A review of sulfur vulcanization of rubber

This one page article is an opinion on the sulfur vulcanization of rubber. It states that combining zinc oxide with a sulfenamide accelerator into one composite powder provides a more efficient method of curing rubber with sulfur, reducing the total curatives requirement by 77wt%

Developing ethylene-propylene-diene rubber compounds for industrial applications using a sulfur-bearing silanized silica nanofiller

The loading of a sulfur-bearing silanized silica nanofiller in ethylene-propylene-diene rubber with 4.5 wt % of ethylidene norbornene diene content was increased progressively to 60 parts per hundred rubber by weight. The rubber compounds were cured via the tetrasulfane groups of the silane by adding sulfenamide accelerator and zinc oxide. The hardness, tensile strength, elongation at break, stored energy density at break, tear strength, Young’s modulus, M50-M300, compression set, cyclic fatigue life and bound rubber content of the rubber vulcanizates were measured. With the exception of the elongation at break and compression set which deteriorated, the remaining properties improved and the rate of cure, optimum cure time and crosslink density benefitted also when the loading of silica was increased in the rubber. The bound rubber content was unchanged and the cyclic fatigue life of the rubber vulcanizate enhanced considerably when silica was added. Optimizing the chemical bonding between the rubber and filler via the tetrasulfane groups of TESPT reduced the chemical curatives in the rubber. This was a major improvement in health, safety and environment

Some factors affecting the flex life of polybutadiene rubber vulcanisate

Flex life of three different grades of polybutadiene rubber (BR) with highly linear chains, linear chains and long-branched chains was measured. The rubbers were reinforced with a precipitated silica nanofiller, the surface of which had been pre-treated with sulphur-bearing bis(3-triethoxysilylpropyl-)-tetrasulphane (TESPT) coupling agent. The rubbers were cured by reacting the sulphur in TESPT with the rubber chains to produce vulcanisates. The mechanical properties of the rubber vulcanisates such as tensile strength, Young’s modulus, elongation at break, stored energy density at break and tear energy were subsequently determined. The flex life of the rubber vulcanisates was also measured at a constant maximum strain amplitude and a test frequency of 3.17 Hz at ambient temperature. Additionally, the flex life of some unfilled rubber vulcanisates of similar Mooney viscosities cured with elemental sulphur was also measured. For the silica-filled rubber vulcanisate, the rubber with the highly linear chains had the longest flex life and the one with long-branched chains, the shortest flex life. It seemed that a correlation between the flex life and the molecular chains structure might exist despite the crosslink density of the rubber vulcanisates being different and the compounds having silica in them. For the unfilled rubber vulcanisates, the rubber with highly linear chains had the longest flex life and the one with linear chains the shortest flex life. Therefore, it was concluded that the flex life of the rubber vulcanisate was determined, to a large extent, by the molecular chains structure of the raw rubber, irrespective of whether the rubber had reinforcing silica filler, different crosslink densities and different initial viscosities or not. A similar trend was also observed for some of the mechanical properties. For example, the elongation at break was lower and Young’s modulus higher for the silica-filled rubber vulcanisates with long-branched chains than those measured for the silica-filled rubber vulcanisate with highly linear chains

Kaolin reinforcement of some rubbers with novel sulfur cure systems

A large amount of kaolin (China clay) was used to reinforce the hardness, tensile strength, elongation at break, stored energy density at break, tear resistance, and Young’s modulus of some sulfur-cured NR, BR and EPDM. The kaolin surface had been pre-treated with 3-mercaptopropyltrimethoxysilane (MPTS) to reduce its polarity and prevent it from adsorbing moisture which could have been detrimental to the cure of the rubbers. For NR, the hardness and Young’s modulus improved, tensile strength and tear resistance were unchanged and the remaining properties deteriorated when kaolin was added. The viscosity increased and the scorch and optimum cure times decreased with kaolin. The highest cure rate ever reported for a sulfur-cured NR-based compound was achieved when kaolin was mixed with the rubber. For BR and EPDM, most of the properties including the viscosity gained significantly from the presence of kaolin in the rubbers. It was concluded that kaolin was an extending or non-reinforcing filler for NR, and highly reinforcing for BR and EPDM. Notably, the scorch and optimum cure times and cure rate of BR benefited so much, whereas with the exception of the scorch time, the optimum cure time and cure rate of EPDM were adversely affected by kaolin. The addition of kaolin increased the crosslink density of NR but had a detrimental effect on the crosslink density of BR and EPDM. The early indications are that kaolin is a viable alternative to carbon black and silica/silane systems in rubber reinforcement

Major reduction in chemical curatives for rubber articles

The sulfur cure system in the ethylene-propylene-diene (EPDM)-based Curtain Wall Seal (CWS) has two accelerators, adding up to 2.75 parts per hundred rubber (phr) by weight, and two activators (ZnO: 5phr, stearic acid:1phr). In total, 8.75phr chemicals are used to fully cure the article with 1phr elemental sulfur. Excessive use of chemical curatives is harmful to health, safety, and the environment. A new method uses experimental results from high temperature cure tests to provide highly efficient cure systems for industrial rubber articles, which requires a lot less chemical curatives without compromising cure efficiency. This method can be applied to reduce chemical curatives in other industrial rubber articles

Perfect couple: optimizing the use of Si69 coupling agent in tire formulation

Perfect couple: optimizing the use of Si69 coupling agent in tire formulatio

A review of the reclaiming of rubber waste and recent work on the recycling of ethylene-propylene-diene rubber waste

Rubbers do not decompose easily and therefore disposal of rubber waste is a serious environmental concern. Raw material costs, diminishing natural resources, and the growing awareness of environmental issues and sustainability have made rubber recycling a major area of concern. Reclaiming and recycling rubber waste is a major scientific and technological challenge facing rubber scientists today. This paper reviews a number of important areas related to the reclaiming, characterizing, testing and recycling of rubber waste. These include: chemical and microbial devulcanization with particular emphasis on main chain scission and kinetics of chemical devulcanization reactions; the cutting-edge techniques for reclaiming devulcanized rubber waste by the action of large shearing forces, heat and chemical agents: and analytical techniques and methods for characterizing composition and testing of devulcanized rubber waste, respectively. In addition, some aspects of the recycling of devulcanized ethylene-propylene-diene rubber (EPDM) waste will be reported. EPDM is used extensively in automotive components world-wide and recycling the rubber at the end of its useful service life is of major importance to manufacturers of automotive components

Effect of various efficient vulcanization cure systems on the compression set of a nitrile rubber filled with different fillers

Effect of various efficient vulcanization (EV) sulfur cure systems on the compression set of a nitrile rubber filled with carbon black and silica/silane fillers was examined. The cure systems had different amounts of thiuram and sulfenamide accelerators and elemental sulfur, whilst the loading of zinc oxide and stearic acid activators was kept constant. The fillers had surface areas from 35 to 175 m 2 /g. In this study, the lowest compression set was measured for the rubber filled with carbon black with 78 m 2 /g surface area, which was cured with an EV cure system made of a small amount of elemental sulfur and large amounts of the two accelerators. Interestingly, a small change in the amount of elemental sulfur had a bigger effect on the compression set than did large changes in the loading of the accelerators in the cure system. Among the fillers, carbon black caused less compression set of the rubber vulcanizate than the silica/silane system did

The potential of kaolin as a reinforcing filler for rubber composites with new sulfur cure systems

The effect of a large amount of kaolin (China clay) on the viscosity, cure, hardness, Young’s modulus, tensile strength, elongation at break, stored energy density at break, tear energy and compression set resistance of some sulfur-cured natural rubber, polybutadiene rubber and ethylene-propylene-diene rubber composites was investigated. The kaolin surface had been pre-treated with 3-mercaptopropyltrimethoxysilane to improve its dispersion in the rubbers. For natural rubber, the hardness and Young’s modulus improved, tensile strength and tear energy were unchanged and the remaining properties deteriorated when kaolin was added. The viscosity increased and the scorch and optimum cure times decreased whilst the cure rate rose with kaolin. For polybutadiene rubber and ethylene-propylene-diene rubber, with the exception of the compression set resistance, all the properties including the viscosity gained from the kaolin. The kaolin was found to be extending or non-reinforcing filler for natural rubber, and highly reinforcing for polybutadiene rubber and EPDM. In addition, the scorch and optimum cure times and cure rate of polybutadiene rubber benefitted, whereas with the exception of the scorch time, the optimum cure time and cure rate of ethylene-propylenediene rubber were adversely affected by kaolin

Effect of hybrid reinforcement based on precipitated silica and montmorillonite nanofillers on the mechanical properties of a silicone rubber

Silicone rubber (SR) nanocomposites containing precipitated silica (PS), montmorillonite (MMT) and PS/MMT hybrid fillers were prepared through melt-mixing technique. In the SR/PS/MMT nanocomposite, the hybrid filler weight ratio was increased progressively from 0.4 to 1.7 while keeping the MMT weight constant. The viscosity, cure characteristics and mechanical properties of the nanocomposites were subsequently measured. The optimum cure time increased and the scorch time and rate of cure decreased. Furthermore, when the hybrid filler weight ratio was raised to its optimum, the tensile strength, Young’s modulus, modulus at 100% and 300% elongation (M100 and M300), elongation at break, stored energy density at break and hardness of the nanocomposite improved. The stress-strain properties of the nanocomposite with the hybrid filler improved at high deformation in comparison with those containing the PS and MMT fillers. The MMT filler exfoliated in the SR/MMT nanocomposite but did not in the nanocomposites containing the hybrid filler. Notably, the mechanical properties of the nanocomposite benefitted from the hybrid filler. This was due to the filler-filler and filler-rubber network formation in the rubber by the PS particles. Finally, effect of the PS, MMT and hybrid fillers on the energy loss or hysteresis of the rubber was measured