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Correlation of filler networking with reinforcement and dynamic properties of SSBR/carbon black/silica composites
Abstract
The use of silica to partially replace carbon black is a common practice in the fabrication of "green tires." Although some degree of consensus has been approached concerning the improved performance conferred by silica substitution, such as the improved dispersion of carbon black, a quantitative understanding of the relationship between filler networking and the performance of rubber composites has not been established. Thus, an investigation focusing on filler network structure and the correlation between the network structure and the reinforcement of rubber composites was conducted. We prepared solution-polymerized styrene-butadiene rubber (SSBR) reinforced by carbon black and carbon black/silica in different ratios. To exclude as much of the effect from changed crosslinking, and figure out how filler blending influences filler dispersion and filler network structure, the silane generally used in the tire industry was not adopted. The quantitative predictor, the mass fractal dimension d(f), was derived from the Kraus model and the Huber-Vilgis model. We found that when the amount of substituted silica increases, the filler cluster branching decreases, accompanied by increased reinforcement efficiency. The depressed filler networking induced by silica substitution at an appropriate proportion leads to improved dynamic properties, including lower rolling resistance and better wet skid. When the silica proportion in the filler is too high, severe filler networking is observed, resulting in decreased reinforcing efficiency and impaired dynamic properties.
... To reduce filler flocculation and the Payne effect of silicafilled composites, the application of bifunctional silanes along with silica is mandatory in green tire technology, although it brings about challenges in the mixing process and raises the final price of the product [8,9]. Recently, "hybrid filler systems" have been widely used as a new approach to obtaining homogeneous filler dispersion [10][11][12][13], synergy in mechanical and electrical properties [14][15][16][17][18], and reduced filler networking or the Payne effect in polymer composites [10,12,19,20]. Carbon black (CB) and silica hybrid fillers, traditional fillers in rubber compounds, have been extensively studied [10,16,19]. ...
... To reduce filler flocculation and the Payne effect of silicafilled composites, the application of bifunctional silanes along with silica is mandatory in green tire technology, although it brings about challenges in the mixing process and raises the final price of the product [8,9]. Recently, "hybrid filler systems" have been widely used as a new approach to obtaining homogeneous filler dispersion [10][11][12][13], synergy in mechanical and electrical properties [14][15][16][17][18], and reduced filler networking or the Payne effect in polymer composites [10,12,19,20]. Carbon black (CB) and silica hybrid fillers, traditional fillers in rubber compounds, have been extensively studied [10,16,19]. ...
... Recently, "hybrid filler systems" have been widely used as a new approach to obtaining homogeneous filler dispersion [10][11][12][13], synergy in mechanical and electrical properties [14][15][16][17][18], and reduced filler networking or the Payne effect in polymer composites [10,12,19,20]. Carbon black (CB) and silica hybrid fillers, traditional fillers in rubber compounds, have been extensively studied [10,16,19]. Sattayanurak et al. [16] observed a synergistic effect on the overall properties of tire tread compounds by the replacement of silica with a small amount of CB (18 wt.%) in the natural rubber (NR) matrix. ...
The present work discusses the effects of reduced graphene oxide (rGO) on the nonlinear viscoelastic behavior, or the Payne effect, of silica/styrene-butadiene rubber compounds. The volume fraction of unmodified silica was constant, while the amount of rGO in these hybrid filler compounds varied. Dynamic-mechanical analysis (DMA) in strain sweep mode showed that adding a small quantity of rGO to the silica-filled compounds resulted in diminished network formation of unmodified silica as well as a reduced Payne effect and corresponding energy dissipation. The state of silica dispersion in the presence of rGO in the rubber matrix was predicted by calculating the work of adhesion in a three-component system and detected by scanning electron microscopy. It was observed that the dispersion of the unmodified silica was improved by the addition of only 0.25 or 0.5 phr rGO, which may be due to the improved silica-rubber interactions that occur during mixing and/or reduced silica flocculation after mixing, as measured by DMA in time sweep mode. The synergy between silica and small quantities of rGO (0.25 or 0.5 phr) resulted in an enhancement in mechanical strength (45%) and abrasion resistance (63%), as well as a reduction in heat build-up (23%). This hybrid system can be considered an alternative to silane modification of silica in green tire technology. Effect of graphene (rGO), as the secondary filler, in rubber compounds filled with silica was investigated. Scanning electron microscopy showed that silica dispersion was improved in the presence of small quantities of rGO, but it deteriorated at higher loadings of rGO due to the formation of compact hybrid filler network. This morphological development affects dynamic-mechanical properties such that the Payne effect reduces in the presence of low concentrations of rGO. Using these observations, the underlying mechanism was explained based on how rGO hinders silica reagglomeration thermodynamically after the mixing.
... The copolymer styrene-butadiene rubber (SBR) with its properties such as higher abrasion resistance, wet skid resistance, and lower rolling resistance has been preferred in tire tread compounds in instead of natural rubber (NR). 1 It has been known that rubber without filler materials has very low physical strength and therefore fillers are added into tire compound for the purpose of either reinforcement or/and cheaper compound. Carbon materials such as graphite, 2,3 carbon nanotube, 4 porous carbon 5,6 and carbon black 7,8 have been utilized to produce different composites with versatile properties. Among them, carbon black (CB) has been the most widely used filler in the rubber industry for more than one century. ...
... Since the 1990s, silica has gained increasing importance in the production of "green tires" as it offers significant advantages over carbon black in terms of lowering rolling resistance and comparable wear resistance and better wet grip performance of rubber tires. 7,8 Organoclay/CB hybrid fillers have been widely studied materials used with rubbers. Recent studies have focused on kaolin, 9 bentonite, 10 nano-calcium carbonate, 11 halloysite nanotubes 12 to improve the dynamic mechanical properties of rubber. ...
... The SBR/ CB/FLD hybrid composites were found to have increased mooney viscosities as compared to 50CB composite. This result can be explained by most probably due to inhibition of formation of large CB filler network by FLD fillers, 8 providing a better CB distribution in the polymer matrix and thus a stronger CB-SBR interaction. In hybrid filler loaded systems, the increase in viscosity values indicates that the hardness and density of the rubber paste in those compositions are high. ...
In this work, the effects of using feldspar (FLD) as an alumina-silicate inorganic filler, with carbon black (CB) as a novel binary filler system, on the properties of SBR compounds were investigated for tire applications. The bis(triethoxysilylpropyl) disulfide (TESPD) was used for modification of FLD. The SBR hybrid composites were produced by replacing 10 phr of CB filler with neat FLD and functionalized FLD (F-FLD). The TESPD was added directly to the rubber mixture including neat FLD. The SBR composite which has only CB filler (50CB) was found to have the highest damping parameter (tan δ) value at 60°C. On the other hand, the composites loaded with the CB and the FLD fillers exhibited relatively lower tan δ at the same temperature showing lower rolling resistance meaning better fuel saving performance. The lowest rolling resistance was achieved for the 40CB-10F-FLD most probably due to its stronger interaction with the SBR elastomer molecules through the silane agent-assisted crosslinks of the F-FLD. As another dynamic property, the storage moduli at −20°C were found to be lower for the SBR hybrid composites as compared to that of the 50CB composite, exhibiting enhanced winter traction performance of the composites having FLD filler together with CB. The composites containing only 10 phr of FLD and F-FLD, on the other hand, exhibited very low tensile strength values which are not acceptable for tire tread materials.
... These elements are included in white fillers, which is beneficial due to the combination of silica and carbon black to exploit the advantages of both fillers in rubber compounds. Successively, different authors [12][13][14] demonstrated that the addition of lesser amounts of silica into rubber compounds decreases the filler cluster branching and increases the reinforcement efficiency, while higher silica loadings induce segregation phenomena, causing a deterioration in the filler-rubber interface and consequently deterioration properties of rubber compound. Based on this experimental evidence, tire industry has developed the use of hybrid filler systems, where carbon black is only partially substituted by precipitated silica functionalized with silane coupling agents [14]. ...
... Successively, different authors [12][13][14] demonstrated that the addition of lesser amounts of silica into rubber compounds decreases the filler cluster branching and increases the reinforcement efficiency, while higher silica loadings induce segregation phenomena, causing a deterioration in the filler-rubber interface and consequently deterioration properties of rubber compound. Based on this experimental evidence, tire industry has developed the use of hybrid filler systems, where carbon black is only partially substituted by precipitated silica functionalized with silane coupling agents [14]. These rubber compounds show improved dynamic response at low and high temperatures with respect to those reinforced solely with carbon black, which results in better rolling resistance and enhanced wet grip, while keeping satisfactory abrasion resistance [12]. ...
Instead of conventional carbon black, an alternative carbon filler (ACB) obtained in the pyrolysis process from tire waste was used for rubber compounds. The fillers were characterized using FTIR and TGA methods. The mechanical properties of the obtained rubber compounds and the influence of the fillers used on the vulcanization process, as well as the Payne effect, were examined. The results confirm the possibility of replacing conventional carbon black with an alternative carbon filler in rubber compounds.
... Usage of E-SBR would be impossible without the reinforcement of fillers, because reinforcement improves tear and rupture strength of rubber [4]. Till last decade, carbon black (CB) was the sole filler used in different applications due to its better rupture re-sistance and improved durability [5,6]. Rubber and CB both are hydrophobic, thus mixing of them is generally physi-sorption. ...
... Solvent uptake (Q) = × 100 (6) where, Weq is the equilibrium weight of the sample and W0 is the initial weight of the solvent. Then, the rubber-filler interaction is measured by Qf/Qg ratio [30], where f and g stand for filled and gum vulcanizate, respectively. ...
In the current context of green mobility and sustainability, the use of new generation natural fillers, namely, α-cellulose, has gained significant recognition. The presence of hydroxyl groups on α-cellulose has generated immense eagerness to map its potency as filler in an elastomeric composite. In the present work, α-cellulose-emulsion-grade styrene butadiene rubber (E-SBR) composite is prepared by conventional rubber processing method by using variable proportions of α-cellulose (1 to 40 phr) to assess its reinforce ability. Rheological, physical, visco-elastic and dynamic-mechanical behavior have clearly established that 10 phr loading of α-cellulose can be considered as an optimized dosage in terms of performance parameters. Morphological characterization with the aid of scanning electron microscope (SEM) and transmission electron microscopy (TEM) also substantiated that composite with 10 phr loading of α-cellulose has achieved the morphological threshold. With this background, synthetic filler (silica) is substituted by green filler (α-cellulose) in an E-SBR-based composite. Characterization of the compound has clearly established the reinforcement ability of α-cellulose.
... There is a growing interest to use a filler combination or hybrid fillers making use of the benefits provided by the individual components. Silica has been used in combination with secondary fillers such as China clay [13], montmorillonite [14,15], kaolin [16], organically modified nanoclay [17] and CB [18][19][20][21][22][23] aiming for a synergistic effect on the rubber properties. The simplest combination should be silica/CB as both types of fillers are already commonly used in tire compounds. ...
... A study on mechanical properties of NR reinforced with various ratios of CB N330/silica hybrid fillers showed that vulcanizates containing 20 and 30 phr of silica in a total of mixed filler of 50 phr exhibited the best overall mechanical properties [20]. The addition of a small amount of silica (VN3) into Solution-Styrene-Butadiene-Rubber (SSBR)/CB (N330) compounds, such as by the use of a CB/silica ratio of 45/5 phr, decreased the filler cluster branching and increased the reinforcement efficiency [21]. This decreased filler networking and more homogeneous filler dispersion subsequently resulted in better abrasion resistance, lower rolling resistance and better wet skid resistance, i.e. better dynamic properties. ...
The partial replacement of silica by high specific surface area and high structure Carbon Black (CB) N134 as secondary filler, keeping the same total filler content at 55 phr, shows a clear synergistic effect on overall performance. At low content of CB, i.e. in the range of 0–36 wt% of CB relative to total filler amount, the Payne effect and tan delta at both 0 °C and 60 °C change marginally, but thereafter gradually increase. Cure times are shortened in the presence of CB, facilitating an increase of productivity. Bound rubber content and mechanical properties show an optimum at 18 wt% of CB relative to total filler amount or at a ratio of silica/CB 45/10 phr. With regard to tire performance as indicated by the laboratory test results, the abrasion resistance, wet grip and ice traction can therefore be enhanced while maintaining the tire rolling resistance at the optimum level for this silica/CB ratio.
... Examples of the reinforcing fillers used in the rubber industry are silica and carbon black which can improve the mechanical properties of rubber products. Rubber containing such fillers has improved tensile strength [1], good abrasion resistance [2], high modulus of elasticity and hardness [2,4]. The silica that is used in the rubber industry includes precipitated silica prepared by precipitation of an aqueous sodium silicate solution and fume silica produced by pyrogenic process. ...
... The cross-link density was calculated according to Eq. (4), where the network chain density, υ e (mol cm −3 ), molar volume of solvent, υ 1 (toluene = 106.3 cm 3 mol −1 ), and the rubber-solvent interaction parameter, χ 1 (0.39 for NRtoluene [21] and 0.37 for SBR-toluene [22]) were substituted in Eq. (4). Figure 1 demonstrates the morphology of BA, which is in fine gray powder form. ...
Possibility of utilizing bagasse ash (BA) as a filler for natural rubber (NR) and styrene–butadiene rubber (SBR) was investigated. Detailed measurement by several techniques was used to characterize. Various loadings of BA (0–30 phr) were then incorporated into NR and SBR. Morphology and properties of the BA filled rubbers were finally investigated. It was found that BA contained SiO as the major constituent with other metal oxides, such as CaO, AlO and KO, as the minor constituents. The average size of the particles and specific surface area of the BA were 48.8 \upmu m and 36.3 m g, respectively. When incorporated into the rubbers, both scorch and cure times decreased, whereas tensile modulus ( and hardness slightly increased with greater loadings of BA. Interestingly, tensile strength and tear strength did not significantly change with the addition of BA up to 30 phr. The results indicate the potential of using BA as a filler in the rubber industry for cost reduction and raising the environmental credentials of the product.
... However, the evolution of having a new grade of filler system was short-lived as material didn't gain the importance within the rubber industry because of various shortcomings associated with material cost and availability [8]. The CSDPF material was developed by adopting the bottom-up approach to produce a new variant of CSDPF and using the same as active filler in rubber compounds to achieve the desired performance properties [9][10][11]. ...
The improvement in performance properties of the tire is required to meet the ever-increasing demand from the automobile industries as well as to comply with the stringent environmental norms. At present, one of the most common methods adopted in the tire industries to balance the performance properties of rubber vulcanisates is either by using carbon black (CB), silica individually or their physical blends as reinforcing filler. However, the difference in surface energies between the two fillers prevents them from forming a collaborative filler network. To overcome this problem, use of advance materials like carbon–silica dual-phase filler (CSDPF) is need of the hour. The synthesis of this advanced CSDPF material involves the post process modification of CB using a surfactant followed by chemical precipitation of silica. In this study, the application of CSDPF series (3%, 5% and 7% silica impregnation on CB surface) is promulgated as an active reinforcing filler by replacing CB in PCR tire tread-based rubber compound. The improvement observed are for higher reinforcement index, improved abrasion resistance index and tear resistance compared to regular compound loaded with N330 CB and silica. The dynamic mechanical properties of rubber compounds indicate improved wet traction, dry handling, ride, and comfort properties while marginal increase in rolling resistance (RR). Among the tested variants of CSDPF material, the composite with 5% silica impregnation shows optimized performance properties. The study highlights the potential of using advanced hybrid CSDPF materials to enhance tire performance.
... In addition, CaCO 3 has no surface functional group to interact with rubber molecules, while CSP has a lot of polar functional groups on its surface (see FTIR results in Fig. 3b), making it incompatible with hydrophobic rubber molecules. At the same filler loading, CB provided a higher BRC or rubber-filler interaction because it not only has a significantly higher specific surface area but also possesses a very rough surface (step-like structure at the CB surface), facilitating the formation of physical interaction or physical locking [51]. Furthermore, it has been reported that CB can form chemical interactions with rubber through its functional group, which plays a role in strengthening the rubber-filler interaction [52]. ...
... Fillers are a typical means of improving the performance of rubber sealing materials in practical manufacturing processes, and commonly used fillers include CB and SC fillers [84][85][86]. The addition of fillers typically inhibited the hydrogen-induced swelling behavior of rubber. ...
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Rubber sealing components are crucial and highly vulnerable parts in high-pressure hydrogen systems, which represent the weakest link where seal failure becomes the crucial factor limiting the increase in working pressure of hydrogen energy equipment. Prolonged exposure to hydrogen environments causes rubber materials to experience volumetric expansion, resulting in decreased sealing reliability and durability, posing significant safety risks. This review focuses on rubber sealing materials used in hydrogen energy equipment. Firstly, the current mainstream mechanisms of hydrogen-induced swelling are introduced, covering the hydrogen exposure and decompression stages. Subsequently, the impact of hydrogen-induced swelling on the micromorphology damage, mechanical performance deterioration and sealing performance reduction of rubber is elucidated. Furthermore, the primary influencing factors of rubber hydrogen-induced swelling are explored and summarized. Based on the analysis of the current state of researches, several recommendations are proposed for the study of hydrogen-induced swelling of rubber sealing materials, including broadening the influencing factors and constructing the correlations between hydrogen-induced swelling and other damages such as frictional wear to contributing the safe application of rubber seal in high-pressure hydrogen systems.
... However, some fillers, e.g., carbon black, have been classified as Group 2B by International Agency for Research on Cancer (IARC) as a human carcinogenic agent [34,35]. Fillers, like graphene [36], fly ash [37], metakaolin [38] and silica [39], have been used as total or partial carbon black replacement. Some other organic or natural fillers, like whitings (chalk) [40] and clays [41] have been widely tested without equaling the carbon black response. ...
The present research aimed to develop natural rubber hybrid composites reinforced with treated ultrafine calcium carbonate/carbon black (CC/CB). The influence of CC/CB with various filler ratios (50/0, 40/10, 30/20, 20/30, 10/40 and 0/50) on mechanical properties and cure characteristics of the composites was investigated. Also filler reinforcing efficiency was compared aiming to achieve the best ratio for CB partial substitution as compared to composites with CC and CB incorporated separately. The CC30/CB20 composites reached around 17.56 ± 0.3 MPa similar strength at break response compared to CC0/CB50 (16.83 ± 0.6 MPa). Elongation at break increased 48% in relation to CC0/CB50. Hardness maintained similar values compared to high concentration of CB composites. The increase of crosslink density is attributed to a strong interaction between CC and CB and showed a synergism between filler and polymeric matrix in hybrid composites. Scanning electron microscopy studies also reveal a good filler dispersion between filler particles and matrix. The results shown that the new material can be an alternative filler for partial substitution of CB conserving mechanical properties.
... The idea is to obtain a synergistic reinforcing effect from each filler type. Hybrid fillers of silica with different types of fillers have been investigated such as silica/CB [23][24][25][26][27][28], silica/kaolin or China clay [29], silica/MMT [30,31], silica/organomodified kaolin [32] and silica/OC [11,33,34]. The utilization of silica/kaolin clay hybrid fillers for a heavy-duty truck tire tread formulation based on NR [29] revealed that the best balance of heat build-up and abrasion resistance was observed at the ratio of silica/clay at 60/20. ...
Organoclay (OC) is one of the potential secondary fillers to be applied in silica-reinforced rubber compounds for tire applications. Commercial OC contains a large proportion of surface modifier, i.e., dimethyl dihydrogenated tallow ammonium chloride (2HT) type, that has an influence on the compound properties. To elucidate the effect of 2HT on the properties of silica-Natural Rubber (NR) compounds, a silica-only system, silica/OC, and silica/montmorillonite (MMT)/2HT added in situ during mixing, were comparatively studied. Irrespective in which form 2HT is added, it has potential to further enhance the performance of silica-NR compounds. Incorporation of 2HT suppresses filler flocculation and improves processability. Overall, the silica-only filled compound shows better mechanical properties than the silica/clay dual filler systems. The use of a small amount (2.4–4.7 phr) of 2HT improves 300% modulus, tear strength and abrasion resistance. The silica/OC gives better mechanical properties than the silica/MMT/2HT. With the optimum content of 2HT, a higher tan δ at –20 °C and lower tan δ at 60 °C can be achieved, all showing the beneficial potential of utilization of the modifying agent to improve wet traction and rolling resistance of silica-based tire tread compounds.
... Silica and carbon black (CB) co-filled composite receives much attention because of its combined advantages of silica and CB, such as low hysteresis, good wet skid resistance, and reinforcement, especially suitable for tire tread (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Because of poor compatibility between silica and hydrocarbon rubber (11)(12)(13), a great effort has been made to improve the filler-rubber interaction with the aim of obtaining optimum performances (14)(15)(16)(17)(18)(19)(20)(21). ...
Silica and carbon black (CB) co-filled rubber composite was widely used for tire tread and other rubber products because of combined advantages of binary fillers, such as low hysteresis, good abrasion resistance, and reinforcement. Numerous studies have been focused on the filler–rubber interaction with the aim of obtaining optimum performances. To investigate the effect of modification on properties of rubber composite, modified silica and CB co-filled rubber composite was prepared with a multi-functional silane coupling agent, 2-aminoethyl-2-(3-triethoxysilylpropyl)aminoethyl disulfide (ATD). Such modification significantly enhanced the filler–rubber interaction and improved the filler dispersion. For the modified composites, the state of cure, hardness, tensile strength before and after aging, stress at 300% elongation, tear strength, abrasion resistance, rebound resilience, compression set, temperature rise, and the value of dynamic loss coefficient ranging from −20°C to 80°C were significantly improved, especially with low ATD dosage (3.0 phr). This modification provides an effective route to prepare silica and CB co-filled rubber composites with improved mechanical properties and dynamic mechanical properties.
... The complex phenomenon occurs in situ of a filled rubber network. Feng et al. 4 showed an overall change in properties due to filler networking. Mechanical behavior for filled rubber is related to the morphological changes in the complex network. ...
The contribution of carbon black (CB) on changes in cross-link density and physical entanglement has been quantified by swelling and uniaxial stress–strain measurements considering Mooney–Rivlin parameters. Solution SBR (SSBR) vulcanizates with varying content of high abrasion furnace (HAF) CB were studied. Rubber–filler networks increase the cross-link density values, which were determined by using Flory–Rehner and modified Guth–Gold equations by equilibrium swelling study. The Mooney–Rivlin parameter C 1 was quantified using cross-link density, whereas parameter C 2 , representing physical entanglement, was determined for filled rubber by correlating with tensile results. The parameter C 2 is monitored to be decreased with increasing CB (HAF) loading. A simple parabolic trend for physical entanglement parameter with increasing CB loading is proposed, and it shows a correlation coefficient of 0.99595. Atomic force microscopy study confirms the generation of filler networking in the rubber matrix. The current findings elucidate a way for quantifying physical network changes due to fillers in an unfilled rubber system.
... The sample T7R3 and T8R4 shows higher Tanδ at 60°C. Dispersion of silica is the one of criteria for achieving better mechanical and dynamic properties in rubber compounds [35].The SEM images of compound with PDMS-OH along with TESPT shows improvement in dispersion with increasing PDMS-OH content from 1 to 4 phr in specimens T4 > T3 > T2 > T1 resulted in uniform and homogeneous dispersion of silica filler in polymer matrix. This is in line with the Payne effect results from RPA and dynamic properties from MTS. ...
This work is aimed to improve the dispersion of silica without compromise on the Mechanical and Dynamic properties, by the addition of Hydroxyl terminated poly dimethyl siloxane (PDMS-OH). PDMS-OH is expected to interact with silica through hydrogen bonding which is reversible, reduces filler–filler interaction and hence improve the silica dispersion. Dissociation of hydrogen bonds which is reversible, provides a way for significant energy dissipation during deformation by the external stress and then promotes the recovery after the stress is removed. This prevents the filler re-agglomeration after deformation which is not possible with only silica-TESPT bonds which are covalent and irreversible. This study also explores the possibilities of reducing the emission of volatile organic compound ethanol by partially replacing the TESPT coupling agent with PDMS-OH without sacrificing in Mechanical and Dynamic properties such as Rolling Resistance and wet Traction.
... e depressed filler networking and more homogeneous filler dispersion resulted in better abrasion resistance, lower rolling resistance, and better wet skid resistance. However, when the silica proportion was high, filler cluster branching increased quickly and deteriorated the properties [20]. e use of semi-reinforcing furnace (SRF) CB/silica hybrid filler in nitrile rubber compounds showed that the replacement of carbon black with silica decreased the material's stiffness, tensile strength, compressive strength, tear strength, and modulus but increased elongation at break and rebound resilience [21]. ...
Modern fuel-saving tire treads are commonly reinforced by silica due to the fact that this leads to lower rolling resistance and higher wet grip compared to carbon black-filled alternatives. The introduction of secondary fillers into the silica-reinforced tread compounds, often named hybrid fillers, may have the potential to improve tire performance further. In the present work, two secondary fillers organoclay nanofiller and N134 carbon black were added to silica-based natural rubber compounds at a proportion of silica/secondary filler of 45/10 phr. The compounds were prepared with variable mixing temperatures based on the mixing procedure commonly in use for silica-filled NR systems. The results of Mooney viscosity, Payne effect, cure behavior, and mechanical properties imply that the silica hydrophobation and coupling reaction of the silane coupling agent with silica and elastomer are significantly influenced by organoclay due to an effect of its modifier: an organic ammonium derivative. This has an effect on scorch safety and cure rate. The compounds where carbon black was added as a secondary filler do not show this behavior. They give inferior filler dispersion compared to the pure silica-filled compound, attributed to an inappropriate high mixing temperature and the high specific surface area of the carbon black used. The dynamic properties indicate that there is a potential to improve wet traction and rolling resistance of a tire tread when using organoclay as secondary filler, while the combination of carbon black in silica-filled NR does not change these properties.
... Thus, hybrid filler recipes combining several kinds of fillers are used in rubber compounds. The filler networking is weakened if a small amount of CB was replaced by silica (Feng et al., 2015). This is because filler-filler interactions are formed by hydrodynamic effect, with this effect being weaker on different fillers than on the same fillers. ...
A byproduct of the power generation industries, fly ash can be used as a potential filler in many commercial products including rubber-based products. Reusing the fly ash in this manner is an efficient way to help prevent air pollution which occurs if such particles are released freely to the atmosphere. The reinforcement efficiency of fly ash for partial replacement of carbon black and silica fillers in styrene-butadiene rubber compounds was investigated in this work. The total content of fillers was held constant at 50 phr (weight ratio of filler to rubber was 0.5) when not using silica fillers at all, and 54 phr when using 4 phr carbon black only with silica fillers, while the content of fly ash increased from 0 to 10 phr. In the evaluation of the rubber compounds, the focus was the mechanical properties and adhesion of steel reinforcement cords to the styrene-butadiene rubber compounds. Adhesion between the compounds and steel wire reinforcement was measured for assessing efficacy of adding fly ash to the rubber compounds in tire applications. Ball mill treatment was used to reduce the size of the fly ash particles while also modifying their surface topography. The comparisons of untreated and ball mill treated fly ash filled rubber compounds and rubber compounds containing different fillers were accomplished subsequently. The results revealed that the partial addition of up to 10 phr fly ash to rubber compounds resulted in increases in elongation at break, adhesion to reinforcement steel cord, wet-grip, as well as lower rolling resistance as attributed to more effective filler dispersion and the reinforcing effect of silica present in fly ash.
... Generally, the use of particulate reinforcing fillers in elastomeric materials is technically essential to achieve the required rubber properties including tensile strength, modulus, and abrasion resistance [1][2][3] while that of non-reinforcing ones is for some other reasons, such as processability improvement and cost reduction [4]. The properties of filled rubber vulcanizates depend strongly on many factors, that is, rubber-filler interaction, filler dispersion, type and number of crosslinks. ...
The influence of silane coupling agent on properties of silica‐filled compounds under peroxide curing was investigated. bis (triethoxysilylpropyl) tetrasulfide (TESPT) was selected in this study and its content was varied from 0 to 12% w/w of silica. It is found that with increasing TESPT content, bound rubber content, tensile strength, elongation at break and tear strength are enhanced. By contrast, magnitude of Payne's effect, modulus at 100% elongation (M100) and heat build‐up are decreased. The changes of such properties are attributed to the reduction of crosslink density in conjunction with the improvements of both rubber–filler interaction and degree of filler dispersion with increasing TESPT content in the peroxide curing system. POLYM. ENG. SCI., 2018. © 2018 Society of Plastics Engineers
... A similar behavior was also observed in previous research. 26,33 A stronger rubber − filler interaction will restrict the rubber chains leading to an 'earlier' increase of * (at smaller strain), while a weaker rubber − filler interaction will result in slipping of rubber chains leading to a 'later' increase of * (at larger strain). 34 Therefore the upturn point of * can be used to compare rubber − filler interaction. ...
Carbon black (CB) and precipitated silica are two major reinforcing fillers in rubbers. CB/silica hybrid filler is also widely used in rubbers to provide balanced properties. CB/silica-hybrid-filler-filled styrene-butadiene rubber (SBR) containing naphthenic oil (NO), soybean oil (SO) and norbornylized SO (NSO) was investigated. The swelling and curing behavior and rheological, mechanical, thermal, aging and dynamic properties were studied and compared with earlier reported data on CB- or silica-filled SBR. NSO provides better scorch safety and faster cure than SO. Compared with NO, the addition of SO and NSO enhances the thermal stability and aging resistance of SBR vulcanizates. SBR/NSO vulcanizates with hybrid filler exhibit a higher tensile and tear strength than SBR/NO and SBR/SO vulcanizates. A synergistic effect in the abrasion resistance of vulcanizates containing the hybrid filler is observed. An increase of sulfur content in the hybrid-filler-filled SBR/NSO vulcanizates provides further improvement in abrasion resistance, wet traction and rolling resistance.
This paper investigated the dispersion of silica exhibiting different specific surface areas in nitrile rubber (NBR) matrices and the interactions between fillers, filled rubber, and rubber networks by regulating the aggregate size. To better characterize and leverage the filler network structure, a comprehensive analysis was conducted using linear and nonlinear rheological tests based on the equilibrium solvation theory and pipe models. The results demonstrated that the incorporation of fillers formed an island‐like network structure. With high specific surface area, the concurrent use of high and low specific surface area silica fillers improved the filler‐rubber interactions and hindered filler‐filler interactions, decreased the filler aggregate size, and enhanced the dispersion. Furthermore, we analyzed the mechanism of the filler network structural enhancement and its relationship with the specific surface area by regulating the filler ratios to adjust the polymer size.
Highlights
Control of Filler Network Structure: Ratio adjustment strengthens interactions.
Large silica surface enhances F‐R interaction, small surface improves dispersion.
Mixing ratios favor robust filler interconnection or dispersion.
Reveals strong correlation of filler network strength with F‐F interactions.
Highlighted effective eco‐friendly means of adjusting filler Mixing ratios.
The increasing demand for biomass‐derived material and its usage in different forms in various commercial applications has become a need for sustainability. In this context, cellulose, the most abundant biodegradable material is modified (FAC) and used in tyre tread formulation. The potential of FAC is appraised against the lubricating nature of process oil due to its restricted usage for the presence of toxic polycyclic aromatic materials. In addition to that, Silane coupling agent is also replaced by FAC to assess its potency as a coupling agent. Multi‐functional nature of FAC is evaluated through morphological, rheological, physicomechanical, and dynamic‐mechanical means. Total replacement of oil with FAC has induced ~30–40% improvement in static modulus across elongation %age. Furthermore, improvement in grip properties (6%) along with a reduction in hysteresis loss (11%) is also portrayed by the composite having a complete substitution of oil by FAC. The efficacy of FAC as a potential replacement for SCA is also evaluated in this study. Replacement of 66% of SCA along with the complete substitution of oil with FAC has depicted comparable physicomechanical, dynamic as well as flow behavior with respect to the reference one. The introduction of fibrous structure along with intermolecular covalent bonding has reinforced FAC with multifunctional behavior. Thus, this multi‐functional behavior of FAC (reinforcing, dispersing, and coupling) can easily be applied in commercial tyre formulation facilitating a breakthrough in cheap and high‐performance biomass‐derived rubber composite.
Since some decades, styrene–butadiene rubber (SBR) and butadiene rubber (BR) polymers have been used to prepare silica‐filled raw mixtures basing on SBR/BR binary blends for green tire technology. Utilization of high filler concentrations and various components in these complex reinforced rubber systems make the analysis of rubber–filler interactions difficult. Developing new characterization methods and carrying out some methodological characterizations are important for the material and property investigations in this field. In this study, direct and indirect characterization methods mostly used for investigations of rubber–filler and filler–filler interactions, their potential relationships to each other and the problems of characterization methods especially imaging techniques at micro and nanoscale, are discussed for silica‐filled SBR and BR systems.
In this study, the effects of silicon carbide (SiC) nanoparticles as a secondary filler on the filler networking in carbon black (CB)/SiC hybrid filled styrene‐butadiene rubber (SBR) were investigated in detail. It was shown that there was a critical loading in the low‐loading range of SiC, which can significantly improve the final dispersion state in the hybrid composite. It was discussed that in the critical loading of SiC due to the surface energy mismatch between CB and SiC the kinetics and the extent of filler networking in the SBR matrix were decreased. It was demonstrated how CB/SiC hybrid filler networking results in synergistic effects in dynamic, and tribological properties of SBR composites. Obtained results demonstrated that the use of nano SiC as a secondary filler in CB filled rubber composites can open up new opportunities to manufacture rubber composites with integrated dynamic‐mechanical and tribological performance.
Epoxidized solution‐polymerized styrene butadiene rubber (ESSBR) with different epoxidation degrees was prepared using formic acid as a catalyst. Experimental methods and density function theory calculation confirms that peroxyformic acid preferentially attacks trans‐1,4‐butadiene, and then cis‐1,4‐butadiene, and 1, 2‐butadiene is not epoxidated due to high energy barrier. Two SiO2/graphene oxide hybrids covalently linked with bis‐[3‐(triethoxysilyl)propyl]‐tetrasulfide or 3‐aminopropyltriethoxysilane (KH550) were prepared and named SiO2@TESPT@GO and SiO2@KH550@GO, respectively. The results for ESSBR composites filled by hybrid fillers indicate that the increase of epoxy degree can greatly improve the wet skid resistance while maintaining rolling resistance. Besides, in the case of the same epoxy degree, the rolling resistance of composites using hybrid fillers is lower than that of using SiO2 only. Notably, the SiO2@TESPT@GO/ESSBR composite with high epoxy degree (10.09%) has a good balance between wet skid resistance and low rolling resistance. Molecular dynamics simulation was further employed to perform fixed and cyclic stretching to give the mechanism for mechanical properties. Binding energy and mean square distance illustrate that that as the epoxy degree increases, on the one hand, the strong filler‐matrix interactions will make the movement of ESSBR chains keep up with the strain. On the other hand, the strong filler‐matrix and inter‐chain interactions provide more friction. These two factors lead to an increase in hysteresis loss. Besides, only moderate filler‐matrix interaction is conducive to the improvement of wet skid resistance, and too strong or too weak interaction is unfavorable.
This study shows how carbon black/silica hybrid filler networking leads to synergistic properties in styrene-butadiene rubber (SBR) composites. The effects of low concentrations of silica, the secondary filler, on flocculation and network formation/breakdown (Payne effect) of carbon black, the primary filler in the SBR composites, were evaluated. There was a critical silica concentration at which this synergy was observed, but it disappeared at higher concentrations due to network formation by silica itself. A mismatch between the carbon black and silica surface energies was shown to be the determining parameter. Critical loading of silica was also observed for vulcanization of rubber composites, at which the enthalpy of vulcanization increased considerably. Enhancements in the final properties, such as mechanical strength and wear resistance, were explained by improvements in the dispersion of carbon black and vulcanization of rubber at the critical loading of silica. Synergistic effects of adding silica, as a secondary filler, to styrene-butadiene rubber composites highly filled with carbon black was investigated. It was shown that there is a critical concentration of silica at which improvements in the Payne effect, mechanical properties, abrasion resistance, and heat build-up were at extrema. This behavior was attributed to the filler networking in the hybrid filler systems, at which work of adhesion in a three-component system was considered as the driving force for flocculation of the primary filler and final morphology of fillers in hybrid composites.
Composite materials based on hybrid filler systems can be a promising approach to produce advanced rubber nanocomposites (NCs). Recently, the positive effect of the combined use of silica and sepiolite on NCs mechanical properties has been reported, compared to those of compounds reinforced with the same amount of the only silica filler. In this context, the present work aims at studying the possible synergistic self-assembly of nanosilica and sepiolite in the generation of a cooperative hybrid filler network in rubber-based NCs, in connection with material performance for tires application. In detail, the influence of the introduction of a secondary anisotropic filler in conjunction with isotropic nanosilica on their dispersion and interaction with the rubber matrix has been comprehensively investigated, in order to define the best formulation ensuring low rolling resistance and significant fuel saving.
NCs, containing simultaneously silica and sepiolite, either pristine (Sep) or chemically modified (mSep) by an acid treatment, were prepared by combining latex compounding technique (LCT) and melt blending. Rheological and dynamic-mechanical analyses highlighted that the use of a double white filler, constituted by particles with different aspect ratio, affords a good balance between efficient reinforcement and low Payne effect.
Tansmission electron microscope (TEM) analysis evidenced the formation, within the rubber matrix, of cooperative superstructures due to the self-assembly of sepiolite and silica nanoparticles containing occluded rubber, when the secondary filler is mSep. The peculiar characteristics of mSep, characterized by fibers shorter than Sep and higher surface silanol bonding sites, bring about significant interactions between mSep and silica, which promote self-assembly of the two fillers in a collaborative hybrid network, improving dynamic-mechanical performances.
These results, even if related to sepiolite/silica NCs, demonstrate the effective role of the collaborative filler network, based on the hybrid double fillers, able to lend enhanced properties to rubber materials.
An accurate prediction of the fatigue life of a rubber product is based on a criterion. Since strain can be measured directly in rubber components during a test, it would help design engineers improve product performance effectively if the strain‐based damage criteria can achieve high accuracy. Hence, the experimental data on the AE42 and AE2 specimens were utilized to test the suitability of the proposed damage criterion for rubber materials. The criterion includes three principal components determined by both a strain range and a current strain. Data from AE42 specimens, made from styrene‐butadiene rubber, contained 40 cases, that is, tension, torsion, and tension‐torsion loadings. An S‐N curve was obtained, with a scatter band of 0.7 and a coefficient of determination R² of 0.81. The curve could be useful at the design stage. A sample of AE2, made from natural rubber filled with carbon black, showed the location and orientation of the crack in a nonproportional case. The predicted location of the fatigue crack was consistent with the experimental observation and the crack orientation matched the experimental measurement, that is, the predicted angle of 33.4° versus the measurement of approximately 40°. It would be possible to combine the proposed approach with the critical plane method in nonproportional loadings to save significant CPU time: using the proposed approach to find the critical loading range and then using the critical plane method to find the maximum value of the required damage variables. More engineering cases are needed to further verify this proposed criterion.
To improve the properties of silica-reinforced truck tire tread compounds, especially abrasion resistance, the effect of vinyl contents in butadiene rubber (BR) or solution styrene–butadiene rubber (SSBR) as secondary polymers in silica-filled natural rubber (NR) compounds at a ratio of 80/20 phr is investigated in the first part of this study. By increasing the levels of vinyl contents in BR in combination with NR, a better Payne effect, 300% modulus, reinforcement index, and tan delta at −20 and 0 ° C are obtained, whereas the tensile strength, elongation at break, and DIN abrasion resistance index decrease with increasing vinyl contents. Higher vinyl contents in SSBR result in improvements in Payne effect, 300% modulus, tan delta at −20 and 0 °C but only a small improvement in DIN abrasion resistance index. Combinations of secondary fillers and polymers in silica-filled NR are covered in the second part of present study. Silica/carbon black–filled NR/BR and NR/SSBR, respectively, and silica/organoclay–filled NR/BR and NR/SSBR show positive effects on scorch time and optimum cure time, with only slight changes in Payne effect, tensile properties, tan delta at −20 and 0 ° C and DIN abrasion resistance as compared with compounds with carbon black N134. The use of organoclay results in an enhanced Payne effect and tan delta at 60 °C, indicative of reduced filler–filler networking and consequently a lower rolling resistance of tire tread compounds as compared with the compound without organoclay. The specific combination of a small amount of organoclay replacing the same amount of silica, together with some of the NR replaced by high-vinyl BR, promises a substantial overall boost in wet and ice traction, abrasion, and wear resistance as compared with straight NR/silica tire treads. This new observation helps to overcome one of the main shortcomings of NR/silica compounds: their generally low wear resistance.
Automotive industry is currently looking for an eco‐friendly tire with low rolling resistance coefficient (RRc), better traction, wear resistance, and fatigue properties. Presently, solution styrene‐butadiene rubber (SSBR)‐silica systems are pursued for balancing between traction and RRc. However, the interaction between SSBR and silica is not enough to give satisfactory results. Functionalized‐SSBR (FSSBR) leads to better rubber‐silica interaction due to introduction of polar groups in the polymer chain. The present study investigates the influence of FSSBR, highly dispersible (HD) silica, and its hybrid filler systems with organically modified nanoclay (ONC) and exfoliated graphene nanoplatelet (xGnP). Both MH, and Δtorque were higher for the FSSBR‐HD silica compound (S1) with the lowest change in storage modulus (∆G') value, due to higher polymer‐filler interaction. S1 exhibited 16% ice traction and 12% wet traction improvement with 29% lower rolling resistance over SSBR‐silica compound. S1 showed the best wet traction rating and wear resistance. Replacing small portion of silica by ONC and xGnP improved the properties further. At 5 phr of nanofiller, TEM images revealed well‐dispersed nanofillers in the FSSBR matrix. The xGnP compound showed the least crack growth. For both the cases, abradability decreased with higher nanofiller amount, due to better reinforcement of the rubber.
The wet traction, rolling resistance and abrasion resistance have rarely been improved simultaneously in tread rubbers, which is regarded as “magic triangle” in tire industry. Recently, we have demonstrated that phosphoniums are effective in lowering rolling resistance of tread via catalyzing the interfacial silanization. In addition, incorporating the C5/C9-based petroleum resin into tread formulation is a well-established technology toward high wet traction. Accordingly, we aim to solve the “magic triangle” dilemma by using phosphonium-modified petroleum resin (PSR), which is prepared through a two-step reaction. PSR is incorporated into the silica-filled styrene-butadiene rubber (SBR) composites with bis [3-(triethoxysilyl)propyl] tetrasulfide (TESPT). Due to the electrostatic interaction between PSR and silica, the dispersion of silica is improved. Moreover, PSR exhibits catalytic effect on the interfacial silanization, leading to the improvement of interfacial interactions. With incorporation of 2 phr of PSR, the tan δ at 0 °C and abrasion loss of the rubber composite are increased by 19% and decreased by 28%, respectively, which suggests that the wet traction and abrasion resistance are increased. The tan δ at 60 °C of the rubber composite is decreased by 14%, indicating that the rolling resistance is decreased. In addition, the overall excellent “magic triangle” performance of a typical tread rubber is also demonstrated by incorporating PSR, indicating that PSR has great potential in practical applications. We envisage that this study provides a new solution for high-performance tread rubber for green tires.
Silane coupling agent has been used for ages to improve the performances of silica-filled rubber composites. To improve the degree of silanization of silica, ionic liquids (ILs) as a catalyst are incorporated to the styrene-butadiene rubber (SBR)/silica composites. The reaction between bis [3-(triethoxysilyl) propyl] tetrasulfide (TESPT) and silica with different basic ILs is investigated. The results show that the ILs with stronger alkalinity exhibit higher catalytic efficiency. The silanization occurs at lower temperature with the incorporation of ILs. The parameters characterizing interfacial interactions show that the interfacial adhesion is gradually improved with increasing alkalinity of ILs. Consequently, the resulting composite with ILs possessing strong alkalinity exhibits excellent whole performance compared with the composites without ILs. Especially, the energy loss of rubber wheel in rolling process is gradually decreased. The composites exhibit excellent abrasion resistance and heat build-up.
Adding silica nanofiller in silicone rubber can toughen the matrix 3 orders in terms of fracture energy, which is far larger than most other nanofiller–rubber systems. To unveil the astonishing toughening mechanism, we employ in situ synchrotron radiation X-ray nanocomputed tomography (Nano-CT) technique with high spatial resolution (64 nm) to study the structural evolution of silica nanofiller in silicone rubber matrix at different strains. The imaging results show that silica nanofiller forms three-dimensional connected network, which couples with silicone chain network to construct a double-network structure. Stress-induced phase separation between silica nanofiller and silicone polymer chain networks is observed during tensile deformation. Unexpectedly, though the spatial position and morphology of nanofiller network changes greatly at large strains, the connectivity of nanofiller network shows negligible reduction. This indicates that nanofiller network undergoes destruction and reconstruction simultaneously, during which silica nanofiller serves as reversible high functionality cross-linker. The reversible bonding between silica nanofiller and silicone rubber or between nanofiller particles can dissipate mechanical energy effectively, which may account for the 3 orders enhancement of toughness.
A novel compound diethyl acetylphosphonate has been explored as efficient additive in iron based catalyst for stereo-polymerization of 1,3-butadiene to afford high crystalline 1,2-syndiotactic polybutadiene. Excellent 1,2 selectivity in range of 91.0–98.4% with controllable crystallinity has been achieved at high catalytic efficiency in wide ranges of cocatalyst and additive feeding as well as at large temperature scope. As reinforcing agent, two crystalline polymers differing in crystallinity 4.4% and 51.9% are blended and co-cured with cis-1,4 polybutadiene (PB) with 10 wt-%, providing samples PB1 and PB2, respectively. SEM from the sample fracturesurface shows the s-PBD particles are intimately mixed and homogeneously dispersed in PB matrix due to the strong interfacial interaction. The analysis of the mechanical properties of sample PB2 finds the tensile strength of increases by one-fold and the elongation at break increases by two-fold when head to head comparison to those of the CB filled PB, while the shear modulus G′ and loss factor (tan δ) are as good as those charged with CB. These results highlight the role of s-PBD as reinforcing agent of PB rubber, yielding high performance rubber materials with improved mechanical properties.
Epoxy group-functionalized bio-based elastomer poly (dibutyl itaconate-ter-isoprene-ter-glycidyl methacrylate) (PDBIIG) was synthesized via redox emulsion polymerization using glycidyl methacrylate (GMA) as the epoxy group-included monomer. The silica/PDBIIG nanocomposite was prepared without adding silane coupling agents. Ring-opening reaction, which occurred between the hydroxyl groups on the silica surfaces and the epoxy groups of the PDBIIG chains during mixing and vulcanization, was confirmed via bound rubber tests and Fourier transform infrared spectroscopy. This reaction was facilitated through heat treatment at 150 °C effectively. The introduction of covalent bonds significantly improved the interfacial interaction and dispersion of silica, which was indicated by transmission electron microscopy and rubber process analyzer (RPA) results. With the same silica loading and compounding procedure, the inclusion of 3.7 wt.% GMA increased the modulus at 100% strain by 150.0% and the modulus at 300% strain by 152.3%. For the dynamic mechanical properties, the nanocomposite with GMA exhibited higher wet skid resistance and lower rolling resistance than the nanocomposite without GMA.
We report the unusual mechanical percolation behavior of expanded clay nanoparticles in a natural rubber (NR) matrix. This phenomenon is discussed in terms of fractal dimensions of the nanoparticle cluster. Highly exfoliated structures of nanoparticles in NR are obtained by a process we call the ‘propping-open approach’. The impact of filler dispersion and rubber–filler interactions on the viscoelastic behavior of NR–clay nanocomposites is systematically investigated. We observe non-linear viscoelastic behavior (Payne effect) at very low nanoparticle concentrations which we attribute to the formation of a network-like structure of the exfoliated clay particles. We rely on the Kraus and Maier–Göritz models to interpret such nonlinear viscoelastic behavior. We find that the chain mobility of the NR is greatly reduced based on the viscoelastic master curves. The value of the mechanical percolation threshold (φp) and the fractal nature of nanoparticle clusters are determined through an analysis of the experimental data based on a theory put forward by Huber and Vilgis. The nature of rubber–filler interactions is further understood from swelling experiments utilizing the Kraus and Cunneen–Russell equations.
Use of reinforcing fillers in elastomers ranks as one of the two most important processes in rubber technology—only vulcanization can be considered to surpass it in its universal application. From the time of the earliest observations that certain pigments are capable of imparting reinforcement to natural rubber, particularly against wear, people have been concerned with interactions between filler surfaces and rubbers and their role in the mechanism of reinforcement. Progress, initially painfully slow, received a great boost about 30 years ago with the application of the electron microscope to establish the role of particle size. However, it very soon became apparent that particle size, while undoubtedly the single most important variable in rubber reinforcement, cannot account for all the effects of fillers in elastomers and that specific interactions between rubbers and fillers must also play an important part. Today the importance of these interactions is universally recognized, although much remains to be learned about the exact mechanisms by which they give rise to reinforcing effects.
1. Up to now, the application of the Einstein-Guth-Gold equation seemed to be limited to inactive fillers. 2. However, in the form of Equation (6), it describes with high accuracy the moduli of vulcanizates containing active fillers as a function of the filler volume fraction at least up to ϕ=0.22 at uniaxial elongations and for any given value of λ. 3. The effectiveness factor ƒ is independent of crosslinking density, but is dependent on deformation, temperature, and the surface activity of the filler. 4. If ƒ as a function of elongation is known, the respective stress-strain curves of filled networks can be calculated in advance for any given crosslinking density. 5. The interpretation of the effectiveness factor will require further investigations, especially with regard to the influence of the structure and surface activity of the filler.
Dispersion values in rubber are usually subjective values or the result of a comparison against empirical standards. we present a method to measure the filler dispersion in rubber compounds reinforced beyond the percolation threshold. Applying this method to an actual technical formulationwith high filler loading, the dispersability of different silica grades, as well as the effect of coupling agent concentration in the dispersion has been showed. To carry out the measurements, the finished rubber is sliced in very thin films and then examined with transmission electron microscopy (TEM). Those images are processed to obtain information on the filler aggregation properties. As expected, the highly dispersible silica presents a smaller aggregate size and more contact surface with the rubber than the conventional and easily dispersible grades. In addition, increasing the amount of silane does diminish the aggregate size but with a lesser effect than that of the silica grade.
The introduction of silanes to improve processability and properties of silica-reinforced rubber compounds is critical to the successful commercial use of silica as a filler in tires and other applications. The use of silanes to promote polymer-filler interactions is expected to limit the development of a percolated filler network and may also affect the mobility of polymer chains near the particles. Styrene-butadiene rubber (SBR) was reinforced with silica particles at a filler volume fraction of 0.19, and various levels of filler-filler shielding agent (n-octyltriethoxysilane) and polymer- filler coupling agent (3-mercaptopropyltrimethoxysilane) were incorporated. Both types of silane inhibited the filler flocculation process during annealing the uncured rubber materials, thus reducing the magnitude of the Payne effect. In contrast to the significant reinforcement effects noted in the strain-dependent shear modulus, the bulk modulus from hydrostatic compression was largely unaltered by the silanes. Addition of polymer-filler linkages using the coupling agent yielded bound rubber values up to 71%; however, this bound rubber exhibited glass transition behavior which was similar to the bulk SBR response, as determined by calorimetry and viscoelastic testing. Modifying the polymer-filler interface had a strong effect on the nature of the filler network, but it had very little influence on the segmental dynamics of polymer chains proximate to filler particles.
In the past few years, an enormous amount of work has been reported on the progress in the application of conventional fillers and the development of new products to improve the reinforcement of rubber, dynamic properties in particular. While all agree that the filler as one of the main components of the filled-rubber composite, has a very important role in improving the dynamic performances of the rubber products; many new ideas, theories, practices, phenomena, and observations about how and especially why the filler alters the dynamic stress-strain response have been presented. This, of course, suggests that not only is the real world of the filled rubber complex and sophisticated but also multiple mechanisms may be involved. However, it must be admitted that the possibility exists for explaining the effect of all fillers on rubber properties ultimately in similar and relatively nonspecific terms, i.e., the phenomenon related to all filler parameters should follow a general rule or principle. I...
Thermogravimetric analysis (TGA) has been used to study the kinetics of bound-rubber formation on the surface of silica modified with a bi-functional alkoxysilane coupling agent (CA) over the temperature range of 110 to 150 degrees C. The bound-rubber formation is attributed to the direct binding of a polymer chain with a number of nonpolar interactive sites provided by the CA molecules on the silica surface. A kinetic model developed for the reaction process suggests that the bound-rubber morphology is altered at temperatures above 110 degrees C.
It was shown that the physical filler-polymer and filler-filler interactions, apart from the filler surface chemistry, has a substantial role in controlling the vulcanization kinetics of styrene butadiene rubber filled with nano-silica in a sulfur vulcanization system. Kinetic studies by the oscillating disc rheometer, differential scanning calorimeter, and swelling tests revealed that the vulcanization rate goes through a maximum as loading of silica increases, but conversion in crosslinking continuously decreases as the amount of silica increases. The effect of silica loadings on the vulcanization reactions was linked to the immobilization of rubber chains around particles as well as in a polymer-mediated filler network, which were differentiated by the nonlinear viscoelastic behavior of rubber vulcanizates. By surface modification of nano-silica, the accelerating/decelerating effects of nano-silica on the vulcanization reactions were altered corresponding to the non-linear viscoelastic behavior of the vulcanizates. Therefore, a mechanism was proposed which correlates vulcanization kinetics of rubber to the dynamics of chains influenced by the reinforcing fillers.
The stress softening effect of nature rubber (NR) reinforced by in situ prepared zinc dimethacrylate (ZDMA) was studied. Degree of stress softening effect (Ds) in the 4th stress–strain cycle of the NR with 10 phr (parts per hundreds of rubber) ZDMA was only 2.23 (strain = 100%), whereas it reached to 59.98 at 50 phr ZDMA (strain = 200%). The stress softening effects of carbon black filled into NR, and compared with the ZDMA effect, was also studied here. Mooney–Rivlin semiempirical equation was introduced here to analysis the stress–strain behavior of the NR vulcanize filled with in situ prepared ZDMA, and the results showed that the ZDMA/NR system has an obvious Payne effect which is in good agreement with the stress softening effect. Crosslink density analysis indicated a high ionic crosslink density in the NR filled with high content ZDMA, which contributed to the low elastic recovery of the stress softening. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
The dynamic properties, including the dynamic mechanical properties, flex fatigue properties, dynamic compression properties, and rolling loss properties, of star-shaped solution-polymerized styrene–butadiene rubber (SSBR) and organically modified nanosilica powder/star-shaped styrene–butadiene rubber cocoagulated rubber (N-SSBR), both filled with silica/carbon black (CB), were studied. N-SSBR was characterized by 1H-NMR, gel permeation chromatography, energy dispersive spectrometry, and transmission electron microscopy. The results show that the silica particles were homogeneously dispersed in the N-SSBR matrix. In addition, the N-SSBR/SiO2/CB–rubber compounds' high bound rubber contents implied good filler–polymer interactions. Compared with SSBR filled with silica/CB, the N-SSBR filled with these fillers exhibited better flex fatigue resistance and a lower Payne effect, internal friction loss, compression permanent set, compression heat buildup, and power loss. The nanocomposites with excellent flex fatigue resistance showed several characteristics of branched, thick, rough, homogeneously distributed cross-sectional cracks, tortuous flex crack paths, few stress concentration points, and obscure interfaces with the matrix. Accordingly, N-SSBR would be an ideal matrix for applications in the tread of green tires. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40348.
This study investigates novel hybrid fillers for lowering of viscoelastic dissipation in rubber compounds by exploiting non-covalent interactions between lignin and carbon black (CB). Lignin is naturally occurring three-dimensional amorphous polymer consisting of phenyl propane units with hydroxyl, methoxy, and carbonyl substitutions and is capable of producing non-covalent interactions via pi-pi stacking with CB particles. The hybrid fillers are obtained by precipitating lignin from solutions onto carbon black particles. The fractal nature similar to CB particles and the presence of lignin coating layers on CB particles are confirmed by electron microscopy images. The coating layers are promoted by strong pi-pi interactions as revealed from Raman spectroscopy and H-1 spin-lattice relaxation data and supported by a drop in zeta potential values. The hybrid fillers show much less networking than CB and reduce the viscoelastic dissipation in model rubber compounds by as much as 10% in comparison to the compounds of only CB.
J-integral theory and fatigue testing were adopted to investigate the fracture and fatigue properties of silica/carbon black(CB)/natural rubber composites with total filler content of 50 phr. Critical J-value JIC and tearing modulus TR, were obtained. JIC, as an indicator of crack initiation resistance, was dependent on the pre-cut length. TR was related to the crack propagation of the composite. With increasing the silica/CB ratio, both JIC and TR were enhanced, indicating that the resistance to crack initiation and propagation were improved. The strain energy density at a fixed strain decreased with an increase in the silica/CB ratio. Fatigue testing under constant tensile strain conditions demonstrated that the composite with higher silica/CB ratio exhibited lower cyclic crack growth rate and longer fatigue life. This was in accordance with the results of TR, JIC and strain energy density of the composite, hence TR, JIC and strain energy density of the composite can be used to predict its fatigue properties.
For styrene-butadiene rubber (SBR) compounds filled with the same volume fraction of carbon black (CB), precipitated silica and carbon–silica dual phase filler (CSDPF), filler-rubber interactions were investigated thru bound rubber content (BRC) of the compounds and solid-state 1H low-field nuclear magnetic resonance (NMR) spectroscopy. The results indicated that the BRC of the compound was highly related to the amount of surface area for interaction between filler and rubber, while the solid-state 1H low-field NMR spectroscopy was an effective method to evaluate the intensity of filler-rubber interaction. The silica-filled compound showed the highest BRC, whereas the CB-filled compound had the strongest filler-rubber interfacial interaction, verified by NMR transverse relaxation. The strain sweep measurements of the compounds were conducted thru a rubber process analyzer; the results showed that the CSDPF-filled compound presented the lowest Payne effect, which is mainly related to the weakened filler network structure in polymer matrix. The temperature sweep measurement, tested by dynamic mechanical thermal analysis, indicated that the glass transition temperature did not change when SBR was filled with different fillers, whereas the storage modulus in rubbery state and the tanδ peak height were greatly affected by the filler network structure of composites.
The morphological structure and mechanical properties of the star-shaped solution-polymerized styrene-butadiene rubber (SSBR) and organically modified nanosilica powder/star-shaped SSBR co-coagulated rubber (N-SSBR) both filled with silica/carbon black (CB) were studied. The results showed that, compared with SSBR, silica powder could be mixed into N-SSBR much more rapidly, and N-SSBR/SiO2 nanocomposite had better filler-dispersion and processability. N-SSBR/SiO2/CB vulcanizates displayed higher glass-transition temperature and lower peak value of internal friction loss than SSBR/SiO2/CB vulcanizates. In the N-SSBR/SiO2/CB vulcanizates, filler was dispersed in nano-scale resulting in good mechanical properties. Composites filled with silica/CB doped filler exhibited more excellent mechanical properties than those filled with a single filler because of the better filler-dispersion and stronger interfacial interaction with macromolecular chains. N-SSBR/SiO2/CB vulcanizates exhibited preferable performance in abrasion resistance and higher bound rubber content as the blending ratio of silica to CB was 20:30. Copyright © 2008 John Wiley & Sons, Ltd.
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., 2013. © 2013 Society of Plastics Engineers
Mechanical properties and cross-link density of model composites being solution styrene–butadiene rubbers filled with different amounts of nanosized silica particles or mixtures of nanosized silica particles and micrometer-sized borosilicate glass particles are studied. The cross-link density of the rubber matrix is measured based on a double-quantum NMR spectroscopy method. Shear data show that reinforcement and dissipation G″ in the rubber plateau range depend systematically on the total surface area of the filler per unit composite. Different contributions to reinforcement due to hydrodynamic effects, “filler network”, glassy polymer layer, and “occluded rubber” are quantified based on a comparison of linear response measurements with strain sweeps performed at different temperatures. The results show a percolation threshold at silica volume fractions of about 0.15. The load-carrying capacity of the “filler network” decreases significantly with temperature. This may indicate the existence of a glassy polymer layer on the surface of the filler particles which softens several ten degrees above the bulk Tg of the rubber matrix. Two regimes are found in the dissipation above Tg which both depend systematically on the surface area of the filler system: A strongly frequency-dependent dissipation regime with power-law behavior is observed in G″(ω) at temperatures up to 70 K above the bulk Tg, and a nearly frequency-independent G″ regime dominates at higher temperatures. The molecular nature and importance of this finding for tire applications are discussed.
To fully exhibit the potentials of the fascinating characteristics of graphene oxide (GO) in polymer, the achievement of strong interface interactions and fine dispersion of GO in the hybrids is essential. In the present work, the elastomeric hybrids consisting of GO sheets are fabricated by utilizing butadiene–styrene–vinyl pyridine rubber (VPR) as the host through co-coagulation process and in situ formation of an ionic bonding interface. The VPR/GO composites with a normal hydrogen bonding interface are also prepared. The mechanical properties and gas permeability of these hybrids with an ionic bonding interface are obviously superior to those of the composites with a hydrogen bonding interface. With the ionic interfacial bonding, inclusion of 3.6 vol% of GO in VPR generates a 21-fold increase in glassy modulus, 7.5-fold increase in rubbery modulus, and 3.5-fold increase in tensile strength. The very fine dispersion of GO and the strong ionic interface in the hybrids are responsible for such unprecedented reinforcing efficiency of GO towards VPR. This work contributes new insights on the preparation of GO-based polymer hybrids with high performance.
The combination of reinforcing fillers is one of the most promising tendencies in elastomer reinforcement, where a synergic effect between them is desired. Up to now, the use of mixed fillers has been focused on the preparation of dual fillers based on a complex synthesis process where silica particles are in situ generated in a carbon black matrix. In this paper, mixed filler systems are prepared following a straightforward methodology, where carbon black is gradually and partially substituted by modified fumed silica. The presence of reinforcing fillers with different surface energies significantly decreases filler networking, reducing the non-linear viscoelastic response of the composites. The hybrid reinforcing systems prepared were easily incorporated into the elastomer matrix by conventional methods in rubber technology. Physical and dynamic responses of the elastomeric composites were characterized in order to find the optimum mixed system combination. Filler–rubber interface was characterized combining 1H low field DQ (Double Quantum) NMR spectroscopy and equilibrium swelling experiments.
Elastomeric composites have been prepared using pre-treated fumed silica as a reinforcing system. The processing disadvantages of fumed silica were overcome by a novel one-pot modification method based on silanization treatment of silica particles after an ultra-high energy sonication process that breaks down the micro-aggregates/agglomerates of pristine silica into nanoparticles. Grafted organosilane molecules on the nanoparticle surfaces avoid the natural tendency for silica particles to re-agglomerate obtaining a stable dispersion of organo nanosilica particles that are compatible with the rubber matrix. The modified nanosilica can be easily incorporated into the elastomer matrix by conventional methods employed in rubber technology, contrary to pristine fumed silica which shows significant compounding disadvantages leading to high viscosity compounds. The improved dispersion and enhanced interface significantly enhance the final properties of the composites. Finally, the filler–rubber interface was characterized combining 1H low field Double Quantum (DQ) NMR spectroscopy and equilibrium swelling experiments. This novel experimental methodology demonstrates the existence of improved interactions in the interface between silica particles and rubber macromolecules.
Crack growth property of natural rubber (NR) vulcanizate with varying silica/carbon black content was examined. Tensile specimen
with edge cut was used for estimating fracture properties. All filled NR specimens showed critical cut-size (C
cr
), which is related to abrupt decrease in tensile strength. Carbon black-filled NR, S0 (Si/N330=0/50) has higher tensile strength
than equivalently loaded silica-filled NR vulcanizates, S5 (Si/N330=50/0). When the precut size of specimen was less than
critical cut-size, tensile strength of S1 (Si/N330=10/40) composition was the highest and that of S5 was the lowest. The critical
cut-size passes through a maximum for S2 (Si/N330=20/30) and then decreases gradually with silica loading. An interesting
result was that silica and carbon black-blended compounds gave higher critical cut size than the all-carbon black compounds,
S0. The inherent flaw size decreased from 246 μm for S0 to 80 μm for S5 as the silica content increased.
Carbon black (CB) and silica have been used as the main reinforcing fillers that increase the usefulness of rubbers. As each filler possesses its own advantages, the use of silica/CB blends should enhance the mechanical and dynamic properties of natural rubber (NR) vulcanizates. However, the optimum silica/CB ratio giving rise to the optimum properties needs to be clarified. In this research, reinforcement of NR with silica/CB hybrid filler at various ratios was studied in order to determine the optimum silica/CB ratio. The total hybrid filler content was 50phr. The mechanical properties indicating the reinforcement of NR vulcanizates, such as tensile strength, tear strength, abrasion resistance, crack growth resistance, heat buildup resistance and rolling resistance, were determined. The results reveal that the vulcanizates containing 20 and 30phr of silica in hybrid filler exhibit the better overall mechanical properties.
An exact formula is obtained for the term of order c2 in the expression for the bulk stress in a suspension of force-free spherical particles in Newtonian ambient fluid, where c is the volume fraction of the spheres and c [double less-than sign] 1. The particles may be of different sizes, and composed of either solid or fluid of arbitrary viscosity. The method of derivation circumvents the familiar obstacle, of non-absolutely convergent integrals representing the effect of all pair interactions in which one specified particle takes part, by the judicious use of a certain quantity which is affected by the presence of distant particles in a similar way and whose mean value is known exactly. The bulk stress is in general of non-Newtonian form and depends on the statistical properties of the suspension which in turn are dependent on the type of bulk flow.
Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds show smooth rheological behaviour in measurement of Mooney viscosity or Mooney scorch time. Variation in rheological behaviour was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica (carbon black/silica = 60/20,40/40, and 20/60 phr). The compound filled with carbon black/silica of 60/20 phr showed normal rheological behaviour. However, the compounds filled with carbon black/silica of 40/40 and 20/60 phr showed abnormal rheological behaviour, in which the viscosity increased suddenly and then decreased at a certain point during the measurement. The abnormal behaviour was explained by the strong filler–filler interaction of silica. Moreover, the abnormal rheological behaviour was displayed more clearly as the storage time of compounds is increased.
© 2003 Society of Chemical Industry
The dynamic properties of a natural vulcanized rubber containing carbon black were studied for dynamic tensions of amplitude varying greatly. It was shown that both the elastic responses and viscosity change with amplitude of oscillation and with concentration and type of carbon black. The effects of thermal treatment on the dynamic modulus were also studied. Beginning with conditions of equilibrium between the hard and soft regions of the vulcanizate for very weak stresses, the values for the formation of hard regions from soft regions were determined by means of the Van't hoff isochore.
The composites of solution polymerized styrene-butadiene rubber (SSBR) filled with SiO2/carbon black (CB) were prepared by reaction blending. The mechanical and antistatic properties were studied. The morphology and dispersion of the two kinds of nano-fillers in the composites were observed. The results showed that CB presented 30 nm spherical particles and formed filler networks in the SSBR/CB composite. Payne effect of the SSBR/CB composite was large and the antistatic property was excellent; SiO2 powder presented 20–40 nm irregular particles and also formed filler networks in the SSBR/SiO2 composite. The internal friction of the SSBR/SiO2 composite was low, however, the static accumulation was obviously large; SSBR/SiO2/CB composites exhibited good filler dispersion, high mechanical properties and low internal friction. The rolling resistance, wet-skid resistance and wear resistance are well balanced. Among these, the composite filled with SiO2/CB in 20/50 achieved the best overall performances. The surface and volume resistivity of the composites was increased with increasing amount of SiO2. For the researched formulation, the ratio of SiO2/CB in 35/35 was the percolation threshold for the antistatic property of the composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
The stress-strain behavior of carbon black filled rubber is recognized to be nonlinearly elastic in its main part (see e.g. Gent [1]). In addition, inelastic effects occur under monotonic and cyclic processes. The inelastic behavior includes nonlinear rate dependence as well as equilibrium hysteresis. Moreover, the first periods of a stress-strain curve differ significantly from the shape of subsequent cycles; a characteristic feature, which is called the Mullins effect, because it has been pointed out by Mullins [2]. All inelastic phenomena are strongly influenced by the volume fraction of the filler particles (see e.g. Payne [3], So and Chen [4], Meinecke and Taftaf [5]).The aim of the present paper is to design a constitutive model, representing this kind of material behavior as a phenomenological theory of continuum mechanics. In order to motivate the basic structure of the constitutive theory, a series of uniaxial experiments between 100% in tension and 30% in compression are presented and analyzed. First of all, monotonic strain controlled experiments show the nonlinear rate dependence of the stress response. Then, a series of inserted relaxation periods at constant strain yields the monotonic equilibrium stress-strain curve, which is strongly nonlinear and unsymmetric with respect to the origin. Finally, cyclic experiments under strain control display pronounced hysteresis behavior. The hysteresis effects are mainly rate dependent, but there exists also a weak equilibrium hysteresis (compare to similar observations of Orschall and Peeken [6]). The Mullins effect corresponds to a softening phenomenon during the first few cycles. By means of an appropriate preprocess, this effect was excluded during the above experiments. Apart from the Mullins effect, neither hardening nor significant softening phenomena were observed in the context of cyclic loadings.These results motivate the structure of a constitutive model of finite strain viscoplasticity: The total stress is decomposed into an equilibrium stress and an overstress, where the overstress is a rate dependent functional of the strain history. The overstress represents the rate dependence of the material behavior and tends asymptotically to zero during relaxation processes. The nonlinearity of the rate dependence is incorporated by means of a stress dependent relaxation time. The equilibrium stress is assumed to be a rate independent functional of the strain history. For this quantity, we make use of an arclength representation, which was originally introduced by Valanis [7]. In case of vanishing equilibrium hysteresis and vanishing rate dependence our constitutive model reduces to finite strain hyperelasticity, which is the first approximation of the constitutive properties. In more general cases the main shape of a stress-strain curve is determined by hyperelasticity, superimposed by rate dependent and equilibrium hysteresis. The representation of the Mullins effect is incorporated by a continuum damage model.Some numerical simulations at the end of the paper demonstrate that the presented theory is able to represent the observed phenomena qualitatively and quantitatively with sufficient approximation.
Natural rubber (NR)/nanoclay and NR/carbon nanofiber (CNF) nanocomposites were consolidated with different loadings and grades
of carbon blacks (CBs) to obtain ternary nanocomposites. It was observed that the mechanical and dynamic mechanical properties
of these nanocomposites were much better compared with those of either NR/clay or NR/CNF nanocomposites or the NR/black control
microcomposite. Thus, not only the grueling and at times conflicting property requirements of modern day applications were
met, but also the tendency of saturation of property enhancements at high loadings could be mitigated. These nanocomposites
exhibited 18% increment in tear strength, 40% in modulus at 300% elongation, and 326% in room temperature storage modulus,
over the control microcomposite. Viscous loss properties were influenced favorably, as well. This indicated the presence of
a much sought after synergy between CB and nanofillers. Transmission electron micrographs of the nanocomposites showed that
CB formed “nano-blocks” of reinforcement—close association of nanofiller and black—driven by zeta potential differences between
the black and the nanofillers. This unique ternary architectural base, with the space between nanofillers (clay/fiber) occupied
by small CB aggregates forming networks or “nano-channels”, accounted for the synergistic improvements.
Synergistic effect of carbon black (CB) in presence of nanofillers (nanoclay and nanofiber) on mechanical and dynamic mechanical
properties was discussed in light of electrostatic interactions and the concomitant microstructural developments, in Part
I of this series. These interactions enhanced filler dispersion and ensured efficient stress transfer from the matrix resulting
in improvement in properties, undiminished even by continual increase in CB loading. In this part, the micromechanical processes
that influence wear behavior have been addressed conjointly with dynamic mechanical properties. Tribological characteristics
were studied by sliding rubber wheel samples against a steel blade, in a specially designed abrader, in both transient and
steady state conditions. Wear loss was reduced in the dual filler nanocomposites by 33% (over the CB microcomposite) in less
stringent and 75% under severe wear conditions. These CB filled nanocomposites also illustrated lowering of coefficient of
friction and temperature build-up. This was attributed to efficient heat dissipation due to the formation of a unique microstructural
architecture by the participating fillers and also an adhering transfer film on the abraders’ counterface. From viscoelastic
measurements, the CB filled nanocomposites were also found to lie in the high performance window of good wet skid and low
rolling resistance.
Nano-strengthening by employing nanoparticles is necessary for high-efficiency strengthening of elastomers, which has already been validated by numerous researches and industrial applications, but the underlying mechanism is still an open challenge. In this work, we mainly focus our attention on studying the variation of the tensile strength of nanofilled elastomers by gradually increasing the filler content, within a low loading range. Interestingly, the percolation phenomenon is observed in the relationship between the tensile strength and the filler loading, which shares some similarities with the percolation phenomenon occurring in rubber toughened plastics. That is, as the loading of nanofillers (carbon black, zinc oxide) increases, the tensile strength of rubber nanocomposites (SBR, EPDM) increases slowly at first, then increases abruptly and finally levels off. Meanwhile, the bigger the particle size, the higher the filler content at the percolation point, and the lower the corresponding tensile strength of rubber nanocomposites. The concept of a critical particle-particle distance (CPD) is proposed to explain the observed percolation phenomenon. It is suggested that rubber strengthening through nanoparticles is attributed to the formation of stretched straight polymer chains between neighbor particles, induced by the slippage of adsorbed polymer chains on the filler surface during tension. Meanwhile, the factors to govern this CPD and the critical minimum particle size (CMPS) figured out in this work are both discussed and analyzed in detail. Within the framework of this percolation phenomenon, this paper also clearly answers two important and intriguing issues: (1) why is it necessary and essential to strengthen elastomers through nanofillers; (2) why does it need enough loading of nanofillers to effectively strengthen elastomers. Moreover, on the basis of the percolation phenomenon, we give out some guidance for reinforcement design of rubbery materials: the interfacial interactions between rubber and fillers cannot be complete chemical bonding, and partial physical absorption of macromolecular chains on the filler surface is necessary, otherwise the formation of stretched straight chains would be seriously hindered. There should exist such an optimum crosslinking density for a certain filler reinforced rubber system, and as well an optimum filler loading for rubber strengthening. Additionally, the different percolation behaviors of Young's modulus, the tensile strength and the electrical conductivity are compared and analyzed in our work. Lastly, molecular simulation indicates that it is not possible to strengthen glassy or hard polymer matrices by incorporating spherical nanoparticles. In general, by providing substantial experimental data and detailed analyses, this work is believed to promote the fundamental understanding of rubber reinforcement, as well provide better guidance for the design of high-performance and multi-functional rubber nanocomposites.
Dynamic strain-induced nonlinearity in the modulus of filled rubbers shows a striking similarity to what is known about the glass transition of solid materials and the jamming transition of granular materials. This analogy stems from the reality that shear strain in dynamic mechanical measurements introduces fluctuations in a filler network by forcing the system to explore different configurations. Such fluctuations can be described by an "effective temperature" that has many attributes of a true temperature, and particularly is proportional to the strain amplitude. Thus, filled rubbers with respect to strain will display many unusual phenomena that are usually observed in glass-forming materials, but now demonstrated in filled rubbers, including asymmetric kinetics, crossover effects, and glasslike kinetic transitions. The nonlinearity in the modulus of filled rubbers simply reflects a dejamming transition of fillers in rubber matrices. The agglomeration of filler in an elastomeric matrix shares a common ground of physics with the jamming process and glass formation.