Structure Of Rubber Research Articles

Thermal annealing of natural rubber films controls wettability and enhances cytocompatibility

In spite of the widespread use of natural rubber in regenerative therapies, thermally induced modifications of its complex chemical structure and their effect on the surface properties and the cell response (attachment-adhesion-proliferation) are still an unexplored topic. Here, we demonstrate how thermal treatments enhance the cell response due to changes to the inner and surface structures of natural rubber. In situ studies of the temperature effects conducted via infrared spectroscopy revealed both molecular rearrangements and anharmonic effects in the polymeric lattices. Thermal treatments at different temperatures allowed to control the wetting regime. Contributions of different surface parameters to the wettability were decoupled by statistical analysis of the principal component. The polar component of the surface free energy was recognized as the main surface player, which influences cell spreading, attachment, proliferation, and tissue growth. A simple thermal annealing of the natural rubber film at 373 K alters the local structure of the latex inducing an increase in cell viability. The experimental-statistical analysis approach allows an accurate correlation of physicochemical properties with cell supportability. The results highlight the potential of natural rubber polymers by tuning surface wettability, via simple thermal treatment, for biomedical applications.

Dynamic heterogeneity and nanophase separation in rubber-toughened amine-cured highly cross-linked polymer networks

Solid state nuclear magnetic resonance (NMR) spectroscopy and small-to wide-angle X-ray scattering (SWAXS) methods were used to characterize the heterogeneous dynamics and polymer domain structure in rubber modified thermoset materials containing the diglycidyl ether of bisphenol A (DGEBA) epoxy resin and a mixture of Jeffamine reactive rubber and 4,4-diaminodicyclohexylmethane (PACM) amine curing agent. The polymer chain dynamics and morphologies as a function of the PACM/Jeffamine ratio were determined. Using dipolar-filtered NMR experiments, the resulting networks are shown to be composed of mobile and rigid regions that are separated on nanometer length scales, along with a dynamically immobilized interface region. Proton NMR spin diffusion experiments measured the dimensions of the mobile phase to range between 9 and 66 nm and varied with the relative PACM concentration. Solid state 13C magic angle spinning NMR experiments show that the highly mobile phase is composed entirely of the dynamically flexible polyether chains of the Jeffamine rubber, the immobilized interface region is a mixture of DGEBA, PACM, and the Jeffamine rubber, with the PACM cross-linked to DGEBA predominantly residing in the rigid phase. The SWAXS results showed compositional nanophase separation spanning the 11–77 nm range. These measurements of the nanoscale compositional and dynamic heterogeneity provide molecular level insight into the very broad and controllable glass transition temperature distributions observed for these highly cross-linked polymer networks.

Removal of Proteins and Its Effect on Molecular Structure and Properties of Natural Rubber

Removal of protein from natural rubber was carried out via deproteinization of natural rubber in the latex stage. Then, its effect on the molecular structure and properties of natural rubber was investigated. Urea, SDS, and acetone were used as denaturing agent, a surfactant, and a polar solvent in the deproteinization, respectively. Various deproteinized natural rubbers were obtained after one, two, and three times of centrifugation with and without acetone, namely DPNR1, DPNR2, DPNR3, DPNR1-A, DPNR2-A, and DPNR3-A. It was found that the total protein content significantly decreased as increasing the number of centrifugations; however, the total fatty acid contents showed a slight decrease. Structural characteristics analyzed by nuclear magnetic resonance spectroscopy indicated no changes in the chemical structure of natural rubber after deproteinization. However, the removal of proteins significantly enhanced the resolution of the NMR signals. Gel content and tensile properties of natural rubber showed a decrease in the removal of proteins, which was associated with the decrease in the number of the inherent branching points formed in natural rubber.

Mechanism of the foaming agent‐assisted microwave drying process on the construction of natural raw rubber network and cross‐linking network

AbstractThe drying process of natural rubber latex significantly affects the structure of the raw rubber network and vulcanizate crosslinking network, resulting in various anti‐aging performances. In the present study, a microwave generator was used as an efficient source of clean energy; potassium oleate was introduced as a foaming agent to increase the porosity and water loss channel of the latex system. Aiming at dehydrating and drying natural rubber latex efficiently, an aging resistant rubber composite was prepared. Meanwhile, the mechanism of the foaming agent‐assisted microwave drying process on the raw rubber network and the cross‐linking network was studied. The experimental results show that the prepared rubber using by this process has higher plastic retention and fluidity. Moreover, it contains more non‐rubber components (e.g. protein and acetone extract) and better network structure of raw rubber and vulcanized rubber. It is found that applying this process increases the tensile product by 13.5% and the retention rate of the tensile product after aging by 15.3 times. This process is important for the development of the rubber industry in the direction of green environmental protection, energy conservation, and high efficiency.

Synthetic Rubber with the Tensile Strength of Natural Rubber

The preparation of synthetic rubber with tensile strength identical to that of natural rubber is a long-standing unsolved problem in chemistry despite extensive related research. Here, we prepare synthetic rubber with tensile strength identical to that of natural rubber as a result of our discovery that natural rubber is a naturally occurring nanocomposite with proteins and lipids. The synthetic rubber is prepared by chemically attaching nanoparticles onto microparticles of synthetic cis-1,4-polyisoprene dispersed in water as a colloidal dispersion, followed by drying to form an “island-nanomatrix structure” similar to that of natural rubber. The stress at break of synthetic cis-1,4-polyisoprene increases dramatically from 0.1 to 3.9 MPa. The cis-1,4-polyisoprene with an island-nanomatrix structure exhibits almost the same mechanical properties as natural rubber. In addition, the synthetic cis-1,4-polyisoprene with an island-nanomatrix structure is vulcanized in the conventional manner using sulfur, zinc oxide, a vulcanization accelerator, and stearic acid at 150 °C and 15 MPa for an optimal vulcanization time after mechanical mixing. The stress at break of the resulting vulcanized cis-1,4-polyisoprene with an island-nanomatrix structure is 35.2 MPa, which is higher than that of vulcanized natural rubber. The preparation of synthetic rubber with mechanical properties identical to those of natural rubber is achieved by the formation of an island-nanomatrix structure in the synthetic rubber and is demonstrated by the mechanical properties of the vulcanized synthetic rubber being identical to those of vulcanized natural rubber.

Rubber–Bitumen Interaction of Plant-Blended Rubberized Bitumen Prepared under Various Blending Conditions

Abstract Rubberized bitumen produced from waste tire rubber has been widely used as a sustainable paving material worldwide. However, different production conditions may lead to rubberized bitumens with different performances. This study aims to understand the mechanism of the physicochemical interaction between rubber particles and virgin bitumen of the rubberized bitumens prepared in the plant under various blending conditions. To achieve this objective, samples of the rubberized bitumens prepared in the plant under four conditions were first collected and then characterized through various laboratory tests. The infrared spectra and gel permeation chromatograph test results demonstrated that the main crosslinking structures of rubber remain stable and undamaged during the whole production period, although some chemical reactions—such as oxidation, decarboxylation, and devulcanization—occur. The storage stability test results implied that the plant-blended rubberized bitumen exhibits no obvious phase separation after storage at 163°C for 48 h and becomes more stable as the blending time prolongs. The rheological test results indicated that the rubber–bitumen interaction is mainly composed of early stage absorption and swelling of rubber particles, continuous emission of volatile bitumen components, and late-stage partial degradation of fully swollen rubber particles. The surface images of the rubberized bitumen confirmed that as the blending time increases, the surface of rubberized bitumen becomes smoother, as a result of the improved rubber–bitumen interaction.

Process and Characterization of Natural Rubber Modification (Sir-20) With Grafting Maleat Anhydride

Modification of natural rubber by Grafting method using monomer maleate anhydride is a technique of modification of natural rubber polymers that aims to change the physical and chemical sifak of natural rubber polymers. The grafting process is carried out by comparing the amount of MA that is graphed based on the type of peroxide, the variation of peroxide concentration and the variation of MA concentration. FTIR test results showed the appearance of peak absorption at the wave number of 1710-cm cluster C=O carbonyl from MA that is graphed in natural rubber.. Based on the comparison of ir analysis of peroxide concentration used i.e. (0.01, 0.05 and 0.1) molar ratio obtained the largest carbonyl index at DCP concentration of 0.05 mr similarly, the comparison of IR analysis results of MA concentration variations (3, 6, 9, 12) phr shows the largest carbonyl index that appears in the C=O absorption area is in the KA-g-MA sample with a MA variation of 12 phr with Carbonyl index = 45.81. The degree of MA grafting on natural rubber structures increases with increased MA concentration.

Effect of non-rubber components on the crosslinking structure and thermo-oxidative degradation of natural rubber

Non-rubber components (NRCs) in natural rubber (NR), including proteins, phospholipids, fatty acids, etc., determine to a large extent the structure and properties of NR. In this study, the effects of NRCs on the network structure and thermo-oxidative aging behavior of unvulcanized and vulcanized NR were investigated. NRCs were found to form physically crosslinked networks in the unvulcanized NR and acted as a natural antioxidant to scavenge free radicals, which contributed to improved thermo-oxidative stability of the unvulcanized NR. Swell analysis, chemical probe analysis (DPPH), and XPS results showed that the NRCs accelerated the vulcanization reaction and increased the crosslink density, and promoted the formation of more mono- and disulfide bonds during vulcanization. When aged at high temperatures, more monosulfide bonds were formed in the vulcanized rubber with high contents of NRCs by cleaving and rearranging the poly- and disulfide bonds. NRCs were also found to increase the activation energy of thermal degradation and led to the better mechanical stability of vulcanized NR against thermal oxidation.

Bleed-out suppression of silicone rubber by electron beam crosslinking

A silicone rubber with a highly crosslinked surface layer was synthesized by a two-step crosslinking reaction with thermal processing and subsequent electron beam (EB) irradiation. The effect of the EB irradiation on the silicone rubber was evaluated by measuring the volume swelling ratio, shore hardness, tensile breaking strength, and water contact angle of the EB-crosslinked silicone rubber. The silicone rubber was effectively crosslinked as the EB irradiation increased. The optimal EB irradiation dose to form the EB-crosslinked structure in the silicone rubber was 500 kGy. Insufficient EB irradiation does not form a sufficient EB-crosslinked structure, while excessive EB irradiation dose would decompose the silicone rubber. The finer crosslinked structures of the surface layer of the silicone rubber formed by EB irradiation could function as a leak-proof filter to prevent the bleed-out of low-molecular-weight siloxanes inside the silicone rubber. The effect of the type of EB-crosslinking agent on the bleed-out suppression effect was investigated. The bleed-out suppression effect was improved in the following order: no EB-crosslinking agent < ethylene glycol dimethacrylate < silicone diacrylate < trimethylolpropane trimethacrylate (TMPTMA). The thermally and EB-crosslinked silicone rubber with TMPTMA successfully reduced the bleed-out ratio by approximately 60%, compared to the thermally crosslinked silicone rubber without EB irradiation and EB crosslinking agent.

ENHANCING PERFORMANCE OF MECHANICALLY OPERATED PACKER

During hydraulic fracturing operations of low-permeability reservoirs, packers are the key component to ensure the success of multistage fracturing. Packers enable sections of the wellbore to be sealed of and separately fractured by hydraulic pressure, one at a time, while the remainder of the wellbore is not afected. However, reliable sealing properties of the packer rubber are required to meet the high-pressure and high-temperature (HPHT) conditions of reservoirs (such as 70 MPa and 170 °C). In this study, the structures of the packer rubber with two diferent materials are optimized numerically by ABAQUS and validated by experiments. The optimization process starts from the packer rubber with a conventional structure, and then, the weakest spots are identifed by ABAQUS and improved by slightly varying its structure. This process is iterative, and the fnal optimized structure of a single rubber barrel with expanding back-up rings is achieved. For the structure of three rubber barrels with metallic protective covers, both HNBR and AFLAS fail under HPHT conditions. For the fnal optimized structure, the packer rubber made of AFLAS can work better under HPHT than that made of HNBR which ruptures after setting. The results show that the optimized structure of a single rubber barrel with expanding back-up rings and the material AFLAS are a good combination for the packer rubber playing an excellent sealing performance in multistage fracturing in horizontal wells. Keywords: packer rubber, sealing property, structure optimization, hydrogenated nitrile–butadiene rubber (HNBR), AFLAS rubber.

ПРОГНОЗИРОВАНИЕ СРОКА СЛУЖБЫ РЕЗИН ДЛЯ МОРСКОГО КЛИМАТА

The purpose of this study is to determine the possibility of using serial rubber compounds for the production of shock absorbers with a 25-year service life, including storage and operation. Four rubber compounds with different polymer bases were tested for resistance to accelerated thermal aging. During the analysis and mathematical processing of experimental data of changes occurring in the structure of rubbers in the process of aging, the regularity of changes in the rate of aging of rubbers depending on temperature was mathematically described. By means of the revealed regularity, predictive calculations of the characteristic indicators of the rubbers of each of the four compositions were made, after comparison of which a justification was given for the selected composition

Setting Relationships between Structure and Devulcanization of Ground Tire Rubber and Their Effect on Self-Healing Elastomers.

The use of devulcanized tire powder as an effective reinforcement in self-healing styrene-butadiene rubber (SBR) compounds has been investigated for the first time in this work. For this purpose, the evolution of the microstructure of the rubber from end-of-life tires (ELTs) was studied during granulation, grinding and devulcanization through an exhaustive characterization work in order to relate the final microstructure with the mechanical response of the repaired systems. Different morphologies (particle size distribution and specific surface area) obtained by cryogenic and water jet grinding processes, as well as different devulcanization techniques (thermo-mechanical, microwave, and thermo-chemical), were analyzed. The results demonstrated the key influence of the morphology of the ground tire rubber (GTR) on the obtained devulcanized products (dGTR). The predictions of the Horikx curves regarding the selectivity of the applied devulcanization processes were validated, thereby; a model of the microstructure of these materials was defined. This model made it possible to relate the morphology of GTR and dGTR with their activity as reinforcement in self-healing formulations. In this sense, higher specific surface area and percentage of free surface polymeric chains resulted in better mechanical performance and more effective healing. Such a strategy enabled an overall healing efficiency of more than 80% in terms of a real mechanical recovery (tensile strength and elongation at break), when adding 30 phr of dGTR. These results open a great opportunity to find the desired balance between the mechanical properties before and after self-repair, thus providing a high technological valorization to waste tires.

Influence of Oligopeptide Length and Distribution on Polyisoprene Properties.

The tuning of binding modes of polar groups is the key step to mimicking the structure and properties of natural rubber through the molecular design of synthetic polyisoprenes. Herein, the ordering and binding distances of oligopeptides could be altered systematically by changing their lengths and distribution along the polyisoprene chain, which impose huge impacts on the mechanical properties and chain dynamics of green rubber. In detail, a series of peptide-functionalized polyisoprenes with terminal blocks (B-2A-PIP, B-3A-PIP) or random sequences (R-2A-PIP, R-3A-PIP) are fabricated by using dipeptides (2A) or tripeptides (3A) as crosslinkers to explore the mechanism of terminal interaction on mechanism properties and chain dynamics. B-4A-PIP and R-4A-PIP served as control samples. It is found that the increased oligopeptide length and the block distribution improves the mechanical properties and confine the chain movement by elevate the contents of ordered and compact microstructures, which is indicated by XRD, broadband dielectric spectroscopy (BDS) and consistent with the result of molecular dynamics simulation. New relaxation signals belonging to oligopeptide aggregates are found which showed elevated dielectric strengths upon temperatures increase. Additionally, it also reveals that the binding modes of oligopeptide do not significantly influence the entanglements of polyisoprene.

Fabrication of silicone microcups on periodic microswelling structure of silicone rubber by 193-nm ArF excimer laser

A new morphology for micro/nanocontainer, silicone hemispherical microcup on periodic microswelling structure of silicone rubber, was successfully fabricated by a 193-nm ArF excimer laser. The laser-irradiated silicone rubber underneath silica glass microspheres were periodically and photochemically swelled by the photodissociation of Si-O-Si bonds of silicone rubber. A little later, lower molecular weight silicones which were generated by the photodissociation might be ejected from the microswelled silicone rubber during laser irradiation along a curvature of each the microsphere. After removing the microspheres, chemical bonding state of the fabricated microcups was analyzed to be a silicone. Small amount of liquid could be trapped in the microcups under scanning electron microscope. A superhydrophobic property was also obtained on the fabricated silicone microcups.

Probe the terminal interactions and their synergistic effects on polyisoprene properties by mimicking the structure of natural rubber

Biosynthetic residues in vulcanized natural rubber (VNR) create a blend end-linking network through two kinds of terminal groups dispersed in the covalent network, leading to excellent mechanical properties, such as high tensile strength and high crack growth resistance. However, due to the complex composition of natural rubber (NR), it is not likely to rebuild the terminal structures directly. In this circumstance, this work designs the terminal structures of synthetic polyisoprene by mimicking the structure of NR at the principal level. In detail, oligopeptide groups and phosphate groups were attached at the end of polyisoprene respectively, to form similar end-linking network as found in VNR. Three terminal functionalized model polymers containing oligopeptides (4A), phosphates (P) or both oligopeptides and phosphates (PA) were synthesized and vulcanized to generate V4A, VP and VPA, respectively. The oligopeptides and phosphates interact with each other to form new blended aggregates, which makes the end-linking network integrated. Blended aggregates are captured by the CLSM and TEM. The rheological tests demonstrate that the formation of blend aggregates is the foundation of synergistic effect on shear modulus, which will disappear at high temperature or solution state. It is also found that the mechanical properties of VPA are superior to that of VP and V4A, which is attributed to the more integrated end-linking network structure. Further analysis showed that the synergistic effect between terminals makes the entanglements near the blended aggregates difficult to unwrap and become permanent entanglements, thereby increasing the crosslinking density. The more complete end-linking network endow VPA higher crystallization ability than VP and V4A. These results expand our understanding of how terminals work in NR and provide new insight into the generic design of mechanically strong elastomer.

Smart Table Tennis Racket with Tunable Stiffness for Diverse Play Styles and Unconventional Technique Training (Adv. Mater. Technol. 10/2021)

Smart Table Tennis Racket In article number 2100535, Mengying Zhang, Jinbo Wu, and coworkers invent a smart table tennis racket with tunable stiffness based on electrorheological elastomers. The racket face is a multilayer structure of rubber, soft electrode, anisotropic electrorheological elastomer and copper electrode. By applying an electric field, the smart racket successfully changed the trajectory of balls, reduced ejection angle and increased ejection velocity to adapt to diverse play styles and improve unconventional play technique.

Effect of radiation on mechanical properties and molecular structure of rubbers for nuclear robots

As polymers, rubber materials are easily affected by radiation; therefore, their radiation resistance must be considered for their use in robots and automation equipment in high-radiation environments. In this study, the properties of several common rubber materials, ethylene propylene diene monomer (EPDM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), fluororubber (FKM), and acrylate rubber (ACM), were investigated under high-dose gamma-ray irradiation. The dose rate of gamma rays was 66.76 Gy/min, and the cumulative dose was 1214965.24 Gy. Oxidative decomposition of the double bond of EPDM occurred, leading to slight decreases in the strength and elongation. NBR and HNBR were mainly subjected to crosslinking of the molecular structure, resulting in small increases in strength and significant decreases in elongation. The cyano decomposition reaction occurred in ACM, and its crystallinity increased, leading to embrittlement and decreases in the strength and elongation. Oxidative decomposition and cross-linking simultaneously occurred in FKM, resulting in an increase in strength and decreases in elongation and the elastic modulus.

New Principles of Polymer Composite Preparation. MQ Copolymers as an Active Molecular Filler for Polydimethylsiloxane Rubbers.

Colorless transparent vulcanizates of silicone elastomers were prepared by mixing the components in a common solvent followed by solvent removal. We studied the correlation between the mechanical behavior of polydimethylsiloxane (PDMS)-rubber compositions prepared using MQ (mono-(M) and tetra-(Q) functional siloxane) copolymers with different ratios of M and Q parts as a molecular filler. The composition and molecular structure of the original rubber, MQ copolymers, and carboxyl-containing PDMS oligomers were also investigated. The simplicity of the preparation of the compositions, high strength and elongation at break, and their variability within a wide range allows us to consider silicone elastomers as a promising alternative to silicone materials prepared by traditional methods.

Characterization of the trans-structure in the molecular chain structure of natural rubber

Natural rubber (NR) has excellent mechanical properties due to its unique molecular chain structure. In previous studies, the signal of the cis- and trans-isoprene units was deduced by 13C-NMR spectrum of the low molecular weight fraction of NR. In this study, through investigating the 1H-NMR spectra of ribbed smoked sheet 1 (RSS-1) and standard Chinese rubber whole fraction (SCR-WF), and Eucommia ulmoides gum (EUG), trans-1,4-polyisoprene (TPI), found that the methyl-proton in the cis- and trans-isoprene units in 1H-NMR spectra of NR showed signals at 1.61 and 1.53 ppm, respectively. Further, the content of trans-structure in the molecular chain of NR of different producing areas was calculated. The results show that the content of trans-structure in the molecular chain structure of RSS-1 and SCR-WF were 1.500 and 1.054%, respectively.

Comparative study of the microstructure of solid rubber from Ficus carica and Hevea brasiliensis

AbstractNatural rubber from Hevea brasiliensis (Hb) is known to have a characteristic network structure, with branch points formed by minor nonrubber components such as proteins and phospholipids that connect the major rubber component, cis‐1,4‐polyisoprene chains. However, the structure of solid rubber from Ficus carica (Fc) is not well known. In this study, we examined the microstructure and protein composition of solid rubber from Fc. Transmission electron microscopy analysis of Fc solid rubber revealed that the nonrubber components formed a nonuniform framework in the rubber matrix, and that many rubber particles were fused together. We determined that ficin, a cysteine endoproteolytic protease, was a major protein in the Fc rubber. It appears that ficin degrades the proteins associated with rubber particles rather than acting as a protein connecting the cis‐1,4‐polyisoprene chains in Fc rubber. We also found that a macrogel fraction, which separated after the dissolution of Hb solid rubber in toluene, was absent in the Fc solid rubber. These results suggest that there are no proteinous branch points in Fc rubber. Furthermore, size exclusion chromatography with multiangle light scattering (SEC‐MALS) analysis of the transesterified rubber demonstrated that no branch points composed of phospholipids were involved in Fc rubber. On the basis of our results, we propose a microstructure for the rubber particles in Fc solid rubber and discuss the relationship between the microstructure and the structure of the rubber chains within it.