Natural rubber (NR)/expandable graphite (EG) vulcanizates have been prepared using linseed oil plasticizer. The effects of linseed oil on the cure and mechanical properties of the NR/EG vulcanizates such as cure time, tensile strength, tear strength, modulus, elongation at break and swelling behavior have been studied to evaluate its suitability as plasticizer. Naphthenic oil was used as a reference. The linseed oil vulcanizates showed good processing behavior in terms of torques and scorch. With the incorporation of linseed oil there was improvement in the cure time and the mechanical properties of the EG/NR vulcanizates. 2–4 phr linseed oil in the NR/EG vulcanizates showed maximum tensile strengths. The higher value of cross link density at 4 phr for the linseed oil vulcanizates indicates better reinforcement of the EG–rubber matrix. The NR/EG/linseed oil vulcanizates exhibited higher thermal stability compared to NR/EG vulcanizates. The scanning electron micrographs revealed that incorporation of linseed oil up to 4 phr hinders the crack formation apparently with no major crack present in the NR/EG/LO composites minimizing the failure when compared to similar composites with naphthenic oil. The results indicate that the optimum level of linseed oil in the vulcanizates is 2–4 phr.

Natural Rubber (NR), filled with 2 to 8 phr of nano CaCO3 and 2 phr of linseed oil as an extender were compounded using a two-roll mill and moulded on a compression moulding machine. Effects of filler dosage on the cure and mechanical properties of the NR vulcanizates were examined. Because of the reduction in the size of the nano CaCO3, and the presence of linseed oil as an extender, that helped in the homogenous dispersion of the nano CaCO3, better cure and mechanical properties was observed. The composite with 6 phr of nano CaCO3 and 2 phr of linseed oil showed the optimum properties.

A comparative study was performed of nano-CaCO3 and precipitated calcium carbonate as fillers in natural rubber/expandable graphite vulcanizates. A number of vulcanizates with different loadings of the fillers were prepared using a two-roll mill and moulded on a compression moulding machine. Effects of filler dosage on the cure and mechanical properties of the flame retardant natural rubber/expandable graphite vulcanizates were examined. Because of the reduction in the size of the nano CaCO3, drastic improvement in the mechanical properties were found in comparison with precipitated calcium carbonate filled natural rubber/expandable graphite composites. Furthermore, cure properties showed that nano CaCO3 filled natural rubber vulcanizates exhibited lower cure time than the precipitated calcium carbonate filled natural rubber/expandable graphite vulcanizates. The values of the swelling ratio of the nano CaCO3 filled vulcanizates decreased remarkably and are lower than the precipitated calcium carbonate filled natural rubber vulcanizates. There is an indication that that the optimum level of incorporation of nano CaCO3 is 6 phr.

The diffusion and transport of inhibitor-free methyl methacrylate monomer through crosslinked natural rubber (NR) have been studied at different temperatures. NR has been vulcanised by conventional, efficient and peroxide vulcanisation technique. ESR spin probe spectroscopy was used to study the flexibility of NR network chains at different temperatures. The dependence of diffusion coefficient on the nature of crosslinks and temperature has been studied. The intrinsic diffusion coefficient was found to increase with increase of temperature. The interaction parameter, permeability, sorption coefficient and molecular weight between crosslinks have been evaluated using diffusion data. The morphology of the swollen network and thermodynamic parameters has been determined using diffusion data. The efficient and peroxide system showed the least uptake and the conventional system showed the highest uptake. This study also proved that same extent of crosslinking can be achieved for different vulcanising systems by curing the samples to a common rheometric torque. The theoretical modelling shows Fickian mode of diffusion with a slight deviation.

The ageing behavior due to the effects of heat, ozone, gamma- radiation, and water on ethylene propylene diene monomer rubber/styrene butadiene rubber (EPDM/SBR) blends was studied. The tensile strength, crack initiation, ozone ageing, gamma radiation, and water resistance of the blends were measured and used to determine the extent of ageing. Tensile strength of blends of different compositions increased after thermal ageing for 96 h at 100 degrees C probably due to the continued cross-linking. It has been observed that an increase in EPDM in the blends improves the ozone resistance of the blends. Crack initiation was noted only in blends with lesser amount of EPDM and the cracks in such blends were found deeper, wider and continuous. With 15 kGy irradiation dose, the tensile strength of the blends found to be decreased while it increased with 80 kGy dosage of gamma-radiation. The elongation at break showed a decreasing trend with increased dosage of gamma-radiation. It has also been observed that the EPDM rich blends showed negligible water uptake. (c) 2007 Wiley Periodicals, Inc.

Blends of natural rubber and ethylene propylene diene monomer rubber in three blend ratios were prepared and the variation in mechanical properties was investigated with different non-black fillers at different loadings. The fillers used were clay and silica in the ratio 50, 100, 200 and 20, 10, 10 parts per hundred parts of rubber. respectively. Among the three blends the one with 75 weight % of natural rubber gave better tensile properties. The increased filler loadings lowered the tensile strength in all blend ratios. The hardness in general was increased with increased filler loadings in all blends and was recorded maximum for blend with 75 weight % of natural rubber. The thermal ageing studies revealed that the thermal stability increased considerably with increased weight % of ethylene propylene diene monomer rubber. The enhanced thermal stability is evidenced from the tensile strength and elongation at break measurements before and after ageing.

Several new complexes of chiral and achiral tetradentate Schiff bases with copper (II), nickel (II) and oxovanadyl (IV) ions have been synthesised and characterised and the structures of [Cu (R-salpn) (OH2)] and [Cu (±-busalcx)] have been elucidated by X-ray analysis. [Cu (R-salpn) (OH2)] is essentially square pyramidal with an unusually long bond [2.494 (4) Å] from Cu to the oxygen of the apical water molecule. Molecules are linked by hydrogen bonding between the coordinated water and the salpn oxygens of neighbouring molecules. A long contact between a salpn CH2 hydrogen and a neighbouring copper atom [H(3B). . .Cu = 2.966 (1) Å] might be regarded as a CH···Cu hydrogen bond and completes a pseudo-octahedral coordination about copper. [Cu (±-busalcx)] displays tetrahedrally-distorted planar coordination about the copper atom and has no significant intermolecular contacts. The copper, nickel and vanadyl complexes were screened as homogeneous catalysts for the oxidation by ButOOH or H2O2 of PhMeS to PhMeSO. All of them are active catalysts but of the chiral complexes only [Cu (R,R-busalcx)] produced a reasonable enantiomeric excess (14%). Supporting the complexes on silica improved the enantioselectivity of the less sterically hindered [Cu (R-salpn) (OH2)] ( from 2 to 10%), but diminished that of the more hindered [Cu (R,R-busalcx)], probably by slowing the reaction to such an extent that the uncatalysed oxidation could compete effectively. Finally [Cu (salen)], [Cu (R-salpn)] and [Ni (R-salpn)] were synthesised in the pores of zeolites X and Y. These were shown to be active heterogeneous catalysts for the sulfide to sulfoxide oxidations, but no significant e.e. resulted from the use of the chiral catalysts.

Nine complexes of lanthanide nitrates with 4-benzoyl-3-methyl- 1-phenylpyrazol-5-one (BMPP) having the general formula [Ln(BMPP) 2 (NO 3 ) 3 ] (where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Y) have been synthesized and their IR spectra obtained. In these complexes BMPP acts as a bidentate ligand coordinating through the oxygen of both the carbonyl groups and the nitrate ion acts as a unidentate ligand coordinating through one of the oxygen atoms with the lanthanide ion.