Interfacial interactions and properties of natural rubber–silica composites with liquid natural rubber as a compatibilizer and prepared by a wet‐compounding method

Natural rubber–silica [W(NR–SiO₂)] composites were prepared by wet‐compounding technology with liquid natural rubber (LNR) as a compatibilizer. The effects of the LNR content and wet‐compounding technology on the filler dispersion, Payne effect, curing characteristics, mechanical properties, and interfacial interactions were investigated. The results show that the incorporation of LNR promoted vulcanization and decreased the Payne effect of the W(NR–SiO₂) composites. With the addition of 5 phr LNR, the remarkable improvements in the mechanical properties of the W(NR–SiO₂) vulcanizates were correlated with the improved silica dispersion and strengthened interfacial bonding. Furthermore, the W(NR–SiO₂) vulcanizates containing LNR exhibited improvements in both the wet‐skid resistance and rolling‐resistance performance. The interfacial interactions, quantitatively evaluated by the Mooney–Rivlin equation and Lorenz–Park equation on the basis of the rubber elasticity and reinforcement theory, were strengthened in the presence of LNR. Accordingly, an interfacial structural model was proposed to illustrate the improvements in the mechanical properties of the W(NR–SiO₂) composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46457.     

Viscoelasticity behaviors of lightly cured natural rubber/zinc dimethacrylate composites

Zinc dimethacrylate (ZDMA) can be polymerized during peroxide curing to form the polymerized ZDMA (PZDMA) at nanoscales. At the same time, the covalent crosslink of the rubber matrix and ionic crosslink introduced by the graft‐PZDMA also are formed. The structure evolution of this type of composites is complex. In this article, the dynamic viscoelasticity characteristics of lightly cured ZDMA/natural rubber (NR) composites were investigated using a Rubber Process Analyzer 2000 (RPA2000). Our goal was to study the internal structures of this type of composites in an early curing stage. The dynamical viscoelasticity of the composites cured for 1 min was focused. The results of RPA2000 indicated that the PZDMA could act as particles to form a strong filler–filler structure which resulted in apparent Payne effect. A “primary network” structure might be formed which contained covalent crosslink points, ionic crosslinks, physical adsorption, and PZDMA. The stress‐softening behavior was also investigated. At last, the scanning electron microscope analysis verified that most of the ZDMA had been polymerized to form PZDMA “nanoparticle” when the composites were cured for 1 min. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Self‐crosslinkable epoxidized natural rubber–silica hybrids

Epoxidized natural rubber (ENR)–silica hybrids without any other additives were prepared by an open‐mill mixing method at room temperature. The curing characteristics, crosslinking density, mechanical properties, and dynamical mechanical properties were investigated. The results indicate that the ENR–silica hybrid materials could be cured with silica as a crosslinking and reinforcing agent. Attenuated total reflection–Fourier transform infrared spectroscopy and solid‐state ¹³C‐NMR spectroscopy exposed the characteristics of the interfacial interaction in the hybrids and confirmed the existence of chemical bonds and hydrogen bonds between the epoxy group and Si? OH. Scanning electron microscopy illustrated a good dispersion of silica in the ENR matrix. Meanwhile, the modulus at 100% elongation of the hybrid reached 9.64 MPa when 100‐phr silica was loaded; a similar trend was observed for the hardness. Finally, our findings might extend the concept of rubber curing and open a new space for making an environmentally friendly rubber composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44605.     

Preparation and performance of oleylamine modified silica-reinforced natural rubber composites

Oleylamine (OA) modified silica (SiO₂-g-OA) was prepared using γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560) and OA, silica/natural rubber (NR) and SiO₂-g-OA/NR composites were prepared by mechanical blending in an internal mixer, and SiO₂-g-OA was characterized by Fourier transform infrared spectroscopy, thermal gravimetric analyzer, and contact angle analyzer. The mechanical properties, abrasion resistance, curing characteristics, Payne effect, and morphology of silica/NR and SiO₂-g-OA /NR composites were investigated using universal testing machine, Akron abrasion tester, rubber processing analyzer, and scanning electron microscope, respectively. The results showed that SiO₂-g-OA became more hydrophobic and had better compatibility with NR. Moreover, SiO₂-g-OA/NR had weaker Payne effect, better vulcanization performance, and more excellent mechanical properties. As the content of filler was more than 30 phr, SiO₂-g-OA/NR had lower rolling resistance and higher wet skid resistance. Compared with silica modified by other coupling agents, SiO₂-g-OA had the best reinforcement effect on NR.     

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.     

Effect of silane integrated sol–gel derived in situ silica on the properties of nitrile rubber

Nitrile rubber/silica composites are prepared by a sol–gel process using tetraethoxysilane as precursor in the presence of γ‐mercaptopropyltrimethoxysilane as a silane coupling agent. Here, we follow a novel processing route where the silica particles are generated inside the rubber matrix before compounding with vulcanizing ingredients. The effect of in situ generated silanized silica on the properties of the rubber composite has been evaluated by studying curing characteristics, morphology, mechanical and dynamic mechanical properties. Enhanced rubber–filler interaction of these composites is revealed from stress–strain studies and dynamic mechanical analysis. Excessive use of silane shows an adverse effect on mechanical properties of the composites. Due to finer dispersed state of the in situ silica and enhanced rubber–filler interaction, the mechanical properties and thermal stability of the composites are improved compared to corresponding ex situ processed composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40054.     

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     

Synthesis and characterization of acrylic rubber/silica hybrid composites prepared by sol‐gel technique

The organic–inorganic hybrid composites comprising acrylic rubber and silica were synthesized through sol–gel technique at ambient temperature. The composites were generated through the acid‐catalyzed hydrolysis and subsequent condensations of inorganic tetraethoxysilane (TEOS) in the organic acrylic rubber (ACM), solvated in tetrahydrofuran. The morphology of the hybrid materials was investigated by using the transmission electron microscope (TEM) and scanning electron microscope (SEM). Transmission electron micrographs revealed that the silica particles, uniformly distributed over the rubber matrix, are of nanometer scale (20–90 nm). The scanning electron micrographs demonstrated the existence of silica frameworks dispersed in the rubber matrix of the hybrid composites. The X‐ray silicon mapping also supported that observation. There was no evidence of chemical interaction between the rubber phase and the dispersed inorganic phase, as confirmed from the infrared spectroscopic analysis and solubility measurements. Dynamic mechanical analysis indicated mechanical reinforcements within the hybrid composites. The composites containing in situ silica, formed by sol–gel technique, demonstrated superior tensile strengths and tensile modulus values at 300% elongations with increasing proportions of tetraethoxysilane. However, the improvements in physical properties with similar proportions of precipitated silica were not significant. Maximum tensile strength and tensile modulus were obtained when the rubber phase in the hybrid composites was cured with ammonium benzoate and hexamethylenediamine carbamate system, as compared with benzoyl peroxide cured system. Thermal stability of the hybrid composites was not improved appreciably with respect to the virgin rubber specimen. Residue analysis from thermogravimetric study together with infrared spectroscopic analysis indicated the presence of unhydrolyzed tetraethoxysilane in the hybrid composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2579–2589, 2004     

天然虾青素改性白炭黑/天然橡胶复合材料的制备与性能

采用天然虾青素对白炭黑表面进行物理改性，并与天然橡胶（NR）制备成复合材料。利用RPA、DMA、SEM等测试手段对天然虾青素改性白炭黑/天然橡胶复合材料的结构与性能进行表征。结果表明，在硫化特性方面，与未采用天然虾青素改性白炭黑相比，采用天然虾青素改性白炭黑所得胶料的焦烧时间和工艺正硫化时间均缩短，促进了橡胶的硫化过程；在物理力学性能方面，所得硫化胶的拉伸强度基本不变，回弹性和耐磨性明显增加，压缩生热降低；在动态黏弹性方面，所得硫化胶的Payne效应明显降低，填料的分散性在一定程度上得到改善；在动态力学性能方面，所得硫化胶的滚动阻力降低，玻璃化转变温度提高。特别地，在耐老化方面，天然虾青素改性白炭黑/天然橡胶复合材料的耐热空气老化性能明显提高。     

Exploring a highly dispersible silica–elastomer composite for tire applications

In this article, we provide an extensive analyses of various properties that are required for tire tread based on developed highly dispersible (HD) silica‐filled epoxidized natural rubber composites. Silica in an HD form has become a staple filler in tire tread applications because of its inherent advantages. In this study, epoxidized natural rubber with 25 mol % epoxide (ENR 25) and natural rubber were mixed with two different types of HD silica for superior reinforcement. A standard tire tread formulation was used as the base compound. The magic triangle properties were conspicuously influenced by the viscoelastic characteristics of the vulcanizates. The introduction of polar rubber (ENR 25) into the HD silica greatly improved rheological, physicomechanical, bound rubber content, and dynamic mechanical properties, and this led to a better, fuel‐efficient tire. We successfully achieved this, even in the absence of a silane coupling agent. ENR 25 played an imperative role in showing an extraordinary rubber–filler interactions and was primarily responsible for these observations. In this study, we explored the HD silica dispersion with transmission electron microscopy observations. Morphological studies revealed well‐dispersed HD silica with the formation of a rubber–filler network. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43531.     

Influence of silane coupling agents on vulcanised natural rubber: dynamic properties and heat buildup

We explore the influence of surface modification of SiO₂ on dynamic properties and heat buildup of semi-ef?cient vulcanisates filled by both SiO₂ and carbon black. Compared with untreated-SiO₂-filled natural rubber (NR), vulcanisates reinforced by modified-SiO₂ presents not only better filler dispersity, mechanical properties and dynamic properties, as confirmed by scanning electron microscope and rubber processing analyser, but also lower heat buildup. Fourier infrared spectroscopy and cure characteristics indicates that silane coupling agent molecules grafted on the silica surface provoke an enhanced mobility of rubber chain and adsorb onto filler surface and then decrease the barrier of crosslink reaction. Moreover, composites with Si69-modified-SiO₂ show obviously the highest tear strength and lowest heat buildup attributed to that more sulphur released by Si69 also participate the vulcanisation reaction.     

低共熔溶剂与偶联剂协同改性白炭黑对胎面胶性能的影响

研究了硅烷偶联剂(TESPT)与低共熔溶剂(DES)协同改性白炭黑对作为胎面胶的天然橡胶复合材料性能的影响.用傅里叶变换红外光谱分析了 TESPT和DES与白炭黑之间的相互作用,用橡胶加工分析仪和扫描电镜分析了白炭黑之间的相互作用,并测试了复合材料的硫化特性、力学性能和耐磨性,通过动态力学分析仪考察了其滚动阻力和抗湿滑...     

Synergistic effect of carbon black and carbon–silica dual phase filler in natural rubber matrix

In this article, the synergistic effects of carbon black (CB) and modified carbon–silica dual phase filler (MCSDPF) on the properties of natural rubber (NR) were investigated. MCSDPF was prepared by modifying carbon–silica dual phase filler (CSDPF) with bis(3‐triethoxysilylpropyl)tetrasulphane (Si‐69). Fourier transform infrared spectroscopy and thermogravimetric analyzer analyses revealed that Si‐69 was successfully grafted to CSDPF. NR‐based compounds containing various combinations of MCSDPF and CB were prepared through a mechanical mixing. Investigations of mechanical properties, ageing resistance, abrasion resistance, dynamic mechanical properties, and morphology of tear fractured surface of MCSDPF/CB/NR vulcanizates were conducted. Our study shows that adding MCSDPF led to significant improvement in the tear resistance, fatigue life, and elongation at break of MCSDPF/CB/NR vulcanizates. Optimum stoichiometric combination of MCSDPF and CB inside the NR matrix was derived (ratio of MCSDPF and CB in wt% = 15/50), which showed synergistic effects of MCSDPF upon CB that was ultimately reflected in their tensile strength, wet skid resistance, and rolling resistance. POLYM. COMPOS., 35:1466–1472, 2014. © 2013 Society of Plastics Engineers     

Interaction Between Fumed-Silica and Epoxidized Natural Rubber

Epoxidized natural rubber (ENR)/fumed silica vulcanizates were prepared by mechanical mixing method. Fumed silica content can affect mechanical properties of the composites, and ten parts per hundreds of rubber (phr) fumed silica lead to the best tensile strength. The interaction between ENR and fumed silica was characterized by Kraus equation, crosslink density (tested by NMR), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). The results showed that the dispersion of silica in ENR was better than in natural rubber (NR), hydrogen bond was produced between ENR and fumed-silica in ENR/silica blends, and glass transition temperature of ENR/silica vulcanizate was higher than pure ENR vulcanizate. TGA and DMA confirmed that there was intense interaction between ENR and silica.     

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。     

The mechanism of carbon–silica dual phase filler modified by ionic liquid and its reinforcing on natural rubber

The carbon–silica dual phase filler (CSDPF) was modified by ionic liquids (ILs): 1‐allyl‐3‐methyl‐imidazolium chloride (AMI) and 1‐butlyl‐3‐methyl‐imidazolium hexafluorophosphate (BMI). The modified CSDPF was then incorporated into natural rubber (NR) through mechanical mixing. The interactions between CSDPF and ILs were investigated using differential scanning calorimetry (DSC), Fourier‐transform infrared spectroscopy (FTIR), and Raman spectroscopy. The bound rubber of NR compounds, the mechanical properties, and dynamic properties of NR vulcanizates filled with ILs modified CSDPF (ILs‐CSDPF/NR) were measured. The results showed that the AMI interacted with CSDPF through both hydrogen bonds and van der Waals forces, while the interaction between BMI and CSDPF was merely weak van der Waals force. The modification of CSDPF by ILs could improve the tensile strength, tear resistance, and fatigue life of NR vulcanizates. The AMI‐CSDPF/NR gave the superior mechanical and dynamic properties among the NR vulcanizates with the highest bound rubber content and the most homogeneous filler dispersion, which was displayed in scanning electron microscope (SEM) images. POLYM. COMPOS., 36:1721–1730, 2015. © 2014 Society of Plastics Engineers     

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     

硅藻土/白炭黑复合填料的补强性研究

为拓展硅藻土在高分子复合材料中的应用,将硅藻土/白炭黑填充到天然橡胶/丁苯橡胶/顺丁橡胶中制备了复合材料。通过RPA2000和扫描电镜分析了复合填料的Payne效应和分散性,考察了硅藻土用量对复合材料工艺性能、力学性能、耐磨耗性能影响。结果表明:少量硅藻土的加入有利于白炭黑在橡胶中的分散,能降低复合材料的门尼粘度和Payne效应,提高复合材料的硫化速度,缩短硫化时间,复合填料的补强效果较好;随着硅藻土用量的增加,复合填料容易聚集,其力学性能呈下降趋势,而磨耗性能变化不大;当硅藻土用量10~20份时,复合材料的综合性能最好。     

Investigation of rubber–rubber blends miscibility

Polybutadiene rubber, poly(styrene‐co‐butadiene) rubber, natural rubber, and their blends were investigated to estimate the degree of miscibility of components in the blends. The morphology of a rubber–rubber blend controls its rheological properties and glass transition behavior. Therefore, two different measuring techniques were used: rheological characterization of blends by the rubber process analyzer (RPA) and temperature modulated differential scanning calorimetry (TMDSC). To study the dependence of complex viscosity on blend composition, two commonly used empirical mixing rules were applied: the log‐additivity mixing rule and the quadratic mixing rule. Viscoelastic properties of the examined samples were described by mechanical and relaxation spectra. Since the RPA measurements cannot be performed in a wide frequency range, the experimental results cannot offer a complete overview. Also, the quantitative analysis using the differential of the heat capacity, dC_p/dT, versus the temperature signal from TMDSC did not allow to calculate the weight fraction of the interface for all types of the blends under investigation. However, the combination of the two techniques applied provided complementary information on blend morphology and rubber–rubber miscibility. POLYM. ENG. SCI. 46:1649–1659, 2006. © 2006 Society of Plastics Engineers.     

Presence of vacuoles in natural rubber–Cloisite 15A nanocomposites

We studied natural rubber (NR) filled with frequently used organoclay Cloisite 15A using transmission electron microscopy (TEM), cryoporosimetry, and electron spin resonance (ESR) spectroscopy. Quantitative analysis of the TEM micrographs showed a high level of dispersion without the formation of a rigid filler network. The presence of vacuoles was established on the surface of Cloisite 15A; this indicated weak filler–matrix interactions. The mechanism of reinforcement is, therefore, discussed. The volume of vacuoles was found to be proportional to the crosslinking density; this was confirmed with ESR spin‐probe method. The shape of the ESR spectra was highly influenced by the presence of vacuoles. In the NR–Cloisite 10A nanocomposites, vacuoles were absent. The strong interactions implied by this result were confirmed by ESR measurements and are discussed further. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44776.