Ali Ansarifar

Assessment of the effect of a bifunctional organosilane on the bound rubber and properties of some natural rubber compounds

The effect of the coupling agent bis-(3-triethoxysilylpropyl) tetrasulphane (TESPT) on the properties of a filled natural rubber compound has been measured. The rubber was cured with a conventional accelerator and sulphur system, and contained silica particles. TESPT was added to prevent the silica from interfering with the reaction mechanism of sulphur cure in the rubber. This study showed that the hardness, cyclic fatigue life, cohesive tear strength, maximum tensile strength, elongation at break, and stored energy density at rupture were optimised when 7 phr TESPT was added to the rubber, whereas bound rubber was maximised with 5 phr TESPT. There was also evidence that the silica was poorly dispersed in the rubber and probably had not been properly silanised before addition to the raw elastomer. Interestingly, in spite of these inadequacies, there was consistency within the body of the work, and the trends observed were valid even though the full potential of the filler for optimising properties might not have been achieved.

Reinforcing Effect of Silica and Silane Fillers on the Properties of Some Natural Rubber Vulcanizates

Abstract The reinforcing effect of up to 6 parts per hundred rubber by weight (phr) bis- (3-triethoxysilylpropyl) tetrasulfide (TESPT), a bifunctional organosilane, on the crosslink density, bound rubber, and technical properties of some conventional accelerator/sulfur compounds of natural rubber, containing 30 phr precipitated amorphous white silica was studied. The crosslink density and bound rubber improved as a function of TESPT loading. The tensile strength, elongation at break, stored energy density at rupture, and cohesive tear strength deteriorated at low loading of TESPT, but they subsequently increased after the full amount of TESPT was introduced into the compound. The improved properties of the vulcanizate was due to the better dispersion of the filler in the rubber matrix. However, the cyclic fatigue life was adversely affected, and the hardness hardly changed as a result of adding TESPT to the rubber.

The Reinforcement and Crosslinking of Styrene Butadiene Rubber with Silanized Precipitated Silica Nanofiller

Abstract Synthetic precipitated amorphous white silica nanofiller was used to reinforce and crosslink styrene-butadiene rubber (SBR). The silica surfaces were pre-treated with bis[3-triethoxysilylpropyl-)tetrasulfide (TESPT) bifunctional organosilane. TESPT chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur-cure. The silica particles were fully dispersed in the rubber, which was cured primarily by using sulfur in TESPT, or, by adding elemental sulfur to the cure system. The cure was also optimized by incorporating different accelerators and activators in the rubber. This study showed that the silica particles could be used both as crosslinking and reinforcing filler in the rubber.

ASSESSING EFFECT OF THE MIGRATION OF A PARAFFIN WAX ON THE SURFACE FREE ENERGY OF NATURAL RUBBER

Abstract The effect of the migration of paraffin wax on the surface free energy of natural rubber (NR) was investigated. The rubber was mixed with the wax and then stored at ambient temperature for up to 168 hrs before its surface free energy was measured using contact angle measurement. Static secondary ion mass spectrometry was also used to provide a chemical fingerprint of the rubber surfaces. The surface free energy decreased as a function of storage time because of the migration of the wax to the rubber surface. The highest rate of reduction was recorded up to 3 hrs and thereafter, the surface free energy decreased at a much slower rate, reaching a plateau after 48 hrs in storage. In total, the surface free energy reduced by approximately 46% as a result of the migration of the wax to the rubber surface. The reduction in surface free energy could adversely affect ability of the rubber to stick to itself and to other dissimilar elastomers.

Devulcanization of ethylene–propylene–diene waste rubber by microwaves and chemical agents

Extensive use of rubber in industrial articles and their eventual disposal at the end of their useful service life has created a major concern for the environment. In automotive applications, ethylene–propylene–diene rubber (EPDM) is used to manufacture various parts which will be difficult to dispose of or scrap. A microwave oven was used as a heating source, and with the aid of some chemical agents and aromatic and aliphatic oils, cured EPDM waste powder was devulcanized at temperatures ranging from 200°C to 260°C. The devulcanized waste powder was then revulcanized with a sulfur cure system and its cure and mechanical properties were measured. It emerged that with the aid of the chemical agents, the waste powder devulcanized more efficiently in the aromatic oil than it did in the aliphatic one. The chemical agents had different effects on the devulcanization of the waste powder and mechanical properties of the revulcanized compound. In addition, devulcanization was more efficient at higher temperatures. The hardness, tensile strength, and elongation at break of the revulcanized compounds were in the range of 49–79 Shore A, 2.0–3.7 MPa, and 34–211%, respectively. These properties were influenced mainly by the composition and devulcanization conditions of the waste powder. There is scope to recycle and reuse some of these compounds in automotive applications.

Reinforcement of Natural Rubber with Silanized Precipitated Silica Nanofiller

Abstract The effect of a large amount of precipitated amorphous white silica nanofiller, pre-treated with bis[3-triethoxysilylpropyl-)tetrasulfide (TESPT), on the mechanical properties of a sulfur-cured natural rubber (NR) was studied. TESPT chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur-cure. The silica particles were fully dispersed in the rubber, which was cured primarily by using sulfur in TESPT, or, by adding a small amount of elemental sulfur to the cure system. The cure was also optimized by incorporating sulphenamide accelerator and zinc oxide into the rubber. The hardness, tear strength, tensile strength, and stored energy density at break of the vulcanizate were substantially improved when the filler was added. Interestingly, these properties were also enhanced when the rubber was cured primarily by using sulfur in TESPT.

Devulcanization and recycling of waste automotive EPDM rubber powder by using shearing action and chemical additive

In automotive applications, ethylene-propylene-diene rubber (EPDM) is used to manufacture various components and therefore recycling scrap rubber is a major issue. The primary aim of this study was to develop a new method for devulcanizing waste automotive EPDM rubber powder by using shearing action and chemical additive and recycle the devulcanized powder. A semi-industrial twin screw extruder with a shearing action and reactor along with 2-mercaptobenzothiazole-disulfide (MBTS) chemical were used to devulcanize the waste powder at two different feed screw speeds and main rotor speeds at a constant temperature of 220°C. To recycle the devulcanized powder, different amounts of the devulcanized powder were mixed with a commercial EPDM-based automotive rubber strips compound to produce blends. The blends, commercial compound and devulcanized powder were cured with a semi-efficient (SEV) vulcanization system and their viscosity, cure and mechanical properties measured. For the blends, the Mooney viscosity was unchanged with 40 wt%, crosslink density with 20 wt%, tensile strength and elongation at break with 10 wt%, and compression set with 20 wt% of the devulcanized powder. Interestingly, the hardness benefitted from 50 wt% of the devulcanized powder in the blends. The scorch and optimum cure times shortened and the cure rate index rose when the loading of the devulcanized powder in the blends was raised. This new method offered a major new route for devulcanizing and recycling the waste powder.

Measurement of the interaction forces between polymer coated surfaces

Abstract Polymers adsorbed onto particulate dispersions have been used to stabilise particles for many thousands of years. The dominant factor which controls the stability is the inter-particulate force. In this paper we report measurements of the interaction force profile for polymers adsorbed onto two mica surfaces. Results are presented for the case of a homopolymer, polyethylene oxide, and a block copolymer poly-2-vinylpyridene/poly-t-butyl-styrene adsorbed onto mica in a good solvent (toluene). The force profile is repulsive in both cases. However, the range of the interaction is much greater for the case of the copolymer, due to the polymer being attached to the mica in only one position (the poly-2-vinylpyridine end).

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-propylene-diene rubber were adversely affected by kaolin.

Using a sulfur-bearing silane to improve rubber formulations for potential use in industrial rubber articles

The availability of the coupling agent bis (3-triethoxysilylpropyl)-tetrasulfide (TESPT) has provided an opportunity for enhancing the reinforcing capabilities of precipitated amorphous white silica in rubber. Styrene-butadiene rubber, synthetic polyisoprene rubber (IR), acrylonitrile-butadiene rubber, and natural rubber (NR) containing the same loading of a precipitated silica filler were prepared. The silica surface was pretreated with TESPT, which is a sulfur-bearing bifunctional organosilane to chemically bond silica to the rubber. The rubber compounds were subsequently cured by reacting the tetrasulfane groups of TESPT with double bonds in the rubber chains and the cure was optimized by adding sulfenamide accelerator and zinc oxide. The IR and NR needed more accelerators for curing. Surprisingly, there was no obvious correlation between the internal double bond content and the accelerator requirement for the optimum cure of the rubbers. Using the TESPT pretreated silanized silica was a very efficient method for cross-linking and reinforcing the rubbers. It reduced the use of the chemical curatives significantly while maintaining excellent mechanical properties of the cured rubbers. Moreover, it improved health and safety at work-place, reduced cost, and minimized damage to the environment because less chemical curatives were used. Therefore, TESPT was classified as “green silane” for use in rubber formulations.