obtained for the composites containing 20 and 30 parts of silica per hundred parts of rubber were 231 and 197 kJ/mol, respectively. These results indicated an increasing filler–filler interaction, instead of filler–polymer interactions, with respect to the more charged composite. A microscopic analysis with energy‐dispersive spectroscopy showed silica agglomerates and matched the decreasing E_a values for the SBR–BR/30SiO₂ composite well. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2273–2279, 2005