Synergistic effect of plasma‐modified halloysite nanotubes and carbon black in natural rubber—butadiene rubber blend

Halloysite nanotubes (HNTs) were investigated concerning their suitability for rubber reinforcement. As they have geometrical similarity with carbon nanotubes, they were expected to impart a significant reinforcement effect on the rubber compounds but the dispersion of the nanofillers is difficult. In this work, HNTs were surface‐modified by plasma polymerization to change their surface polarity and chemistry and used in a natural rubber/butadiene rubber blend in the presence of carbon black. The aim of the treatment was to improve the rubber–filler interaction and the dispersion of the fillers. A thiophene modification of HNTs improved stress–strain properties more than a pyrrole treatment. The surface modification resulted in a higher bound rubber content and lower Payne effect indicating better filler–polymer interaction. Scanning electron microscopy measurements showed an increased compatibility of elastomers and fillers. As visualized by transmission electron microscopy, the thiophene‐modified HNTs formed a special type of clusters with carbon black particles, which was ultimately reflected in the final mechanical properties of the nanocomposites. The addition of HNTs increased loss angle. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Tailoring Silica Surface Properties by Plasma Polymerization for Elastomer Applications

The surface properties of reinforcing fillers are a crucial factor for dispersion and filler–polymer interaction in rubber compounds, as they strongly influence the final vulcanized properties of the rubber article. Silica is gaining more and more importance as reinforcing filler for rubbers, as it allows for a reduction of rolling resistance and thus energy losses in tires, compared to the use of carbon black as filler. However, silica and common elastomers differ greatly in polarity and, therefore, are difficult to mix and thus have little interaction. In the present study plasma-coating of silica-filler with acetylene, thiophene and pyrrole is applied, and the surface-treated silicas are blended with S-SBR rubber, in an attempt to enhance the compatibility between the two. The dispersion and reinforcing effects of the modified silicas are investigated and compared with untreated and silanized silica. The relative rankings of the various coatings in reduction of filler–filler interaction, improved dispersion, enhanced polymer–filler interaction, apparent crosslink density and tensile mechanical properties are mutually different. Where the best silica dispersion and largest reduction in filler–filler interaction are obtained with polyacetylene coating and the worst with polythiophene coating, but the tensile properties achieved with the polythiophene coating are far better than all others. Apparently, the sulfur contained in the thiophene-moiety enhances the filler–polymer interaction and contributes to the degree of crosslinking. Unmodified silica performs worst in all aspects, also because its acidic nature harms the preferably alkaline vulcanization process. Silane treatment of silica has a positive effect on reduction of filler–filler interaction and improved dispersion, but has little effect on polymer–filler interaction in the still unvulcanized state. Its tensile properties after vulcanization are comparable with polyacetylene- or polypyrrole-coated silica. This investigation shows that the compatibility and interaction of silica with a polymer can be controlled by tailoring the surface energy of the filler by coating with plasma polymers. An appropriate monomer for the plasma polymerization process allows to improve the cured rubber properties.     

Styrene butadiene rubber/epoxidized natural rubber/carbon filler nanocomposites: microstructural development and cure characterization

Microstructural development of elastomeric nanocomposites based on (50/50 wt%) styrene butadiene rubber (SBR) and epoxidized natural rubber (50 mol% epoxidation, ENR50) as the rubber matrix including two types of carbon fillers, carbon black (CB) and functionalized multiwall carbon nanotube (NH₂-MWCNT), which were prepared through melt mixing, was studied. The results from FTIR analysis show that there is interaction between functional groups on MWCNT surface and the rubber chains. The AFM analysis also indicates good dispersion of filler particles in the rubber phases. FESEM images from cryo-fractured surface of samples have revealed that nanotubes were rarely pulled out of matrix and their diameter increased, resulting from good interaction between MWCNTs and rubber chains. The DMA results confirm good interfacial interaction between them. Furthermore, the reduced difference between the two T_gs of phases (ΔT_g) shows that the incorporation of 3 phr MWCNT into the blend leads to increment in rubber phase compatibility but at higher MWCNT content (5 phr) due to lower Mooney viscosity of SBR phase, MWCNTs tend to remain in this phase. The bound rubber was adopted to characterize the polymer–filler interaction, showing that bound rubber content has an increasing trend with increasing in fillers content. The cure rheometric studies reveal that MWCNTs accelerate the cure process due to the presence of amine groups on the nanotube surface. In addition, the mechanical properties of samples show an increasing trend by increasing nano-filler content.

     

新型胺基官能化溶聚丁苯橡胶的性能

采用一种新型胺基化合物制备引发剂,并以此合成官能化溶聚丁苯橡胶,分别利用炭黑和白炭黑体系对其进行增强,测试了二者的动态力学性能和物理机械性能。结果显示,采用炭黑增强体系时,与未官能化的溶聚丁苯橡胶相比,改性后溶聚丁苯橡胶拉伸强度的变化不大,硬度增加,物理机械性能变化不大,动态力学性能得到明显提高;采用白炭黑增强体系时,官能化改性后的溶聚丁苯橡胶的物理机械性能得到提高,60 ℃的损耗因子明显降低,滚动阻力得到改善,胶料的交联密度有所提高。     

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

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

Nonreinforcing filler–elastomer systems. II. Silane–treated ammonium perchlorate in polybutadiene

The adhesion between ammonium perchlorate filler and the polybutadiene rubber matrix was investigated. The aggregate composite was modified by surface pretreatment of the filler with various organofunctional silanes. For comparison, the adhesion of glass beads and glass powder, each coated with a fluorocarbon release agent, and carbon black were used as fillers in the cured polybutadiene matrix. Common testing methods used included the determination of Poisson's ratio, photographic analysis, and absorption of water. A new type of stress–strain analysis was introduced. Results closely agreed with established composite theory. The presence of methacryloxy- and amino-functional silanes improved adhesion to the resin system. Epoxy- and vinyl functional silanes proved to be detrimental at the filler–rubber interface. A major function of the coupling agents appears to be to eliminate the weak boundary layer of surface moisture on the filler particles.     

The role of adhesion in the mechanical properties of filled polymer composites

Filled polymer composites have been prepared in which the energetics of the filler surfaces was systematically varied in order to investigate the dependence of the mechanical properties of the composite on the interfacial strength as predicted by the thermodynamic work of adhesion at the filler-matrix interface. A high-purity silica filler was used, treated with three different organofunctional silane coupling agents (two alkylsilanes and an aminosilane) to varying degrees from zero to complete coverage. The surface energetics of the modified fillers was characterized using both inverse gas chromatography (IGC) and dynamic contact angle analysis (DCA). While the surface energy assessments from IGC were higher than those obtained with wetting measurements, as expected, the trends with fractional coverage of silane were the same for each method, and were used to evaluate the thermodynamic work of adhesion. Highly filled polymer composites were prepared by dispersing the variously treated silica fillers into the amorphous thermoplastic matrix polymers: poly(methyl methacrylate) and poly(vinyl butyral). Specimens of the composites were tested mechanically to give the yield stress. The poly(methyl methacrylate) composites all failed cohesively in the matrix, unaffected by any of the filler surface treatments. The poly(vinyl butyral) composites, however, all displayed purely interfacial failure, with the yield stress strongly dependent on the type and extent of the filler surface treatment. While all three silanes were found to decrease the filler surface energy, and consequently the thermodynamic work of adhesion, with higher surface coverage, corresponding decreases in the yield stress were found only for the alkylsilanes. For the aminosilane, the measured yield stress was found to increase with surface coverage and therefore to decrease with the work of adhesion. The difference in behavior between the two types of coupling agent is explained in terms of acid-base effects.     

A molecular explanation for the origin of bound rubber in carbon black filled rubber compounds

Some of the theories that have been developed to explain the origin of bound rubber are critically reviewed and discussed with respect to published data. Theories for carbon black filled compounds and for silica–silicone rubber mixtures are considered; the phenomena involved are likely to be very different, with clear chemical aspects for the latter systems. A common feature emerges, however, from these theories: the area of the polymer–filler interaction site, which is generally considered as a fitting parameter in most approaches. This article concentrates on this aspect and suggests that, with respect to recent findings about the very surface of carbon black particles, an explanation for bound rubber can be offered that considers strong topological constraints exerted by the filler surface on rubber segments. Calculations of interaction site area made with experimental data give values close to a fraction of the half-lateral surface of the structural unit representative of the rubber considered. It follows that the bound rubber variation during storage can now be understood by considering a slow replacement of short rubber chains initially adsorbed on filler particles by larger ones, as demonstrated by calculated data. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2257–2268, 1997     

A Review on Hybrid Fillers in Rubber Composites

This review article is aimed at reporting the recent development of hybrid fillers used in vulcanized rubber. This review will consider the synergistic effect of rubber hybrid composites that consist exclusively of conventional fillers; carbon black and/or silica as the primary filler, which are combined with secondary fillers from various sources. The discussions are mainly focused on the analyses and comparisons of the curing characteristics, morphology, and mechanical properties of the rubber composite-filled hybrid fillers. The compatibility and the existence of synergistic effects between the different types of fillers show the potential for development and application in rubber industries.     

Application of rice husk ash as fillers in the natural rubber industry

Rice husk ash (RHA) obtained from agricultural waste, by using rice husk as a power source, is mainly composed of silica and carbon black. A two‐stage conventional mixing procedure was used to incorporate rice husk ash into natural rubber. For comparison purposes, two commercial reinforcing fillers, silica and carbon black, were also used. The effect of these fillers on cure characteristics and mechanical properties of natural rubber materials at various loadings, ranging from 0 to 40 phr, was investigated. The results indicated that RHA filler resulted in lower Mooney viscosity and shorter cure time of the natural rubber materials. The incorporation of RHA into natural rubber improved hardness but decreased tensile strength and tear strength. Other properties, such as Young's modulus and abrasion loss, show no significant change. However, RHA is characterized by a better resilience property than that of silica and carbon black. Scanning electron micrographs revealed that the dispersion of RHA filler in the rubber matrix is discontinuous, which in turn generates a weak structure compared with that of carbon black and silica. Overall results indicate that RHA can be used as a cheaper filler for natural rubber materials where improved mechanical properties are not critical. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 34–41, 2005     

The effect of fillers on relaxation phenomena of vulcanized styrene–butadiene elastomers

Standard recipe mixtures, based on styrene/butadiene rubber SBR 1500 and oil-extended SBR 1712, with varying amounts of carbon black, silica, or kaoline fillers were prepared and the stress relaxation curves of vulcanized samples were determined. The measurements were restricted to slow relaxation phenomena, observed after 50% initial elongation. Three λ-processes and a fourth ?-process, existing only in filled rubbers, were observed. The relaxation times and activation energies, determined graphically, reflect the amount and activity of the fillers. All relaxation times are lower for filled vulcanizates and decrease with increasing temperature; however, the type of filler does not affect the activation energy. The higher parameters observed for the ?-processes are discussed in terms of filler particle mobilities and rearrangements and of filler/rubber contact layer phenomena. © 1994 John Wiley & Sons, Inc.     

Bound rubber in chlorobutyl compounds: Influence of filler type and storage time

Bound rubber (BdR) is considered as a measure of the filler–polymer interaction in rubber compounds. The variation of the BdR content with storage time was studied in chlorobutyl compounds filled with fillers like carbon black, carbon–silica dual phase filler (CSDPf), silica, and nanoclays. The effect of the addition of a silane coupling agent on the BdR in carbon black and silica filled compounds was also studied. The BdR content increased with storage time in all compounds. The increase in BdR was higher during the initial 15 days of storage. Thereafter there was only a marginal increase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 715–720, 2006     

Large strain and toughness enhancement of poly(dimethyl siloxane) composite films filled with electrospun polyacrylonitrile-graft-poly(dimethyl siloxane) fibres and multi-walled carbon nanotubes

Unfilled cross-linked poly(dimethyl siloxane) (PDMS) is a weak material and is generally filled with high levels of particulate fillers such as silica, calcium carbonate and carbon black to improve its mechanical properties. The use of fibrous fillers such as electrospun nanofibres and multi-walled carbon nanotubes as fillers for PDMS has not been widely studied. In this study anew copolymer, polyacrylonitrile-graft-poly(dimethyl siloxane) (PAN-g-PDMS), is used as fibrous filler for PDMS. The graft copolymer is electrospun to produce the fibre filler material. It is shown how the PDMS content of the graft copolymer provides increased compatibility with silicone matrices and excellent dispersion of the fibre fillers throughout a silicone matrix. It is also shown that it is possible to include multi-walled carbon nanotubes in the electrospun fibres which are subsequently dispersed in the PDMS matrix. Fibre mats were used in the non-woven and the aligned forms. The differently prepared fibre composites have significantly different mechanical properties. Conventional composites using fibrous fillers usually show increased strength and stiffness but usually with a resultant loss of strain. In the case of the composites produced in this study there is a dramatic improvement in the extensibility of the non-woven PAN-g-PDMS fibre mat filled silicone films of up to 470%.     

Nylon 11/silica nanocomposite coatings applied by the HVOF process. I. Microstructure and morphology

Nylon 11 coatings filled with nanosized silica and carbon black have been produced using the high velocity oxy‐fuel (HVOF) combustion spray process. The physical properties and microstructure of coatings produced from nylon 11 powders with starting particle sizes of 30 and 60 μm have been evaluated as a function of the filler content, filler chemistry, and processing conditions. The nominal filler content was varied from 5 to 20 vol %. Co‐milling of the nano‐sized fillers with the polymer powders produced an embedded 4–8 μm thick filler layer on the surfaces of the polymer particles. Optimization of the HVOF processing parameters based on an assessment of the degree of splatting of polymer particles was accomplished by varying the jet temperature (via hydrogen/oxygen ratio). Gas mixtures with low hydrogen contents minimized polymer particle degradation. The filler was found to be agglomerated at the splat boundaries in the final coating microstructures. Aggregates of silanated silica and carbon black were of the order of 50 nm in size, whereas the aggregates of untreated silica and hydrophilic silica were of the order of 100 nm. The morphology of the polymer and the microstructure of the coatings depended on the filler surface chemistry and the volume fraction of the filler, as well as the initial nylon 11 particle size. Although all filled coatings had higher crystallinities than pure nylon 11 coatings, coatings produced from a smaller starting polymer particle size exhibited improved spatial distribution of the silica in the matrix and lower crystallinity. In addition, coatings prepared from smaller polymer particles had a higher density and lower porosity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1684–1699, 2000     

Effects of radiation pretreatments on the rubber adsorption power and reinforcing properties of fillers in rubber compounds

Radiation damage to fillers such as carbon black, graphite and silica induced by high doses of γ‐radiation or neutrons dramatically increases their ability to adsorb rubber irreversibly. In fact, the ‘bound rubber’, ie the amount of non‐extractable rubber which remains irreversibly linked to the filler matrix, increases dramatically in radiation‐treated fillers. The increased adsorption power of radiation‐damaged fillers has been attributed to the formation of a higher concentration of surface defects in the form of trapped free radicals, fullerene‐like structures and other kinds of defects. The mechanical properties of rubber compounds filled with radiation‐treated carbon blacks show a significant increase in their reinforcing effects, in line with the increased ability to form ‘bound rubber’. © 2001 Society of Chemical Industry     

Location of dispersing agent in rubber nanocomposites during mixing process

In the present work, the development of morphology and selective wetting of nanoclay and carbon nanotubes (CNTs) in rubber nanocomposites were characterized qualitatively by means of the optical microscopy, TEM and AFM and quantitatively by means of the wetting concept. Carboxylated hydrogenated nitrile butadiene rubber (XHNBR), ionic liquid and ethanol were used as dispersing agent and they show very good effect on the macro- and microdispersion of nanofillers in different rubbers. It was found that the selective wetting of filler surface by the dispersing agent and rubber matrix is controlled by thermodynamic and kinetic factors. A model basing on surface energy data of polymer components (rubber and dispersing agent) and filler was introduced in order to determine the thermodynamic equilibrium state of filler wetting, which is found to be simultaneously determined by the filler–polymer affinity and the rubber/dispersing agent mass ratio. During the mixing process a replacement process of bound polymer components takes place on the filler surface until the predicted state is reached.     

The effect of carbon black and colloidal silica fillers on interfacial adhesion at polystyrene interfaces

We have shown that the addition of small amounts of carbon black can drastically reduce the interfacial fracture toughness between polymers. This is interpreted as being due to strong interactions between the filler particles and the polymer chains which hinder interfacial adhesion. The effect is less severe when graphitic carbon black particles are used. The fracture toughness was found to increase with time as t ^{1 / 2}, regardless of filler concentration, indicating that interface formation was diffusion limited. A distinct minimum with filler concentration in the fracture toughness of interfaces annealed for times longer than 5 min was found. This feature could be explained as a balance between the increase in modulus and the decrease in polymer chain dynamics as a function of carbon black concentration. The addition of colloidal silica, where the surface interactions are screened, was found to reinforce the interface, as predicted by the Guth–Gold relationship. Mixing small quantities (<2%) of inert fillers with interfacially active ones restored the fracture toughness. This observation has practical importance since one can now obtain optimum adhesion without compromising the mechanical integrity provided by the reactive filler.     

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

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

UV-Ozone Surface Treatment of SBS Rubbers Containing Fillers: Influence of the Filler Nature on the Extent of Surface Modification and Adhesion

SBS rubbers containing different loadings of calcium carbonate and/or silica fillers were surface treated with UV-ozone to improve their adhesion to polyurethane adhesive. The surface modifications produced on the treated filled SBS rubbers have been analyzed by contact angle measurements, ATR-IR spectroscopy, XPS and SEM. The adhesion properties have been evaluated by T-peel strength tests on treated filled SBS rubber/polyurethane adhesive/leather joints. The UV-ozone treatment improved the wettability of all rubber surfaces, and chemical (oxidation) and morphological modifications (roughness, ablation, surface melting) were produced. The increase in the time of UV-ozone treatment to 30 min led to surface cleaning (removal of silicon-based moieties) due to ablation and/or melting of rubber layers and also incorporation of more oxidized moieties was produced. Although chemical modifications were produced earlier in an unfilled rubber for short time of treatment with UV-ozone, they were more noticeable in filled rubbers for extended length of treatment, mainly for S6S and S6T rubbers containing silica filler. The oxidation process seemed to be inhibited for S6C and S6T rubbers (containing calcium carbonate filler). On the other hand, the S6S rubber containing silica filler and the lowest filler loading showed the higher extent of modification as a consequence of the UV-ozone treatment. The UV-ozone increased the joint strength in all joints, more noticeably in the rubbers containing silica filler, in agreement with the greater extents of chemical and morphological modifications produced by the treatment in these rubbers. Finally, the nature and content of fillers determined the extent of surface modification and adhesion of SBS rubber treated with UV-ozone.     

Biopolymers as effective fillers in natural rubber: Composites versus biocomposites

Biocomposites of natural rubber (NR) blends were prepared with a variety of fillers obtained from renewable resources by a mastication technique. They were characterized for their mechanical properties and morphologies and compared with composites of the conventional filler carbon black (c‐black). The biopolymers exhibited an interesting trend and imparted strength to NR that was quite comparable to c‐black. Up to 30 phr of the fillers could be successfully incorporated; this led to enhancements in the mechanical strength. The properties were found to vary with the type and ratio of filler, namely, starch, cellulose, and chitin. The optimum mechanical strength of the biocomposites was observed at 10 phr. The results were interpreted on the basis of the morphology by scanning electron microscopy, which revealed strong filler–polymer interactions. The moisture‐uptake characteristics of the composites were studied. It was found that addition of biofillers did not lead to a significant increase in the moisture absorption. Furthermore, as the adhesion between the polymer matrix and fillers increased, the water uptake decreased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012