Isoprene Rubber Research Articles

Effect of Pretreated CZ/S on the Vulcanization and Rheological Behaviors of Isoprene Rubber Vulcanizates

Effect of Pretreated CZ/S on the Vulcanization and Rheological Behaviors of Isoprene Rubber Vulcanizates

Ethylene-Propylene-Methylene/Isoprene Rubber/SiO2 Nanocomposites with Enhanced Mechanical Performances and Deformation Recovery Ability by a Combination of Synchronously Vulcanizing and Nanoparticle Reinforcement.

It is highly desired yet challenging to develop advanced elastomers with excellent mechanical properties, including high strength and toughness. In this work, strong and tough rubber/rubber compound vulcanizates were facilely prepared by blending ethylene-propylene-methylene (EPM) and isoprene rubber (IR) together with dicumyl peroxide (DCP) and subsequent vulcanization, since both EPM and IR can be vulcanized synchronously by DCP and the well-crosslinked structure of EPM/IR vulcanizate presented a stable phase separation state. By tuning their composition, EPM/IR vulcanizates could present remarkably improved mechanical strength and toughness, as well as excellent energy dissipation and deformation recovery abilities. Furthermore, EPM/IR/SiO2 nanocomposites with better properties were prepared by introducing silica nanoparticles into EPM/IR vulcanizates. It was found that the high toughness and strength of EPM/IR vulcanizates and EPM/IR/SiO2 nanocomposites mainly resulted from the combination of stretchability of EPM and strain hardening of IR. Their excellent energy dissipation and deformation recovery abilities were related to the macromolecular characteristics of EPM and IR, compatibility between EPM and IR, and their crosslinking dynamics.

Mechanical and Thermal Properties of Polypropylene, Polyoxymethylene and Poly (Methyl Methacrylate) Modified with Adhesive Resins

Polyoxymethylene (POM), polypropylene (PP), and poly(methyl methacrylate) (PMMA) have been blended with adhesive-grade ethylene vinyl acetate (EVA), propylene elastomer (VMX), isobutylene–isoprene rubber (IIR) and an acrylic block copolymer (MMA-nBA-MMA). The blends were prepared using a two-roll mill and injection molding. The mechanical properties of the blends, such as tensile strength, tensile modulus, elongation at maximum load, and impact resistance, were investigated. The water contact angle, melt flow rate (MFR), and differential scanning calorimetry were ascertained to evaluate the blends. The blend samples exhibited the following properties: all POM/EVA blends showed reduced crystallinity compared to neat POM; the 80% PMMA/20% MMA-nBA-MMA blend showed improved impact resistance by 243% compared to the neat PMMA. An antiplasticization effect was observed for POM/EVA 1% blends and PMMA/EVA 1% blends, with MFR reduced by 1% and 3%, respectively. The MFR of the PP/IIR 1% blend increased by 5%, then decreased below the MFR near the polymer for the remaining IIR concentrations.

Influence of 1,1′-Azobis(cyclohexanezonitrile) on the thermo-oxidative aging performance of diolefin elastomers

Abstract Diolefin elastomers play an important role in production and life, but their unsaturated structure leads to extreme vulnerability to heat and oxygen attack, so research into the aging of diolefin elastomers has been a hot spot in the industry. To overcome this limitation, a strategy based on the thermal decomposition of 1,1′-Azobis(cyclohexanezonitrile) (Azo) is devised, which forms stabilized compounds with imine groups during the heat process and captures radical. The diolefin elastomer was combined with azo, and isoprene rubber (IR) is chosen as a model material. Azo was added to IR to prepare the composite material (IR-Azo), and the thermo-oxidative resistance of the composite was significantly improved. Such as, after being exposed to thermo-oxidative conditions for 24 h, IR-Azo showed a tensile strength of 14.96 MPa with a retention rate of 68.25% which exceeded that of many traditional antioxidants. This study provides new insights into the development of elastomers with excellent thermo-oxidative resistance.

Thermal responsive polyurethane/brominated isobutylene isoprene rubber co-continuous IPNs elastomer: From tunable shape memory behavior to high damping properties

Shape memory polymers may have the highest potential as materials for aerospace engineering because of their low density, adjustable stiffness, and controlled deformation; however, large shock effects are inevitable during the deformation process of space deployment structures. To overcome the impact of shock vibrations on such complex integrated structures, an innovative interpenetrating polymer network (IPN) preparation scheme through phase distribution adjustment is proposed. In this work, thermally responsive shape memory IPNs consisting of polycaprolactone-based polyurethane (PUPCL) and brominated isobutylene isoprene rubber (BIIR) were reported for the first time. The BIIR/PUPCL (5:5) IPNs exhibited high shape fixity and recovery rates (94.4 % and 89.6 %, respectively) and repeatable shape memory behavior. Furthermore, the IPNs presented a favorable loss factor (tan δ) of 0.60 and exhibited effective damping temperature range (tan δ > 0.3) covering 83.6 K (−43.4 °C to 40.2 °C), resulting in impressive damping properties. Finally, the working process of the hinge was simulated by constructing a layer-by-layer panel with smooth deployment 30 s after heating. In addition, a gripper-shaped module based on bending deformation was successfully fabricated, exhibiting particular energy-loss properties and acting as a shock absorber. This study provides a novel design for the preparation of multifunctional polymers with potential applications in hinges and booms for aerospace engineering and intelligent protective devices.

Natural and synthetic isoprene rubbers obtained using Ziegler–Natta catalysts

Objectives. To compare the properties of rubber compounds and rubbers based on natural rubber RSS1 and synthetic isoprene rubbers obtained using Ti, Nd, Gd catalysts, both when used individually in the formulation of rubber compounds and when synthetic analogues partially replace natural rubber.Methods. Rubber compounds were prepared using a laboratory roll and a 100 cm3 rubber mixer. For rubber compounds, the following factors were determined: Mooney viscosity, cohesive strength, and vulcanization characteristics. For rubbers, the following factors were determined: physical and mechanical parameters, Shore A hardness, rebound resilience, and volume loss upon abrasion.Results. Based on the results of the rubber compound tests, the study showed that compounds based on all the synthetic polyisoprenes studied are significantly inferior to compounds based on natural rubber in terms of cohesive strength. The partial replacement of natural rubber with synthetic rubber (regardless of the type of catalytic system) leads to a significant decrease in the cohesive strength of the blends. Despite the differences observed in the properties of the rubber compounds, the results of the rubbers based on individual rubbers do not manifest significant differences.Conclusions. The study demonstrated the influence of defects (oligomers, gel, low molecular weight fractions, branches, and 3,4-units) in the structure of synthetic polyisoprenes on the cohesive strength index of rubber compounds based on them, in which the number of 3,4-units plays a decisive role. The study also showed the potential of studying synthetic polyisoprenes as analogues of natural rubber in formulations of rubber compounds in the aims of resolving the problem of import substitution in the tire and rubber goods industry.

Nucleophiles realizing the reduction of ZnO content for vulcanization accompanied by the improvement in thermo‐oxidative resistance for vulcanized isoprene rubbers

AbstractAt present, vulcanization is an indispensable process in rubber industries and ZnO is an important ingredient in vulcanization reactions. However, ZnO is toxic to aquatic organisms and the use of ZnO is unfavorable to the sustainable development of rubber industry. The decrease of ZnO content without the reduction in properties of rubbers has been an open question in rubber industries. In this work, our group designs nucleophiles with an ability to open the ring of sulfur. With the decrease of ZnO content, the addition of nucleophiles maintains the ring‐opening capacity of sulfur. As a result, changes in several properties of rubbers such as tensile strength, tear strength, and crosslinking density are negligible with the reduction of ZnO content. Also, the thermo‐oxidative resistance of rubbers improves dramatically with the decrease of ZnO content and addition of nucleophiles. Through designing nucleophiles to reduce the content of ZnO, this work provides a strategy to develop sustainable rubber industries.

Coupling effect of non‐relaxing and high temperature on fatigue properties of carbon‐black filled isoprene rubber

AbstractThis paper presents an extensive experimental investigation on fatigue properties of carbon‐black filled isoprene rubber under complex loadings. A basic life prediction model taking strain energy density as fatigue parameter is first proposed based on fatigue crack growth tests and uniaxial tension fatigue tests under relaxing loads at room temperature. A database of fatigue life including relaxing and non‐relaxing is established through a great number of fatigue tests under five temperatures. Based on the database, two empirical parameters, that is, temperature factor (NRT/NHT) and life reinforcement factor (Re), are introduced to quantitatively characterize the coupling effects of high temperature and non‐relaxing loads on fatigue life. The fatigue mechanisms under different conditions are compared via wide‐angle x‐ray diffraction tests and postmortem analysis. It reveals that the weakening of life reinforcement at high temperatures is closely related to the strain induced crystallization behavior of rubber.

Swelling of rubbers of different chemical natures in supercritical carbon dioxide

Objectives. To investigate the swelling of the main types of rubbers used in the rubber industry in carbon dioxide in a supercritical state (SC-CO2), in order to assess the possibility of obtaining elastomeric materials with porous structures using fluid technology, based on them.Methods. The process of swelling of rubbers in SC-CO2 and subsequent foaming was carried out according to a specially developed technique using the original installation. This is a high-pressure apparatus with transparent windows, allowing for the use of an optical technique to directly measure the geometric dimensions of samples during swelling and foaming using a digital video camera. The study of the porous structure of foamed rubbers was carried out using scanning electron microscopy.Results. The study established experimental curves of the swelling kinetics in SC-CO2 of isoprene, butadiene, styrene butadiene, ethylene propylene, chloroprene, ethylene acrylate, siloxane, and organofluorine rubbers. The influence of temperature and pressure on the rate and equilibrium degree of swelling was studied. The diffusion coefficients of SC-CO2 in rubbers of various chemical natures were also determined.Conclusions. It was shown that the equilibrium swelling degree of rubbers in SC-CO2 depends on the chemical nature of rubbers. It does not correlate with the value of their solubility parameters, changes directly proportional to the diffusion coefficient and increases with increasing temperature and pressure. It was found that irrespective of the degree of swelling in SC-CO2, all the rubbers studied are intensively foamed at a sharp pressure drop. The size of the pores formed is tens of microns: significantly smaller than the size of pores formed when chemical pore formers are used.

Network Formation, Properties, and Actuation Performance of Functionalized Liquid Isoprene Rubber.

Due to some useful mechanical, dynamic, and dielectric properties along with the ease of processing and forming, liquid rubbers are ideal materials for fabricating dielectric elastomer actuators in various configurations and for many potential applications ranging from automation to automobile and medical industry. In this study, we present a cross-linkable liquid rubber composition where amine-catalyzed esterification reactions lead to the formation of a network structure based on anhydride functional isoprene rubber, carboxyl-terminated nitrile-butadiene rubber, and epoxy end-capped prepolymers. The success of this intricate network formation procedure was verified by HR-MAS NMR spectroscopy. The new isoprene-based elastomeric material exhibits actuation-relevant attributes including a low elastic modulus of 0.45 MPa, soft response to an applied load up to a large deformation of 300%, and a dielectric constant value (2.6) higher than the conventional Elastosil silicone (2.2). A dot actuator comprising of an isoprene dielectric elastomer film in unstretched state and carbon paste electrodes was fabricated that demonstrated an electrode deformation of 0.63%, which is nearly twice as high as for the commercial Elastosil 2030 film (∼0.30%) at 5 kV. Compared to the Elastosil silicone film, the enhanced performance is attributed to the low modulus and high dielectric constant value of the new isoprene elastomer.

Confinement of Oligopeptides by Terminally Functionalized Polyisoprene to Improve Their Mechanical Strength, Creep Resistance, and Antifatigue Properties.

A small amount of terminal polar phase endows natural rubber (NR) with excellent comprehensive properties superior to those of synthetic isoprene rubber. In this work, the comprehensive properties of synthetic rubber were remarkably improved by introducing a stable terminal nanoconfinement structure by combining terminal hydroxyl groups and pentapeptide molecules noncovalently into the same phases. The results show that the stable terminal phases hardly affect the free chain motion but enhance the entanglement. Under cyclic loading, the terminal polar phases undergo hierarchically structural changes such as reversible dissociation of the weak bonds, phase deformation, and crystalline reorganization, all of which dissipate the stress and are beneficial for high strength and extensibility. At the same time, synthetic rubbers demonstrate much superior fatigue resistance and lower hysteresis relative to NR and maintain comparable dimensional stability. This strategy suggests that the comprehensive properties of elastomers can be regulated and upgraded by facile terminal noncovalent interactions.

Inhomogeneities of sulfidic linkages and mullins effect in isoprene rubber vulcanizates vulcanized with sulfur donor agents

Gum vulcanizates exhibit the Mullins effect during large-strain cyclic tension. However, the details of the Mullins effect remain unclarified due to the difficulty of analysis of a complicated network structure. The Mullins effect in isoprene rubber (IR) vulcanizates has been systematically investigated to clarify the impacts of network inhomogeneities caused by the distribution of sulfidic linkages. Chemical probe experiments and paraffin swelling have been performed in an attempt to clarify the contribution of the presence of different types of sulfidic linkages. Thermo-oxidative aging at a moderate temperature (353 K) has been used to assess the effect of changes in structural inhomogeneity on the Mullins effect in aged vulcanizates. During cyclic tension deformations, the recovery hysteresis and accumulated softening energy densities normalized by theoretical shear modulus of elastically effective network are influenced by the heterogeneity of network structure only before the onset of crystallization. These findings can be used to inform the design of the network structure and enhance the performance of rubber products.

In-situ decorating diene-rubber with carbamyl maleamic handles as sacrificial units toward network reinforcement

The decoration of sacrificial units (SUs) into rubber network has gained momentum as a non-filling alternative toward efficient network reinforcement. However, most established methods, including the copolymerization with SUs-containing monomers or the post-modification of rubber backbone, still suffer from the multi-step and time-consuming backbone preparation with poor designability. In this work, we proposed a facile and practical strategy to achieve efficient network reinforcement through in-situ decorating isoprene rubber (IR) network with N-carbamyl maleamic acid (NCMA) as SUs. Model compound vulcanization experiment demonstrated that during sulfur vulcanization, the poly/disulfides in active sulfurating agents or crosslinking precursors can cleave into reactive sulfur radicals, which subsequently proceeded radical addition reaction with the unsaturated NCMA. The decorated carbamyl maleamic handles can spontaneously form multiple hydrogen-bonding linkages to serve as SUs. Upon deformation, the reversible detachment/reattachment of the SUs will smooth out the local stress concentration, but also facilitate the orientation of network chains. Therefore, as the NCMA loading increases, the onset of strain-induced crystallization and the overall crystallinity of the obtained IR network are simultaneously promoted, giving rise to a gradual increase in the tensile modulus (∼80 %) of the system. By virtue of the rich variety, commercial availability and facile structural tunability of maleamic acid-derivatives, we envisage that the present study can open up a novel strategy to achieve in-situ decoration of rubber with various functional handles toward efficient network reinforcement and functionalization.

Assessing the Biodegradability of Tire Tread Particles and Influencing Factors.

Abrasion of tire tread, caused by friction between vehicle tires and road surfaces, causes release of tire wear particles (TWPs) into various environmental compartments. These TWPs contribute to chemical, microplastic, and particulate matter pollution. Their fate remains largely unknown, especially regarding the extent and form in which they persist in the environment. The present study investigated (1) the biodegradability of tread particles (TPs) in the form of ground tire tread, (2) how accelerated ultraviolet (UV) weathering affects their biodegradability, and (3) which TP constituents are likely contributors to TP biodegradability based on their individual biodegradability. A series of closed-bottle tests, with aerobic aqueous medium inoculated with activated sludge, were carried out for pristine TPs, UV-weathered TPs, and selected TP constituents; natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and treated distillate aromatic extracts (TDAE). Biodegradation was monitored by manometric respirometry, quantifying biological oxygen consumption over 28 days. Pristine TP biodegradability was found to be 4.5%; UV-weathered TPs showed higher biodegradability of 6.7% and 8.0% with similar and increased inoculum concentrations, respectively. The observed TP biodegradation was mainly attributed to biodegradation of NR and TDAE, with individual biodegradability of 35.4% and 8.0%, respectively; IR and BR showed negligible biodegradability. These findings indicate that biodegradability of individual constituents is decreased by a factor of 2 to 5 when compounded into TPs. Through scanning electron microscopy analysis, biodegradation was found to cause surface erosion. Processes of TP biodegradation are expected to change throughout their lifetime as new constituents are incorporated from the road and others degrade and/or leach out. Tire emissions likely persist as particles with an increased fraction of synthetic rubbers and carbon black. Environ Toxicol Chem 2024;43:31-41. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effect of deep eutectic solvents on vulcanization and rheological behaviors of rubber vulcanizates

Deep eutectic solvents (DESs) are able to promote vulcanization of rubbers while the mechanisms remain unclear. Herein 4-methyl-5,7-dihydroxycoumarin (DHMC) as hydrogen bond donor (HBD) was used to synthesize DES by reaction with tetrabutylammonium bromide (TBAB) as hydrogen bond acceptor (HBA). The effects of DHMC, TBAB and DES on vulcanization of natural rubber (NR) and isoprene rubber (IR) were studied. It is shown that DES could participate in crosslinking network and adjust crosslinking density (vc) of the vulcanizates through physical and chemical interactions with NR non-rubber components, zinc oxide (ZnO) activator and N-cyclohexyl-2-benzothiazolesulfenamide (CZ) accelerator. Furthermore, DES influences linear and nonlinear rheological responses and mechanical behaviors of NR vulcanizates. The NR vulcanizates cured at 120 °C with 0.1–0.3 phr (part per hundred parts of rubber) DES exhibit higher tensile strengths and lower vc in comparison with the control one cured at 140 °C, which is assigned to the more homogenous crosslinking network in the former. This work provides an effective way to modulate the crosslinking network to produce high-strength vulcanizates at lowered vulcanization temperatures and ZnO amount, which is beneficial for the preparation of rubber products with high strengths and low hysteresis energies.

Self-Repair of Cement Paste with Gas-Sensitive Graft Polymer

Summary To solve the problem of annular gas channeling in natural gas well cementing, isoprene rubber was used as graft matrix material, natural gas absorbing methyl methacrylate and octadecyl acrylate were used as functional monomers, a gas-inspired expansion graft polymer was prepared by graft copolymerization, and a natural gas-triggered self-repair cementing slurry was developed. The structure of gas-sensitive grafted polymer was characterized by Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR), and the effects of monomer concentration and copolymer feed ratio on equilibrium swelling degree were investigated. For the cement stone (ring) samples with microcracks and microgaps, the gas-triggered repair performance of the system was evaluated by using a self-designed testing instrument. The results show that the gas-sensitive material can increase the gas channeling resistance of fractured cement paste by one to two orders of magnitude. The material system has been applied to 20 deep gas wells in Daqing Field, and the test results show that the system can guarantee the effective sealing of the cement sheath.

Influence of filler concentration and type on rheological and mechanical properties of liquid isoprene rubber for high-strength parts via material extrusion

This study investigates the rheological behavior and material extrusion performance of liquid isoprene rubber (LIR) compounds filled with carbon black (CB), silica (Si), and recycled crumb rubber (CR) fillers for potential additive manufacturing applications. The rheological properties of the LIR mixtures were characterized using flow curve analysis and temperature sweeps, identifying shear-thinning behavior and temperature-dependent viscosity ultimately reflecting the final dimensional tolerance of the prints. Vulcanization time (t90) was determined using oscillatory rheometry, and the effect of filler concentration on t90 was evaluated. Mechanical testing was conducted to assess the hardness and tensile properties. The results demonstrate the influence of filler concentration on the rheological properties, printability, and mechanical performance of the LIR compounds thus resulting in the printing of high-strength (σu > 5 MPa) isoprene rubber parts capable of being additively manufactured.

Modulus self-recovery phenomenon after shearing of natural rubber based on supramolecular network aggregation structure

Natural rubber (NR) and isoprene rubber (IR) exhibit a similar shear-thinning phenomenon, in which NR has the inverse ‘S′ shape stress-strain curve and IR has the yield stress-strain curve. Different from IR, NR exhibits the modulus self-recovery phenomenon after shearing. The experimental data showed that the 300% modulus of NR could recover 41.84% after it was sheared 5 times and stored for 30 days. The tensile strength would even recover completely. The modulus self-recovery efficiency (MSRE) would decrease with increasing shearing times. A mechanism model of the structure self-healing efficiency (SSHE) was proposed based on the supramolecular network aggregation structure (SNAS) formed by the weak valence bond of the non-rubber components (NRCs) at the terminal group of the NR macromolecular chains. The mechanical shearing force would break the SNAS of NR and the short molecular chains would fall off from the SNAS. The dropped shorted molecular chains of NR would re-enter the SNAS under the hydrogen-bond interaction generated by the NRCs after storing for a while, increasing the molecular weight and improving the mechanical properties. The 300% modulus would recover partly and the tensile strength might exceed the initial value if the NR was sheared slightly. On the contrary, as the same molecular structure without NRCs, IR did not show any modulus self-recovery phenomenon after shearing. Except it was confirmed by the increased molecular weight and gel content after shearing and storing, this mechanism model could be confirmed by the de-structured transesterification natural rubber (TENR) which did not exhibit the modulus self-recovery phenomenon anymore after removing the NRCs, such as proteins and phospholipids.

Effect of Polynorbornene on Physico-Mechanical, Dynamic, and Dielectric Properties of Vulcanizates Based on Isoprene, α-Methylstyrene-Butadiene, and Nitrile-Butadiene Rubbers for Rail Fasteners Pads

The article studies the effect of polynorbornene (PNB) in the composition of PNB with Norman 747 LV plasticizer (RC) on the curing characteristics of the rubber compound and the physico-mechanical, dynamic, dielectric properties and the thermal behavior of vulcanizates based on a combination of isoprene, α-methylstyrene-butadiene, and nitrile-butadiene rubbers. It is shown that vulcanizates containing PNB in the composition of the RC had lower conditional tensile strength, hardness, and tear resistance compared to the vulcanizate of the base version of the rubber compound. Studies of dynamic mechanical analysis indicate that an increase in the content of RC, and hence PNB, in the rubber compound contributes to an increase in the mechanical loss factor (tanδ) and a decrease in the storage modulus of vulcanizates. It was found that vulcanized rubber, containing 24.0 parts per hundred of rubber (phr) (8.98 wt. %) PNB as part of the RC, is characterized by stable physico-mechanical, improved vibration-absorbing properties, as well as increased dielectric parameters. This rubber compound can be used as a base for rail fasteners for railroad tracks.

Synergistic effect of compound rubber and SiO2 nanoparticles on low-temperature toughening and balanced stiffness-toughness of random copolymer polypropylene nanocomposites

Random copolymer polypropylene (PPR)/rubber/silica nanocomposites with excellent low-temperature toughness and balanced rigidity-toughness were prepared by using compound rubber composed of ethylene propylene rubber (EPR) and isoprene rubber (IR). Effects of compound rubber on reinforcement and toughening of PPR were systematically investigated through mechanical properties, dynamic mechanical behavior, morphologies and rheological behavior. Mechanical results showed compound rubber had higher efficiency in both reinforcement and toughening than single rubber. According to morphological analysis and rheological results, it was found that the EPR/IR compound rubber had a better distribution in PPR matrix due to the close viscosity to PPR matrix and maintained the characteristics of silica distribution at the interface between rubber and matrix. Dynamic mechanical results revealed PPR/compound rubber blends showed larger area of loss factor. Consequently, the better toughening effect and achieving good rigidity-toughness balance of compound rubber in PPR nanocomposites was ascribed to the synergistic effect of compound rubber and SiO2 nanoparticles, which results in smaller particle spacing and larger loss factor area of rubber phase in nanocomposites without changing preferential loading of nanoparticles at polymeric interface.