Plasma polymerization of acetylene onto silica: an approach to control the distribution of silica in single elastomers and immiscible blends

Surface modification of silica by acetylene plasma polymerization is applied in order to improve the dispersion in and compatibility with single rubbers and their blends. Silica, used as a reinforcing filler for elastomers, is coated with a polyacetylene (PA) film under vacuum conditions. Water penetration measurements show a change in surface energy due to the PA‐film deposition. The weight loss measured by thermo‐gravimetric analysis (TGA) is higher for the PA‐coated silica compared to the untreated filler, confirming the deposition of the PA film on the silica surface. Time of flight‐secondary ion mass spectrometry (ToF‐SIMS) shows the well‐defined PA cluster peaks in the high mass region. Scanning electron microscopy (SEM) measurements show silica aggregates, coalesced by the coating with smooth and uniform surfaces, but without significant change in specific surface area. Elemental analysis by energy dispersive X‐ray spectroscopy (EDX) measurements also confirms the deposition of the polymeric film on the silica surface, as the carbon content is increased. The performance of single polymers and their incompatible blends based on S‐SBR and EPDM, filled with untreated, PA‐ and silane‐treated silica, is investigated by measurements of the bound rubber content, weight loss related to bound rubber, cure kinetics, reinforcement parameter, Payne effect, and mechanical properties. The PA‐ and silane‐modified silica‐filled pure S‐SBR and EPDM samples show a lower filler–filler networking compared to the unmodified silica‐filled elastomers. Decrease in the reinforcement parameter (α_F) for the plasma‐polymerized silica‐filled samples also proves a better dispersion compared to silane‐modified and untreated silica‐filled samples. On the other hand, the PA‐silica‐filled samples show a higher bound rubber content due to stronger filler–polymer interactions. Finally, the PA‐silica‐filled pure EPDM and S‐SBR/EPDM blends show high tensile strength and elongation at break values, considered to be the result of best dispersion and compatibilization with EPDM. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of silane coupling agent on the polymer‐filler interaction and mechanical properties of silica‐filled NR

The effects of filler loading and a new silane coupling agent 3‐octanoylthio‐1‐ propyltriethoxysilane (NXT silane) on the polymer‐filler interaction and mechanical properties of silica‐filled and carbon black‐filled natural rubber (NR) compounds were studied. Silica (high dispersion silica7000GR, VN2, and VN3) and carbon black (N330) were used as the fillers, and the loading range was from 0 to 50 phr. The loading of NXT silane was from 0 to 6 phr. Experimental results show that the maximum and minimum torques of silica and carbon black‐filled NR increase with increasing filler loading. With increasing filler loading, the scorch time and optimum cure time decrease for carbon black‐filled NR, but increase for silica‐filled NR. The minimum torque, scorch time, and optimum cure time decrease because of the presence of NXT silane. For the carbon black and silica‐filled NR, the tensile strength and elongation at break have maximum values, but the hardness, M300, M100, and tear strength keep increasing with filler loading. The mechanical properties of silica‐filled NR were improved in the presence of NXT silane. With increasing filler loading, the storage modulus of filled NR increases, but the loss factor decreases. Carbon black shows the strongest polymer‐filler interaction, followed by VN3, 7000GR, and VN2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 573–584, 2005     

The influence of non-rubber constituents on performance of silica reinforced natural rubber compounds

An in-rubber study of the interaction of silica with proteins present in natural rubber show that the latter compete with the silane coupling agent during the silanisation reaction; the presence of proteins makes the silane less efficient for improving dispersion and filler–polymer coupling, and thus influences the final properties of the rubber negatively. Furthermore, the protein content influences the rheological properties as well as filler–filler and filler–polymer interactions. Stress strain properties also vary with protein content, as do dynamic properties. With high amounts of proteins present in natural rubber, the interactions between proteins and silica are able to disrupt the silica–silica network and improve silica dispersion. High amounts of proteins reduce the thermal sensitivity of the filler–polymer network formation. The effect of proteins is most pronounced when no silane is used, but they are not able to replace a coupling agent.     

Filler‐polymer interactions of styrene and butadiene units in silica‐filled styrene–butadiene rubber compounds

Styrene–butadiene rubber (SBR) is a copolymer of styrene and butadiene, and the butadiene unit is composed of cis‐1,4‐, trans‐1,4‐, and 1,2‐components. Filler‐polymer interactions of each component of SBR in silica‐filled SBR compounds were examined by microstructure analysis of the bound and unbound rubbers. The composition ratio of butadiene and styrene units (butadiene/styrene) of the bound rubber was higher than that of the compounded rubber. Of the butadiene units, the 1,2‐component of the bound rubber was more abundant than the cis‐1,4‐ and trans‐1,4‐components. The filler‐polymer interaction of the butadiene unit with silica was stronger than that of the styrene unit, and the interaction of the 1,2‐component was stronger as compared with the others. The butadiene–styrene ratio of the bound rubber of the compounds containing the silane coupling agent was lower than for the compounds without the silane. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 577–584, 2004     

Preparation and Application of Chemically Bonded Silica Supported Calix[4]arene as Reinforced Filler in NR/BR Blend Based Rubber Compounds

In this study, we tried to reduce polarization of silica surface by chemically bonding cholorosulfonyl calix[4]arene (CSC[4]A) and silica (Si–O–Cl) to improve dispersion between filler and elastomer. To confirm synthesis of CSC[4]A, ¹H NMR, ¹³C NMR, and IR spectrophotometry were used. Obtained composite of chemically bonded silica and CSC[4]A was characterized by TGA. Compounds (contained silica, silica and silane, silica-calix system) were prepared to investigate the effect of silica-calix system (CSC[4]A-SiO₂) on the rheological and mechanical properties of rubber compounds based on natural rubber/cis-butadiene rubber (NR/BR) blend in tire tread formulation. The rheological and mechanical properties of three samples were investigated by different devices and a surface morphology was evaluated by FESEM technique. The results revealed that the curing behavior of the compound with CSC[4]A-SiO₂ did not significantly differ from other compounds, while reversion was considerably reduced compared with that to other compounds. Also, the mechanical properties of compound with CSC[4]A-SiO₂ were improved dramatically especially in fatigue resistance.

     

Thermal stability of CR/CSM rubber blends filled with nano- and micro-silica particles

The properties of filled polymers depend on the properties of the matrix and the filler, the concentration of the components and their interactions. In this research we investigated the rheological and mechanical properties and thermal stability of polychloroprene/chlorosulfonated polyethylene (CR/CSM) rubber blends filled with nano- and micro-silica particles. The density of the nano-silica filled CR/CSM rubber blends was lower than that of the micro-silica filled samples but the tensile strength and elongation at break were much higher. The nano-silica filled CR/CSM rubber blend has higher V _r0/V _rf values than micro-silica composites and show better polymer–filler interaction according to Kraus equation. The nano-silica filled CR/CSM rubber blends were transparent at all filler concentration, and have higher glass transition values than micro-silica filled compounds. The higher values of the glass transition temperatures for the nano- than the micro-filled cross-linked systems are indicated by DMA analysis. The nano-filled cross-linked systems have a larger number of SiO–C links than micro-filled cross-linked systems and hence increased stability.     

Filler–polymer interactions in both silica and carbon black‐filled styrene–butadiene rubber compounds

Bound rubber in a filled rubber compound is formed by physical adsorption and chemisorption between the rubber and the filler. Styrene–butadiene rubber (SBR) is composed of four components of styrene, cis‐1,4‐, trans‐1,4‐, and 1,2‐units. Filler–polymer interactions in both silica and carbon black‐filled SBR compounds were studied by analyzing microstructures of the bound rubbers with pyrolysis‐gas chromatography. Differences in the filler–polymer interactions of the styrene, cis‐1,4‐, trans‐1,4‐, and 1,2‐units were investigated. The filler–polymer interactions of the butadiene units were found to be stronger than that of the styrene unit. The interactions of the cis‐1,4‐ and trans‐1,4‐units were stronger with carbon black than with silica, whereas the 1,2‐unit interacted more strongly with silica than with carbon black. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 439–445, 2001     

Nonlinear rheological behavior of silica filled solution‐polymerized styrene butadiene rubber

The reinforcement and nonlinear viscoelastic behavior have been investigated for silica (SiO₂) filled solution‐polymerized styrene butadiene rubber (SSBR). Experimental results reveal that the nonlinear viscoelastic behavior of the filled rubber is similar to that of unfilled SSBR, which is inconsistent with the general concept that this characteristic comes from the breakdown and reformation of the filler network. It is interesting that the curves of either dynamic storage modulus (G′) or loss tangent (tan δ) versus strain amplitude (γ) for the filled rubber can be superposed, respectively, on those for the unfilled one, suggesting that the primary mechanism for the Payne effect is mainly involved in the nature of the entanglement network in rubbery matrix. It is believed there exists a cooperation between the breakdown and reformation of the filler network and the molecular disentanglement, resulting in enhancing the Payne effect and improving the mechanical hysteresis at high strain amplitudes. Moreover, the vertical and the horizontal shift factors for constructing the master curves could be well understood on the basis of the reinforcement factor f(φ) and the strain amplification factor A(φ), respectively. The surface modification of SiO₂ causes a decrease in f(φ), which is ascribed to weakeness of the filler–filler interaction and improvement of the filler dispersion. However, the surface nature of SiO₂ hardly affects A(φ). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2594‐2602, 2007     

Filler-filler interaction and filler-polymer interaction in carbon black and silica filled ExxproTM polymer

Due to the presence of reactive benzylic bromide, Exxpro has much better interaction with silica in comparison with polybutadiene as demonstrated by the high bound rubber level. The better silica/Exxpro interaction is further substantiated by the low degree of filler network formation in comparison to that observed for silica filled polybutadiene as demonstrated by the much smaller deviation of low strain shear modulus from the Guth-Gold relationship for the silica filled Exxpro. Silane treatement of silica reduces filler network formation in polybutadiene but has only slight effect on silica filled Exxpro indicating that even without silane treatment silica already disperse well in Exxpro due to high degree of filler/polymer interaction. This result in silica filled Exxpro compound exhibiting better processability (lower shear viscosity) as well as dynamic performances for tire applications (higher tan δ at −20 and 0°C, lower tan δ at 60°C). We speculate that nucleophilic substitution reaction takes place between benzylic bromide and surface hydroxide group of silica.     

Multiaxial deformations of end‐linked poly(dimethylsiloxane) networks. III. Effect of entanglement density on strain‐energy density function

Strain‐energy density functions (W) of end‐linked polydimethylsiloxane (PDMS) networks with different entanglement densities were estimated as a function of the first and second invariants I₁ and I₂ of Green's deformation tensor on the basis of the quasi‐equilibrium biaxial stress‐strain data. Entanglement densities in the PDMS networks were controlled by varying the precursor PDMS concentration (?₀) in end‐linking. The deduced functional form of W [W = C₁₀(I₁ ? 3) + C₀₁(I₂ ? 3) + C₁₁(I₁ ? 3)(I₂ ? 3) + C₂₀(I₁ ? 3)² + C₀₂(I₂ ? 3)²] is independent of the degree of dilution at network preparation. The contribution of each term in I₁ and I₂ to total energy depends on whether the precursor PDMS solution before end‐linking belongs to the concentrated regime ?₀ > ?_c where many entanglement couplings of precursor chains exist or the moderately concentrated regime ?₀ < ?_c where pronounced entanglement couplings of precursor chains are absent. These results suggest that the rubber elasticity of the end‐linked networks is significantly influenced by the entangled state of precursor chains before end‐linking, and the extra terms in the estimated W that are absent in the prediction of the classical rubber elasticity theories [W = C (I₁ ? 3)] mainly originate from the effect of trapped entanglements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2780–2790, 2002     

Effects of carbon filler on sorption and diffusion of gases through rubbery materials

Effects of carbon filler on the sorption and diffusion of carbon dioxide in natural rubber and in styrene-butadiene rubber have been studied. Sorption isotherms conform to Henry's law in unfilled rubber and to Langmuir's law in carbon black. The isotherms in filled rubber exhibit a combination of the two sorption modes. The Henry's law solubility parameter k_D increases with carbon filler content; the Langmuir saturation constant C′_A initially is constant with filler level, but then decreases abruptly when carbon particles begin to aggregate. The diffusion coefficient decreases with increasing filler content, presumably owing to geometric effects and to polymer chain immobilization in the interfacial regions.     

Six cation-templated halometal complexes and C–H activation of alkylene-bridged azoles

Six dication-templated complexes were discovered in efforts to investigate the effect of linear imidazolium-based template, 1,ω-bis(3,3′-methylimidazolium)alkyl dibromide, on pure inorganic halometal clusters. Complexes {[C₄(Mim)₂](Pb₂I₆)}_n (1) (ω?=?4), {[C₁(Mim)₂] (Ag₂I₄)}_n (2) (ω?=?1), {[C₃(Mim)₂](Ag₂I₄)}_n (3) (ω?=?3), and {[C₄(Mim)₂](Ag₂I₄)}_n (4) (ω?=?4) possess 1-D chain architecture with different organic cations trapped in it. Compound {[C₃′(Mim)₂](CuBr₃)} (5) (ω?=?3) contains the mononuclear anion (CuBr₃)^2? and intra-molecular coupled organic cation with the formed seven-membered ring. {[C₂(Mim)₂S₂]₂(Cu₂I₂)}_n (6) (ω?=?2) presents an infinite 2-D coordination polymer as the first representative polyrotaxane example featuring the biimidazolium thiolate cation ligand. All compounds were further characterized with IR spectra and thermal analysis properties.     

Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds shows smooth rheological behavior and mechanical properties. Variation in rheological behavior and mechanical properties was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica CB/Si = 0/60, 20/40, 30/30, 40/20 and 60/0 phr (parts per hundred rubber is parts of any non-rubbery material per hundred parts of raw gum elastomer (rubbery material)). The rheological behaviour can be showed in measurement of Mooney viscosity and cure time. The Mooney viscosity of rubber compounds increase with the increasing the carbon black in the compounds. The compound filled with CB/Si of 30/30 and 60/0 showed abnormal rheological behaviour in which the cure time decreased suddenly and the increased at certain ratio during the measurement. The mechanical properties such as hardness, abrasion resistance and tensile stress at 300% elongation were studied. In the hardness and abrasion resistance measurement, the higher ratio CB/Si decrease contribution of silica, which resulting smaller of hardness value. Ratio CB/Si 40/20 gives an optimum filler blended. It is also clearly understood that higher abrasion resistance mainly due to the lower hardness value under the same condition. The tensile stress at 300% elongation of rubber compound increased with the increasing carbon black filler.     

Polymer–filler interactions in sol–gel derived polymer/silica hybrid nanocomposites

The effect of polymer–filler interaction on solvent swelling and dynamic mechanical properties of the sol–gel derived acrylic rubber (ACM)/silica, epoxidized natural rubber (ENR)/silica, and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites has been described for the first time. Tetraethoxysilane (TEOS) at three different concentrations (10, 30, and 50 wt %) was used as the precursor for in situ silica generation. Equilibrium swelling of the hybrid nanocomposites in respective solvents at ambient condition showed highest volume fraction of the polymer in the swollen gel in PVA/silica system and least in ACM/silica, with ENR/silica recording an intermediate value. The Kraus constant (C) also followed a similar trend. In dynamic mechanical analysis, the storage modulus dropped at higher strain (>1%), which indicated disengagement of polymer segments from the filler surfaces. This drop was maximum in ACM/silica, intermediate in ENR/silica, and minimum in PVA/silica, both at 50 and 70 °C. The drop in modulus with theoretical volume fraction of silica (ϕ) was interpreted with the help of a Power law model ΔE′ = a₁ϕ, where a₁ was a constant and b₁ was primarily a filler attachment parameter. Strain dependence of loss modulus was observed in ACM/silica hybrid nanocomposites, while ENR/silica and PVA/silica nanocomposites showed almost strain‐independent behavior. The storage modulus showed sharp increase with increasing frequency in ACM/silica system, while that was lower in both ENR/silica (at higher frequency) and PVA/silica systems (in the entire frequency spectrum). The increase in modulus with ϕ also followed similar model ΔE′ = a₂ϕ proposed in the strain sweep mode. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2399–2412, 2005     

Structure and properties of star‐shaped solution‐polymerized styrene‐butadiene rubber and its co‐coagulated rubber filled with silica/carbon black‐I: morphological structure and mechanical properties

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.     

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites were studied. Scorch time, t₂ and cure time, t₉₀ of the composites decrease with increasing filler loading and with the presence of a silane coupling agent, Si69. Mooney viscosity also increases with increasing filler loading but at a similar filler loading shows lower value with the presence of Si69. The mechanical properties of composites viz tensile strength, tear strength, hardness and tensile modulus were also improved with the addition of Si69.     

Polymer blends filled with carbon black: structure and electrical properties

Morphology and electrical conductivity of polymer blends based on polypropylene, polyethylene, polyoxymethylene, polyamide 12, co‐polymer ABS filled with carbon black (CB) were studied. When filler is introduced in polymer blend, three cases of filler spatial distribution can be obtained. CB can be distributed randomly within polymer matrix, can be situated in one of the polymer components or can be localized on the boundary of the polymer components. The existence of different cases of filled blends structure is defined by following reasons: thermodynamic factors (relationship between interface surface tensions of polymer‐filler γ_pf and polymer‐polymer surface tension γ_pp); kinetic factors (relationship between viscosities of polymer components); processing factors (methods of the filler introduction in the complex polymer matrix, which can enhance or depress the influence of thermodynamic and kinetic factors).