Photocrosslinking of acrylated natural rubber

Photocrosslinkable elastomers with pendent acrylate groups have been synthesized by ringopening reaction of epoxidized natural rubber with acrylic acid. The kinetics of the acrylation reaction has been studied by infrared spectroscopy and shown to obey a simple first-order law. The acrylated natural rubber undergoes a fast crosslinking-polymerization when it is exposed to UV radiation in the presence of an aryl ketone photoinitiator, with formation of a tridimensional polymer network within a few seconds. The cure kinetics has been studied in real time by monitoring the disappearance of the IR absorption of the grafted acrylate double bond. The rate of polymerization was found to increase linearly with the degree of acrylation of the rubber, reaching values up to 3 mol kg^?1 s^?1. The isoprene double bond, which is inactive in virgin natural rubber, also undergoes polymerization upon UV exposure when epoxy or acrylate groups are present. The UV-cured polymer becomes totally insoluble in the organic solvents and exhibits remarkable mechanical properties, such as hardness, flexibility, and impact resistance. The gel fraction and the hardness were both shown to increase with the degree of acrylation and with the cure extent. © 1993 John Wiley & Sons, Inc.     

Correlations between natural rubber protein content and rapid predictions of rheological properties,compression set and hardness of rubber compound

In this study the correlations between protein contents of different kinds of natural rubber were considered with rheological behavior, compression set and hardness of rubber compounds based on natural rubber. At the first stage, protein contents were obtained by Kjeldahl method and correlated with normalized absorbance of amine band in NR's attenuated total reflection Fourier transform infrared spectra and shown linear behavior. At the second stage, correlations between the protein contents obtained by the spectra were considered with rheological behavior, compression set and hardness of rubber compounds and shown second order fitting models. The introduced models were applied to predict these features in case studies. Results were shown that Mooney viscosity, torque difference, optimum cure time, scorch time, cure rate index and hardness can be predicted by lower than 10% while compression set can be estimated by lower than 20% error. This significant attitude is a nondestructive and fast technique that uses little quantity of NR for prediction of some NR based compounds properties, before compounding.     

Thermogravimetric study of rubber waste-polyurethane composites

Granulated rubber obtained from used tyres, below 1.5 mm granularity (fine rubber) and polyurethane prepolymers (Chemolan M, Chemolan M50 and Chemolan B3) were used for the synthesis of rubber waste-polyurethane composites, containing 90, 85, 80, 75 and 70% w/w of fine rubber. The influence of the kind of polyurethane resin on hardness, elasticity, glass transition temperature and thermal stability of composites was studied. Kinetic parameters of the thermal degradation process of composites were calculated from thermogravimetric analysis (TG) data.This work has been financially supported by the State Committee for Scientific Research, Poland (research project-grant no. 3 T09B 043 19).     

Improvement of properties of silica‐filled styrene‐butadiene rubber composites through plasma surface modification of silica

The performance of plasma surface modified silica filler in styrene‐butadiene rubber (SBR) matrix has been analyzed. The conditions of plasma modification have been optimized by taking secant modulus as a standard parameter and the occurrence of the modification has been confirmed by surface area determination and Fourier transform infrared spectroscopy. The plasma‐modified surface of silica has been found to be composed of carbon–carbon double bonds and carbon–hydrogen bonds. Silane treatment also has been carried out on silica filler surface for a comparative assessment of its influence in the curing behavior and filler–rubber interaction. The cure reactions of all the rubber compounds have been found to be proceeded according to first‐order kinetics. A reduction in the cure reaction rate constant has been observed with the loading of unmodified and surface modified silica, emphasizing the cure deactivation of the matrix rubber by the silica filler. The filler dispersion, as revealed by scanning electron microscopy, has been found to be greatly improved by the plasma as well as silane treatment. The filler–rubber interaction has been found to be greatly improved by both surface treatments, but the best balance of mechanical properties has been observed with plasma surface modification only. Copyright © 2004 John Wiley & Sons, Ltd.     

Study of a new route by which to make fully cured thermoplastic elastomers with plastics and ultrafine powdered rubber

A series of fully cured thermoplastic elastomers (TPEs) have been developed by mixing plastics and fully cured, ultra-fine powdered rubbers (UFPRs). The fully cured UFPRs were prepared by the irradiation of rubber latexes and drying of the irradiated rubber latexes. The average particle size of the UFPRs ranged from 50 to 500nm. The influences of the dose rate, absorbed dose and content of cross-linking agent on the cross-linking of rubber latexes were studied. It was found that a new type of TPEs with excellent properties can be easily made by blending UFPRs with plastics.     

Photocrosslinking of functionalized rubber. II. Photoinitiated cationic polymerization of epoxidized liquid natural rubber

Low molecular weight epoxidized natural rubber has been crosslinked within seconds by UV irradiation in the presence of a triarylsulfonium salt. The photoinitiated cationic ring-opening polymerization was studied quantitatively by infrared spectroscopy and shown to proceed with surprisingly long kinetic chains in such solid medium. The high conversion (60%) needed for complete insolubilization, together with the presence of tetrahydrofuran structures, argue in favor of an intramolecular polymerization process involving neighboring epoxy groups. The photoinitiator concentration has a strong influence on the rate and extent of the reaction, as well as on the depth of cure profile. Because of an efficient dark process, close to 100% conversion was reached upon storage of the irradiated elastomer at ambient, with a concomitant increase of the gel fraction and the polymer hardness. The grafting of pendent acrylate groups onto the polymer chain leads to a three-fold decrease of the initial rate of polymerization of the epoxide. The photocuring of natural rubber bearing both epoxy and acrylate groups generates a dual polymer network which combines the properties of the two moieties. © 1995 John Wiley & Sons, Inc.     

Mechanical properties,surface morphology and failure mode of γ-ray irradiated blends of polypropylene and ethylene-vinyl acetate rubber

The effect of ⁶⁰Co γ-radiation on the mechanical properties, surface morphology and failure characteristics of blends of polypropylene [PP] and ethylene-vinyl acetate rubber [EVA] has been studied with specific reference to the effect of blend ratio, dynamic crosslinking of the rubber phase and absorbed radiation doses. Samples were subjected to radiation in the dose range of 1 to 100 Mrad in air at room temperature at the rate of 0·321 Mrad/h. Both chain scission and crosslinking occur simultaneously in the blend samples. PP and blends containing higher proportions of PP (≥50%) undergo predominant chain scission at lower doses (≤50 Mrad), which causes a drastic drop in tensile strength, followed by a levelling out at higher doses of 100 Mrad. EVA undergoes crosslinking at lower doses resulting in an increase in tensile strength in the dose range 1 to 10 Mrad followed by a decrease in the range 10–25 Mrad. Further increase in radiation dose has little effect on tensile strength. The effect of radiation on stress-strain behaviour, elongation at break, energy at rupture and hardness was also studied. The morphology of the irradiated surfaces after an absorbed dose of 100 Mrad has been examined by scanning electron microscopy (SEM). In order to understand the effect of γ-radiation on the failure mechanism, tensile failure surfaces of both unirradiated and irradiated samples have also been examined by SEM.     

Microbial desulfurization of SBR ground rubber by Sphingomonas sp. and its utilization as filler in NR compounds

Microbial desulfurization of waste tyre rubber has been investigated with great efforts since 1990s, because waste rubber has created serious ecological and environmental problems. A microbial desulfurization technique for SBR ground rubber has been developed by a novel sulfur‐oxidizing bacterium Sphingomonas sp. The adaptability of Sphingomonas sp. with SBR ground rubber was tested with the amounts of SBR ground rubber varying from 0.5 to 4% g/l. The sol fraction of desulfurized SBR ground rubber increased 70%, compared with SBR ground rubber without desulfurization. Fourier transform infrared spectroscopy‐attenuated total reflectance (FTIR‐ATR) spectrum and X‐ray photoelectron spectroscopy (XPS) analysis of the desulfurized surface of vulcanized SBR flakes revealed that not only the oxidation of crosslinked S? S and S? C bonds, but also the rupture of C?C double bonds had happened to SBR vulcanizates during microbial desulfurization. The cure characteristics, such as scorch time and optimum cure time of natural rubber (NR) vulcanizates filled, were found to decrease with increasing contents of desulfurized SBR ground rubber, due to some reactive groups on its surface. NR vulcanizates filled with desulfurized SBR ground rubber had lower crosslink density and hardness, higher tensile strength and elongation at break, compared with those filled with SBR ground rubber of the same amount. Dynamic mechanical properties indicated that there were better crosslink distribution and stronger interfacial bonding between NR matrix and desulfurized SBR ground rubber. Scanning electron microscope (SEM) photographs showed that the fracture surfaces of NR vulcanizates filled with desulfurized SBR ground rubber had more smooth morphologies. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of alkaline treatment and acetone extraction of natural rubber matrix on properties of carbon black filled natural rubber vulcanizates

In this study, air dried sheet (ADS) showed higher molecular weight, proteins, lipids and more gel content than the low protein natural rubber (LPNR) from alkaline treatment or acetone-extracted natural rubber (AENR). After removal of proteins and lipids, LPNR and AENR had shorter scorch and cure times among the rubber compounds observed. This is due to higher content of free fatty acids, glycerides and sodium salts of fatty acid that might act as cure activators with sulfur curing. Furthermore, a finer dispersion of CB was found in ADS, due to chemical interactions of CB with proteins and lipids at terminal ends of NR molecules. Also, high molecular weight and gel in ADS could induce a higher reinforcing index (α) resulting to superior mechanical, dynamic, thermo-mechanical, hardness and crosslink density. In contrast, CB agglomerates occurred in LPNR and AENR with low molecular weight and reduced proteins and lipids, causing inferior mechanical, dynamic, thermo-mechanical, along with loss of stiffness and crosslink density.     

Vulcanization kinetics study of natural rubber compounds having different formulation variables

Vulcanization kinetics of natural rubber (NR) compounds with efficient vulcanization system was studied through phenomenological approach using the experimentally cure data obtained from a moving die rheometer. The cure kinetic parameters were defined using the proposed models by Claxton?CLiska and Deng?CIsayev with the support of curve fitting software. The effects of the amount of accelerators, sulfur and silica in the formulations on the cure characteristics and cure kinetic parameters at high cure temperatures were investigated. Kinetic data results showed that the above two models were able to describe the curing behaviour of the studied compounds satisfactorily. It showed that the fitting of the experimental data with Claxton?CLiska and Deng?CIsayev could provide a good platform to investigate the cure kinetics of the prepared NR compounds.     

The effect of grass fiber filler on curing characteristics and mechanical properties of natural rubber

Natural rubber is reinforced with a novel type of grass fiber (Cyperus Tegetum Rox b). The effects of fiber loading of different mesh sizes on curing characteristics and mechanical properties of grass fiber filled natural rubber composite are studied. Since 400 mesh grass fiber loaded natural rubber composite shows superior mechanical properties, therefore the effect of silane coupling agent was studied for this particular composite. Here composites were prepared by using water leached grass fiber. Optimum cure time increases with the increase in fiber loading but the change in scorch time is less. The same trend of increase in optimum cure time is observed in the presence of Si69. But the value is higher compared to that of rubber composite without Si69. With increase in the fiber loading, modulus and hardness of the composite increases but tensile strength decreases. The mechanical properties of the composite, namely moduli at 200 and 300% elongation and hardness increase in the presence of Si69 but tensile strength is less compared to that of the composite without Si69. Elongation at break is not much affected due to the presence of Si69. Copyright © 2004 John Wiley & Sons, Ltd.     

Properties Investigation of novel nitrile rubber composites with rockwool fibers

Rockwool is an inorganic fiber with interesting properties obtained from basaltic rocks. It can possibly be used in rubber technical products which work under critical conditions in several industries. This study aims to investigate properties of three short rockwool fibers/nitrile rubber composites. Ten formulations were prepared with 10, 25 and 40 phr of rockwool fibers with different length and modification. The composites were assessed on its morphological aspects, thermal, rheological, and mechanical behaviors. The results remarked that the rockwool fiber with chemical modification had better interfacial interaction with the polymer enhancing modulus at 100% of deformation, Shore A hardness, tear strength, Payne effect and stress relaxation under a compressive regime. An outstanding result was observed for the composite with 10 phr of fiber with chemical modification that had less stress relaxation when compared with the unfilled NBR indicating an excellent possibility of use of this fiber in materials that work under compressive forces. The difference in length of the rockwool fibers (125 μm–300 μm) did not interfere significantly on most of the results.     

Comparison of the mechanical properties at similar hardness level of natural rubber filled with various reinforcing-fillers

Commercially, the alteration of a rubber formulation is usually made in such a way as to keep the hardness of the rubber product constant. This is because a specific hardness of the rubber product sets the limit to its practical applications. Therefore, in this paper, natural rubber (NR) vulcanizates containing various fillers were prepared to have the same hardness level, and their mechanical properties were compared and related to the degree of filler dispersion. The results show that higher amounts of carbon black (CB) and silica are needed for CB- and silica-filled natural rubber vulcanizates to achieve the same hardness value as a NR vulcanizate containing 6 phr of montmorillonite clay. At equal loading of fillers, clay-filled vulcanizate exhibits higher modulus, hardness, tensile strength and compression set, but lower heat build-up resistance and crack growth resistance than those of the vulcanizates containing conventional fillers. For the vulcanizate having the same hardness value, CB-filled vulcanizate gives the better overall mechanical properties followed by the clay-filled and silica-filled vulcanizates, respectively. The explanation is given as the better dispersion of carbon black, as can be seen in the SEM micrograph.     

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.     

Effect of mold temperature and cure enthalpy on the state of cure at the midplane of thin rubber sheets

This work is concerned with the application of calorimetry in isothermal conditions for the study of the vulcanization in rubber. The effect of the mold temperature and cure enthalpy on the temperature and the state of cure is examined by considering the midplane which is an interesting location within the rubber sheet. A variation of 20% in the cure enthalpy is proved to be of slight importance, while a variation in the mold temperature of ～ 10°C is shown to be decisive.     

Effect of radiation dose on the properties of natural rubber nanocomposite

Effect of radiation dose and carbon nanotubes (CNT) on the mechanical properties of standard Malaysian rubber (SMR) was investigated in this study. SMR nanocomposites containing 1–7 phr CNT were prepared using the solvent casting method and the nanocomposites were radiated at doses of 50–200 kGy. The change in mechanical properties, especially, tensile strength (Ts), elongation at break (Eb), hardness and tensile modulus at 100% elongation (M₁₀₀) were studied as a function of radiation dose. The structure and morphology of reinforced natural rubber was investigated by FESEM, TEM and AFM in order to gain further evidence on the radiation-induced crosslinking. It was found that the Ts, M₁₀₀ and the hardness of the SMR/CNT nanocomposites significantly increased with radiation dose; the elongation at break exhibited an increase up to 100 kGy, and a downward trend thereafter. Results on gel fraction further confirmed the crosslinking of SMR/CNT nanocomposites upon radiation.     

The sulfur reversion process in natural rubber in terms of crosslink density and crosslink density distribution

Unfilled natural rubber compounds composed of conventional (CV), semi-efficient (SEV), efficient (EV) and sulfur donor (SD) vulcanization systems were heat aged to promote sulfur reversion. Rheometry, hardness, strain-strain characteristics including Mooney-Rivlin analysis, equilibrium solvent swell and Double Quantum (DQ) Nuclear Magnetic Resonance (NMR) were used to monitor crosslink density changes. A loss of crosslink density was observed by rheometry, C₁, equilibrium swelling and by DQ NMR as a function of cure extent. No chain scission reactions were operating in the time/temperature conditions used. All crosslink distributions were unimodal and the network homogeneity followed the order of EV > SD > SEV > CV. The crosslink distribution narrowed during the curing process for the CV and SEV systems. Non-oxidative maturation reactions were advantageous in promoting a more random distribution of crosslinks in the polymer matrix.     

The effect of alkanolamide loading on properties of carbon black-filled natural rubber (SMR-L), epoxidised natural rubber (ENR), and styrene-butadiene rubber (SBR) compounds

The effect of Alkanolamide (ALK) loading on properties on three different types of carbon black (CB)-filled rubbers (SMR-L, ENR-25, and SBR) was investigated. The ALK loadings were 1.0, 3.0, 5.0 and 7.0 phr. It was found that ALK gave cure enhancement, better filler dispersion and greater rubber–filler interaction. ALK also enhanced modulus, hardness, resilience and tensile strength, especially up to 5.0 phr of loading in SMR-L and SBR compounds, and at 1.0 phr in ENR-25 compound. Scanning electron microscopy (SEM) proved that each optimum ALK loading exhibited the greatest matrix tearing line and surface roughness due to better rubber - filler interaction.     

Improvement of properties of silica-filled styrene-butadiene rubber (SBR) compounds using acrylonitrile-styrene-butadiene rubber (NSBR)

Since silica has strong filler–filler interactions and adsorbs polar materials, a silica-filled rubber compound wil have poor dispersion of the filler and a poor cure characteristic. Improvement of properties of silica-filled styrene-butadiene rubber (SBR) compounds has been studied using emulsion SBR-based acrylonitrile-styrene-butadiene rubber (NSBR). The silica dispersion is improved by adding NSBR to the compound. The bound rubber content increases with increase in the NSBR content. The scorch time and cure rate become faster as the NSBR content increases. The crosslink density also increases by increasing the NSBR content. The wear property is improved by adding the NSBR. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of nature and type of flaw on the properties of a natural rubber compound

Fracture in rubber, like in all other materials, is initiated at imperfections inadvertently present or introduced in the body of the material or on the surface during processing. The point of initiation of fracture in the rubber is usually at flaws which are macroscopic or microscopic imperfections or inhomogeneities in the rubber. In order to investigate the effect of these flaws on the properties of a natural rubber compound, cuts to mimic weld lines were introduced before and near scorch at various cure temperatures, and the time for a complete healing of these cuts determined. The tensile properties were not significantly affected by the introduction of weld lines before scorch provided sufficient time was allowed for healing. Healing time reduced with increase in cure temperature. The intrinsic flaw sizes in a material inherently affect the material tensile properties and depend significantly on the size of the flaw. Pinhole flaws of varying sizes introduced after cure had a significant effect on both tensile strength and fatigue life with the pinhole equivalent intrinsic flaw size estimated to be about 200 μm.