Comparative role of Interface in reinforcing mechanisms of Nano silica modified by Silanes and liquid rubber in SBR composites

The objective of the present study is to discuss the role of silica-rubber interfacial interactions on vulcanization kinetics, morphology, mechanical and viscoelastic behavior of silica filled styrene butadiene rubber (SBR) composites. Three types of modifiers, namely mono- and bi-functional silanes as well as hydroxyl-terminated poly butadiene (HTPB) liquid rubber were grafted to silica surface, and composites prepared by these fillers were characterized. Results showed that modified silica, especially grafted by bi-functional silane and liquid rubber, accelerated vulcanization reactions, while pristine silica slowed down vulcanization kinetics of SBR. Morphological studies indicated that all modifications improved dispersion of silica, but HTPB-grafted silica was dispersed to a greater extent in SBR. The observed differences in mechanical and dynamic-mechanical properties of vulcanizates were correlated to the significant differences in silica-rubber and silica-silica interactions. Type of interfacial interactions, i.e. rigid covalent bonds in the bi-functional silane, flexible polymeric bonds in the liquid rubber, and weak energetic bonds in the mono-functional silane, could explain the observed differences. Although all modifications reduced filler networking, rigid covalent bonding by bi-functional silane significantly improved mechanical properties and stabilized the filler network. The mono-functional silane lacks these mechanisms. The soft and flexible interphase of HTPB could create bonds and transfer stresses between the rubber matrix and silica to some extent, however it could not improve the mechanical properties and reduce the Payne effect as much as the bi-functional silane did.     

Effect of silica particle size on chain dynamics and frictional properties of styrene butadiene rubber nano and micro composites

Size and curvature of filler particles affect dynamics of polymer chains in composites. In this work, effects of filler particle size, in two scales of nano- and micro-meters, on dynamics of rubbery chains and frictional properties of composites were studied. Surface modification of nano- and micro-fumed silica by grafting low molecular weight hydroxyl-terminated polybutadiene (HTPB) guaranteed similar surface energy for fillers as measured by their surface tension. Nano- and micro-composites of styrene butadiene rubber were prepared by solvent assisted mixing and progressively increasing volume fraction of fillers. Achievement of nano and micro-composites was confirmed by the scanning electron microscopy. Effect of silica aggregate size on the dynamics of rubber chains was measured by dynamic-mechanical-thermal analyzer and compared through calculation of the activation energy for mobilization of slow-dynamic chains in the rubbery region. It was shown that nano-silica immobilizes the rubber chains more than micro-silica even at equal total interfacial area between filler aggregates and rubber matrix, especially above the percolation limit. Similar trend was seen for the coefficient of friction of composites against rough surfaces, showing the strong effect of chain dynamics on friction properties of rubber vulcanizates.     

Thiol‐containing ionic liquid for the modification of styrene–butadiene rubber/silica composites

To introduce thiol–ene chemistry in the modification of composites by ionic liquid (IL), a novel functional IL, 1‐methylimidazolium mercaptopropionate (MimMP), was synthesized and investigated as a modifier for styrene–butadiene rubber/silica composites. MimMP could be hydrogen‐bonded with silica and react with the double bonds of rubber chains via thiol–ene chemistry. The filler networking, curing behavior, filler dispersion, crosslink density, and mechanical performance were fully studied. The filler networking in the uncured rubber compounds was effectively restrained. The vulcanization was largely accelerated by MimMP. The interfacial interaction was quantitatively evaluated and found to consistently increase with increasing MimMP. The mechanical performance and abrasion resistance of the modified vulcanizates improved considerably. The remarkable improvements were mainly ascribed to the improved interfacial structure comprised of MimMP–silica hydrogen bonding and MimMP–rubber covalent bonds via thiol–ene chemistry. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

NH3-modified swelling of silica-filled silicone rubber

The NH₃-modified swelling method was used for fume silica-filled silicone rubber compounds and vulcanizates. The method provides an estimation of the polymer–filler interaction in the system. Bound rubber reduction due to the modified swelling is shown to be dependent on the silica surface silanol content in the compound. The swelling behavior of silica-filled vulcanizates was also studied in an NH₃ atmosphere. The fraction of polymer–filler attachments in the vulcanizates was found not to depend on the particle size of silica and its surface modification, depending only on the total polymer–filler contact area in the system. No relation was found between bound rubber content in a compound and swelling of a filled vulcanizate of the same composition. The strong rubber-to-filler adherence found in toluene changed to nonadherence under NH₃-modified swelling conditions. The NH₃-induced cleavage of silica–silicone rubber attachments was found to be nearly completely reversible. In the silica-filled silicone rubber vulcanizates, the fraction of polymer–filler attachments due to polymer–filler interaction represents a substantial contribution to the total number of network chains.     

A comparison of white rice husk ash and silica as fillers in ethylene–propylene–diene terpolymer vulcanizates

White rice husk ash (WRHA) and silica filled ethylene–propylene–diene terpolymer (EPDM) vulcanizates were prepared using a laboratory size two‐roll mill. Curing characteristics and physical properties of vulcanizates were studied with respect to the filler loading and filler type. Filler loading was varied from 0–50 parts per hundred resin (phr) at 10 phr intervals. Curing was carried out using a semi‐efficient vulcanization system in a Monsanto rheometer. Enhancement of the curing rate was observed with increasing WRHA loading, whereas the opposite trend was observed for silica‐filled vulcanizates. It was also indicated by the maximum torque and Mooney viscosity results that WRHA offers processing advantages over silica. Compared to the silica‐filled vulcanizates, the effect of filler loading on the physical properties of WRHA‐filled vulcanizates was not significant. According to these observations, WRHA could be used as a diluent filler for EPDM rubber, while silica can be used as a reinforcing filler. © 2001 Society of Chemical Industry     

The effects of natural astaxanthin-modified silica on properties of natural rubber

Natural astaxanthin is a natural substance extracted from algae such as Haematococcus pluvialis. Its molecular structure contains conjugated double bonds as well as keto and hydroxyl groups, and therefore it has high activity. In this research, natural astaxanthin was used to modify the surface of the silica, and its effects on natural rubber vulcanization properties, physical and mechanical properties, dynamic properties, and antiaging properties were studied by means of rubber process analyzer, dynamic mechanical anaylsis, and scanning electron microscopy. The results showed that natural astaxanthin-modified silica could reduce the degree of delayed vulcanization. At the same time, the resilience and abrasion resistance of the obtained vulcanizates were increased. The DIN abrasion volume of the vulcanizates modified and reinforced by the second strategy decreased by 19.2% and 23.6%, respectively; the Payne effect of the natural astaxanthin-modified silica/NR composites was weakened, and the dispersibility of the filler and the compatibility with the rubber matrix was significantly improved. Regardless of which strategy was used to modify the silica, the vulcanizates had a lower rolling resistance. Specially, it could greatly improve the hot air aging resistance property of rubber. Natural astaxanthin as being a renewable feedstock is expected to have a quite broad applications in the rubber industry. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 136, 47287.     

白炭黑/炭黑复合填充对NR性能的影响

在白炭黑和炭黑填料总量一定的情况下,研究了不同白炭黑/炭黑配比对NR性能的影响。结果表明,白炭黑用量增加,NR硫化速率下降,体系中炭黑填料网络被破坏且白炭黑-橡胶间较弱的相互作用也会对NR硫化胶力学性能产生一系列影响。DMA结果表明,加入20~25份白炭黑对提高硫化胶的抗湿滑性和降低滚动阻力最为有效。     

Cardanol grafted natural rubber: A green substitute to natural rubber for enhancing silica filler dispersion

Natural rubber (NR) usage is wide‐spread from pencil erasers to aero tyres. Carbon black and silica are the most common reinforcing fillers in the rubber industries. Carbon black enhances the mechanical properties, while silica reduces the rolling resistance and enhances the wet grip characteristics. However, the dispersion of polar silica fillers in the nonpolar hydrocarbon rubbers like natural rubber is a serious issue to be resolved. In recent years, cardanol, an agricultural by‐product of the cashew industry is already established as a multifunctional additive in the rubber. The present study focuses on dispersion of silica filler in natural rubber grafted with cardanol (CGNR) and determination of its technical properties. The optimum cure time reduces and the cure rate increases for the CGNR vulcanizates as compared to that of the NR vulcanizates at all loadings of silica varying from 30 to 60 phr. The interaction between the phenolic moiety of cardanol and the siloxane as well as silanol functional groups present on the silica surface enhances the rubber–filler interaction which leads to better reinforcement. The crosslink density and bound rubber content are found to be higher for the silica reinforced CGNR vulcanizates. The physico‐mechanical properties of the silica reinforced CGNR vulcanizates are superior to those of the NR vulcanizates. The CGNR vulcanizates show lower compression set and lower abrasion loss. The dynamic‐mechanical properties exhibit less Payne effect for silica reinforced CGNR vulcanizates as compared to the NR vulcanizates. The transmission electron photomicrographs show uniform dispersion of silica filler in the CGNR matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43057.     

Influence of polymer–filler interactions on retraction behaviors of natural rubber vulcanizates reinforced with silica and carbon black

In general, silica‐filled rubber compounds contain a silane coupling agent to improve the filler dispersion and polymer–filler interactions. The silane coupling agent modifies the silica surface and makes crosslinks between the rubber and the silica. Influence of the modification of silica on the retraction behaviors of natural rubber (NR) vulcanizates reinforced with silica and carbon black was studied. Variation of the retraction behaviors of NR vulcanizates with filler composition was also investigated. The vulcanizates containing the silane coupling agent were recovered faster than those without the silane coupling agent. The recovery difference between the vulcanizates without and with the silane coupling agent increased with increased silica content. For the vulcanizates containing the silane coupling agent, the retraction behaviors were nearly the same, irrespective of filler composition. But, for the vulcanizates without the silane coupling agent, the vulcanizate was recovered more and more slowly as the silica content increased. The experimental results are explained with the polymer–filler interactions, modification of silica surface, and formation of crosslinks between silica and rubber. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 691–696, 2006     

Effects of rubber/filler interactions on deformation behavior of silica filled SBR systems

Effect of rubber/filler interactions on the stress-strain behavior for silica filled styrene-butadiene rubber (SBR) vulcanizates were studied in relation to the chain scissions of rubber molecules during deformation. The rubber/filler interactions were controlled by the modification of silica surface using several kinds of silane coupling agents. Information on the chain scission was obtained by the electron spin resonance (ESR) measurements. The combination of ESR results and stress-strain data revealed that, at a given strain, the tensile stress increased with increasing the interfacial interactions between rubber molecules and silica surface, and simultaneously the chain scission became remarkable. Further, the degree of chain scission was closely related to the mechanical energy applied to the vulcanizates. The cyclic tests of stress-strain measurements suggested that the chain scissions contributed to the Mullins effect.     

Experimental analysis of viscoelastic properties in carbon black‐filled natural rubber compounds

Processability and viscoelastic properties of natural rubber (NR) compounds filled with different carbon black loadings and types were investigated with the use of a steady shear rheometer, namely, the Mooney viscometer, and an oscillatory rheometer, namely, the Rubber Process Analyser (RPA2000). It was found that the type and amount of carbon black strongly influence the viscoelastic properties of rubber compounds. Both the dilution effect and filler transient network are responsible for the viscoelastic properties, depending on the vulcanization state. In the case of uncured compounds, the damping factor of the uncured NR decreases with increasing black loading. This is attributed to the reduction of mobilized rubber content in the compound (or the dilution effect). However, in the case of the cured NR vulcanizates, the filler transient network is the dominant factor governing the damping factor of the vulcanizate. With increasing black loading, the damping factor of the vulcanizate clearly increases. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2197–2203, 2005     

An investigation on the reinforcing potential of red earth as filler for natural rubber compounds

Locally sourced red earth (RE) was air‐dried, pulverized, and screened with a sieve of mesh size 75 nm. It was characterized in terms of its moisture content, loss on ignition, silica content, iodine adsorption number, oil absorption, pH, and metal oxide compositions. Natural rubber, standard Nigerian rubber used for this work was first characterized in terms of its dirt, ash and nitrogen contents, volatile matter, plasticity retention index, and Mooney viscosity. The RE was applied as filler wholly and in blends with standard carbon black, CB (N330) filler in the natural rubber compounding using efficient vulcanization system. The cure and the physicomechanical properties of the compounds and vulcanizates were, respectively, measured as function of filler loading. The results were compared with those of the standard carbon black (N330)‐filled natural rubber. It was found, that the RE‐filled natural rubber showed substantial reinforcement of the rubber, though inferior to carbon black (N330) filled vulcanizates, the tensile strength of the carbon black‐filled vulcanizates is about one half times that of the RE‐filled vulcanizates. The tensile properties of the RE‐filled vulcanizates improved markedly by blending the RE‐filler with the carbon black (N330). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of fillers on the viscoelastic behavior of rubbers

The different reinforcing effects of carbon blacks are determined by measurements of the linear and nonlinear viscoelastic behavior of natural rubber samples subjected to prestrains at different levels. The transition from linear to nonlinear viscoelastic behavior occurs at lower strains as the carbon black content is increased. At a given filler concentration, the limiting strain is highest for the most reinforcing carbon black. Prestraining increases the limiting strain. The reinforcing effect of carbon black can be estimated by determining the extent to which prestraining influences the linear viscoelastic properties of vulcanizates.     

Effect of clay on vulcanization,network structure,and technical properties of natural rubber in the presence of silane coupling agents

The presence of silane coupling agents do not cause a change in network structure in clay-filled natural rubber vulcanizates, both in sulfur vulcanization and peroxide vulcanization systems. However, the improvement in technical properties in the presence of silane coupling agents is more in the peroxide vulcanization system and is accompanied by enhanced polymer—filler interactions. Scanning electron microscopy (SEM) studies have been made in order to understand the failure behavior.     

原位改性纳米氧化镁/顺丁橡胶复合材料的制备与性能

采用原位改性的方法制备了硅烷偶联剂Si 75 改性纳米氧化镁/顺丁橡胶复合材料,通过橡胶加工分析仪、扫描电镜等研究了其硫化特性、物理机械性能及动态力学性能。结果表明,当改性剂的用量为填料质量的3%时能有效提高纳米氧化镁/顺丁橡胶胶料的硫化速率和交联程度,且硫化胶的综合物理机械性能最好; 与未改性氧化镁填充的顺丁橡胶相比,改性氧化镁与橡胶之间的相互作用得到了增强,纳米氧化镁在橡胶中的分散性有了较大程度的改善,从而提高了改性纳米氧化镁/顺丁橡胶硫化胶的物理机械性能和损耗因子。     

A Comparative Study on Curing Characteristics,Mechanical Properties,Swelling Behavior,Thermal Stability,and Morphology of Feldspar and Silica in SMR L Vulcanizates

Abstract

Comparison studies on effects of feldspar and silica (Vulcasil C) as a filler in (SMR L grade natural rubber) vulcanizates on curing characteristics, mechanical properties, swelling behavior, thermal analysis, and morphology were examined. The incorporation of both fillers increases the scorch time, t ₂, and cure time, t ₉₀, of SMR L vulcanizates. At a similar filler loading, feldspar exhibited longer t ₂ and t ₉₀ but lower values of maximum torque, M_HR, and torque difference, M_HR–M_L than did silica-filled SMR L vulcanizates. For mechanical properties, both fillers were found to be effective in enhancing the tensile strength (up to 10 phr), tensile modulus, and hardness of the vulcanizates. However, feldspar-filled SMR L vulcanizates showed lower values of mechanical properties than did silica-filled SMR L vulcanizates. Swelling measurement indicates that swelling percentages of both fillers-filled SMR L vulcanizates decrease with increasing filler loading whereas silica shows a lower swelling percentage than feldspar-filled SMR L vulcanizates. Scanning electron microscopy (SEM) on fracture surface of tensile samples showed poor filler–matrix adhesion for both fillers with increasing filler loading in the vulcanizates. However, feldspar-filled SMR L vulcanizates showed poorer filler–matrix adhesion than did silica-filled SMR L vulcanizates. Thermogravimetric analysis (TGA) results indicate that the feldspar-filled SMR L vulcanizates have higher thermal stability than do silica-filled SMR L vulcanizates.     

Mechanical and dynamic mechanical properties of rice husk ash–filled natural rubber compounds

A laboratory‐sized two‐roll mill was used to incorporate rice husk ash into natural rubber (NR). A conventional vulcanization system was used for curing and cure studies were carried out on a Monsanto rheometer. Physical testing of the NR vulcanizates involved determining tensile and tear resistances and hardness. Swelling behavior of NR compounds and scanning electron microscopy were used to investigate the interaction between rice husk ash and natural rubber. Also, dynamical mechanical thermal analysis was used to assess filler–rubber interactions in terms of storage modulus (E′) and loss tangent (tan δ). For comparison purposes, two commercial fillers, precipitated silica (Zeosil‐175) and carbon black (N774), were also used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2331–2346, 2002     

Kinetic study and crosslink density in styrenebutadiene rubber compounds filled with boron-amine-modified silica

Vulcanization kinetics and crosslink density of styrene-butadiene rubber compounds have been studied with two vulcanization systems, an efficient (EV) and a conventional (CV) one. A surface-modified silica with boron-amine groups (Si? O? B? (NH₂)₂) was employed as filler. Untreated and modified silica with two silanes (γ-mercaptopropyl-trimethoxysilane and γ-aminopropyl-triethoxysilane) have been used as reference. The best kinetic parameters, such as highest vulcanization rate, longest induction time and lowest activation energy, were obtained for the compound with boronaminated silica. The crosslink density, achieved with this compound, is similar to that with silane-modified silica, probably because of the better surface distribution of boron-amine groups on the silica. These facts lead to important technological improvements: better processing safety, faster vulcanization rate and improved physical properties.     

Improvement of properties of silica‐filled natural rubber compounds using polychloroprene

Because silica has strong filler–filler interactions, a silica‐filled rubber compound is characterized by a poor dispersion of the filler. Properties of silica‐filled natural rubber (NR) compounds were improved using polychloroprene (chloroprene rubber [CR]). The bound rubber content of the compound increases and the filler dispersion is also improved by adding CR to the compound. Physical properties such as modulus, tensile strength, abrasion, and crack resistance are improved by adding CR. Elongation at break of the vulcanizates containing CR is longer than that of the vulcanizate without CR, although crosslink density of the former is higher than that of the latter. The improved physical properties are attributed to the good dispersion of silica by adding CR. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2609–2616, 2002