Natural Rubber Composites Research Articles

Self‐reinforced natural rubber composites: Preparation and properties study

AbstractIn the contemporary modern mining sector, rubber conveyor belts are extensively and frequently utilized. Exceptional tear resistance and high elongation of the top cover rubber of the belt are imperative. In this investigation, a portion of natural rubber (NR) underwent partial vulcanization in advance. Subsequently, this pre‐vulcanized NR (PNR) was mixed with the NR matrix via mechanical blending. Due to the increased viscosity resulting from pre‐vulcanization, the PNR may disperse in the NR matrix, maintaining a specific microstructure without complete dissolution. During subsequent vulcanization, the PNR could co‐vulcanize with the NR matrix, forming a well‐bonded interface and ultimately yielding self‐reinforced NR (SNR) composites. The influences of the mass ratio of PNR to the NR matrix, sulfur content in PNR and pre‐vulcanization time on the mechanical properties of the SNR composites were thoroughly investigated. The results indicated that adding PNR effectively improved the tear strength of NR. When the PNR replaced 20 wt% of NR, sulfur content in PNR was 2.4 phr and pre‐vulcanization time was 2 min, the tear strength, stress at 300% elongation and wear resistance of SNR composites increased by 34.1%, 16.6%, and 10.2% compared to NR control sample, while elongation at break remained at 898%. These findings suggest that it is possible to enhance the tear strength of rubber without compromising elongation at break.

Diffusion Behavior of Organic Solvents in Graphene Oxide/Nano Silica Hybrid Natural Rubber Latex Nanocomposite: Experimental and Theoretical Approach

AbstractThis study explores the impact of a graphene oxide (GO)/nano silica (NS) hybrid (GO/NS) filler on the diffusion characteristics of natural rubber (NR) composites when exposed to toluene, xylene, and hexane solvents. The lowest solvent uptake is observed for NR GO/NS 3 (3 phr), which is attributed to forming a robust filler network within the composite. The calculation of crosslink density using the Flory‐Rehner equation reveals significantly higher values for NR GO/NS 3, indicating good crosslinking density in the presence of the hybrid filler. Furthermore, molecular mass between crosslinks (Mc) is calculated, demonstrating a favorable fit with the Affine model. The investigation extends to theoretical modeling, where the Korsemeyer–Peppas and Peppas–Sahlin models are employed to predict solvent uptake behavior. Strikingly, the experimental values exhibit a strong alignment with the Peppas–Sahlin model. This comprehensive analysis provides valuable insights into the diffusion behavior of graphene oxide/nano silica (GO/NS) hybrid‐reinforced natural rubber latex in organic solvents, highlighting potential applications in areas such as solvent‐resistant coatings, barrier materials for chemical storage, and enhanced performance in protective gloves and seals used in harsh chemical environments.

Effect of Mixing Methods and Black Conductive Fillers on Properties of Natural Rubber Composites

Carbon black, graphite, carbon nanofibers, carbon nanotubes, and metal fillers increase composite conductivity in natural rubber, which is electrically insulating. Depending on dispersion, conductive filler lowers insulating material resistivity. These materials are frequently used for electromagnetic/radio frequency interference (EMI/RFI) shielding, conductive flexible seals gaskets, and conductive mats used to prevent electrostatic damage to electronic devices. These elastomers could be used to make flexible solar cells or mechanical-to-electricity devices. Temperature, mixing time, shear rate, and cross-linking during vulcanization affect rubber electrical conductivity of composite. To study shear rate effects, vulcanizate of Natural Rubber-based composites filled with carbon black, millable carbon fiber powder, and synthetic graphite powder was prepared by open mixing (two roll mill) and close mixing (internal mixer). We compared how shear rate affects cure, stress-strain, and volume resistivity of conductive filler-based Natural Rubber composites. Increment in clearance of two roll mill during addition of rubber additives along with rubber of reduced the shearing force resulted in less dispersive and distributive mixing and stagnant points due to band formation on roll surface compared to intermix where compound movement had no stagnation point and long wings pushed material axially and two nogs pushed material in other chamber. Compared to two roll mill samples, the compound reached every point of the mixing chamber for best homogeneity, reducing cure time and improving stress-strain and volume resistivity.

Utilizing Coconut Biochar as a Bio‐reinforcing Agent in Natural Rubber Composites

AbstractThis research investigates the pyrolysis of biochar from different parts of residual aromatic young coconut waste, namely coconut fruit, coconut bunch, and coconut leaf, to be used as fillers in natural rubber (NR). Scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy reveals that biochar has a flake‐like structure with a high carbon content (67%–77%). The biochar is mixed with NR using a two‐roll mill at filler contents of 0, 10, 20, 30, and 40 phr (part per hundred of rubber). Adding coconut fruit biochar at 40 phr increases the Shore A hardness to 59.62, a remarkable 47% improvement compared with unfilled NR. The maximum tensile strength occurs at 20 phr, while the highest tensile modulus (4.53 MPa) and tear strength (17,344 N m−1) are observed at 40 phr. Moreover, the swelling index of composites in toluene decreases slightly as biochar content increases, and the crosslink density is higher for NR filled with coconut fruit biochar than for other biochar types. Based on these results, coconut fruit biochar is identified as the most effective reinforcement filler for NR among the biochar types studied. Consequently, it can be used as a bio‐reinforcing agent in NR composites, contributing to sustainability and eco‐friendliness.

Influence of Different Grafted Natural Rubbers on Electrical and Mechanical Properties of Natural Rubber/Carbon Nanotubes Composites

This study investigates the augmentation of electrical and mechanical characteristics of natural rubber (NR) film with different forms by integrating carbon nanotubes (CNTs). NR with different forms (i.e., natural rubber grafted with polystyrene (NR–g–PS) and polybutyl methacrylate (NR–g–PBMA)) were successfully synthesized. The success of these grafting was confirmed through Proton Nuclear Magnetic Resonance (1H–NMR) and Attenuated Total Reflectance–Fourier Transform Infrared (ATR–FTIR) analyses, which showed that the grafting efficiency exceeded 90%. The properties of ungrafted NR and grafted NRs with CNTs were compared and analyzed. It was found that the NR/CNTs composites with grafting displayed significantly improved electrical properties and mechanical strength when compared to the NR/CNTs composites without grafting. It was found that the NR–g–PBMA exhibited an 860% increase in electrical conductivity at 100 kHz compared to ungrafted NR. This might be attributed to the synergistic of the high specific surface of CNTs and the high polarization of functional groups, which gave a higher value for the CNTs filled grafted NR than the ungrafted NR. Moreover, the mechanical properties of NR–g–PS composites showed a 114% increase in 100% modulus, 127% in tensile strength, and 37% in hardness, while the NR–g–PBMA composites exhibited a 159% increase in 100% modulus, 95% in tensile strength, and 34% in hardness compared to ungrafted NR. This enhancement can be attributed to the formation of chemical linkages between the grafted NR matrix and CNTs through functional groups from both. Consequently, it can be concluded that introducing functional groups on grafted NR assists in establishing a crosslinking network, enhancing both the mechanical and electrical properties. Additionally, this research emphasizes the benefits of producing flexible conductive materials with high modulus and enhanced electrical properties. Keywords: Natural rubber latex, Graft copolymerization, Glutaraldehyde, Natural rubber composites, Electrical properties

Effect of Nanoclay Modification on Properties of Natural Rubber Nanocomposites Using Zinc Compound

This study investigates the effect of nanoclay modification on the properties of natural rubber (NR) nanocomposites using zinc stearate (ZS) and di(hydrogenated tallow) dimethylammonium chloride (DHDT). The aim is to enhance the compatibility of modified nanoclay (NC) and NR molecules for determining cure characteristics, mechanical properties, and morphologies. The effect of unmodified and modified NC as the secondary filler was studied using the 10 phr NC regarding the received properties of the silica-based composites. Results indicated that the NR composites with modified NC exhibited a significant improvement of 32.06% estimated crosslink density, 16.6% tensile strength, 30.1% Payne effect together with the production time of 3.9 min relative to the composites with unmodified NC. This related to the dispersion and distribution degree of the NC and it suggests that the modification of nanoclay with ZS and DHDT can positively impact to the NR nanocomposites, enhancing their mechanical performance and processing characteristics. Keywords: Modified nanoclay, Natural rubber, Nanocomposites

Wear and friction properties of pineapple leaf fibers‐reinforced natural rubber composites with the influence of multi‐walled carbon nanotubes

Wear and friction properties of pineapple leaf fibers‐reinforced natural rubber composites with the influence of multi‐walled carbon nanotubes

Application of bio-based vegetable oils as processing aids in industrial natural rubber composites

Application of bio-based vegetable oils as processing aids in industrial natural rubber composites

High-value application of kaolin by wet mixing method in low heat generation and high wear-resistant natural rubber composites

In this study, a silane coupling agent and kaolin, a natural mineral resource, were introduced into the wet mixing process of natural rubber latex, the high wear-resistant and low-generation heat natural rubber composites were prepared. The sputtering, collision, and deposition of coupling agent/fillers/natural rubber latex mixed emulsion onto the roller effectively could break up the filler aggregates, enable fillers to be better infiltrated, distributed, and dispersed in the rubber. The effects of dry/wet mixing processes and the ratio of kaolin to silica on the crosslinking density, filler dispersion, extrusion rheological properties, gas barrier properties, dynamic mechanical properties and thermal stability of NR composites were investigated, and the silanization mechanism was summarized by FTIR and XRD. The experimental results showed that kaolin improved the crosslinking density and failure temperature, reduced the Payne effect, extrusion swell, and rolling resistance. Compared with 60 phr silica-filled natural rubber, the gas barrier property and wear resistance of 60 phr kaolin-filled natural rubber were improved by 64 % and 27 %, respectively, and the rolling resistance was reduced by 57 %. When the ratios of silica to kaolin were both 20:40, the crosslinking density, gas barrier property, and wear resistance of wet mixing were improved by 24 %, 45 %, and 9 %, respectively, compared with dry mixing. This study provided a new method for the high-value application of kaolin in wet mixing and green tires.

Surface one-step modification of graphene oxide with N-cyclohexylbenzothiazole-2-sulfonamide to enhance the wear resistance of natural rubber/butadiene rubber composites

Natural rubber (NR) and butadiene rubber (BR) composites are frequently used in manufacturing tires and conveyor belts, which are susceptible to severe wear, leading to product failure and significant losses. To enhance the wear resistance of NR/BR composites, we prepared NR/BR composites reinforced with a synergy of N-cyclohexylbenzothiazole-2-sulfonamide surface one-step modified reduced graphene oxide (CZ-rGO) and carbon black N234 (CB) using a latex co-precipitation method. This study explored the effects of GO content and CZ modification on the structure, wear resistance, thermal conductivity, and mechanical properties of the NR/BR blended composites. It showed that adding 2 phr of GO resulted in excellent filler dispersion, significantly improving the tensile strength, elongation at break, tear strength, thermal conductivity, and wear resistance of the composites. The incorporation of CZ-rGO further increased the crosslinking density, vulcanization performance, and filler dispersion with enhanced mechanical properties, thermal conductivity, and wear resistance of the composites. Notably, the DIN abrasion volume was reduced to 77.88 mm³, surpassing the ISO 10247 standard for conveyor belt cover rubber in terms of wear resistance. The wear resistance of NR/BR/CZ-rGO composites is not only significantly higher than that of single NR- or SBR-based rubber composites, but also significantly higher than that of other binary rubber blend composites, and the CZ-rGO filler is simpler in composition and structure and exhibits a more prominent wear enhancement. This work provides guidance for an efficient and environmentally friendly approach to GO surface modification, as well as useful insights for the development of high wear-resistant rubber composites with excellent overall performance.

Bio-functionalization of fillers with natural phytic acid for sustainable flame-retardant agents for natural rubber composites

The current challenge for sustainable flame retardants has led to innovative approaches, including the utilization of natural substances to enhance the fire resistance of elastomer composites. This paper presents the design of eco-friendly hybrid flame-retardant additives based on mineral fillers (hydrotalcite (LDH) and sepiolite (SEP)) modified with aminosilane (APTS) and phytic acid (PA) for natural rubber (NR) biocomposites. The synergistic effects of the PA and silanized mineral fillers resulted in NR composites with improved thermal, mechanical, and barrier properties, as well as increased flame retardancy. Importantly, it was proven that direct in-situ application of PA into elastomer cured with sulphur-based crosslinking systems is ineffective, due to its negative effect on the curing process (significantly reducing torque moment). Binding the PA onto silanized fillers enabled the creation of hybrid additives that leverage the flame-retardant benefits of PA without compromising the other properties of the polymer. The addition of PA-modified fillers to NR reduced the heat release rate (HRR) by around 40 %, indicating outstanding flame retardancy. This work makes a significant contribution and expands the understanding of using eco-friendly natural compounds to reduce the flammability of sulfur-cured elastomers.

Application of low‐molecular‐weight polyethylene glycol‐modified silica in natural rubber composites

AbstractSilica serves as the primary filler in the fabrication of eco‐friendly tires, and achieving an optimal dispersion of polar silica within the natural rubber matrix is crucial for crafting high‐performance rubber composites. In this study, biodegradable surfactants polyethylene glycol (PEG) with molecular weights of 200, 400, and 800 were employed to modify silica. The modified silica was characterized by Fourier‐transform infrared spectroscopy; PEG‐modified silica with different molecular weights was compounded with Si69, a conventional silane coupling agent, in the formulation. This aimed to reduce Si69 dosage and mitigate the emission of volatile organic gases, such as ethanol, generated during the silanization reaction between Si69 and silica. Experimental findings revealed that compared with natural rubber composites containing six parts of Si69, the addition of PEG‐modified silica enhanced filler dispersion in the composite while reducing Si69 dosage by three parts. This led to accelerated vulcanization rates, effectively decreased energy consumption during production, and significantly improved wet slip resistance, while maintaining optimal rolling resistance. Rubber composites prepared with PEG800‐modified silica exhibited a 10% increase in elongation at break, a 12% increase in tensile product coefficient, and a 19% enhancement in wet slip resistance.Highlights Silica is modified by polyethylene glycol with molecular weight of 200, 400, and 800. The amount of silane coupling agent and VOC emissions are reduced. The interfacial bonding between silica and rubber matrix is enhanced. The tensile product coefficient and wet slip resistance are improved by 12% and 19%.

Preparation of aqueous silane‐graphene oxide co‐modified cellulose fibers/natural rubber composites via flash extrusion dispersion process

AbstractCellulose fibers were modified via aqueous silane‐graphene oxide (GO) coordination by flash drying and extrusion dispersion process. The adsorption of GO reduced the polarity of the cellulose fiber surface and attenuated the agglomeration effect between the cellulose fibers, thus facilitating the dispersion of fibers in the rubber matrix. Adding aqueous 3‐aminopropylsilane oligomer (8150) incorporated active sites on the surface of cellulose fibers, thereby improving the interfacial binding properties of cellulose nano fibers (CNFs) and natural rubber (NR). After blending the modified CNFs with NR latex, high‐temperature flocculation was performed using an atomised flash device. Finally, CNF/NR was pre‐dispersed through a twin‐screw extruder, after which a CNF/NR masterbatch with excellent performance was prepared. Experimental results revealed that composites prepared using GO‐8150 via the flash drying‐twin‐screw dispersion process exhibited excellent dispersion characteristics, processing properties, mechanical properties, rolling resistance, wear resistance, and heat generation properties. Compared with traditional dry mixing, the composites prepared by flash drying‐twin‐screw dispersion process showed a 16.95% increase in tensile strength, 16.07% increase in 300% constant elongation, 19.01% reduction in abrasion consumption, 42.26% reduction in rolling resistance, and a reduction in the Payne effect. This study offers an efficient and environmentally friendly method for the high‐value utilization of natural fibers and the preparation of NR composites with excellent properties, while providing a green and nonpolluting modification process with no acidic liquid discharge.Highlights GO‐8150 reduces the polarity of the fibers and promotes dispersion. The flash extrusion dispersion process achieves green flocculation. 42% lower rolling resistance for rubber composites.

Glycidyl methacrylate-modified diatomite as reinforcing filler for natural rubber composite

Glycidyl methacrylate-modified diatomite as reinforcing filler for natural rubber composite

Waste nylon fishing net fiber incorporated natural rubber composites as a remedy for waste reusing into a value‐added material

AbstractThis study focuses on reusing the waste fishing nets with natural rubber (NR) to create a value‐added composite material. WNF fibers at different loadings (2, 4, and 6 phr) and lengths (2, 3, 5, and 7 mm) were investigated for a general tire formulation. The anisotropic nature of WNF was evident in tear strength, with optimal results for 2 mm, 2 phr fiber loading. It displayed 15.87% improvement longitudinally compared with the control. Further, it displayed improved 5.55% hardness, whereas resilience, abrasion volume loss, and tensile strength were decreased. In the second stage, these fibers treated with KOH (2%, 6%, and 10%) with the expectation of enhancing the mechanical properties. The 2% KOH‐treated sample presented a significant escalation in hardness (+12.50%), resilience (+6.25%), abrasion volume loss (+3.63%), tear strength (+17.23%), and tensile strength (+8.20%) as of the control. Partial replacement of carbon black (CB) with 2% KOH treated 2 mm 2 phr WNF was evaluated. A 9% of CB in rubber compound was easily supersede by WNF. Our findings indicated that WNF fibers could be reuse as a filler in rubber composite where special property enhancements are advantageous in tire technology.

Natural Rubber/Styrene-Butadiene Rubber Blend Composites Potentially Applied in Damping Bearings.

Natural rubber (NR) composites have been widely applied in damping products to reduce harmful vibrations, while rubber with only a single composition barely meets performance requirements. In this study, rubber blend composites including various ratios of NR and styrene butadiene rubber (SBR) were prepared via the conventional mechanical blending method. The effects of the rubber components on the compression set, compression fatigue temperature rising and the thermal oxidative aging properties of the NR/SBR blend composites were investigated. Meanwhile, the dynamic mechanical thermal analyzer and rubber processing analyzer were used to characterize the dynamic viscoelasticity of the NR/SBR blend composites. It was shown that, with the increase in the SBR ratio, the vulcanization rate of the composites increased significantly, while the compression fatigue temperature rising of the composites decreased gradually from 47 °C (0% SBR ratio) to 31 °C (50% SBR ratio). The compression set of the composites remained at ~33% when the SBR ratio was no more than 20%, and increased gradually when the SBR ratio was more than 20%.

Preparation and characterization of lignin copolymerized phenolic resins with superior stiffening effect for natural rubber composites

The development of lignin-derived functional additives for rubber composites has gained growing importance in light of biomass valorization. This work aims at preparing phenolic novolak resin with lignin as one building block for reinforcing natural rubber. A one-pot two-step synthetic approach involving phenolation and copolymerization was developed to prepare lignin-phenol-formaldehyde resins (LPF), wherein 30 wt% of phenol was substituted by lignin. With increasing the ratio of formaldehyde/phenol functionality (F/P), resins show increased molecular weight, elevated glass transition temperature and declined curing activity. The resin with F/P of 0.68/1 exhibits a higher stiffening effect compared to the control without lignin. This enhancement is attributed to lignin's ability to form a hyperbranched structure with multiple phenolic arms as implied by GPC results, acting as a crosslinking hub and facilitating the formation of an effective network. Furthermore, we introduced cardanol with a flexible alkene chain to prepare cardanol-lignin-phenol-formaldehyde resins (CLPF). The CLPF15 resin with cardanol/lignin/phenol of 15/30/55 wt% achieves the maximum stiffening effect due to improved compatibility with natural rubber. This study provides insights into the design and optimization of lignin-copolymerized resins for enhancing the mechanical properties of rubber composites.

Research Progress of Natural Rubber Wet Mixing Technology.

The performance of natural rubber (NR), a naturally occurring and sustainable material, can be greatly enhanced by adding different fillers to the NR matrix. The homogeneous dispersion of fillers in the NR matrix is a key factor in their ability to reinforce. As a novel method, wet mixing technology may effectively provide good filler dispersion in the NR matrix while overcoming the drawbacks of conventional dry mixing. This study examines the literature on wet mixing fillers, such as graphene, carbon nanotubes, silica, carbon black, and others, to prepare natural rubber composites. It also focuses on the wet preparation techniques and key characteristics of these fillers. Furthermore, the mechanism of filler reinforcement is also examined. To give guidance for the future development of wet mixing technology, this study also highlights the shortcomings of the current system and the urgent need to address them.

Physico-Mechanical Properties of Cellulose Fibers Reinforced Thermoplastic Natural Rubber Composites: Effects of Fiber Size and Fiber Content

Physico-Mechanical Properties of Cellulose Fibers Reinforced Thermoplastic Natural Rubber Composites: Effects of Fiber Size and Fiber Content

Green, simple, and rapid construction of coating on aramid fiber surfaces and their effects on the mechanical properties of aramid fiber/rubber composite interfaces

First, the surface of aramid fibers (AF) was etched using plasma to enhance the roughness of the AF. The coating was then formed on the surface of the AF by solution dip-coating using a polymerizable deep eutectic solvent (PDES) and in-situ UV cured for 10 s. The study examined the impact of varying etching times on the interfacial properties between AF and natural rubber (NR). The atomic force microscopy images showed that the surface roughness gradually increased with the increase of etching time, and the interphase width gradually increased. A modulus interfacial layer with a platform role was established between high-modulus aramid fibers and low-modulus rubber. And when the etching time was 4 s/cm, the H pull-out force increased by 193.51% compared to the original AF and reached 18.08 N of the maximum strength. Comprehensively comparing the single fiber tensile strength, composite tensile strength and composite fatigue resistance, the AF-reinforced NR composites can be optimized when the treatment time is 3 s/cm. In sum up, this method of constructing a coating on the AF surface by etching first will lead to a great improvement in the interfacial properties between AF and NR, this method enables simple, green and continuous construction of coating on AF surfaces, making them have great application prospects in the field of aviation tires.