Unvulcanized Rubber Research Articles

History and Future of Anti-Adhesive Agent

An anti-adhesive agent is used to prevent the adhesion when unvulcanized rubber is stacked and stocked. We have been developing various types of anti-adhesive agents such as soap based type, powder type and polymer component based type from the environment and productivity. These anti-adhesive agents have received a certain evaluation from rubber producer, but the properties of the anti-adhesion are affected by wettability, sinking, stretching of the anti-adhesion film to rubber surface, and improvement requests from rubber producer are still strong. We hope that we can contribute to the development of the rubber industry by developing new anti-adhesive agent.

A thermo-mechanical finite element material model for the rubber forming and vulcanization process: From unvulcanized to vulcanized rubber

In this contribution, the transition in the thermo-mechanical properties of unvulcanized rubber during the vulcanization (curing) process is modeled by a material model for unvulcanized and vulcanized rubber (two-phase material) in the context of finite strain thermo-mechanics within the finite element method (FEM). For the vulcanization rate, a constitutive approach with few parameters is proposed representing the monotonic increase of the degree of vulcanization as a function of current temperature and the curing history. The material model taking into account the two phases of rubber uses different constitutive approaches for the isochoric part and the volumetric part for which a multiplicative split of the deformation gradient is considered. The isochoric part of the model consists of a hyperelastic spring and a dashpot device in series forming a Maxwell element with properties depending on the degree of vulcanization and temperature. Inelastic isochoric deformations during the forming and vulcanization process of rubber parts can be captured. The volumetric part consists of a hyperelastic spring and takes into account volume changes due to mechanical loads and temperature variations (thermal expansion). The proposed material model is formulated based on the displacement field, the temperature field, the degree of vulcanization and its kinetics. It is implemented into the thermo-mechanically coupled framework of the FEM in 3D for finite strains.

Influence of nonrubber components on properties of unvulcanized natural rubber

Low‐protein natural rubber (LPNR) and acetone‐extracted natural rubber (AENR) were prepared in solid form by alkaline treatment and acetone extraction to remove proteins and lipids. The content of proteins and lipids along with gel content were characterized by Fourier‐transform infrared spectroscopy (FTIR) and size exclusion chromatography with multiangle light scattering (SEC‐MALS) analysis. It was found that natural rubber (NR) treatment by alkaline hydrolysis or acetone extraction decreased proteins or lipids along with gel content. Also, having less proteins and lipids changed the network structure from macroaggregates to microaggregates. This resulted in inferior plasticity and poor mechanical, rheological, and dynamic properties. Furthermore, decreased strain‐induced crystallization and storage hardening were confirmed by temperature scanning stress relaxation (TSSR), after removal of proteins and lipids. Therefore, protein and lipid contents together with gel content play essential roles in controlling various properties of unvulcanized NR.

Adhesion and heat build-up of rubber for energy-saved tyre

The objective of this study was to investigate the effect of crosslinking systems (conventional and efficient systems) on the contact mechanics and heat build-up of natural rubber (NR) tyre mimicking samples. The JKR (Johnson, Kendall and Roberts) experiment has been established to measure the contact mechanics in NR samples at different vulcanization systems. Work of adhesion obtained from JKR model is in good agreement with that calculated from contact angle measurement. From the contact mechanics point of view, the adsorption of the rubber to the glass slide surface plays a major role in the strain energy release rate. Higher rubber free chain samples (unvulcanized rubber) represent higher adhesion hysteresis and higher heat build-up compared to vulcanized rubbers whichever was the vulcanization system. Finally, rubber sample obtained using efficient vulcanization has the lowest adhesion hysteresis and heat build-up. These results suggest that the rubber with efficient vulcanization is preferable for the application of energy-saving tyres.

Adhesive-free adhesion between heat-assisted plasma-treated fluoropolymers (PTFE, PFA) and plasma-jet-treated polydimethylsiloxane (PDMS) and its application

Conventional low-temperature plasma treatment was reported to minimally improve the adhesion property of polytetrafluoroethylene (PTFE), whereas heat-assisted plasma (HAP) treatment significantly improved the same. An unvulcanized rubber was previously used as an adherent for PTFE. This study aimed to achieve strong adhesive-free adhesion between PTFE and vulcanized polydimethylsiloxane (PDMS) rubber. As-received vulcanized PDMS rubber did not adhere to HAP-treated PTFE, and as-received PTFE did not adhere to vulcanized rubber of plasma-jet (PJ) treated PDMS rubber; however, HAP-treated PTFE strongly adhered to vulcanized PJ-treated PDMS rubber, and both PTFE and PDMS exhibited cohesion failure in the T-peel test. The surface chemical compositions of the PTFE and PDMS sides were determined using X-ray photoelectron spectroscopy. The strong PTFE/PDMS adhesion was explained via hydrogen and covalent bond formation (C–O–Si and/or C(=O)–O–Si) between hydroxyl (C–OH) or carboxyl (C(=O)–OH) groups of the HAP-treated PTFE. This process was also applied to adhesive-free adhesion between a tetrafluoroethylene–perfluoroalkylvinylether copolymer (PFA) and PDMS; subsequently, a translucent PFA/PDMS assembly with strong adhesion was realized together with the PTFE/PDMS assembly. Strong adhesive-free adhesion between fluoropolymers (PTFE, PFA) and vulcanized PDMS rubber without using any adhesives and graft polymer was successfully realized upon plasma treatment of both the fluoropolymer and PDMS sides. Additionally, a PDMS sheet, which was PJ-treated on both sides, was applied to strongly adhere fluoropolymers (PTFE, PFA) to materials such as metal and glass. PJ-treated PDMS was used as an intermediate layer rather than a strong adhesive, achieving PTFE/PDMS/metal and PTFE/PDMS/glass assemblies. The PTFE/PDMS, PDMS/metal, and PDMS/glass adhesion strengths exceeded 2 N/mm.

Fourier-transform rheology of unvulcanized styrene butadiene rubber filled with increasingly silanized silica

ABSTRACTSilica as one the most important fillers for rubber material is routinely modified by silane to improve its compatibility with the rubber matrix. Silanization of the silica particle affects both the linear and nonlinear rheological behaviors of the compounds. Their rheological nonlinearity, however, is mostly analyzed in an indirect way from linear rheological parameters, e.g. G′(ω1, γ0) and G″(ω1, γ0), which lose their physical meaning in the nonlinear viscoelastic regime. In the present work, the nonlinearity is directly quantified by the Fourier-transform rheology (FT-Rheology) technique in terms of I3/1(ω1, γ0), the third relative higher harmonic, for unvulcanized styrene butadiene rubber compounds filled with a fixed amount of silica, but varying dosages of silane. With the proposed model for I3/1(γ0), the contributions toward nonlinearity from the filler networks at a low strain amplitude and the one from the polymer networks at high strain amplitude can be successfully separated for filled systems. The utmost nonlinearity contribution from the filler networks decreases with the silane content, which is assigned to the weakening interparticle interaction of the filler. With increasing silanization of silica, the utmost nonlinearity contribution from the polymer networks is found to increase. This nonlinear mechanical response is attributed to the enhanced interfacial interaction between the filler and polymer.

Mechanical properties of SFRC using blended Recycled Tyre Steel Cords (RTSC) and Recycled Tyre Steel Fibres (RTSF)

Processed high-specification steel cords (RTSC) extracted from un-vulcanised rubber belt off-cuts have the potential to substitute (manufactured steel fibres) MSF in concrete, leading to enhanced structural performance and significant environmental benefits. The target of this research is to demonstrate that recycled-only fibre mixes could meet or exceed the performance of MSF-only mixes, at the same total fibre dosage. Direct tensile and single-fibre pull-out tests are carried out, to evaluate the tensile strength of RTSC and the interfacial bond behaviour between RTSC and concrete matrix, respectively. It is found that RTSC have a tensile strength greater than 2600 MPa and their critical embedded length is in the range of 25–40 mm. The flexural characteristics of 8 steel fibre reinforced concrete (SFRC) mixes at fibre dosages of 30 and 45 kg/m3 are examined by using EN 14651:2005 3-point notched prism tests. RTSC with lengths of 60 mm are used on their own, or blended with post-processed steel fibres recovered from end-of-life tyres (RTSF) at varying dosages. The performance of two manufactured steel fibres (MSF)-only mixes and one RTSF-only mix is also examined. Comparisons in terms of flexural performance are made between MSF-only mixes versus recycled-fibre (RTSC on their own or blended with RTSF) mixes at the same total dosage. RTSC are found to be extremely well mobilised at larger crack widths and the post-cracking strength of recycled-fibre mixes is significantly higher (up to 103%) than MSF-only mixes at the same total fibre dosage. In addition, the flexural performance of concrete with recycled-fibre blends improves with increasing amounts of RTSC.

Preparation and Physical Properties of Porous Starch/Natural Rubber Composites

Porous starch is modified by the addition of dodecenyl succinate anhydride (DDSA), to decrease the self‐aggregation, and then blended with natural rubber (NR) latex to obtain the modified starch/NR composites. The composites are found to have improved properties compared with the corresponding pure NR. Results of a thermal analysis show that the thermal degradation reaction of modified starch/NR composites is a two‐step reaction, with the initial (T0) and the final (Tf) temperatures of main reaction being increased, and glass transition temperature (Tg) slightly reduced compared with the corresponding pure NR. The curves of elastic modulus (G′) and loss factor (tanδ) versus the strain of unvulcanized rubber compounds are obtained using a rubber process analyzer. Dynamic mechanical thermal analysis shows that the rolling resistance of the composites is improved by the addition of modified starch.

Development of an electrode for carrots using conductive unvulcanized rubber

AbstractElectrical impedance of plants is related to condition of the plant's cell tissue. In existing works, the impedance has been utilized for understanding the condition of the plant. There are three kinds of electrode for measuring the impedance: a needle electrode, a metallic foil electrode, and a conductive gel electrode. However, these electrodes have problems. The needle electrode injures the plants. The metallic foil electrode does not stably contact to the plant because the plants has curve and convexo–concave surface. The conductive gel electrode including NaCl blasts the plants. We proposed a conductive unvulcanized rubber electrode for measuring the electrical impedance of the carrots. Characteristics of the conductive unvulcanized rubber electrode were soft, deformable, and self‐adhesive. Thus, the electrode was noninvasive and did not damage to the carrots. In experiments, we showed that the conductive unvulcanized rubber electrode could be utilized for measuring electrical impedance of a carrot for 912 h. Moreover, we observed that the contact area of the electrode was larger than the contact area of a conductive adhesive tape electrode.

Biodegradation of unvulcanized natural rubber by microorganisms isolated from soil and rubber surface: A preliminary study

ABSTRACTThe Natural rubber (NR) biodegradation by three microorganisms has been evaluated: a yeast (Rhodotorula mucilaginosa) and a bacterium (Pseudomonas sp.), isolated in a liquid culture from soil, and a filamentous fungus (Alternaria alternata), isolated on a solid culture from an NR surface, were tested. The biodegradation was conducted for four months in liquid culture, at 30°C, in agitated and stationary conditions, using a Mineral Salt Medium with NR as the only carbon source. The growth behaviour of the yeast and the bacterium was evaluated by means of optical density measurements (OD650). At the end of the incubation, the dry weight biomass of the microorganisms was measured. R. mucilaginosa showed a higher biomass production in the agitated culture, while a more efficient production was observed in static conditions for the Pseudomonas and A. alternata strains. The highest enzymatic activity of Lignin peroxidase (LiP) and Manganese-dependent peroxidase (MnP) was obtained in static conditions for A. alternata. The laccase production was probed by guaiacol oxidative polymerization on agar plates. The microorganism biodegradation capability was assessed through a combination of SEM analysis, FTIR-ATR spectroscopy, and Size Exclusion Chromatography techniques. An extended mycelium-substrate interphase and a decrease in the NR molecular weight were observed.

Novel approach to determine non-rubber content in Hevea brasiliensis: Influence of clone variation on properties of un-vulcanized natural rubber

The mesostructure and non-rubber content, including proteins and lipids, in natural rubber from three different Hevea brasiliensis clones, namely RRIT408, PB235 and RRIM600, were investigated by a new technique, temperature scanning stress relaxation (TSSR), along with other relevant methods It was found that the significant relaxation spectrum of TSSR was found as broad peaks in the temperature ranges of 58–60 °C which indicated level of interaction for proteins and lipids at the chain terminals. This directly relates to storage hardening phenomenon. Furthermore, we found that the molecular mass distribution is bimodal for RRIM600 clone while it is unimodal for RRIT408 and PB235. Furthermore, the RRIM600 clone contained high aggregates and non-rubber components that enhanced the mechanical and rheological properties and caused strong storage hardening phenomenon. This might be attributed to the high fraction of short chains providing many chain ends, and to the total content of proteins and lipids. However, the unimodal rubber from PB235 clone exhibited poorer mechanical and physical properties and less storage hardening than those from RRIM600 and RRIT408. This might be attributed to lower content of proteins and lipids and longer molecular chains (low number of chain ends), causing less formation of aggregates or lower gel content.

Development of an Electrode for Carrots using Conductive Unvulcanized Rubber

Development of an Electrode for Carrots using Conductive Unvulcanized Rubber

DEPENDENCE OF THE ONSET OF STRAIN-INDUCED CRYSTALLIZATION OF NATURAL RUBBER AND ITS SYNTHETIC ANALOGUE ON CROSSLINK AND ENTANGLEMENT BY USING SYNCHROTRON X-RAY

ABSTRACT Strain-induced crystallization (SIC) and stress–strain relations of varied crosslink structures and varied crosslink densities of vulcanized natural rubber (NR), vulcanized synthetic polyisoprene rubber (IR), and un-vulcanized natural rubber are compared using a synchrotron X-ray. The onset strain of SIC does not depend on crosslink density and crosslink structures. Un-vulcanized NR shows a smaller onset strain of SIC than that of vulcanized NR. Therefore, entanglements in NR are pivot points to induce SIC, just as entanglements in semi-crystalline plastics induce flow-induced crystallization (FIC). During deformation, complicated phenomena occur simultaneously such as cavitation, crosslink breakdown, SIC with temperature upturn, and limited extensibility of chains between crosslinks, because rubber is a significantly inhomogeneous material. It is still difficult to evaluate the contribution of SIC to stress-upturn of the stress–strain relation of rubber.

The influence of natural rubber – butadiene rubber and carbon black type on the mechanical properties of tread compound

The objective of this study is to optimize the performance of the tread compound, by mixing of specified ingredients, such as Natural Rubber (NR) and Butadiene Rubber (BR) at various compositions, and also the type of carbon black as filler. The composition of NR and BR are used as follows 100:0; 95:5 and 85:15. Other materials used as rubber additives are peptizer, ZnO, stearic acid, additives, processing oil, and curatives. Two types of carbon black namely N220 and N234 are used in this research. The un-vulcanized rubber from each formula was characterized of curing characteristics and Mooney viscosity. The vulcanized rubber was then characterized its mechanical and thermal properties. It is clear from the research that, the addition of BR into the NR compound increases the abrasion resistance, rebound resilience and hardness, yet the glass transition temperature of the rubber compounds decreases. On the other hand, it seems that the rubber compound reinforced N220 or N234 gives comparable results on both mechanical and thermal properties.

Compressibility of unvulcanized natural and EPDM rubber: New experimental protocol and data evaluation in the framework of large strain elasticity theory

Despite considerable ongoing efforts, accurate computational simulation of the flow behavior of (unvulcanized) rubber remains an open challenge. There is growing evidence that one of the reasons for that is insufficient consideration of, or knowledge on, the mechanical compressibility of the material. As a contribution to tackle this open question, we here report on a series of hydrostatic compression tests performed on natural rubber, as well as on two types of EPDM (ethylene-propylene-diene-monomer) rubber compounds. These materials were filled into a capillary rheometer with closed extrusion canal, and then compressed and released through volume changes realized at different speeds, while monitoring the corresponding hydrostatic pressures acting on the investigated rubbers. The volume changes then entered various relevant strain measures (Green-Lagrange strains, Hencky strains, linearized strains), while the pressures were mathematically transformed into energetically conjugate stress measures (second Piola-Kirchhoff stress, Kirchhoff stress, Cauchy stress). Insertion of these measures into the dissipation inequality resulting from the two fundamental laws of thermodynamics, revealed that the investigated materials behave purely elastically under hydrostatic pressure, albeit in a non-linear fashion. Irrespective of the format chosen for elasticity theory, the elastic bulk modulus appears as a power function of the hydrostatic pressure; the former increasing under-linearly, but non-asymptotically, with the latter. Careful statistical evaluation of the corresponding power law coefficients allows for derivation of upper and lower bounds of the bulk modulus, as functions of the hydrostatic pressure, an information which may prove essential for improving the accuracy of rubber extrusion simulations.

Effect of naturally occurring crosslinking junctions on green strength of natural rubber

The effect of the naturally occurring crosslinking junctions on green strength of natural rubber, isolated from Hevea brasiliensis, was investigated by using rubber extracted from Parthenium argentatum Gray (Guayule) as a model. Guayule rubber and natural rubber were characterized through nuclear magnetic resonance spectroscopy and size exclusion chromatography. The non‐rubber components of Guayule rubber and natural rubber were characterized by Kjeldahl method and Fourier transform infrared spectroscopy. It was found that Guayule rubber contains a much higher amount of fatty acids and their esters while it contains no proteins. The gel content, determined by swelling method, was related to a number of naturally occurring crosslinking junctions of Guayule rubber and natural rubber. The outstanding green strength of natural rubber was attributed to the effect of naturally occurring crosslinking junctions, when stress–strain curve and tensile properties of unvulcanized Guayule rubber were compared with those of unvulcanized natural rubber. Copyright © 2016 John Wiley & Sons, Ltd.

Aspects of Interfacial Structure of Silane Coupling Agents in Particulate-Filled Polymer Composites and the Reinforcement Effect: A Critical Review

In order to form an effective interphase in a polymer composite, the preparation and characterization of silane structure on particle surface and in the interfacial layer in the composite are reviewed. The polycondensation of silane is affected by the concentration and pH of silane solution and the pH of inorganic particle. Pulsed 1H nuclear magnetic resonance (pulsed NMR) analysis is useful to characterize the structure of silane layer on the particle surface. It is found that the linear chain structure formed from dialkoxy type silane is flexible, whereas the network structure formed from trialkoxy type silane is rigid. To form an effective interphase, the linear chain structure formed from dialkoxy type is more useful than the network structure formed from trialkoxy type in the silica-filled rubber composites. The pre-treatment method and the integral blend method are compared in the silica-filled rubber composites. As a result, the dialkoxy type is found to be suitable for the pre-treatment method, whereas the trialkoxy type is suitable for the integral blend method. In the pre-treatment method, the linear silane chains form entanglements with the rubber chains in the interfacial region and improve the reinforcement effect. In the integral blend of trialkoxy type, the formation of the silane network and the entanglement proceed simultaneously during the preparation process and a well-entangled interfacial region is formed. Pulsed NMR analysis for the silica-filled unvulcanized rubber composites is useful to analyze the interfacial layer in the composites. The surface treatment of CaCO3 with a mixture of amino and mercapto functional silanes is found to be useful to improve the reinforcement effect in rubber/CaCO3 composites.

Multilayer coextrusion of rubber compounds

This research work presents the first continuous multilayer coextrusion system for high viscosity elastomeric materials. Three unvulcanized rubber materials were chosen to validate the system: two butyl rubbers and a polyisoprene. The elastomers were characterized under oscillatory shear and the results used to perform computational flow simulations to investigate the effect of geometry on the flow path and flow rate. Successful extrudates of 8 and 32 layers were extruded at two different throughput rates for rheologically matched and rheologically mismatched material pairs. The results show good layering performance for both systems with little existence of viscous encapsulation and acceptable pressure drops. Computational and experimental results both show a nonuniform layer thickness distribution due to the geometric design of the layer multiplier extrusion dies, which were designed to minimize pressure drop in the system. This nonuniformity decreases with increasing number of layers. POLYM. ENG. SCI., 55:1520–1527, 2015. © 2015 Society of Plastics Engineers

Evaluation of Rubber Processing in Unvulcanised Rubber

Evaluation of Rubber Processing in Unvulcanised Rubber

Evaluation of Rubber Processing for Unvulcanized Rubber

Evaluation of Rubber Processing for Unvulcanized Rubber