Polyisoprene Rubber Research Articles

Biomimetic design of polyisoprene rubber with terminal synergistic effects leading to mechanical properties and creep resistance boost

The enhancement of polyisoprene rubber performance through biomimetic simulation of the terminal effect of natural rubber has been explored. So far, the presence of synergistic effects between different terminal groups and the challenge of controlling the relaxation behavior of non-covalent bonds while preserving their advantages remain open questions. In this study, we successfully prepared natural rubber biomimetic polymers with different functionalized terminals. Specifically, we constructed terminal-olefin cross-linking points at one end of the polymer chains, while dissociable oligopeptide assemblies were formed at the other end. Investigation of the viscoelastic behavior of the polymers and the structure of the rubber network confirmed the existence of synergistic effects between different terminal groups. The terminal-olefin cross-linking points effectively anchored the rubber network and stabilized the non-covalent bonds. Simultaneously, the non-covalent bonds formed by the oligopeptides acted as weak bonds, dissipating energy and improving the dimensional stability and mechanical properties of the vulcanized rubber.

Critical parameters governing elastocaloric effect in polyisoprene rubbers for solid-state cooling

The aim of this work is to study the critical parameters governing the eCe (elastocaloric effect) of poly-isoprene rubber (NR and IR) in use conditions of a cooling device, i.e. under partial cyclic loading. The effect of mechanical cyclic loading parameters (pre-extension ratio, waveform and frequency) on eCe was first studied. It shows that the eCe increases when the mimimum pre-extension ratio is increased and frequency is lowered from 1Hz to 0.001Hz, as it promotes strain-induced crystallization. However, it also leads to a decrease in potential cooling power, from 7 to 0.01 MW/m3 (i.e. 8 kW/kg to 0.01 kW/kg). At intermediate frequency (f ≈ 0.1 Hz), the comparison of square and triangular waveforms demonstrated that the former enables greater temperature variation. This is due to its holding step (at maximum extension ratio), which maximizes crystallization but also promotes stress relaxation, resulting in increased mechanical losses. Consequently, the square and triangular loadings have a COPmat of 12 and 25, with a temperature variation of 4.2K and 3.6K, respectively. Regarding the formulation, rubbers that do not have a great tendency to crystallize such as synthetic polyisoprene rubber seem to have the best COPmat, while to maximize ΔT, the best of our formulations are NR crosslinked with sulfur and having a crosslink density close to 1.5 × 10−4 mol/cm3, which combine large strain induced crystallization and entropic elasticity. This material has a COPmat of about 27 and allows a ΔT≈4K, i.e.performance comparable to that of the best Shape Memory Alloys (at equivalent COPmat).

The enhancement effects of multiple hydrogen bonds between bi-terminal groups and penta-alanine assemblies on creep resistance and mechanical strength of polyisoprene rubbers

Along with the continuously advanced requirements for high performance rubbers such as in aircraft tires, natural rubbers show limitations in achieving high temperature creep resistance and high mechanical strength simultaneously. Meanwhile, the bi-terminal interactions of natural rubber (NR) exhibit unique reinforcement effects, which are difficult to realize in synthetic rubbers. In this article, four different types of bi-terminal polyisoprenes with distinct groups were synthesized, and they were assembled with penta-alanine molecule (5 A) to obtain high-performance rubbers by terminal hydrogen bonding reinforcement. Infrared tests indicate that the strong hydrogen bonds can be formed between two terminals and turn stronger after adding 5 A. Thus, the network of rubbers remains stable under different strains and temperatures and the activation energy of networks is elevated. As a result, this biomimetic design endows polyisoprene with high tensile strength compared with Malaysian NR and greater creep resistance. Further Mooney fitting and DMA test suggests that these confined hydrogen bonds not only increased the number of crosslinking points and entanglements of network, but also are beneficial for the segmental chain motion. In contrast to our common sense on hydrogen bonds which present large relaxation and hysteresis, this study proposes a facile method for preparing high-temperature creep-resistant rubbers by introducing confined hydrogen bonds, which represents a great advance in the structural biomimicry of NR.

Effect of crosslinking agent types on the tensile properties of polyisoprene rubber

The impacts of crosslinking bond types on the equilibrium kinetics and uniaxial tensile properties of polyisoprene rubber were investigated by using molecular dynamics (MD) simulations. We analyze the changes in mean square displacement, glass transition temperature, and end-to-end vector autocorrelation function of different crosslinked systems during the equilibrium process. It was found that the mobility of polysulfide crosslinked systems was more limited compared with that of monosulfide and disulfide bonds. In addition, during uniaxial stretching, the polysulfide-bonded crosslinked system could exhibit better tensile strength, and the stress response was significantly improved. The above research results help to understand the mechanical properties and deformation mechanism of crosslinked polyisoprene rubber and provide certain reference values for improving the performance of related materials.

Bioinspired Organic Porous Coupling Agent for Enhancement of Nanoparticle Dispersion and Interfacial Strength.

Composite materials have significantly advanced with the integration of inorganic nanoparticles as fillers in polymers. Achieving fine dispersion of these nanoparticles within the composites, however, remains a challenge. This study presents a novel solution inspired by the natural structure of Xanthium. We have developed a polymer of intrinsic microporosity (PIM)-based porous coupling agent, named PCA. PCA's rigid backbone structure enhances interfacial interactions through a unique intermolecular interlocking mechanism. This approach notably improves the dispersion of SiO2 nanoparticles in various organic solvents and low-polarity polymers. Significantly, PCA-modified SiO2 nanoparticles embedded in polyisoprene rubber showed enhanced mechanical properties. The Young's modulus increases to 30.7 MPa, compared to 5.4 MPa in hexadecyltrimethoxysilane-modified nanoparticles. Further analysis shows that PCA-modified composites not only become stiffer but also gain strength and ductility. This research demonstrates a novel biomimetic strategy for enhancing interfacial interactions in composites, potentially leading to stronger, more versatile composite materials.

Novel IP2C sensors with flexible electrodes based on plasma-treated conductive elastomeric nanocomposites

Ionic polymer-metal composites (IPMC) are devices composed of metallic electrodes and an ionomeric polymer membrane in a ‘sandwich’ architecture and. Their main property is electromechanical actuation or sensing based on the movement of ions. Metallic electrodes are commonly used for their high electrical conductivity, malleability, and chemical resistance. However, the high cost of noble metals, such as platinum, long manufacturing time, and fatigue failure limit their application. Therefore, the replacement of metallic electrodes with conductive elastomeric nanocomposites (CENs) was evaluated to reduce the costs and complexity of manufacturing the device and increase its working life. In this work, carbon nanotubes were used as the conductive fillers. The dispersion to achieve high electrical conductivity was carried out directly in the synthetic or natural polyisoprene rubber latex assisted by surfactant and high-power sonication. To improve the adhesion between the elastomeric electrode and the ionic membrane (Nafion), plasma treatment with atmospheric air was applied as a surface modifier. This treatment improved the hydrophilicity and adhesion of the rubbers by forming oxygenated groups and increasing the surface nanoroughness. In this way, ionomeric polymer–polymer composite (IP2C) devices were fabricated using Nafion and plasma-modified CENs, this type of electrode is unprecedented in the literature for this application. These devices showed displacement and strain sensing capacity at levels close to the conventional IPMC in all tested frequency ranges and applied accelerations. Notably, the IP2C obtained better resolution at low frequencies than the control.

The Effect of Silica Filler Source on the Mechanical Properties of Composite Rubber

Rubber composite is a high molecular weight polymer, produced from natural or synthetic rubber with sulfur as its common crosslinking agent. To improve the mechanical properties of rubber, filler with high silica content was usually added. Hence in this experiment, due to their high silica content, Risk husk ash (RHA), along with chemizil and zeosil were used as the composite filler. Sulfur was chosen as the crosslinking agent of a rubber mixture that consists of polyisoprene rubber (IR), acrylonitrile butadiene rubber (KNB), and polybutadiene rubber (BR). The composition of the other component was fixed at Per Hundred Rubber (PHR) of 51.43. During mixing, the temperature and mixing time were kept constant at 60-70oC and 6 minutes. The properties of rubber composite were characterized based on their physical and mechanical properties. Based on the rheological test, RHA has a faster vulcanization time compared to chemisil and zeosil. Improvement of the mechanical properties of the RHA rubber mixture was also observed, with 300% modulus, elongation, and tear at 42 kg/cm2, 867%, and 51 kg/cm2. Meanwhile, insignificance differences in tensile strength, hardness, and specific gravity of RHA compared to chemisil and zeosil, were observed.

Functionalized liquid polyisoprene as a promising toughening agent for poly(lactic acid): Combining stiffness and toughness

AbstractLiquid polyisoprene rubbers (LIR) containing anhydride and carboxylic groups along their chains were successfully employed as toughening agent for poly(lactic acid) (PLA) without great influence on the stiffness of the matrix. In fact, the addition of 5% of these functionalized LIR resulted in an improvement of toughness and impact resistance of more than 2000%, whereas the reduction of the yield stress stayed in the range of 12%. No significant variation of the Young modulus was observed for the modified PLA samples. The effect of the LIR on the rheological and thermal properties of PLA was also investigated. The glass transition temperature obtained from dynamic‐mechanical analysis of the PLA matrix was not affected by the addition of 10% of the liquid rubber. The scanning electron microscopy analysis revealed a significant decrease in the rubber domains for the blends containing LIR functionalized with anhydride groups. Finally, the modified PLA with anhydride‐functionalized LIR was able to produce transparent film with outstanding mechanical performance than neat PLA, making this material a good option for food packaging.

Synthetic Polyisoprene Rubber as a Mimic of Natural Rubber: Recent Advances on Synthesis, Nanocomposites, and Applications.

Up to now, rubber materials have been used in a wide range of applications, from automotive parts to special-design engineering pieces, as well as in the pharmaceutical, food, electronics, and military industries, among others. Since the discovery of the vulcanization of natural rubber (NR) in 1838, the continuous demand for this material has intensified the quest for a synthetic substitute with similar properties. In this regard, synthetic polyisoprene rubber (IR) emerged as an attractive alternative. However, despite the efforts made, some properties of natural rubber have been difficult to match (i.e., superior mechanical properties) due not only to its high content of cis-1,4-polyisoprene but also because its structure is considered a naturally occurring nanocomposite. In this sense, cutting-edge research has proposed the synthesis of nanocomposites with synthetic rubber, obtaining the same properties as natural rubber. This review focuses on the synthesis, structure, and properties of natural and synthetic rubber, with a special interest in the synthesis of IR nanocomposites, giving the reader a comprehensive reference on how to achieve a mimic of NR.

Natural cardanol modified liquid polyisoprene rubber and its surface adhesion performance

Inspired by mussel protein, the adhesives based on dopamine boom due to its perfect adhesion performance. However, limited by its high price, it is of great significance to study adhesives originated from natural and renewable phenolic and polyphenol compounds which structure is similar to dopamine. The application of natural products can also reduce the consumption of non-renewable petrochemical resources. Herein, the agriculture and forestry by-products cardanol (CA) was grafted onto liquid polyisoprene rubber (LIR) molecular chains to improve its surface energy. Then, the grafting product (LCA) experienced complex formulation (GLCA) and vulcanization (v-LCA). The vulcanization crosslinking was confirmed by the weakening of double bonds absorption in IR spectra and C-C peak in XPS spectra, the enhancement of methyl proton in the α-position of quaternary carbon atom in 1H NMR spectra. The GLCA adhesive agent showed good adhesion performance on wet polar substrates because the drainage effect of LIR and the alkyl chains of CA. Moreover, CA provides the possibility of the multiple interactions as metal bonding, hydrogen bonding, cation-π interaction, π-π stacking, hydrophobic interaction and entanglement between chains. The v-LCA adhesive layer exhibits good solvent resistance. This study provides a prospect of the natural phenolic compounds from agriculture and forestry by-products to be used in the wet adhesion of industry, agriculture, or daily life.

Environmentally safe preservation and stabilization of natural rubber latex in an acidic environment

AbstractNatural rubber is an indispensable raw material that supplies about half of the world's rubber consumption. The latex that is extracted from the trees is composed of polyisoprene rubber, proteins, sugars, amino acids, lipids, and minerals. When the liquid latex emanates from the trees, it comes into contact with bacteria that cause it to decompose and coagulate. To hinder the decomposition and destabilization process, ammonia and other environmental and health hazard chemicals are added to the latex. The addition of these chemicals affects the health of plantation and rubber industry workers and results in residues that are contaminated with these chemicals, which require that processing facility effluents undergo costly treatment processes. Here, we present two novel liquid latex preservation and stabilization methods in an acid medium free of ammonia or other dangerous chemicals. The first method uses dodecyl benzene sulfonic acid to both stabilise and preserve the liquid latex, and the second uses ethoxylated tridecyl alcohol to stabilise and hydrofluoric acid to preserve the colloidal suspension. Both formulations result in rubber with superior mechanical properties, that is safe for the rubber plantation and industry workers, and with residues that no longer adversely affect the environment.

Promoted Comprehensive Properties of Polyisoprene Rubber with Extremely High Fatigue Resistance Enabled by Oligopeptide Aggregates

Promoted Comprehensive Properties of Polyisoprene Rubber with Extremely High Fatigue Resistance Enabled by Oligopeptide Aggregates

PNP-Ligated Rare-Earth Metal Catalysts for Efficient Polymerization of Isoprene

The tridentate PNP ligand-supported rare-earth metal complexes, i.e., bis[o-diphenylphosphinophenyl]amido-Re-bis[o-dimethylaminobenzyl], [(Ph2P-o-C6H4)2N]Re[(CH2-o-Me2N(C6H4))2]: (Re = Y, 1; Nd, 2; Gd, 3) were applied to isoprene polymerization. When activated with borate activator ([PhMe2NH][B(C6F5)4] (NH-BARF), catalysts 1 and 3 exhibited excellent catalytic efficiency in aromatic media, produced very-high to ultrahigh molecular weight (Mw over 130 × 104 g/moL) polyisoprene rubber (PIR), and the obtained PIR contained over 98% cis-1,4 head-to-tail repeating unites. In most cases, the borate-activated polymerization reaction proceeded in a quasi-living pattern (PDI = 1.2–1.5) under controlled monomer conversion; whereas, activated with the commercially available modified methylaluminoxane (MMAO3A) in aliphatic hydrocarbon media, complexes 1, 2 and 3 all showed high catalytic efficiency, produced high molecular weight PIR with narrow molecular weight distribution (PDI ≤ 2.0) and high cis-1,4 head-to tail repeating unites in the range of 91–95%. Thus, the catalyst systems that consisted of 1, 2 and 3/MMAO3A, are closely relevant to the current industrial polybutadiene rubber (PBR) and PIR production processes.

A Model Study of the Influence of the Natural Rubber (NR)- Endogenous Gel Fraction on the Rheological Performance of NR Using Synthetic Polyisoprene Rubber (IR) Blends with Different Ratios of Gel

A Model Study of the Influence of the Natural Rubber (NR)- Endogenous Gel Fraction on the Rheological Performance of NR Using Synthetic Polyisoprene Rubber (IR) Blends with Different Ratios of Gel

Epoxy networks modified with functionalized liquid polyisoprene rubbers with enhanced toughness and stiffness

Epoxy networks modified with functionalized liquid polyisoprene rubbers with enhanced toughness and stiffness

Converting polyisoprene rubbers into bio-jet fuels via a cascade hydropyrolysis and vapor-phase hydrogenation process

Producing alternative drop-in bio-jet fuels from biomass provides a promising approach to achieve carbon neutrality. To upcycle biomass-based polyisoprene rubbers into jet-fuel range C10 cycloalkane, we proposed a cascade hydropyrolysis and vapor-phase hydrogenation process in a flow-through two-stage pressurized fixed-bed reactor. The hydropyrolysis temperature in the first stage is of vital importance for the formation of primary limonene intermediate in the non-catalytic degradation of polyisoprene rubbers, and a reaction temperature of 460 °C maximized limonene yield to 588.6 mg/g for natural rubber and 546.2 mg/g for Eucommia rubber. Over a Pt/C catalyst loaded in the second stage, the limonene intermediate produced from the first-stage reactor can be completely hydrogenated, giving a 642.7 mg/g yield of jet-fuel range C10 cycloalkane with 83.6% selectivity. The depolymerization mechanism of polyisoprene rubbers was thoroughly studied, and a competitive reaction between limonene hydrogenation and limonene dehydrogenation was observed. This is the first report on producing C10 cycloalkane from natural rubbers via a cascade hydropyrolysis and hydrogenation process, providing a promising strategy to upcycle polyisoprene rubbers into bio-jet fuels.

Nonprestretching double-network enabled by physical interaction-induced aggregation

The design of double-network (DN) improves the properties of matrix effectively, which has attracted wide attention. The recently reported construction of DN structure usually involves the prestretching process (swelling process). However, such complicated multistep swelling processes become more difficult in high molecular weight matrix, which are not suitable for constructing DN structure in the universal elastomers (for example, natural rubber and polyisoprene rubber). To expand the application fields of DN, this work designs the dense crosslinking domain and the sparse crosslinking domain to construct nonprestretching DN structure through physical interaction-induced aggregation. We find that physical interaction induced-aggregation form the dense crosslinking domain and the sparse crosslinking domain, which builds the two contrasting DN structures. Double-quantum nuclear magnetic resonance, dynamic mechanical analyzer, and mechanical property characterization demonstrate that the dense crosslinking domain as the brittle first network is preferentially ruptured upon deformation, leading to a large energy dissipation. This design concept represents a general approach to develop the nonprestretching DN structure, which expands the application fields of DN structure in the elastomer matrix.

Effect of main chain modification during reversion on strain‐induced crystallization of polyisoprene rubbers

AbstractThe effect of main chain modification during reversion on strain‐induced crystallization (SIC) of unfilled natural rubber (NR) and synthetic polyisoprene rubber (IR) cured with a conventional vulcanization system has been investigated. To eliminate the interference of crosslink density, vulcanizates were prepared using different amounts of curatives, chosen to give mainly monosulfidic or carbon–carbon crosslinks, having similar crosslink densities to the conventional compound at different states of reversion. Crystallinity was characterized by the degree of stress softening, and the contents of trans‐methine were qualitatively and quantitatively analyzed by Fourier transform infrared spectroscopy. It was found that crosslink density exerts much greater influence on crystallinity than crosslink structure. At the same crosslink density, SIC of NR vulcanizates after reversion is lower than that of samples cured with tetramethylthiuram disulfide or dicumyl peroxid to the optimum cure state, which might be attributed to molecular main chain modification during reversion. NR was found to have better reversion resistance than IR.

Organosolv Lignin Improved Thermoplastic Elastomeric Behavior of Polyethylene/Polyisoprene Blend.

Thermoplastic elastomers are considered the fastest-growing elastomers in recent years because of their thermomechanical recyclability, in contrast to traditional thermoset rubbers. Polyolefins such as low-density polyethylene (LDPE) show low mechanical properties, particularly poor elongation when compared with an elastomer or rubber. In this study, LDPE resin is converted to highly ductile rubber-like materials with high elongation and low modulus properties on blending with polyisoprene rubber (IR), followed by treating with dicumyl peroxide as a curing agent and organosolv lignin as an additive. The technique of high shear melt-mixing, in conjunction with vulcanization or crosslinking using organic peroxide, is used to develop hybrid materials based on the LDPE/IR blend at a 70/30 mass ratio, where LDPE is replaced partly with lignin. Various characteristics such as tensile, viscoelasticity, melt flow, crystallinity, and phase morphology of the materials are analyzed. As expected, vulcanization with peroxide can improve the mechanical performance of the LDPE/IR blends, which is further improved with the application of lignin (2 to 5 wt. %), particularly tensile strain is profoundly increased. For example, the average values of the tensile strength, the modulus, and the ultimate elongation of neat LDPE resin are 7.8 MPa, 177 MPa, and 62%, respectively, and those of LDPE/IR/lignin/DCP 65/30/05/2 are 8.1 MPa, 95 MPa, and 238%, respectively. It indicates that the application of lignin/DCP has a profound effect on improving the ductility and elastomeric characteristics of the materials; thus, this material can have the potential to replace traditional rubber products.

Quantum‐chemical studies of the antioxidant effectiveness of para‐phenylene diamines

AbstractThe purpose of this review is to highlight how the antioxidant effectiveness (AE) of rubber additives can be quantitatively interpreted using results from quantum‐chemical calculations. The relationships between the AE of para‐phenylene diamines (PPD), evaluated through non‐isothermal differential scanning calorimetry measurements in styrene‐butadiene and polyisoprene rubber matrices, and various parameters obtained by quantum‐chemical calculations are reviewed. The N atom between both phenyl rings (A site) is more significant than the N atom between the phenyl ring and the alkyl chain (B site). The preferred formation of ketimine structures (instead of the quinonediimine ones) during dehydrogenation despite the higher stability of the NA‐centered radicals indicates a kinetic control of the antioxidant action. In most cases, the AE decreases with the strength of the NA–HA bond and increases with the chemical shifts of NA and HA. In hypothetical Cu(II) complexes, the AE rises with the affinity of NA to Cu, and the extent of electron density transfer from NA to Cu. Most deviations from linearity might be explained by steric hindrances. Reverse trends for the NA and NB chemical shifts are observed, despite the fact that similar reactions are supposed at both sites.