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sulphur (98% soluble in CS2 ), AECI, South Africa; and polyisoprene (IR), Karbochem, South Africa.X-ray diffraction analysis (XRD) of modified p5 was conducted using a Philips PW 1729 X-ray generator coupled to a PW 1840 diffractometer and electron micrographs of filler particles were obtained using a Philips XL30 scanning electron microscope. Scanning X-ray photoelectron spectroscopy (SXPS) analyses of fillers were performed with a Quantum 2000 Scanning ESCA Microprobe. The nitrogen surface area of fillers was determined using a Gemini 2370C V4.01 BET multipoint surface area analyser. The Du Pont thermal analysis equipment and techniques, i.e. differential scanning calorimetry and thermal gravimetry (TG) have been described previously.8To obtain an adsorption isotherm, weighed amounts of silica were added to a number of TESPTbenzene solutions of known concentrations and allowed to stand for 2 h. The supernatant solutions were then filtered and analysed for TESPT by UV absorption spectroscopy.For bound rubber determination a modification of the method involving a wire cage9 as a sample holder was used. Rubber samples of ~0•2 g, containing 40 phr filler, were cut into smaller pieces (~0•02 g) and placed in wire cages. The wire cages were made by folding 320 mesh (45 mm) stainless steel wire cloth into square pouches (25×25 mm), and sealing them by crimping the edges with thin strips of sheeted aluminium. Caged samples were then placed individually in 120 mL glass bottles containing 100 mL cyclohexane, which was replaced every 24 h for 3 days. Samples were swirled three times a day and maintained at 18-20°C. After 3 days, samples (in their

When appropriately sourced, bioethanol and biodiesel fuels provide an opportunity for nations to increase their energy independence or to reduce greenhouse gas emissions by supplying energy-dense fuels which are miscible with fossilderived gasoline and diesel. These fuels can be used in low concentrations in vehicles with no modifications; in the case of ethanol, only minor changes in the fuel system materials together with a low-cost alcohol sensor are necessary for compatibility with a high concentration. Ethanol provides the beneficial property of having a high research octane number which can be exploited at the high-load operating conditions in modern pressure-charged spark ignition engines. However, the availability of sustainable feedstocks constrains the supply of biofuels, and this limits the level at which they are able to displace fossil fuels. The miscibility of methanol with both ethanol and gasoline enables the penetration of alcohols in the fuel pool to be increased. The present work describes the properties of specific mixtures of gasoline, ethanol and methanol which are blended to be iso-stoichiometric and iso-energetic replacements for mixtures of gasoline and ethanol. A simple analytical approach to the formulation of these ternary blends is described on the basis of the volumetric energy density of the pre-blended components, and a number of further physicochemical properties are characterised, including their stoichiometries, vapour pressures, distillation characteristics and propensities to phase separate. Data on the octane numbers of the blends are reported. The properties of quaternary iso-stoichiometric blends of water, gasoline, ethanol and methanol (the so-called hydrous ternary blends) are also examined.

Data relating to the vulcanization of mercaptan-grade polychloroprene (CR) by ZnO and MgO (alone or in combination) are examined. Compounds were vulcanized through the isothermal heating of samples at 1408C in a laboratory press and at programmed rates in a differential scanning calorimeter. The reaction was stopped at various points during the heating process. The crosslink densities were determined via swelling. Extractable ZnCl 2 and MgCl 2 were analyzed by atomic absorption spectrometry. Three different crosslinking processes were identified. The first crosslinking process involved the activation of the highly reactive tertiary allylic 1,2-units along the polymer chain, whereas the second and third crosslinking processes were attributed to the activation toward crosslinking of 3,4-and 1,4-units, respectively. The crosslinking reactions of the 1,2-units comprised three distinct steps: isomerization (promoted by ZnO), dechlorination, and crosslinking. ZnCl 2 (which formed during compounding and upon crosslinking) promoted crosslinking, and its addition to formulations decreased but did not eliminate the induction period before crosslinking. MgO retarded the crosslinking process by limiting the formation of ZnCl 2 during mixing. The results of the CR/ZnO system are discussed, and a modified cationic mechanism for crosslinking is proposed.

The soluble macromolecular oxidatively reactive species (SMORS) mechanism has recently been applied to jet fuel thermal oxidative degradation at high temperatures (250–550 °C). The primary purpose of this work is to further test the extant SMORS mechanism with carefully designed experiments at lower temperatures. First, synthetic SMORS precursors, 2-methylindole and 1,4-benzoquinone, were doped into a stable Jet A-1 in both mono- and oligomeric forms. Flask oxidative stress of these solutions at 90 °C for 60 min with an oxygen sparge significantly increases jet fuel thermal oxidative degradation. Second, a model compound experiment suggests SMORS precursors, phenol and 1,4-benzoquinone, are generated in situ from flask oxidation of a natural jet fuel component cumene (isopropylbezene) at 160 °C with an air sparge for 300 min. This observation is particularly significant for the thermal oxidative degradation of ultra-low sulfur diesel (ULSD) because it suggests that fuels with low heteroatom content may oxidatively degrade by the SMORS mechanism. Third, doping parts per million (ppm) levels of 2,4-dimethylpyrrole into oxidatively stable jet fuels followed by flask oxidation at 95 °C with an air sparge for 30 min results in significant oxidation of the jet fuels. This observation is particularly significant for the storage and thermal oxidative stability of Athabasca-tar-sands-derived middle distillates, which have previously been shown to contain alkylpyrroles; these middle distillates are predominate across the northern tier of the United States.

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ABSTRACT:The tensile properties of conventional and peroxide vulcanisates were studied over a range of crosslink densities at room temperature and at 90°C. At 90°C the tensile strength and elongation at break of vulcanisates of lower crosslink density are superior to those at room temperature, while for vulcanisates of higher crosslink density the reverse applies. When strain-induced crystallites form, they act as crosslinks shortening chains within the network. Shortened chains have lower entropies and a larger force is required for their continued extension, i.e., for a further reduction in their entropy. It is proposed that because these stiffer chains resist deformation, other less stiff chains are preferentially extended. This alters the network deformation pattern, forcing more chains to become load bearing and delaying the development of taut chains or chain sequences. Thus the formation of strain-induced crystals leads to the slope of the stress-strain curve rising rapidly. At elevated temperatures the rate of nucleation of strain-induced crystallites is slower but data on stress-strain curves obtained with different temperature programs show that, while strain-induced crystallization is essential for the development of high tensile strength, delaying their formation to higher elongations is advantageous for high tensile properties. In vulcanisates of higher crosslink density the rate of crystallization at high temperatures becomes too slow. Rupture occurs before strain-induced crystallites can form and protect the network by altering the network deformation pattern.