Filled Rubber Composites Research Articles

Characterization and transport properties of ceramic filler incorporated natural rubber composites

AbstractCrystalline glass–ceramic fillers were prepared from calcium carbonate, silica, alumina, and calcium fluoride by heating and subsequent quenching in cold water. The fillers were incorporated into natural rubber (1,4‐cis‐polyisoprene) and the filled rubber composites were crosslinked with sulfur in the presence of different rubber additives. The unfilled and filled rubber composites were characterized. The transport properties of benzene, toluene, and p‐xylene (BTX) through the rubber composites were studied in terms of sorption, diffusion, permeation, and mass transfer coefficients. The effect of the ceramic fillers on the mechanical, thermal and transport properties were studied. The sorption data at different temperatures were used for calculating activation energy of diffusion, permeation, free energy, and enthalpy of sorption. The BTX remained in the liquid state within the composite matrix as evident from negative ΔS. The diffusion coefficient (D) and mass transfer coefficient (kmtc) of BTX decreased with the increase in filler loading. Accordingly, for the transport of BTX the unfilled rubber showed a D (D × 107 cm2/s) and mass transfer coefficient (kmtc × 104 cm/s) of 5.67/3.97/2.96 and 7.71/7.08/7.04, respectively which decreased to 5.06/2.95/2.57 and 7.53/6.95/6.90, respectively for the composite containing 50 wt.% ceramic filler.

Enhanced fatigue resistance of plasma modified pyrolysis carbon black filled natural rubber composites

Owning to the requirement of cost reduction and environmental protection, the application of pyrolysis carbon black (CBp) in dynamic rubber products becomes a hot topic in recent years. However, the fatigue resistance of CBp filled rubber composite is poor. Therefore, the evolution of micro- mesoscopic structure in modified CBp filled natural rubber (NR) composites during the tensile fatigue process is investigated to find the influencing factor for enhancing the fatigue resistance in this study. Results indicate that the particle/aggregate size distribution turns to be narrower after the aggregate size filtering treatment while a decreased particle/aggregate size and an improved polarity can be observed after argon plasma treatment. As a result, the average fatigue life of NR composites filled with CBp treated by air classifier, plasma modification and their combination are increased by 21%, 57% and 107%, respectively. It is found that the filler dispersion and the filler-polymer interaction deteriorate during the fatigue process. This evolution is inhibited by filler modification. Besides, the fatigue lives of filled rubber show a correspondence to their total and physical cross-linking densities as well as the bound rubber contents. The filler-polymer interaction can be proposed as an important factor in extending the fatigue life of rubber composites. These findings provide not only a promotion on the application value of CBp in fatigue resistance of rubber composite by different modification methods, but also an innovative perspective for exploring the fatigue resistance of rubber material from the aspects of filler-rubber interaction, and a scientific guidance for the development of long-life dynamic rubber products.

Nut shell and grain husk waste biochar as carbon black replacements in styrene-butadiene rubber composites and improvements through steam activation

Biochar has been used in research as a full or partial replacement of carbon black in rubber composites to varying degrees of success. Choosing the right feedstocks and developing effective treatment methods of biochar can improve its properties and lead to more effective reinforcement filler. This study creates and characterizes biochar from two different low-ash nut shell feedstocks (hazelnut and walnut) and two high-silica grain husk feedstocks (oat and rice). These biochars are subjected to slurry-based steam activation and used to create and characterize vulcanized rubber composite formulations and compared to a traditional carbon black filled rubber composite. The results demonstrate that the nut shell biochars provide high reinforcement properties that meet or exceed those of carbon black and that slurry-based activation of biochar improves mechanical properties in the filled composite. The study presents correlations of low ash content in potential feedstocks with improved reinforcement performance.

Reinforcing behavior of reclaimed rubber filled natural rubber composites

AbstractWith the growing volume of waste rubber products, the pressures on the environment and resources become increasingly serious. The reclamation of waste rubber products is one of the practical methods to meet this challenge. Therefore, the application of reclaimed rubber (RR) attracts researchers’ attention. In this work, different contents of natural rubber (NR) matrix are replaced by RR and the reinforcing behavior of the RR phase is discussed. The results show that the crosslinking density, Payne effect and 100% modulus increase with increase in RR content in the NR/RR blends when the RR content is not more than 60 phr, and then drop when the RR content gets to 80 phr. It is inferred that both the NR and the RR constitute co‐continuous phases when the RR content is 60 phr, and the RR phase is the only continuous phase when its content reaches 80 phr, which can be confirmed by SEM observation. Besides, the curing rate is enhanced with increase of the RR content. It is also found that structures with high crosslinking density appear when the RR is incorporated into the NR matrix. Finally, it is proposed that carbon black in the RR, a structure with high crosslinking density and a continuous rubber matrix are important factors influencing the reinforcement behaviour in RR filled rubber composites. © 2023 Society of Chemical Industry.

The Influence of Carbon Black Colloidal Properties on the Parameters of the Kraus Model.

The Payne Effect (also known as the Fletcher-Gent Effect) has a fundamental impact on the behavior of filled rubber composites and therefore must be considered during their design. This study investigates the influence of carbon black (CB) surface area and structure on the observed Payne Effect and builds on the existing models of Kraus and Ulmer to explain this phenomenon. Dynamic strain sweeps were carried out on natural rubber (NR) compounds containing eight different grades of CB at equivalent volume fractions. The loss and storage moduli were modeled according to the Kraus and Ulmer equations, using a curve optimization tool in SciPy. Subsequent regression analysis provided strong correlations between the fitting parameters and the CB structure and surface area. Using this regression analysis, this work provides further insight into the physical meaning behind the Kraus and Ulmer models, which are phenomenological in nature.

Effects of β‐dextranase in raw natural rubber on the interface and performance of natural rubber/silica composites via simulation with an outer same protein

AbstractAs one of the non‐isoprene components in raw natural rubber (NR), proteins always act an important role to the final performance of the filled rubber composites. In this work, we involved a natural protein β‐dextranase externally to simulate the same protease in raw NR, and analyzed the effects of β‐dextranase content on the dispersion of silica particles, mechanical performance, viscoelastic loss of NR/silica composites. β‐dextranase acts with silica through an intense hydrogen bond interaction, which improves silica dispersion and strengthens the mechanical properties of NR/silica composites obviously when loading 4 wt% β‐dextranase, as well as the ameliorative UV aging resistance. As a consequence, the energy loss of the composites is decreased remarkably, showing great advantage in low rolling resistance tire. Besides, the results could offer the data reference to the breeding, deep processing and application of NR.

Copper-coated hollow glass microspheres filled rubber composites: Lightweight, interface bonding and mechanical properties

Copper-coated hollow glass microspheres filled rubber composites: Lightweight, interface bonding and mechanical properties

Detailed understanding of the carbon black–polymer interface in filled rubber composites

To characterize the nature of the interface between styrene-butadiene rubber (SBR) and carbon black (CB) in a filled rubber compound, we introduce an extraction protocol that uses toluene solvent in a high-pressure autoclave with sequential temperature steps of 90, 110, and 150 °C. This new approach removes unbound and physically bound (physisorbed) polymer from the CB-filled SBR compound to leave only chemically bound polymer which is 0.86% (0.0172 g polymer/g CB) and not zero as implied from extrapolating prior literature results. Rheological time sweeps on the unfilled gum SBR indicate that significant crosslinking can occur during annealing at 150 °C for this unsaturated polymer. This was the motivation for using the sequential extraction procedure versus direct extraction at 150 °C which gives a nearly six-fold higher amount of unextracted polymer due to such crosslinking. Analysis of the temperature dependence of bound rubber from 23 to 150 °C indicates that the physical interactions between the polymer and CB surface have a weaker component with a desorption energy (Ed) of 6.8 kJ/mol and a stronger component with Ed = 90.7 kJ/mol, the latter requiring an extraction temperature of 110 °C to remove the majority of it from the CB.

STUDIES ON THE THERMODYNAMIC PROPERTIES OF NATURAL RUBBER COMPOSITES FILLED WITH CLAY AND CORN COB

The mechanical properties of materials such as natural rubber composites determine their usefulness as engineering or biological materials. The thermodynamic properties of natural rubber composites filled with clay and corn cob at varying volume fraction of filler were studied with a view of relating and comparing thermodynamic parameters (ΔG, ΔH and ΔS) to mechanical properties (Young’s modulus, tensile strength, elongation at break, etc) of natural rubber composites. The rubber composites were prepared using a standard compounding recipe. The tension observed for each rubber composite as a result of changes in temperature was used in evaluating thermodynamic parameters via Arrhenius equation and plot. These properties have been evaluated by measuring the thermodynamic parameters of natural rubber composites compounded with varying percent volume fractions (5% - 25%) of two fillers- clay and corn cob. The results indicated that the maximum values of ΔG and ΔH was obtained for corn cob filled composites at 10% volume fraction, while the optimal values of ΔS for the same composites was found to be at 5% and 25% volume fraction. At lower filler concentration (5 – 17.5%), corn cob filled composites were observed to have higher modulus than clay filled rubber composites, while at these concentration ranges, clay was found to impact higher tensile strength to natural rubber than corn cob filler.

Enhancement of mechanical properties of styrene‐butadiene rubber composites by carbon black/silicone carbide hybrid filler networking

AbstractIn 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.

Influence of Sepiolite Addition Methods and Contents on Physical Properties of Natural Rubber Composites

The influence of sepiolite loadings (1-10 phr) and sepiolite addition procedures (mill and latex mixing approaches) on properties improvement of natural rubber composites was investigated. The viscosity, curing behavior, and tensile test were used to assess the property changes whereas the rubber-filler interactions was confirmed by using stress relaxation, swelling, Mooney-Rivlin and rheological methods. It was found that the characteristics of rubber composites influenced by both mixing methods and filler contents. Comparing between two different mixing methods, the slower stress relaxation rate and less swelling capability were achieved from mill mixing technique. This method also lowered the strain where the upturn of stress was occurred as suggested by Mooney-Rivlin plot. The greater properties enhancement of composites was obtained from milling method because of the better rubber-filler interactions, probably as a result of the nature of filler used. The greatest tensile strength improvement was achieved at 1 phr sepiolite loading where the smallest damping characteristics (tan ????) indicating the highest elastic behavior were obtained as revealed by rheological measurements. The simplicity of production and shortened step of milling procedure would be more favorable than the latex mixing approach for fabrication sepiolite filled rubber composites.

Preparation of Natural Rubber Composites with High Silica Contents Using a Wet Mixing Process.

A wet mixing process is proposed for filled rubber composites with a high silica loading to overcome the drawbacks of high energy consumption and workplace contamination of the conventional dry mixing process. Ball milling was adopted for preparing the silica dispersion because it has a simple structure, is easy to operate, and is a low-cost process that can be easily scaled up for industrial production. The response surface methodology was used to optimize the making of the silica dispersion. The optimum conditions for a well-dispersed silica suspension with the smallest silica particle size of 4.9 mm were an about 22% silica content and 62 h of ball milling. The effects of dry and wet mixing methods on the properties of silica-filled rubber composites were investigated in a broad range of silica levels from low to high loadings. The mixing method choice had little impact on the properties of rubber composites with low silica loadings. The silica-filled rubber demonstrated in this study, however, shows superior characteristics over the rubber composite prepared with conventional dry mixing, particularly with high silica loadings. When compared to silica-filled natural rubbers prepared by dry mixing (dry silica rubber, DSR), the wet mixing (for WSR) produced smaller silica aggregates with better dispersion. Due to the shorter heat history, the WSR exhibits superior curing characteristics such as a longer scorch time (2.2–3.3 min for WSR and 1.0–2.1 min for DSR) and curing time (4.1–4.5 min for WSR and 2.2–3.1 min for DSR). Additionally, the WSR has superior mechanical properties (hardness, modulus, tensile strength, and especially the elongation at break (420–680% for WSR and 360–620% DSR)) over the DSR. The rolling resistance of WSR is lower than that of DSR. However, the reversed trend on the wet skid resistance is observed.

Preparation and application of carbon black-filled rubber composite modified with a multi-functional silane coupling agent

Abstract Carbon black (CB)-filled rubber composites are widely used for tire tread and other rubber products due to their good abrasion resistance and reinforcement. Numerous studies have been focused on the filler-rubber interaction with the aim of obtaining optimum performances. In order to investigate the effect of modification on properties of diene rubber composites, a modified CB-filled isoprene rubber (IR) composite was prepared with a multi-functional silane coupling agent, 2-aminoethyl-2-(3-triethoxysilylpropyl)aminoethyl disulfide (ATD). This modification significantly enhanced the CB-IR interaction and improved CB dispersion. For the modified CB/IR vulcanizates, the tensile strength, stress at 300% elongation, temperature rise, and dynamic loss coefficient were significantly improved at low ATD dosage (1.5 phr). Such modification provides an effective route to prepare CB-reinforced diene rubber composites with low hysteresis and improved mechanical properties.

Application of Different Vegetable Oils as Processing Aids in Industrial Rubber Composites: A Sustainable Approach.

Rubber composites based on renewable vegetable oils are being increasingly developed, as these materials significantly reduce the use of petroleum-based carcinogenic oils as plasticizers in rubber products. Apart from renewability, vegetable oils have some major advantages, such as easy availability, biodegradability, and environmentally friendly nature. Until now, vegetable oils, such as palm oil, soybean oil, and linseed oil, have been successfully used as processing oils to replace petroleum-based oils in engineered rubber composites. So far, the concept of a vegetable-oil-based plasticizer has been applied to rubber composites containing different industrially important fillers, like carbon black, silica, calcium carbonate, and expandable graphite. In the near future, the trend of utilizing vegetable-oil-based plasticizers may bring considerable advancements in the performance of filled rubber composites in an environmentally acceptable and sustainable manner.

Recent advances of natural fibers based green rubber composites: Properties, current status, and future perspectives

AbstractThe searching of suitable alternatives to petroleum‐based fillers is an uncompromising challenge in present day rubber research. Recently, natural fibers are the part of great attention of both academic and industrial researchers due to their easy availability, environmental friendliness, and biodegradability. Natural fiber is cellulose‐rich material, which is preferentially used as alternative filler in rubber technology. This article reviews current advances in natural fibers filled rubber composites in terms of mechanical, thermal, and biodegradable properties (2010–2020). The incorporation of unmodified natural fibers as filler is not able to offer desired reinforcement in rubber composites. Several surface modification methods can be introduced to improve the overall performances of natural fibers filled rubber composites. Finally, the review clarifies present status and future prospects of natural fibers based advanced rubber composites in automobile industry. The successful designing of natural fibers based sustainable rubber composites can introduce a new era in green rubber technology.

Low frequency electromagnetic shielding efficiency of composites based on ethylene propylene diene monomer and multi‐walled carbon nanotubes

Ethylene propylene diene monomer rubber was filled with multi‐walled carbon nanotubes to prepare composite materials with the effect of electromagnetic radiation (EMR) shielding. Sulfur‐based curing system as well as peroxide curing system were used for vulcanization of rubber compounds. The main goal of the work was the investigation of curing system composition and filler content on curing process, physical‐mechanical properties, cross‐link density, and shielding efficiency of the prepared composites. The results showed that curing characteristics and cross‐link density of composites were dependent on both, amount of carbon nanotubes and curing system composition. The incorporation of filler resulted in the enhancement of physical‐mechanical properties of composites. Higher values of tensile strength were found to have composites cured with organic peroxide in combination with co‐agent. The achieved results also demonstrated that carbon nanotubes filled rubber composites are suitable candidates for applications, in which shielding of EMR at low frequencies is based on reflection.

Effect of surface treatments and filler loading on the properties of hemp fiber/natural rubber composites

The aim of this present work was to study the effect of surface treatment methods, i.e., silane and permanganate on curing characteristics, dynamic mechanical, mechanical morphological and thermal properties of hemp fiber filled natural rubber composites. Hemp fiber surfaces were pretreated with an alkali solution and followed by a KMnO4 solution or (3-triethoxysilylpropyl) tetrasulfide (Si69). After that, the chemical, physical and morphological properties of untreated and treated hemp fiber samples were investigated by attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. It was found that the KMnO4 and silane (Si69) treatments affected the surface characteristics of hemp fibers. The curing characteristics of the rubber composites, i.e., scorch and curing times increased with increased fiber loading, except for 15 parts per hundred of rubber (phr) fiber level. The curing characteristics improved with the addition of KMnO4 or silane treated hemp fiber compared to unfilled natural rubber composites. At 5 phr fiber loading, it was found that silane treated hemp fiber filled natural rubber composite showed greater tensile strength and crosslink density in comparison with KMnO4 treated and untreated hemp fiber filled rubber composites. Good interface interaction between the silane treated hemp fiber and rubber matrix was observed in SEM images. Additionally, the thermal stability of rubber composites was unaltered with the incorporation of KMnO4 or silane treated hemp fibers.

A critical review on the utilization of various reinforcement modifiers in filled rubber composites

Presently, the development of high-performance filled rubber composites offers a new era in the industrial field of polymer research. This article reviews the utilization of various reinforcement modifiers on the successive property enhancement of rubber composites containing different commonly used fillers like silica, nanoclay, carbon nanotube, natural fibers, and so on. The practical importance of reinforcement modifiers in rubber technology is systematically described in the light of filler dispersion, processing, and mechanical properties of filled rubber compounds. A special emphasis is given on the mechanism of interaction between reinforcement modifiers and filler surface in filled rubber composites. Filler dispersion in the rubber matrix is the key parameter that controls the ultimate performance and rubber–filler interaction of filled rubber system. The use of some fixed reinforcement modifiers is an innovative way not only to solve the dispersion problem of filler particles but also to increase the reinforcing ability of most of the fillers in filled rubber products. Thus, the concept of reinforcement modifiers has the potential to facilitate further development of filler reinforcement technology for rubber-based composite materials.

Study on Microstructure Effect of Carbon Black Particles in Filled Rubber Composites

The cross sections of blended natural/styrene-butadiene (NSBR) composites filled with different volume fractions of carbon particles were observed using a Quanta 250 scanning electron microscope. In addition, the sizes and distributions of the carbon particles were analyzed using Nano Measurer. A two-dimensional representative volume element model (RVE) for a rubber composite reinforced with circular carbon particles was established, and the uniaxial tensile behaviors of polymer nanocomposites with different particle size distribution patterns were simulated using the ABAQUS software. The results showed the following. (1) For the random models, if the difference of particle size was larger and particle distance was closer, stress distribution would be denser as well as the stress concentration would become greater. However, if the difference of particle size was small, for the case of same particle volume fraction, the particle size has little influence on the macromechanical properties whether the average size is large or small. (2) The correlation between the volume fraction and distribution of the carbon particles revealed that when the volume fraction of carbon black particles was larger than 12%, clusters between carbon particles in the polymer nanocomposites could not be avoided and the modulus of the composites increased with an increase in the cluster number.

Effect of reinforcement filler on vulcanization, diffusion, mechanical, and electrical properties of natural rubber

The present work investigates the properties of natural rubber (NR) filled with different contents of reinforcing carbon black (CB) and other compounding ingredients. The curing characteristics were tested at 157°C. It was found that the equilibrium solvent uptake ( Qmax) decreases with the increase of the CB concentration due to reduction of the free volume. Mechanical properties such as tensile strength and hardness of CB filled rubber composites were remarkably improved, indicating the inherent reinforcing potential of CB. The percentage of elongation at break of filled CB rubber was found to be lower than that of pure NR. The dielectric constants ( ε′), dielectric loss ( ε″), and alternating current (AC) electrical conductivity ( σAC) were investigated for all samples as a function of frequency and temperature. It is concluded that the high CB content causes the formation of channels, increasing the AC conductivity of the composites.