Molecular Chains Of Rubber Research Articles

Investigation on recycling and reprocessing ability of self-healing natural rubber based on ionic crosslink network

Abstract Natural rubber (NR) is a complex material that is often discarded due to its three-dimensional structure. Recycling of rubber is difficult due to its complex structure, and only 1.7 million tonnes of waste, such as tyres and gloves, are considered recyclable. This study aims to develop self-healing rubber, which allows a product to recover without affecting structural reliability. Commercial NR was ionically crosslinked with zinc thiolate, forming an ionic crosslink network between rubber chains and zinc thiolate ions. The ionic crosslinks allow the rearrangement of rubber molecular chains under external heat, providing self-healing capabilities. The highest ionic crosslink density was found in NR with 35 phr zinc thiolate. The self-healing NR can recover 90 % of its initial properties at room temperature for 10 min and can be reprocessed and recycled three times without compromising its properties. It also shows excellent weldability, making it a promising material for repairing existing rubber products in heavy engineering applications.

Self-Healing Flexible Sensor Based on Epoxidized Natural Rubber with the Synergistic Effect of Coordination and Hydrogen Bonds.

The use of highly tensile and self-healing conductive composites has gained considerable interest due to their wide range of applications in healthcare, sensors, and robotics. Epoxidized natural rubber (ENR), known for its ability to undergo highly reversible deformation, can be utilized in strain sensors to effectively transmit a broader range of signal changes. In this study, we introduced a self-healing ENR composite specifically designed for high-strain sensors. The rubber molecular chains were enhanced with hydrogen bonds and metal coordination bonds, allowing the matrix material to autonomously repair itself through these interactions. Following a repair period of 12 h at 45 °C, the composites achieve a repair efficiency exceeding 90%. Furthermore, by incorporating conductive fillers into the matrix using multistage layering, the resulting composite has good electrical conductivity, thermal conductivity, and hydrophobicity. In addition, this composite presents good sensitivity even at large strain (strain in the range of 50-200%, GF = 7.65). In conclusion, this self-healing nanocomposite, characterized by its high strain sensitivity, holds immense potential for various strain sensor applications.

Predicting the glass transition temperature and solubility parameter between rubber/silica and rubber/resins via all‐atom molecular dynamics simulation

AbstractResin is a widely used additive in rubber composites, which not only improves the processing properties of the composites but also enhances their mechanical properties, rolling resistance and wear resistance. However, there are specific differences in compatibility among resin, rubber and silica, which directly affect the performance of the composite materials. In this work, we first computed the glass transition temperature () of five resins in styrene−butadiene rubber (SBR) composites to prove the reliability of the computational method. Then, we explored the effects of different components and resin types on of SBR and found that the addition of silica can increase due to weak attractive interactions between silica and rubber molecular chains, which restrict the movement of the molecular chains. Furthermore, using solubility parameters, we analyzed the compatibility of rubber and five different resins and found that all five resins had good compatibility with rubber, especially C5/C9 copolymerized petroleum resin and hydrogenated resin. Finally, we revealed that there is a mutually attractive force between resin and silica. In summary, understanding the interactions among resins, silica and rubber is crucial for optimizing the performance of composite materials. © 2024 Society of Chemical Industry.

Facile Preparation of Lightweight Natural Rubber Nanocomposite Foams with High Wear Resistance.

The light weight and excellent mechanical properties of rubber foam means that it is widely applied in the aerospace, automobile, and military industries. However, its poor wear resistance contributes directly to a short service life and a waste of resources. Therefore, the design and development of high-wear-resistance rubber foam are of great importance. In this work, some nanoclay/rubber composite foams were prepared by blending NR/EPDM with different kinds of nanoclays containing layered double hydroxide (LDH), montmorillonite (MMT), and attapulgite (ATP) to indicate the effects of the kinds of nanoclays on the wear resistance and mechanical properties of nanoclay/rubber composite foams. The kinds of nanoclay/rubber composite foams were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The results showed that nanoclay has heterogeneous nucleation in composite foamed materials. The wear resistance of the composite foam materials with added nanoclay was significantly improved, and the MMT of the lamellar structure (increased by 43.35%) and LDH (increased by 38.57%) were significantly higher than the ATP of the rod-like structure (increased by 13.04%). The improvement in the wear resistance of the matrix was even higher. Compared with other foams, the wear resistance of the OMMT-NR/EPDM foam (increased by 58.89%) with a lamellar structure had the best wear resistance. Due to the increase in the lamellar spacing of the modified OMMT, the exfoliation of worn rubber molecular chains has little effect on the adjacent molecular chains, which prevents the occurrence of crimp wear and further improves the wear resistance of composite foaming materials. Therefore, this work lays the foundation for the manufacturing of rubber foams for wear-resistant applications.

Simultaneously achieving excellent heat aging resistance and grip performance in carbon black/glass flake/EPDM rubber composite for overhead line spacers

The preparation of wire clamp rubber with semiconductivity, low compression set (C-Set), high mechanical strength, heat aging resistance, and high grip strength is vital for overhead line spacers. This study delves into the formulation design of high-performance ethylene-propylene-diene monomer (EPDM) composite materials for wire clamp rubber. The effects of the vulcanization system, carbon black type, and loading on the essential material properties of EPDM rubber were investigated. The results showed that a hybrid vulcanization system containing peroxide and sulfur simultaneously endowed EPDM rubber with high elasticity and tear strength. N330 carbon black-filled EPDM rubber had the advantages of semiconductivity and high tensile strength, and N774 carbon black-filled EPDM rubber exhibited low C-Set and high heat aging resistance. When EPDM rubber was reinforced with the mixture of 50 phr N330 and 20 phr N774 carbon black, the rubber synchronously exhibited semiconductivity (2.64×106 Ω·cm), high tensile strength (20.2 MPa), low C-Set (32.5%, 150°C×3d), and high heat aging resistance (maintaining 98% of its initial tensile strength after aging at 150°C for 3d). In addition, introducing a 10-phr glass flake into EPDM wire clamp rubber improved the grip force by 83%. The improvement mechanism may be attributed to the increased compression stress of wire clamp rubber on cable and the restricted slippage of rubber molecular chains.

The impact of synergistic action of methacrylic acid/zinc oxide/carbon nanotubes on metal Friction and wear

The continuous operation of essential refining equipment, internal mixers, leads to wear on their end faces, resulting in an increased gap between the mixer chamber and the end face. This, in turn, causes material leakage, reducing mixing efficiency and adversely impacting rubber performance. Therefore, investigating metal wear on the mixer's end face during the mixing process is essential. Scholars have introduced dynamic covalent bonds into rubber molecular chains, bestowing self-repairing capabilities upon the materials. This innovation has significant implications for extending rubber lifespan and lowering production costs. It involves adding methacrylic acid (MAA) and excess zinc oxide (ZnO) to construct an ionic crosslinking network, limiting covalent crosslinking of rubber molecules and enabling in-situ polymerization of MAA/ZnO, resulting in self-repairing properties. However, it is crucial to consider corrosive wear induced by MAA's strong acidity on metals. This study combines MAA, ZnO, and multi-walled carbon nanotubes (MWCNTs) through mechanical mixing to create a composite material called zinc methacrylate (ZDMA)/MWCNTs/rubber. The research investigates the in-situ synthesis mechanism of MAA and ZnO and the synergistic mechanism of ZDMA and MWCNTs. The study analyzes the impact of MWCNTs additive amount on the frictional wear of the internal mixer's metal end face. During the mixing process, ZDMA is grafted and polymerized onto rubber's macromolecular chains, forming ionic pairs with strong electrostatic interactions, creating a primarily reversible supramolecular network dominated by ion crosslinking. This ion crosslinking network, along with the three-dimensional mesh structure of MWCNTs, establishes a stable spatial structure within the rubber matrix. The study reveals that increasing the MWCNTs content to 3 phr reduces the aggregation of SiO2 particles and ZDMA granules within the rubber matrix, resulting in reduced friction coefficients, roughness, and wear rates of the metal. However, exceeding 3 phr of MAA content leads to excessive MWCNT aggregation within the rubber matrix, increasing wear rates, roughness, and friction coefficients due to hindrance of rubber macromolecular chain crosslinking and reduced SiO2 particle dispersion within the rubber matrix. These findings provide valuable insights into the dynamics of frictional wear in internal mixers.

Two-stage thiol-ene click reaction for fluorine-free superhydrophobic fabrics with buoyancy boost and drag reduction

Superhydrophobic fabrics suggest tremendous potential in some emerging fields such as electronic skin, bioelectronic sensors and special clothing due to their excellent liquid repellency and self-cleaning properties. However, currently reported superhydrophobic materials are usually prepared using biologically toxic fluorinated compounds, which severely restricts their practical applications. Herein, we propose a two-step thiol-ene click reaction strategy to fabricate fluorine-free superhydrophobic cotton fibers (Fabric-SH-PB-SiO2). The 1,2-polybutadiene (1,2-PB) with flexible rubber molecular chains and low surface energy was coated by cotton fiber through thiol-ene click reaction. Subsequently, based on this reaction, the coated cotton fiber was used to establish chemical bonds with hydrophobic silica. The Fabric-SH-PB-SiO2 possesses a rich multi-level micro-nano structure that can form stable air layer on the surface of the fabric, which showed a high hydrophobic angle of 156° and exhibited some distinct advantages such as anti-fouling and self-cleaning characteristics, high buoyancy, and reduced drag. More remarkably, the Fabric-SH-PB-SiO2 could float on the water surface after carrying 34 times its weight. Compared with unmodified fabrics, the Fabric-SH-PB-SiO2 demonstrated a high drag reduction rate of up to 102 %, among the highest values for the reported hydrophobic materials. The strategy developed here provides insights towards fabricating high-buoyancy fluorine-free superhydrophobic cotton fibers.

Enhancing self‐healing efficiency of natural rubber composites using halloysite nanotubes

AbstractThis study aimed to explore the reinforcement effect of halloysite nanotubes (HNTs) in self‐healing natural rubber based on metal thiolate ion networks. The amount of HNTs was varied at five levels (2, 4, 6, 8, and 10 phr) in order to assess the optimum amount of filler for self‐healing efficiency and mechanical recovery performance. Fourier‐transform infrared (FTIR) provides evidence for the reversible ionic bonding, facilitated by Zn2+ and S− bonding from the metal thiolate vulcanization with rubber molecular chains. Scanning electron microscopy (SEM) revealed that the NR/HNTs composites with lower filler loading exhibited better recovery, as there were no observable gaps between the cut surfaces of the samples. The results also revealed that addition of HNTs resulted in a significant improvement in the mechanical performance, particularly the tensile strength, which increased by approximately 20%–75%. Furthermore, the extent of healing after the broken pieces were brought in contact with each other varied from 87% to 98%, depending on HNT concentration.Highlights Fabrication of self‐healing elastomers based on natural rubber. Self‐healing NR presented enhanced mechanical performance with addition of HNTs. HNTs lumen endows the composites with excellent self‐healing efficiency. Developed NR/HNTs composite exhibited room temperature self‐healing properties. Reversible ionic bonding expedited by Zn2+ contributes in excellent self‐healing.

Coordinated control study of oil, wax, and antioxidants on tire sidewall rubber discoloration and fatigue properties

AbstractSidewall discoloration and fatigue directly affect the aesthetic value and functional efficiency of tires during their service life. This study designed L9 orthogonal experiments with oil, wax, and antioxidant as factors to study their effects on the discoloration and fatigue performance of tire sidewall rubber. Molecular dynamics simulation calculations, nonlinear finite element analysis, and modern characterization methods were adopted for the investigation. The findings indicated that antioxidant precipitation was the main cause of sidewall discoloration; aromatic oil accelerated sidewall discoloration and the expansion of tire sidewall fatigue cracks; and microcrystalline wax enhanced the fatigue properties of rubber compounds by halting the aging and breakdown of rubber molecular chains. This paper provides insights into the coordinated control and formulation optimization of tire sidewall material discoloration and fatigue life. Furthermore, it helps to reduce waste tires and sidewall chemical release into the environment.

Preparation of potassium oleate-kaolin/natural rubber composites by ball milling combined with gas-phase spray drying technology

In order to realize the high value-added utilization of natural clay materials in natural rubber composites, an environment-friendly animal glycerol potassium salt was introduced to modify kaolin, and the natural rubber with excellent performance were prepared by high-energy ball milling combined with gas-phase spray drying technology. The impact of the ball milling reduced the particle size and increased the specific surface area of kaolin, promoting the chemical modification of kaolin by potassium oleate. The gas-phase spray technology effectively broke the filler aggregates, and the high-temperature roller realized the instantaneous drying, reducing the oxidation and fracture of the rubber molecular chains. In this paper, the gas barrier properties, mechanical properties, anti-aging properties, dynamic mechanical properties and Payne effect of the composites were investigated. The FTIR, XPS and interfacial contact angle demonstrated the existence of a stable chemical bonding in the process of potassium oleate-modified kaolin, and the hydrophilicity of kaolin was reduced. Kaolin was uniformly and finely dispersed in the rubber matrix by spray drying technology. Compared with the traditional dry mixing, the composites prepared by the technology improved the gas barrier properties, processing properties, comprehensive mechanical properties, and the aging coefficient increased by 23.1%, and had excellent wet skid resistance and rolling resistance.

Facile preparation of Cross-linked polyester composite rubber with excellent mechanical strength and high toughness by loading adjustable Low-cost clay

Preparing polymeric elastomer materials with high strength, high toughness yet low energy dissipation has been a long-standing challenge. In this work, we report a dual synergistic strengthening strategy, based on building a vulcanized cross-linked network and regulating nano clay loading, for preparing a novel butyl phenyl polyester nano clay composite rubber. The molecular monomers 2-hydroxyethyl acrylate (HEA) and acrylonitrile (AN) were grafted on the rubber molecular chains, which facilitated the optimization of the crosslinking of the flexible segments. Meanwhile, a rigid unit-flexible chain segment network structure is constructed by regulating the grafting of functionally modified ball clay (BC) in the molecular chain segments. This cross-linking and filling structure provides maximum resistance to energy loss and reinforces the mechanical properties of the composite rubber. Experiments confirmed that BC strengthens the intermolecular forces through Si-O bond and Si-N bond on the macromolecular chain. Compared with raw rubber, the composite rubber with BC loading of 20 wt% has a 327.3% increase in tensile strength and a 249.5% increase in toughness, and presents huge advantages in fatigue resistance and environmental stability, yet the BC filler has extremely low cost. This work provides a new insight in creating rubber/nano clay composites with excellent mechanical strength and dynamic properties, showing high potential for industrialization.

Self‐healing natural rubber based on dynamic disulphide exchange towards fatigue lifetime extension

AbstractDynamic disulphide exchange mechanism was introduced to promote self‐healing characteristics to natural rubber compound and the corresponding healing mechanism and mechanical properties are presented. The formation of reversible dynamic disulphide bonds within rubber molecular chains was evidenced via FTIR and the total crosslink density of dynamic disulphide crosslinks was quantitatively measured by equilibrium swelling test. Scanning Electron Microscopy (SEM) results revealed that the healed area of the fractured surface adhered well with minor scar on the contact surface, suggesting that intermolecular diffusion occur at the fracture surface. It was also found that the tensile strength and tear strength of the broken samples able to recover 91% and 103%, respectively, under thermal healing at 150°C for 10 min. The fatigue lifespan of the materials increased 154.9% compared with the conventional rubber. The successful fabrication of self‐healing natural rubber through dynamically reversible disulphide exchange mechanism would be expected to open up new opportunities for development of sustainable rubber products.

Designing the cross-linked network to tailor the mechanical fracture of elastomeric polymer materials

Understanding the elastomer fatigue mechanism under a cyclic loading is of vital importance in fabricating elastomer nanocomposites with high performance. Based on the microstructural evolution and the mechanical response under the dynamic periodic loading, the molecular mechanism about the effect of cross-linked network (including crosslink bond type and crosslink density) on the fatigue resistance was examined by adopting coarse-grained molecular dynamics simulation. The result shows that the elastomer molecular chains are more prone to disentangle and orientate in the polysulfide system, compared to those monosulfide and disulfide systems. Rubber molecular chains can uniformly sustain the external tensile stress in the polysulfide system, which is beneficial to avoid the rapture of rubber molecules. With the increase of the crosslink density, increase to a plateau. In the presence of saturated network size, an optimum crosslink density and distribution for rubber nanocomposites appears, avoiding the possibilities of rubber molecule rupture. This work provides some insights on understanding the relationship between the cross-linked network and the fatigue performance of the rubber composites at the molecular level, expecting to provide some guidelines for preparing elastomeric materials with high fatigue resistance. • Investigation on the microstructural evolution and the mechanical response of elastomer under the dynamic periodic loading by MD simulation. • Quantified the size of the cross-linked network by the molecular weight (Mc, Mc n , Mt n ) of the network chain. • The polysulfide crosslinker is conducive to the disentangle and orientate of elastomer chains which inhibits the rupture of the chemical bonds. • The optimal crosslinking density corresponds to saturated crosslinking network size.

Preparation of silica/natural rubber masterbatch using solution compounding

There are increasing concerns about the global issues of carbon peak and carbon neutrality. The tire labeling laws about rolling resistance performance requirements have been revised accordingly. Energy-efficient “green tires,” with a lower rolling resistance, are becoming an important development direction for the tire industry. Herein, a method is proposed for preparing a silica/natural rubber (NR) masterbatch using solution compounding. The dispersion of silica in the rubber matrix was improved through the liquid-phase mixing process. Further, the loss factor (tanδ) of the rubber was reduced, ultimately reducing the rolling resistance of the material. Specifically, the modified silica slurry was prepared in cyclohexane with an interfacial modification technology, and the mixing between the silica and rubber molecular chains was completed in the organic phase. Favorable processing properties were confirmed using the Mooney viscosity test. Compared with the in situ modified silica/NR composites made using dry blending, the silica/NR composites made via solution compounding had better filler dispersion, better mechanical properties, lower tanδ and lower rolling resistance. Thus, the preparation of a silica/NR masterbatch using solution compounding provides a new procedure for the preparation of silica/NR compounds with excellent performance for “green tires.”

Molecule Dynamics Simulation of the Effect of Oxidative Aging on Properties of Nitrile Rubber.

The effects of oxidative aging on the static and dynamic properties of nitrile rubber at the molecular scale were investigated by molecular dynamics simulation. The aged nitrile rubber models were constructed by introducing hydroxyl groups and carbonyl groups into rubber molecular chains to mimic oxidative aging. The static and dynamic properties of the unaged and aged nitrile rubber under different conditions were evaluated by mean square displacement, self-diffusion coefficients, hydrogen bond, fractional free volume, radial distribution function, cohesive energy density and solubility parameter. The results show that the elevated temperature intensified significantly the mobility of rubber molecular chains and fractional free volume, while the compressive strain displayed the opposite effect resulting in packing and rearrangement of rubber chains. The introduction of hydroxyl groups and carbonyl groups enhanced the polarity, intermolecular interactions, the volume and rigidity of molecular chains, implying weaker mobility of molecular chains as compared to unaged models. The compressive strain and oxidative aging both decreased the fractional free volume, which inhibited gaseous and liquid diffusion into the rubber materials, and slowed down the oxidative aging rate. This study provides insights to better understand the effect of molecular changes due to oxidative aging on the structural and dynamic properties of rubber materials at the molecular level.

Self‐healable and recyclable nitrile rubber based on thermoreversible ionic crosslink network

AbstractIn this work, commercial carboxylated nitrile butadiene rubber (XNBR) was ionically crosslinked with zinc thiolate forming reversible ionic salt bonding between carboxy groups (COOH) in XNBR chains and Zn2+ ions from zinc thiolate. The reversible nature of the ionic crosslinks allows rearrangement of rubber molecular chains under an external heat and provides self‐healing capability to the materials. The amount of zinc thiolate was varied at five levels (10, 20, 30, 40, and 50 per hundred rubber (phr) to assess the maximum reaction between COOH and Zn2+ ion for the formation of ionic crosslink networks. Evidence that ionic crosslinks formed within the materials was determined by the increased of curing torque and the chemical interaction was identified by Fourier transform infrared spectroscopy. An equilibrium swelling testing quantitatively measured the ionic crosslink density within the material and XNBR with 30‐phr zinc thiolate showed the highest ionic crosslink density. The results revealed that, damaged XNBR with 30 phr zinc thiolate able to recover 98% of its initial properties under thermal healing at 150°C for 10 min. Furthermore, the material can be reprocessed and recycled for three times without compromising its initial properties. Perhaps, the tensile strength increased 360% at approximately 23 MPa, after third recycling process. In addition, the self‐healing XNBR also have excellent weldability on the damage sample, which shows high potential for repairing of existing rubber products installed in heavy engineering applications.

Facile Fabrication of Eucommia Rubber Composites with High Shape Memory Performance.

We processed a series of shape memory Eucommia rubber (ER) composites with both carbon–carbon and ionic cross-linking networks via a chemical cross-linking method. The influence of the carbon–carbon cross-linking and ion cross-linking degree of ER composites on curing, mechanical, thermal, and shape memory properties were studied by DSC, DMA, and other analytical techniques. Dicumyl peroxide (DCP) and zinc dimethacrylate (ZDMA) played a key role in preparing ER composites with a double cross-linking structure, where DCP initiated polymerization of ZDMA, and grafted ZDMA onto polymer molecular chains and cross-linked rubber molecular chains. Meanwhile, ZDMA combined with rubber macromolecules to build ionic cross-linking bonds in composites under the action of DCP and reinforced the ER composites. The result showed that the coexistence of these two cross-linking networks provide a sufficient restoring force for deformation of shape memory composites. The addition of ZDMA not only improved the mechanical properties of materials, but also significantly enhanced shape memory performance of composites. In particular, Eucommia rubber composites exhibited outstanding mechanical properties and shape memory performance when DCP content was 0.2 phr.

Degeneration and damage mechanism of Pseudomorphic Glass under 170 keV proton irradiation

As the covering layer of flexible solar cells, Pseudomorphic Glass (PMG) needs brilliant optical, mechanical and radiation protection properties to ensure the long-term stable operation of cells. In this paper, the evolution law and mechanism analysis of PMG optical and mechanical properties under 170 keV proton irradiation were studied systematically. The surface morphology and the occurrence of cracks before and after irradiation were observed by OLYMPUS optical microscope and SEM. The degradation characteristics of PMG optical performance were researched by comparing the changes of RTV sheet and PMG transmittance. FT-IR and XPS were used to study the vicissitudes of surface composition and chemical bonds, and based on this, the degradation and crosslinking mechanism of silicon rubber molecular chains after proton irradiation was given. In addition, the stress-strain test was selected to characterize the mechanical properties of PMG.

Role of endogenous glucose on natural rubber molecular chains and natural network architecture based on biological action and chelation

Natural rubber (NR) is widely applied in automobile industry, surgical rubber goods, and daily necessities due to its outstanding comprehensive properties originated from the unique non-rubber component and network architecture. Glucose as an endogenous component virtually exert an important influence during the microorganism or spontaneous coagulation of natural latex. However, such role of glucose on the reconstruction of NR molecular chains and corresponding network has not been paid wide attention to. Hence, we here examined the difference of molecular chain parameters and molecular chains network composition of raw NR coagulated by different glucose content. The results demonstrated that glucose exerted an important role on the molecular chain and molecular chain architecture via two main related action of glucose: metabolism and chelation. In this work, a possible mechanism was proposed to reveal the role of glucose on the reconstruction of natural network in raw NR from spontaneous coagulation assisted by glucose.

Antioxidant effects on curing/processing and thermo-oxidative aging of filled nitrile rubber

Since anti-aging agents are widely used to improve the heat resistance of magnetic composites, the exploration to the effect of anti-aging agents on the magnetic composites is of great significance to the practical application. In this work, nitrile rubber/iron oxide/zinc dimethacrylate composites were prepared by incorporating various commercial anti-aging agents which are commonly used. It is found that the cross-linking density of the composites was obviously reduced after adding the anti-aging agents, which had a great influence on the mechanical properties. For example, compared with the composite without antioxidants, after adding the anti-aging agent DAPD, the elongation at break of the composite increased by ~ 4-fold, the hardness of shore A decreased by ~23°, and stress at 100% elongation decreased by ~4.5 MPa. Furthermore, the addition of the anti-aging agents was beneficial to promote the relative slip between rubber molecular chains and internal lubrication of the rubber compounds, thus improving the processing performance of the composites. Finally, the thermo-oxidative aging of composites with different anti-aging agents at different time and temperatures was evaluated. This paper provides constructive suggestions to further modify and select the antioxidants for the magnetic composites.