Natural Rubber Compounds Research Articles

Effect of carbon black properties on cut and chip wear of natural rubber

The effect of carbon black colloidal properties on cut and chip wear of natural rubber compounds is investigated across a wide range of applied impact normal forces using an Instrumented Cut and Chip Analyzer (ICCA). The objective of the study is to determine the basic fatigue and fracture mechanisms that drive cut and chip wear. Natural rubber compounds reinforced with eight different carbon blacks varying in structure and surface area are studied. The loading of the carbon blacks in the rubber compounds is fixed at 50 parts per hundred rubber (phr). The cut and chip performance strongly correlates to both the carbon black morphological properties and the resulting compound mechanical and fracture properties. The cut and chip performance also depends on the applied impact normal force level. At low forces, high structure carbon blacks result in compounds which are stiffer and deflect less under the applied impact normal forces and minimize cut and chip wear. At high forces, low structure carbon black compounds, which are softer and more readily able to crystallize under force-controlled deflection, minimize cut and chip wear. It is argued that at low applied impact normal forces, the cut and chip behavior is dominated by a force-controlled fatigue crack growth mechanism which transitions to a critical tearing energy dominated mechanism at high applied impact normal forces. It is therefore important to understand the severity of application to select optimum compound properties such as the carbon black type to minimize cut and chip wear in application.

Unleashing the Power of Nanoparticles: Enhancing Natural Rubber (NR)/Nitrile Butadiene Rubber (NBR) Blends for Ultimate Performance

Our research described in this article examined the physical aging of natural rubber (NR) and nitrile rubber (NBR) compounds reinforced with nano-silica (n-SiO2) particles. The impact of NR and nano-silica content on the mechanical, spectral, and thermal properties of the composites was assessed using Shore hardness, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results showed that after 8 days of aging in toluene or xylene at room temperature, high NR content caused significant swelling in the non-polar solvents, unlike NBR, which prevented rubber chain stretching and reduced the free volume. The transport mechanism of the toluene and xylene was pseudo-Fickian and slightly dependent on the nano-silica content. The hardness of the vulcanized blends increased with NBR and silica incorporation due to better dispersion of the particules and rubber-filler interaction, leading to high cross-linking density. XRD patterns confirmed the filler intercalation within the polymer matrix, causing a diffraction shift to a lower 2θ value of the various reflectures. Differential thermogravimetric analysis (DTGA) revealed that the n-SiO2 nanoparticles enhanced the thermal stability due to strong polymer chain interactions. These findings suggest that nano-silica-filled NR/NBR blends have significantly improved physical, mechanical, and thermal properties, supporting their potential for advanced elastomer-based materials in industrial applications.

Enhancement of the Reinforcement Effect of Calcium Carbonate or Silica on Natural Rubber Using Lauryl Alcohol

Calcium carbonate (CaCO3) and silica are two types of additives for rubber. Through the implementation of a typical semi-efficient (Semi-EV) vulcanisation formulation, those additives were added separately into the compound of natural rubber (NR). The CaCO3 or silica was added as the reinforcing filler and, incorporated into NR at a constant concentration i.e., 30 parts per hundred NR (phr). It was found that the CaCO3 or silica have successfully provided an increase in mechanical properties including a greater tensibility (tensile strength) and abrasion resistance of the compound of NR. However, as hydrophilic fillers, the CaCO3 or silica is hard to disperse homogeneously and hence, lauryl alcohol was used to improve their dispersion degrees. It was combined into the NR compound with varied concentrations such as 1, 3, 5 and 7 phr. Therefore, the effect of lauryl alcohol concentration on the processing and reinforcement properties of CaCO3 or silica-filled NR was investigated. It could be found that lauryl alcohol has increased the rate coefficient of vulcanisation (Rv) of the CaCO3 or silica-filled-NR. The greater the lauryl alcohol concentration; the greater the Rv value, tensile strength, and abrasion resistance. Overall, lauryl alcohol has a successful function as a plasticizing agent which increased the reinforcement effects of the fillers on NR through the increasing of crosslink density of CaCO3-NR or silica-NR especially at the 5 phr of addition.

Recyclable sulfur cured natural rubber with controlled disulfide metathesis

Traditionally, sulfur-cured natural rubber compounds exhibit limited recyclability due to a significant drop in mechanical performance after reprocessing. Maintaining physical and chemical properties after recycling of a cross-linked polymer is an essential requirement for the global rubber industry to become more sustainable. Here, we demonstrate that tuning the curing process to favour a reversible cross-linked network based on disulfide and polysulfide bonds enables recyclability. We use a sulfur-based vulcanization system optimized with copper (II) methacrylate at concentrations of 2.47, 4.94, and 9.89 phr to control disulfide metathesis at low temperatures and enhance recyclability. Mechanical characterization identifies 2.47 phr as optimal for maintaining mechanical properties after initial moulding and full recovery after recycling. Additionally, we demonstrate that copper (II) methacrylate can be incorporated into existing rubber waste streams to promote recyclability.

Why the fracture resistance of natural rubber compound reduced when subjected to thermal ageing?

Why the fracture resistance of natural rubber compound reduced when subjected to thermal ageing?

Effect of proteins as constituents of island-nanomatrix structure on vulcanization of natural rubber

Effect of proteins, constituents of the island-nanomatrix structure, on dispersion of zinc to natural rubber was investigated by transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) and focused ion beam-scanning electron microscopy-energy dispersive X-ray spectroscopy (FIB-SEM-EDX). Films of natural rubber and deproteinized natural rubber (DPNR) prepared with urea were embedded in a mixture of ZnO, vulcanization accelerator and sulfur, and they were heated at 150 °C for 5 h. Migration of Zn from surface to inside of the films was observed by FIB-SEM-EDX. The Zn migrated from the surface to 14 μm for natural rubber, but not for DPNR. The optimum vulcanization time for natural rubber was short, i.e., about 4 min, whereas it was long for DPNR, i.e., about 15 min. To confirm the effect of the proteins, a latex-mixed rubber compound was prepared by mixing the latex with sulfur, ZnO and vulcanization accelerator followed by drying with a hotplate at 150 °C for 45 s since the proteins are segregated on the surface of natural rubber particles in the latex stage. Vulcanization was accelerated for the latex-mixed natural rubber compared with mechanically mixed natural rubber compound that was prepared by mixing natural rubber with ZnO, vulcanization accelerator and sulfur with a two-roll mill. The resulting latex-mixed natural rubber vulcanizate was superior in mechanical properties to the mechanically mixed natural rubber vulcanizate. It was found by rubber-state NMR spectroscopy that the difference in mechanical properties was attributed to the difference in the cis-1,4-average sequence length of the vulcanizates, which came from the difference in the dispersion of Zn.

Sustainable multi-functional additives: Zinc soaps from vegetable oil and fatty acids in natural rubber compounds

Zinc soaps derived from various vegetable oils and fatty acids were synthesized, and the product with the highest yield was chosen for compounding with silica-filled natural rubber (NR). Specifically, zinc soaps of coconut oil and palm oil, with yields of 72% and 73%, respectively, were prepared through precipitation and metathesis methods. Additionally, zinc soaps from palm fatty acid distillate (PFAD) and stearic acid, both with a yield of 70%, were synthesized using modified fusion and precipitation methods, respectively. Subsequently, these zinc soaps were incorporated into silica-filled NR compounds and compared with the commercial dispersing aid, Ultra flow 700 s. The results indicated that the zinc soaps played a significant role in plasticizing and lubricating the rubber compounds, as evidenced by reductions in Mooney viscosity, Mooney relaxation rate, and minimum torque (ML). Furthermore, the zinc soaps influenced curing properties by accelerating the cure process, as reflected in decreased cure time (tc90) and increased cure rate and torque difference compared to compounds without processing aid. Moreover, NR compounded with zinc soap exhibited superior mechanical properties, including higher tensile strength, elongation at break, tear strength, and hardness.

Effect of multi-walled carbon nanotubes reinforcement on self-healing performance of natural rubber

Abstract This work is motivated by the desire to restore the quality of rubber-based product properties with the intention of prolonging the service life period, thus helping create a sustainable environment by proposing effective rubber waste management. This study experimentally investigated an intrinsically self-healing zinc thiolate grafted natural rubber (NRZT) compound filled with multi-walled carbon nanotubes (MWCNT) to assess its influence on mechanical properties and self-healing performance. The MWCNT loading varied to 0, 2, 4, 6, and 8 phr. The Equilibrium swelling test was used to quantify the amount of ionic and covalent crosslinks formed. Fourier Transform Infrared (FTIR) spectra were used to detect the presence of MWCNT in the compound. The mechanical properties computed by the tensile and tear strength tests showed that the incorporation of MWCNT increased both properties up to three and twofold, respectively. However, as expected, the elongation at break (Eb) value was reduced. The unfilled sample showed that it can heal up to ∼98 %, measured from the tensile strength. However, the healing efficiency obtained from tensile strength reduces to ∼88 % by incorporating 2 phr MWCNT. The Eb and its self-healing efficiency gradually decreased as the MWCNT amount increased. All samples showed outstanding properties under the tearing mode, where the healed samples produced higher tear strength (>100 % healing) than the initial value. Scanning Electron Microscopy (SEM) micrographs revealed a noticeable gap along the healed cut line with increased MWCNT numbers, possibly due to the lower reaction between polymerized zinc thiolate (PZTh) radicals with zinc thiolate (ZT) and rubber molecules. The work aims to investigate the influence of MWCNTs on the mechanical and healing performance of self-healing NR composites by comparing them to their unfilled sample.

Enhancing airless tire performance for military vehicles: natural rubber compound with carbon black Fillers N220 and N550 with dynamic mechanical analysis approach

Enhancing airless tire performance for military vehicles: natural rubber compound with carbon black Fillers N220 and N550 with dynamic mechanical analysis approach

Fatty alcohols as sustainable compatibilizer agents for the compound of natural rubber/silica: The curing, rubberiness and tensile strength behaviours

Fatty alcohols are derived from palm oil production and, stearyl and lauryl alcohols are examples of them. The stearyl and lauryl alcohols have the potential to be used as rubber additives for the compounding and vulcanizing processes. These materials are relatively new as rubber additives and, they were added into silica-filled natural rubber (NR) compound. The aim of using them is to increase the grade of silica dispersion inside the NR matrix. Initially, the NR was filled by (precipitate) silica at 30 parts per hundred of NR, whilst the fatty alcohols were added into the silica-filled NR with variable concentrations from 1 to 4 phr, separately. The compounds of NR/silica/stearyl alcohol and NR/silica/lauryl alcohol have been vulcanised at 150 °C by implementing a semi-efficient rubber composition. From the vulcanization behaviour, it was observed that both fatty alcohols have the role of compatibilizer and plasticising agents for the compound of NR/silica. Those fatty alcohols decreased the viscousness but increased the curing rate index (CRI). The more concentration of fatty alcohols was supplied, the less viscousness and the higher the CRI. Those fatty alcohols also shifted the crosslinking level and tensile strength. It also observed that the break elongation or rubberiness has been shifted up. Tensile strength has been shifted to a maximal value with a 2 phr of stearyl alcohol or 3 phr of lauryl alcohol addition.

Synergistic effects of silane‐modified carbon black and nano‐silica hybrid fillers on the performance of natural rubber compounds

AbstractThis study investigates the efficiency of already developed surface‐modified carbon black (CB), both independently and in conjunction with nano‐silica, as a hybrid filler, to the properties of natural rubber (NR) compounds. The modification process, followed by coupling agent treatment, enhanced cross‐link density and curing characteristics, though the inclusion of nano‐silica alone negatively affected curing due to its inherent polarity and tendency to agglomerate. The filled compounds with modified CB exhibited significant improvements in mechanical properties, notably tear resistance. Moreover, the combination of nano‐silica with modified CB yielded compounds with superior tear resistance, attributed to synergistic effects. CB surface modification exhibited varying effects on the glass transition temperature, with enhancements observed in tan δ at lower temperatures, indicating improved ice and wet grip potential. Also, it reduced rolling resistance after treatment with a coupling agent. While thermal stability remained consistent across the studied compounds, swelling resistance varies with filler type and ratio. Thermodynamic analysis confirmed the positive impact of CB surface modification on the elasticity and chain mobility of the investigated rubber compounds. It was concluded that the strategic selection of fillers and modification approaches were essential for achieving optimal results in the rubber compound's performance and application.

Enhancing the tire performances of truck tire tread based on rubber compounds containing biobased processing oil by adjusting sulfur contents

The mechanical properties of the rubber compounds such as modulus and tensile strength are very important to rubber products especially for tire applications. However, the presence of palm oil (PO) as a biobased processing oil in eco-friendly truck tire tread compounds encounters the low mechanical properties because PO molecules can consume sulfur as a curing agent. Therefore, this study focuses on incorporation of sulfur in varying contents on the properties of rubber compounds. The PO-added natural rubber compounds with different sulfur contents of 2.50, 2.75, and 3.00 parts per hundred rubber (phr) were prepared by taking the use of distillated aromatic extract (DAE) in natural rubber compound with 2.50 phr sulfur as a reference. The levels of crosslinking of the PO-added natural rubber compounds increased as the sulfur content increased, resulting in improvement in mechanical properties. Results showed that an additional incorporation of 0.25 phr sulfur content led to superior mechanical properties. Furthermore, PO improved the abrasion resistance by 38%, reduced heat buildup by 17%, and lowered tan δ at 60°C by 21%, when compared to the compound as a reference. Based on the results, the additional incorporation of sulfur not only improved the mechanical properties, but also enhanced tire performances especially low rolling resistance as reflected by energy-saving tires. Thus, PO can be an alternative to DAE in the natural rubber compounds for the application of truck tire treads when the additional incorporation of sulfur was applied.

Enhancing the performance of waste-paper particleboard using silica and aluminum hydroxide fillers

Composites used as particleboard have recently been developed using waste-paper fibers mixed with natural rubber compound at a weight ratio of 70/30 %. The effects of silica and aluminum hydroxide fillers were studied at 0, 15, 30, 45, and 60 phr. The results showed that the hardness of the waste-paper particleboard increased with the filler content. Both types of fillers led to a slight increase in the density of the composites. Moreover, the fillers reduced the hygroscopicity and swelling of the particleboard. The use of silica resulted in lower hygroscopicity, providing greater flexural resistance and elastic modulus compared to using aluminum hydroxide. Additionally, the minimum limiting oxygen index (LOI) required to ignite the sample was slightly higher with the addition of both fillers, with silica exhibiting a higher value than filled aluminum hydroxide. Furthermore, the thermal decomposition of the specimens from the TGA test was reduced as both fillers were added, especially at temperatures above 350°C.

New role of ionic liquid as accelerator activator in rubber compounds and its influence on curing and mechanical properties

AbstractThis study focuses on the effect of ionic liquids (ILs) on the cure characteristics and filler dispersion of natural rubber (NR) and styrene‐butadiene rubber (SBR) gum and filled compounds. The complexation of ionic liquid with zinc oxide (ZnO) increases the activity of ZnO and the cure rate together with improved filler dispersion. This has also increased the rubber filler interaction. Imidazolium and chloride based ionic liquids with different cationic groups were compared and characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, and differential scanning calorimetry to understand the thermal and chemical behavior of the compounds. Interestingly, it was found that the ionic liquid can act as an activator and is able to accelerate the vulcanization rate with improved rubber filler interaction. The complexes formed by IL‐Zn were shown to be much more reactive than Zn‐stearic acid complexes. The dispersion of carbon black in the NR and SBR compounds was studied by using Field Emission Scanning Electron Microscope and Transmission Electron Microscope and the results demonstrate that ILs could significantly improve the filler dispersion. Thus, this study has revealed the multifunctional role of ionic liquids in rubber compounds.Highlights This article describes the dual role of the ionic liquid (IL) in rubber compounds. It can act both as an accelerator‐activator as well as an efficient dispersing aid. The complexation of IL with zinc oxide (ZnO) plays a crucial role in enhancing the activity of ZnO. As a result, the physico‐mechanical properties of both natural rubber and styrene‐butadiene rubber based compounds are significantly improved.

Strain-induced crystallisation of reinforced elastomers using surface calorimetry

The crystallinity of rubbers which are amenable to crystallisation upon stretching is classically measured using X-ray diffraction (XRD) techniques. Recently, an alternative method for evaluating the crystallinity in unfilled natural rubber (NR) during stretching was proposed. This method is based on surface calorimetry principles (Le Cam, 2018) and was validated by XRD measurements in Le Cam et al. (2018). For reinforced rubber composites, the calorimetric response is not only due to the elastic couplings and the crystallisation/melting process, but also due to the intrinsic dissipation and additional viscoelastic dissipation resulting from the presence of fillers. This makes estimating the crystallinity of carbon black (CB) reinforced rubber compounds from calorimetric techniques typically more challenging. In this paper, however, the calorimetric approach for measuring crystallinity for CB reinforced rubber compounds was investigated. Crystallinity measurements were performed using both an unfilled and three CB reinforced NR compounds. A comparative study was performed using the XRD technique on the same four compounds. The results confirmed the appropriateness of the calorimetric technique for determining the crystallinity in the unfilled NR. The combination of the XRD and the calorimetric techniques allowed the different heat sources under strain to be identified and therefore, the thermal energy associated with crystallisation to be determined. This was done initially using one of the CB reinforced NR compounds and validated using the two other CB reinforced NR compounds. The results show reasonable correlation between the crystallinity measured using the novel calorimetric technique and the classical XRD technique for CB reinforced NR compounds. The development of this methodology has potentially significant impact. The calorimetric approach does not require the measurement of the mechanical response during testing. This is useful for measuring crystallinity gradients from infrared thermography coupled with full kinematic field measurements, typically at crack tips, where estimating the local mechanical response is very difficult or inaccurate.

Degradation during Mixing of Silica-Reinforced Natural Rubber Compounds.

The optimal mixing conditions for silica-filled NR compounds dictate the need to proceed at a high temperature, i.e., 150 °C, to achieve a sufficient degree of silanization. On the other hand, natural rubber is prone to degradation due to mechanical shear and thermal effects during mixing, particularly at long exposure times. The present work investigates NR rubber degradation during mixing in relation to prolonged silanization times. The Mooney viscosity and stress relaxation rates, bound rubber content, storage modulus (G'), and delta δ were investigated to indicate the changes in the elastic/viscous responses of NR molecules related to rubber degradation, molecular chain modifications, and premature crosslinking/interaction. In Gum NR (unfilled), an increase in the viscous response with increasing mixing times indicates a major chain scission that causes a decreased molecular weight and risen chain mobility. For silica-filled NR, an initial decrease in the Mooney viscosity with increasing silanization time is attributed to the chain scission first, but thereafter the effect of the degradation is counterbalanced by a sufficient silanization/coupling reaction which leads to leveling off of the viscous response. Finally, the higher viscous response due to degradation leads to the deterioration of the mechanical properties and rolling resistance performance of tire treads made from such silica-filled NR, particularly when the silanization time exceeds 495 s.

Renewable Compatibilizing Agent for Silica Reinforced Natural Rubber

The main problem in utilizing silica as an alternative reinforcing filler for natural rubber (NR) compounds is a weak rubber-filler interaction and poor filler distribution due to their incompatibility feature. The particles of silica have a strong tendency to filler interactions which leads to form silica agglomeration. To solve this drawback, this work has utilized ethanolamine-modified palm stearin (EMPS) as a renewable compatibilizer agent to improve NR-silica compatibility. The EMPS was prepared by a typical chemical reaction between ethanolamine and refined bleach-deodorized palm stearin (a byproduct of cooking oil production) on a laboratory scale. The influence of the EMPS on the improvement of rubber-filler interaction was investigated by studying the processing characteristics and the tensile properties of silica-reinforced NR compound (silica content was fixed at 30 phr). Compared to the silica-reinforced NR with no EMPS, it was found that EMPS caused a greater coefficient of vulcanization, tensile strength, and reinforcement effect for the silica-reinforced NR. It was due to an active reaction between silanol groups of silica with EMPS which increased the NR-silica compatibility, and the Fourier Transform Infra-Red (FTIR) analysis has confirmed the typical reaction.

Processing and Tensile Properties of Natural Rubber Filled with Calcium Carbonate or Silica in the Presences of Lauryl Alcohol

The processing and tensile properties of the compounds of natural rubber (NR) filled with calcium carbonate (CaCO3) or silica filler in the presence of lauryl alcohol have been investigated. The NR was filled with each of those fillers at a fixed concentration, i.e., 30 phr, and they were compounded with lauryl alcohol as a filler dispersant with varied concentrations on a laboratory mill by applying the semi-efficient vulcanization recipe. A typical oscillating disc rheometer (ODR) was utilized for the determination of processing properties. From the results, it was observed that CaCO3 or silica with lauryl alcohol had increased the rate coefficient of vulcanization (RV) of the filled NR compounds with a reduction in viscousness or minimal torsion. The results also showed that the lauryl alcohol additions have enhanced the tensile properties of obtained filled NR compounds. The greater the lauryl alcohol concentration, the greater the rate coefficient of vulcanization and tensile strength of both types of filled NR. The overall results have indicated that the lauryl alcohol performance in enhancements of processing and tensile properties was more pronounced on calcium carbonate than silica.

Influence of Processing Oil Content on Rubber-Filler Interactions in Silica/Carbon Black-Filled Natural Rubber Compounding

To ensure the production of high-quality rubber products, establishing effective compatibility and robusting interactions between rubber and fillers is crucial. Since the rubber production industry faces significant environmental challenges, sustainability is becoming a necessity in the rubber business. Various materials, such as the presence of processing aids, might influence rubber-filler and filler-filler interactions. Petroleum oil as general processing oil has environmental issues, thus it is urgent to replace it with bio-based oil. This study addresses these concerns by investigating the impact of paraffinic oil and bio-based oil content on the interactions between silica/carbon black and natural rubber chains. Ranging from 0 to 10 phr, different dosages of these oils were employed. The rubber compound underwent milling using two rolled laboratory open mills post-blending with a laboratory internal mixer. Subsequently, mechanical properties were assessed. A Rubber Processing Analyzer was utilized to characterize interactions between uncured and cured silica/carbon black-filled natural rubber blends. The results revealed that all variations were distributed uniformly. Tan Delta results confirm that a chemical with a high bio-based oil concentration is easier to process. The carbon black with the largest peak of modulus values at low strain has the highest reinforcing or the poorest dispersion. Compounding with paraffinic oil has a high peak modulus value, resulting in poor dispersion when compared to bio-based oil. This research sheds light on the potential of bio-based oils as an eco-friendly alternative in rubber processing, contributing to sustainability efforts in the industry.

Characterization and properties of silica-filled natural rubber compounds using poly(vinyl propionate)‐grafted natural rubber as compatibilizer

Characterization and properties of silica-filled natural rubber compounds using poly(vinyl propionate)‐grafted natural rubber as compatibilizer