Vulcanization kinetics of nano-silica filled styrene butadiene rubber

Effects of the surface chemical groups of cellulose nanocrystals on the vulcanization and mechanical properties of natural rubber/cellulose nanocrystals nanocomposites

Cellulose nanocrystals (CNCs), as the promising reinforcing fillers in the rubber industry, their surface chemical groups have vital effects on the vulcanization kinetics, cross-linking densities, and mechanical properties of rubber composites. Herein, CNCs with acidic carboxyl (CCA) and alkaline amino groups (CCP) were produced by modifying the sulfonic CNCs (CCS) in environment-friendly ways. Studies found the CCS and CCA with acid groups have obvious inhibiting effects on the vulcanization of natural rubber (NR), while CCP with alkaline amino groups accelerates the vulcanization of NR. Differential scanning calorimeter, Fourier transform infrared spectroscopy, and Electron paramagnetic resonance, etc. were performed to clarify the effecting mechanisms of CNCs surface groups on NR vulcanization. It was found that NR/CCS and NR/CCA nanocomposites vulcanize through radical reactions, and the surface acidic groups of CCS and CCA, i.e., hydroxyl, sulfonate, and carboxyl groups inactivate the sulfur radicals generated during vulcanization and depress the vulcanization activity. The amino groups of the polyethyleneimine of CCP promote the ring opening of sulfur (S₈) or the breaking of polysulfide bonds connected to NR molecular chains to form sulfur anion with a strong nucleophilic ability, which leads to the cross-linking of NR/CCP reacts via ionic reaction mainly. The vulcanization rate and cross-linking density of NR/CCP are improved by the ionic reaction. And benefiting from the higher cross-linking density and the reinforcement of CCP, NR/CCP had the best physical and mechanical properties. Our work elucidates the mechanism of the surface chemical groups of CNCs affecting NR vulcanization and may provide ideas for the preparation of high-performance rubber composites reinforced by CNCs.

Effect of Modified Silica Fume Using MPTMS for the Enhanced EPDM Foam Insulation

Silica fume (SF) is a by-product from the production of silicon metal, which has a relatively high silica concentration. The surface modified silica fume (mSF) is treated with (3-mercaptopropyl) trimethoxysilane (MPTMS) as filler in ethylene propylene diene monomer (EPDM) foam. The FTIR spectra of mSF clearly indicated that MPTMS can be successfully bonded to the SF surface. The reinforcing efficiency of mSF-filled EPDM foam insulation indicated that the mechanical properties such as hardness, tensile strength, modulus, and compression set enhanced higher than in case of SF and calcium carbonate. While the cure characteristics such as the maximum torque (M_H), the minimum torque (M_L) and the differential torque (M_H-M_L) are increasing in proportion to increasing filler contents, mainly with mSF. For the cure behavior, the mSF-filled EPDM foam insulation showed the fastest cure time (t_c90) and scorch time (t_s2) due to reduced accelerator adsorption. Whereas, the calcium carbonate-filled EPDM foam insulation increased the cure time (t_c90) and scorch time (t_s2), therefore, it also prevents compound scorching. The results indicated that the mSF with MPTMS can be used as an alternative filler for EPDM foam insulation.

Film and latex forms of silica-reinforced natural rubber composite vulcanized using electron beam irradiation

A thorough study was undertaken of the synthesis of natural rubber-silica treated with bis-(3-triethoxysilylpropyl) tetrasulfane (NR/TSi) vulcanized using electron beam irradiation (EB) and sulfur by varying the EB dose. The surface treatment of silica was confirmed using Fourier-transform infrared spectroscopy and scanning electron microscopy images. Composites were cast and vulcanized in film and latex forms compared with sulfur vulcanization. Investigation covered the mechanical properties, thermal stability, swelling resistance, and degradation under heat and humidity testing of the NR/TSi composites. It was found that the TSi had great dispersal in the NR matrix. TSi in NR matrix had a positive effect on mechanical properties, swelling in water and toluene, and thermal stability. Increasing the radiation intensity up to 250 kGy led to superior mechanical properties but for further increase in the radiation intensity, the tensile strength dropped. Degradation under thermal and humidity testing showed that the un-vulcanized composite had higher physical degradation than the vulcanized samples. Therefore, NR/TSi vulcanized using 200 kGy EB vulcanized in latex form had the greatest mechanical properties for various applications without producing any residual vulcanizing agent.

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Silane-69 treated silica/natural rubber composite was irradiated by electron beam.

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SEM images indicated good dispersion of treated silica in the NR matrix.

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10 phr NR/TSi at 200 kGy in latex form had the best mechanical properties.

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EB vulcanized NR/TSi composites had less chemical residue than those by sulfur.

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Degradation under thermal and humidity was performed and compared with TGA.

Comparison between SBR Compounds Filled with In-Situ and Ex-Situ Silanized Silica

The main advantages of the use of silica instead of carbon black in rubber compounds are based on the use of a silane coupling agent. The use of a coupling agent to modify the silica surface improves the compatibility between the silica and the rubber. There are two different possibilities of modifying the silica surface by silane: ex-situ and in-situ. The present work studies the differences between these processes and how they affect the in-rubber properties of silica filled SBR compounds.

Poly(acrylonitrile-co-butadiene) as polymeric crosslinking accelerator for sulphur network formation

The major controlling factors that determine the various mechanical properties of an elastomer system are type of chemical crosslinking and crosslink density of the polymer network. In this study, a catalytic amount of acrylonitrile butadiene copolymer (NBR) was used as a co-accelerator for the curing of polybutadiene (BR) elastomer. After the addition of this copolymer along with other conventional sulphur ingredients in polybutadiene compounds, a clear and distinct effect on the curing and other physical characteristics was noticed. The crosslinking density of BR was increased, as evidenced by rheometric properties, solid-state NMR and swelling studies. The vulcanization kinetics study revealed a substantial lowering of the activation energy of the sulphur crosslinking process when acrylonitrile butadiene copolymer was used in the formulation. The compounds were also prepared in the presence of carbon black and silica, and it was found that in the carbon black filled system the catalytic effect of the NBR was eminent. The effect was not only reflected in the mechanical performance but also the low-temperature crystallization behavior of BR systems was altered.

Isostructural softening of vulcanized nanocomposites

Following previous work evidencing that short poly-propylene glycol (PPG) chains incorporated into crude SBR/silica nanocomposites act as filler-network softeners without changing their structure, we propose in the present report to examine more operative cross-linked materials. We first evidence that the adsorption of PPG onto silica deactivates progressively the particle's catalytic effect on vulcanization, without perturbing however the cross-link density distribution that we investigate through multiple-quantum NMR. In addition, electron microscopy confirms that the silica structure is conserved after vulcanization and that it does not depend on the PPG content either. Composites containing various amounts of PPG can thus be seen as structurally identical, both from a matrix and filler point of view - which is confirmed by small and medium amplitude oscillation shear rheology showing strikingly identical viscoelastic properties. The PPG signature only appears above 100% in tensile deformation where it is observed to soften dramatically the filler network. Our discovery makes it consequently possible to decorrelate the mechanical behavior of reinforced rubbers under normal conditions of use and urgent needs of energy dissipation.

Functionalized Halloysite Nanotubes⁻Silica Hybrid for Enhanced Curing and Mechanical Properties of Elastomers

Vulcanization and reinforcement are critical factors in governing the ultimate practical applications of elastomer composites. Here we achieved a simultaneous improvement of curing and mechanical properties of elastomer composites by the incorporation of a functionalized halloysite nanotubes–silica hybrid (HS-s-M). Typically, HS-s-M was synthesized by 2-mercapto benzothiazole (M) immobilized on the surface of halloysite nanotubes–silica hybrid (HS). It was found that the HS-s-M uniformly dispersed in the styrene-butadiene rubber (SBR) matrix, offering more opportunity for M molecules to communicate with rubber. In addition, the physical loss of accelerator M from migration and volatilization was efficiently suspended. Therefore, SBR/HS-s-M composites showed a lower curing activation energy and a higher crosslinking density than SBR/HS composites. Moreover, a stronger interfacial interaction between HS-s-M and SBR was formed by the cross-linking reaction, giving a positive contribution to the eventual mechanical properties. The possible vulcanization and reinforcement mechanisms of SBR/HS-s-M composites were also analyzed in detail.

ENHANCING THE REVERSION RESISTANCE, CROSSLINKING DENSITY AND THERMO-MECHANICAL PROPERTIES OF ACCELERATED SULFUR CURED CHLOROBUTYL RUBBER USING 4,4′-BIS (MALEIMIDO) DIPHENYL METHANE

Vulcanizates of chlorobutyl rubber (CIIR) with the accelerated sulfur generally exhibit poor crosslinking density owing to the low level of unsaturation in the backbone of CIIR. Therefore, the sulfur cured CIIR shows inferior thermo-mechanical properties at elevated temperature. In addition to this, the vulcanization of CIIR with accelerated sulfur is limited at higher temperature due to reversion. To solve these problems, 4,4′-bis (maleimido) diphenyl methane (BMDM) was applied as a crosslinking additive along with the accelerated sulfur. The detailed curing studies have proved that the presence of BMDM greatly enhanced the rheometric torque and the reversion resistance while curing CIIR with accelerated sulfur even at higher vulcanization temperature. Moreover, the crosslinking densities of the sulfur cured CIIR have increased by 109% with the use of 1 phr BMDM and further rose to 380% with 5 phr BMDM. The improved crosslink density could enable reduction of the compression set of the sulfur cured CIIR to around 40% at 100 °C when it was vulcanized in the presence of 5 phr BMDM. The kinetic studies revealed that incorporation of this additive does not adversely affect the original vulcanization behavior of CIIR with accelerated sulfur, instead it marginally improved the speed of the vulcanization.

Catalytic and networking effects of carbon black on the kinetics and conversion of sulfur vulcanization in styrene butadiene rubber

The present work discusses the effects of carbon-black (CB) on the kinetics and conversion of sulfur vulcanization in styrene butadiene rubber (SBR) compounds. Kinetic studies revealed that the onset of the vulcanization reaction shortens monotonically by incorporation of CB, but the rate of vulcanization goes through a maximum at a critical loading of CB. It was demonstrated that CB has two roles in the kinetics of vulcanization: a catalytic effect on accelerating the initial reactions among vulcanization agents and a networking effect on retarding the crosslinking of macro-radicals. It was shown that the latter effect dominates the former one at high concentrations of CB where the rubber-mediated network of CB is formed and a large portion of rubber is immobilized as bound rubber. By using two types of CBs with very different specific surface areas, it was discussed that the critical loading at which the retarding effect begins coincides with the rheological percolation threshold of CBs. Moreover, conversion of vulcanization under isothermal conditions was continuously reduced as the concentration of CBs increased. This was correlated to the magnitude of the physical restrictions exerted by CBs, depending on the specific surface area of each CB. However, it was also shown that this restriction could be alleviated at higher temperatures during non-isothermal vulcanization, which enhances the degree of conversion in crosslinking.

NONLINEAR VISCOELASTIC DISSIPATION IN VULCANIZATES CONTAINING CARBON BLACK AND SILANIZED SILICA HYBRID FILLERS

Different mechanisms of large-strain viscoelastic dissipation in vulcanizates containing carbon black or silanized silica and their synergistic effects in hybrid filler tread vulcanizates were investigated. In addition, the pure effects of fillers were examined while the degree of chemical cross-linking in the rubber matrix was similar in the vulcanizates. The results revealed that nonlinear viscoelastic loss modulus under strain-controlled dynamic tests, as a measure of dissipation mechanism, is high in both carbon black and silanized silica tread vulcanizates. However, a synergistic effect in reducing loss modulus was observed in the hybrid filler vulcanizates. Conversely, storage modulus in the vulcanizates containing more silanized silica is distinguishably higher and results in a lower loss factor representing load-controlled cyclic deformation of vulcanizates, such as in the heat buildup test. Both loss factor and heat build-up reduced nonlinearly as the amount of silanized silica increased in the vulcanizates, verifying the synergistic effect of hybrid carbon black–silanized silica filler in reducing dissipative mechanisms in large-strain dynamic loadings. This feature is highly favorable for the tire industry, where the lowering of viscoelastic dissipation in tread vulcanizates is of great importance.

Fabrication of EPYR/GNP/MWCNT carbon-based composite materials for promoted epoxy coating performance

The present study is aimed to fabricate composite materials containing epoxy resin (EPYR) reinforced by mixed carbon-based nano-fillers in the form of graphene nano-platelet (GNP) and multi-walled carbon nanotube (MWCNT) using the dissolution casting technique with the help of ultrasonic assistance. The pure epoxy resin was reinforced by variable loading of mixed GNP/MWCNT in situ, and the epoxy resin is denoted as EPYR/GNP/MWCNT_2–30. The numbers 2–30 corresponded to the final mass ratio of the nano-fillers. The designed products were reinforced by variable percentages of GNP/MWCNTs. XRD, FT-IR, thermal analyses, FE-SEM, TEM and electrical conductivity were utilized as identification techniques to confirm the structures of these composite materials. An excellent evidence for the composite formation was given by XRD diffraction patterns and FT-IR spectroscopy. The introduced amounts of mixed nano-fillers showed significant effects on the thermal, conducting and coating behaviors of pure EPYR. Pure EPYR and EPYR/GNP/MWCNT_20,30 showed higher thermal stabilities than other materials in the range of 400–410 °C. EPYR/GNP/MWCNT₂₀ also showed remarkable increase in the thermal stability compared to other materials. T₁₀ represents the temperatures at which 10% weight losses are examined. Pure EPYR and its related EPYR/GNP/MWCNT_2–30 displayed similar thermal stabilities at T₁₀ temperature (330 ± 4 °C). The morphological features were examined by SEM and TEM; these features showed that the nanocomposite components were extremely compatible. The in situ electrical conductivity values showed noticeable enhancement for the formulations of EPYR/GNP/MWCNT_2–10. Moreover, the coating performance of EPYR was tested by water uptake experiments and electrochemical impedance; both tests proved that the mixed GNP/MWCNT nano-fillers remarkably improved the pure EPYR coating due to the ionic charge transfer resistance and elevated barrier behaviour. The coating resistance variations values (CRv) of EPYR/GNP/MWCNT₁₀ were the highest among the measured composition values, closely followed by those of EPYR/GNP/MWCNT₂₀ and EPYR/GNP/MWCNT₃₀.

Composite materials containing epoxy resin and reinforced by mixed carbon-based nano-fillers (GNP/MWCNT) have been fabricated using the dissolution casting technique with the help of ultrasonic assistance for promoted epoxy coating performance.

Graphene oxide as a compatibilizer for polyvinyl chloride/rice straw composites

In this study, polyvinyl chloride (PVC)/rice straw (RS)/graphene oxide (GO) sustainable nanocomposite was prepared using the direct compounding method. Structural, morphological and mechanical properties of fabricated sustainable nanocomposites were compared with unfilled and RS-filled PVC compounds. Mechanical characteristics of PVC decreased with loading RS fibers. The main reason for the mechanical failure of PVC/RS composite is the incompatibility between PVC and RS fibers. GO nanosheets are used here to improve the compatibility between RS fibers and PVC macromolecules. Compared to the neat PVC, maximum strength of the RS/GO-loaded PVC composite increased up to 31%, with incorporating only 1 wt% of GO nanosheets. This enhancement in the mechanical characteristics of PVC/RS/GO nanocomposite can only be due to the role of GO nanosheets as a compatibilizer, as 1 wt% GO loading can only increase the mechanical strength of PVC compounds up to 9%. Fourier transform infrared spectroscopy results are used here to study the nature of these behaviors. It is suggested that the non-covalent and physical interactions between cellulose/hemicellulose portions of RS fibers and GO functional groups result in the enhancement of mechanical characteristics. Consequently, GO can be considered as a new compatibilizer for fabricating high performance PVC-based sustainable nanocomposites.

Effect of multifunctional samarium lysine dithiocarbamate on curing properties, static and dynamic mechanical properties of SBR/silica composites

In this work, a novel multifunctional rubber agent named as samarium lysine dithiocarbamate (Sm-LDC) was synthesized by a nucleophilic addition reaction and coordination reaction.

The effect of bound rubber on vulcanization kinetics in silica filled silicone rubber

Different filler networks mediated by bound rubber show obviously different effects on vulcanization kinetics.

CORRELATION OF FILLER NETWORKING WITH REINFORCEMENT AND DYNAMIC PROPERTIES OF SSBR/CARBON BLACK/SILICA COMPOSITES

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 df, 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.

Influences of sodium dodecyl sulfate on vulcanization kinetics and mechanical performance of EPDM/graphene oxide nanocomposites

In this work, influence of SDS presence on the physical interactions between EPDM macromolecules and graphene oxide functional groups are investigated.