Natural Rubber Composites Research Articles

Effect of 1‐ethylpyridinium bromide on enhancing the dispersion of silica and interfacial strength in rubber‐silica composite

AbstractImproving the interfacial interaction between silica and rubber is always a key issue to be solved for silica‐filled rubbers. In this paper, composites are prepared by an in‐situ modification method using 1‐ethylpyridinium bromide ([EPy]Br) as the raw material, and the effect of its dosage on the interfacial interactions and macroscopic properties of silica‐filled natural rubber (NR) composites is investigated. The effect of [EPy]Br on silica dispersion and interfacial interaction between silica and NR is verified through rheological tests and calculations of glass layers. Compared with the original samples, composite performance is optimized when the usage amount is at 1phr which increases tensile strength by 5 MPa, enhances abrasion resistance by 24%, and shortens optimum curing time in half. This study is expected to provide a new strategy for improving the processability of silica‐containing composites while reducing energy consumption.Highlights [EPy]Br enhances the interaction between rubber and filler while modifying the surface of silica. Increasing the dosage of [EPy]Br leads to a reduction in the Payne effect. The addition of [EPy]Br enhances the dispersion of silica in natural rubber. [EPy]Br significantly reduces the duration of the induction period for vulcanization. The dosage of [EPy]Br allows for controlling the mechanical properties of NR/SiO2.

Tea Grounds as a Waste Biofiller for Natural Rubber.

The aim of this study was the utilization of ground tea waste (GT) left after brewing black tea as a biofiller in natural rubber (NR) composites. Ionic liquids (ILs), i.e., 1-ethyl-3-methylimidazolium lactate and 1-benzyl-3-methylimidazolium chloride, often used to extract phytochemicals from tea, were applied to improve the dispersibility of GT particles in the elastomeric matrix. The influence of GT loading and ILs on curing characteristics, crosslink density, mechanical properties, thermal stability and resistance of NR composites to thermo-oxidative aging was investigated. The amount of GT did not significantly affect curing characteristics and crosslink density of NR composites, but had serious impact on tensile properties. Applying 10 phr of GT improved the tensile strength by 40% compared to unfilled NR. Further increasing GT content worsened the tensile strength due to the agglomeration of biofiller in the elastomer matrix. ILs significantly improved the dispersion of GT particles in the elastomer and increased the crosslink density by 20% compared to the benchmark. Owing to the poor thermal stability of pure GT, it reduced the thermal stability of vulcanizates compared to unfilled NR. Above all, GT-filled NR exhibited enhanced resistance to thermo-oxidation since the aging factor increased by 25% compared to the unfilled vulcanizate.

Application of plasma‐activated silanized cellulose nanofibers in natural rubber composites

AbstractCellulose nanofiber (CNF) is an advanced bio‐nanomaterial. However, the hydroxyl groups on the surface of CNFs are highly polar, leading to its weak interfacial compatibility with natural rubber (NR). Therefore, it is necessary to organically modify CNFs by silanization to improve the interfacial compatibility between CNFs and NR, which can then be used to prepare high‐performance CNF/NR composites. In this study, the effect of plasma‐activated pre‐silanization of CNFs on the vulcanization characteristics, mechanical properties, Payne effect, and dynamic mechanical properties of CNF/NR composites is investigated. The high‐energy impact of the plasma weakens the agglomeration of CNFs and increased the fiber surface roughness, providing a larger contact reaction area for the silanization reaction between the silane coupling agent and CNFs. The results show that the prepared CNF/NR composites have excellent physical and mechanical properties and processing safety. Compared with the unmodified CNF, its DIN wear increases by 4%, tensile strength increases by 23%, reinforcement factor increases by 7%, rolling resistance decreases by 6.3%, and Mooney viscosity decreases by 17.6%. Overall, this study presents a novel approach for the high‐value utilization of CNFs and the preparation of NR composites with exceptional properties, thereby establishing a solid foundation for the application of all‐steel treads.

Methacrylic acid in situ modified steel converter slag/natural rubber composites: Resourceful utilization of steelmaking solid wastes

As a by-product of the steelmaking industry, the large-volume production and accumulation of steel converter slag cause environmental issues such as land occupation and dust pollution. Since metal salts of unsaturated carboxylic acid can be used to reinforce rubber, this study explores the innovative application of in-situ modified steel slag, mainly comprising metal oxides, with methacrylic acid (MAA) as a rubber filler partially replacing carbon black. By etching the surface of steel slag particles with MAA, their surface roughness was increased, and the chemical bonding of metal methacrylate salt was introduced to enhance their interaction with the molecular chain of natural rubber (NR). The results showed that using the steel slag filler effectively shortened the vulcanization molding cycle of NR composites. The MAA in-situ modification effectively improved the interaction between steel slag and NR molecular chains. Meanwhile, the physical and mechanical properties, fatigue properties, and dynamic mechanical properties of the experimental group with MAA in-situ modified steel slag (MAA-in-situ-m-SS) were significantly enhanced compared with those of NR composites partially filled with unmodified slag. With the dosage of 7.5 phr or 10 phr, the above properties matched or even exceeded those of NR composites purely filled with carbon black. More importantly, partially replacing carbon black with modified steel slag reduced fossil fuel consumption and greenhouse gas emission from carbon black production. This study pioneered an effective path for the resourceful utilization of steel slag and the green development of the steelmaking and rubber industries.

Effect of the ratio of carbon nanotubes and carbon black on the properties of natural rubber

In this experiment, the effect of carbon nanotubes (CNTs) replacing some carbon black (CB) on the properties of natural rubber composites was investigated. 5 phr of CNTs were used to replace part of CB in the ratio of m(CNTs) : m(CB reduction) = 1 : X (X from 1 to 4.5). The properties of the vulcanized rubber such as vulcanization, thermal conductivity, tensile, heat generation and processing were investigated experimentally. The results showed that when the ratio of CNTs/CB(reduction) was 1:1, it could substantially improve the crosslink density of the sample and reduce the vulcanization time, while having better processing safety and having the best thermal conductivity. At this time, 5 phr of CNTs and 40 phr of CB were added to the sample, and the dispersion of CB and CNTs in the sample was studied by CB dispersion tester and rubber processing analyzer. The tensile property change regularity tested by rubber tensile tester matched with the experimental results of CB dispersion tester and rubber processing analyzer. When the ratio of CNTs/CB(reduction) was 1:1, it increased the heat generation of the sample significantly. When the ratio of CNTs/CB(reduction) was 1:3.5, all the properties of the sample were better than those of the 1# sample.

Mechanical properties and quantum mechanical simulations of natural rubber composites with cerium complexes under aging conditions

Abstract Enhancing the service life of natural rubber (NR) products, including antioxidants, is crucial to prevent rubber degradation and enhance its oxidation resistance. Phenolic antioxidant 2246 and cerium complex of p-amino salicylic acid (PAS-Ce) are utilized as NR antioxidants. Numerous studies have qualitatively analyzed the antioxidant mechanisms of these compounds. Building upon this perspective, this study quantitatively assessed the protective mechanisms of these antioxidants by combining experimental data with molecular simulations. Additionally, it compared their impacts on the thermal oxidative aging performance of NR. The findings revealed that the PAS-Ce/NR system exhibited the highest mechanical performance retention following multiple days of thermal-oxidative aging. Analyzing the PAS-Ce/NR system through ATR-FTIR and DTA techniques demonstrated that it had the lowest C=O content after thermal-oxidative aging. Furthermore, calculating the activation energy required for thermal-oxidative aging decomposition using the Kissinger and FWO methods indicated that PAS-Ce/NR had the highest activation energy, suggesting superior inhibitory effects against thermal-oxidative aging. Quantum mechanical simulations also illustrated that the dissociation energy of the O-H bond in antioxidants 2246 and PAS-Ce was lower than that of the C-H bond in NR. However, PAS-Ce exhibited a quicker capture of radical species, effectively delaying the oxidation reaction rate of NR molecular chains and thus more efficiently inhibiting the aging process. These insights contribute significantly to comprehending the antioxidative mechanisms in NR aging.

Effect of dispersants on the hydroxyapatite‐filled natural rubber biocomposites with enhanced functional properties

AbstractThe aim of this work was application of the hydroxyapatite (HAP) in various amounts by weight as a filler of natural rubber (NR) biocomposites. Innovatively, silanes, that is, (3‐aminopropyl)‐triethoxysilane (APTES) and bis[3‐(triethoxysilyl)propyl] tetrasulfide (TESPTS), surfactant, that is, cetyltrimethylammonium bromide (CTAB), and alkylimidazolium ionic liquids (ILs) with halide anions, that is, 1‐butyl‐3‐methylimidazolium chloride (BmiCl) and 1‐decyl‐3‐methylimidazolium bromide (DmiBr), were used to improve the dispersion of the HAP and curatives particles in the rubber matrix, and consequently the curing characteristics and properties of NR biocomposites. The influence of HAP and dispersants on the crosslink density, tensile properties, thermal stability, resistance to thermo‐oxidative aging, and ability to damp vibration of vulcanizates were investigated. It has been proven, that HAP can be efficiently used as a filler of NR biocomposites alternatively to commercial inactive or active fillers, for example, chalk, talc, or silica. The optimal HAP content is 30 phr. HAP did not detrimentally affect the curing characteristics of NR composites, crosslink density, and damping properties of the vulcanizates, while significantly raised their tensile strength, thermal stability, and resistance to thermo‐oxidative aging. Most importantly, CTAB and ILs considerably improved the dispersion of HAP and curatives particles in the NR matrix and consequently lowered the vulcanization temperature by approximately 25°C and enhanced by approximately 50% the crosslink density and tensile strength of the NR biocomposites.

Scratch performance of natural rubber and natural rubber composites reinforced with nylon, kevlar, and carbon fabrics

The scratch performance of natural rubber (NR) and fibre-reinforced NR was investigated using a scratch test with acoustic emission (AE). Both maximum penetration depth and maximum tangential force were characterised by two procedures. Procedure 1 applied the corner of a steel cube at face leading orientation. Procedure 2 applied a steel pyramid indenter with a spherical tip at the edge leading orientation. AE was adopted in Procedure 2 for evaluation of cutting damage mode that varied from ploughing/tearing the matrix to cutting both the matrix and fabric. The scratched regions of all specimens were observed using an optical microscope to estimate the damage level and examine damage mechanisms. The results show that scratch resistance improved as fibre content and fibre stiffness increased. The maximum tangential force depended on the damage modes. Two or more fabric layers could further increase penetration resistance, but the damage level is more serious in most cases.

Rapid formation of carbon nanotubes–natural rubber films cured with glutaraldehyde for reducing percolation threshold concentration

Carbon nanotubes (CNTs) filled natural rubber (NR) composites with various CNT contents at 0, 1, 2, 3, 4 and 5 phr were prepared by latex mixing method using glutaraldehyde as curing agent. This work aims to improve the electrical and mechanical properties of CNT filled NR vulcanizates. The CNT dispersion of NR composites was clarified using dispersion grader, optical microscopy and scanning electron microscopy. The electrical properties of NR composites in the existing of CNT networks were studied by following the well-known percolation theory. It was observed that the NR composites exhibited low percolation threshold at 0.98 phr of CNT. Moreover, a three-dimensional network formation of CNT in the NR composites was observed and it is indicated by the t-value of 1.67. The mechanical properties of NR composites in terms of modulus, tensile strength and hardness properties were increased upon the addition of CNT to the optimum mechanical properties at 1 phr of CNT. Therefore, the present work is found the novelty of the study that the conductive rubber latex film can be produced using GA as low-temperature curing agent which enhanced good electrical properties. Moreover, this work is found to be beneficial in case of conductive rubber latex film that requires high modulus at low strain. The additional advantage of this system is the curing process occurs at low-temperature using GA and it can be easily processed.Graphical abstract

Enhancing Natural Rubber Composites with Spent Coffee Ground: Physical Properties, Odor Absorption, and Processing

AbstractThis research aims to enhance natural rubber (NR) properties by incorporating spent coffee grounds (SCGs). Scanning electron microscope (SEM) reveals well‐dispersed SCG particles in the NR matrix without interaction. Shore A hardness notably increases by up to 49.90 (19% higher than unmodified), but tensile and tear strength decline with higher SCG levels. Optimal tear strength occurs at 10 phr of SCG due to uniform dispersion. The 300% modulus remains unchanged. The odor of composites (CO2 absorption) sees a 69.2% increase at 25 phr, while odor absorption efficiency peaks at 2%. Additionally, unmodified SCG affects scorch time (2.12%–23.40% increase from 1 to 20 phr) and cure time (3.12% to 76.82% improvement from 1 to 20 phr). These findings showcase improved hardness, enhanced CO2 absorption capacity, and effective odor control. Additionally, this study sheds light on the influence of SCG on processing times, contributing valuable insights for eco‐friendly applications.

Advancing mechanical performance in sustainable engineering: Synergistic effects of graphene oxide/nano‐silica hybrid nanofiller via latex coagulation in natural rubber composites

AbstractThis research investigates the utilization of a hybrid nanofiller comprising graphene oxide (GO) and amine‐modified nano silica in natural rubber matrix via the latex stage coagulation method. The resulting novel composite materials were characterized comprehensively for their static and dynamic mechanical properties. The hybrid nanofiller exhibited excellent dispersion within the rubber latex, facilitating the formation of a well‐interconnected network structure. The formed network resulted in remarkable improvements in tensile strength, elongation at break, and modulus of the composites. Dynamic mechanical analysis revealed that the hybrid filler (GO/nano‐silica hybrid (GO/NS)) could effectively reinforce the rubber matrix by constraining the mobility of rubber chains, leading to increased stiffness and mechanical strength. In fact, the confinement effect of the nanofillers has been carefully evaluated from dynamic mechanical spectroscopy. The increased glass transition temperature of the rubber nanocomposites specifies the restricted segmental mobility of the rubber chains. Moreover, the hybrid composites displayed significantly low rolling resistance, particularly GO/NS 2 (31% reduction), indicating their potential application as tire treads for fuel‐efficient and green tire manufacturing. The mechanical and rolling resistance properties achieved in these composites can be attributed to the efficient dispersion of the GO/nano‐silica hybrid(GO/NS) nanofiller and the resulting network formation within the rubber matrix. Findings emphasized the composites' viability as sustainable and eco‐friendly tire materials, potential for enhanced fuel efficiency, and reduced environmental footprint in tire manufacturing technology.Highlights The hybrid nanofiller (GO/nano silica hybrid) exhibited excellent dispersion within the rubber latex, leading to the formation of a well‐interconnected network structure. The resulting network structure significantly improved the tensile strength, elongation at break, and modulus of the composite materials. Dynamic mechanical analysis demonstrated that the hybrid filler effectively reinforced the rubber matrix, increasing stiffness and mechanical strength by constraining the mobility of rubber chains. Our hybrid composites displayed a remarkable reduction in rolling resistance, particularly GO/NS2, with a 31% reduction, indicating their potential application as tire treads for fuel‐efficient and green tire manufacturing. The study emphasized the composites viability as sustainable and eco‐friendly tire materials, offering potential benefits for enhanced fuel efficiency and reduced environmental footprint in tire manufacturing technology.

Effect of low-cost mussel-inspired poly(catechol/polyamine) modification of waste brick powder followed by grafting of epoxy elastomers on natural rubber composites

Effect of low-cost mussel-inspired poly(catechol/polyamine) modification of waste brick powder followed by grafting of epoxy elastomers on natural rubber composites

Numerical and Experimental Investigation of Nano zinc Oxide's Effect on the Mechanical Properties of Chloroprene and Natural Rubber (CR/NR) Composites

Nanocomposites, especially natural rubber (NR), have been extensively studied for their unique features and superior performance in tire applications. The present research investigated the impact of zinc oxide nanoparticles (ZnO) on the performance of typical rotary machine seals made of chloroprene rubber / natural rubber (CR/NR) composites. An ordinary standard rubber two-roll mill and hydraulic press were used to prepare high-temperature vulcanized CR/NR samples filled with ZnO nanoparticles. Tensile strength, tear resistance, abrasion resistance, resilience, and hardness were measured to determine the effects of nanoparticles on these physical and mechanical properties. Based on the various hyperelastic modeling schemes, enhancement in multiple characteristics of the control sample, such as overhaul properties, was observed. Furthermore, results show that increasing nanoparticle content in the vulcanisates increased the physicomechanical characteristics, such as hardness, resilience, tensile strength, and elastic Modulus at 200% strain. Moreover, hyperelastic analytical modeling shows that the differences with experimental results are less than 5%.

Preparation of Chitin Nanofibers and Natural Rubber Composites and Their Triboelectric Nanogenerator Applications.

Triboelectric nanogenerators (TENGs) have gained significant attention as promising energy-harvesting devices that convert mechanical energy into electrical energy through charge separation induced by friction and electrostatic induction. In this study, we explore the utilization of biowaste shrimp shell-extracted chitin nanofiber (ChNF) as a viable eco-friendly material for TENG applications. Composite materials were prepared by incorporating ChNF into natural rubber (NRL) at loading levels of 0.1 and 0.2 wt% (NRL/ChNF) to form the TENG triboelectric layer. ChNFs with a uniform width of approximately 10-20 nm were successfully extracted from the shrimp shells through a simple mechanical procedure. The NRL/ChNF composites exhibited enhanced mechanical properties, as evidenced by a higher Young's modulus (3.4 GPa) compared to pure NRL. Additionally, the NRL/ChNF composites demonstrated an increased dielectric constant of 3.3 at 0.1 MHz. Moreover, the surface potential difference of NRL increased from 0.182 V to 1.987 V in the NRL/ChNF composite. When employed as the triboelectric layer in TENG, the NRL/ChNF composites exhibited significant improvement in their output voltage, with it reaching 106.04 ± 2.3 V. This enhancement can be attributed to the increased dielectric constant of NRL/ChNF, leading to enhanced charge exchange and charge density. This study presents a straightforward and environmentally friendly technique for preparing sustainable natural materials suitable for energy-harvesting devices.

Electrically Conductive Natural Rubber Composite Films Reinforced with Graphite Platelets.

Green natural rubber (NR) composites reinforced with synthetic graphite platelets, using alginate as a thickening and dispersing agent, were successfully developed to improve mechanical properties, chemical resistance, and electrical conductivity. The fabrication was performed using a latex aqueous microdispersion process. The research demonstrated the effective incorporation of graphite platelets into the NR matrix up to 60 parts per hundred rubbers (phr) without causing agglomeration or phase separation. Graphite incorporation significantly improved the mechanical strength of the composite films. NR with 60 phr of graphite exhibited the highest Young's modulus of 12.3 MPa, roughly 100 times that of the neat NR film. The reinforcement also strongly improved the hydrophilicity of the composite films, resulting in a higher initial water absorption rate compared to the neat NR film. Moreover, the incorporation of graphite significantly improved the chemical resistance of the composite films against nonpolar solvents, such as toluene. The composite films exhibited biodegradability at about 21% to 30% after 90 days in soil. The electrical conductivity of the composite films was considerably enhanced up to 2.18 × 10-4 S/cm at a graphite loading of 60 phr. According to the improved properties, the developed composites have potential applications in electronic substrates.

Cellulose nanocrystals from oil palm trunk biomass as a bio‐reinforcing filler for improved mechanical properties of modified natural rubber composites

AbstractCellulose nanocrystals (CNC) obtained from biomass are increasingly demanding as a candidate for rubber composite reinforcement due to their sustainability and environmentally friendly characteristics. This work explored CNC extracted from oil palm trunks, an agricultural waste, for its reinforcing efficacy for natural rubber (NR) composite. To achieve good compatibility of the hydrophilic CNC in non‐polar NR, the NR was modified in a simple and green epoxidation condition via its latex stage. The epoxidized natural rubbers (ENR) containing 15% and 25% epoxide content, symbolized as 15E and 25E, respectively, were prepared. The ENR/CNC nanocomposites were fabricated by mixing CNC aqueous suspension and ENR latex, followed by co‐coagulation by methanol. A low amount of CNC (0.5–5 phr) was incorporated into the rubber and it was found that the ENR/CNC nanocomposites showed improvement in mechanical properties compared to the NR/CNC nanocomposite. The 25E/CNC nanocomposite with 1 phr of CNC achieved a 22.6% increase in tensile strength while the 25E/CNC nanocomposite with 2 phr of CNC resulted in a 27.1% increase in tear strength. The enhanced performance of the fully bio‐based rubber nanocomposites is attributed to the CNC–rubber interaction and good CNC dispersion in the ENR matrices, evidenced by the results of SEM and crosslink density.Highlights Cellulose nanocrystal (CNC) was successfully obtained from the oil palm trunk. NR was modified into epoxidized natural rubber (ENR) for increased polarity. ENR/CNC mixing was done in a simple and environmentally friendly latex process. Only 2 phr of CNC resulted in a 27.1% increased tear strength of rubber composite. SEM clearly evidenced improvement of CNC–ENR interaction.

Unveiling the synergistic effect of zinc oxide and carbon black nanoparticles on the dielectric properties of vulcanized natural rubber

Flexible nanocomposite materials were prepared by introducing Zinc Oxide (ZnO) and Carbon Black (CB) as nano-fillers separately into vulcanized natural rubber (NR). The impact of curing agents and filler integration on the structure and electrical characteristics of NR was thoroughly examined. Electrical properties such as dielectric constant, dielectric loss, and ac conductivity were assessed. Pure NR exhibited higher dielectric properties and ac conductivity compared to NR cured with pentane-1,5-deylidenediamine (PDD), which gradually decreased up to a certain threshold due to the immobilization of non-rubber constituents. Dielectric Constant of pure NR decreases from 148.81 to 6.87 upon the addition of 2 ml crosslinking agent into NR. Furthermore, NR composites filled with CB demonstrated lower dielectric properties compared to those filled with ZnO, likely attributed to the polar nature of ZnO. Dielectric Constant of cured NR was increased and exhibited 20.7 for the NR composite with 0.06 % ZnO. The surface roughness of the resulting nanocomposites was analyzed using optical profilometry, and its correlation with dielectric and ac conductivity was investigated.

Influences of compatibilizer type and loading on properties of phenolic resin-crosslinked natural rubber composites filled with sepiolite

Influences of compatibilizer type and loading on properties of phenolic resin-crosslinked natural rubber composites filled with sepiolite

Eugenol and cloves as plant-origin stabilizers in epoxidized natural rubber compositions

Eugenol and cloves as plant-origin stabilizers in epoxidized natural rubber compositions

Role of nanocellulose geometric structures on the properties of green natural rubber composites

Role of nanocellulose geometric structures on the properties of green natural rubber composites